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| author | Nick Lewycky <nicholas@mxc.ca> | 2014-02-06 06:29:19 +0000 |
|---|---|---|
| committer | Nick Lewycky <nicholas@mxc.ca> | 2014-02-06 06:29:19 +0000 |
| commit | 44e40408eebdd38831501fc2fab59d550e951808 (patch) | |
| tree | ac922edd0cba6bb8000e4635f02bc2adf2fc569e | |
| parent | a4f328f68b83dd5fc8387523f0df956816c53384 (diff) | |
| download | llvm-44e40408eebdd38831501fc2fab59d550e951808.tar.gz llvm-44e40408eebdd38831501fc2fab59d550e951808.tar.bz2 llvm-44e40408eebdd38831501fc2fab59d550e951808.tar.xz | |
A memcpy out of an fresh alloca is a no-op, delete it. Patch by Patrick Walton!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200907 91177308-0d34-0410-b5e6-96231b3b80d8
| -rw-r--r-- | lib/Transforms/Scalar/MemCpyOptimizer.cpp | 12 | ||||
| -rw-r--r-- | test/Transforms/MemCpyOpt/memcpy-undef.ll | 25 |
2 files changed, 36 insertions, 1 deletions
diff --git a/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/lib/Transforms/Scalar/MemCpyOptimizer.cpp index 3c24e6d364..6619d54288 100644 --- a/lib/Transforms/Scalar/MemCpyOptimizer.cpp +++ b/lib/Transforms/Scalar/MemCpyOptimizer.cpp @@ -843,9 +843,12 @@ bool MemCpyOpt::processMemCpy(MemCpyInst *M) { ConstantInt *CopySize = dyn_cast<ConstantInt>(M->getLength()); if (CopySize == 0) return false; - // The are two possible optimizations we can do for memcpy: + // 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. MemDepResult DepInfo = MD->getDependency(M); if (DepInfo.isClobber()) { if (CallInst *C = dyn_cast<CallInst>(DepInfo.getInst())) { @@ -865,6 +868,13 @@ bool MemCpyOpt::processMemCpy(MemCpyInst *M) { if (SrcDepInfo.isClobber()) { if (MemCpyInst *MDep = dyn_cast<MemCpyInst>(SrcDepInfo.getInst())) return processMemCpyMemCpyDependence(M, MDep, CopySize->getZExtValue()); + } else if (SrcDepInfo.isDef()) { + if (isa<AllocaInst>(SrcDepInfo.getInst())) { + MD->removeInstruction(M); + M->eraseFromParent(); + ++NumMemCpyInstr; + return true; + } } return false; diff --git a/test/Transforms/MemCpyOpt/memcpy-undef.ll b/test/Transforms/MemCpyOpt/memcpy-undef.ll new file mode 100644 index 0000000000..fd4965f4dc --- /dev/null +++ b/test/Transforms/MemCpyOpt/memcpy-undef.ll @@ -0,0 +1,25 @@ +; RUN: opt < %s -basicaa -memcpyopt -S | FileCheck %s + +target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128" +target triple = "x86_64-apple-macosx10.8.0" + +%struct.foo = type { i8, [7 x i8], i32 } + +define i32 @test1(%struct.foo* nocapture %foobie) nounwind noinline ssp uwtable { + %bletch.sroa.1 = alloca [7 x i8], align 1 + %1 = getelementptr inbounds %struct.foo* %foobie, i64 0, i32 0 + store i8 98, i8* %1, align 4 + %2 = getelementptr inbounds %struct.foo* %foobie, i64 0, i32 1, i64 0 + %3 = getelementptr inbounds [7 x i8]* %bletch.sroa.1, i64 0, i64 0 + call void @llvm.memcpy.p0i8.p0i8.i64(i8* %2, i8* %3, i64 7, i32 1, i1 false) + %4 = getelementptr inbounds %struct.foo* %foobie, i64 0, i32 2 + store i32 20, i32* %4, align 4 + ret i32 undef + +; Check that the memcpy is removed. +; CHECK-LABEL: @test1( +; CHECK-NOT: call void @llvm.memcpy +} + +declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32, i1) nounwind + |