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//===- Local.cpp - Functions to perform local transformations -------------===//
//
// 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 various local transformations to the
// program.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/Analysis/EHPersonalities.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemorySSAUpdater.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Analysis/VectorUtils.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalObject.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
#include <algorithm>
#include <cassert>
#include <climits>
#include <cstdint>
#include <iterator>
#include <map>
#include <utility>
using namespace llvm;
using namespace llvm::PatternMatch;
#define DEBUG_TYPE "local"
STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
//===----------------------------------------------------------------------===//
// Local constant propagation.
//
/// ConstantFoldTerminator - If a terminator instruction is predicated on a
/// constant value, convert it into an unconditional branch to the constant
/// destination. This is a nontrivial operation because the successors of this
/// basic block must have their PHI nodes updated.
/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
/// conditions and indirectbr addresses this might make dead if
/// DeleteDeadConditions is true.
bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
const TargetLibraryInfo *TLI,
DomTreeUpdater *DTU) {
Instruction *T = BB->getTerminator();
IRBuilder<> Builder(T);
// Branch - See if we are conditional jumping on constant
if (auto *BI = dyn_cast<BranchInst>(T)) {
if (BI->isUnconditional()) return false; // Can't optimize uncond branch
BasicBlock *Dest1 = BI->getSuccessor(0);
BasicBlock *Dest2 = BI->getSuccessor(1);
if (auto *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
// Are we branching on constant?
// YES. Change to unconditional branch...
BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
// Let the basic block know that we are letting go of it. Based on this,
// it will adjust it's PHI nodes.
OldDest->removePredecessor(BB);
// Replace the conditional branch with an unconditional one.
Builder.CreateBr(Destination);
BI->eraseFromParent();
if (DTU)
DTU->deleteEdgeRelaxed(BB, OldDest);
return true;
}
if (Dest2 == Dest1) { // Conditional branch to same location?
// This branch matches something like this:
// br bool %cond, label %Dest, label %Dest
// and changes it into: br label %Dest
// Let the basic block know that we are letting go of one copy of it.
assert(BI->getParent() && "Terminator not inserted in block!");
Dest1->removePredecessor(BI->getParent());
// Replace the conditional branch with an unconditional one.
Builder.CreateBr(Dest1);
Value *Cond = BI->getCondition();
BI->eraseFromParent();
if (DeleteDeadConditions)
RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
return true;
}
return false;
}
if (auto *SI = dyn_cast<SwitchInst>(T)) {
// If we are switching on a constant, we can convert the switch to an
// unconditional branch.
auto *CI = dyn_cast<ConstantInt>(SI->getCondition());
BasicBlock *DefaultDest = SI->getDefaultDest();
BasicBlock *TheOnlyDest = DefaultDest;
// If the default is unreachable, ignore it when searching for TheOnlyDest.
if (isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg()) &&
SI->getNumCases() > 0) {
TheOnlyDest = SI->case_begin()->getCaseSuccessor();
}
// Figure out which case it goes to.
for (auto i = SI->case_begin(), e = SI->case_end(); i != e;) {
// Found case matching a constant operand?
if (i->getCaseValue() == CI) {
TheOnlyDest = i->getCaseSuccessor();
break;
}
// Check to see if this branch is going to the same place as the default
// dest. If so, eliminate it as an explicit compare.
if (i->getCaseSuccessor() == DefaultDest) {
MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
unsigned NCases = SI->getNumCases();
// Fold the case metadata into the default if there will be any branches
// left, unless the metadata doesn't match the switch.
if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
// Collect branch weights into a vector.
SmallVector<uint32_t, 8> Weights;
for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
++MD_i) {
auto *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i));
Weights.push_back(CI->getValue().getZExtValue());
}
// Merge weight of this case to the default weight.
unsigned idx = i->getCaseIndex();
Weights[0] += Weights[idx+1];
// Remove weight for this case.
std::swap(Weights[idx+1], Weights.back());
Weights.pop_back();
SI->setMetadata(LLVMContext::MD_prof,
MDBuilder(BB->getContext()).
createBranchWeights(Weights));
}
// Remove this entry.
BasicBlock *ParentBB = SI->getParent();
DefaultDest->removePredecessor(ParentBB);
i = SI->removeCase(i);
e = SI->case_end();
if (DTU)
DTU->deleteEdgeRelaxed(ParentBB, DefaultDest);
continue;
}
// Otherwise, check to see if the switch only branches to one destination.
// We do this by reseting "TheOnlyDest" to null when we find two non-equal
// destinations.
if (i->getCaseSuccessor() != TheOnlyDest)
TheOnlyDest = nullptr;
// Increment this iterator as we haven't removed the case.
++i;
}
if (CI && !TheOnlyDest) {
// Branching on a constant, but not any of the cases, go to the default
// successor.
TheOnlyDest = SI->getDefaultDest();
}
// If we found a single destination that we can fold the switch into, do so
// now.
if (TheOnlyDest) {
// Insert the new branch.
Builder.CreateBr(TheOnlyDest);
BasicBlock *BB = SI->getParent();
std::vector <DominatorTree::UpdateType> Updates;
if (DTU)
Updates.reserve(SI->getNumSuccessors() - 1);
// Remove entries from PHI nodes which we no longer branch to...
for (BasicBlock *Succ : successors(SI)) {
// Found case matching a constant operand?
if (Succ == TheOnlyDest) {
TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
} else {
Succ->removePredecessor(BB);
if (DTU)
Updates.push_back({DominatorTree::Delete, BB, Succ});
}
}
// Delete the old switch.
Value *Cond = SI->getCondition();
SI->eraseFromParent();
if (DeleteDeadConditions)
RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
if (DTU)
DTU->applyUpdates(Updates, /*ForceRemoveDuplicates*/ true);
return true;
}
if (SI->getNumCases() == 1) {
// Otherwise, we can fold this switch into a conditional branch
// instruction if it has only one non-default destination.
auto FirstCase = *SI->case_begin();
Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
FirstCase.getCaseValue(), "cond");
// Insert the new branch.
BranchInst *NewBr = Builder.CreateCondBr(Cond,
FirstCase.getCaseSuccessor(),
SI->getDefaultDest());
MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
if (MD && MD->getNumOperands() == 3) {
ConstantInt *SICase =
mdconst::dyn_extract<ConstantInt>(MD->getOperand(2));
ConstantInt *SIDef =
mdconst::dyn_extract<ConstantInt>(MD->getOperand(1));
assert(SICase && SIDef);
// The TrueWeight should be the weight for the single case of SI.
NewBr->setMetadata(LLVMContext::MD_prof,
MDBuilder(BB->getContext()).
createBranchWeights(SICase->getValue().getZExtValue(),
SIDef->getValue().getZExtValue()));
}
// Update make.implicit metadata to the newly-created conditional branch.
MDNode *MakeImplicitMD = SI->getMetadata(LLVMContext::MD_make_implicit);
if (MakeImplicitMD)
NewBr->setMetadata(LLVMContext::MD_make_implicit, MakeImplicitMD);
// Delete the old switch.
SI->eraseFromParent();
return true;
}
return false;
}
if (auto *IBI = dyn_cast<IndirectBrInst>(T)) {
// indirectbr blockaddress(@F, @BB) -> br label @BB
if (auto *BA =
dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
BasicBlock *TheOnlyDest = BA->getBasicBlock();
std::vector <DominatorTree::UpdateType> Updates;
if (DTU)
Updates.reserve(IBI->getNumDestinations() - 1);
// Insert the new branch.
Builder.CreateBr(TheOnlyDest);
for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
if (IBI->getDestination(i) == TheOnlyDest) {
TheOnlyDest = nullptr;
} else {
BasicBlock *ParentBB = IBI->getParent();
BasicBlock *DestBB = IBI->getDestination(i);
DestBB->removePredecessor(ParentBB);
if (DTU)
Updates.push_back({DominatorTree::Delete, ParentBB, DestBB});
}
}
Value *Address = IBI->getAddress();
IBI->eraseFromParent();
if (DeleteDeadConditions)
RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
// If we didn't find our destination in the IBI successor list, then we
// have undefined behavior. Replace the unconditional branch with an
// 'unreachable' instruction.
if (TheOnlyDest) {
BB->getTerminator()->eraseFromParent();
new UnreachableInst(BB->getContext(), BB);
}
if (DTU)
DTU->applyUpdates(Updates, /*ForceRemoveDuplicates*/ true);
return true;
}
}
return false;
}
//===----------------------------------------------------------------------===//
// Local dead code elimination.
//
/// isInstructionTriviallyDead - Return true if the result produced by the
/// instruction is not used, and the instruction has no side effects.
///
bool llvm::isInstructionTriviallyDead(Instruction *I,
const TargetLibraryInfo *TLI) {
if (!I->use_empty())
return false;
return wouldInstructionBeTriviallyDead(I, TLI);
}
bool llvm::wouldInstructionBeTriviallyDead(Instruction *I,
const TargetLibraryInfo *TLI) {
if (I->isTerminator())
return false;
// We don't want the landingpad-like instructions removed by anything this
// general.
if (I->isEHPad())
return false;
// We don't want debug info removed by anything this general, unless
// debug info is empty.
if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
if (DDI->getAddress())
return false;
return true;
}
if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
if (DVI->getValue())
return false;
return true;
}
if (DbgLabelInst *DLI = dyn_cast<DbgLabelInst>(I)) {
if (DLI->getLabel())
return false;
return true;
}
if (!I->mayHaveSideEffects())
return true;
// Special case intrinsics that "may have side effects" but can be deleted
// when dead.
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
// Safe to delete llvm.stacksave and launder.invariant.group if dead.
if (II->getIntrinsicID() == Intrinsic::stacksave ||
II->getIntrinsicID() == Intrinsic::launder_invariant_group)
return true;
// Lifetime intrinsics are dead when their right-hand is undef.
if (II->isLifetimeStartOrEnd())
return isa<UndefValue>(II->getArgOperand(1));
// Assumptions are dead if their condition is trivially true. Guards on
// true are operationally no-ops. In the future we can consider more
// sophisticated tradeoffs for guards considering potential for check
// widening, but for now we keep things simple.
if (II->getIntrinsicID() == Intrinsic::assume ||
II->getIntrinsicID() == Intrinsic::experimental_guard) {
if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0)))
return !Cond->isZero();
return false;
}
}
if (isAllocLikeFn(I, TLI))
return true;
if (CallInst *CI = isFreeCall(I, TLI))
if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
return C->isNullValue() || isa<UndefValue>(C);
if (CallSite CS = CallSite(I))
if (isMathLibCallNoop(CS, TLI))
return true;
return false;
}
/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
/// trivially dead instruction, delete it. If that makes any of its operands
/// trivially dead, delete them too, recursively. Return true if any
/// instructions were deleted.
bool llvm::RecursivelyDeleteTriviallyDeadInstructions(
Value *V, const TargetLibraryInfo *TLI, MemorySSAUpdater *MSSAU) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I || !isInstructionTriviallyDead(I, TLI))
return false;
SmallVector<Instruction*, 16> DeadInsts;
DeadInsts.push_back(I);
RecursivelyDeleteTriviallyDeadInstructions(DeadInsts, TLI, MSSAU);
return true;
}
void llvm::RecursivelyDeleteTriviallyDeadInstructions(
SmallVectorImpl<Instruction *> &DeadInsts, const TargetLibraryInfo *TLI,
MemorySSAUpdater *MSSAU) {
// Process the dead instruction list until empty.
while (!DeadInsts.empty()) {
Instruction &I = *DeadInsts.pop_back_val();
assert(I.use_empty() && "Instructions with uses are not dead.");
assert(isInstructionTriviallyDead(&I, TLI) &&
"Live instruction found in dead worklist!");
// Don't lose the debug info while deleting the instructions.
salvageDebugInfo(I);
// Null out all of the instruction's operands to see if any operand becomes
// dead as we go.
for (Use &OpU : I.operands()) {
Value *OpV = OpU.get();
OpU.set(nullptr);
if (!OpV->use_empty())
continue;
// If the operand is an instruction that became dead as we nulled out the
// operand, and if it is 'trivially' dead, delete it in a future loop
// iteration.
if (Instruction *OpI = dyn_cast<Instruction>(OpV))
if (isInstructionTriviallyDead(OpI, TLI))
DeadInsts.push_back(OpI);
}
if (MSSAU)
MSSAU->removeMemoryAccess(&I);
I.eraseFromParent();
}
}
bool llvm::replaceDbgUsesWithUndef(Instruction *I) {
SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
findDbgUsers(DbgUsers, I);
for (auto *DII : DbgUsers) {
Value *Undef = UndefValue::get(I->getType());
DII->setOperand(0, MetadataAsValue::get(DII->getContext(),
ValueAsMetadata::get(Undef)));
}
return !DbgUsers.empty();
}
/// areAllUsesEqual - Check whether the uses of a value are all the same.
/// This is similar to Instruction::hasOneUse() except this will also return
/// true when there are no uses or multiple uses that all refer to the same
/// value.
static bool areAllUsesEqual(Instruction *I) {
Value::user_iterator UI = I->user_begin();
Value::user_iterator UE = I->user_end();
if (UI == UE)
return true;
User *TheUse = *UI;
for (++UI; UI != UE; ++UI) {
if (*UI != TheUse)
return false;
}
return true;
}
/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
/// dead PHI node, due to being a def-use chain of single-use nodes that
/// either forms a cycle or is terminated by a trivially dead instruction,
/// delete it. If that makes any of its operands trivially dead, delete them
/// too, recursively. Return true if a change was made.
bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
const TargetLibraryInfo *TLI) {
SmallPtrSet<Instruction*, 4> Visited;
for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
I = cast<Instruction>(*I->user_begin())) {
if (I->use_empty())
return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
// If we find an instruction more than once, we're on a cycle that
// won't prove fruitful.
if (!Visited.insert(I).second) {
// Break the cycle and delete the instruction and its operands.
I->replaceAllUsesWith(UndefValue::get(I->getType()));
(void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
return true;
}
}
return false;
}
static bool
simplifyAndDCEInstruction(Instruction *I,
SmallSetVector<Instruction *, 16> &WorkList,
const DataLayout &DL,
const TargetLibraryInfo *TLI) {
if (isInstructionTriviallyDead(I, TLI)) {
salvageDebugInfo(*I);
// Null out all of the instruction's operands to see if any operand becomes
// dead as we go.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
Value *OpV = I->getOperand(i);
I->setOperand(i, nullptr);
if (!OpV->use_empty() || I == OpV)
continue;
// If the operand is an instruction that became dead as we nulled out the
// operand, and if it is 'trivially' dead, delete it in a future loop
// iteration.
if (Instruction *OpI = dyn_cast<Instruction>(OpV))
if (isInstructionTriviallyDead(OpI, TLI))
WorkList.insert(OpI);
}
I->eraseFromParent();
return true;
}
if (Value *SimpleV = SimplifyInstruction(I, DL)) {
// Add the users to the worklist. CAREFUL: an instruction can use itself,
// in the case of a phi node.
for (User *U : I->users()) {
if (U != I) {
WorkList.insert(cast<Instruction>(U));
}
}
// Replace the instruction with its simplified value.
bool Changed = false;
if (!I->use_empty()) {
I->replaceAllUsesWith(SimpleV);
Changed = true;
}
if (isInstructionTriviallyDead(I, TLI)) {
I->eraseFromParent();
Changed = true;
}
return Changed;
}
return false;
}
/// SimplifyInstructionsInBlock - Scan the specified basic block and try to
/// simplify any instructions in it and recursively delete dead instructions.
///
/// This returns true if it changed the code, note that it can delete
/// instructions in other blocks as well in this block.
bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB,
const TargetLibraryInfo *TLI) {
bool MadeChange = false;
const DataLayout &DL = BB->getModule()->getDataLayout();
#ifndef NDEBUG
// In debug builds, ensure that the terminator of the block is never replaced
// or deleted by these simplifications. The idea of simplification is that it
// cannot introduce new instructions, and there is no way to replace the
// terminator of a block without introducing a new instruction.
AssertingVH<Instruction> TerminatorVH(&BB->back());
#endif
SmallSetVector<Instruction *, 16> WorkList;
// Iterate over the original function, only adding insts to the worklist
// if they actually need to be revisited. This avoids having to pre-init
// the worklist with the entire function's worth of instructions.
for (BasicBlock::iterator BI = BB->begin(), E = std::prev(BB->end());
BI != E;) {
assert(!BI->isTerminator());
Instruction *I = &*BI;
++BI;
// We're visiting this instruction now, so make sure it's not in the
// worklist from an earlier visit.
if (!WorkList.count(I))
MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
}
while (!WorkList.empty()) {
Instruction *I = WorkList.pop_back_val();
MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
}
return MadeChange;
}
//===----------------------------------------------------------------------===//
// Control Flow Graph Restructuring.
//
/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
/// method is called when we're about to delete Pred as a predecessor of BB. If
/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
///
/// Unlike the removePredecessor method, this attempts to simplify uses of PHI
/// nodes that collapse into identity values. For example, if we have:
/// x = phi(1, 0, 0, 0)
/// y = and x, z
///
/// .. and delete the predecessor corresponding to the '1', this will attempt to
/// recursively fold the and to 0.
void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
DomTreeUpdater *DTU) {
// This only adjusts blocks with PHI nodes.
if (!isa<PHINode>(BB->begin()))
return;
// Remove the entries for Pred from the PHI nodes in BB, but do not simplify
// them down. This will leave us with single entry phi nodes and other phis
// that can be removed.
BB->removePredecessor(Pred, true);
WeakTrackingVH PhiIt = &BB->front();
while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
Value *OldPhiIt = PhiIt;
if (!recursivelySimplifyInstruction(PN))
continue;
// If recursive simplification ended up deleting the next PHI node we would
// iterate to, then our iterator is invalid, restart scanning from the top
// of the block.
if (PhiIt != OldPhiIt) PhiIt = &BB->front();
}
if (DTU)
DTU->deleteEdgeRelaxed(Pred, BB);
}
/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
/// predecessor is known to have one successor (DestBB!). Eliminate the edge
/// between them, moving the instructions in the predecessor into DestBB and
/// deleting the predecessor block.
void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB,
DomTreeUpdater *DTU) {
// If BB has single-entry PHI nodes, fold them.
while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
Value *NewVal = PN->getIncomingValue(0);
// Replace self referencing PHI with undef, it must be dead.
if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
PN->replaceAllUsesWith(NewVal);
PN->eraseFromParent();
}
BasicBlock *PredBB = DestBB->getSinglePredecessor();
assert(PredBB && "Block doesn't have a single predecessor!");
bool ReplaceEntryBB = false;
if (PredBB == &DestBB->getParent()->getEntryBlock())
ReplaceEntryBB = true;
// DTU updates: Collect all the edges that enter
// PredBB. These dominator edges will be redirected to DestBB.
SmallVector<DominatorTree::UpdateType, 32> Updates;
if (DTU) {
Updates.push_back({DominatorTree::Delete, PredBB, DestBB});
for (auto I = pred_begin(PredBB), E = pred_end(PredBB); I != E; ++I) {
Updates.push_back({DominatorTree::Delete, *I, PredBB});
// This predecessor of PredBB may already have DestBB as a successor.
if (llvm::find(successors(*I), DestBB) == succ_end(*I))
Updates.push_back({DominatorTree::Insert, *I, DestBB});
}
}
// Zap anything that took the address of DestBB. Not doing this will give the
// address an invalid value.
if (DestBB->hasAddressTaken()) {
BlockAddress *BA = BlockAddress::get(DestBB);
Constant *Replacement =
ConstantInt::get(Type::getInt32Ty(BA->getContext()), 1);
BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
BA->getType()));
BA->destroyConstant();
}
// Anything that branched to PredBB now branches to DestBB.
PredBB->replaceAllUsesWith(DestBB);
// Splice all the instructions from PredBB to DestBB.
PredBB->getTerminator()->eraseFromParent();
DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
new UnreachableInst(PredBB->getContext(), PredBB);
// If the PredBB is the entry block of the function, move DestBB up to
// become the entry block after we erase PredBB.
if (ReplaceEntryBB)
DestBB->moveAfter(PredBB);
if (DTU) {
assert(PredBB->getInstList().size() == 1 &&
isa<UnreachableInst>(PredBB->getTerminator()) &&
"The successor list of PredBB isn't empty before "
"applying corresponding DTU updates.");
DTU->applyUpdates(Updates, /*ForceRemoveDuplicates*/ true);
DTU->deleteBB(PredBB);
// Recalculation of DomTree is needed when updating a forward DomTree and
// the Entry BB is replaced.
if (ReplaceEntryBB && 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(*(DestBB->getParent()));
}
}
else {
PredBB->eraseFromParent(); // Nuke BB if DTU is nullptr.
}
}
/// CanMergeValues - Return true if we can choose one of these values to use
/// in place of the other. Note that we will always choose the non-undef
/// value to keep.
static bool CanMergeValues(Value *First, Value *Second) {
return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
}
/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
/// almost-empty BB ending in an unconditional branch to Succ, into Succ.
///
/// Assumption: Succ is the single successor for BB.
static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
LLVM_DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
<< Succ->getName() << "\n");
// Shortcut, if there is only a single predecessor it must be BB and merging
// is always safe
if (Succ->getSinglePredecessor()) return true;
// Make a list of the predecessors of BB
SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
// Look at all the phi nodes in Succ, to see if they present a conflict when
// merging these blocks
for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
// If the incoming value from BB is again a PHINode in
// BB which has the same incoming value for *PI as PN does, we can
// merge the phi nodes and then the blocks can still be merged
PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
if (BBPN && BBPN->getParent() == BB) {
for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
BasicBlock *IBB = PN->getIncomingBlock(PI);
if (BBPreds.count(IBB) &&
!CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
PN->getIncomingValue(PI))) {
LLVM_DEBUG(dbgs()
<< "Can't fold, phi node " << PN->getName() << " in "
<< Succ->getName() << " is conflicting with "
<< BBPN->getName() << " with regard to common predecessor "
<< IBB->getName() << "\n");
return false;
}
}
} else {
Value* Val = PN->getIncomingValueForBlock(BB);
for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
// See if the incoming value for the common predecessor is equal to the
// one for BB, in which case this phi node will not prevent the merging
// of the block.
BasicBlock *IBB = PN->getIncomingBlock(PI);
if (BBPreds.count(IBB) &&
!CanMergeValues(Val, PN->getIncomingValue(PI))) {
LLVM_DEBUG(dbgs() << "Can't fold, phi node " << PN->getName()
<< " in " << Succ->getName()
<< " is conflicting with regard to common "
<< "predecessor " << IBB->getName() << "\n");
return false;
}
}
}
}
return true;
}
using PredBlockVector = SmallVector<BasicBlock *, 16>;
using IncomingValueMap = DenseMap<BasicBlock *, Value *>;
/// Determines the value to use as the phi node input for a block.
///
/// Select between \p OldVal any value that we know flows from \p BB
/// to a particular phi on the basis of which one (if either) is not
/// undef. Update IncomingValues based on the selected value.
///
/// \param OldVal The value we are considering selecting.
/// \param BB The block that the value flows in from.
/// \param IncomingValues A map from block-to-value for other phi inputs
/// that we have examined.
///
/// \returns the selected value.
static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
IncomingValueMap &IncomingValues) {
if (!isa<UndefValue>(OldVal)) {
assert((!IncomingValues.count(BB) ||
IncomingValues.find(BB)->second == OldVal) &&
"Expected OldVal to match incoming value from BB!");
IncomingValues.insert(std::make_pair(BB, OldVal));
return OldVal;
}
IncomingValueMap::const_iterator It = IncomingValues.find(BB);
if (It != IncomingValues.end()) return It->second;
return OldVal;
}
/// Create a map from block to value for the operands of a
/// given phi.
///
/// Create a map from block to value for each non-undef value flowing
/// into \p PN.
///
/// \param PN The phi we are collecting the map for.
/// \param IncomingValues [out] The map from block to value for this phi.
static void gatherIncomingValuesToPhi(PHINode *PN,
IncomingValueMap &IncomingValues) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *BB = PN->getIncomingBlock(i);
Value *V = PN->getIncomingValue(i);
if (!isa<UndefValue>(V))
IncomingValues.insert(std::make_pair(BB, V));
}
}
/// Replace the incoming undef values to a phi with the values
/// from a block-to-value map.
///
/// \param PN The phi we are replacing the undefs in.
/// \param IncomingValues A map from block to value.
static void replaceUndefValuesInPhi(PHINode *PN,
const IncomingValueMap &IncomingValues) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *V = PN->getIncomingValue(i);
if (!isa<UndefValue>(V)) continue;
BasicBlock *BB = PN->getIncomingBlock(i);
IncomingValueMap::const_iterator It = IncomingValues.find(BB);
if (It == IncomingValues.end()) continue;
PN->setIncomingValue(i, It->second);
}
}
/// Replace a value flowing from a block to a phi with
/// potentially multiple instances of that value flowing from the
/// block's predecessors to the phi.
///
/// \param BB The block with the value flowing into the phi.
/// \param BBPreds The predecessors of BB.
/// \param PN The phi that we are updating.
static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
const PredBlockVector &BBPreds,
PHINode *PN) {
Value *OldVal = PN->removeIncomingValue(BB, false);
assert(OldVal && "No entry in PHI for Pred BB!");
IncomingValueMap IncomingValues;
// We are merging two blocks - BB, and the block containing PN - and
// as a result we need to redirect edges from the predecessors of BB
// to go to the block containing PN, and update PN
// accordingly. Since we allow merging blocks in the case where the
// predecessor and successor blocks both share some predecessors,
// and where some of those common predecessors might have undef
// values flowing into PN, we want to rewrite those values to be
// consistent with the non-undef values.
gatherIncomingValuesToPhi(PN, IncomingValues);
// If this incoming value is one of the PHI nodes in BB, the new entries
// in the PHI node are the entries from the old PHI.
if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
PHINode *OldValPN = cast<PHINode>(OldVal);
for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
// Note that, since we are merging phi nodes and BB and Succ might
// have common predecessors, we could end up with a phi node with
// identical incoming branches. This will be cleaned up later (and
// will trigger asserts if we try to clean it up now, without also
// simplifying the corresponding conditional branch).
BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
Value *PredVal = OldValPN->getIncomingValue(i);
Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
IncomingValues);
// And add a new incoming value for this predecessor for the
// newly retargeted branch.
PN->addIncoming(Selected, PredBB);
}
} else {
for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
// Update existing incoming values in PN for this
// predecessor of BB.
BasicBlock *PredBB = BBPreds[i];
Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
IncomingValues);
// And add a new incoming value for this predecessor for the
// newly retargeted branch.
PN->addIncoming(Selected, PredBB);
}
}
replaceUndefValuesInPhi(PN, IncomingValues);
}
/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
/// unconditional branch, and contains no instructions other than PHI nodes,
/// potential side-effect free intrinsics and the branch. If possible,
/// eliminate BB by rewriting all the predecessors to branch to the successor
/// block and return true. If we can't transform, return false.
bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
DomTreeUpdater *DTU) {
assert(BB != &BB->getParent()->getEntryBlock() &&
"TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
// We can't eliminate infinite loops.
BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
if (BB == Succ) return false;
// Check to see if merging these blocks would cause conflicts for any of the
// phi nodes in BB or Succ. If not, we can safely merge.
if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
// Check for cases where Succ has multiple predecessors and a PHI node in BB
// has uses which will not disappear when the PHI nodes are merged. It is
// possible to handle such cases, but difficult: it requires checking whether
// BB dominates Succ, which is non-trivial to calculate in the case where
// Succ has multiple predecessors. Also, it requires checking whether
// constructing the necessary self-referential PHI node doesn't introduce any
// conflicts; this isn't too difficult, but the previous code for doing this
// was incorrect.
//
// Note that if this check finds a live use, BB dominates Succ, so BB is
// something like a loop pre-header (or rarely, a part of an irreducible CFG);
// folding the branch isn't profitable in that case anyway.
if (!Succ->getSinglePredecessor()) {
BasicBlock::iterator BBI = BB->begin();
while (isa<PHINode>(*BBI)) {
for (Use &U : BBI->uses()) {
if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
if (PN->getIncomingBlock(U) != BB)
return false;
} else {
return false;
}
}
++BBI;
}
}
// We cannot fold the block if it's a branch to an already present callbr
// successor because that creates duplicate successors.
for (auto I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
if (auto *CBI = dyn_cast<CallBrInst>((*I)->getTerminator())) {
if (Succ == CBI->getDefaultDest())
return false;
for (unsigned i = 0, e = CBI->getNumIndirectDests(); i != e; ++i)
if (Succ == CBI->getIndirectDest(i))
return false;
}
}
LLVM_DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
SmallVector<DominatorTree::UpdateType, 32> Updates;
if (DTU) {
Updates.push_back({DominatorTree::Delete, BB, Succ});
// All predecessors of BB will be moved to Succ.
for (auto I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
Updates.push_back({DominatorTree::Delete, *I, BB});
// This predecessor of BB may already have Succ as a successor.
if (llvm::find(successors(*I), Succ) == succ_end(*I))
Updates.push_back({DominatorTree::Insert, *I, Succ});
}
}
if (isa<PHINode>(Succ->begin())) {
// If there is more than one pred of succ, and there are PHI nodes in
// the successor, then we need to add incoming edges for the PHI nodes
//
const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
// Loop over all of the PHI nodes in the successor of BB.
for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
}
}
if (Succ->getSinglePredecessor()) {
// BB is the only predecessor of Succ, so Succ will end up with exactly
// the same predecessors BB had.
// Copy over any phi, debug or lifetime instruction.
BB->getTerminator()->eraseFromParent();
Succ->getInstList().splice(Succ->getFirstNonPHI()->getIterator(),
BB->getInstList());
} else {
while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
// We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
assert(PN->use_empty() && "There shouldn't be any uses here!");
PN->eraseFromParent();
}
}
// If the unconditional branch we replaced contains llvm.loop metadata, we
// add the metadata to the branch instructions in the predecessors.
unsigned LoopMDKind = BB->getContext().getMDKindID("llvm.loop");
Instruction *TI = BB->getTerminator();
if (TI)
if (MDNode *LoopMD = TI->getMetadata(LoopMDKind))
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
BasicBlock *Pred = *PI;
Pred->getTerminator()->setMetadata(LoopMDKind, LoopMD);
}
// Everything that jumped to BB now goes to Succ.
BB->replaceAllUsesWith(Succ);
if (!Succ->hasName()) Succ->takeName(BB);
// Clear the successor list of BB to match updates applying to DTU later.
if (BB->getTerminator())
BB->getInstList().pop_back();
new UnreachableInst(BB->getContext(), BB);
assert(succ_empty(BB) && "The successor list of BB isn't empty before "
"applying corresponding DTU updates.");
if (DTU) {
DTU->applyUpdates(Updates, /*ForceRemoveDuplicates*/ true);
DTU->deleteBB(BB);
} else {
BB->eraseFromParent(); // Delete the old basic block.
}
return true;
}
/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
/// nodes in this block. This doesn't try to be clever about PHI nodes
/// which differ only in the order of the incoming values, but instcombine
/// orders them so it usually won't matter.
bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
// This implementation doesn't currently consider undef operands
// specially. Theoretically, two phis which are identical except for
// one having an undef where the other doesn't could be collapsed.
struct PHIDenseMapInfo {
static PHINode *getEmptyKey() {
return DenseMapInfo<PHINode *>::getEmptyKey();
}
static PHINode *getTombstoneKey() {
return DenseMapInfo<PHINode *>::getTombstoneKey();
}
static unsigned getHashValue(PHINode *PN) {
// Compute a hash value on the operands. Instcombine will likely have
// sorted them, which helps expose duplicates, but we have to check all
// the operands to be safe in case instcombine hasn't run.
return static_cast<unsigned>(hash_combine(
hash_combine_range(PN->value_op_begin(), PN->value_op_end()),
hash_combine_range(PN->block_begin(), PN->block_end())));
}
static bool isEqual(PHINode *LHS, PHINode *RHS) {
if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
RHS == getEmptyKey() || RHS == getTombstoneKey())
return LHS == RHS;
return LHS->isIdenticalTo(RHS);
}
};
// Set of unique PHINodes.
DenseSet<PHINode *, PHIDenseMapInfo> PHISet;
// Examine each PHI.
bool Changed = false;
for (auto I = BB->begin(); PHINode *PN = dyn_cast<PHINode>(I++);) {
auto Inserted = PHISet.insert(PN);
if (!Inserted.second) {
// A duplicate. Replace this PHI with its duplicate.
PN->replaceAllUsesWith(*Inserted.first);
PN->eraseFromParent();
Changed = true;
// The RAUW can change PHIs that we already visited. Start over from the
// beginning.
PHISet.clear();
I = BB->begin();
}
}
return Changed;
}
/// enforceKnownAlignment - If the specified pointer points to an object that
/// we control, modify the object's alignment to PrefAlign. This isn't
/// often possible though. If alignment is important, a more reliable approach
/// is to simply align all global variables and allocation instructions to
/// their preferred alignment from the beginning.
static unsigned enforceKnownAlignment(Value *V, unsigned Align,
unsigned PrefAlign,
const DataLayout &DL) {
assert(PrefAlign > Align);
V = V->stripPointerCasts();
if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
// TODO: ideally, computeKnownBits ought to have used
// AllocaInst::getAlignment() in its computation already, making
// the below max redundant. But, as it turns out,
// stripPointerCasts recurses through infinite layers of bitcasts,
// while computeKnownBits is not allowed to traverse more than 6
// levels.
Align = std::max(AI->getAlignment(), Align);
if (PrefAlign <= Align)
return Align;
// If the preferred alignment is greater than the natural stack alignment
// then don't round up. This avoids dynamic stack realignment.
if (DL.exceedsNaturalStackAlignment(PrefAlign))
return Align;
AI->setAlignment(PrefAlign);
return PrefAlign;
}
if (auto *GO = dyn_cast<GlobalObject>(V)) {
// TODO: as above, this shouldn't be necessary.
Align = std::max(GO->getAlignment(), Align);
if (PrefAlign <= Align)
return Align;
// If there is a large requested alignment and we can, bump up the alignment
// of the global. If the memory we set aside for the global may not be the
// memory used by the final program then it is impossible for us to reliably
// enforce the preferred alignment.
if (!GO->canIncreaseAlignment())
return Align;
GO->setAlignment(PrefAlign);
return PrefAlign;
}
return Align;
}
unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
const DataLayout &DL,
const Instruction *CxtI,
AssumptionCache *AC,
const DominatorTree *DT) {
assert(V->getType()->isPointerTy() &&
"getOrEnforceKnownAlignment expects a pointer!");
KnownBits Known = computeKnownBits(V, DL, 0, AC, CxtI, DT);
unsigned TrailZ = Known.countMinTrailingZeros();
// Avoid trouble with ridiculously large TrailZ values, such as
// those computed from a null pointer.
TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
unsigned Align = 1u << std::min(Known.getBitWidth() - 1, TrailZ);
// LLVM doesn't support alignments larger than this currently.
Align = std::min(Align, +Value::MaximumAlignment);
if (PrefAlign > Align)
Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
// We don't need to make any adjustment.
return Align;
}
///===---------------------------------------------------------------------===//
/// Dbg Intrinsic utilities
///
/// See if there is a dbg.value intrinsic for DIVar before I.
static bool LdStHasDebugValue(DILocalVariable *DIVar, DIExpression *DIExpr,
Instruction *I) {
// Since we can't guarantee that the original dbg.declare instrinsic
// is removed by LowerDbgDeclare(), we need to make sure that we are
// not inserting the same dbg.value intrinsic over and over.
BasicBlock::InstListType::iterator PrevI(I);
if (PrevI != I->getParent()->getInstList().begin()) {
--PrevI;
if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
if (DVI->getValue() == I->getOperand(0) &&
DVI->getVariable() == DIVar &&
DVI->getExpression() == DIExpr)
return true;
}
return false;
}
/// See if there is a dbg.value intrinsic for DIVar for the PHI node.
static bool PhiHasDebugValue(DILocalVariable *DIVar,
DIExpression *DIExpr,
PHINode *APN) {
// Since we can't guarantee that the original dbg.declare instrinsic
// is removed by LowerDbgDeclare(), we need to make sure that we are
// not inserting the same dbg.value intrinsic over and over.
SmallVector<DbgValueInst *, 1> DbgValues;
findDbgValues(DbgValues, APN);
for (auto *DVI : DbgValues) {
assert(DVI->getValue() == APN);
if ((DVI->getVariable() == DIVar) && (DVI->getExpression() == DIExpr))
return true;
}
return false;
}
/// Check if the alloc size of \p ValTy is large enough to cover the variable
/// (or fragment of the variable) described by \p DII.
///
/// This is primarily intended as a helper for the different
/// ConvertDebugDeclareToDebugValue functions. The dbg.declare/dbg.addr that is
/// converted describes an alloca'd variable, so we need to use the
/// alloc size of the value when doing the comparison. E.g. an i1 value will be
/// identified as covering an n-bit fragment, if the store size of i1 is at
/// least n bits.
static bool valueCoversEntireFragment(Type *ValTy, DbgVariableIntrinsic *DII) {
const DataLayout &DL = DII->getModule()->getDataLayout();
uint64_t ValueSize = DL.getTypeAllocSizeInBits(ValTy);
if (auto FragmentSize = DII->getFragmentSizeInBits())
return ValueSize >= *FragmentSize;
// We can't always calculate the size of the DI variable (e.g. if it is a
// VLA). Try to use the size of the alloca that the dbg intrinsic describes
// intead.
if (DII->isAddressOfVariable())
if (auto *AI = dyn_cast_or_null<AllocaInst>(DII->getVariableLocation()))
if (auto FragmentSize = AI->getAllocationSizeInBits(DL))
return ValueSize >= *FragmentSize;
// Could not determine size of variable. Conservatively return false.
return false;
}
/// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
/// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
void llvm::ConvertDebugDeclareToDebugValue(DbgVariableIntrinsic *DII,
StoreInst *SI, DIBuilder &Builder) {
assert(DII->isAddressOfVariable());
auto *DIVar = DII->getVariable();
assert(DIVar && "Missing variable");
auto *DIExpr = DII->getExpression();
Value *DV = SI->getOperand(0);
if (!valueCoversEntireFragment(SI->getValueOperand()->getType(), DII)) {
// FIXME: If storing to a part of the variable described by the dbg.declare,
// then we want to insert a dbg.value for the corresponding fragment.
LLVM_DEBUG(dbgs() << "Failed to convert dbg.declare to dbg.value: "
<< *DII << '\n');
// For now, when there is a store to parts of the variable (but we do not
// know which part) we insert an dbg.value instrinsic to indicate that we
// know nothing about the variable's content.
DV = UndefValue::get(DV->getType());
if (!LdStHasDebugValue(DIVar, DIExpr, SI))
Builder.insertDbgValueIntrinsic(DV, DIVar, DIExpr, DII->getDebugLoc(),
SI);
return;
}
if (!LdStHasDebugValue(DIVar, DIExpr, SI))
Builder.insertDbgValueIntrinsic(DV, DIVar, DIExpr, DII->getDebugLoc(),
SI);
}
/// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
/// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
void llvm::ConvertDebugDeclareToDebugValue(DbgVariableIntrinsic *DII,
LoadInst *LI, DIBuilder &Builder) {
auto *DIVar = DII->getVariable();
auto *DIExpr = DII->getExpression();
assert(DIVar && "Missing variable");
if (LdStHasDebugValue(DIVar, DIExpr, LI))
return;
if (!valueCoversEntireFragment(LI->getType(), DII)) {
// FIXME: If only referring to a part of the variable described by the
// dbg.declare, then we want to insert a dbg.value for the corresponding
// fragment.
LLVM_DEBUG(dbgs() << "Failed to convert dbg.declare to dbg.value: "
<< *DII << '\n');
return;
}
// We are now tracking the loaded value instead of the address. In the
// future if multi-location support is added to the IR, it might be
// preferable to keep tracking both the loaded value and the original
// address in case the alloca can not be elided.
Instruction *DbgValue = Builder.insertDbgValueIntrinsic(
LI, DIVar, DIExpr, DII->getDebugLoc(), (Instruction *)nullptr);
DbgValue->insertAfter(LI);
}
/// Inserts a llvm.dbg.value intrinsic after a phi that has an associated
/// llvm.dbg.declare or llvm.dbg.addr intrinsic.
void llvm::ConvertDebugDeclareToDebugValue(DbgVariableIntrinsic *DII,
PHINode *APN, DIBuilder &Builder) {
auto *DIVar = DII->getVariable();
auto *DIExpr = DII->getExpression();
assert(DIVar && "Missing variable");
if (PhiHasDebugValue(DIVar, DIExpr, APN))
return;
if (!valueCoversEntireFragment(APN->getType(), DII)) {
// FIXME: If only referring to a part of the variable described by the
// dbg.declare, then we want to insert a dbg.value for the corresponding
// fragment.
LLVM_DEBUG(dbgs() << "Failed to convert dbg.declare to dbg.value: "
<< *DII << '\n');
return;
}
BasicBlock *BB = APN->getParent();
auto InsertionPt = BB->getFirstInsertionPt();
// The block may be a catchswitch block, which does not have a valid
// insertion point.
// FIXME: Insert dbg.value markers in the successors when appropriate.
if (InsertionPt != BB->end())
Builder.insertDbgValueIntrinsic(APN, DIVar, DIExpr, DII->getDebugLoc(),
&*InsertionPt);
}
/// Determine whether this alloca is either a VLA or an array.
static bool isArray(AllocaInst *AI) {
return AI->isArrayAllocation() ||
AI->getType()->getElementType()->isArrayTy();
}
/// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
/// of llvm.dbg.value intrinsics.
bool llvm::LowerDbgDeclare(Function &F) {
DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false);
SmallVector<DbgDeclareInst *, 4> Dbgs;
for (auto &FI : F)
for (Instruction &BI : FI)
if (auto DDI = dyn_cast<DbgDeclareInst>(&BI))
Dbgs.push_back(DDI);
if (Dbgs.empty())
return false;
for (auto &I : Dbgs) {
DbgDeclareInst *DDI = I;
AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
// If this is an alloca for a scalar variable, insert a dbg.value
// at each load and store to the alloca and erase the dbg.declare.
// The dbg.values allow tracking a variable even if it is not
// stored on the stack, while the dbg.declare can only describe
// the stack slot (and at a lexical-scope granularity). Later
// passes will attempt to elide the stack slot.
if (!AI || isArray(AI))
continue;
// A volatile load/store means that the alloca can't be elided anyway.
if (llvm::any_of(AI->users(), [](User *U) -> bool {
if (LoadInst *LI = dyn_cast<LoadInst>(U))
return LI->isVolatile();
if (StoreInst *SI = dyn_cast<StoreInst>(U))
return SI->isVolatile();
return false;
}))
continue;
for (auto &AIUse : AI->uses()) {
User *U = AIUse.getUser();
if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
if (AIUse.getOperandNo() == 1)
ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
} else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
} else if (CallInst *CI = dyn_cast<CallInst>(U)) {
// This is a call by-value or some other instruction that takes a
// pointer to the variable. Insert a *value* intrinsic that describes
// the variable by dereferencing the alloca.
auto *DerefExpr =
DIExpression::append(DDI->getExpression(), dwarf::DW_OP_deref);
DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(), DerefExpr,
DDI->getDebugLoc(), CI);
}
}
DDI->eraseFromParent();
}
return true;
}
/// Propagate dbg.value intrinsics through the newly inserted PHIs.
void llvm::insertDebugValuesForPHIs(BasicBlock *BB,
SmallVectorImpl<PHINode *> &InsertedPHIs) {
assert(BB && "No BasicBlock to clone dbg.value(s) from.");
if (InsertedPHIs.size() == 0)
return;
// Map existing PHI nodes to their dbg.values.
ValueToValueMapTy DbgValueMap;
for (auto &I : *BB) {
if (auto DbgII = dyn_cast<DbgVariableIntrinsic>(&I)) {
if (auto *Loc = dyn_cast_or_null<PHINode>(DbgII->getVariableLocation()))
DbgValueMap.insert({Loc, DbgII});
}
}
if (DbgValueMap.size() == 0)
return;
// Then iterate through the new PHIs and look to see if they use one of the
// previously mapped PHIs. If so, insert a new dbg.value intrinsic that will
// propagate the info through the new PHI.
LLVMContext &C = BB->getContext();
for (auto PHI : InsertedPHIs) {
BasicBlock *Parent = PHI->getParent();
// Avoid inserting an intrinsic into an EH block.
if (Parent->getFirstNonPHI()->isEHPad())
continue;
auto PhiMAV = MetadataAsValue::get(C, ValueAsMetadata::get(PHI));
for (auto VI : PHI->operand_values()) {
auto V = DbgValueMap.find(VI);
if (V != DbgValueMap.end()) {
auto *DbgII = cast<DbgVariableIntrinsic>(V->second);
Instruction *NewDbgII = DbgII->clone();
NewDbgII->setOperand(0, PhiMAV);
auto InsertionPt = Parent->getFirstInsertionPt();
assert(InsertionPt != Parent->end() && "Ill-formed basic block");
NewDbgII->insertBefore(&*InsertionPt);
}
}
}
}
/// Finds all intrinsics declaring local variables as living in the memory that
/// 'V' points to. This may include a mix of dbg.declare and
/// dbg.addr intrinsics.
TinyPtrVector<DbgVariableIntrinsic *> llvm::FindDbgAddrUses(Value *V) {
// This function is hot. Check whether the value has any metadata to avoid a
// DenseMap lookup.
if (!V->isUsedByMetadata())
return {};
auto *L = LocalAsMetadata::getIfExists(V);
if (!L)
return {};
auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L);
if (!MDV)
return {};
TinyPtrVector<DbgVariableIntrinsic *> Declares;
for (User *U : MDV->users()) {
if (auto *DII = dyn_cast<DbgVariableIntrinsic>(U))
if (DII->isAddressOfVariable())
Declares.push_back(DII);
}
return Declares;
}
void llvm::findDbgValues(SmallVectorImpl<DbgValueInst *> &DbgValues, Value *V) {
// This function is hot. Check whether the value has any metadata to avoid a
// DenseMap lookup.
if (!V->isUsedByMetadata())
return;
if (auto *L = LocalAsMetadata::getIfExists(V))
if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
for (User *U : MDV->users())
if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(U))
DbgValues.push_back(DVI);
}
void llvm::findDbgUsers(SmallVectorImpl<DbgVariableIntrinsic *> &DbgUsers,
Value *V) {
// This function is hot. Check whether the value has any metadata to avoid a
// DenseMap lookup.
if (!V->isUsedByMetadata())
return;
if (auto *L = LocalAsMetadata::getIfExists(V))
if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
for (User *U : MDV->users())
if (DbgVariableIntrinsic *DII = dyn_cast<DbgVariableIntrinsic>(U))
DbgUsers.push_back(DII);
}
bool llvm::replaceDbgDeclare(Value *Address, Value *NewAddress,
Instruction *InsertBefore, DIBuilder &Builder,
bool DerefBefore, int Offset, bool DerefAfter) {
auto DbgAddrs = FindDbgAddrUses(Address);
for (DbgVariableIntrinsic *DII : DbgAddrs) {
DebugLoc Loc = DII->getDebugLoc();
auto *DIVar = DII->getVariable();
auto *DIExpr = DII->getExpression();
assert(DIVar && "Missing variable");
DIExpr = DIExpression::prepend(DIExpr, DerefBefore, Offset, DerefAfter);
// Insert llvm.dbg.declare immediately before InsertBefore, and remove old
// llvm.dbg.declare.
Builder.insertDeclare(NewAddress, DIVar, DIExpr, Loc, InsertBefore);
if (DII == InsertBefore)
InsertBefore = InsertBefore->getNextNode();
DII->eraseFromParent();
}
return !DbgAddrs.empty();
}
bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
DIBuilder &Builder, bool DerefBefore,
int Offset, bool DerefAfter) {
return replaceDbgDeclare(AI, NewAllocaAddress, AI->getNextNode(), Builder,
DerefBefore, Offset, DerefAfter);
}
static void replaceOneDbgValueForAlloca(DbgValueInst *DVI, Value *NewAddress,
DIBuilder &Builder, int Offset) {
DebugLoc Loc = DVI->getDebugLoc();
auto *DIVar = DVI->getVariable();
auto *DIExpr = DVI->getExpression();
assert(DIVar && "Missing variable");
// This is an alloca-based llvm.dbg.value. The first thing it should do with
// the alloca pointer is dereference it. Otherwise we don't know how to handle
// it and give up.
if (!DIExpr || DIExpr->getNumElements() < 1 ||
DIExpr->getElement(0) != dwarf::DW_OP_deref)
return;
// Insert the offset immediately after the first deref.
// We could just change the offset argument of dbg.value, but it's unsigned...
if (Offset) {
SmallVector<uint64_t, 4> Ops;
Ops.push_back(dwarf::DW_OP_deref);
DIExpression::appendOffset(Ops, Offset);
Ops.append(DIExpr->elements_begin() + 1, DIExpr->elements_end());
DIExpr = Builder.createExpression(Ops);
}
Builder.insertDbgValueIntrinsic(NewAddress, DIVar, DIExpr, Loc, DVI);
DVI->eraseFromParent();
}
void llvm::replaceDbgValueForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
DIBuilder &Builder, int Offset) {
if (auto *L = LocalAsMetadata::getIfExists(AI))
if (auto *MDV = MetadataAsValue::getIfExists(AI->getContext(), L))
for (auto UI = MDV->use_begin(), UE = MDV->use_end(); UI != UE;) {
Use &U = *UI++;
if (auto *DVI = dyn_cast<DbgValueInst>(U.getUser()))
replaceOneDbgValueForAlloca(DVI, NewAllocaAddress, Builder, Offset);
}
}
/// Wrap \p V in a ValueAsMetadata instance.
static MetadataAsValue *wrapValueInMetadata(LLVMContext &C, Value *V) {
return MetadataAsValue::get(C, ValueAsMetadata::get(V));
}
bool llvm::salvageDebugInfo(Instruction &I) {
SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
findDbgUsers(DbgUsers, &I);
if (DbgUsers.empty())
return false;
return salvageDebugInfoForDbgValues(I, DbgUsers);
}
bool llvm::salvageDebugInfoForDbgValues(
Instruction &I, ArrayRef<DbgVariableIntrinsic *> DbgUsers) {
auto &Ctx = I.getContext();
auto wrapMD = [&](Value *V) { return wrapValueInMetadata(Ctx, V); };
for (auto *DII : DbgUsers) {
// Do not add DW_OP_stack_value for DbgDeclare and DbgAddr, because they
// are implicitly pointing out the value as a DWARF memory location
// description.
bool StackValue = isa<DbgValueInst>(DII);
DIExpression *DIExpr =
salvageDebugInfoImpl(I, DII->getExpression(), StackValue);
// salvageDebugInfoImpl should fail on examining the first element of
// DbgUsers, or none of them.
if (!DIExpr)
return false;
DII->setOperand(0, wrapMD(I.getOperand(0)));
DII->setOperand(2, MetadataAsValue::get(Ctx, DIExpr));
LLVM_DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
}
return true;
}
DIExpression *llvm::salvageDebugInfoImpl(Instruction &I,
DIExpression *SrcDIExpr,
bool WithStackValue) {
auto &M = *I.getModule();
auto &DL = M.getDataLayout();
// Apply a vector of opcodes to the source DIExpression.
auto doSalvage = [&](SmallVectorImpl<uint64_t> &Ops) -> DIExpression * {
DIExpression *DIExpr = SrcDIExpr;
if (!Ops.empty()) {
DIExpr = DIExpression::prependOpcodes(DIExpr, Ops, WithStackValue);
}
return DIExpr;
};
// Apply the given offset to the source DIExpression.
auto applyOffset = [&](uint64_t Offset) -> DIExpression * {
SmallVector<uint64_t, 8> Ops;
DIExpression::appendOffset(Ops, Offset);
return doSalvage(Ops);
};
// initializer-list helper for applying operators to the source DIExpression.
auto applyOps =
[&](std::initializer_list<uint64_t> Opcodes) -> DIExpression * {
SmallVector<uint64_t, 8> Ops(Opcodes);
return doSalvage(Ops);
};
if (auto *CI = dyn_cast<CastInst>(&I)) {
if (!CI->isNoopCast(DL))
return nullptr;
// No-op casts are irrelevant for debug info.
return SrcDIExpr;
} else if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
unsigned BitWidth =
M.getDataLayout().getIndexSizeInBits(GEP->getPointerAddressSpace());
// Rewrite a constant GEP into a DIExpression.
APInt Offset(BitWidth, 0);
if (GEP->accumulateConstantOffset(M.getDataLayout(), Offset)) {
return applyOffset(Offset.getSExtValue());
} else {
return nullptr;
}
} else if (auto *BI = dyn_cast<BinaryOperator>(&I)) {
// Rewrite binary operations with constant integer operands.
auto *ConstInt = dyn_cast<ConstantInt>(I.getOperand(1));
if (!ConstInt || ConstInt->getBitWidth() > 64)
return nullptr;
uint64_t Val = ConstInt->getSExtValue();
switch (BI->getOpcode()) {
case Instruction::Add:
return applyOffset(Val);
case Instruction::Sub:
return applyOffset(-int64_t(Val));
case Instruction::Mul:
return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_mul});
case Instruction::SDiv:
return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_div});
case Instruction::SRem:
return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_mod});
case Instruction::Or:
return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_or});
case Instruction::And:
return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_and});
case Instruction::Xor:
return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_xor});
case Instruction::Shl:
return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_shl});
case Instruction::LShr:
return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_shr});
case Instruction::AShr:
return applyOps({dwarf::DW_OP_constu, Val, dwarf::DW_OP_shra});
default:
// TODO: Salvage constants from each kind of binop we know about.
return nullptr;
}
} else if (isa<LoadInst>(&I)) {
// Rewrite the load into DW_OP_deref.
return DIExpression::prepend(SrcDIExpr, DIExpression::WithDeref);
}
return nullptr;
}
/// A replacement for a dbg.value expression.
using DbgValReplacement = Optional<DIExpression *>;
/// Point debug users of \p From to \p To using exprs given by \p RewriteExpr,
/// possibly moving/deleting users to prevent use-before-def. Returns true if
/// changes are made.
static bool rewriteDebugUsers(
Instruction &From, Value &To, Instruction &DomPoint, DominatorTree &DT,
function_ref<DbgValReplacement(DbgVariableIntrinsic &DII)> RewriteExpr) {
// Find debug users of From.
SmallVector<DbgVariableIntrinsic *, 1> Users;
findDbgUsers(Users, &From);
if (Users.empty())
return false;
// Prevent use-before-def of To.
bool Changed = false;
SmallPtrSet<DbgVariableIntrinsic *, 1> DeleteOrSalvage;
if (isa<Instruction>(&To)) {
bool DomPointAfterFrom = From.getNextNonDebugInstruction() == &DomPoint;
for (auto *DII : Users) {
// It's common to see a debug user between From and DomPoint. Move it
// after DomPoint to preserve the variable update without any reordering.
if (DomPointAfterFrom && DII->getNextNonDebugInstruction() == &DomPoint) {
LLVM_DEBUG(dbgs() << "MOVE: " << *DII << '\n');
DII->moveAfter(&DomPoint);
Changed = true;
// Users which otherwise aren't dominated by the replacement value must
// be salvaged or deleted.
} else if (!DT.dominates(&DomPoint, DII)) {
DeleteOrSalvage.insert(DII);
}
}
}
// Update debug users without use-before-def risk.
for (auto *DII : Users) {
if (DeleteOrSalvage.count(DII))
continue;
LLVMContext &Ctx = DII->getContext();
DbgValReplacement DVR = RewriteExpr(*DII);
if (!DVR)
continue;
DII->setOperand(0, wrapValueInMetadata(Ctx, &To));
DII->setOperand(2, MetadataAsValue::get(Ctx, *DVR));
LLVM_DEBUG(dbgs() << "REWRITE: " << *DII << '\n');
Changed = true;
}
if (!DeleteOrSalvage.empty()) {
// Try to salvage the remaining debug users.
Changed |= salvageDebugInfo(From);
// Delete the debug users which weren't salvaged.
for (auto *DII : DeleteOrSalvage) {
if (DII->getVariableLocation() == &From) {
LLVM_DEBUG(dbgs() << "Erased UseBeforeDef: " << *DII << '\n');
DII->eraseFromParent();
Changed = true;
}
}
}
return Changed;
}
/// Check if a bitcast between a value of type \p FromTy to type \p ToTy would
/// losslessly preserve the bits and semantics of the value. This predicate is
/// symmetric, i.e swapping \p FromTy and \p ToTy should give the same result.
///
/// Note that Type::canLosslesslyBitCastTo is not suitable here because it
/// allows semantically unequivalent bitcasts, such as <2 x i64> -> <4 x i32>,
/// and also does not allow lossless pointer <-> integer conversions.
static bool isBitCastSemanticsPreserving(const DataLayout &DL, Type *FromTy,
Type *ToTy) {
// Trivially compatible types.
if (FromTy == ToTy)
return true;
// Handle compatible pointer <-> integer conversions.
if (FromTy->isIntOrPtrTy() && ToTy->isIntOrPtrTy()) {
bool SameSize = DL.getTypeSizeInBits(FromTy) == DL.getTypeSizeInBits(ToTy);
bool LosslessConversion = !DL.isNonIntegralPointerType(FromTy) &&
!DL.isNonIntegralPointerType(ToTy);
return SameSize && LosslessConversion;
}
// TODO: This is not exhaustive.
return false;
}
bool llvm::replaceAllDbgUsesWith(Instruction &From, Value &To,
Instruction &DomPoint, DominatorTree &DT) {
// Exit early if From has no debug users.
if (!From.isUsedByMetadata())
return false;
assert(&From != &To && "Can't replace something with itself");
Type *FromTy = From.getType();
Type *ToTy = To.getType();
auto Identity = [&](DbgVariableIntrinsic &DII) -> DbgValReplacement {
return DII.getExpression();
};
// Handle no-op conversions.
Module &M = *From.getModule();
const DataLayout &DL = M.getDataLayout();
if (isBitCastSemanticsPreserving(DL, FromTy, ToTy))
return rewriteDebugUsers(From, To, DomPoint, DT, Identity);
// Handle integer-to-integer widening and narrowing.
// FIXME: Use DW_OP_convert when it's available everywhere.
if (FromTy->isIntegerTy() && ToTy->isIntegerTy()) {
uint64_t FromBits = FromTy->getPrimitiveSizeInBits();
uint64_t ToBits = ToTy->getPrimitiveSizeInBits();
assert(FromBits != ToBits && "Unexpected no-op conversion");
// When the width of the result grows, assume that a debugger will only
// access the low `FromBits` bits when inspecting the source variable.
if (FromBits < ToBits)
return rewriteDebugUsers(From, To, DomPoint, DT, Identity);
// The width of the result has shrunk. Use sign/zero extension to describe
// the source variable's high bits.
auto SignOrZeroExt = [&](DbgVariableIntrinsic &DII) -> DbgValReplacement {
DILocalVariable *Var = DII.getVariable();
// Without knowing signedness, sign/zero extension isn't possible.
auto Signedness = Var->getSignedness();
if (!Signedness)
return None;
bool Signed = *Signedness == DIBasicType::Signedness::Signed;
if (!Signed) {
// In the unsigned case, assume that a debugger will initialize the
// high bits to 0 and do a no-op conversion.
return Identity(DII);
} else {
// In the signed case, the high bits are given by sign extension, i.e:
// (To >> (ToBits - 1)) * ((2 ^ FromBits) - 1)
// Calculate the high bits and OR them together with the low bits.
SmallVector<uint64_t, 8> Ops({dwarf::DW_OP_dup, dwarf::DW_OP_constu,
(ToBits - 1), dwarf::DW_OP_shr,
dwarf::DW_OP_lit0, dwarf::DW_OP_not,
dwarf::DW_OP_mul, dwarf::DW_OP_or});
return DIExpression::appendToStack(DII.getExpression(), Ops);
}
};
return rewriteDebugUsers(From, To, DomPoint, DT, SignOrZeroExt);
}
// TODO: Floating-point conversions, vectors.
return false;
}
unsigned llvm::removeAllNonTerminatorAndEHPadInstructions(BasicBlock *BB) {
unsigned NumDeadInst = 0;
// Delete the instructions backwards, as it has a reduced likelihood of
// having to update as many def-use and use-def chains.
Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
while (EndInst != &BB->front()) {
// Delete the next to last instruction.
Instruction *Inst = &*--EndInst->getIterator();
if (!Inst->use_empty() && !Inst->getType()->isTokenTy())
Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
if (Inst->isEHPad() || Inst->getType()->isTokenTy()) {
EndInst = Inst;
continue;
}
if (!isa<DbgInfoIntrinsic>(Inst))
++NumDeadInst;
Inst->eraseFromParent();
}
return NumDeadInst;
}
unsigned llvm::changeToUnreachable(Instruction *I, bool UseLLVMTrap,
bool PreserveLCSSA, DomTreeUpdater *DTU) {
BasicBlock *BB = I->getParent();
std::vector <DominatorTree::UpdateType> Updates;
// Loop over all of the successors, removing BB's entry from any PHI
// nodes.
if (DTU)
Updates.reserve(BB->getTerminator()->getNumSuccessors());
for (BasicBlock *Successor : successors(BB)) {
Successor->removePredecessor(BB, PreserveLCSSA);
if (DTU)
Updates.push_back({DominatorTree::Delete, BB, Successor});
}
// Insert a call to llvm.trap right before this. This turns the undefined
// behavior into a hard fail instead of falling through into random code.
if (UseLLVMTrap) {
Function *TrapFn =
Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
CallTrap->setDebugLoc(I->getDebugLoc());
}
auto *UI = new UnreachableInst(I->getContext(), I);
UI->setDebugLoc(I->getDebugLoc());
// All instructions after this are dead.
unsigned NumInstrsRemoved = 0;
BasicBlock::iterator BBI = I->getIterator(), BBE = BB->end();
while (BBI != BBE) {
if (!BBI->use_empty())
BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
BB->getInstList().erase(BBI++);
++NumInstrsRemoved;
}
if (DTU)
DTU->applyUpdates(Updates, /*ForceRemoveDuplicates*/ true);
return NumInstrsRemoved;
}
/// changeToCall - Convert the specified invoke into a normal call.
static void changeToCall(InvokeInst *II, DomTreeUpdater *DTU = nullptr) {
SmallVector<Value*, 8> Args(II->arg_begin(), II->arg_end());
SmallVector<OperandBundleDef, 1> OpBundles;
II->getOperandBundlesAsDefs(OpBundles);
CallInst *NewCall = CallInst::Create(
II->getFunctionType(), II->getCalledValue(), Args, OpBundles, "", II);
NewCall->takeName(II);
NewCall->setCallingConv(II->getCallingConv());
NewCall->setAttributes(II->getAttributes());
NewCall->setDebugLoc(II->getDebugLoc());
NewCall->copyMetadata(*II);
II->replaceAllUsesWith(NewCall);
// Follow the call by a branch to the normal destination.
BasicBlock *NormalDestBB = II->getNormalDest();
BranchInst::Create(NormalDestBB, II);
// Update PHI nodes in the unwind destination
BasicBlock *BB = II->getParent();
BasicBlock *UnwindDestBB = II->getUnwindDest();
UnwindDestBB->removePredecessor(BB);
II->eraseFromParent();
if (DTU)
DTU->deleteEdgeRelaxed(BB, UnwindDestBB);
}
BasicBlock *llvm::changeToInvokeAndSplitBasicBlock(CallInst *CI,
BasicBlock *UnwindEdge) {
BasicBlock *BB = CI->getParent();
// Convert this function call into an invoke instruction. First, split the
// basic block.
BasicBlock *Split =
BB->splitBasicBlock(CI->getIterator(), CI->getName() + ".noexc");
// Delete the unconditional branch inserted by splitBasicBlock
BB->getInstList().pop_back();
// Create the new invoke instruction.
SmallVector<Value *, 8> InvokeArgs(CI->arg_begin(), CI->arg_end());
SmallVector<OperandBundleDef, 1> OpBundles;
CI->getOperandBundlesAsDefs(OpBundles);
// Note: we're round tripping operand bundles through memory here, and that
// can potentially be avoided with a cleverer API design that we do not have
// as of this time.
InvokeInst *II =
InvokeInst::Create(CI->getFunctionType(), CI->getCalledValue(), Split,
UnwindEdge, InvokeArgs, OpBundles, CI->getName(), BB);
II->setDebugLoc(CI->getDebugLoc());
II->setCallingConv(CI->getCallingConv());
II->setAttributes(CI->getAttributes());
// Make sure that anything using the call now uses the invoke! This also
// updates the CallGraph if present, because it uses a WeakTrackingVH.
CI->replaceAllUsesWith(II);
// Delete the original call
Split->getInstList().pop_front();
return Split;
}
static bool markAliveBlocks(Function &F,
SmallPtrSetImpl<BasicBlock *> &Reachable,
DomTreeUpdater *DTU = nullptr) {
SmallVector<BasicBlock*, 128> Worklist;
BasicBlock *BB = &F.front();
Worklist.push_back(BB);
Reachable.insert(BB);
bool Changed = false;
do {
BB = Worklist.pop_back_val();
// Do a quick scan of the basic block, turning any obviously unreachable
// instructions into LLVM unreachable insts. The instruction combining pass
// canonicalizes unreachable insts into stores to null or undef.
for (Instruction &I : *BB) {
if (auto *CI = dyn_cast<CallInst>(&I)) {
Value *Callee = CI->getCalledValue();
// Handle intrinsic calls.
if (Function *F = dyn_cast<Function>(Callee)) {
auto IntrinsicID = F->getIntrinsicID();
// Assumptions that are known to be false are equivalent to
// unreachable. Also, if the condition is undefined, then we make the
// choice most beneficial to the optimizer, and choose that to also be
// unreachable.
if (IntrinsicID == Intrinsic::assume) {
if (match(CI->getArgOperand(0), m_CombineOr(m_Zero(), m_Undef()))) {
// Don't insert a call to llvm.trap right before the unreachable.
changeToUnreachable(CI, false, false, DTU);
Changed = true;
break;
}
} else if (IntrinsicID == Intrinsic::experimental_guard) {
// A call to the guard intrinsic bails out of the current
// compilation unit if the predicate passed to it is false. If the
// predicate is a constant false, then we know the guard will bail
// out of the current compile unconditionally, so all code following
// it is dead.
//
// Note: unlike in llvm.assume, it is not "obviously profitable" for
// guards to treat `undef` as `false` since a guard on `undef` can
// still be useful for widening.
if (match(CI->getArgOperand(0), m_Zero()))
if (!isa<UnreachableInst>(CI->getNextNode())) {
changeToUnreachable(CI->getNextNode(), /*UseLLVMTrap=*/false,
false, DTU);
Changed = true;
break;
}
}
} else if ((isa<ConstantPointerNull>(Callee) &&
!NullPointerIsDefined(CI->getFunction())) ||
isa<UndefValue>(Callee)) {
changeToUnreachable(CI, /*UseLLVMTrap=*/false, false, DTU);
Changed = true;
break;
}
if (CI->doesNotReturn()) {
// If we found a call to a no-return function, insert an unreachable
// instruction after it. Make sure there isn't *already* one there
// though.
if (!isa<UnreachableInst>(CI->getNextNode())) {
// Don't insert a call to llvm.trap right before the unreachable.
changeToUnreachable(CI->getNextNode(), false, false, DTU);
Changed = true;
}
break;
}
} else if (auto *SI = dyn_cast<StoreInst>(&I)) {
// Store to undef and store to null are undefined and used to signal
// that they should be changed to unreachable by passes that can't
// modify the CFG.
// Don't touch volatile stores.
if (SI->isVolatile()) continue;
Value *Ptr = SI->getOperand(1);
if (isa<UndefValue>(Ptr) ||
(isa<ConstantPointerNull>(Ptr) &&
!NullPointerIsDefined(SI->getFunction(),
SI->getPointerAddressSpace()))) {
changeToUnreachable(SI, true, false, DTU);
Changed = true;
break;
}
}
}
Instruction *Terminator = BB->getTerminator();
if (auto *II = dyn_cast<InvokeInst>(Terminator)) {
// Turn invokes that call 'nounwind' functions into ordinary calls.
Value *Callee = II->getCalledValue();
if ((isa<ConstantPointerNull>(Callee) &&
!NullPointerIsDefined(BB->getParent())) ||
isa<UndefValue>(Callee)) {
changeToUnreachable(II, true, false, DTU);
Changed = true;
} else if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) {
if (II->use_empty() && II->onlyReadsMemory()) {
// jump to the normal destination branch.
BasicBlock *NormalDestBB = II->getNormalDest();
BasicBlock *UnwindDestBB = II->getUnwindDest();
BranchInst::Create(NormalDestBB, II);
UnwindDestBB->removePredecessor(II->getParent());
II->eraseFromParent();
if (DTU)
DTU->deleteEdgeRelaxed(BB, UnwindDestBB);
} else
changeToCall(II, DTU);
Changed = true;
}
} else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(Terminator)) {
// Remove catchpads which cannot be reached.
struct CatchPadDenseMapInfo {
static CatchPadInst *getEmptyKey() {
return DenseMapInfo<CatchPadInst *>::getEmptyKey();
}
static CatchPadInst *getTombstoneKey() {
return DenseMapInfo<CatchPadInst *>::getTombstoneKey();
}
static unsigned getHashValue(CatchPadInst *CatchPad) {
return static_cast<unsigned>(hash_combine_range(
CatchPad->value_op_begin(), CatchPad->value_op_end()));
}
static bool isEqual(CatchPadInst *LHS, CatchPadInst *RHS) {
if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
RHS == getEmptyKey() || RHS == getTombstoneKey())
return LHS == RHS;
return LHS->isIdenticalTo(RHS);
}
};
// Set of unique CatchPads.
SmallDenseMap<CatchPadInst *, detail::DenseSetEmpty, 4,
CatchPadDenseMapInfo, detail::DenseSetPair<CatchPadInst *>>
HandlerSet;
detail::DenseSetEmpty Empty;
for (CatchSwitchInst::handler_iterator I = CatchSwitch->handler_begin(),
E = CatchSwitch->handler_end();
I != E; ++I) {
BasicBlock *HandlerBB = *I;
auto *CatchPad = cast<CatchPadInst>(HandlerBB->getFirstNonPHI());
if (!HandlerSet.insert({CatchPad, Empty}).second) {
CatchSwitch->removeHandler(I);
--I;
--E;
Changed = true;
}
}
}
Changed |= ConstantFoldTerminator(BB, true, nullptr, DTU);
for (BasicBlock *Successor : successors(BB))
if (Reachable.insert(Successor).second)
Worklist.push_back(Successor);
} while (!Worklist.empty());
return Changed;
}
void llvm::removeUnwindEdge(BasicBlock *BB, DomTreeUpdater *DTU) {
Instruction *TI = BB->getTerminator();
if (auto *II = dyn_cast<InvokeInst>(TI)) {
changeToCall(II, DTU);
return;
}
Instruction *NewTI;
BasicBlock *UnwindDest;
if (auto *CRI = dyn_cast<CleanupReturnInst>(TI)) {
NewTI = CleanupReturnInst::Create(CRI->getCleanupPad(), nullptr, CRI);
UnwindDest = CRI->getUnwindDest();
} else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(TI)) {
auto *NewCatchSwitch = CatchSwitchInst::Create(
CatchSwitch->getParentPad(), nullptr, CatchSwitch->getNumHandlers(),
CatchSwitch->getName(), CatchSwitch);
for (BasicBlock *PadBB : CatchSwitch->handlers())
NewCatchSwitch->addHandler(PadBB);
NewTI = NewCatchSwitch;
UnwindDest = CatchSwitch->getUnwindDest();
} else {
llvm_unreachable("Could not find unwind successor");
}
NewTI->takeName(TI);
NewTI->setDebugLoc(TI->getDebugLoc());
UnwindDest->removePredecessor(BB);
TI->replaceAllUsesWith(NewTI);
TI->eraseFromParent();
if (DTU)
DTU->deleteEdgeRelaxed(BB, UnwindDest);
}
/// removeUnreachableBlocks - Remove blocks that are not reachable, even
/// if they are in a dead cycle. Return true if a change was made, false
/// otherwise. If `LVI` is passed, this function preserves LazyValueInfo
/// after modifying the CFG.
bool llvm::removeUnreachableBlocks(Function &F, LazyValueInfo *LVI,
DomTreeUpdater *DTU,
MemorySSAUpdater *MSSAU) {
SmallPtrSet<BasicBlock*, 16> Reachable;
bool Changed = markAliveBlocks(F, Reachable, DTU);
// If there are unreachable blocks in the CFG...
if (Reachable.size() == F.size())
return Changed;
assert(Reachable.size() < F.size());
NumRemoved += F.size()-Reachable.size();
SmallPtrSet<BasicBlock *, 16> DeadBlockSet;
for (Function::iterator I = ++F.begin(), E = F.end(); I != E; ++I) {
auto *BB = &*I;
if (Reachable.count(BB))
continue;
DeadBlockSet.insert(BB);
}
if (MSSAU)
MSSAU->removeBlocks(DeadBlockSet);
// Loop over all of the basic blocks that are not reachable, dropping all of
// their internal references. Update DTU and LVI if available.
std::vector<DominatorTree::UpdateType> Updates;
for (auto *BB : DeadBlockSet) {
for (BasicBlock *Successor : successors(BB)) {
if (!DeadBlockSet.count(Successor))
Successor->removePredecessor(BB);
if (DTU)
Updates.push_back({DominatorTree::Delete, BB, Successor});
}
if (LVI)
LVI->eraseBlock(BB);
BB->dropAllReferences();
}
for (Function::iterator I = ++F.begin(); I != F.end();) {
auto *BB = &*I;
if (Reachable.count(BB)) {
++I;
continue;
}
if (DTU) {
// Remove the terminator of BB to clear the successor list of BB.
if (BB->getTerminator())
BB->getInstList().pop_back();
new UnreachableInst(BB->getContext(), BB);
assert(succ_empty(BB) && "The successor list of BB isn't empty before "
"applying corresponding DTU updates.");
++I;
} else {
I = F.getBasicBlockList().erase(I);
}
}
if (DTU) {
DTU->applyUpdates(Updates, /*ForceRemoveDuplicates*/ true);
bool Deleted = false;
for (auto *BB : DeadBlockSet) {
if (DTU->isBBPendingDeletion(BB))
--NumRemoved;
else
Deleted = true;
DTU->deleteBB(BB);
}
if (!Deleted)
return false;
}
return true;
}
void llvm::combineMetadata(Instruction *K, const Instruction *J,
ArrayRef<unsigned> KnownIDs, bool DoesKMove) {
SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
K->dropUnknownNonDebugMetadata(KnownIDs);
K->getAllMetadataOtherThanDebugLoc(Metadata);
for (const auto &MD : Metadata) {
unsigned Kind = MD.first;
MDNode *JMD = J->getMetadata(Kind);
MDNode *KMD = MD.second;
switch (Kind) {
default:
K->setMetadata(Kind, nullptr); // Remove unknown metadata
break;
case LLVMContext::MD_dbg:
llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
case LLVMContext::MD_tbaa:
K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
break;
case LLVMContext::MD_alias_scope:
K->setMetadata(Kind, MDNode::getMostGenericAliasScope(JMD, KMD));
break;
case LLVMContext::MD_noalias:
case LLVMContext::MD_mem_parallel_loop_access:
K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
break;
case LLVMContext::MD_access_group:
K->setMetadata(LLVMContext::MD_access_group,
intersectAccessGroups(K, J));
break;
case LLVMContext::MD_range:
// If K does move, use most generic range. Otherwise keep the range of
// K.
if (DoesKMove)
// FIXME: If K does move, we should drop the range info and nonnull.
// Currently this function is used with DoesKMove in passes
// doing hoisting/sinking and the current behavior of using the
// most generic range is correct in those cases.
K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD));
break;
case LLVMContext::MD_fpmath:
K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD));
break;
case LLVMContext::MD_invariant_load:
// Only set the !invariant.load if it is present in both instructions.
K->setMetadata(Kind, JMD);
break;
case LLVMContext::MD_nonnull:
// If K does move, keep nonull if it is present in both instructions.
if (DoesKMove)
K->setMetadata(Kind, JMD);
break;
case LLVMContext::MD_invariant_group:
// Preserve !invariant.group in K.
break;
case LLVMContext::MD_align:
K->setMetadata(Kind,
MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
break;
case LLVMContext::MD_dereferenceable:
case LLVMContext::MD_dereferenceable_or_null:
K->setMetadata(Kind,
MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
break;
}
}
// Set !invariant.group from J if J has it. If both instructions have it
// then we will just pick it from J - even when they are different.
// Also make sure that K is load or store - f.e. combining bitcast with load
// could produce bitcast with invariant.group metadata, which is invalid.
// FIXME: we should try to preserve both invariant.group md if they are
// different, but right now instruction can only have one invariant.group.
if (auto *JMD = J->getMetadata(LLVMContext::MD_invariant_group))
if (isa<LoadInst>(K) || isa<StoreInst>(K))
K->setMetadata(LLVMContext::MD_invariant_group, JMD);
}
void llvm::combineMetadataForCSE(Instruction *K, const Instruction *J,
bool KDominatesJ) {
unsigned KnownIDs[] = {
LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
LLVMContext::MD_noalias, LLVMContext::MD_range,
LLVMContext::MD_invariant_load, LLVMContext::MD_nonnull,
LLVMContext::MD_invariant_group, LLVMContext::MD_align,
LLVMContext::MD_dereferenceable,
LLVMContext::MD_dereferenceable_or_null,
LLVMContext::MD_access_group};
combineMetadata(K, J, KnownIDs, KDominatesJ);
}
void llvm::patchReplacementInstruction(Instruction *I, Value *Repl) {
auto *ReplInst = dyn_cast<Instruction>(Repl);
if (!ReplInst)
return;
// Patch the replacement so that it is not more restrictive than the value
// being replaced.
// Note that if 'I' is a load being replaced by some operation,
// for example, by an arithmetic operation, then andIRFlags()
// would just erase all math flags from the original arithmetic
// operation, which is clearly not wanted and not needed.
if (!isa<LoadInst>(I))
ReplInst->andIRFlags(I);
// FIXME: If both the original and replacement value are part of the
// same control-flow region (meaning that the execution of one
// guarantees the execution of the other), then we can combine the
// noalias scopes here and do better than the general conservative
// answer used in combineMetadata().
// In general, GVN unifies expressions over different control-flow
// regions, and so we need a conservative combination of the noalias
// scopes.
static const unsigned KnownIDs[] = {
LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
LLVMContext::MD_noalias, LLVMContext::MD_range,
LLVMContext::MD_fpmath, LLVMContext::MD_invariant_load,
LLVMContext::MD_invariant_group, LLVMContext::MD_nonnull,
LLVMContext::MD_access_group};
combineMetadata(ReplInst, I, KnownIDs, false);
}
template <typename RootType, typename DominatesFn>
static unsigned replaceDominatedUsesWith(Value *From, Value *To,
const RootType &Root,
const DominatesFn &Dominates) {
assert(From->getType() == To->getType());
unsigned Count = 0;
for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
UI != UE;) {
Use &U = *UI++;
if (!Dominates(Root, U))
continue;
U.set(To);
LLVM_DEBUG(dbgs() << "Replace dominated use of '" << From->getName()
<< "' as " << *To << " in " << *U << "\n");
++Count;
}
return Count;
}
unsigned llvm::replaceNonLocalUsesWith(Instruction *From, Value *To) {
assert(From->getType() == To->getType());
auto *BB = From->getParent();
unsigned Count = 0;
for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
UI != UE;) {
Use &U = *UI++;
auto *I = cast<Instruction>(U.getUser());
if (I->getParent() == BB)
continue;
U.set(To);
++Count;
}
return Count;
}
unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
DominatorTree &DT,
const BasicBlockEdge &Root) {
auto Dominates = [&DT](const BasicBlockEdge &Root, const Use &U) {
return DT.dominates(Root, U);
};
return ::replaceDominatedUsesWith(From, To, Root, Dominates);
}
unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
DominatorTree &DT,
const BasicBlock *BB) {
auto ProperlyDominates = [&DT](const BasicBlock *BB, const Use &U) {
auto *I = cast<Instruction>(U.getUser())->getParent();
return DT.properlyDominates(BB, I);
};
return ::replaceDominatedUsesWith(From, To, BB, ProperlyDominates);
}
bool llvm::callsGCLeafFunction(const CallBase *Call,