From: Eric Christopher <echristo@apple.com>
Date: Sat, 25 Sep 2010 00:57:26 +0000 (+0000)
Subject: If we're changing the source of a memcpy we need to use the alignment
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=c69a00047013a0e2e07ae44c38e013a7d905b10e;p=oota-llvm.git

If we're changing the source of a memcpy we need to use the alignment
of the source, not the original alignment since it may no longer
be valid.

Fixes rdar://8400094


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114781 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 24fae423d2f..f94c9e22576 100644
--- a/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -697,14 +697,16 @@ bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
                                  M->getParent()->getParent()->getParent(),
                                  M->getIntrinsicID(), ArgTys, 3);
     
+  // Make sure to use the alignment of the source since we're changing the
+  // location we're reading from.
+  // TODO: Is this worth it if we're creating a less aligned memcpy? For
+  // example we could be moving from movaps -> movq on x86.
   Value *Args[5] = {
     M->getRawDest(), MDep->getRawSource(), M->getLength(),
-    M->getAlignmentCst(), M->getVolatileCst()
+    MDep->getAlignmentCst(), M->getVolatileCst()
   };
-  
   CallInst *C = CallInst::Create(MemCpyFun, Args, Args+5, "", M);
   
-  
   // If C and M don't interfere, then this is a valid transformation.  If they
   // did, this would mean that the two sources overlap, which would be bad.
   if (MD.getDependency(C) == dep) {