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//===- BasicBlockUtils.cpp - BasicBlock Utilities --------------------------==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This family of functions perform manipulations on basic blocks, and
// instructions contained within basic blocks.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Analysis/MemorySSAUpdater.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
#include <cassert>
#include <cstdint>
#include <string>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "basicblock-utils"
static cl::opt<unsigned> MaxDeoptOrUnreachableSuccessorCheckDepth(
"max-deopt-or-unreachable-succ-check-depth", cl::init(8), cl::Hidden,
cl::desc("Set the maximum path length when checking whether a basic block "
"is followed by a block that either has a terminating "
"deoptimizing call or is terminated with an unreachable"));
void llvm::detachDeadBlocks(
ArrayRef<BasicBlock *> BBs,
SmallVectorImpl<DominatorTree::UpdateType> *Updates,
bool KeepOneInputPHIs) {
for (auto *BB : BBs) {
// Loop through all of our successors and make sure they know that one
// of their predecessors is going away.
SmallPtrSet<BasicBlock *, 4> UniqueSuccessors;
for (BasicBlock *Succ : successors(BB)) {
Succ->removePredecessor(BB, KeepOneInputPHIs);
if (Updates && UniqueSuccessors.insert(Succ).second)
Updates->push_back({DominatorTree::Delete, BB, Succ});
}
// Zap all the instructions in the block.
while (!BB->empty()) {
Instruction &I = BB->back();
// If this instruction is used, replace uses with an arbitrary value.
// Because control flow can't get here, we don't care what we replace the
// value with. Note that since this block is unreachable, and all values
// contained within it must dominate their uses, that all uses will
// eventually be removed (they are themselves dead).
if (!I.use_empty())
I.replaceAllUsesWith(PoisonValue::get(I.getType()));
BB->back().eraseFromParent();
}
new UnreachableInst(BB->getContext(), BB);
assert(BB->size() == 1 &&
isa<UnreachableInst>(BB->getTerminator()) &&
"The successor list of BB isn't empty before "
"applying corresponding DTU updates.");
}
}
void llvm::DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU,
bool KeepOneInputPHIs) {
DeleteDeadBlocks({BB}, DTU, KeepOneInputPHIs);
}
void llvm::DeleteDeadBlocks(ArrayRef <BasicBlock *> BBs, DomTreeUpdater *DTU,
bool KeepOneInputPHIs) {
#ifndef NDEBUG
// Make sure that all predecessors of each dead block is also dead.
SmallPtrSet<BasicBlock *, 4> Dead(BBs.begin(), BBs.end());
assert(Dead.size() == BBs.size() && "Duplicating blocks?");
for (auto *BB : Dead)
for (BasicBlock *Pred : predecessors(BB))
assert(Dead.count(Pred) && "All predecessors must be dead!");
#endif
SmallVector<DominatorTree::UpdateType, 4> Updates;
detachDeadBlocks(BBs, DTU ? &Updates : nullptr, KeepOneInputPHIs);
if (DTU)
DTU->applyUpdates(Updates);
for (BasicBlock *BB : BBs)
if (DTU)
DTU->deleteBB(BB);
else
BB->eraseFromParent();
}
bool llvm::EliminateUnreachableBlocks(Function &F, DomTreeUpdater *DTU,
bool KeepOneInputPHIs) {
df_iterator_default_set<BasicBlock*> Reachable;
// Mark all reachable blocks.
for (BasicBlock *BB : depth_first_ext(&F, Reachable))
(void)BB/* Mark all reachable blocks */;
// Collect all dead blocks.
std::vector<BasicBlock*> DeadBlocks;
for (BasicBlock &BB : F)
if (!Reachable.count(&BB))
DeadBlocks.push_back(&BB);
// Delete the dead blocks.
DeleteDeadBlocks(DeadBlocks, DTU, KeepOneInputPHIs);
return !DeadBlocks.empty();
}
bool llvm::FoldSingleEntryPHINodes(BasicBlock *BB,
MemoryDependenceResults *MemDep) {
if (!isa<PHINode>(BB->begin()))
return false;
while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
if (PN->getIncomingValue(0) != PN)
PN->replaceAllUsesWith(PN->getIncomingValue(0));
else
PN->replaceAllUsesWith(PoisonValue::get(PN->getType()));
if (MemDep)
MemDep->removeInstruction(PN); // Memdep updates AA itself.
PN->eraseFromParent();
}
return true;
}
bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI,
MemorySSAUpdater *MSSAU) {
// Recursively deleting a PHI may cause multiple PHIs to be deleted
// or RAUW'd undef, so use an array of WeakTrackingVH for the PHIs to delete.
SmallVector<WeakTrackingVH, 8> PHIs;
for (PHINode &PN : BB->phis())
PHIs.push_back(&PN);
bool Changed = false;
for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
Changed |= RecursivelyDeleteDeadPHINode(PN, TLI, MSSAU);
return Changed;
}
bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
LoopInfo *LI, MemorySSAUpdater *MSSAU,
MemoryDependenceResults *MemDep,
bool PredecessorWithTwoSuccessors,
DominatorTree *DT) {
if (BB->hasAddressTaken())
return false;
// Can't merge if there are multiple predecessors, or no predecessors.
BasicBlock *PredBB = BB->getUniquePredecessor();
if (!PredBB) return false;
// Don't break self-loops.
if (PredBB == BB) return false;
// Don't break unwinding instructions or terminators with other side-effects.
Instruction *PTI = PredBB->getTerminator();
if (PTI->isSpecialTerminator() || PTI->mayHaveSideEffects())
return false;
// Can't merge if there are multiple distinct successors.
if (!PredecessorWithTwoSuccessors && PredBB->getUniqueSuccessor() != BB)
return false;
// Currently only allow PredBB to have two predecessors, one being BB.
// Update BI to branch to BB's only successor instead of BB.
BranchInst *PredBB_BI;
BasicBlock *NewSucc = nullptr;
unsigned FallThruPath;
if (PredecessorWithTwoSuccessors) {
if (!(PredBB_BI = dyn_cast<BranchInst>(PTI)))
return false;
BranchInst *BB_JmpI = dyn_cast<BranchInst>(BB->getTerminator());
if (!BB_JmpI || !BB_JmpI->isUnconditional())
return false;
NewSucc = BB_JmpI->getSuccessor(0);
FallThruPath = PredBB_BI->getSuccessor(0) == BB ? 0 : 1;
}
// Can't merge if there is PHI loop.
for (PHINode &PN : BB->phis())
if (llvm::is_contained(PN.incoming_values(), &PN))
return false;
LLVM_DEBUG(dbgs() << "Merging: " << BB->getName() << " into "
<< PredBB->getName() << "\n");
// Begin by getting rid of unneeded PHIs.
SmallVector<AssertingVH<Value>, 4> IncomingValues;
if (isa<PHINode>(BB->front())) {
for (PHINode &PN : BB->phis())
if (!isa<PHINode>(PN.getIncomingValue(0)) ||
cast<PHINode>(PN.getIncomingValue(0))->getParent() != BB)
IncomingValues.push_back(PN.getIncomingValue(0));
FoldSingleEntryPHINodes(BB, MemDep);
}
if (DT) {
assert(!DTU && "cannot use both DT and DTU for updates");
DomTreeNode *PredNode = DT->getNode(PredBB);
DomTreeNode *BBNode = DT->getNode(BB);
if (PredNode) {
assert(BBNode && "PredNode unreachable but BBNode reachable?");
for (DomTreeNode *C : to_vector(BBNode->children()))
C->setIDom(PredNode);
}
}
// DTU update: Collect all the edges that exit BB.
// These dominator edges will be redirected from Pred.
std::vector<DominatorTree::UpdateType> Updates;
if (DTU) {
assert(!DT && "cannot use both DT and DTU for updates");
// To avoid processing the same predecessor more than once.
SmallPtrSet<BasicBlock *, 8> SeenSuccs;
SmallPtrSet<BasicBlock *, 2> SuccsOfPredBB(succ_begin(PredBB),
succ_end(PredBB));
Updates.reserve(Updates.size() + 2 * succ_size(BB) + 1);
// Add insert edges first. Experimentally, for the particular case of two
// blocks that can be merged, with a single successor and single predecessor
// respectively, it is beneficial to have all insert updates first. Deleting
// edges first may lead to unreachable blocks, followed by inserting edges
// making the blocks reachable again. Such DT updates lead to high compile
// times. We add inserts before deletes here to reduce compile time.
for (BasicBlock *SuccOfBB : successors(BB))
// This successor of BB may already be a PredBB's successor.
if (!SuccsOfPredBB.contains(SuccOfBB))
if (SeenSuccs.insert(SuccOfBB).second)
Updates.push_back({DominatorTree::Insert, PredBB, SuccOfBB});
SeenSuccs.clear();
for (BasicBlock *SuccOfBB : successors(BB))
if (SeenSuccs.insert(SuccOfBB).second)
Updates.push_back({DominatorTree::Delete, BB, SuccOfBB});
Updates.push_back({DominatorTree::Delete, PredBB, BB});
}
Instruction *STI = BB->getTerminator();
Instruction *Start = &*BB->begin();
// If there's nothing to move, mark the starting instruction as the last
// instruction in the block. Terminator instruction is handled separately.
if (Start == STI)
Start = PTI;
// Move all definitions in the successor to the predecessor...
PredBB->splice(PTI->getIterator(), BB, BB->begin(), STI->getIterator());
if (MSSAU)
MSSAU->moveAllAfterMergeBlocks(BB, PredBB, Start);
// Make all PHI nodes that referred to BB now refer to Pred as their
// source...
BB->replaceAllUsesWith(PredBB);
if (PredecessorWithTwoSuccessors) {
// Delete the unconditional branch from BB.
BB->back().eraseFromParent();
// Update branch in the predecessor.
PredBB_BI->setSuccessor(FallThruPath, NewSucc);
} else {
// Delete the unconditional branch from the predecessor.
PredBB->back().eraseFromParent();
// Move terminator instruction.
BB->back().moveBeforePreserving(*PredBB, PredBB->end());
// Terminator may be a memory accessing instruction too.
if (MSSAU)
if (MemoryUseOrDef *MUD = cast_or_null<MemoryUseOrDef>(
MSSAU->getMemorySSA()->getMemoryAccess(PredBB->getTerminator())))
MSSAU->moveToPlace(MUD, PredBB, MemorySSA::End);
}
// Add unreachable to now empty BB.
new UnreachableInst(BB->getContext(), BB);
// Inherit predecessors name if it exists.
if (!PredBB->hasName())
PredBB->takeName(BB);
if (LI)
LI->removeBlock(BB);
if (MemDep)
MemDep->invalidateCachedPredecessors();
if (DTU)
DTU->applyUpdates(Updates);
if (DT) {
assert(succ_empty(BB) &&
"successors should have been transferred to PredBB");
DT->eraseNode(BB);
}
// Finally, erase the old block and update dominator info.
DeleteDeadBlock(BB, DTU);
return true;
}
bool llvm::MergeBlockSuccessorsIntoGivenBlocks(
SmallPtrSetImpl<BasicBlock *> &MergeBlocks, Loop *L, DomTreeUpdater *DTU,
LoopInfo *LI) {
assert(!MergeBlocks.empty() && "MergeBlocks should not be empty");
bool BlocksHaveBeenMerged = false;
while (!MergeBlocks.empty()) {
BasicBlock *BB = *MergeBlocks.begin();
BasicBlock *Dest = BB->getSingleSuccessor();
if (Dest && (!L || L->contains(Dest))) {
BasicBlock *Fold = Dest->getUniquePredecessor();
(void)Fold;
if (MergeBlockIntoPredecessor(Dest, DTU, LI)) {
assert(Fold == BB &&
"Expecting BB to be unique predecessor of the Dest block");
MergeBlocks.erase(Dest);
BlocksHaveBeenMerged = true;
} else
MergeBlocks.erase(BB);
} else
MergeBlocks.erase(BB);
}
return BlocksHaveBeenMerged;
}
/// Remove redundant instructions within sequences of consecutive dbg.value
/// instructions. This is done using a backward scan to keep the last dbg.value
/// describing a specific variable/fragment.
///
/// BackwardScan strategy:
/// ----------------------
/// Given a sequence of consecutive DbgValueInst like this
///
/// dbg.value ..., "x", FragmentX1 (*)
/// dbg.value ..., "y", FragmentY1
/// dbg.value ..., "x", FragmentX2
/// dbg.value ..., "x", FragmentX1 (**)
///
/// then the instruction marked with (*) can be removed (it is guaranteed to be
/// obsoleted by the instruction marked with (**) as the latter instruction is
/// describing the same variable using the same fragment info).
///
/// Possible improvements:
/// - Check fully overlapping fragments and not only identical fragments.
/// - Support dbg.declare. dbg.label, and possibly other meta instructions being
/// part of the sequence of consecutive instructions.
static bool
DbgVariableRecordsRemoveRedundantDbgInstrsUsingBackwardScan(BasicBlock *BB) {
SmallVector<DbgVariableRecord *, 8> ToBeRemoved;
SmallDenseSet<DebugVariable> VariableSet;
for (auto &I : reverse(*BB)) {
for (DbgRecord &DR : reverse(I.getDbgRecordRange())) {
if (isa<DbgLabelRecord>(DR)) {
// Emulate existing behaviour (see comment below for dbg.declares).
// FIXME: Don't do this.
VariableSet.clear();
continue;
}
DbgVariableRecord &DVR = cast<DbgVariableRecord>(DR);
// Skip declare-type records, as the debug intrinsic method only works
// on dbg.value intrinsics.
if (DVR.getType() == DbgVariableRecord::LocationType::Declare) {
// The debug intrinsic method treats dbg.declares are "non-debug"
// instructions (i.e., a break in a consecutive range of debug
// intrinsics). Emulate that to create identical outputs. See
// "Possible improvements" above.
// FIXME: Delete the line below.
VariableSet.clear();
continue;
}
DebugVariable Key(DVR.getVariable(), DVR.getExpression(),
DVR.getDebugLoc()->getInlinedAt());
auto R = VariableSet.insert(Key);
// If the same variable fragment is described more than once it is enough
// to keep the last one (i.e. the first found since we for reverse
// iteration).
if (R.second)
continue;
if (DVR.isDbgAssign()) {
// Don't delete dbg.assign intrinsics that are linked to instructions.
if (!at::getAssignmentInsts(&DVR).empty())
continue;
// Unlinked dbg.assign intrinsics can be treated like dbg.values.
}
ToBeRemoved.push_back(&DVR);
continue;
}
// Sequence with consecutive dbg.value instrs ended. Clear the map to
// restart identifying redundant instructions if case we find another
// dbg.value sequence.
VariableSet.clear();
}
for (auto &DVR : ToBeRemoved)
DVR->eraseFromParent();
return !ToBeRemoved.empty();
}
static bool removeRedundantDbgInstrsUsingBackwardScan(BasicBlock *BB) {
if (BB->IsNewDbgInfoFormat)
return DbgVariableRecordsRemoveRedundantDbgInstrsUsingBackwardScan(BB);
SmallVector<DbgValueInst *, 8> ToBeRemoved;
SmallDenseSet<DebugVariable> VariableSet;
for (auto &I : reverse(*BB)) {
if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(&I)) {
DebugVariable Key(DVI->getVariable(),
DVI->getExpression(),
DVI->getDebugLoc()->getInlinedAt());
auto R = VariableSet.insert(Key);
// If the variable fragment hasn't been seen before then we don't want
// to remove this dbg intrinsic.
if (R.second)
continue;
if (auto *DAI = dyn_cast<DbgAssignIntrinsic>(DVI)) {
// Don't delete dbg.assign intrinsics that are linked to instructions.
if (!at::getAssignmentInsts(DAI).empty())
continue;
// Unlinked dbg.assign intrinsics can be treated like dbg.values.
}
// If the same variable fragment is described more than once it is enough
// to keep the last one (i.e. the first found since we for reverse
// iteration).
ToBeRemoved.push_back(DVI);
continue;
}
// Sequence with consecutive dbg.value instrs ended. Clear the map to
// restart identifying redundant instructions if case we find another
// dbg.value sequence.
VariableSet.clear();
}
for (auto &Instr : ToBeRemoved)
Instr->eraseFromParent();
return !ToBeRemoved.empty();
}
/// Remove redundant dbg.value instructions using a forward scan. This can
/// remove a dbg.value instruction that is redundant due to indicating that a
/// variable has the same value as already being indicated by an earlier
/// dbg.value.
///
/// ForwardScan strategy:
/// ---------------------
/// Given two identical dbg.value instructions, separated by a block of
/// instructions that isn't describing the same variable, like this
///
/// dbg.value X1, "x", FragmentX1 (**)
/// <block of instructions, none being "dbg.value ..., "x", ...">
/// dbg.value X1, "x", FragmentX1 (*)
///
/// then the instruction marked with (*) can be removed. Variable "x" is already
/// described as being mapped to the SSA value X1.
///
/// Possible improvements:
/// - Keep track of non-overlapping fragments.
static bool
DbgVariableRecordsRemoveRedundantDbgInstrsUsingForwardScan(BasicBlock *BB) {
SmallVector<DbgVariableRecord *, 8> ToBeRemoved;
DenseMap<DebugVariable, std::pair<SmallVector<Value *, 4>, DIExpression *>>
VariableMap;
for (auto &I : *BB) {
for (DbgVariableRecord &DVR : filterDbgVars(I.getDbgRecordRange())) {
if (DVR.getType() == DbgVariableRecord::LocationType::Declare)
continue;
DebugVariable Key(DVR.getVariable(), std::nullopt,
DVR.getDebugLoc()->getInlinedAt());
auto VMI = VariableMap.find(Key);
// A dbg.assign with no linked instructions can be treated like a
// dbg.value (i.e. can be deleted).
bool IsDbgValueKind =
(!DVR.isDbgAssign() || at::getAssignmentInsts(&DVR).empty());
// Update the map if we found a new value/expression describing the
// variable, or if the variable wasn't mapped already.
SmallVector<Value *, 4> Values(DVR.location_ops());
if (VMI == VariableMap.end() || VMI->second.first != Values ||
VMI->second.second != DVR.getExpression()) {
if (IsDbgValueKind)
VariableMap[Key] = {Values, DVR.getExpression()};
else
VariableMap[Key] = {Values, nullptr};
continue;
}
// Don't delete dbg.assign intrinsics that are linked to instructions.
if (!IsDbgValueKind)
continue;
// Found an identical mapping. Remember the instruction for later removal.
ToBeRemoved.push_back(&DVR);
}
}
for (auto *DVR : ToBeRemoved)
DVR->eraseFromParent();
return !ToBeRemoved.empty();
}
static bool
DbgVariableRecordsRemoveUndefDbgAssignsFromEntryBlock(BasicBlock *BB) {
assert(BB->isEntryBlock() && "expected entry block");
SmallVector<DbgVariableRecord *, 8> ToBeRemoved;
DenseSet<DebugVariable> SeenDefForAggregate;
// Returns the DebugVariable for DVI with no fragment info.
auto GetAggregateVariable = [](const DbgVariableRecord &DVR) {
return DebugVariable(DVR.getVariable(), std::nullopt,
DVR.getDebugLoc().getInlinedAt());
};
// Remove undef dbg.assign intrinsics that are encountered before
// any non-undef intrinsics from the entry block.
for (auto &I : *BB) {
for (DbgVariableRecord &DVR : filterDbgVars(I.getDbgRecordRange())) {
if (!DVR.isDbgValue() && !DVR.isDbgAssign())
continue;
bool IsDbgValueKind =
(DVR.isDbgValue() || at::getAssignmentInsts(&DVR).empty());
DebugVariable Aggregate = GetAggregateVariable(DVR);
if (!SeenDefForAggregate.contains(Aggregate)) {
bool IsKill = DVR.isKillLocation() && IsDbgValueKind;
if (!IsKill) {
SeenDefForAggregate.insert(Aggregate);
} else if (DVR.isDbgAssign()) {
ToBeRemoved.push_back(&DVR);
}
}
}
}
for (DbgVariableRecord *DVR : ToBeRemoved)
DVR->eraseFromParent();
return !ToBeRemoved.empty();
}
static bool removeRedundantDbgInstrsUsingForwardScan(BasicBlock *BB) {
if (BB->IsNewDbgInfoFormat)
return DbgVariableRecordsRemoveRedundantDbgInstrsUsingForwardScan(BB);
SmallVector<DbgValueInst *, 8> ToBeRemoved;
DenseMap<DebugVariable, std::pair<SmallVector<Value *, 4>, DIExpression *>>
VariableMap;
for (auto &I : *BB) {
if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(&I)) {
DebugVariable Key(DVI->getVariable(), std::nullopt,
DVI->getDebugLoc()->getInlinedAt());
auto VMI = VariableMap.find(Key);
auto *DAI = dyn_cast<DbgAssignIntrinsic>(DVI);
// A dbg.assign with no linked instructions can be treated like a
// dbg.value (i.e. can be deleted).
bool IsDbgValueKind = (!DAI || at::getAssignmentInsts(DAI).empty());
// Update the map if we found a new value/expression describing the
// variable, or if the variable wasn't mapped already.
SmallVector<Value *, 4> Values(DVI->getValues());
if (VMI == VariableMap.end() || VMI->second.first != Values ||
VMI->second.second != DVI->getExpression()) {
// Use a sentinel value (nullptr) for the DIExpression when we see a
// linked dbg.assign so that the next debug intrinsic will never match
// it (i.e. always treat linked dbg.assigns as if they're unique).
if (IsDbgValueKind)
VariableMap[Key] = {Values, DVI->getExpression()};
else
VariableMap[Key] = {Values, nullptr};
continue;
}
// Don't delete dbg.assign intrinsics that are linked to instructions.
if (!IsDbgValueKind)
continue;
ToBeRemoved.push_back(DVI);
}
}
for (auto &Instr : ToBeRemoved)
Instr->eraseFromParent();
return !ToBeRemoved.empty();
}
/// Remove redundant undef dbg.assign intrinsic from an entry block using a
/// forward scan.
/// Strategy:
/// ---------------------
/// Scanning forward, delete dbg.assign intrinsics iff they are undef, not
/// linked to an intrinsic, and don't share an aggregate variable with a debug
/// intrinsic that didn't meet the criteria. In other words, undef dbg.assigns
/// that come before non-undef debug intrinsics for the variable are
/// deleted. Given:
///
/// dbg.assign undef, "x", FragmentX1 (*)
/// <block of instructions, none being "dbg.value ..., "x", ...">
/// dbg.value %V, "x", FragmentX2
/// <block of instructions, none being "dbg.value ..., "x", ...">
/// dbg.assign undef, "x", FragmentX1
///
/// then (only) the instruction marked with (*) can be removed.
/// Possible improvements:
/// - Keep track of non-overlapping fragments.
static bool removeUndefDbgAssignsFromEntryBlock(BasicBlock *BB) {
if (BB->IsNewDbgInfoFormat)
return DbgVariableRecordsRemoveUndefDbgAssignsFromEntryBlock(BB);
assert(BB->isEntryBlock() && "expected entry block");
SmallVector<DbgAssignIntrinsic *, 8> ToBeRemoved;
DenseSet<DebugVariable> SeenDefForAggregate;
// Returns the DebugVariable for DVI with no fragment info.
auto GetAggregateVariable = [](DbgValueInst *DVI) {
return DebugVariable(DVI->getVariable(), std::nullopt,
DVI->getDebugLoc()->getInlinedAt());
};
// Remove undef dbg.assign intrinsics that are encountered before
// any non-undef intrinsics from the entry block.
for (auto &I : *BB) {
DbgValueInst *DVI = dyn_cast<DbgValueInst>(&I);
if (!DVI)
continue;
auto *DAI = dyn_cast<DbgAssignIntrinsic>(DVI);
bool IsDbgValueKind = (!DAI || at::getAssignmentInsts(DAI).empty());
DebugVariable Aggregate = GetAggregateVariable(DVI);
if (!SeenDefForAggregate.contains(Aggregate)) {
bool IsKill = DVI->isKillLocation() && IsDbgValueKind;
if (!IsKill) {
SeenDefForAggregate.insert(Aggregate);
} else if (DAI) {
ToBeRemoved.push_back(DAI);
}
}
}
for (DbgAssignIntrinsic *DAI : ToBeRemoved)
DAI->eraseFromParent();
return !ToBeRemoved.empty();
}
bool llvm::RemoveRedundantDbgInstrs(BasicBlock *BB) {
bool MadeChanges = false;
// By using the "backward scan" strategy before the "forward scan" strategy we
// can remove both dbg.value (2) and (3) in a situation like this:
//
// (1) dbg.value V1, "x", DIExpression()
// ...
// (2) dbg.value V2, "x", DIExpression()
// (3) dbg.value V1, "x", DIExpression()
//
// The backward scan will remove (2), it is made obsolete by (3). After
// getting (2) out of the way, the foward scan will remove (3) since "x"
// already is described as having the value V1 at (1).
MadeChanges |= removeRedundantDbgInstrsUsingBackwardScan(BB);
if (BB->isEntryBlock() &&
isAssignmentTrackingEnabled(*BB->getParent()->getParent()))
MadeChanges |= removeUndefDbgAssignsFromEntryBlock(BB);
MadeChanges |= removeRedundantDbgInstrsUsingForwardScan(BB);
if (MadeChanges)
LLVM_DEBUG(dbgs() << "Removed redundant dbg instrs from: "
<< BB->getName() << "\n");
return MadeChanges;
}
void llvm::ReplaceInstWithValue(BasicBlock::iterator &BI, Value *V) {
Instruction &I = *BI;
// Replaces all of the uses of the instruction with uses of the value
I.replaceAllUsesWith(V);
// Make sure to propagate a name if there is one already.
if (I.hasName() && !V->hasName())
V->takeName(&I);
// Delete the unnecessary instruction now...
BI = BI->eraseFromParent();
}
void llvm::ReplaceInstWithInst(BasicBlock *BB, BasicBlock::iterator &BI,
Instruction *I) {
assert(I->getParent() == nullptr &&
"ReplaceInstWithInst: Instruction already inserted into basic block!");
// Copy debug location to newly added instruction, if it wasn't already set
// by the caller.
if (!I->getDebugLoc())
I->setDebugLoc(BI->getDebugLoc());
// Insert the new instruction into the basic block...
BasicBlock::iterator New = I->insertInto(BB, BI);
// Replace all uses of the old instruction, and delete it.
ReplaceInstWithValue(BI, I);
// Move BI back to point to the newly inserted instruction
BI = New;
}
bool llvm::IsBlockFollowedByDeoptOrUnreachable(const BasicBlock *BB) {
// Remember visited blocks to avoid infinite loop
SmallPtrSet<const BasicBlock *, 8> VisitedBlocks;
unsigned Depth = 0;
while (BB && Depth++ < MaxDeoptOrUnreachableSuccessorCheckDepth &&
VisitedBlocks.insert(BB).second) {
if (isa<UnreachableInst>(BB->getTerminator()) ||
BB->getTerminatingDeoptimizeCall())
return true;
BB = BB->getUniqueSuccessor();
}
return false;
}
void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
BasicBlock::iterator BI(From);
ReplaceInstWithInst(From->getParent(), BI, To);
}
BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, DominatorTree *DT,
LoopInfo *LI, MemorySSAUpdater *MSSAU,
const Twine &BBName) {
unsigned SuccNum = GetSuccessorNumber(BB, Succ);
Instruction *LatchTerm = BB->getTerminator();
CriticalEdgeSplittingOptions Options =
CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA();
if ((isCriticalEdge(LatchTerm, SuccNum, Options.MergeIdenticalEdges))) {
// If it is a critical edge, and the succesor is an exception block, handle
// the split edge logic in this specific function
if (Succ->isEHPad())
return ehAwareSplitEdge(BB, Succ, nullptr, nullptr, Options, BBName);
// If this is a critical edge, let SplitKnownCriticalEdge do it.
return SplitKnownCriticalEdge(LatchTerm, SuccNum, Options, BBName);
}
// If the edge isn't critical, then BB has a single successor or Succ has a
// single pred. Split the block.
if (BasicBlock *SP = Succ->getSinglePredecessor()) {
// If the successor only has a single pred, split the top of the successor
// block.
assert(SP == BB && "CFG broken");
(void)SP;
return SplitBlock(Succ, &Succ->front(), DT, LI, MSSAU, BBName,
/*Before=*/true);
}
// Otherwise, if BB has a single successor, split it at the bottom of the
// block.
assert(BB->getTerminator()->getNumSuccessors() == 1 &&
"Should have a single succ!");
return SplitBlock(BB, BB->getTerminator(), DT, LI, MSSAU, BBName);
}
void llvm::setUnwindEdgeTo(Instruction *TI, BasicBlock *Succ) {
if (auto *II = dyn_cast<InvokeInst>(TI))
II->setUnwindDest(Succ);
else if (auto *CS = dyn_cast<CatchSwitchInst>(TI))
CS->setUnwindDest(Succ);
else if (auto *CR = dyn_cast<CleanupReturnInst>(TI))
CR->setUnwindDest(Succ);
else
llvm_unreachable("unexpected terminator instruction");
}
void llvm::updatePhiNodes(BasicBlock *DestBB, BasicBlock *OldPred,
BasicBlock *NewPred, PHINode *Until) {
int BBIdx = 0;
for (PHINode &PN : DestBB->phis()) {
// We manually update the LandingPadReplacement PHINode and it is the last
// PHI Node. So, if we find it, we are done.
if (Until == &PN)
break;
// Reuse the previous value of BBIdx if it lines up. In cases where we
// have multiple phi nodes with *lots* of predecessors, this is a speed
// win because we don't have to scan the PHI looking for TIBB. This
// happens because the BB list of PHI nodes are usually in the same
// order.
if (PN.getIncomingBlock(BBIdx) != OldPred)
BBIdx = PN.getBasicBlockIndex(OldPred);
assert(BBIdx != -1 && "Invalid PHI Index!");
PN.setIncomingBlock(BBIdx, NewPred);
}
}
BasicBlock *llvm::ehAwareSplitEdge(BasicBlock *BB, BasicBlock *Succ,
LandingPadInst *OriginalPad,
PHINode *LandingPadReplacement,
const CriticalEdgeSplittingOptions &Options,
const Twine &BBName) {
auto *PadInst = Succ->getFirstNonPHI();
if (!LandingPadReplacement && !PadInst->isEHPad())
return SplitEdge(BB, Succ, Options.DT, Options.LI, Options.MSSAU, BBName);
auto *LI = Options.LI;
SmallVector<BasicBlock *, 4> LoopPreds;
// Check if extra modifications will be required to preserve loop-simplify
// form after splitting. If it would require splitting blocks with IndirectBr
// terminators, bail out if preserving loop-simplify form is requested.
if (Options.PreserveLoopSimplify && LI) {
if (Loop *BBLoop = LI->getLoopFor(BB)) {
// The only way that we can break LoopSimplify form by splitting a
// critical edge is when there exists some edge from BBLoop to Succ *and*
// the only edge into Succ from outside of BBLoop is that of NewBB after
// the split. If the first isn't true, then LoopSimplify still holds,
// NewBB is the new exit block and it has no non-loop predecessors. If the
// second isn't true, then Succ was not in LoopSimplify form prior to
// the split as it had a non-loop predecessor. In both of these cases,
// the predecessor must be directly in BBLoop, not in a subloop, or again
// LoopSimplify doesn't hold.
for (BasicBlock *P : predecessors(Succ)) {
if (P == BB)
continue; // The new block is known.
if (LI->getLoopFor(P) != BBLoop) {
// Loop is not in LoopSimplify form, no need to re simplify after
// splitting edge.
LoopPreds.clear();
break;
}
LoopPreds.push_back(P);
}
// Loop-simplify form can be preserved, if we can split all in-loop
// predecessors.
if (any_of(LoopPreds, [](BasicBlock *Pred) {
return isa<IndirectBrInst>(Pred->getTerminator());
})) {
return nullptr;
}
}
}
auto *NewBB =
BasicBlock::Create(BB->getContext(), BBName, BB->getParent(), Succ);
setUnwindEdgeTo(BB->getTerminator(), NewBB);
updatePhiNodes(Succ, BB, NewBB, LandingPadReplacement);
if (LandingPadReplacement) {
auto *NewLP = OriginalPad->clone();
auto *Terminator = BranchInst::Create(Succ, NewBB);
NewLP->insertBefore(Terminator);
LandingPadReplacement->addIncoming(NewLP, NewBB);
} else {
Value *ParentPad = nullptr;
if (auto *FuncletPad = dyn_cast<FuncletPadInst>(PadInst))
ParentPad = FuncletPad->getParentPad();
else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(PadInst))
ParentPad = CatchSwitch->getParentPad();
else if (auto *CleanupPad = dyn_cast<CleanupPadInst>(PadInst))
ParentPad = CleanupPad->getParentPad();
else if (auto *LandingPad = dyn_cast<LandingPadInst>(PadInst))
ParentPad = LandingPad->getParent();
else
llvm_unreachable("handling for other EHPads not implemented yet");
auto *NewCleanupPad = CleanupPadInst::Create(ParentPad, {}, BBName, NewBB);
CleanupReturnInst::Create(NewCleanupPad, Succ, NewBB);
}
auto *DT = Options.DT;
auto *MSSAU = Options.MSSAU;
if (!DT && !LI)
return NewBB;
if (DT) {
DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
SmallVector<DominatorTree::UpdateType, 3> Updates;
Updates.push_back({DominatorTree::Insert, BB, NewBB});
Updates.push_back({DominatorTree::Insert, NewBB, Succ});
Updates.push_back({DominatorTree::Delete, BB, Succ});
DTU.applyUpdates(Updates);
DTU.flush();
if (MSSAU) {
MSSAU->applyUpdates(Updates, *DT);
if (VerifyMemorySSA)
MSSAU->getMemorySSA()->verifyMemorySSA();
}
}
if (LI) {
if (Loop *BBLoop = LI->getLoopFor(BB)) {
// If one or the other blocks were not in a loop, the new block is not
// either, and thus LI doesn't need to be updated.
if (Loop *SuccLoop = LI->getLoopFor(Succ)) {
if (BBLoop == SuccLoop) {
// Both in the same loop, the NewBB joins loop.
SuccLoop->addBasicBlockToLoop(NewBB, *LI);
} else if (BBLoop->contains(SuccLoop)) {
// Edge from an outer loop to an inner loop. Add to the outer loop.
BBLoop->addBasicBlockToLoop(NewBB, *LI);
} else if (SuccLoop->contains(BBLoop)) {
// Edge from an inner loop to an outer loop. Add to the outer loop.
SuccLoop->addBasicBlockToLoop(NewBB, *LI);
} else {
// Edge from two loops with no containment relation. Because these
// are natural loops, we know that the destination block must be the
// header of its loop (adding a branch into a loop elsewhere would
// create an irreducible loop).
assert(SuccLoop->getHeader() == Succ &&
"Should not create irreducible loops!");
if (Loop *P = SuccLoop->getParentLoop())
P->addBasicBlockToLoop(NewBB, *LI);
}
}
// If BB is in a loop and Succ is outside of that loop, we may need to
// update LoopSimplify form and LCSSA form.
if (!BBLoop->contains(Succ)) {
assert(!BBLoop->contains(NewBB) &&
"Split point for loop exit is contained in loop!");
// Update LCSSA form in the newly created exit block.
if (Options.PreserveLCSSA) {
createPHIsForSplitLoopExit(BB, NewBB, Succ);
}
if (!LoopPreds.empty()) {
BasicBlock *NewExitBB = SplitBlockPredecessors(
Succ, LoopPreds, "split", DT, LI, MSSAU, Options.PreserveLCSSA);
if (Options.PreserveLCSSA)
createPHIsForSplitLoopExit(LoopPreds, NewExitBB, Succ);
}
}
}
}
return NewBB;
}
void llvm::createPHIsForSplitLoopExit(ArrayRef<BasicBlock *> Preds,
BasicBlock *SplitBB, BasicBlock *DestBB) {
// SplitBB shouldn't have anything non-trivial in it yet.
assert((SplitBB->getFirstNonPHI() == SplitBB->getTerminator() ||
SplitBB->isLandingPad()) &&
"SplitBB has non-PHI nodes!");
// For each PHI in the destination block.
for (PHINode &PN : DestBB->phis()) {
int Idx = PN.getBasicBlockIndex(SplitBB);
assert(Idx >= 0 && "Invalid Block Index");
Value *V = PN.getIncomingValue(Idx);
// If the input is a PHI which already satisfies LCSSA, don't create
// a new one.
if (const PHINode *VP = dyn_cast<PHINode>(V))
if (VP->getParent() == SplitBB)
continue;
// Otherwise a new PHI is needed. Create one and populate it.
PHINode *NewPN = PHINode::Create(PN.getType(), Preds.size(), "split");
BasicBlock::iterator InsertPos =
SplitBB->isLandingPad() ? SplitBB->begin()
: SplitBB->getTerminator()->getIterator();
NewPN->insertBefore(InsertPos);
for (BasicBlock *BB : Preds)
NewPN->addIncoming(V, BB);
// Update the original PHI.
PN.setIncomingValue(Idx, NewPN);
}
}
unsigned
llvm::SplitAllCriticalEdges(Function &F,
const CriticalEdgeSplittingOptions &Options) {
unsigned NumBroken = 0;
for (BasicBlock &BB : F) {
Instruction *TI = BB.getTerminator();
if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI))
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
if (SplitCriticalEdge(TI, i, Options))
++NumBroken;
}
return NumBroken;
}
static BasicBlock *SplitBlockImpl(BasicBlock *Old, BasicBlock::iterator SplitPt,
DomTreeUpdater *DTU, DominatorTree *DT,
LoopInfo *LI, MemorySSAUpdater *MSSAU,
const Twine &BBName, bool Before) {
if (Before) {
DomTreeUpdater LocalDTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
return splitBlockBefore(Old, SplitPt,
DTU ? DTU : (DT ? &LocalDTU : nullptr), LI, MSSAU,
BBName);
}
BasicBlock::iterator SplitIt = SplitPt;
while (isa<PHINode>(SplitIt) || SplitIt->isEHPad()) {
++SplitIt;
assert(SplitIt != SplitPt->getParent()->end());
}
std::string Name = BBName.str();
BasicBlock *New = Old->splitBasicBlock(
SplitIt, Name.empty() ? Old->getName() + ".split" : Name);
// The new block lives in whichever loop the old one did. This preserves
// LCSSA as well, because we force the split point to be after any PHI nodes.
if (LI)
if (Loop *L = LI->getLoopFor(Old))
L->addBasicBlockToLoop(New, *LI);
if (DTU) {
SmallVector<DominatorTree::UpdateType, 8> Updates;
// Old dominates New. New node dominates all other nodes dominated by Old.
SmallPtrSet<BasicBlock *, 8> UniqueSuccessorsOfOld;
Updates.push_back({DominatorTree::Insert, Old, New});
Updates.reserve(Updates.size() + 2 * succ_size(New));
for (BasicBlock *SuccessorOfOld : successors(New))
if (UniqueSuccessorsOfOld.insert(SuccessorOfOld).second) {
Updates.push_back({DominatorTree::Insert, New, SuccessorOfOld});
Updates.push_back({DominatorTree::Delete, Old, SuccessorOfOld});
}
DTU->applyUpdates(Updates);
} else if (DT)
// Old dominates New. New node dominates all other nodes dominated by Old.
if (DomTreeNode *OldNode = DT->getNode(Old)) {
std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
DomTreeNode *NewNode = DT->addNewBlock(New, Old);
for (DomTreeNode *I : Children)
DT->changeImmediateDominator(I, NewNode);
}
// Move MemoryAccesses still tracked in Old, but part of New now.
// Update accesses in successor blocks accordingly.
if (MSSAU)
MSSAU->moveAllAfterSpliceBlocks(Old, New, &*(New->begin()));
return New;
}
BasicBlock *llvm::SplitBlock(BasicBlock *Old, BasicBlock::iterator SplitPt,
DominatorTree *DT, LoopInfo *LI,
MemorySSAUpdater *MSSAU, const Twine &BBName,
bool Before) {
return SplitBlockImpl(Old, SplitPt, /*DTU=*/nullptr, DT, LI, MSSAU, BBName,
Before);
}
BasicBlock *llvm::SplitBlock(BasicBlock *Old, BasicBlock::iterator SplitPt,
DomTreeUpdater *DTU, LoopInfo *LI,
MemorySSAUpdater *MSSAU, const Twine &BBName,
bool Before) {
return SplitBlockImpl(Old, SplitPt, DTU, /*DT=*/nullptr, LI, MSSAU, BBName,
Before);
}
BasicBlock *llvm::splitBlockBefore(BasicBlock *Old, BasicBlock::iterator SplitPt,
DomTreeUpdater *DTU, LoopInfo *LI,
MemorySSAUpdater *MSSAU,
const Twine &BBName) {
BasicBlock::iterator SplitIt = SplitPt;
while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
++SplitIt;
std::string Name = BBName.str();
BasicBlock *New = Old->splitBasicBlock(
SplitIt, Name.empty() ? Old->getName() + ".split" : Name,
/* Before=*/true);
// The new block lives in whichever loop the old one did. This preserves
// LCSSA as well, because we force the split point to be after any PHI nodes.
if (LI)
if (Loop *L = LI->getLoopFor(Old))
L->addBasicBlockToLoop(New, *LI);
if (DTU) {
SmallVector<DominatorTree::UpdateType, 8> DTUpdates;
// New dominates Old. The predecessor nodes of the Old node dominate
// New node.
SmallPtrSet<BasicBlock *, 8> UniquePredecessorsOfOld;
DTUpdates.push_back({DominatorTree::Insert, New, Old});
DTUpdates.reserve(DTUpdates.size() + 2 * pred_size(New));
for (BasicBlock *PredecessorOfOld : predecessors(New))
if (UniquePredecessorsOfOld.insert(PredecessorOfOld).second) {
DTUpdates.push_back({DominatorTree::Insert, PredecessorOfOld, New});
DTUpdates.push_back({DominatorTree::Delete, PredecessorOfOld, Old});
}
DTU->applyUpdates(DTUpdates);
// Move MemoryAccesses still tracked in Old, but part of New now.
// Update accesses in successor blocks accordingly.
if (MSSAU) {
MSSAU->applyUpdates(DTUpdates, DTU->getDomTree());
if (VerifyMemorySSA)
MSSAU->getMemorySSA()->verifyMemorySSA();
}
}
return New;
}
/// Update DominatorTree, LoopInfo, and LCCSA analysis information.
/// Invalidates DFS Numbering when DTU or DT is provided.
static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
ArrayRef<BasicBlock *> Preds,
DomTreeUpdater *DTU, DominatorTree *DT,
LoopInfo *LI, MemorySSAUpdater *MSSAU,
bool PreserveLCSSA, bool &HasLoopExit) {
// Update dominator tree if available.
if (DTU) {
// Recalculation of DomTree is needed when updating a forward DomTree and
// the Entry BB is replaced.
if (NewBB->isEntryBlock() && DTU->hasDomTree()) {
// The entry block was removed and there is no external interface for
// the dominator tree to be notified of this change. In this corner-case
// we recalculate the entire tree.
DTU->recalculate(*NewBB->getParent());
} else {
// Split block expects NewBB to have a non-empty set of predecessors.
SmallVector<DominatorTree::UpdateType, 8> Updates;
SmallPtrSet<BasicBlock *, 8> UniquePreds;
Updates.push_back({DominatorTree::Insert, NewBB, OldBB});
Updates.reserve(Updates.size() + 2 * Preds.size());
for (auto *Pred : Preds)
if (UniquePreds.insert(Pred).second) {
Updates.push_back({DominatorTree::Insert, Pred, NewBB});
Updates.push_back({DominatorTree::Delete, Pred, OldBB});
}
DTU->applyUpdates(Updates);
}
} else if (DT) {
if (OldBB == DT->getRootNode()->getBlock()) {
assert(NewBB->isEntryBlock());
DT->setNewRoot(NewBB);
} else {
// Split block expects NewBB to have a non-empty set of predecessors.
DT->splitBlock(NewBB);
}
}
// Update MemoryPhis after split if MemorySSA is available
if (MSSAU)
MSSAU->wireOldPredecessorsToNewImmediatePredecessor(OldBB, NewBB, Preds);
// The rest of the logic is only relevant for updating the loop structures.
if (!LI)
return;
if (DTU && DTU->hasDomTree())
DT = &DTU->getDomTree();
assert(DT && "DT should be available to update LoopInfo!");
Loop *L = LI->getLoopFor(OldBB);
// If we need to preserve loop analyses, collect some information about how
// this split will affect loops.
bool IsLoopEntry = !!L;
bool SplitMakesNewLoopHeader = false;
for (BasicBlock *Pred : Preds) {
// Preds that are not reachable from entry should not be used to identify if
// OldBB is a loop entry or if SplitMakesNewLoopHeader. Unreachable blocks
// are not within any loops, so we incorrectly mark SplitMakesNewLoopHeader
// as true and make the NewBB the header of some loop. This breaks LI.
if (!DT->isReachableFromEntry(Pred))
continue;
// If we need to preserve LCSSA, determine if any of the preds is a loop
// exit.
if (PreserveLCSSA)
if (Loop *PL = LI->getLoopFor(Pred))
if (!PL->contains(OldBB))
HasLoopExit = true;
// If we need to preserve LoopInfo, note whether any of the preds crosses
// an interesting loop boundary.
if (!L)
continue;
if (L->contains(Pred))
IsLoopEntry = false;
else
SplitMakesNewLoopHeader = true;
}
// Unless we have a loop for OldBB, nothing else to do here.
if (!L)
return;
if (IsLoopEntry) {
// Add the new block to the nearest enclosing loop (and not an adjacent
// loop). To find this, examine each of the predecessors and determine which
// loops enclose them, and select the most-nested loop which contains the
// loop containing the block being split.
Loop *InnermostPredLoop = nullptr;
for (BasicBlock *Pred : Preds) {
if (Loop *PredLoop = LI->getLoopFor(Pred)) {
// Seek a loop which actually contains the block being split (to avoid
// adjacent loops).
while (PredLoop && !PredLoop->contains(OldBB))
PredLoop = PredLoop->getParentLoop();
// Select the most-nested of these loops which contains the block.
if (PredLoop && PredLoop->contains(OldBB) &&
(!InnermostPredLoop ||
InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
InnermostPredLoop = PredLoop;
}
}
if (InnermostPredLoop)
InnermostPredLoop->addBasicBlockToLoop(NewBB, *LI);
} else {
L->addBasicBlockToLoop(NewBB, *LI);
if (SplitMakesNewLoopHeader)
L->moveToHeader(NewBB);
}
}
/// Update the PHI nodes in OrigBB to include the values coming from NewBB.
/// This also updates AliasAnalysis, if available.
static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
ArrayRef<BasicBlock *> Preds, BranchInst *BI,
bool HasLoopExit) {
// Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end());
for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
PHINode *PN = cast<PHINode>(I++);
// Check to see if all of the values coming in are the same. If so, we
// don't need to create a new PHI node, unless it's needed for LCSSA.
Value *InVal = nullptr;
if (!HasLoopExit) {
InVal = PN->getIncomingValueForBlock(Preds[0]);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
if (!PredSet.count(PN->getIncomingBlock(i)))
continue;
if (!InVal)
InVal = PN->getIncomingValue(i);
else if (InVal != PN->getIncomingValue(i)) {
InVal = nullptr;
break;
}
}
}
if (InVal) {
// If all incoming values for the new PHI would be the same, just don't
// make a new PHI. Instead, just remove the incoming values from the old
// PHI.
PN->removeIncomingValueIf(
[&](unsigned Idx) {
return PredSet.contains(PN->getIncomingBlock(Idx));
},
/* DeletePHIIfEmpty */ false);
// Add an incoming value to the PHI node in the loop for the preheader
// edge.
PN->addIncoming(InVal, NewBB);
continue;
}
// If the values coming into the block are not the same, we need a new
// PHI.
// Create the new PHI node, insert it into NewBB at the end of the block
PHINode *NewPHI =
PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI->getIterator());
// NOTE! This loop walks backwards for a reason! First off, this minimizes
// the cost of removal if we end up removing a large number of values, and
// second off, this ensures that the indices for the incoming values aren't
// invalidated when we remove one.
for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
BasicBlock *IncomingBB = PN->getIncomingBlock(i);
if (PredSet.count(IncomingBB)) {
Value *V = PN->removeIncomingValue(i, false);
NewPHI->addIncoming(V, IncomingBB);
}
}
PN->addIncoming(NewPHI, NewBB);
}
}
static void SplitLandingPadPredecessorsImpl(
BasicBlock *OrigBB, ArrayRef<BasicBlock *> Preds, const char *Suffix1,
const char *Suffix2, SmallVectorImpl<BasicBlock *> &NewBBs,
DomTreeUpdater *DTU, DominatorTree *DT, LoopInfo *LI,
MemorySSAUpdater *MSSAU, bool PreserveLCSSA);
static BasicBlock *
SplitBlockPredecessorsImpl(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
const char *Suffix, DomTreeUpdater *DTU,
DominatorTree *DT, LoopInfo *LI,
MemorySSAUpdater *MSSAU, bool PreserveLCSSA) {
// Do not attempt to split that which cannot be split.
if (!BB->canSplitPredecessors())
return nullptr;
// For the landingpads we need to act a bit differently.
// Delegate this work to the SplitLandingPadPredecessors.
if (BB->isLandingPad()) {
SmallVector<BasicBlock*, 2> NewBBs;
std::string NewName = std::string(Suffix) + ".split-lp";
SplitLandingPadPredecessorsImpl(BB, Preds, Suffix, NewName.c_str(), NewBBs,
DTU, DT, LI, MSSAU, PreserveLCSSA);
return NewBBs[0];
}
// Create new basic block, insert right before the original block.
BasicBlock *NewBB = BasicBlock::Create(
BB->getContext(), BB->getName() + Suffix, BB->getParent(), BB);
// The new block unconditionally branches to the old block.
BranchInst *BI = BranchInst::Create(BB, NewBB);
Loop *L = nullptr;
BasicBlock *OldLatch = nullptr;
// Splitting the predecessors of a loop header creates a preheader block.
if (LI && LI->isLoopHeader(BB)) {
L = LI->getLoopFor(BB);
// Using the loop start line number prevents debuggers stepping into the
// loop body for this instruction.
BI->setDebugLoc(L->getStartLoc());
// If BB is the header of the Loop, it is possible that the loop is
// modified, such that the current latch does not remain the latch of the
// loop. If that is the case, the loop metadata from the current latch needs
// to be applied to the new latch.
OldLatch = L->getLoopLatch();
} else
BI->setDebugLoc(BB->getFirstNonPHIOrDbg()->getDebugLoc());
// Move the edges from Preds to point to NewBB instead of BB.
for (BasicBlock *Pred : Preds) {
// This is slightly more strict than necessary; the minimum requirement
// is that there be no more than one indirectbr branching to BB. And
// all BlockAddress uses would need to be updated.
assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
"Cannot split an edge from an IndirectBrInst");
Pred->getTerminator()->replaceSuccessorWith(BB, NewBB);
}
// Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
// node becomes an incoming value for BB's phi node. However, if the Preds
// list is empty, we need to insert dummy entries into the PHI nodes in BB to
// account for the newly created predecessor.
if (Preds.empty()) {
// Insert dummy values as the incoming value.
for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
cast<PHINode>(I)->addIncoming(PoisonValue::get(I->getType()), NewBB);
}
// Update DominatorTree, LoopInfo, and LCCSA analysis information.
bool HasLoopExit = false;
UpdateAnalysisInformation(BB, NewBB, Preds, DTU, DT, LI, MSSAU, PreserveLCSSA,
HasLoopExit);
if (!Preds.empty()) {
// Update the PHI nodes in BB with the values coming from NewBB.
UpdatePHINodes(BB, NewBB, Preds, BI, HasLoopExit);
}
if (OldLatch) {
BasicBlock *NewLatch = L->getLoopLatch();
if (NewLatch != OldLatch) {
MDNode *MD = OldLatch->getTerminator()->getMetadata(LLVMContext::MD_loop);
NewLatch->getTerminator()->setMetadata(LLVMContext::MD_loop, MD);
// It's still possible that OldLatch is the latch of another inner loop,
// in which case we do not remove the metadata.
Loop *IL = LI->getLoopFor(OldLatch);
if (IL && IL->getLoopLatch() != OldLatch)
OldLatch->getTerminator()->setMetadata(LLVMContext::MD_loop, nullptr);
}
}
return NewBB;
}
BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix, DominatorTree *DT,
LoopInfo *LI, MemorySSAUpdater *MSSAU,
bool PreserveLCSSA) {
return SplitBlockPredecessorsImpl(BB, Preds, Suffix, /*DTU=*/nullptr, DT, LI,
MSSAU, PreserveLCSSA);
}
BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix,
DomTreeUpdater *DTU, LoopInfo *LI,
MemorySSAUpdater *MSSAU,
bool PreserveLCSSA) {
return SplitBlockPredecessorsImpl(BB, Preds, Suffix, DTU,
/*DT=*/nullptr, LI, MSSAU, PreserveLCSSA);
}
static void SplitLandingPadPredecessorsImpl(
BasicBlock *OrigBB, ArrayRef<BasicBlock *> Preds, const char *Suffix1,
const char *Suffix2, SmallVectorImpl<BasicBlock *> &NewBBs,
DomTreeUpdater *DTU, DominatorTree *DT, LoopInfo *LI,
MemorySSAUpdater *MSSAU, bool PreserveLCSSA) {
assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
// Create a new basic block for OrigBB's predecessors listed in Preds. Insert
// it right before the original block.
BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
OrigBB->getName() + Suffix1,
OrigBB->getParent(), OrigBB);
NewBBs.push_back(NewBB1);
// The new block unconditionally branches to the old block.
BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
BI1->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
// Move the edges from Preds to point to NewBB1 instead of OrigBB.
for (BasicBlock *Pred : Preds) {
// This is slightly more strict than necessary; the minimum requirement
// is that there be no more than one indirectbr branching to BB. And
// all BlockAddress uses would need to be updated.
assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
"Cannot split an edge from an IndirectBrInst");
Pred->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
}
bool HasLoopExit = false;
UpdateAnalysisInformation(OrigBB, NewBB1, Preds, DTU, DT, LI, MSSAU,
PreserveLCSSA, HasLoopExit);
// Update the PHI nodes in OrigBB with the values coming from NewBB1.
UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, HasLoopExit);
// Move the remaining edges from OrigBB to point to NewBB2.
SmallVector<BasicBlock*, 8> NewBB2Preds;
for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
i != e; ) {
BasicBlock *Pred = *i++;
if (Pred == NewBB1) continue;
assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
"Cannot split an edge from an IndirectBrInst");
NewBB2Preds.push_back(Pred);
e = pred_end(OrigBB);
}
BasicBlock *NewBB2 = nullptr;
if (!NewBB2Preds.empty()) {
// Create another basic block for the rest of OrigBB's predecessors.
NewBB2 = BasicBlock::Create(OrigBB->getContext(),
OrigBB->getName() + Suffix2,
OrigBB->getParent(), OrigBB);
NewBBs.push_back(NewBB2);
// The new block unconditionally branches to the old block.
BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
BI2->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
// Move the remaining edges from OrigBB to point to NewBB2.
for (BasicBlock *NewBB2Pred : NewBB2Preds)
NewBB2Pred->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
// Update DominatorTree, LoopInfo, and LCCSA analysis information.
HasLoopExit = false;
UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, DTU, DT, LI, MSSAU,
PreserveLCSSA, HasLoopExit);
// Update the PHI nodes in OrigBB with the values coming from NewBB2.
UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, HasLoopExit);
}
LandingPadInst *LPad = OrigBB->getLandingPadInst();
Instruction *Clone1 = LPad->clone();
Clone1->setName(Twine("lpad") + Suffix1);
Clone1->insertInto(NewBB1, NewBB1->getFirstInsertionPt());
if (NewBB2) {
Instruction *Clone2 = LPad->clone();
Clone2->setName(Twine("lpad") + Suffix2);
Clone2->insertInto(NewBB2, NewBB2->getFirstInsertionPt());
// Create a PHI node for the two cloned landingpad instructions only
// if the original landingpad instruction has some uses.
if (!LPad->use_empty()) {
assert(!LPad->getType()->isTokenTy() &&
"Split cannot be applied if LPad is token type. Otherwise an "
"invalid PHINode of token type would be created.");
PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad->getIterator());
PN->addIncoming(Clone1, NewBB1);
PN->addIncoming(Clone2, NewBB2);
LPad->replaceAllUsesWith(PN);
}
LPad->eraseFromParent();
} else {
// There is no second clone. Just replace the landing pad with the first
// clone.
LPad->replaceAllUsesWith(Clone1);
LPad->eraseFromParent();
}
}
void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
ArrayRef<BasicBlock *> Preds,
const char *Suffix1, const char *Suffix2,
SmallVectorImpl<BasicBlock *> &NewBBs,
DomTreeUpdater *DTU, LoopInfo *LI,
MemorySSAUpdater *MSSAU,
bool PreserveLCSSA) {
return SplitLandingPadPredecessorsImpl(OrigBB, Preds, Suffix1, Suffix2,
NewBBs, DTU, /*DT=*/nullptr, LI, MSSAU,
PreserveLCSSA);
}
ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
BasicBlock *Pred,
DomTreeUpdater *DTU) {
Instruction *UncondBranch = Pred->getTerminator();
// Clone the return and add it to the end of the predecessor.
Instruction *NewRet = RI->clone();
NewRet->insertInto(Pred, Pred->end());
// If the return instruction returns a value, and if the value was a
// PHI node in "BB", propagate the right value into the return.
for (Use &Op : NewRet->operands()) {
Value *V = Op;
Instruction *NewBC = nullptr;
if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
// Return value might be bitcasted. Clone and insert it before the
// return instruction.
V = BCI->getOperand(0);
NewBC = BCI->clone();
NewBC->insertInto(Pred, NewRet->getIterator());
Op = NewBC;
}
Instruction *NewEV = nullptr;
if (ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(V)) {
V = EVI->getOperand(0);
NewEV = EVI->clone();
if (NewBC) {
NewBC->setOperand(0, NewEV);
NewEV->insertInto(Pred, NewBC->getIterator());
} else {
NewEV->insertInto(Pred, NewRet->getIterator());
Op = NewEV;
}
}
if (PHINode *PN = dyn_cast<PHINode>(V)) {
if (PN->getParent() == BB) {
if (NewEV) {
NewEV->setOperand(0, PN->getIncomingValueForBlock(Pred));
} else if (NewBC)
NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
else
Op = PN->getIncomingValueForBlock(Pred);
}
}
}
// Update any PHI nodes in the returning block to realize that we no
// longer branch to them.
BB->removePredecessor(Pred);
UncondBranch->eraseFromParent();
if (DTU)
DTU->applyUpdates({{DominatorTree::Delete, Pred, BB}});
return cast<ReturnInst>(NewRet);
}
Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
BasicBlock::iterator SplitBefore,
bool Unreachable,
MDNode *BranchWeights,
DomTreeUpdater *DTU, LoopInfo *LI,
BasicBlock *ThenBlock) {
SplitBlockAndInsertIfThenElse(
Cond, SplitBefore, &ThenBlock, /* ElseBlock */ nullptr,
/* UnreachableThen */ Unreachable,
/* UnreachableElse */ false, BranchWeights, DTU, LI);
return ThenBlock->getTerminator();
}
Instruction *llvm::SplitBlockAndInsertIfElse(Value *Cond,
BasicBlock::iterator SplitBefore,
bool Unreachable,
MDNode *BranchWeights,
DomTreeUpdater *DTU, LoopInfo *LI,
BasicBlock *ElseBlock) {
SplitBlockAndInsertIfThenElse(
Cond, SplitBefore, /* ThenBlock */ nullptr, &ElseBlock,
/* UnreachableThen */ false,
/* UnreachableElse */ Unreachable, BranchWeights, DTU, LI);
return ElseBlock->getTerminator();
}
void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, BasicBlock::iterator SplitBefore,
Instruction **ThenTerm,
Instruction **ElseTerm,
MDNode *BranchWeights,
DomTreeUpdater *DTU, LoopInfo *LI) {
BasicBlock *ThenBlock = nullptr;
BasicBlock *ElseBlock = nullptr;
SplitBlockAndInsertIfThenElse(
Cond, SplitBefore, &ThenBlock, &ElseBlock, /* UnreachableThen */ false,
/* UnreachableElse */ false, BranchWeights, DTU, LI);
*ThenTerm = ThenBlock->getTerminator();
*ElseTerm = ElseBlock->getTerminator();
}
void llvm::SplitBlockAndInsertIfThenElse(
Value *Cond, BasicBlock::iterator SplitBefore, BasicBlock **ThenBlock,
BasicBlock **ElseBlock, bool UnreachableThen, bool UnreachableElse,
MDNode *BranchWeights, DomTreeUpdater *DTU, LoopInfo *LI) {
assert((ThenBlock || ElseBlock) &&
"At least one branch block must be created");
assert((!UnreachableThen || !UnreachableElse) &&
"Split block tail must be reachable");
SmallVector<DominatorTree::UpdateType, 8> Updates;
SmallPtrSet<BasicBlock *, 8> UniqueOrigSuccessors;
BasicBlock *Head = SplitBefore->getParent();
if (DTU) {
UniqueOrigSuccessors.insert(succ_begin(Head), succ_end(Head));
Updates.reserve(4 + 2 * UniqueOrigSuccessors.size());
}
LLVMContext &C = Head->getContext();
BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
BasicBlock *TrueBlock = Tail;
BasicBlock *FalseBlock = Tail;
bool ThenToTailEdge = false;
bool ElseToTailEdge = false;
// Encapsulate the logic around creation/insertion/etc of a new block.
auto handleBlock = [&](BasicBlock **PBB, bool Unreachable, BasicBlock *&BB,
bool &ToTailEdge) {
if (PBB == nullptr)
return; // Do not create/insert a block.
if (*PBB)
BB = *PBB; // Caller supplied block, use it.
else {
// Create a new block.
BB = BasicBlock::Create(C, "", Head->getParent(), Tail);
if (Unreachable)
(void)new UnreachableInst(C, BB);
else {
(void)BranchInst::Create(Tail, BB);
ToTailEdge = true;
}
BB->getTerminator()->setDebugLoc(SplitBefore->getDebugLoc());
// Pass the new block back to the caller.
*PBB = BB;
}
};
handleBlock(ThenBlock, UnreachableThen, TrueBlock, ThenToTailEdge);
handleBlock(ElseBlock, UnreachableElse, FalseBlock, ElseToTailEdge);
Instruction *HeadOldTerm = Head->getTerminator();
BranchInst *HeadNewTerm =
BranchInst::Create(/*ifTrue*/ TrueBlock, /*ifFalse*/ FalseBlock, Cond);
HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
if (DTU) {
Updates.emplace_back(DominatorTree::Insert, Head, TrueBlock);
Updates.emplace_back(DominatorTree::Insert, Head, FalseBlock);
if (ThenToTailEdge)
Updates.emplace_back(DominatorTree::Insert, TrueBlock, Tail);
if (ElseToTailEdge)
Updates.emplace_back(DominatorTree::Insert, FalseBlock, Tail);
for (BasicBlock *UniqueOrigSuccessor : UniqueOrigSuccessors)
Updates.emplace_back(DominatorTree::Insert, Tail, UniqueOrigSuccessor);
for (BasicBlock *UniqueOrigSuccessor : UniqueOrigSuccessors)
Updates.emplace_back(DominatorTree::Delete, Head, UniqueOrigSuccessor);
DTU->applyUpdates(Updates);
}
if (LI) {
if (Loop *L = LI->getLoopFor(Head); L) {
if (ThenToTailEdge)
L->addBasicBlockToLoop(TrueBlock, *LI);
if (ElseToTailEdge)
L->addBasicBlockToLoop(FalseBlock, *LI);
L->addBasicBlockToLoop(Tail, *LI);
}
}
}
std::pair<Instruction*, Value*>
llvm::SplitBlockAndInsertSimpleForLoop(Value *End, Instruction *SplitBefore) {
BasicBlock *LoopPred = SplitBefore->getParent();
BasicBlock *LoopBody = SplitBlock(SplitBefore->getParent(), SplitBefore);
BasicBlock *LoopExit = SplitBlock(SplitBefore->getParent(), SplitBefore);
auto *Ty = End->getType();
auto &DL = SplitBefore->getModule()->getDataLayout();
const unsigned Bitwidth = DL.getTypeSizeInBits(Ty);
IRBuilder<> Builder(LoopBody->getTerminator());
auto *IV = Builder.CreatePHI(Ty, 2, "iv");
auto *IVNext =
Builder.CreateAdd(IV, ConstantInt::get(Ty, 1), IV->getName() + ".next",
/*HasNUW=*/true, /*HasNSW=*/Bitwidth != 2);
auto *IVCheck = Builder.CreateICmpEQ(IVNext, End,
IV->getName() + ".check");
Builder.CreateCondBr(IVCheck, LoopExit, LoopBody);
LoopBody->getTerminator()->eraseFromParent();
// Populate the IV PHI.
IV->addIncoming(ConstantInt::get(Ty, 0), LoopPred);
IV->addIncoming(IVNext, LoopBody);
return std::make_pair(LoopBody->getFirstNonPHI(), IV);
}
void llvm::SplitBlockAndInsertForEachLane(ElementCount EC,
Type *IndexTy, Instruction *InsertBefore,
std::function<void(IRBuilderBase&, Value*)> Func) {
IRBuilder<> IRB(InsertBefore);
if (EC.isScalable()) {
Value *NumElements = IRB.CreateElementCount(IndexTy, EC);
auto [BodyIP, Index] =
SplitBlockAndInsertSimpleForLoop(NumElements, InsertBefore);
IRB.SetInsertPoint(BodyIP);
Func(IRB, Index);
return;
}
unsigned Num = EC.getFixedValue();
for (unsigned Idx = 0; Idx < Num; ++Idx) {
IRB.SetInsertPoint(InsertBefore);
Func(IRB, ConstantInt::get(IndexTy, Idx));
}
}
void llvm::SplitBlockAndInsertForEachLane(
Value *EVL, Instruction *InsertBefore,
std::function<void(IRBuilderBase &, Value *)> Func) {
IRBuilder<> IRB(InsertBefore);
Type *Ty = EVL->getType();
if (!isa<ConstantInt>(EVL)) {
auto [BodyIP, Index] = SplitBlockAndInsertSimpleForLoop(EVL, InsertBefore);
IRB.SetInsertPoint(BodyIP);
Func(IRB, Index);
return;
}
unsigned Num = cast<ConstantInt>(EVL)->getZExtValue();
for (unsigned Idx = 0; Idx < Num; ++Idx) {
IRB.SetInsertPoint(InsertBefore);
Func(IRB, ConstantInt::get(Ty, Idx));
}
}
BranchInst *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
BasicBlock *&IfFalse) {
PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
BasicBlock *Pred1 = nullptr;
BasicBlock *Pred2 = nullptr;
if (SomePHI) {
if (SomePHI->getNumIncomingValues() != 2)
return nullptr;
Pred1 = SomePHI->getIncomingBlock(0);
Pred2 = SomePHI->getIncomingBlock(1);
} else {
pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
if (PI == PE) // No predecessor
return nullptr;
Pred1 = *PI++;
if (PI == PE) // Only one predecessor
return nullptr;
Pred2 = *PI++;
if (PI != PE) // More than two predecessors
return nullptr;
}
// We can only handle branches. Other control flow will be lowered to
// branches if possible anyway.
BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
if (!Pred1Br || !Pred2Br)
return nullptr;
// Eliminate code duplication by ensuring that Pred1Br is conditional if
// either are.
if (Pred2Br->isConditional()) {
// If both branches are conditional, we don't have an "if statement". In
// reality, we could transform this case, but since the condition will be
// required anyway, we stand no chance of eliminating it, so the xform is
// probably not profitable.
if (Pred1Br->isConditional())
return nullptr;
std::swap(Pred1, Pred2);
std::swap(Pred1Br, Pred2Br);
}
if (Pred1Br->isConditional()) {
// The only thing we have to watch out for here is to make sure that Pred2
// doesn't have incoming edges from other blocks. If it does, the condition
// doesn't dominate BB.
if (!Pred2->getSinglePredecessor())
return nullptr;
// If we found a conditional branch predecessor, make sure that it branches
// to BB and Pred2Br. If it doesn't, this isn't an "if statement".
if (Pred1Br->getSuccessor(0) == BB &&
Pred1Br->getSuccessor(1) == Pred2) {
IfTrue = Pred1;
IfFalse = Pred2;
} else if (Pred1Br->getSuccessor(0) == Pred2 &&
Pred1Br->getSuccessor(1) == BB) {
IfTrue = Pred2;
IfFalse = Pred1;
} else {
// We know that one arm of the conditional goes to BB, so the other must
// go somewhere unrelated, and this must not be an "if statement".
return nullptr;
}
return Pred1Br;
}
// Ok, if we got here, both predecessors end with an unconditional branch to
// BB. Don't panic! If both blocks only have a single (identical)
// predecessor, and THAT is a conditional branch, then we're all ok!
BasicBlock *CommonPred = Pred1->getSinglePredecessor();
if (CommonPred == nullptr || CommonPred != Pred2->getSinglePredecessor())
return nullptr;
// Otherwise, if this is a conditional branch, then we can use it!
BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
if (!BI) return nullptr;
assert(BI->isConditional() && "Two successors but not conditional?");
if (BI->getSuccessor(0) == Pred1) {
IfTrue = Pred1;
IfFalse = Pred2;
} else {
IfTrue = Pred2;
IfFalse = Pred1;
}
return BI;
}
// After creating a control flow hub, the operands of PHINodes in an outgoing
// block Out no longer match the predecessors of that block. Predecessors of Out
// that are incoming blocks to the hub are now replaced by just one edge from
// the hub. To match this new control flow, the corresponding values from each
// PHINode must now be moved a new PHINode in the first guard block of the hub.
//
// This operation cannot be performed with SSAUpdater, because it involves one
// new use: If the block Out is in the list of Incoming blocks, then the newly
// created PHI in the Hub will use itself along that edge from Out to Hub.
static void reconnectPhis(BasicBlock *Out, BasicBlock *GuardBlock,
const SetVector<BasicBlock *> &Incoming,
BasicBlock *FirstGuardBlock) {
auto I = Out->begin();
while (I != Out->end() && isa<PHINode>(I)) {
auto Phi = cast<PHINode>(I);
auto NewPhi =
PHINode::Create(Phi->getType(), Incoming.size(),
Phi->getName() + ".moved", FirstGuardBlock->begin());
for (auto *In : Incoming) {
Value *V = UndefValue::get(Phi->getType());
if (In == Out) {
V = NewPhi;
} else if (Phi->getBasicBlockIndex(In) != -1) {
V = Phi->removeIncomingValue(In, false);
}
NewPhi->addIncoming(V, In);
}
assert(NewPhi->getNumIncomingValues() == Incoming.size());
if (Phi->getNumOperands() == 0) {
Phi->replaceAllUsesWith(NewPhi);
I = Phi->eraseFromParent();
continue;
}
Phi->addIncoming(NewPhi, GuardBlock);
++I;
}
}
using BBPredicates = DenseMap<BasicBlock *, Instruction *>;
using BBSetVector = SetVector<BasicBlock *>;
// Redirects the terminator of the incoming block to the first guard
// block in the hub. The condition of the original terminator (if it
// was conditional) and its original successors are returned as a
// tuple <condition, succ0, succ1>. The function additionally filters
// out successors that are not in the set of outgoing blocks.
//
// - condition is non-null iff the branch is conditional.
// - Succ1 is non-null iff the sole/taken target is an outgoing block.
// - Succ2 is non-null iff condition is non-null and the fallthrough
// target is an outgoing block.
static std::tuple<Value *, BasicBlock *, BasicBlock *>
redirectToHub(BasicBlock *BB, BasicBlock *FirstGuardBlock,
const BBSetVector &Outgoing) {
assert(isa<BranchInst>(BB->getTerminator()) &&
"Only support branch terminator.");
auto Branch = cast<BranchInst>(BB->getTerminator());
auto Condition = Branch->isConditional() ? Branch->getCondition() : nullptr;
BasicBlock *Succ0 = Branch->getSuccessor(0);
BasicBlock *Succ1 = nullptr;
Succ0 = Outgoing.count(Succ0) ? Succ0 : nullptr;
if (Branch->isUnconditional()) {
Branch->setSuccessor(0, FirstGuardBlock);
assert(Succ0);
} else {
Succ1 = Branch->getSuccessor(1);
Succ1 = Outgoing.count(Succ1) ? Succ1 : nullptr;
assert(Succ0 || Succ1);
if (Succ0 && !Succ1) {
Branch->setSuccessor(0, FirstGuardBlock);
} else if (Succ1 && !Succ0) {
Branch->setSuccessor(1, FirstGuardBlock);
} else {
Branch->eraseFromParent();
BranchInst::Create(FirstGuardBlock, BB);
}
}
assert(Succ0 || Succ1);
return std::make_tuple(Condition, Succ0, Succ1);
}
// Setup the branch instructions for guard blocks.
//
// Each guard block terminates in a conditional branch that transfers
// control to the corresponding outgoing block or the next guard
// block. The last guard block has two outgoing blocks as successors
// since the condition for the final outgoing block is trivially
// true. So we create one less block (including the first guard block)
// than the number of outgoing blocks.
static void setupBranchForGuard(SmallVectorImpl<BasicBlock *> &GuardBlocks,
const BBSetVector &Outgoing,
BBPredicates &GuardPredicates) {
// To help keep the loop simple, temporarily append the last
// outgoing block to the list of guard blocks.
GuardBlocks.push_back(Outgoing.back());
for (int i = 0, e = GuardBlocks.size() - 1; i != e; ++i) {
auto Out = Outgoing[i];
assert(GuardPredicates.count(Out));
BranchInst::Create(Out, GuardBlocks[i + 1], GuardPredicates[Out],
GuardBlocks[i]);
}
// Remove the last block from the guard list.
GuardBlocks.pop_back();
}
/// We are using one integer to represent the block we are branching to. Then at
/// each guard block, the predicate was calcuated using a simple `icmp eq`.
static void calcPredicateUsingInteger(
const BBSetVector &Incoming, const BBSetVector &Outgoing,
SmallVectorImpl<BasicBlock *> &GuardBlocks, BBPredicates &GuardPredicates) {
auto &Context = Incoming.front()->getContext();
auto FirstGuardBlock = GuardBlocks.front();
auto Phi = PHINode::Create(Type::getInt32Ty(Context), Incoming.size(),
"merged.bb.idx", FirstGuardBlock);
for (auto In : Incoming) {
Value *Condition;
BasicBlock *Succ0;
BasicBlock *Succ1;
std::tie(Condition, Succ0, Succ1) =
redirectToHub(In, FirstGuardBlock, Outgoing);
Value *IncomingId = nullptr;
if (Succ0 && Succ1) {
// target_bb_index = Condition ? index_of_succ0 : index_of_succ1.
auto Succ0Iter = find(Outgoing, Succ0);
auto Succ1Iter = find(Outgoing, Succ1);
Value *Id0 = ConstantInt::get(Type::getInt32Ty(Context),
std::distance(Outgoing.begin(), Succ0Iter));
Value *Id1 = ConstantInt::get(Type::getInt32Ty(Context),
std::distance(Outgoing.begin(), Succ1Iter));
IncomingId = SelectInst::Create(Condition, Id0, Id1, "target.bb.idx",
In->getTerminator()->getIterator());
} else {
// Get the index of the non-null successor.
auto SuccIter = Succ0 ? find(Outgoing, Succ0) : find(Outgoing, Succ1);
IncomingId = ConstantInt::get(Type::getInt32Ty(Context),
std::distance(Outgoing.begin(), SuccIter));
}
Phi->addIncoming(IncomingId, In);
}
for (int i = 0, e = Outgoing.size() - 1; i != e; ++i) {
auto Out = Outgoing[i];
auto Cmp = ICmpInst::Create(Instruction::ICmp, ICmpInst::ICMP_EQ, Phi,
ConstantInt::get(Type::getInt32Ty(Context), i),
Out->getName() + ".predicate", GuardBlocks[i]);
GuardPredicates[Out] = Cmp;
}
}
/// We record the predicate of each outgoing block using a phi of boolean.
static void calcPredicateUsingBooleans(
const BBSetVector &Incoming, const BBSetVector &Outgoing,
SmallVectorImpl<BasicBlock *> &GuardBlocks, BBPredicates &GuardPredicates,
SmallVectorImpl<WeakVH> &DeletionCandidates) {
auto &Context = Incoming.front()->getContext();
auto BoolTrue = ConstantInt::getTrue(Context);
auto BoolFalse = ConstantInt::getFalse(Context);
auto FirstGuardBlock = GuardBlocks.front();
// The predicate for the last outgoing is trivially true, and so we
// process only the first N-1 successors.
for (int i = 0, e = Outgoing.size() - 1; i != e; ++i) {
auto Out = Outgoing[i];
LLVM_DEBUG(dbgs() << "Creating guard for " << Out->getName() << "\n");
auto Phi =
PHINode::Create(Type::getInt1Ty(Context), Incoming.size(),
StringRef("Guard.") + Out->getName(), FirstGuardBlock);
GuardPredicates[Out] = Phi;
}
for (auto *In : Incoming) {
Value *Condition;
BasicBlock *Succ0;
BasicBlock *Succ1;
std::tie(Condition, Succ0, Succ1) =
redirectToHub(In, FirstGuardBlock, Outgoing);
// Optimization: Consider an incoming block A with both successors
// Succ0 and Succ1 in the set of outgoing blocks. The predicates
// for Succ0 and Succ1 complement each other. If Succ0 is visited
// first in the loop below, control will branch to Succ0 using the
// corresponding predicate. But if that branch is not taken, then
// control must reach Succ1, which means that the incoming value of
// the predicate from `In` is true for Succ1.
bool OneSuccessorDone = false;
for (int i = 0, e = Outgoing.size() - 1; i != e; ++i) {
auto Out = Outgoing[i];
PHINode *Phi = cast<PHINode>(GuardPredicates[Out]);
if (Out != Succ0 && Out != Succ1) {
Phi->addIncoming(BoolFalse, In);
} else if (!Succ0 || !Succ1 || OneSuccessorDone) {
// Optimization: When only one successor is an outgoing block,
// the incoming predicate from `In` is always true.
Phi->addIncoming(BoolTrue, In);
} else {
assert(Succ0 && Succ1);
if (Out == Succ0) {
Phi->addIncoming(Condition, In);
} else {
auto Inverted = invertCondition(Condition);
DeletionCandidates.push_back(Condition);
Phi->addIncoming(Inverted, In);
}
OneSuccessorDone = true;
}
}
}
}
// Capture the existing control flow as guard predicates, and redirect
// control flow from \p Incoming block through the \p GuardBlocks to the
// \p Outgoing blocks.
//
// There is one guard predicate for each outgoing block OutBB. The
// predicate represents whether the hub should transfer control flow
// to OutBB. These predicates are NOT ORTHOGONAL. The Hub evaluates
// them in the same order as the Outgoing set-vector, and control
// branches to the first outgoing block whose predicate evaluates to true.
static void
convertToGuardPredicates(SmallVectorImpl<BasicBlock *> &GuardBlocks,
SmallVectorImpl<WeakVH> &DeletionCandidates,
const BBSetVector &Incoming,
const BBSetVector &Outgoing, const StringRef Prefix,
std::optional<unsigned> MaxControlFlowBooleans) {
BBPredicates GuardPredicates;
auto F = Incoming.front()->getParent();
for (int i = 0, e = Outgoing.size() - 1; i != e; ++i)
GuardBlocks.push_back(
BasicBlock::Create(F->getContext(), Prefix + ".guard", F));
// When we are using an integer to record which target block to jump to, we
// are creating less live values, actually we are using one single integer to
// store the index of the target block. When we are using booleans to store
// the branching information, we need (N-1) boolean values, where N is the
// number of outgoing block.
if (!MaxControlFlowBooleans || Outgoing.size() <= *MaxControlFlowBooleans)
calcPredicateUsingBooleans(Incoming, Outgoing, GuardBlocks, GuardPredicates,
DeletionCandidates);
else
calcPredicateUsingInteger(Incoming, Outgoing, GuardBlocks, GuardPredicates);
setupBranchForGuard(GuardBlocks, Outgoing, GuardPredicates);
}
BasicBlock *llvm::CreateControlFlowHub(
DomTreeUpdater *DTU, SmallVectorImpl<BasicBlock *> &GuardBlocks,
const BBSetVector &Incoming, const BBSetVector &Outgoing,
const StringRef Prefix, std::optional<unsigned> MaxControlFlowBooleans) {
if (Outgoing.size() < 2)
return Outgoing.front();
SmallVector<DominatorTree::UpdateType, 16> Updates;
if (DTU) {
for (auto *In : Incoming) {
for (auto Succ : successors(In))
if (Outgoing.count(Succ))
Updates.push_back({DominatorTree::Delete, In, Succ});
}
}
SmallVector<WeakVH, 8> DeletionCandidates;
convertToGuardPredicates(GuardBlocks, DeletionCandidates, Incoming, Outgoing,
Prefix, MaxControlFlowBooleans);
auto FirstGuardBlock = GuardBlocks.front();
// Update the PHINodes in each outgoing block to match the new control flow.
for (int i = 0, e = GuardBlocks.size(); i != e; ++i)
reconnectPhis(Outgoing[i], GuardBlocks[i], Incoming, FirstGuardBlock);
reconnectPhis(Outgoing.back(), GuardBlocks.back(), Incoming, FirstGuardBlock);
if (DTU) {
int NumGuards = GuardBlocks.size();
assert((int)Outgoing.size() == NumGuards + 1);
for (auto In : Incoming)
Updates.push_back({DominatorTree::Insert, In, FirstGuardBlock});
for (int i = 0; i != NumGuards - 1; ++i) {
Updates.push_back({DominatorTree::Insert, GuardBlocks[i], Outgoing[i]});
Updates.push_back(
{DominatorTree::Insert, GuardBlocks[i], GuardBlocks[i + 1]});
}
Updates.push_back({DominatorTree::Insert, GuardBlocks[NumGuards - 1],
Outgoing[NumGuards - 1]});
Updates.push_back({DominatorTree::Insert, GuardBlocks[NumGuards - 1],
Outgoing[NumGuards]});
DTU->applyUpdates(Updates);
}
for (auto I : DeletionCandidates) {
if (I->use_empty())
if (auto Inst = dyn_cast_or_null<Instruction>(I))
Inst->eraseFromParent();
}
return FirstGuardBlock;
}
void llvm::InvertBranch(BranchInst *PBI, IRBuilderBase &Builder) {
Value *NewCond = PBI->getCondition();
// If this is a "cmp" instruction, only used for branching (and nowhere
// else), then we can simply invert the predicate.
if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
CmpInst *CI = cast<CmpInst>(NewCond);
CI->setPredicate(CI->getInversePredicate());
} else
NewCond = Builder.CreateNot(NewCond, NewCond->getName() + ".not");
PBI->setCondition(NewCond);
PBI->swapSuccessors();
}
bool llvm::hasOnlySimpleTerminator(const Function &F) {
for (auto &BB : F) {
auto *Term = BB.getTerminator();
if (!(isa<ReturnInst>(Term) || isa<UnreachableInst>(Term) ||
isa<BranchInst>(Term)))
return false;
}
return true;
}
bool llvm::isPresplitCoroSuspendExitEdge(const BasicBlock &Src,
const BasicBlock &Dest) {
assert(Src.getParent() == Dest.getParent());
if (!Src.getParent()->isPresplitCoroutine())
return false;
if (auto *SW = dyn_cast<SwitchInst>(Src.getTerminator()))
if (auto *Intr = dyn_cast<IntrinsicInst>(SW->getCondition()))
return Intr->getIntrinsicID() == Intrinsic::coro_suspend &&
SW->getDefaultDest() == &Dest;
return false;
}