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author | Nick Lewycky <nicholas@mxc.ca> | 2014-03-26 23:45:15 +0000 |
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committer | Nick Lewycky <nicholas@mxc.ca> | 2014-03-26 23:45:15 +0000 |
commit | ce49ab2b0571074fefd093160f68e5889578e21b (patch) | |
tree | b1d0cd3f615291c848290417ad26cf88e7ca263c | |
parent | 1e0751bd4c515b3d36f051e3aa4ececf2c056201 (diff) | |
download | llvm-ce49ab2b0571074fefd093160f68e5889578e21b.tar.gz llvm-ce49ab2b0571074fefd093160f68e5889578e21b.tar.bz2 llvm-ce49ab2b0571074fefd093160f68e5889578e21b.tar.xz |
Treat lifetime.start'd memory like we treat freshly alloca'd memory. Patch by Björn Steinbrink!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204876 91177308-0d34-0410-b5e6-96231b3b80d8
-rw-r--r-- | lib/Transforms/Scalar/MemCpyOptimizer.cpp | 20 | ||||
-rw-r--r-- | test/Transforms/MemCpyOpt/memcpy-undef.ll | 21 |
2 files changed, 37 insertions, 4 deletions
diff --git a/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/lib/Transforms/Scalar/MemCpyOptimizer.cpp index 143ba38ec9..2603c969c5 100644 --- a/lib/Transforms/Scalar/MemCpyOptimizer.cpp +++ b/lib/Transforms/Scalar/MemCpyOptimizer.cpp @@ -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; diff --git a/test/Transforms/MemCpyOpt/memcpy-undef.ll b/test/Transforms/MemCpyOpt/memcpy-undef.ll index fd4965f4dc..663b8dcfd3 100644 --- a/test/Transforms/MemCpyOpt/memcpy-undef.ll +++ b/test/Transforms/MemCpyOpt/memcpy-undef.ll @@ -21,5 +21,26 @@ define i32 @test1(%struct.foo* nocapture %foobie) nounwind noinline ssp uwtable ; CHECK-NOT: call void @llvm.memcpy } +define void @test2(i8* sret noalias nocapture %out, i8* %in) nounwind noinline ssp uwtable { + call void @llvm.lifetime.start(i64 8, i8* %in) + call void @llvm.memcpy.p0i8.p0i8.i64(i8* %out, i8* %in, i64 8, i32 1, i1 false) + ret void + +; Check that the memcpy is removed. +; CHECK-LABEL: @test2( +; CHECK-NOT: call void @llvm.memcpy +} + +define void @test3(i8* sret noalias nocapture %out, i8* %in) nounwind noinline ssp uwtable { + call void @llvm.lifetime.start(i64 4, i8* %in) + call void @llvm.memcpy.p0i8.p0i8.i64(i8* %out, i8* %in, i64 8, i32 1, i1 false) + ret void + +; Check that the memcpy is not removed. +; CHECK-LABEL: @test3( +; CHECK: call void @llvm.memcpy +} + declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32, i1) nounwind +declare void @llvm.lifetime.start(i64, i8* nocapture) nounwind |