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//==-- llvm/CodeGen/ExecutionDomainFix.h - Execution Domain Fix -*- C++ -*--==//
// 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 Execution Domain Fix pass.
/// Some X86 SSE instructions like mov, and, or, xor are available in different
/// variants for different operand types. These variant instructions are
/// equivalent, but on Nehalem and newer cpus there is extra latency
/// transferring data between integer and floating point domains. ARM cores
/// have similar issues when they are configured with both VFP and NEON
/// pipelines.
/// This pass changes the variant instructions to minimize domain crossings.
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/LoopTraversal.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/ReachingDefAnalysis.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
namespace llvm {
class MachineBasicBlock;
class MachineInstr;
class TargetInstrInfo;
/// A DomainValue is a bit like LiveIntervals' ValNo, but it also keeps track
/// of execution domains.
/// An open DomainValue represents a set of instructions that can still switch
/// execution domain. Multiple registers may refer to the same open
/// DomainValue - they will eventually be collapsed to the same execution
/// domain.
/// A collapsed DomainValue represents a single register that has been forced
/// into one of more execution domains. There is a separate collapsed
/// DomainValue for each register, but it may contain multiple execution
/// domains. A register value is initially created in a single execution
/// domain, but if we were forced to pay the penalty of a domain crossing, we
/// keep track of the fact that the register is now available in multiple
/// domains.
struct DomainValue {
/// Basic reference counting.
unsigned Refs = 0;
/// Bitmask of available domains. For an open DomainValue, it is the still
/// possible domains for collapsing. For a collapsed DomainValue it is the
/// domains where the register is available for free.
unsigned AvailableDomains;
/// Pointer to the next DomainValue in a chain. When two DomainValues are
/// merged, Victim.Next is set to point to Victor, so old DomainValue
/// references can be updated by following the chain.
DomainValue *Next;
/// Twiddleable instructions using or defining these registers.
SmallVector<MachineInstr *, 8> Instrs;
DomainValue() { clear(); }
/// A collapsed DomainValue has no instructions to twiddle - it simply keeps
/// track of the domains where the registers are already available.
bool isCollapsed() const { return Instrs.empty(); }
/// Is domain available?
bool hasDomain(unsigned domain) const {
assert(domain <
static_cast<unsigned>(std::numeric_limits<unsigned>::digits) &&
"undefined behavior");
return AvailableDomains & (1u << domain);
/// Mark domain as available.
void addDomain(unsigned domain) { AvailableDomains |= 1u << domain; }
// Restrict to a single domain available.
void setSingleDomain(unsigned domain) { AvailableDomains = 1u << domain; }
/// Return bitmask of domains that are available and in mask.
unsigned getCommonDomains(unsigned mask) const {
return AvailableDomains & mask;
/// First domain available.
unsigned getFirstDomain() const {
return countTrailingZeros(AvailableDomains);
/// Clear this DomainValue and point to next which has all its data.
void clear() {
AvailableDomains = 0;
Next = nullptr;
class ExecutionDomainFix : public MachineFunctionPass {
SpecificBumpPtrAllocator<DomainValue> Allocator;
SmallVector<DomainValue *, 16> Avail;
const TargetRegisterClass *const RC;
MachineFunction *MF;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
std::vector<SmallVector<int, 1>> AliasMap;
const unsigned NumRegs;
/// Value currently in each register, or NULL when no value is being tracked.
/// This counts as a DomainValue reference.
using LiveRegsDVInfo = std::vector<DomainValue *>;
LiveRegsDVInfo LiveRegs;
/// Keeps domain information for all registers. Note that this
/// is different from the usual definition notion of liveness. The CPU
/// doesn't care whether or not we consider a register killed.
using OutRegsInfoMap = SmallVector<LiveRegsDVInfo, 4>;
OutRegsInfoMap MBBOutRegsInfos;
ReachingDefAnalysis *RDA;
ExecutionDomainFix(char &PassID, const TargetRegisterClass &RC)
: MachineFunctionPass(PassID), RC(&RC), NumRegs(RC.getNumRegs()) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
bool runOnMachineFunction(MachineFunction &MF) override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
/// Translate TRI register number to a list of indices into our smaller tables
/// of interesting registers.
regIndices(unsigned Reg) const;
/// DomainValue allocation.
DomainValue *alloc(int domain = -1);
/// Add reference to DV.
DomainValue *retain(DomainValue *DV) {
if (DV)
return DV;
/// Release a reference to DV. When the last reference is released,
/// collapse if needed.
void release(DomainValue *);
/// Follow the chain of dead DomainValues until a live DomainValue is reached.
/// Update the referenced pointer when necessary.
DomainValue *resolve(DomainValue *&);
/// Set LiveRegs[rx] = dv, updating reference counts.
void setLiveReg(int rx, DomainValue *DV);
/// Kill register rx, recycle or collapse any DomainValue.
void kill(int rx);
/// Force register rx into domain.
void force(int rx, unsigned domain);
/// Collapse open DomainValue into given domain. If there are multiple
/// registers using dv, they each get a unique collapsed DomainValue.
void collapse(DomainValue *dv, unsigned domain);
/// All instructions and registers in B are moved to A, and B is released.
bool merge(DomainValue *A, DomainValue *B);
/// Set up LiveRegs by merging predecessor live-out values.
void enterBasicBlock(const LoopTraversal::TraversedMBBInfo &TraversedMBB);
/// Update live-out values.
void leaveBasicBlock(const LoopTraversal::TraversedMBBInfo &TraversedMBB);
/// Process he given basic block.
void processBasicBlock(const LoopTraversal::TraversedMBBInfo &TraversedMBB);
/// Visit given insturcion.
bool visitInstr(MachineInstr *);
/// Update def-ages for registers defined by MI.
/// If Kill is set, also kill off DomainValues clobbered by the defs.
void processDefs(MachineInstr *, bool Kill);
/// A soft instruction can be changed to work in other domains given by mask.
void visitSoftInstr(MachineInstr *, unsigned mask);
/// A hard instruction only works in one domain. All input registers will be
/// forced into that domain.
void visitHardInstr(MachineInstr *, unsigned domain);
} // namespace llvm