CodeGen: Copy tail padding when we're not dealing with a trivial copy assign or move assign operator.

This fixes a regression from r162254, the optimizer has problems reasoning
about the smaller memcpy as it's often not safe to widen a store but making it
smaller is.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164917 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 4 deletions

diff --git a/lib/CodeGen/CGExprAgg.cpp b/lib/CodeGen/CGExprAgg.cpp
index c9ffc19a8b..200b43aa6d 100644
--- a/lib/CodeGen/CGExprAgg.cpp
+++ b/lib/CodeGen/CGExprAgg.cpp
@@ -1274,7 +1274,8 @@ LValue CodeGenFunction::EmitAggExprToLValue(const Expr *E) {
 void CodeGenFunction::EmitAggregateCopy(llvm::Value *DestPtr,
                                         llvm::Value *SrcPtr, QualType Ty,
                                         bool isVolatile,
-                                        CharUnits alignment) {
+                                        CharUnits alignment,
+                                        bool isAssignment) {
   assert(!Ty->isAnyComplexType() && "Shouldn't happen for complex");
 
   if (getContext().getLangOpts().CPlusPlus) {
@@ -1303,9 +1304,13 @@ void CodeGenFunction::EmitAggregateCopy(llvm::Value *DestPtr,
   // implementation handles this case safely.  If there is a libc that does not
   // safely handle this, we can add a target hook.
 
-  // Get data size and alignment info for this aggregate.
-  std::pair<CharUnits, CharUnits> TypeInfo = 
-    getContext().getTypeInfoDataSizeInChars(Ty);
+  // Get data size and alignment info for this aggregate. If this is an
+  // assignment don't copy the tail padding. Otherwise copying it is fine.
+  std::pair<CharUnits, CharUnits> TypeInfo;
+  if (isAssignment)
+    TypeInfo = getContext().getTypeInfoDataSizeInChars(Ty);
+  else
+    TypeInfo = getContext().getTypeInfoInChars(Ty);
 
   if (alignment.isZero())
     alignment = TypeInfo.second;