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//===- InstrRefBasedImpl.cpp - Tracking Debug Value MIs -------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
/// \file InstrRefBasedImpl.cpp
/// This is a separate implementation of LiveDebugValues, see
/// LiveDebugValues.cpp and VarLocBasedImpl.cpp for more information.
/// This pass propagates variable locations between basic blocks, resolving
/// control flow conflicts between them. The problem is much like SSA
/// construction, where each DBG_VALUE instruction assigns the *value* that
/// a variable has, and every instruction where the variable is in scope uses
/// that variable. The resulting map of instruction-to-value is then translated
/// into a register (or spill) location for each variable over each instruction.
/// This pass determines which DBG_VALUE dominates which instructions, or if
/// none do, where values must be merged (like PHI nodes). The added
/// complication is that because codegen has already finished, a PHI node may
/// be needed for a variable location to be correct, but no register or spill
/// slot merges the necessary values. In these circumstances, the variable
/// location is dropped.
/// What makes this analysis non-trivial is loops: we cannot tell in advance
/// whether a variable location is live throughout a loop, or whether its
/// location is clobbered (or redefined by another DBG_VALUE), without
/// exploring all the way through.
/// To make this simpler we perform two kinds of analysis. First, we identify
/// every value defined by every instruction (ignoring those that only move
/// another value), then compute a map of which values are available for each
/// instruction. This is stronger than a reaching-def analysis, as we create
/// PHI values where other values merge.
/// Secondly, for each variable, we effectively re-construct SSA using each
/// DBG_VALUE as a def. The DBG_VALUEs read a value-number computed by the
/// first analysis from the location they refer to. We can then compute the
/// dominance frontiers of where a variable has a value, and create PHI nodes
/// where they merge.
/// This isn't precisely SSA-construction though, because the function shape
/// is pre-defined. If a variable location requires a PHI node, but no
/// PHI for the relevant values is present in the function (as computed by the
/// first analysis), the location must be dropped.
/// Once both are complete, we can pass back over all instructions knowing:
/// * What _value_ each variable should contain, either defined by an
/// instruction or where control flow merges
/// * What the location of that value is (if any).
/// Allowing us to create appropriate live-in DBG_VALUEs, and DBG_VALUEs when
/// a value moves location. After this pass runs, all variable locations within
/// a block should be specified by DBG_VALUEs within that block, allowing
/// DbgEntityHistoryCalculator to focus on individual blocks.
/// This pass is able to go fast because the size of the first
/// reaching-definition analysis is proportional to the working-set size of
/// the function, which the compiler tries to keep small. (It's also
/// proportional to the number of blocks). Additionally, we repeatedly perform
/// the second reaching-definition analysis with only the variables and blocks
/// in a single lexical scope, exploiting their locality.
/// Determining where PHIs happen is trickier with this approach, and it comes
/// to a head in the major problem for LiveDebugValues: is a value live-through
/// a loop, or not? Your garden-variety dataflow analysis aims to build a set of
/// facts about a function, however this analysis needs to generate new value
/// numbers at joins.
/// To do this, consider a lattice of all definition values, from instructions
/// and from PHIs. Each PHI is characterised by the RPO number of the block it
/// occurs in. Each value pair A, B can be ordered by RPO(A) < RPO(B):
/// with non-PHI values at the top, and any PHI value in the last block (by RPO
/// order) at the bottom.
/// (Awkwardly: lower-down-the _lattice_ means a greater RPO _number_. Below,
/// "rank" always refers to the former).
/// At any join, for each register, we consider:
/// * All incoming values, and
/// * The PREVIOUS live-in value at this join.
/// If all incoming values agree: that's the live-in value. If they do not, the
/// incoming values are ranked according to the partial order, and the NEXT
/// LOWEST rank after the PREVIOUS live-in value is picked (multiple values of
/// the same rank are ignored as conflicting). If there are no candidate values,
/// or if the rank of the live-in would be lower than the rank of the current
/// blocks PHIs, create a new PHI value.
/// Intuitively: if it's not immediately obvious what value a join should result
/// in, we iteratively descend from instruction-definitions down through PHI
/// values, getting closer to the current block each time. If the current block
/// is a loop head, this ordering is effectively searching outer levels of
/// loops, to find a value that's live-through the current loop.
/// If there is no value that's live-through this loop, a PHI is created for
/// this location instead. We can't use a lower-ranked PHI because by definition
/// it doesn't dominate the current block. We can't create a PHI value any
/// earlier, because we risk creating a PHI value at a location where values do
/// not in fact merge, thus misrepresenting the truth, and not making the true
/// live-through value for variable locations.
/// This algorithm applies to both calculating the availability of values in
/// the first analysis, and the location of variables in the second. However
/// for the second we add an extra dimension of pain: creating a variable
/// location PHI is only valid if, for each incoming edge,
/// * There is a value for the variable on the incoming edge, and
/// * All the edges have that value in the same register.
/// Or put another way: we can only create a variable-location PHI if there is
/// a matching machine-location PHI, each input to which is the variables value
/// in the predecessor block.
/// To accommodate this difference, each point on the lattice is split in
/// two: a "proposed" PHI and "definite" PHI. Any PHI that can immediately
/// have a location determined are "definite" PHIs, and no further work is
/// needed. Otherwise, a location that all non-backedge predecessors agree
/// on is picked and propagated as a "proposed" PHI value. If that PHI value
/// is truly live-through, it'll appear on the loop backedges on the next
/// dataflow iteration, after which the block live-in moves to be a "definite"
/// PHI. If it's not truly live-through, the variable value will be downgraded
/// further as we explore the lattice, or remains "proposed" and is considered
/// invalid once dataflow completes.
/// ### Terminology
/// A machine location is a register or spill slot, a value is something that's
/// defined by an instruction or PHI node, while a variable value is the value
/// assigned to a variable. A variable location is a machine location, that must
/// contain the appropriate variable value. A value that is a PHI node is
/// occasionally called an mphi.
/// The first dataflow problem is the "machine value location" problem,
/// because we're determining which machine locations contain which values.
/// The "locations" are constant: what's unknown is what value they contain.
/// The second dataflow problem (the one for variables) is the "variable value
/// problem", because it's determining what values a variable has, rather than
/// what location those values are placed in. Unfortunately, it's not that
/// simple, because producing a PHI value always involves picking a location.
/// This is an imperfection that we just have to accept, at least for now.
/// TODO:
/// Overlapping fragments
/// Entry values
/// Add back DEBUG statements for debugging this
/// Collect statistics
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/UniqueVector.h"
#include "llvm/CodeGen/LexicalScopes.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/CodeGen/TargetFrameLowering.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/TypeSize.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <functional>
#include <queue>
#include <tuple>
#include <utility>
#include <vector>
#include <limits.h>
#include <limits>
#include "LiveDebugValues.h"
using namespace llvm;
#define DEBUG_TYPE "livedebugvalues"
STATISTIC(NumInserted, "Number of DBG_VALUE instructions inserted");
STATISTIC(NumRemoved, "Number of DBG_VALUE instructions removed");
// Act more like the VarLoc implementation, by propagating some locations too
// far and ignoring some transfers.
static cl::opt<bool> EmulateOldLDV("emulate-old-livedebugvalues", cl::Hidden,
cl::desc("Act like old LiveDebugValues did"),
// Rely on isStoreToStackSlotPostFE and similar to observe all stack spills.
static cl::opt<bool>
ObserveAllStackops("observe-all-stack-ops", cl::Hidden,
cl::desc("Allow non-kill spill and restores"),
namespace {
// The location at which a spilled value resides. It consists of a register and
// an offset.
struct SpillLoc {
unsigned SpillBase;
StackOffset SpillOffset;
bool operator==(const SpillLoc &Other) const {
return std::make_pair(SpillBase, SpillOffset) ==
std::make_pair(Other.SpillBase, Other.SpillOffset);
bool operator<(const SpillLoc &Other) const {
return std::make_tuple(SpillBase, SpillOffset.getFixed(),
SpillOffset.getScalable()) <
std::make_tuple(Other.SpillBase, Other.SpillOffset.getFixed(),
class LocIdx {
unsigned Location;
// Default constructor is private, initializing to an illegal location number.
// Use only for "not an entry" elements in IndexedMaps.
LocIdx() : Location(UINT_MAX) { }
#define NUM_LOC_BITS 24
LocIdx(unsigned L) : Location(L) {
assert(L < (1 << NUM_LOC_BITS) && "Machine locations must fit in 24 bits");
static LocIdx MakeIllegalLoc() {
return LocIdx();
bool isIllegal() const {
return Location == UINT_MAX;
uint64_t asU64() const {
return Location;
bool operator==(unsigned L) const {
return Location == L;
bool operator==(const LocIdx &L) const {
return Location == L.Location;
bool operator!=(unsigned L) const {
return !(*this == L);
bool operator!=(const LocIdx &L) const {
return !(*this == L);
bool operator<(const LocIdx &Other) const {
return Location < Other.Location;
class LocIdxToIndexFunctor {
using argument_type = LocIdx;
unsigned operator()(const LocIdx &L) const {
return L.asU64();
/// Unique identifier for a value defined by an instruction, as a value type.
/// Casts back and forth to a uint64_t. Probably replacable with something less
/// bit-constrained. Each value identifies the instruction and machine location
/// where the value is defined, although there may be no corresponding machine
/// operand for it (ex: regmasks clobbering values). The instructions are
/// one-based, and definitions that are PHIs have instruction number zero.
/// The obvious limits of a 1M block function or 1M instruction blocks are
/// problematic; but by that point we should probably have bailed out of
/// trying to analyse the function.
class ValueIDNum {
uint64_t BlockNo : 20; /// The block where the def happens.
uint64_t InstNo : 20; /// The Instruction where the def happens.
/// One based, is distance from start of block.
uint64_t LocNo : NUM_LOC_BITS; /// The machine location where the def happens.
// XXX -- temporarily enabled while the live-in / live-out tables are moved
// to something more type-y
ValueIDNum() : BlockNo(0xFFFFF),
LocNo(0xFFFFFF) { }
ValueIDNum(uint64_t Block, uint64_t Inst, uint64_t Loc)
: BlockNo(Block), InstNo(Inst), LocNo(Loc) { }
ValueIDNum(uint64_t Block, uint64_t Inst, LocIdx Loc)
: BlockNo(Block), InstNo(Inst), LocNo(Loc.asU64()) { }
uint64_t getBlock() const { return BlockNo; }
uint64_t getInst() const { return InstNo; }
uint64_t getLoc() const { return LocNo; }
bool isPHI() const { return InstNo == 0; }
uint64_t asU64() const {
uint64_t TmpBlock = BlockNo;
uint64_t TmpInst = InstNo;
return TmpBlock << 44ull | TmpInst << NUM_LOC_BITS | LocNo;
static ValueIDNum fromU64(uint64_t v) {
uint64_t L = (v & 0x3FFF);
return {v >> 44ull, ((v >> NUM_LOC_BITS) & 0xFFFFF), L};
bool operator<(const ValueIDNum &Other) const {
return asU64() < Other.asU64();
bool operator==(const ValueIDNum &Other) const {
return std::tie(BlockNo, InstNo, LocNo) ==
std::tie(Other.BlockNo, Other.InstNo, Other.LocNo);
bool operator!=(const ValueIDNum &Other) const { return !(*this == Other); }
std::string asString(const std::string &mlocname) const {
return Twine("Value{bb: ")
Twine(", inst: ")
.concat((InstNo ? Twine(InstNo) : Twine("live-in"))
.concat(Twine(", loc: ").concat(Twine(mlocname)))
static ValueIDNum EmptyValue;
} // end anonymous namespace
namespace {
/// Meta qualifiers for a value. Pair of whatever expression is used to qualify
/// the the value, and Boolean of whether or not it's indirect.
class DbgValueProperties {
DbgValueProperties(const DIExpression *DIExpr, bool Indirect)
: DIExpr(DIExpr), Indirect(Indirect) {}
/// Extract properties from an existing DBG_VALUE instruction.
DbgValueProperties(const MachineInstr &MI) {
DIExpr = MI.getDebugExpression();
Indirect = MI.getOperand(1).isImm();
bool operator==(const DbgValueProperties &Other) const {
return std::tie(DIExpr, Indirect) == std::tie(Other.DIExpr, Other.Indirect);
bool operator!=(const DbgValueProperties &Other) const {
return !(*this == Other);
const DIExpression *DIExpr;
bool Indirect;
/// Tracker for what values are in machine locations. Listens to the Things
/// being Done by various instructions, and maintains a table of what machine
/// locations have what values (as defined by a ValueIDNum).
/// There are potentially a much larger number of machine locations on the
/// target machine than the actual working-set size of the function. On x86 for
/// example, we're extremely unlikely to want to track values through control
/// or debug registers. To avoid doing so, MLocTracker has several layers of
/// indirection going on, with two kinds of ``location'':
/// * A LocID uniquely identifies a register or spill location, with a
/// predictable value.
/// * A LocIdx is a key (in the database sense) for a LocID and a ValueIDNum.
/// Whenever a location is def'd or used by a MachineInstr, we automagically
/// create a new LocIdx for a location, but not otherwise. This ensures we only
/// account for locations that are actually used or defined. The cost is another
/// vector lookup (of LocID -> LocIdx) over any other implementation. This is
/// fairly cheap, and the compiler tries to reduce the working-set at any one
/// time in the function anyway.
/// Register mask operands completely blow this out of the water; I've just
/// piled hacks on top of hacks to get around that.
class MLocTracker {
MachineFunction &MF;
const TargetInstrInfo &TII;
const TargetRegisterInfo &TRI;
const TargetLowering &TLI;
/// IndexedMap type, mapping from LocIdx to ValueIDNum.
using LocToValueType = IndexedMap<ValueIDNum, LocIdxToIndexFunctor>;
/// Map of LocIdxes to the ValueIDNums that they store. This is tightly
/// packed, entries only exist for locations that are being tracked.
LocToValueType LocIdxToIDNum;
/// "Map" of machine location IDs (i.e., raw register or spill number) to the
/// LocIdx key / number for that location. There are always at least as many
/// as the number of registers on the target -- if the value in the register
/// is not being tracked, then the LocIdx value will be zero. New entries are
/// appended if a new spill slot begins being tracked.
/// This, and the corresponding reverse map persist for the analysis of the
/// whole function, and is necessarying for decoding various vectors of
/// values.
std::vector<LocIdx> LocIDToLocIdx;
/// Inverse map of LocIDToLocIdx.
IndexedMap<unsigned, LocIdxToIndexFunctor> LocIdxToLocID;
/// Unique-ification of spill slots. Used to number them -- their LocID
/// number is the index in SpillLocs minus one plus NumRegs.
UniqueVector<SpillLoc> SpillLocs;
// If we discover a new machine location, assign it an mphi with this
// block number.
unsigned CurBB;
/// Cached local copy of the number of registers the target has.
unsigned NumRegs;
/// Collection of register mask operands that have been observed. Second part
/// of pair indicates the instruction that they happened in. Used to
/// reconstruct where defs happened if we start tracking a location later
/// on.
SmallVector<std::pair<const MachineOperand *, unsigned>, 32> Masks;
/// Iterator for locations and the values they contain. Dereferencing
/// produces a struct/pair containing the LocIdx key for this location,
/// and a reference to the value currently stored. Simplifies the process
/// of seeking a particular location.
class MLocIterator {
LocToValueType &ValueMap;
LocIdx Idx;
class value_type {
value_type(LocIdx Idx, ValueIDNum &Value) : Idx(Idx), Value(Value) { }
const LocIdx Idx; /// Read-only index of this location.
ValueIDNum &Value; /// Reference to the stored value at this location.
MLocIterator(LocToValueType &ValueMap, LocIdx Idx)
: ValueMap(ValueMap), Idx(Idx) { }
bool operator==(const MLocIterator &Other) const {
assert(&ValueMap == &Other.ValueMap);
return Idx == Other.Idx;
bool operator!=(const MLocIterator &Other) const {
return !(*this == Other);
void operator++() {
Idx = LocIdx(Idx.asU64() + 1);
value_type operator*() {
return value_type(Idx, ValueMap[LocIdx(Idx)]);
MLocTracker(MachineFunction &MF, const TargetInstrInfo &TII,
const TargetRegisterInfo &TRI, const TargetLowering &TLI)
LocIdxToLocID(0) {
NumRegs = TRI.getNumRegs();
LocIDToLocIdx.resize(NumRegs, LocIdx::MakeIllegalLoc());
assert(NumRegs < (1u << NUM_LOC_BITS)); // Detect bit packing failure
// Always track SP. This avoids the implicit clobbering caused by regmasks
// from affectings its values. (LiveDebugValues disbelieves calls and
// regmasks that claim to clobber SP).
Register SP = TLI.getStackPointerRegisterToSaveRestore();
if (SP) {
unsigned ID = getLocID(SP, false);
/// Produce location ID number for indexing LocIDToLocIdx. Takes the register
/// or spill number, and flag for whether it's a spill or not.
unsigned getLocID(Register RegOrSpill, bool isSpill) {
return (isSpill) ? + NumRegs - 1 :;
/// Accessor for reading the value at Idx.
ValueIDNum getNumAtPos(LocIdx Idx) const {
assert(Idx.asU64() < LocIdxToIDNum.size());
return LocIdxToIDNum[Idx];
unsigned getNumLocs(void) const { return LocIdxToIDNum.size(); }
/// Reset all locations to contain a PHI value at the designated block. Used
/// sometimes for actual PHI values, othertimes to indicate the block entry
/// value (before any more information is known).
void setMPhis(unsigned NewCurBB) {
CurBB = NewCurBB;
for (auto Location : locations())
Location.Value = {CurBB, 0, Location.Idx};
/// Load values for each location from array of ValueIDNums. Take current
/// bbnum just in case we read a value from a hitherto untouched register.
void loadFromArray(ValueIDNum *Locs, unsigned NewCurBB) {
CurBB = NewCurBB;
// Iterate over all tracked locations, and load each locations live-in
// value into our local index.
for (auto Location : locations())
Location.Value = Locs[Location.Idx.asU64()];
/// Wipe any un-necessary location records after traversing a block.
void reset(void) {
// We could reset all the location values too; however either loadFromArray
// or setMPhis should be called before this object is re-used. Just
// clear Masks, they're definitely not needed.
/// Clear all data. Destroys the LocID <=> LocIdx map, which makes most of
/// the information in this pass uninterpretable.
void clear(void) {
//SpillLocs.reset(); XXX UniqueVector::reset assumes a SpillLoc casts from 0
SpillLocs = decltype(SpillLocs)();
LocIDToLocIdx.resize(NumRegs, LocIdx::MakeIllegalLoc());
/// Set a locaiton to a certain value.
void setMLoc(LocIdx L, ValueIDNum Num) {
assert(L.asU64() < LocIdxToIDNum.size());
LocIdxToIDNum[L] = Num;
/// Create a LocIdx for an untracked register ID. Initialize it to either an
/// mphi value representing a live-in, or a recent register mask clobber.
LocIdx trackRegister(unsigned ID) {
assert(ID != 0);
LocIdx NewIdx = LocIdx(LocIdxToIDNum.size());
// Default: it's an mphi.
ValueIDNum ValNum = {CurBB, 0, NewIdx};
// Was this reg ever touched by a regmask?
for (const auto &MaskPair : reverse(Masks)) {
if (MaskPair.first->clobbersPhysReg(ID)) {
// There was an earlier def we skipped.
ValNum = {CurBB, MaskPair.second, NewIdx};
LocIdxToIDNum[NewIdx] = ValNum;
LocIdxToLocID[NewIdx] = ID;
return NewIdx;
LocIdx lookupOrTrackRegister(unsigned ID) {
LocIdx &Index = LocIDToLocIdx[ID];
if (Index.isIllegal())
Index = trackRegister(ID);
return Index;
/// Record a definition of the specified register at the given block / inst.
/// This doesn't take a ValueIDNum, because the definition and its location
/// are synonymous.
void defReg(Register R, unsigned BB, unsigned Inst) {
unsigned ID = getLocID(R, false);
LocIdx Idx = lookupOrTrackRegister(ID);
ValueIDNum ValueID = {BB, Inst, Idx};
LocIdxToIDNum[Idx] = ValueID;
/// Set a register to a value number. To be used if the value number is
/// known in advance.
void setReg(Register R, ValueIDNum ValueID) {
unsigned ID = getLocID(R, false);
LocIdx Idx = lookupOrTrackRegister(ID);
LocIdxToIDNum[Idx] = ValueID;
ValueIDNum readReg(Register R) {
unsigned ID = getLocID(R, false);
LocIdx Idx = lookupOrTrackRegister(ID);
return LocIdxToIDNum[Idx];
/// Reset a register value to zero / empty. Needed to replicate the
/// VarLoc implementation where a copy to/from a register effectively
/// clears the contents of the source register. (Values can only have one
/// machine location in VarLocBasedImpl).
void wipeRegister(Register R) {
unsigned ID = getLocID(R, false);
LocIdx Idx = LocIDToLocIdx[ID];
LocIdxToIDNum[Idx] = ValueIDNum::EmptyValue;
/// Determine the LocIdx of an existing register.
LocIdx getRegMLoc(Register R) {
unsigned ID = getLocID(R, false);
return LocIDToLocIdx[ID];
/// Record a RegMask operand being executed. Defs any register we currently
/// track, stores a pointer to the mask in case we have to account for it
/// later.
void writeRegMask(const MachineOperand *MO, unsigned CurBB, unsigned InstID) {
// Ensure SP exists, so that we don't override it later.
Register SP = TLI.getStackPointerRegisterToSaveRestore();
// Def any register we track have that isn't preserved. The regmask
// terminates the liveness of a register, meaning its value can't be
// relied upon -- we represent this by giving it a new value.
for (auto Location : locations()) {
unsigned ID = LocIdxToLocID[Location.Idx];
// Don't clobber SP, even if the mask says it's clobbered.
if (ID < NumRegs && ID != SP && MO->clobbersPhysReg(ID))
defReg(ID, CurBB, InstID);
Masks.push_back(std::make_pair(MO, InstID));
/// Find LocIdx for SpillLoc \p L, creating a new one if it's not tracked.
LocIdx getOrTrackSpillLoc(SpillLoc L) {
unsigned SpillID = SpillLocs.idFor(L);
if (SpillID == 0) {
SpillID = SpillLocs.insert(L);
unsigned L = getLocID(SpillID, true);
LocIdx Idx = LocIdx(LocIdxToIDNum.size()); // New idx
LocIdxToLocID[Idx] = L;
return Idx;
} else {
unsigned L = getLocID(SpillID, true);
LocIdx Idx = LocIDToLocIdx[L];
return Idx;
/// Set the value stored in a spill slot.
void setSpill(SpillLoc L, ValueIDNum ValueID) {
LocIdx Idx = getOrTrackSpillLoc(L);
LocIdxToIDNum[Idx] = ValueID;
/// Read whatever value is in a spill slot, or None if it isn't tracked.
Optional<ValueIDNum> readSpill(SpillLoc L) {
unsigned SpillID = SpillLocs.idFor(L);
if (SpillID == 0)
return None;
unsigned LocID = getLocID(SpillID, true);
LocIdx Idx = LocIDToLocIdx[LocID];
return LocIdxToIDNum[Idx];
/// Determine the LocIdx of a spill slot. Return None if it previously
/// hasn't had a value assigned.
Optional<LocIdx> getSpillMLoc(SpillLoc L) {
unsigned SpillID = SpillLocs.idFor(L);
if (SpillID == 0)
return None;
unsigned LocNo = getLocID(SpillID, true);
return LocIDToLocIdx[LocNo];
/// Return true if Idx is a spill machine location.
bool isSpill(LocIdx Idx) const {
return LocIdxToLocID[Idx] >= NumRegs;
MLocIterator begin() {
return MLocIterator(LocIdxToIDNum, 0);
MLocIterator end() {
return MLocIterator(LocIdxToIDNum, LocIdxToIDNum.size());
/// Return a range over all locations currently tracked.
iterator_range<MLocIterator> locations() {
return llvm::make_range(begin(), end());
std::string LocIdxToName(LocIdx Idx) const {
unsigned ID = LocIdxToLocID[Idx];
if (ID >= NumRegs)
return Twine("slot ").concat(Twine(ID - NumRegs)).str();
return TRI.getRegAsmName(ID).str();
std::string IDAsString(const ValueIDNum &Num) const {
std::string DefName = LocIdxToName(Num.getLoc());
return Num.asString(DefName);
void dump() {
for (auto Location : locations()) {
std::string MLocName = LocIdxToName(Location.Value.getLoc());
std::string DefName = Location.Value.asString(MLocName);
dbgs() << LocIdxToName(Location.Idx) << " --> " << DefName << "\n";
void dump_mloc_map() {
for (auto Location : locations()) {
std::string foo = LocIdxToName(Location.Idx);
dbgs() << "Idx " << Location.Idx.asU64() << " " << foo << "\n";
/// Create a DBG_VALUE based on machine location \p MLoc. Qualify it with the
/// information in \pProperties, for variable Var. Don't insert it anywhere,
/// just return the builder for it.
MachineInstrBuilder emitLoc(Optional<LocIdx> MLoc, const DebugVariable &Var,
const DbgValueProperties &Properties) {
DebugLoc DL = DILocation::get(Var.getVariable()->getContext(), 0, 0,
const_cast<DILocation *>(Var.getInlinedAt()));
auto MIB = BuildMI(MF, DL, TII.get(TargetOpcode::DBG_VALUE));
const DIExpression *Expr = Properties.DIExpr;
if (!MLoc) {
// No location -> DBG_VALUE $noreg
MIB.addReg(0, RegState::Debug);
MIB.addReg(0, RegState::Debug);
} else if (LocIdxToLocID[*MLoc] >= NumRegs) {
unsigned LocID = LocIdxToLocID[*MLoc];
const SpillLoc &Spill = SpillLocs[LocID - NumRegs + 1];
auto *TRI = MF.getSubtarget().getRegisterInfo();
Expr = TRI->prependOffsetExpression(Expr, DIExpression::ApplyOffset,
unsigned Base = Spill.SpillBase;
MIB.addReg(Base, RegState::Debug);
} else {
unsigned LocID = LocIdxToLocID[*MLoc];
MIB.addReg(LocID, RegState::Debug);
if (Properties.Indirect)
MIB.addReg(0, RegState::Debug);
return MIB;
/// Class recording the (high level) _value_ of a variable. Identifies either
/// the value of the variable as a ValueIDNum, or a constant MachineOperand.
/// This class also stores meta-information about how the value is qualified.
/// Used to reason about variable values when performing the second
/// (DebugVariable specific) dataflow analysis.
class DbgValue {
union {
/// If Kind is Def, the value number that this value is based on.
ValueIDNum ID;
/// If Kind is Const, the MachineOperand defining this value.
MachineOperand MO;
/// For a NoVal DbgValue, which block it was generated in.
unsigned BlockNo;
/// Qualifiers for the ValueIDNum above.
DbgValueProperties Properties;
typedef enum {
Undef, // Represents a DBG_VALUE $noreg in the transfer function only.
Def, // This value is defined by an inst, or is a PHI value.
Const, // A constant value contained in the MachineOperand field.
Proposed, // This is a tentative PHI value, which may be confirmed or
// invalidated later.
NoVal // Empty DbgValue, generated during dataflow. BlockNo stores
// which block this was generated in.
} KindT;
/// Discriminator for whether this is a constant or an in-program value.
KindT Kind;
DbgValue(const ValueIDNum &Val, const DbgValueProperties &Prop, KindT Kind)
: ID(Val), Properties(Prop), Kind(Kind) {
assert(Kind == Def || Kind == Proposed);
DbgValue(unsigned BlockNo, const DbgValueProperties &Prop, KindT Kind)
: BlockNo(BlockNo), Properties(Prop), Kind(Kind) {
assert(Kind == NoVal);
DbgValue(const MachineOperand &MO, const DbgValueProperties &Prop, KindT Kind)
: MO(MO), Properties(Prop), Kind(Kind) {
assert(Kind == Const);
DbgValue(const DbgValueProperties &Prop, KindT Kind)
: Properties(Prop), Kind(Kind) {
assert(Kind == Undef &&
"Empty DbgValue constructor must pass in Undef kind");
void dump(const MLocTracker *MTrack) const {
if (Kind == Const) {
} else if (Kind == NoVal) {
dbgs() << "NoVal(" << BlockNo << ")";
} else if (Kind == Proposed) {
dbgs() << "VPHI(" << MTrack->IDAsString(ID) << ")";
} else {
assert(Kind == Def);
dbgs() << MTrack->IDAsString(ID);
if (Properties.Indirect)
dbgs() << " indir";
if (Properties.DIExpr)
dbgs() << " " << *Properties.DIExpr;
bool operator==(const DbgValue &Other) const {
if (std::tie(Kind, Properties) != std::tie(Other.Kind, Other.Properties))
return false;
else if (Kind == Proposed && ID != Other.ID)
return false;
else if (Kind == Def && ID != Other.ID)
return false;
else if (Kind == NoVal && BlockNo != Other.BlockNo)
return false;
else if (Kind == Const)
return MO.isIdenticalTo(Other.MO);
return true;
bool operator!=(const DbgValue &Other) const { return !(*this == Other); }
/// Types for recording sets of variable fragments that overlap. For a given
/// local variable, we record all other fragments of that variable that could
/// overlap it, to reduce search time.
using FragmentOfVar =
std::pair<const DILocalVariable *, DIExpression::FragmentInfo>;
using OverlapMap =
DenseMap<FragmentOfVar, SmallVector<DIExpression::FragmentInfo, 1>>;
/// Collection of DBG_VALUEs observed when traversing a block. Records each
/// variable and the value the DBG_VALUE refers to. Requires the machine value
/// location dataflow algorithm to have run already, so that values can be
/// identified.
class VLocTracker {
/// Map DebugVariable to the latest Value it's defined to have.
/// Needs to be a MapVector because we determine order-in-the-input-MIR from
/// the order in this container.
/// We only retain the last DbgValue in each block for each variable, to
/// determine the blocks live-out variable value. The Vars container forms the
/// transfer function for this block, as part of the dataflow analysis. The
/// movement of values between locations inside of a block is handled at a
/// much later stage, in the TransferTracker class.
MapVector<DebugVariable, DbgValue> Vars;
DenseMap<DebugVariable, const DILocation *> Scopes;
MachineBasicBlock *MBB;
VLocTracker() {}
void defVar(const MachineInstr &MI, const DbgValueProperties &Properties,
Optional<ValueIDNum> ID) {
assert(MI.isDebugValue() || MI.isDebugRef());
DebugVariable Var(MI.getDebugVariable(), MI.getDebugExpression(),
DbgValue Rec = (ID) ? DbgValue(*ID, Properties, DbgValue::Def)
: DbgValue(Properties, DbgValue::Undef);
// Attempt insertion; overwrite if it's already mapped.
auto Result = Vars.insert(std::make_pair(Var, Rec));
if (!Result.second)
Result.first->second = Rec;
Scopes[Var] = MI.getDebugLoc().get();
void defVar(const MachineInstr &MI, const MachineOperand &MO) {
// Only DBG_VALUEs can define constant-valued variables.
DebugVariable Var(MI.getDebugVariable(), MI.getDebugExpression(),
DbgValueProperties Properties(MI);
DbgValue Rec = DbgValue(MO, Properties, DbgValue::Const);
// Attempt insertion; overwrite if it's already mapped.
auto Result = Vars.insert(std::make_pair(Var, Rec));
if (!Result.second)
Result.first->second = Rec;
Scopes[Var] = MI.getDebugLoc().get();
/// Tracker for converting machine value locations and variable values into
/// variable locations (the output of LiveDebugValues), recorded as DBG_VALUEs
/// specifying block live-in locations and transfers within blocks.
/// Operating on a per-block basis, this class takes a (pre-loaded) MLocTracker
/// and must be initialized with the set of variable values that are live-in to
/// the block. The caller then repeatedly calls process(). TransferTracker picks
/// out variable locations for the live-in variable values (if there _is_ a
/// location) and creates the corresponding DBG_VALUEs. Then, as the block is
/// stepped through, transfers of values between machine locations are
/// identified and if profitable, a DBG_VALUE created.
/// This is where debug use-before-defs would be resolved: a variable with an
/// unavailable value could materialize in the middle of a block, when the
/// value becomes available. Or, we could detect clobbers and re-specify the
/// variable in a backup location. (XXX these are unimplemented).
class TransferTracker {
const TargetInstrInfo *TII;
/// This machine location tracker is assumed to always contain the up-to-date
/// value mapping for all machine locations. TransferTracker only reads
/// information from it. (XXX make it const?)
MLocTracker *MTracker;
MachineFunction &MF;
/// Record of all changes in variable locations at a block position. Awkwardly
/// we allow inserting either before or after the point: MBB != nullptr
/// indicates it's before, otherwise after.
struct Transfer {
MachineBasicBlock::iterator Pos; /// Position to insert DBG_VALUes
MachineBasicBlock *MBB; /// non-null if we should insert after.
SmallVector<MachineInstr *, 4> Insts; /// Vector of DBG_VALUEs to insert.
typedef struct {
LocIdx Loc;
DbgValueProperties Properties;
} LocAndProperties;
/// Collection of transfers (DBG_VALUEs) to be inserted.
SmallVector<Transfer, 32> Transfers;
/// Local cache of what-value-is-in-what-LocIdx. Used to identify differences
/// between TransferTrackers view of variable locations and MLocTrackers. For
/// example, MLocTracker observes all clobbers, but TransferTracker lazily
/// does not.
std::vector<ValueIDNum> VarLocs;
/// Map from LocIdxes to which DebugVariables are based that location.
/// Mantained while stepping through the block. Not accurate if
/// VarLocs[Idx] != MTracker->LocIdxToIDNum[Idx].
std::map<LocIdx, SmallSet<DebugVariable, 4>> ActiveMLocs;
/// Map from DebugVariable to it's current location and qualifying meta
/// information. To be used in conjunction with ActiveMLocs to construct
/// enough information for the DBG_VALUEs for a particular LocIdx.
DenseMap<DebugVariable, LocAndProperties> ActiveVLocs;
/// Temporary cache of DBG_VALUEs to be entered into the Transfers collection.
SmallVector<MachineInstr *, 4> PendingDbgValues;
/// Record of a use-before-def: created when a value that's live-in to the
/// current block isn't available in any machine location, but it will be
/// defined in this block.
struct UseBeforeDef {
/// Value of this variable, def'd in block.
ValueIDNum ID;
/// Identity of this variable.
DebugVariable Var;
/// Additional variable properties.
DbgValueProperties Properties;
/// Map from instruction index (within the block) to the set of UseBeforeDefs
/// that become defined at that instruction.
DenseMap<unsigned, SmallVector<UseBeforeDef, 1>> UseBeforeDefs;
/// The set of variables that are in UseBeforeDefs and can become a location
/// once the relevant value is defined. An element being erased from this
/// collection prevents the use-before-def materializing.
DenseSet<DebugVariable> UseBeforeDefVariables;
const TargetRegisterInfo &TRI;
const BitVector &CalleeSavedRegs;
TransferTracker(const TargetInstrInfo *TII, MLocTracker *MTracker,
MachineFunction &MF, const TargetRegisterInfo &TRI,
const BitVector &CalleeSavedRegs)
: TII(TII), MTracker(MTracker), MF(MF), TRI(TRI),
CalleeSavedRegs(CalleeSavedRegs) {}
/// Load object with live-in variable values. \p mlocs contains the live-in
/// values in each machine location, while \p vlocs the live-in variable
/// values. This method picks variable locations for the live-in variables,
/// creates DBG_VALUEs and puts them in #Transfers, then prepares the other
/// object fields to track variable locations as we step through the block.
/// FIXME: could just examine mloctracker instead of passing in \p mlocs?
void loadInlocs(MachineBasicBlock &MBB, ValueIDNum *MLocs,
SmallVectorImpl<std::pair<DebugVariable, DbgValue>> &VLocs,
unsigned NumLocs) {
auto isCalleeSaved = [&](LocIdx L) {
unsigned Reg = MTracker->LocIdxToLocID[L];
if (Reg >= MTracker->NumRegs)
return false;
for (MCRegAliasIterator RAI(Reg, &TRI, true); RAI.isValid(); ++RAI)
if (CalleeSavedRegs.test(*RAI))
return true;
return false;
// Map of the preferred location for each value.
std::map<ValueIDNum, LocIdx> ValueToLoc;
// Produce a map of value numbers to the current machine locs they live
// in. When emulating VarLocBasedImpl, there should only be one
// location; when not, we get to pick.
for (auto Location : MTracker->locations()) {
LocIdx Idx = Location.Idx;
ValueIDNum &VNum = MLocs[Idx.asU64()];
auto it = ValueToLoc.find(VNum);
// In order of preference, pick:
// * Callee saved registers,
// * Other registers,
// * Spill slots.
if (it == ValueToLoc.end() || MTracker->isSpill(it->second) ||
(!isCalleeSaved(it->second) && isCalleeSaved(Idx.asU64()))) {
// Insert, or overwrite if insertion failed.
auto PrefLocRes = ValueToLoc.insert(std::make_pair(VNum, Idx));
if (!PrefLocRes.second)
PrefLocRes.first->second = Idx;
// Now map variables to their picked LocIdxes.
for (auto Var : VLocs) {
if (Var.second.Kind == DbgValue::Const) {
emitMOLoc(Var.second.MO, Var.first, Var.second.Properties));
// If the value has no location, we can't make a variable location.
const ValueIDNum &Num = Var.second.ID;
auto ValuesPreferredLoc = ValueToLoc.find(Num);
if (ValuesPreferredLoc == ValueToLoc.end()) {
// If it's a def that occurs in this block, register it as a
// use-before-def to be resolved as we step through the block.
if (Num.getBlock() == (unsigned)MBB.getNumber() && !Num.isPHI())
addUseBeforeDef(Var.first, Var.second.Properties, Num);
LocIdx M = ValuesPreferredLoc->second;
auto NewValue = LocAndProperties{M, Var.second.Properties};
auto Result = ActiveVLocs.insert(std::make_pair(Var.first, NewValue));
if (!Result.second)
Result.first->second = NewValue;
MTracker->emitLoc(M, Var.first, Var.second.Properties));
flushDbgValues(MBB.begin(), &MBB);
/// Record that \p Var has value \p ID, a value that becomes available
/// later in the function.
void addUseBeforeDef(const DebugVariable &Var,
const DbgValueProperties &Properties, ValueIDNum ID) {
UseBeforeDef UBD = {ID, Var, Properties};
/// After the instruction at index \p Inst and position \p pos has been
/// processed, check whether it defines a variable value in a use-before-def.
/// If so, and the variable value hasn't changed since the start of the
/// block, create a DBG_VALUE.
void checkInstForNewValues(unsigned Inst, MachineBasicBlock::iterator pos) {
auto MIt = UseBeforeDefs.find(Inst);
if (MIt == UseBeforeDefs.end())
for (auto &Use : MIt->second) {
LocIdx L = Use.ID.getLoc();
// If something goes very wrong, we might end up labelling a COPY
// instruction or similar with an instruction number, where it doesn't
// actually define a new value, instead it moves a value. In case this
// happens, discard.
if (MTracker->LocIdxToIDNum[L] != Use.ID)
// If a different debug instruction defined the variable value / location
// since the start of the block, don't materialize this use-before-def.
if (!UseBeforeDefVariables.count(Use.Var))
PendingDbgValues.push_back(MTracker->emitLoc(L, Use.Var, Use.Properties));
flushDbgValues(pos, nullptr);
/// Helper to move created DBG_VALUEs into Transfers collection.
void flushDbgValues(MachineBasicBlock::iterator Pos, MachineBasicBlock *MBB) {
if (PendingDbgValues.size() > 0) {
Transfers.push_back({Pos, MBB, PendingDbgValues});
/// Change a variable value after encountering a DBG_VALUE inside a block.
void redefVar(const MachineInstr &MI) {
DebugVariable Var(MI.getDebugVariable(), MI.getDebugExpression(),
DbgValueProperties Properties(MI);
const MachineOperand &MO = MI.getOperand(0);
// Ignore non-register locations, we don't transfer those.
if (!MO.isReg() || MO.getReg() == 0) {
auto It = ActiveVLocs.find(Var);
if (It != ActiveVLocs.end()) {
// Any use-before-defs no longer apply.
Register Reg = MO.getReg();
LocIdx NewLoc = MTracker->getRegMLoc(Reg);
redefVar(MI, Properties, NewLoc);
/// Handle a change in variable location within a block. Terminate the
/// variables current location, and record the value it now refers to, so
/// that we can detect location transfers later on.
void redefVar(const MachineInstr &MI, const DbgValueProperties &Properties,
Optional<LocIdx> OptNewLoc) {
DebugVariable Var(MI.getDebugVariable(), MI.getDebugExpression(),
// Any use-before-defs no longer apply.
// Erase any previous location,
auto It = ActiveVLocs.find(Var);
if (It != ActiveVLocs.end())
// If there _is_ no new location, all we had to do was erase.
if (!OptNewLoc)
LocIdx NewLoc = *OptNewLoc;
// Check whether our local copy of values-by-location in #VarLocs is out of
// date. Wipe old tracking data for the location if it's been clobbered in
// the meantime.
if (MTracker->getNumAtPos(NewLoc) != VarLocs[NewLoc.asU64()]) {
for (auto &P : ActiveMLocs[NewLoc]) {
VarLocs[NewLoc.asU64()] = MTracker->getNumAtPos(NewLoc);
if (It == ActiveVLocs.end()) {
std::make_pair(Var, LocAndProperties{NewLoc, Properties}));
} else {
It->second.Loc = NewLoc;
It->second.Properties = Properties;
/// Explicitly terminate variable locations based on \p mloc. Creates undef
/// DBG_VALUEs for any variables that were located there, and clears
/// #ActiveMLoc / #ActiveVLoc tracking information for that location.
void clobberMloc(LocIdx MLoc, MachineBasicBlock::iterator Pos) {
auto ActiveMLocIt = ActiveMLocs.find(MLoc);
if (ActiveMLocIt == ActiveMLocs.end())
VarLocs[MLoc.asU64()] = ValueIDNum::EmptyValue;
for (auto &Var : ActiveMLocIt->second) {
auto ActiveVLocIt = ActiveVLocs.find(Var);
// Create an undef. We can't feed in a nullptr DIExpression alas,
// so use the variables last expression. Pass None as the location.
const DIExpression *Expr = ActiveVLocIt->second.Properties.DIExpr;
DbgValueProperties Properties(Expr, false);
PendingDbgValues.push_back(MTracker->emitLoc(None, Var, Properties));
flushDbgValues(Pos, nullptr);
/// Transfer variables based on \p Src to be based on \p Dst. This handles
/// both register copies as well as spills and restores. Creates DBG_VALUEs
/// describing the movement.
void transferMlocs(LocIdx Src, LocIdx Dst, MachineBasicBlock::iterator Pos) {
// Does Src still contain the value num we expect? If not, it's been
// clobbered in the meantime, and our variable locations are stale.
if (VarLocs[Src.asU64()] != MTracker->getNumAtPos(Src))
// assert(ActiveMLocs[Dst].size() == 0);
//^^^ Legitimate scenario on account of un-clobbered slot being assigned to?
ActiveMLocs[Dst] = ActiveMLocs[Src];
VarLocs[Dst.asU64()] = VarLocs[Src.asU64()];
// For each variable based on Src; create a location at Dst.
for (auto &Var : ActiveMLocs[Src]) {
auto ActiveVLocIt = ActiveVLocs.find(Var);
assert(ActiveVLocIt != ActiveVLocs.end());
ActiveVLocIt->second.Loc = Dst;
assert(Dst != 0);
MachineInstr *MI =
MTracker->emitLoc(Dst, Var, ActiveVLocIt->second.Properties);
flushDbgValues(Pos, nullptr);
// XXX XXX XXX "pretend to be old LDV" means dropping all tracking data
// about the old location.
if (EmulateOldLDV)
VarLocs[Src.asU64()] = ValueIDNum::EmptyValue;
MachineInstrBuilder emitMOLoc(const MachineOperand &MO,
const DebugVariable &Var,
const DbgValueProperties &Properties) {
DebugLoc DL = DILocation::get(Var.getVariable()->getContext(), 0, 0,
const_cast<DILocation *>(Var.getInlinedAt()));
auto MIB = BuildMI(MF, DL, TII->get(TargetOpcode::DBG_VALUE));
if (Properties.Indirect)
return MIB;
class InstrRefBasedLDV : public LDVImpl {
using FragmentInfo = DIExpression::FragmentInfo;
using OptFragmentInfo = Optional<DIExpression::FragmentInfo>;
// Helper while building OverlapMap, a map of all fragments seen for a given
// DILocalVariable.
using VarToFragments =
DenseMap<const DILocalVariable *, SmallSet<FragmentInfo, 4>>;
/// Machine location/value transfer function, a mapping of which locations
/// are assigned which new values.
using MLocTransferMap = std::map<LocIdx, ValueIDNum>;
/// Live in/out structure for the variable values: a per-block map of
/// variables to their values. XXX, better name?
using LiveIdxT =
DenseMap<const MachineBasicBlock *, DenseMap<DebugVariable, DbgValue> *>;
using VarAndLoc = std::pair<DebugVariable, DbgValue>;
/// Type for a live-in value: the predecessor block, and its value.
using InValueT = std::pair<MachineBasicBlock *, DbgValue *>;
/// Vector (per block) of a collection (inner smallvector) of live-ins.
/// Used as the result type for the variable value dataflow problem.
using LiveInsT = SmallVector<SmallVector<VarAndLoc, 8>, 8>;
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
const TargetFrameLowering *TFI;
BitVector CalleeSavedRegs;
LexicalScopes LS;
TargetPassConfig *TPC;
/// Object to track machine locations as we step through a block. Could
/// probably be a field rather than a pointer, as it's always used.
MLocTracker *MTracker;
/// Number of the current block LiveDebugValues is stepping through.
unsigned CurBB;
/// Number of the current instruction LiveDebugValues is evaluating.
unsigned CurInst;
/// Variable tracker -- listens to DBG_VALUEs occurring as InstrRefBasedImpl
/// steps through a block. Reads the values at each location from the
/// MLocTracker object.
VLocTracker *VTracker;
/// Tracker for transfers, listens to DBG_VALUEs and transfers of values
/// between locations during stepping, creates new DBG_VALUEs when values move
/// location.
TransferTracker *TTracker;
/// Blocks which are artificial, i.e. blocks which exclusively contain
/// instructions without DebugLocs, or with line 0 locations.
SmallPtrSet<const MachineBasicBlock *, 16> ArtificialBlocks;
// Mapping of blocks to and from their RPOT order.
DenseMap<unsigned int, MachineBasicBlock *> OrderToBB;
DenseMap<MachineBasicBlock *, unsigned int> BBToOrder;
DenseMap<unsigned, unsigned> BBNumToRPO;
/// Pair of MachineInstr, and its 1-based offset into the containing block.
using InstAndNum = std::pair<const MachineInstr *, unsigned>;
/// Map from debug instruction number to the MachineInstr labelled with that
/// number, and its location within the function. Used to transform
/// instruction numbers in DBG_INSTR_REFs into machine value numbers.
std::map<uint64_t, InstAndNum> DebugInstrNumToInstr;
// Map of overlapping variable fragments.
OverlapMap OverlapFragments;
VarToFragments SeenFragments;
/// Tests whether this instruction is a spill to a stack slot.
bool isSpillInstruction(const MachineInstr &MI, MachineFunction *MF);
/// Decide if @MI is a spill instruction and return true if it is. We use 2
/// criteria to make this decision:
/// - Is this instruction a store to a spill slot?
/// - Is there a register operand that is both used and killed?
/// TODO: Store optimization can fold spills into other stores (including
/// other spills). We do not handle this yet (more than one memory operand).
bool isLocationSpill(const MachineInstr &MI, MachineFunction *MF,
unsigned &Reg);
/// If a given instruction is identified as a spill, return the spill slot
/// and set \p Reg to the spilled register.
Optional<SpillLoc> isRestoreInstruction(const MachineInstr &MI,
MachineFunction *MF, unsigned &Reg);
/// Given a spill instruction, extract the register and offset used to
/// address the spill slot in a target independent way.
SpillLoc extractSpillBaseRegAndOffset(const MachineInstr &MI);
/// Observe a single instruction while stepping through a block.
void process(MachineInstr &MI);
/// Examines whether \p MI is a DBG_VALUE and notifies trackers.
/// \returns true if MI was recognized and processed.
bool transferDebugValue(const MachineInstr &MI);
/// Examines whether \p MI is a DBG_INSTR_REF and notifies trackers.
/// \returns true if MI was recognized and processed.
bool transferDebugInstrRef(MachineInstr &MI);
/// Examines whether \p MI is copy instruction, and notifies trackers.
/// \returns true if MI was recognized and processed.
bool transferRegisterCopy(MachineInstr &MI);
/// Examines whether \p MI is stack spill or restore instruction, and
/// notifies trackers. \returns true if MI was recognized and processed.
bool transferSpillOrRestoreInst(MachineInstr &MI);
/// Examines \p MI for any registers that it defines, and notifies trackers.
void transferRegisterDef(MachineInstr &MI);
/// Copy one location to the other, accounting for movement of subregisters
/// too.
void performCopy(Register Src, Register Dst);
void accumulateFragmentMap(MachineInstr &MI);
/// Step through the function, recording register definitions and movements
/// in an MLocTracker. Convert the observations into a per-block transfer
/// function in \p MLocTransfer, suitable for using with the machine value
/// location dataflow problem.
produceMLocTransferFunction(MachineFunction &MF,
SmallVectorImpl<MLocTransferMap> &MLocTransfer,
unsigned MaxNumBlocks);
/// Solve the machine value location dataflow problem. Takes as input the
/// transfer functions in \p MLocTransfer. Writes the output live-in and
/// live-out arrays to the (initialized to zero) multidimensional arrays in
/// \p MInLocs and \p MOutLocs. The outer dimension is indexed by block
/// number, the inner by LocIdx.
void mlocDataflow(ValueIDNum **MInLocs, ValueIDNum **MOutLocs,
SmallVectorImpl<MLocTransferMap> &MLocTransfer);
/// Perform a control flow join (lattice value meet) of the values in machine
/// locations at \p MBB. Follows the algorithm described in the file-comment,
/// reading live-outs of predecessors from \p OutLocs, the current live ins
/// from \p InLocs, and assigning the newly computed live ins back into
/// \p InLocs. \returns two bools -- the first indicates whether a change
/// was made, the second whether a lattice downgrade occurred. If the latter
/// is true, revisiting this block is necessary.
std::tuple<bool, bool>
mlocJoin(MachineBasicBlock &MBB,
SmallPtrSet<const MachineBasicBlock *, 16> &Visited,
ValueIDNum **OutLocs, ValueIDNum *InLocs);
/// Solve the variable value dataflow problem, for a single lexical scope.
/// Uses the algorithm from the file comment to resolve control flow joins,
/// although there are extra hacks, see vlocJoin. Reads the
/// locations of values from the \p MInLocs and \p MOutLocs arrays (see
/// mlocDataflow) and reads the variable values transfer function from
/// \p AllTheVlocs. Live-in and Live-out variable values are stored locally,
/// with the live-ins permanently stored to \p Output once the fixedpoint is
/// reached.
/// \p VarsWeCareAbout contains a collection of the variables in \p Scope
/// that we should be tracking.
/// \p AssignBlocks contains the set of blocks that aren't in \p Scope, but
/// which do contain DBG_VALUEs, which VarLocBasedImpl tracks locations
/// through.
void vlocDataflow(const LexicalScope *Scope, const DILocation *DILoc,
const SmallSet<DebugVariable, 4> &VarsWeCareAbout,
SmallPtrSetImpl<MachineBasicBlock *> &AssignBlocks,
LiveInsT &Output, ValueIDNum **MOutLocs,
ValueIDNum **MInLocs,
SmallVectorImpl<VLocTracker> &AllTheVLocs);
/// Compute the live-ins to a block, considering control flow merges according
/// to the method in the file comment. Live out and live in variable values
/// are stored in \p VLOCOutLocs and \p VLOCInLocs. The live-ins for \p MBB
/// are computed and stored into \p VLOCInLocs. \returns true if the live-ins
/// are modified.
/// \p InLocsT Output argument, storage for calculated live-ins.
/// \returns two bools -- the first indicates whether a change
/// was made, the second whether a lattice downgrade occurred. If the latter
/// is true, revisiting this block is necessary.
std::tuple<bool, bool>
vlocJoin(MachineBasicBlock &MBB, LiveIdxT &VLOCOutLocs, LiveIdxT &VLOCInLocs,
SmallPtrSet<const MachineBasicBlock *, 16> *VLOCVisited,
unsigned BBNum, const SmallSet<DebugVariable, 4> &AllVars,
ValueIDNum **MOutLocs, ValueIDNum **MInLocs,
SmallPtrSet<const MachineBasicBlock *, 8> &InScopeBlocks,
SmallPtrSet<const MachineBasicBlock *, 8> &BlocksToExplore,
DenseMap<DebugVariable, DbgValue> &InLocsT);
/// Continue exploration of the variable-value lattice, as explained in the
/// file-level comment. \p OldLiveInLocation contains the current
/// exploration position, from which we need to descend further. \p Values
/// contains the set of live-in values, \p CurBlockRPONum the RPO number of
/// the current block, and \p CandidateLocations a set of locations that
/// should be considered as PHI locations, if we reach the bottom of the
/// lattice. \returns true if we should downgrade; the value is the agreeing
/// value number in a non-backedge predecessor.
bool vlocDowngradeLattice(const MachineBasicBlock &MBB,
const DbgValue &OldLiveInLocation,
const SmallVectorImpl<InValueT> &Values,
unsigned CurBlockRPONum);
/// For the given block and live-outs feeding into it, try to find a
/// machine location where they all join. If a solution for all predecessors
/// can't be found, a location where all non-backedge-predecessors join
/// will be returned instead. While this method finds a join location, this
/// says nothing as to whether it should be used.
/// \returns Pair of value ID if found, and true when the correct value
/// is available on all predecessor edges, or false if it's only available
/// for non-backedge predecessors.
std::tuple<Optional<ValueIDNum>, bool>
pickVPHILoc(MachineBasicBlock &MBB, const DebugVariable &Var,
const LiveIdxT &LiveOuts, ValueIDNum **MOutLocs,
ValueIDNum **MInLocs,
const SmallVectorImpl<MachineBasicBlock *> &BlockOrders);
/// Given the solutions to the two dataflow problems, machine value locations
/// in \p MInLocs and live-in variable values in \p SavedLiveIns, runs the
/// TransferTracker class over the function to produce live-in and transfer
/// DBG_VALUEs, then inserts them. Groups of DBG_VALUEs are inserted in the
/// order given by AllVarsNumbering -- this could be any stable order, but
/// right now "order of appearence in function, when explored in RPO", so
/// that we can compare explictly against VarLocBasedImpl.
void emitLocations(MachineFunction &MF, LiveInsT SavedLiveIns,
ValueIDNum **MInLocs,
DenseMap<DebugVariable, unsigned> &AllVarsNumbering);
/// Boilerplate computation of some initial sets, artifical blocks and
/// RPOT block ordering.
void initialSetup(MachineFunction &MF);
bool ExtendRanges(MachineFunction &MF, TargetPassConfig *TPC) override;
/// Default construct and initialize the pass.
void dump_mloc_transfer(const MLocTransferMap &mloc_transfer) const;
bool isCalleeSaved(LocIdx L) {
unsigned Reg = MTracker->LocIdxToLocID[L];
for (MCRegAliasIterator RAI(Reg, TRI, true); RAI.isValid(); ++RAI)
if (CalleeSavedRegs.test(*RAI))
return true;
return false;
} // end anonymous namespace
// Implementation
ValueIDNum ValueIDNum::EmptyValue = {UINT_MAX, UINT_MAX, UINT_MAX};
/// Default construct and initialize the pass.
InstrRefBasedLDV::InstrRefBasedLDV() {}
// Debug Range Extension Implementation
#ifndef NDEBUG
// Something to restore in the future.
// void InstrRefBasedLDV::printVarLocInMBB(..)
InstrRefBasedLDV::extractSpillBaseRegAndOffset(const MachineInstr &MI) {
assert(MI.hasOneMemOperand() &&
"Spill instruction does not have exactly one memory operand?");
auto MMOI = MI.memoperands_begin();
const PseudoSourceValue *PVal = (*MMOI)->getPseudoValue();
assert(PVal->kind() == PseudoSourceValue::FixedStack &&
"Inconsistent memory operand in spill instruction");
int FI = cast<FixedStackPseudoSourceValue>(PVal)->getFrameIndex();
const MachineBasicBlock *MBB = MI.getParent();
Register Reg;
StackOffset Offset = TFI->getFrameIndexReference(*MBB->getParent(), FI, Reg);
return {Reg, Offset};
/// End all previous ranges related to @MI and start a new range from @MI
/// if it is a DBG_VALUE instr.
bool InstrRefBasedLDV::transferDebugValue(const MachineInstr &MI) {
if (!MI.isDebugValue())
return false;
const DILocalVariable *Var = MI.getDebugVariable();
const DIExpression *Expr = MI.getDebugExpression();
const DILocation *DebugLoc = MI.getDebugLoc();
const DILocation *InlinedAt = DebugLoc->getInlinedAt();
assert(Var->isValidLocationForIntrinsic(DebugLoc) &&
"Expected inlined-at fields to agree");
DebugVariable V(Var, Expr, InlinedAt);
DbgValueProperties Properties(MI);
// If there are no instructions in this lexical scope, do no location tracking
// at all, this variable shouldn't get a legitimate location range.
auto *Scope = LS.findLexicalScope(MI.getDebugLoc().get());
if (Scope == nullptr)
return true; // handled it; by doing nothing
const MachineOperand &MO = MI.getOperand(0);
// MLocTracker needs to know that this register is read, even if it's only
// read by a debug inst.
if (MO.isReg() && MO.getReg() != 0)
// If we're preparing for the second analysis (variables), the machine value
// locations are already solved, and we report this DBG_VALUE and the value
// it refers to to VLocTracker.
if (VTracker) {
if (MO.isReg()) {
// Feed defVar the new variable location, or if this is a
// DBG_VALUE $noreg, feed defVar None.
if (MO.getReg())
VTracker->defVar(MI, Properties, MTracker->readReg(MO.getReg()));
VTracker->defVar(MI, Properties, None);
} else if (MI.getOperand(0).isImm() || MI.getOperand(0).isFPImm() ||
MI.getOperand(0).isCImm()) {
VTracker->defVar(MI, MI.getOperand(0));
// If performing final tracking of transfers, report this variable definition
// to the TransferTracker too.
if (TTracker)
return true;
bool InstrRefBasedLDV::transferDebugInstrRef(MachineInstr &MI) {
if (!MI.isDebugRef())
return false;
// Only handle this instruction when we are building the variable value
// transfer function.
if (!VTracker)
return false;
unsigned InstNo = MI.getOperand(0).getImm();
unsigned OpNo = MI.getOperand(1).getImm();
const DILocalVariable *Var = MI.getDebugVariable();
const DIExpression *Expr = MI.getDebugExpression();
const DILocation *DebugLoc = MI.getDebugLoc();
const DILocation *InlinedAt = DebugLoc->getInlinedAt();
assert(Var->isValidLocationForIntrinsic(DebugLoc) &&
"Expected inlined-at fields to agree");
DebugVariable V(Var, Expr, InlinedAt);
auto *Scope = LS.findLexicalScope(MI.getDebugLoc().get());
if (Scope == nullptr)
return true; // Handled by doing nothing. This variable is never in scope.
const MachineFunction &MF = *MI.getParent()->getParent();
// Various optimizations may have happened to the value during codegen,
// recorded in the value substitution table. Apply any substitutions to
// the instruction / operand number in this DBG_INSTR_REF.
auto Sub = MF.DebugValueSubstitutions.find(std::make_pair(InstNo, OpNo));
while (Sub != MF.DebugValueSubstitutions.end()) {
InstNo = Sub->second.first;
OpNo = Sub->second.second;
Sub = MF.DebugValueSubstitutions.find(std::make_pair(InstNo, OpNo));
// Default machine value number is <None> -- if no instruction defines
// the corresponding value, it must have been optimized out.
Optional<ValueIDNum> NewID = None;
// Try to lookup the instruction number, and find the machine value number
// that it defines.
auto InstrIt = DebugInstrNumToInstr.find(InstNo);
if (InstrIt != DebugInstrNumToInstr.end()) {
const MachineInstr &TargetInstr = *InstrIt->second.first;
uint64_t BlockNo = TargetInstr.getParent()->getNumber();
// Pick out the designated operand.
assert(OpNo < TargetInstr.getNumOperands());
const MachineOperand &MO = TargetInstr.getOperand(OpNo);
// Today, this can only be a register.
assert(MO.isReg() && MO.isDef());
unsigned LocID = MTracker->getLocID(MO.getReg(), false);
LocIdx L = MTracker->LocIDToLocIdx[LocID];
NewID = ValueIDNum(BlockNo, InstrIt->second.second, L);
// We, we have a value number or None. Tell the variable value tracker about
// it. The rest of this LiveDebugValues implementation acts exactly the same
// for DBG_INSTR_REFs as DBG_VALUEs (just, the former can refer to values that
// aren't immediately available).
DbgValueProperties Properties(Expr, false);
VTracker->defVar(MI, Properties, NewID);
// If we're on the final pass through the function, decompose this INSTR_REF
// into a plain DBG_VALUE.
if (!TTracker)
return true;
// Pick a location for the machine value number, if such a location exists.
// (This information could be stored in TransferTracker to make it faster).
Optional<LocIdx> FoundLoc = None;
for (auto Location : MTracker->locations()) {
LocIdx CurL = Location.Idx;
ValueIDNum ID = MTracker->LocIdxToIDNum[CurL];
if (NewID && ID == NewID) {
// If this is the first location with that value, pick it. Otherwise,
// consider whether it's a "longer term" location.
if (!FoundLoc) {
FoundLoc = CurL;
if (MTracker->isSpill(CurL))
FoundLoc = CurL; // Spills are a longer term location.
else if (!MTracker->isSpill(*FoundLoc) &&
!MTracker->isSpill(CurL) &&
!isCalleeSaved(*FoundLoc) &&
FoundLoc = CurL; // Callee saved regs are longer term than normal.
// Tell transfer tracker that the variable value has changed.
TTracker->redefVar(MI, Properties, FoundLoc);
// If there was a value with no location; but the value is defined in a
// later instruction in this block, this is a block-local use-before-def.
if (!FoundLoc && NewID && NewID->getBlock() == CurBB &&
NewID->getInst() > CurInst)
TTracker->addUseBeforeDef(V, {MI.getDebugExpression(), false}, *NewID);
// Produce a DBG_VALUE representing what this DBG_INSTR_REF meant.
// This DBG_VALUE is potentially a $noreg / undefined location, if
// FoundLoc is None.
// (XXX -- could morph the DBG_INSTR_REF in the future).
MachineInstr *DbgMI = MTracker->emitLoc(FoundLoc, V, Properties);
TTracker->flushDbgValues(MI.getIterator(), nullptr);
return true;
void InstrRefBasedLDV::transferRegisterDef(MachineInstr &MI) {
// Meta Instructions do not affect the debug liveness of any register they
// define.
if (MI.isImplicitDef()) {
// Except when there's an implicit def, and the location it's defining has
// no value number. The whole point of an implicit def is to announce that
// the register is live, without be specific about it's value. So define
// a value if there isn't one already.
ValueIDNum Num = MTracker->readReg(MI.getOperand(0).getReg());
// Has a legitimate value -> ignore the implicit def.
if (Num.getLoc() != 0)
// Otherwise, def it here.
} else if (MI.isMetaInstruction())
MachineFunction *MF = MI.getMF();
const TargetLowering *TLI = MF->getSubtarget().getTargetLowering();
Register SP = TLI->getStackPointerRegisterToSaveRestore();
// Find the regs killed by MI, and find regmasks of preserved regs.
// Max out the number of statically allocated elements in `DeadRegs`, as this
// prevents fallback to std::set::count() operations.
SmallSet<uint32_t, 32> DeadRegs;
SmallVector<const uint32_t *, 4> RegMasks;
SmallVector<const MachineOperand *, 4> RegMaskPtrs;
for (const MachineOperand &MO : MI.operands()) {
// Determine whether the operand is a register def.
if (MO.isReg() && MO.isDef() && MO.getReg() &&
Register::isPhysicalRegister(MO.getReg()) &&
!(MI.isCall() && MO.getReg() == SP)) {
// Remove ranges of all aliased registers.
for (MCRegAliasIterator RAI(MO.getReg(), TRI, true); RAI.isValid(); ++RAI)
// FIXME: Can we break out of this loop early if no insertion occurs?
} else if (MO.isRegMask()) {
// Tell MLocTracker about all definitions, of regmasks and otherwise.
for (uint32_t DeadReg : DeadRegs)
MTracker->defReg(DeadReg, CurBB, CurInst);
for (auto *MO : RegMaskPtrs)
MTracker->writeRegMask(MO, CurBB, CurInst);
void InstrRefBasedLDV::performCopy(Register SrcRegNum, Register DstRegNum) {
ValueIDNum SrcValue = MTracker->readReg(SrcRegNum);
MTracker->setReg(DstRegNum, SrcValue);
// In all circumstances, re-def the super registers. It's definitely a new
// value now. This doesn't uniquely identify the composition of subregs, for
// example, two identical values in subregisters composed in different
// places would not get equal value numbers.
for (MCSuperRegIterator SRI(DstRegNum, TRI); SRI.isValid(); ++SRI)
MTracker->defReg(*SRI, CurBB, CurInst);
// If we're emulating VarLocBasedImpl, just define all the subregisters.
// DBG_VALUEs of them will expect to be tracked from the DBG_VALUE, not
// through prior copies.
if (EmulateOldLDV) {
for (MCSubRegIndexIterator DRI(DstRegNum, TRI); DRI.isValid(); ++DRI)
MTracker->defReg(DRI.getSubReg(), CurBB, CurInst);
// Otherwise, actually copy subregisters from one location to another.
// XXX: in addition, any subregisters of DstRegNum that don't line up with
// the source register should be def'd.
for (MCSubRegIndexIterator SRI(SrcRegNum, TRI); SRI.isValid(); ++SRI) {
unsigned SrcSubReg = SRI.getSubReg();
unsigned SubRegIdx = SRI.getSubRegIndex();
unsigned DstSubReg = TRI->getSubReg(DstRegNum, SubRegIdx);
if (!DstSubReg)
// Do copy. There are two matching subregisters, the source value should
// have been def'd when the super-reg was, the latter might not be tracked
// yet.
// This will force SrcSubReg to be tracked, if it isn't yet.
LocIdx SrcL = MTracker->getRegMLoc(SrcSubReg);
LocIdx DstL = MTracker->getRegMLoc(DstSubReg);
ValueIDNum CpyValue = {SrcValue.getBlock(), SrcValue.getInst(), SrcL};
MTracker->setReg(DstSubReg, CpyValue);
bool InstrRefBasedLDV::isSpillInstruction(const MachineInstr &MI,
MachineFunction *MF) {
// TODO: Handle multiple stores folded into one.
if (!MI.hasOneMemOperand())
return false;
if (!MI.getSpillSize(TII) && !MI.getFoldedSpillSize(TII))
return false; // This is not a spill instruction, since no valid size was
// returned from either function.
return true;
bool InstrRefBasedLDV::isLocationSpill(const MachineInstr &MI,
MachineFunction *MF, unsigned &Reg) {
if (!isSpillInstruction(MI, MF))
return false;
// XXX FIXME: On x86, isStoreToStackSlotPostFE returns '1' instead of an
// actual register number.
if (ObserveAllStackops) {
int FI;
Reg = TII->isStoreToStackSlotPostFE(MI, FI);
return Reg != 0;
auto isKilledReg = [&](const MachineOperand MO, unsigned &Reg) {
if (!MO.isReg() || !MO.isUse()) {
Reg = 0;
return false;
Reg = MO.getReg();
return MO.isKill();
for (const MachineOperand &MO : MI.operands()) {
// In a spill instruction generated by the InlineSpiller the spilled
// register has its kill flag set.
if (isKilledReg(MO, Reg))
return true;
if (Reg != 0) {
// Check whether next instruction kills the spilled register.
// FIXME: Current solution does not cover search for killed register in
// bundles and instructions further down the chain.
auto NextI = std::next(MI.getIterator());
// Skip next instruction that points to basic block end iterator.
if (MI.getParent()->end() == NextI)
unsigned RegNext;
for (const MachineOperand &MONext : NextI->operands()) {
// Return true if we came across the register from the
// previous spill instruction that is killed in NextI.
if (isKilledReg(MONext, RegNext) && RegNext == Reg)
return true;
// Return false if we didn't find spilled register.
return false;
InstrRefBasedLDV::isRestoreInstruction(const MachineInstr &MI,
MachineFunction *MF, unsigned &Reg) {
if (!MI.hasOneMemOperand())
return None;
// FIXME: Handle folded restore instructions with more than one memory
// operand.
if (MI.getRestoreSize(TII)) {
Reg = MI.getOperand(0).getReg();
return extractSpillBaseRegAndOffset(MI);
return None;
bool InstrRefBasedLDV::transferSpillOrRestoreInst(MachineInstr &MI) {
// XXX -- it's too difficult to implement VarLocBasedImpl's stack location
// limitations under the new model. Therefore, when comparing them, compare
// versions that don't attempt spills or restores at all.
if (EmulateOldLDV)
return false;
MachineFunction *MF = MI.getMF();
unsigned Reg;
Optional<SpillLoc> Loc;
LLVM_DEBUG(dbgs() << "Examining instruction: "; MI.dump(););
// First, if there are any DBG_VALUEs pointing at a spill slot that is
// written to, terminate that variable location. The value in memory
// will have changed. DbgEntityHistoryCalculator doesn't try to detect this.
if (isSpillInstruction(MI, MF)) {
Loc = extractSpillBaseRegAndOffset(MI);
if (TTracker) {
Optional<LocIdx> MLoc = MTracker->getSpillMLoc(*Loc);
if (MLoc)
TTracker->clobberMloc(*MLoc, MI.getIterator());
// Try to recognise spill and restore instructions that may transfer a value.
if (isLocationSpill(MI, MF, Reg)) {
Loc = extractSpillBaseRegAndOffset(MI);
auto ValueID = MTracker->readReg(Reg);
// If the location is empty, produce a phi, signify it's the live-in value.
if (ValueID.getLoc() == 0)
ValueID = {CurBB, 0, MTracker->getRegMLoc(Reg)};
MTracker->setSpill(*Loc, ValueID);
auto OptSpillLocIdx = MTracker->getSpillMLoc(*Loc);
assert(OptSpillLocIdx && "Spill slot set but has no LocIdx?");
LocIdx SpillLocIdx = *OptSpillLocIdx;
// Tell TransferTracker about this spill, produce DBG_VALUEs for it.
if (TTracker)
TTracker->transferMlocs(MTracker->getRegMLoc(Reg), SpillLocIdx,
} else {
if (!(Loc = isRestoreInstruction(MI, MF, Reg)))
return false;
// Is there a value to be restored?
auto OptValueID = MTracker->readSpill(*Loc);
if (OptValueID) {
ValueIDNum ValueID = *OptValueID;
LocIdx SpillLocIdx = *MTracker->getSpillMLoc(*Loc);
// XXX -- can we recover sub-registers of this value? Until we can, first
// overwrite all defs of the register being restored to.
for (MCRegAliasIterator RAI(Reg, TRI, true); RAI.isValid(); ++RAI)
MTracker->defReg(*RAI, CurBB, CurInst);
// Now override the reg we're restoring to.
MTracker->setReg(Reg, ValueID);
// Report this restore to the transfer tracker too.
if (TTracker)
TTracker->transferMlocs(SpillLocIdx, MTracker->getRegMLoc(Reg),
} else {
// There isn't anything in the location; not clear if this is a code path
// that still runs. Def this register anyway just in case.
for (MCRegAliasIterator RAI(Reg, TRI, true); RAI.isValid(); ++RAI)
MTracker->defReg(*RAI, CurBB, CurInst);
// Force the spill slot to be tracked.
LocIdx L = MTracker->getOrTrackSpillLoc(*Loc);
// Set the restored value to be a machine phi number, signifying that it's
// whatever the spills live-in value is in this block. Definitely has
// a LocIdx due to the setSpill above.
ValueIDNum ValueID = {CurBB, 0, L};
MTracker->setReg(Reg, ValueID);
MTracker->setSpill(*Loc, ValueID);
return true;
bool InstrRefBasedLDV::transferRegisterCopy(MachineInstr &MI) {
auto DestSrc = TII->isCopyInstr(MI);
if (!DestSrc)
return false;
const MachineOperand *DestRegOp = DestSrc->Destination;
const MachineOperand *SrcRegOp = DestSrc->Source;
auto isCalleeSavedReg = [&](unsigned Reg) {
for (MCRegAliasIterator RAI(Reg, TRI, true); RAI.isValid(); ++RAI)
if (CalleeSavedRegs.test(*RAI))
return true;
return false;
Register SrcReg = SrcRegOp->getReg();
Register DestReg = DestRegOp->getReg();
// Ignore identity copies. Yep, these make it as far as LiveDebugValues.
if (SrcReg == DestReg)
return true;
// For emulating VarLocBasedImpl:
// We want to recognize instructions where destination register is callee
// saved register. If register that could be clobbered by the call is
// included, there would be a great chance that it is going to be clobbered
// soon. It is more likely that previous register, which is callee saved, is
// going to stay unclobbered longer, even if it is killed.
// For InstrRefBasedImpl, we can track multiple locations per value, so
// ignore this condition.
if (EmulateOldLDV && !isCalleeSavedReg(DestReg))
return false;
// InstrRefBasedImpl only followed killing copies.
if (EmulateOldLDV && !SrcRegOp->isKill())
return false;
// Copy MTracker info, including subregs if available.
InstrRefBasedLDV::performCopy(SrcReg, DestReg);
// Only produce a transfer of DBG_VALUE within a block where old LDV
// would have. We might make use of the additional value tracking in some
// other way, later.
if (TTracker && isCalleeSavedReg(DestReg) && SrcRegOp->isKill())
MTracker->getRegMLoc(DestReg), MI.getIterator());
// VarLocBasedImpl would quit tracking the old location after copying.
if (EmulateOldLDV && SrcReg != DestReg)
MTracker->defReg(SrcReg, CurBB, CurInst);
return true;
/// Accumulate a mapping between each DILocalVariable fragment and other
/// fragments of that DILocalVariable which overlap. This reduces work during
/// the data-flow stage from "Find any overlapping fragments" to "Check if the
/// known-to-overlap fragments are present".
/// \param MI A previously unprocessed DEBUG_VALUE instruction to analyze for
/// fragment usage.
void InstrRefBasedLDV::accumulateFragmentMap(MachineInstr &MI) {
DebugVariable MIVar(MI.getDebugVariable(), MI.getDebugExpression(),
FragmentInfo ThisFragment = MIVar.getFragmentOrDefault();
// If this is the first sighting of this variable, then we are guaranteed
// there are currently no overlapping fragments either. Initialize the set
// of seen fragments, record no overlaps for the current one, and return.
auto SeenIt = SeenFragments.find(MIVar.getVariable());
if (SeenIt == SeenFragments.end()) {
SmallSet<FragmentInfo, 4> OneFragment;
SeenFragments.insert({MIVar.getVariable(), OneFragment});
OverlapFragments.insert({{MIVar.getVariable(), ThisFragment}, {}});
// If this particular Variable/Fragment pair already exists in the overlap
// map, it has already been accounted for.
auto IsInOLapMap =
OverlapFragments.insert({{MIVar.getVariable(), ThisFragment}, {}});
if (!IsInOLapMap.second)
auto &ThisFragmentsOverlaps = IsInOLapMap.first->second;
auto &AllSeenFragments = SeenIt->second;
// Otherwise, examine all other seen fragments for this variable, with "this"
// fragment being a previously unseen fragment. Record any pair of
// overlapping fragments.
for (auto &ASeenFragment : AllSeenFragments) {
// Does this previously seen fragment overlap?
if (DIExpression::fragmentsOverlap(ThisFragment, ASeenFragment)) {
// Yes: Mark the current fragment as being overlapped.
// Mark the previously seen fragment as being overlapped by the current
// one.
auto ASeenFragmentsOverlaps =
OverlapFragments.find({MIVar.getVariable(), ASeenFragment});
assert(ASeenFragmentsOverlaps != OverlapFragments.end() &&
"Previously seen var fragment has no vector of overlaps");
void InstrRefBasedLDV::process(MachineInstr &MI) {
// Try to interpret an MI as a debug or transfer instruction. Only if it's
// none of these should we interpret it's register defs as new value
// definitions.
if (transferDebugValue(MI))
if (transferDebugInstrRef(MI))
if (transferRegisterCopy(MI))
if (transferSpillOrRestoreInst(MI))
void InstrRefBasedLDV::produceMLocTransferFunction(
MachineFunction &MF, SmallVectorImpl<MLocTransferMap> &MLocTransfer,
unsigned MaxNumBlocks) {
// Because we try to optimize around register mask operands by ignoring regs
// that aren't currently tracked, we set up something ugly for later: RegMask
// operands that are seen earlier than the first use of a register, still need
// to clobber that register in the transfer function. But this information
// isn't actively recorded. Instead, we track each RegMask used in each block,
// and accumulated the clobbered but untracked registers in each block into
// the following bitvector. Later, if new values are tracked, we can add
// appropriate clobbers.
SmallVector<BitVector, 32> BlockMasks;
// Reserve one bit per register for the masks described above.
unsigned BVWords = MachineOperand::getRegMaskSize(TRI->getNumRegs());
for (auto &BV : BlockMasks)
BV.resize(TRI->getNumRegs(), true);
// Step through all instructions and inhale the transfer function.
for (auto &MBB : MF) {
// Object fields that are read by trackers to know where we are in the
// function.
CurBB = MBB.getNumber();
CurInst = 1;
// Set all machine locations to a PHI value. For transfer function
// production only, this signifies the live-in value to the block.
// Step through each instruction in this block.
for (auto &MI : MBB) {
// Also accumulate fragment map.
if (MI.isDebugValue())
// Create a map from the instruction number (if present) to the
// MachineInstr and its position.
if (uint64_t InstrNo = MI.peekDebugInstrNum()) {
auto InstrAndPos = std::make_pair(&MI, CurInst);
auto InsertResult =
DebugInstrNumToInstr.insert(std::make_pair(InstrNo, InstrAndPos));
// There should never be duplicate instruction numbers.
// Produce the transfer function, a map of machine location to new value. If
// any machine location has the live-in phi value from the start of the
// block, it's live-through and doesn't need recording in the transfer
// function.
for (auto Location : MTracker->locations()) {
LocIdx Idx = Location.Idx;
ValueIDNum &P = Location.Value;
if (P.isPHI() && P.getLoc() == Idx.asU64())
// Insert-or-update.
auto &TransferMap = MLocTransfer[CurBB];
auto Result = TransferMap.insert(std::make_pair(Idx.asU64(), P));
if (!Result.second)
Result.first->second = P;
// Accumulate any bitmask operands into the clobberred reg mask for this
// block.
for (auto &P : MTracker->Masks) {
BlockMasks[CurBB].clearBitsNotInMask(P.first->getRegMask(), BVWords);
// Compute a bitvector of all the registers that are tracked in this block.
const TargetLowering *TLI = MF.getSubtarget().getTargetLowering();
Register SP = TLI->getStackPointerRegisterToSaveRestore();
BitVector UsedRegs(TRI->getNumRegs());
for (auto Location : MTracker->locations()) {
unsigned ID = MTracker->LocIdxToLocID[Location.Idx];
if (ID >= TRI->getNumRegs() || ID == SP)
// Check that any regmask-clobber of a register that gets tracked, is not
// live-through in the transfer function. It needs to be clobbered at the
// very least.
for (unsigned int I = 0; I < MaxNumBlocks; ++I) {
BitVector &BV = BlockMasks[I];
BV &= UsedRegs;
// This produces all the bits that we clobber, but also use. Check that
// they're all clobbered or at least set in the designated transfer
// elem.
for (unsigned Bit : BV.set_bits()) {
unsigned ID = MTracker->getLocID(Bit, false);
LocIdx Idx = MTracker->LocIDToLocIdx[ID];
auto &TransferMap = MLocTransfer[I];
// Install a value representing the fact that this location is effectively
// written to in this block. As there's no reserved value, instead use
// a value number that is never generated. Pick the value number for the
// first instruction in the block, def'ing this location, which we know
// this block never used anyway.
ValueIDNum NotGeneratedNum = ValueIDNum(I, 1, Idx);
auto Result =
TransferMap.insert(std::make_pair(Idx.asU64(), NotGeneratedNum));
if (!Result.second) {
ValueIDNum &ValueID = Result.first->second;
if (ValueID.getBlock() == I && ValueID.isPHI())
// It was left as live-through. Set it to clobbered.
ValueID = NotGeneratedNum;
std::tuple<bool, bool>
InstrRefBasedLDV::mlocJoin(MachineBasicBlock &MBB,
SmallPtrSet<const MachineBasicBlock *, 16> &Visited,
ValueIDNum **OutLocs, ValueIDNum *InLocs) {
LLVM_DEBUG(dbgs() << "join MBB: " << MBB.getNumber() << "\n");
bool Changed = false;
bool DowngradeOccurred = false;
// Collect predecessors that have been visited. Anything that hasn't been
// visited yet is a backedge on the first iteration, and the meet of it's
// lattice value for all locations will be unaffected.
SmallVector<const MachineBasicBlock *, 8> BlockOrders;
for (auto Pred : MBB.predecessors()) {
if (Visited.count(Pred)) {
// Visit predecessors in RPOT order.
auto Cmp = [&](const MachineBasicBlock *A, const MachineBasicBlock *B) {
return BBToOrder.find(A)->second < BBToOrder.find(B)->second;
llvm::sort(BlockOrders, Cmp);
// Skip entry block.
if (BlockOrders.size() == 0)
return std::tuple<bool, bool>(false, false);
// Step through all machine locations, then look at each predecessor and
// detect disagreements.
unsigned ThisBlockRPO = BBToOrder.find(&MBB)->second;
for (auto Location : MTracker->locations()) {
LocIdx Idx = Location.Idx;
// Pick out the first predecessors live-out value for this location. It's
// guaranteed to be not a backedge, as we order by RPO.
ValueIDNum BaseVal = OutLocs[BlockOrders[0]->getNumber()][Idx.asU64()];
// Some flags for whether there's a disagreement, and whether it's a
// disagreement with a backedge or not.
bool Disagree = false;
bool NonBackEdgeDisagree = false;
// Loop around everything that wasn't 'base'.
for (unsigned int I = 1; I < BlockOrders.size(); ++I) {
auto *MBB = BlockOrders[I];
if (BaseVal != OutLocs[MBB->getNumber()][Idx.asU64()]) {
// Live-out of a predecessor disagrees with the first predecessor.
Disagree = true;
// Test whether it's a disagreemnt in the backedges or not.
if (BBToOrder.find(MBB)->second < ThisBlockRPO) // might be self b/e
NonBackEdgeDisagree = true;
bool OverRide = false;
if (Disagree && !NonBackEdgeDisagree) {
// Only the backedges disagree. Consider demoting the livein
// lattice value, as per the file level comment. The value we consider
// demoting to is the value that the non-backedge predecessors agree on.
// The order of values is that non-PHIs are \top, a PHI at this block
// \bot, and phis between the two are ordered by their RPO number.
// If there's no agreement, or we've already demoted to this PHI value
// before, replace with a PHI value at this block.
// Calculate order numbers: zero means normal def, nonzero means RPO
// number.
unsigned BaseBlockRPONum = BBNumToRPO[BaseVal.getBlock()] + 1;
if (!BaseVal.isPHI())
BaseBlockRPONum = 0;
ValueIDNum &InLocID = InLocs[Idx.asU64()];
unsigned InLocRPONum = BBNumToRPO[InLocID.getBlock()] + 1;
if (!InLocID.isPHI())
InLocRPONum = 0;
// Should we ignore the disagreeing backedges, and override with the
// value the other predecessors agree on (in "base")?
unsigned ThisBlockRPONum = BBNumToRPO[MBB.getNumber()] + 1;
if (BaseBlockRPONum > InLocRPONum && BaseBlockRPONum < ThisBlockRPONum) {
// Override.
OverRide = true;
DowngradeOccurred = true;
// else: if we disagree in the non-backedges, then this is definitely
// a control flow merge where different values merge. Make it a PHI.
// Generate a phi...
ValueIDNum PHI = {(uint64_t)MBB.getNumber(), 0, Idx};
ValueIDNum NewVal = (Disagree && !OverRide) ? PHI : BaseVal;
if (InLocs[Idx.asU64()] != NewVal) {
Changed |= true;
InLocs[Idx.asU64()] = NewVal;
// TODO: Reimplement NumInserted and NumRemoved.
return std::tuple<bool, bool>(Changed, DowngradeOccurred);
void InstrRefBasedLDV::mlocDataflow(
ValueIDNum **MInLocs, ValueIDNum **MOutLocs,
SmallVectorImpl<MLocTransferMap> &MLocTransfer) {
std::priority_queue<unsigned int, std::vector<unsigned int>,
std::greater<unsigned int>>
Worklist, Pending;
// We track what is on the current and pending worklist to avoid inserting
// the same thing twice. We could avoid this with a custom priority queue,
// but this is probably not worth it.
SmallPtrSet<MachineBasicBlock *, 16> OnPending, OnWorklist;
// Initialize worklist with every block to be visited.
for (unsigned int I = 0; I < BBToOrder.size(); ++I) {
// Set inlocs for entry block -- each as a PHI at the entry block. Represents
// the incoming value to the function.
for (auto Location : MTracker->locations())
MInLocs[0][Location.Idx.asU64()] = Location.Value;
SmallPtrSet<const MachineBasicBlock *, 16> Visited;
while (!Worklist.empty() || !Pending.empty()) {
// Vector for storing the evaluated block transfer function.
SmallVector<std::pair<LocIdx, ValueIDNum>, 32> ToRemap;
while (!Worklist.empty()) {
MachineBasicBlock *MBB = OrderToBB[];
CurBB = MBB->getNumber();
// Join the values in all predecessor blocks.
bool InLocsChanged, DowngradeOccurred;
std::tie(InLocsChanged, DowngradeOccurred) =
mlocJoin(*MBB, Visited, MOutLocs, MInLocs[CurBB]);
InLocsChanged |= Visited.insert(MBB).second;
// If a downgrade occurred, book us in for re-examination on the next
// iteration.
if (DowngradeOccurred && OnPending.insert(MBB).second)
// Don't examine transfer function if we've visited this loc at least
// once, and inlocs haven't changed.
if (!InLocsChanged)
// Load the current set of live-ins into MLocTracker.
MTracker->loadFromArray(MInLocs[CurBB], CurBB);
// Each element of the transfer function can be a new def, or a read of
// a live-in value. Evaluate each element, and store to "ToRemap".
for (auto &P : MLocTransfer[CurBB]) {
if (P.second.getBlock() == CurBB && P.second.isPHI()) {
// This is a movement of whatever was live in. Read it.
ValueIDNum NewID = MTracker->getNumAtPos(P.second.getLoc());
ToRemap.push_back(std::make_pair(P.first, NewID));
} else {
// It's a def. Just set it.
assert(P.second.getBlock() == CurBB);
ToRemap.push_back(std::make_pair(P.first, P.second));
// Commit the transfer function changes into mloc tracker, which
// transforms the contents of the MLocTracker into the live-outs.
for (auto &P : ToRemap)
MTracker->setMLoc(P.first, P.second);
// Now copy out-locs from mloc tracker into out-loc vector, checking
// whether changes have occurred. These changes can have come from both
// the transfer function, and mlocJoin.
bool OLChanged = false;
for (auto Location : MTracker->locations()) {
OLChanged |= MOutLocs[CurBB][Location.Idx.asU64()] != Location.Value;
MOutLocs[CurBB][Location.Idx.asU64()] = Location.Value;
// No need to examine successors again if out-locs didn't change.
if (!OLChanged)
// All successors should be visited: put any back-edges on the pending
// list for the next dataflow iteration, and any other successors to be
// visited this iteration, if they're not going to be already.
for (auto s : MBB->successors()) {
// Does branching to this successor represent a back-edge?
if (BBToOrder[s] > BBToOrder[MBB]) {
// No: visit it during this dataflow iteration.
if (OnWorklist.insert(s).second)
} else {
// Yes: visit it on the next iteration.
if (OnPending.insert(s).second)
std::swap(OnPending, OnWorklist);
// At this point, pending must be empty, since it was just the empty
// worklist
assert(Pending.empty() && "Pending should be empty");
// Once all the live-ins don't change on mlocJoin(), we've reached a
// fixedpoint.
bool InstrRefBasedLDV::vlocDowngradeLattice(
const MachineBasicBlock &MBB, const DbgValue &OldLiveInLocation,
const SmallVectorImpl<InValueT> &Values, unsigned CurBlockRPONum) {
// Ranking value preference: see file level comment, the highest rank is
// a plain def, followed by PHI values in reverse post-order. Numerically,
// we assign all defs the rank '0', all PHIs their blocks RPO number plus
// one, and consider the lowest value the highest ranked.
int OldLiveInRank = BBNumToRPO[OldLiveInLocation.ID.getBlock()] + 1;
if (!OldLiveInLocation.ID.isPHI())
OldLiveInRank = 0;
// Allow any unresolvable conflict to be over-ridden.
if (OldLiveInLocation.Kind == DbgValue::NoVal) {
// Although if it was an unresolvable conflict from _this_ block, then
// all other seeking of downgrades and PHIs must have failed before hand.
if (OldLiveInLocation.BlockNo == (unsigned)MBB.getNumber())
return false;
OldLiveInRank = INT_MIN;
auto &InValue = *Values[0].second;
if (InValue.Kind == DbgValue::Const || InValue.Kind == DbgValue::NoVal)
return false;
unsigned ThisRPO = BBNumToRPO[InValue.ID.getBlock()];
int ThisRank = ThisRPO + 1;
if (!InValue.ID.isPHI())
ThisRank = 0;
// Too far down the lattice?
if (ThisRPO >= CurBlockRPONum)
return false;
// Higher in the lattice than what we've already explored?
if (ThisRank <= OldLiveInRank)
return false;
return true;
std::tuple<Optional<ValueIDNum>, bool> InstrRefBasedLDV::pickVPHILoc(
MachineBasicBlock &MBB, const DebugVariable &Var, const LiveIdxT &LiveOuts,
ValueIDNum **MOutLocs, ValueIDNum **MInLocs,
const SmallVectorImpl<MachineBasicBlock *> &BlockOrders) {
// Collect a set of locations from predecessor where its live-out value can
// be found.
SmallVector<SmallVector<LocIdx, 4>, 8> Locs;
unsigned NumLocs = MTracker->getNumLocs();
unsigned BackEdgesStart = 0;
for (auto p : BlockOrders) {
// Pick out where backedges start in the list of predecessors. Relies on
// BlockOrders being sorted by RPO.
if (BBToOrder[p] < BBToOrder[&MBB])
// For each predecessor, create a new set of locations.
Locs.resize(Locs.size() + 1);
unsigned ThisBBNum = p->getNumber();
auto LiveOutMap = LiveOuts.find(p);
if (LiveOutMap == LiveOuts.end())
// This predecessor isn't in scope, it must have no live-in/live-out
// locations.
auto It = LiveOutMap->second->find(Var);
if (It == LiveOutMap->second->end())
// There's no value recorded for this variable in this predecessor,
// leave an empty set of locations.
const DbgValue &OutVal = It->second;
if (OutVal.Kind == DbgValue::Const || OutVal.Kind == DbgValue::NoVal)
// Consts and no-values cannot have locations we can join on.
assert(OutVal.Kind == DbgValue::Proposed || OutVal.Kind == DbgValue::Def);
ValueIDNum ValToLookFor = OutVal.ID;
// Search the live-outs of the predecessor for the specified value.
for (unsigned int I = 0; I < NumLocs; ++I) {
if (MOutLocs[ThisBBNum][I] == ValToLookFor)
// If there were no locations at all, return an empty result.
if (Locs.empty())
return std::tuple<Optional<ValueIDNum>, bool>(None, false);
// Lambda for seeking a common location within a range of location-sets.
using LocsIt = SmallVector<SmallVector<LocIdx, 4>, 8>::iterator;
auto SeekLocation =
[&Locs](llvm::iterator_range<LocsIt> SearchRange) -> Optional<LocIdx> {
// Starting with the first set of locations, take the intersection with
// subsequent sets.
SmallVector<LocIdx, 4> base = Locs[0];
for (auto &S : SearchRange) {
SmallVector<LocIdx, 4> new_base;
std::set_intersection(base.begin(), base.end(), S.begin(), S.end(),
std::inserter(new_base, new_base.begin()));
base = new_base;
if (base.empty())
return None;
// We now have a set of LocIdxes that contain the right output value in
// each of the predecessors. Pick the lowest; if there's a register loc,
// that'll be it.
return *base.begin();
// Search for a common location for all predecessors. If we can't, then fall
// back to only finding a common location between non-backedge predecessors.
bool ValidForAllLocs = true;
auto TheLoc = SeekLocation(Locs);
if (!TheLoc) {
ValidForAllLocs = false;
TheLoc =
SeekLocation(make_range(Locs.begin(), Locs.begin() + BackEdgesStart));
if (!TheLoc)
return std::tuple<Optional<ValueIDNum>, bool>(None, false);
// Return a PHI-value-number for the found location.
LocIdx L = *TheLoc;
ValueIDNum PHIVal = {(unsigned)MBB.getNumber(), 0, L};
return std::tuple<Optional<ValueIDNum>, bool>(PHIVal, ValidForAllLocs);
std::tuple<bool, bool> InstrRefBasedLDV::vlocJoin(
MachineBasicBlock &MBB, LiveIdxT &VLOCOutLocs, LiveIdxT &VLOCInLocs,
SmallPtrSet<const MachineBasicBlock *, 16> *VLOCVisited, unsigned BBNum,
const SmallSet<DebugVariable, 4> &AllVars, ValueIDNum **MOutLocs,
ValueIDNum **MInLocs,
SmallPtrSet<const MachineBasicBlock *, 8> &InScopeBlocks,
SmallPtrSet<const MachineBasicBlock *, 8> &BlocksToExplore,
DenseMap<DebugVariable, DbgValue> &InLocsT) {
bool DowngradeOccurred = false;
// To emulate VarLocBasedImpl, process this block if it's not in scope but
// _does_ assign a variable value. No live-ins for this scope are transferred
// in though, so we can return immediately.
if (InScopeBlocks.count(&MBB) == 0 && !ArtificialBlocks.count(&MBB)) {
if (VLOCVisited)
return std::tuple<bool, bool>(true, false);
return std::tuple<bool, bool>(false, false);
LLVM_DEBUG(dbgs() << "join MBB: " << MBB.getNumber() << "\n");
bool Changed = false;
// Find any live-ins computed in a prior iteration.
auto ILSIt = VLOCInLocs.find(&MBB);
assert(ILSIt != VLOCInLocs.end());
auto &ILS = *ILSIt->second;
// Order predecessors by RPOT order, for exploring them in that order.
SmallVector<MachineBasicBlock *, 8> BlockOrders(MBB.predecessors());
auto Cmp = [&](MachineBasicBlock *A, MachineBasicBlock *B) {
return BBToOrder[A] < BBToOrder[B];
llvm::sort(BlockOrders, Cmp);
unsigned CurBlockRPONum = BBToOrder[&MBB];
// Force a re-visit to loop heads in the first dataflow iteration.
// FIXME: if we could "propose" Const values this wouldn't be needed,
// because they'd need to be confirmed before being emitted.
if (!BlockOrders.empty() &&
BBToOrder[BlockOrders[BlockOrders.size() - 1]] >= CurBlockRPONum &&
DowngradeOccurred = true;
auto ConfirmValue = [&InLocsT](const DebugVariable &DV, DbgValue VR) {
auto Result = InLocsT.insert(std::make_pair(DV, VR));
auto ConfirmNoVal = [&ConfirmValue, &MBB](const DebugVariable &Var, const DbgValueProperties &Properties) {
DbgValue NoLocPHIVal(MBB.getNumber(), Properties, DbgValue::NoVal);
ConfirmValue(Var, NoLocPHIVal);
// Attempt to join the values for each variable.
for (auto &Var : AllVars) {
// Collect all the DbgValues for this variable.
SmallVector<InValueT, 8> Values;
bool Bail = false;
unsigned BackEdgesStart = 0;
for (auto p : BlockOrders) {
// If the predecessor isn't in scope / to be explored, we'll never be
// able to join any locations.
if (!BlocksToExplore.contains(p)) {
Bail = true;
// Don't attempt to handle unvisited predecessors: they're implicitly
// "unknown"s in the lattice.
if (VLOCVisited && !VLOCVisited->count(p))
// If the predecessors OutLocs is absent, there's not much we can do.
auto OL = VLOCOutLocs.find(p);
if (OL == VLOCOutLocs.end()) {
Bail = true;
// No live-out value for this predecessor also means we can't produce
// a joined value.
auto VIt = OL->second->find(Var);
if (VIt == OL->second->end()) {
Bail = true;
// Keep track of where back-edges begin in the Values vector. Relies on
// BlockOrders being sorted by RPO.
unsigned ThisBBRPONum = BBToOrder[p];
if (ThisBBRPONum < CurBlockRPONum)
Values.push_back(std::make_pair(p, &VIt->second));
// If there were no values, or one of the predecessors couldn't have a
// value, then give up immediately. It's not safe to produce a live-in
// value.
if (Bail || Values.size() == 0)
// Enumeration identifying the current state of the predecessors values.
enum {
Unset = 0,
Agreed, // All preds agree on the variable value.
PropDisagree, // All preds agree, but the value kind is Proposed in some.
BEDisagree, // Only back-edges disagree on variable value.
PHINeeded, // Non-back-edge predecessors have conflicing values.
NoSolution // Conflicting Value metadata makes solution impossible.
} OurState = Unset;
// All (non-entry) blocks have at least one non-backedge predecessor.
// Pick the variable value from the first of these, to compare against
// all others.
const DbgValue &FirstVal = *Values[0].second;
const ValueIDNum &FirstID = FirstVal.ID;
// Scan for variable values that can't be resolved: if they have different
// DIExpressions, different indirectness, or are mixed constants /
// non-constants.
for (auto &V : Values) {
if (V.second->Properties != FirstVal.Properties)
OurState = NoSolution;
if (V.second->Kind == DbgValue::Const && FirstVal.Kind != DbgValue::Const)
OurState = NoSolution;
// Flags diagnosing _how_ the values disagree.
bool NonBackEdgeDisagree = false;
bool DisagreeOnPHINess = false;
bool IDDisagree = false;
bool Disagree = false;
if (OurState == Unset) {
for (auto &V : Values) {
if (*V.second == FirstVal)
continue; // No disagreement.
Disagree = true;
// Flag whether the value number actually diagrees.
if (V.second->ID != FirstID)
IDDisagree = true;
// Distinguish whether disagreement happens in backedges or not.
// Relies on Values (and BlockOrders) being sorted by RPO.
unsigned ThisBBRPONum = BBToOrder[V.first];
if (ThisBBRPONum < CurBlockRPONum)
NonBackEdgeDisagree = true;
// Is there a difference in whether the value is definite or only
// proposed?
if (V.second->Kind != FirstVal.Kind &&
(V.second->Kind == DbgValue::Proposed ||
V.second->Kind == DbgValue::Def) &&
(FirstVal.Kind == DbgValue::Proposed ||
FirstVal.Kind == DbgValue::Def))
DisagreeOnPHINess = true;
// Collect those flags together and determine an overall state for
// what extend the predecessors agree on a live-in value.
if (!Disagree)
OurState = Agreed;
else if (!IDDisagree && DisagreeOnPHINess)
OurState = PropDisagree;
else if (!NonBackEdgeDisagree)
OurState = BEDisagree;