[llvm] r279778 - [MemCpy] Add comments for r279769

[Tim Shen via llvm-commits]

Author: timshen
Date: Thu Aug 25 16:03:46 2016
New Revision: 279778

URL: http://llvm.org/viewvc/llvm-project?rev=279778&view=rev
Log:
[MemCpy] Add comments for r279769

Differential Revision: https://reviews.llvm.org/D23846

Modified:
    llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
    llvm/trunk/test/Transforms/MemCpyOpt/pr29105.ll

Modified: llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp?rev=279778&r1=279777&r2=279778&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/MemCpyOptimizer.cpp Thu Aug 25 16:03:46 2016
@@ -1110,7 +1110,8 @@ bool MemCpyOptPass::performMemCpyToMemSe
                                                MemSetInst *MemSet) {
   AliasAnalysis &AA = LookupAliasAnalysis();
 
-  // This only makes sense on memcpy(..., memset(...), ...).
+  // Make sure that memcpy(..., memset(...), ...), that is we are memsetting and
+  // memcpying from the same address. Otherwise it is hard to reason about.
   if (!AA.isMustAlias(MemSet->getRawDest(), MemCpy->getRawSource()))
     return false;
 

Modified: llvm/trunk/test/Transforms/MemCpyOpt/pr29105.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/MemCpyOpt/pr29105.ll?rev=279778&r1=279777&r2=279778&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/MemCpyOpt/pr29105.ll (original)
+++ llvm/trunk/test/Transforms/MemCpyOpt/pr29105.ll Thu Aug 25 16:03:46 2016
@@ -1,6 +1,7 @@
 ; RUN: opt -memcpyopt -instcombine -S %s | FileCheck %s
 %Foo = type { [2048 x i64] }
 
+; Make sure that all mempcy calls are converted to memset calls, or removed.
 ; CHECK-LABEL: @baz(
 ; CHECK-NOT: call void @llvm.memcpy
 define void @baz() unnamed_addr #0 {