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llvm-project/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
Jeremy Morse 34b139594a
[NFC][DebugInfo] Switch more call-sites to using iterator-insertion (#124283) 
To finalise the "RemoveDIs" work removing debug intrinsics, we're
updating call sites that insert instructions to use iterators instead.
This set of changes are those where it's not immediately obvious that
just calling getIterator to fetch an iterator is correct, and one or two
places where more than one line needs to change.

Overall the same rule holds though: iterators generated for the start of
a block such as getFirstNonPHIIt need to be passed into insert/move
methods without being unwrapped/rewrapped, everything else can use
getIterator.
2025-01-27 16:44:14 +00:00

1931 lines
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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);
}
// 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;
SmallDenseMap<DebugVariable,
std::pair<SmallVector<Value *, 4>, DIExpression *>, 4>
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;
SmallDenseMap<DebugVariable,
std::pair<SmallVector<Value *, 4>, DIExpression *>, 4>
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->getFirstNonPHIIt();
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->getIterator());
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->getFirstNonPHIIt() == 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->getFirstNonPHIIt()->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->getFirstNonPHIIt()->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,
BasicBlock::iterator SplitBefore) {
BasicBlock *LoopPred = SplitBefore->getParent();
BasicBlock *LoopBody = SplitBlock(SplitBefore->getParent(), SplitBefore);
BasicBlock *LoopExit = SplitBlock(SplitBefore->getParent(), SplitBefore);
auto *Ty = End->getType();
auto &DL = SplitBefore->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->getFirstNonPHIIt(), IV);
}
void llvm::SplitBlockAndInsertForEachLane(
ElementCount EC, Type *IndexTy, BasicBlock::iterator InsertBefore,
std::function<void(IRBuilderBase &, Value *)> Func) {
IRBuilder<> IRB(InsertBefore->getParent(), 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, BasicBlock::iterator InsertBefore,
std::function<void(IRBuilderBase &, Value *)> Func) {
IRBuilder<> IRB(InsertBefore->getParent(), 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;
}
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;
}
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