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Treat lifetime.start'd memory like we treat freshly alloca'd memory. Patch by Björn Steinbrink!

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204876 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2014-03-26 23:45:15 +00:00
parent 1e0751bd4c
commit ce49ab2b05
2 changed files with 37 additions and 4 deletions
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20
lib/Transforms/Scalar/MemCpyOptimizer.cpp
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@@ -851,9 +851,9 @@ bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
// The are three possible optimizations we can do for memcpy:
// a) memcpy-memcpy xform which exposes redundance for DSE.
// b) call-memcpy xform for return slot optimization.
// c) memcpy from freshly alloca'd space copies undefined data, and we can
// therefore eliminate the memcpy in favor of the data that was already
// at the destination.
// c) memcpy from freshly alloca'd space or space that has just started its
// lifetime copies undefined data, and we can therefore eliminate the
// memcpy in favor of the data that was already at the destination.
MemDepResult DepInfo = MD->getDependency(M);
if (DepInfo.isClobber()) {
if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) {
@@ -874,7 +874,19 @@ bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst()))
return processMemCpyMemCpyDependence(M, MDep, CopySize->getZExtValue());
} else if (SrcDepInfo.isDef()) {
if (isa<AllocaInst>(SrcDepInfo.getInst())) {
Instruction *I = SrcDepInfo.getInst();
bool hasUndefContents = false;
if (isa<AllocaInst>(I)) {
hasUndefContents = true;
} else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
if (II->getIntrinsicID() == Intrinsic::lifetime_start)
if (ConstantInt *LTSize = dyn_cast<ConstantInt>(II->getArgOperand(0)))
if (LTSize->getZExtValue() >= CopySize->getZExtValue())
hasUndefContents = true;
}
if (hasUndefContents) {
MD->removeInstruction(M);
M->eraseFromParent();
++NumMemCpyInstr;