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Fix Transforms/InstCombine/2007-02-01-LoadSinkAlloca.ll, a serious code

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pessimization where instcombine can sink a load (good for code size) that
prevents an alloca from being promoted by mem2reg (bad for everything).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33771 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-02-01 22:30:07 +00:00
parent 5c70a012c7
commit fd905caa77
1 changed files with 24 additions and 0 deletions
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24
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -7464,12 +7464,36 @@ Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) {
/// of the block that defines it. This means that it must be obvious the value
/// of the load is not changed from the point of the load to the end of the
/// block it is in.
///
/// Finally, it is safe, but not profitable, to sink a load targetting a
/// non-address-taken alloca. Doing so will cause us to not promote the alloca
/// to a register.
static bool isSafeToSinkLoad(LoadInst *L) {
BasicBlock::iterator BBI = L, E = L->getParent()->end();
for (++BBI; BBI != E; ++BBI)
if (BBI->mayWriteToMemory())
return false;
// Check for non-address taken alloca. If not address-taken already, it isn't
// profitable to do this xform.
if (AllocaInst *AI = dyn_cast<AllocaInst>(L->getOperand(0))) {
bool isAddressTaken = false;
for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
UI != E; ++UI) {
if (isa<LoadInst>(UI)) continue;
if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
// If storing TO the alloca, then the address isn't taken.
if (SI->getOperand(1) == AI) continue;
}
isAddressTaken = true;
break;
}
if (!isAddressTaken)
return false;
}
return true;
}