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

llvm-svn: 114781

1 files changed, 5 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 24fae423d2f..f94c9e22576 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/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) {