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[InstCombine] Pull out a helper function to simplify upcoming patch [NFC]

This commit is contained in:
Philip Reames 2022-01-11 13:05:25 -08:00
parent 75de92d3e2
commit 6bf590d6e8
1 changed files with 45 additions and 38 deletions
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83
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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@ -3721,6 +3721,50 @@ Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
return nullptr;
}
/// Check for case where the call writes to an otherwise dead alloca. This
/// shows up for unused out-params in idiomatic C/C++ code. Note that this
/// helper *only* analyzes the write; doesn't check any other legality aspect.
static bool SoleWriteToDeadLocal(Instruction *I, TargetLibraryInfo &TLI) {
auto *CB = dyn_cast<CallBase>(I);
if (!CB)
// TODO: handle e.g. store to alloca here - only worth doing if we extend
// to allow reload along used path as described below. Otherwise, this
// is simply a store to a dead allocation which will be removed.
return false;
Optional<MemoryLocation> Dest = MemoryLocation::getForDest(CB, TLI);
if (!Dest)
return false;
auto *AI = dyn_cast<AllocaInst>(getUnderlyingObject(Dest->Ptr));
if (!AI)
// TODO: allow malloc?
return false;
// TODO: allow memory access dominated by move point? Note that since AI
// could have a reference to itself captured by the call, we would need to
// account for cycles in doing so.
SmallVector<const User *> AllocaUsers;
SmallPtrSet<const User *, 4> Visited;
auto pushUsers = [&](const Instruction &I) {
for (const User *U : I.users()) {
if (Visited.insert(U).second)
AllocaUsers.push_back(U);
}
};
pushUsers(*AI);
while (!AllocaUsers.empty()) {
auto *UserI = cast<Instruction>(AllocaUsers.pop_back_val());
if (isa<BitCastInst>(UserI) || isa<GetElementPtrInst>(UserI) ||
isa<AddrSpaceCastInst>(UserI)) {
pushUsers(*UserI);
continue;
}
if (UserI == CB)
continue;
// TODO: support lifetime.start/end here
return false;
}
return true;
}
/// Try to move the specified instruction from its current block into the
/// beginning of DestBlock, which can only happen if it's safe to move the
/// instruction past all of the instructions between it and the end of its
@ -3755,45 +3799,8 @@ static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock,
// Unless we can prove that the memory write isn't visibile except on the
// path we're sinking to, we must bail.
if (I->mayWriteToMemory()) {
// Check for case where the call writes to an otherwise dead alloca. This
// shows up for unused out-params in idiomatic C/C++ code.
auto *CB = dyn_cast<CallBase>(I);
if (!CB)
// TODO: handle e.g. store to alloca here - only worth doing if we extend
// to allow reload along used path as described below. Otherwise, this
// is simply a store to a dead allocation which will be removed.
if (!SoleWriteToDeadLocal(I, TLI))
return false;
Optional<MemoryLocation> Dest = MemoryLocation::getForDest(CB, TLI);
if (!Dest)
return false;
auto *AI = dyn_cast<AllocaInst>(getUnderlyingObject(Dest->Ptr));
if (!AI)
// TODO: allow malloc?
return false;
// TODO: allow memory access dominated by move point? Note that since AI
// could have a reference to itself captured by the call, we would need to
// account for cycles in doing so.
SmallVector<const User *> AllocaUsers;
SmallPtrSet<const User *, 4> Visited;
auto pushUsers = [&](const Instruction &I) {
for (const User *U : I.users()) {
if (Visited.insert(U).second)
AllocaUsers.push_back(U);
}
};
pushUsers(*AI);
while (!AllocaUsers.empty()) {
auto *UserI = cast<Instruction>(AllocaUsers.pop_back_val());
if (isa<BitCastInst>(UserI) || isa<GetElementPtrInst>(UserI) ||
isa<AddrSpaceCastInst>(UserI)) {
pushUsers(*UserI);
continue;
}
if (UserI == CB)
continue;
// TODO: support lifetime.start/end here
return false;
}
}
// We can only sink load instructions if there is nothing between the load and