[PATCH] [clang/asan] Do not emit memcpy for trivial operator= when -fsanitize-address-field-padding >= 1

[Kostya Serebryany]

================
Comment at: lib/CodeGen/CGExprCXX.cpp:321
@@ -320,3 +320,3 @@
   if ((MD->isCopyAssignmentOperator() || MD->isMoveAssignmentOperator()) &&
-      MD->isTrivial()) {
+      MD->isTrivial() && !MD->getParent()->mayInsertExtraPadding()) {
     llvm::Value *Src = EmitLValue(E->getArg(1)).getAddress();
----------------
rsmith wrote:
> Is `mayInsertExtraPadding` ever `true` for a union? The non-`memcpy` path will not do the right thing for a trivial assignment operator in that case.
It is never true: 

bool RecordDecl::mayInsertExtraPadding(bool EmitRemark) const {
...
  else if (CXXRD->isUnion())
    ReasonToReject = 2;  // is a union.

http://reviews.llvm.org/D6160