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llvm-project/llvm/lib/Transforms/Utils/Local.cpp

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//===-- Local.cpp - Functions to perform local transformations ------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This family of functions perform various local transformations to the
// program.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/EHPersonalities.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#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) {
TerminatorInst *T = BB->getTerminator();
IRBuilder<> Builder(T);
// Branch - See if we are conditional jumping on constant
if (BranchInst *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 (ConstantInt *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;
//cerr << "Function: " << T->getParent()->getParent()
// << "\nRemoving branch from " << T->getParent()
// << "\n\nTo: " << OldDest << endl;
// 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();
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 (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
// If we are switching on a constant, we can convert the switch to an
// unconditional branch.
ConstantInt *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 (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
i != e; ++i) {
// 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) {
ConstantInt *CI =
mdconst::dyn_extract<ConstantInt>(MD->getOperand(MD_i));
assert(CI);
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.
DefaultDest->removePredecessor(SI->getParent());
SI->removeCase(i);
--i; --e;
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;
}
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();
// Remove entries from PHI nodes which we no longer branch to...
for (BasicBlock *Succ : SI->successors()) {
// Found case matching a constant operand?
if (Succ == TheOnlyDest)
TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
else
Succ->removePredecessor(BB);
}
// Delete the old switch.
Value *Cond = SI->getCondition();
SI->eraseFromParent();
if (DeleteDeadConditions)
RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
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.
SwitchInst::CaseIt 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 (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
// indirectbr blockaddress(@F, @BB) -> br label @BB
if (BlockAddress *BA =
dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
BasicBlock *TheOnlyDest = BA->getBasicBlock();
// 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
IBI->getDestination(i)->removePredecessor(IBI->getParent());
}
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);
}
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() || isa<TerminatorInst>(I)) 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 (!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 if dead.
if (II->getIntrinsicID() == Intrinsic::stacksave)
return true;
// Lifetime intrinsics are dead when their right-hand is undef.
if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
II->getIntrinsicID() == Intrinsic::lifetime_end)
return isa<UndefValue>(II->getArgOperand(1));
// Assumptions are dead if their condition is trivially true.
if (II->getIntrinsicID() == Intrinsic::assume) {
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);
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) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
return false;
SmallVector<Instruction*, 16> DeadInsts;
DeadInsts.push_back(I);
do {
I = DeadInsts.pop_back_val();
// 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()) 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);
}
I->eraseFromParent();
} while (!DeadInsts.empty());
return true;
}
/// 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)) {
// 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.
I->replaceAllUsesWith(SimpleV);
I->eraseFromParent();
return true;
}
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) {
// 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);
WeakVH 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();
}
}
/// 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, DominatorTree *DT) {
// 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!");
// 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(llvm::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());
// If the PredBB is the entry block of the function, move DestBB up to
// become the entry block after we erase PredBB.
if (PredBB == &DestBB->getParent()->getEntryBlock())
DestBB->moveAfter(PredBB);
if (DT) {
BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
DT->changeImmediateDominator(DestBB, PredBBIDom);
DT->eraseNode(PredBB);
}
// Nuke BB.
PredBB->eraseFromParent();
}
/// 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!");
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))) {
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))) {
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;
}
typedef SmallVector<BasicBlock *, 16> PredBlockVector;
typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
/// \brief 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;
}
/// \brief 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));
}
}
/// \brief 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);
}
}
/// \brief 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) {
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;
}
}
DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
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();
}
}
// Everything that jumped to BB now goes to Succ.
BB->replaceAllUsesWith(Succ);
if (!Succ->hasName()) Succ->takeName(BB);
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;
}
/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
/// we can determine, return it, otherwise return 0. If PrefAlign is specified,
/// and it is more than the alignment of the ultimate object, see if we can
/// increase the alignment of the ultimate object, making this check succeed.
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!");
unsigned BitWidth = DL.getPointerTypeSizeInBits(V->getType());
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC, CxtI, DT);
unsigned TrailZ = KnownZero.countTrailingOnes();
// 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(BitWidth - 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(const DILocalVariable *DIVar, 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.
llvm::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->getOffset() == 0 &&
DVI->getVariable() == DIVar)
return true;
}
return false;
}
/// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
/// that has an associated llvm.dbg.decl intrinsic.
bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
StoreInst *SI, DIBuilder &Builder) {
auto *DIVar = DDI->getVariable();
auto *DIExpr = DDI->getExpression();
assert(DIVar && "Missing variable");
if (LdStHasDebugValue(DIVar, SI))
return true;
// If an argument is zero extended then use argument directly. The ZExt
// may be zapped by an optimization pass in future.
Argument *ExtendedArg = nullptr;
if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
if (ExtendedArg) {
// We're now only describing a subset of the variable. The piece we're
// describing will always be smaller than the variable size, because
// VariableSize == Size of Alloca described by DDI. Since SI stores
// to the alloca described by DDI, if it's first operand is an extend,
// we're guaranteed that before extension, the value was narrower than
// the size of the alloca, hence the size of the described variable.
SmallVector<uint64_t, 3> NewDIExpr;
unsigned PieceOffset = 0;
// If this already is a bit piece, we drop the bit piece from the expression
// and record the offset.
if (DIExpr->isBitPiece()) {
NewDIExpr.append(DIExpr->elements_begin(), DIExpr->elements_end()-3);
PieceOffset = DIExpr->getBitPieceOffset();
} else {
NewDIExpr.append(DIExpr->elements_begin(), DIExpr->elements_end());
}
NewDIExpr.push_back(dwarf::DW_OP_bit_piece);
NewDIExpr.push_back(PieceOffset); //Offset
const DataLayout &DL = DDI->getModule()->getDataLayout();
NewDIExpr.push_back(DL.getTypeSizeInBits(ExtendedArg->getType())); // Size
Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar,
Builder.createExpression(NewDIExpr),
DDI->getDebugLoc(), SI);
}
else
Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, DIExpr,
DDI->getDebugLoc(), SI);
return true;
}
/// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
/// that has an associated llvm.dbg.decl intrinsic.
bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
LoadInst *LI, DIBuilder &Builder) {
auto *DIVar = DDI->getVariable();
auto *DIExpr = DDI->getExpression();
assert(DIVar && "Missing variable");
if (LdStHasDebugValue(DIVar, LI))
return true;
// 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, 0, DIVar, DIExpr, DDI->getDebugLoc(), (Instruction *)nullptr);
DbgValue->insertAfter(LI);
return true;
}
/// 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)) {
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 alloca.
SmallVector<uint64_t, 1> NewDIExpr;
auto *DIExpr = DDI->getExpression();
NewDIExpr.push_back(dwarf::DW_OP_deref);
NewDIExpr.append(DIExpr->elements_begin(), DIExpr->elements_end());
DIB.insertDbgValueIntrinsic(AI, 0, DDI->getVariable(),
DIB.createExpression(NewDIExpr),
DDI->getDebugLoc(), CI);
}
}
DDI->eraseFromParent();
}
}
return true;
}
/// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
/// alloca 'V', if any.
DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
if (auto *L = LocalAsMetadata::getIfExists(V))
if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
for (User *U : MDV->users())
if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
return DDI;
return nullptr;
}
bool llvm::replaceDbgDeclare(Value *Address, Value *NewAddress,
Instruction *InsertBefore, DIBuilder &Builder,
bool Deref, int Offset) {
DbgDeclareInst *DDI = FindAllocaDbgDeclare(Address);
if (!DDI)
return false;
DebugLoc Loc = DDI->getDebugLoc();
auto *DIVar = DDI->getVariable();
auto *DIExpr = DDI->getExpression();
assert(DIVar && "Missing variable");
if (Deref || Offset) {
// Create a copy of the original DIDescriptor for user variable, prepending
// "deref" operation to a list of address elements, as new llvm.dbg.declare
// will take a value storing address of the memory for variable, not
// alloca itself.
SmallVector<uint64_t, 4> NewDIExpr;
if (Deref)
NewDIExpr.push_back(dwarf::DW_OP_deref);
if (Offset > 0) {
NewDIExpr.push_back(dwarf::DW_OP_plus);
NewDIExpr.push_back(Offset);
} else if (Offset < 0) {
NewDIExpr.push_back(dwarf::DW_OP_minus);
NewDIExpr.push_back(-Offset);
}
if (DIExpr)
NewDIExpr.append(DIExpr->elements_begin(), DIExpr->elements_end());
DIExpr = Builder.createExpression(NewDIExpr);
}
// Insert llvm.dbg.declare immediately after the original alloca, and remove
// old llvm.dbg.declare.
Builder.insertDeclare(NewAddress, DIVar, DIExpr, Loc, InsertBefore);
DDI->eraseFromParent();
return true;
}
bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
DIBuilder &Builder, bool Deref, int Offset) {
return replaceDbgDeclare(AI, NewAllocaAddress, AI->getNextNode(), Builder,
Deref, Offset);
}
void llvm::changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
BasicBlock *BB = I->getParent();
// Loop over all of the successors, removing BB's entry from any PHI
// nodes.
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
(*SI)->removePredecessor(BB);
// 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());
}
new UnreachableInst(I->getContext(), I);
// All instructions after this are dead.
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++);
}
}
/// changeToCall - Convert the specified invoke into a normal call.
static void changeToCall(InvokeInst *II) {
SmallVector<Value*, 8> Args(II->arg_begin(), II->arg_end());
SmallVector<OperandBundleDef, 1> OpBundles;
II->getOperandBundlesAsDefs(OpBundles);
CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, OpBundles,
"", II);
NewCall->takeName(II);
NewCall->setCallingConv(II->getCallingConv());
NewCall->setAttributes(II->getAttributes());
NewCall->setDebugLoc(II->getDebugLoc());
II->replaceAllUsesWith(NewCall);
// Follow the call by a branch to the normal destination.
BranchInst::Create(II->getNormalDest(), II);
// Update PHI nodes in the unwind destination
II->getUnwindDest()->removePredecessor(II->getParent());
II->eraseFromParent();
}
static bool markAliveBlocks(Function &F,
SmallPtrSetImpl<BasicBlock*> &Reachable) {
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 (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
// 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 (IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
if (II->getIntrinsicID() == Intrinsic::assume) {
bool MakeUnreachable = false;
if (isa<UndefValue>(II->getArgOperand(0)))
MakeUnreachable = true;
else if (ConstantInt *Cond =
dyn_cast<ConstantInt>(II->getArgOperand(0)))
MakeUnreachable = Cond->isZero();
if (MakeUnreachable) {
// Don't insert a call to llvm.trap right before the unreachable.
changeToUnreachable(&*BBI, false);
Changed = true;
break;
}
}
if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
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.
++BBI;
if (!isa<UnreachableInst>(BBI)) {
// Don't insert a call to llvm.trap right before the unreachable.
changeToUnreachable(&*BBI, false);
Changed = true;
}
break;
}
}
// 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.
if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
// Don't touch volatile stores.
if (SI->isVolatile()) continue;
Value *Ptr = SI->getOperand(1);
if (isa<UndefValue>(Ptr) ||
(isa<ConstantPointerNull>(Ptr) &&
SI->getPointerAddressSpace() == 0)) {
changeToUnreachable(SI, true);
Changed = true;
break;
}
}
}
TerminatorInst *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) || isa<UndefValue>(Callee)) {
changeToUnreachable(II, true);
Changed = true;
} else if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) {
if (II->use_empty() && II->onlyReadsMemory()) {
// jump to the normal destination branch.
BranchInst::Create(II->getNormalDest(), II);
II->getUnwindDest()->removePredecessor(II->getParent());
II->eraseFromParent();
} else
changeToCall(II);
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);
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
if (Reachable.insert(*SI).second)
Worklist.push_back(*SI);
} while (!Worklist.empty());
return Changed;
}
void llvm::removeUnwindEdge(BasicBlock *BB) {
TerminatorInst *TI = BB->getTerminator();
if (auto *II = dyn_cast<InvokeInst>(TI)) {
changeToCall(II);
return;
}
TerminatorInst *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();
}
/// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
/// if they are in a dead cycle. Return true if a change was made, false
/// otherwise.
bool llvm::removeUnreachableBlocks(Function &F, LazyValueInfo *LVI) {
SmallPtrSet<BasicBlock*, 128> Reachable;
bool Changed = markAliveBlocks(F, Reachable);
// 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();
// Loop over all of the basic blocks that are not reachable, dropping all of
// their internal references...
for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
if (Reachable.count(&*BB))
continue;
for (succ_iterator SI = succ_begin(&*BB), SE = succ_end(&*BB); SI != SE;
++SI)
if (Reachable.count(*SI))
(*SI)->removePredecessor(&*BB);
if (LVI)
LVI->eraseBlock(&*BB);
BB->dropAllReferences();
}
for (Function::iterator I = ++F.begin(); I != F.end();)
if (!Reachable.count(&*I))
I = F.getBasicBlockList().erase(I);
else
++I;
return true;
}
void llvm::combineMetadata(Instruction *K, const Instruction *J,
ArrayRef<unsigned> KnownIDs) {
SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
K->dropUnknownNonDebugMetadata(KnownIDs);
K->getAllMetadataOtherThanDebugLoc(Metadata);
for (unsigned i = 0, n = Metadata.size(); i < n; ++i) {
unsigned Kind = Metadata[i].first;
MDNode *JMD = J->getMetadata(Kind);
MDNode *KMD = Metadata[i].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:
K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
break;
case LLVMContext::MD_range:
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:
// Only set the !nonnull if it is present in both instructions.
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);
}
unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
DominatorTree &DT,
const BasicBlockEdge &Root) {
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 (DT.dominates(Root, U)) {
U.set(To);
DEBUG(dbgs() << "Replace dominated use of '"
<< From->getName() << "' as "
<< *To << " in " << *U << "\n");
++Count;
}
}
return Count;
}
unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
DominatorTree &DT,
const BasicBlock *BB) {
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++;
auto *I = cast<Instruction>(U.getUser());
if (DT.properlyDominates(BB, I->getParent())) {
U.set(To);
DEBUG(dbgs() << "Replace dominated use of '" << From->getName() << "' as "
<< *To << " in " << *U << "\n");
++Count;
}
}
return Count;
}
bool llvm::callsGCLeafFunction(ImmutableCallSite CS) {
if (isa<IntrinsicInst>(CS.getInstruction()))
// Most LLVM intrinsics are things which can never take a safepoint.
// As a result, we don't need to have the stack parsable at the
// callsite. This is a highly useful optimization since intrinsic
// calls are fairly prevalent, particularly in debug builds.
return true;
// Check if the function is specifically marked as a gc leaf function.
if (CS.hasFnAttr("gc-leaf-function"))
return true;
if (const Function *F = CS.getCalledFunction())
return F->hasFnAttribute("gc-leaf-function");
return false;
}
/// A potential constituent of a bitreverse or bswap expression. See
/// collectBitParts for a fuller explanation.
struct BitPart {
BitPart(Value *P, unsigned BW) : Provider(P) {
Provenance.resize(BW);
}
/// The Value that this is a bitreverse/bswap of.
Value *Provider;
/// The "provenance" of each bit. Provenance[A] = B means that bit A
/// in Provider becomes bit B in the result of this expression.
SmallVector<int8_t, 32> Provenance; // int8_t means max size is i128.
enum { Unset = -1 };
};
/// Analyze the specified subexpression and see if it is capable of providing
/// pieces of a bswap or bitreverse. The subexpression provides a potential
/// piece of a bswap or bitreverse if it can be proven that each non-zero bit in
/// the output of the expression came from a corresponding bit in some other
/// value. This function is recursive, and the end result is a mapping of
/// bitnumber to bitnumber. It is the caller's responsibility to validate that
/// the bitnumber to bitnumber mapping is correct for a bswap or bitreverse.
///
/// For example, if the current subexpression if "(shl i32 %X, 24)" then we know
/// that the expression deposits the low byte of %X into the high byte of the
/// result and that all other bits are zero. This expression is accepted and a
/// BitPart is returned with Provider set to %X and Provenance[24-31] set to
/// [0-7].
///
/// To avoid revisiting values, the BitPart results are memoized into the
/// provided map. To avoid unnecessary copying of BitParts, BitParts are
/// constructed in-place in the \c BPS map. Because of this \c BPS needs to
/// store BitParts objects, not pointers. As we need the concept of a nullptr
/// BitParts (Value has been analyzed and the analysis failed), we an Optional
/// type instead to provide the same functionality.
///
/// Because we pass around references into \c BPS, we must use a container that
/// does not invalidate internal references (std::map instead of DenseMap).
///
static const Optional<BitPart> &
collectBitParts(Value *V, bool MatchBSwaps, bool MatchBitReversals,
std::map<Value *, Optional<BitPart>> &BPS) {
auto I = BPS.find(V);
if (I != BPS.end())
return I->second;
auto &Result = BPS[V] = None;
auto BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
if (Instruction *I = dyn_cast<Instruction>(V)) {
// If this is an or instruction, it may be an inner node of the bswap.
if (I->getOpcode() == Instruction::Or) {
auto &A = collectBitParts(I->getOperand(0), MatchBSwaps,
MatchBitReversals, BPS);
auto &B = collectBitParts(I->getOperand(1), MatchBSwaps,
MatchBitReversals, BPS);
if (!A || !B)
return Result;
// Try and merge the two together.
if (!A->Provider || A->Provider != B->Provider)
return Result;
Result = BitPart(A->Provider, BitWidth);
for (unsigned i = 0; i < A->Provenance.size(); ++i) {
if (A->Provenance[i] != BitPart::Unset &&
B->Provenance[i] != BitPart::Unset &&
A->Provenance[i] != B->Provenance[i])
return Result = None;
if (A->Provenance[i] == BitPart::Unset)
Result->Provenance[i] = B->Provenance[i];
else
Result->Provenance[i] = A->Provenance[i];
}
return Result;
}
// If this is a logical shift by a constant, recurse then shift the result.
if (I->isLogicalShift() && isa<ConstantInt>(I->getOperand(1))) {
unsigned BitShift =
cast<ConstantInt>(I->getOperand(1))->getLimitedValue(~0U);
// Ensure the shift amount is defined.
if (BitShift > BitWidth)
return Result;
auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
MatchBitReversals, BPS);
if (!Res)
return Result;
Result = Res;
// Perform the "shift" on BitProvenance.
auto &P = Result->Provenance;
if (I->getOpcode() == Instruction::Shl) {
P.erase(std::prev(P.end(), BitShift), P.end());
P.insert(P.begin(), BitShift, BitPart::Unset);
} else {
P.erase(P.begin(), std::next(P.begin(), BitShift));
P.insert(P.end(), BitShift, BitPart::Unset);
}
return Result;
}
// If this is a logical 'and' with a mask that clears bits, recurse then
// unset the appropriate bits.
if (I->getOpcode() == Instruction::And &&
isa<ConstantInt>(I->getOperand(1))) {
APInt Bit(I->getType()->getPrimitiveSizeInBits(), 1);
const APInt &AndMask = cast<ConstantInt>(I->getOperand(1))->getValue();
// Check that the mask allows a multiple of 8 bits for a bswap, for an
// early exit.
unsigned NumMaskedBits = AndMask.countPopulation();
if (!MatchBitReversals && NumMaskedBits % 8 != 0)
return Result;
auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
MatchBitReversals, BPS);
if (!Res)
return Result;
Result = Res;
for (unsigned i = 0; i < BitWidth; ++i, Bit <<= 1)
// If the AndMask is zero for this bit, clear the bit.
if ((AndMask & Bit) == 0)
Result->Provenance[i] = BitPart::Unset;
return Result;
}
}
// Okay, we got to something that isn't a shift, 'or' or 'and'. This must be
// the input value to the bswap/bitreverse.
Result = BitPart(V, BitWidth);
for (unsigned i = 0; i < BitWidth; ++i)
Result->Provenance[i] = i;
return Result;
}
static bool bitTransformIsCorrectForBSwap(unsigned From, unsigned To,
unsigned BitWidth) {
if (From % 8 != To % 8)
return false;
// Convert from bit indices to byte indices and check for a byte reversal.
From >>= 3;
To >>= 3;
BitWidth >>= 3;
return From == BitWidth - To - 1;
}
static bool bitTransformIsCorrectForBitReverse(unsigned From, unsigned To,
unsigned BitWidth) {
return From == BitWidth - To - 1;
}
/// Given an OR instruction, check to see if this is a bitreverse
/// idiom. If so, insert the new intrinsic and return true.
bool llvm::recognizeBitReverseOrBSwapIdiom(
Instruction *I, bool MatchBSwaps, bool MatchBitReversals,
SmallVectorImpl<Instruction *> &InsertedInsts) {
if (Operator::getOpcode(I) != Instruction::Or)
return false;
if (!MatchBSwaps && !MatchBitReversals)
return false;
IntegerType *ITy = dyn_cast<IntegerType>(I->getType());
if (!ITy || ITy->getBitWidth() > 128)
return false; // Can't do vectors or integers > 128 bits.
unsigned BW = ITy->getBitWidth();
// Try to find all the pieces corresponding to the bswap.
std::map<Value *, Optional<BitPart>> BPS;
auto Res = collectBitParts(I, MatchBSwaps, MatchBitReversals, BPS);
if (!Res)
return false;
auto &BitProvenance = Res->Provenance;
// Now, is the bit permutation correct for a bswap or a bitreverse? We can
// only byteswap values with an even number of bytes.
bool OKForBSwap = BW % 16 == 0, OKForBitReverse = true;
for (unsigned i = 0; i < BW; ++i) {
OKForBSwap &= bitTransformIsCorrectForBSwap(BitProvenance[i], i, BW);
OKForBitReverse &=
bitTransformIsCorrectForBitReverse(BitProvenance[i], i, BW);
}
Intrinsic::ID Intrin;
if (OKForBSwap && MatchBSwaps)
Intrin = Intrinsic::bswap;
else if (OKForBitReverse && MatchBitReversals)
Intrin = Intrinsic::bitreverse;
else
return false;
Function *F = Intrinsic::getDeclaration(I->getModule(), Intrin, ITy);
InsertedInsts.push_back(CallInst::Create(F, Res->Provider, "rev", I));
return true;
}
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