Track whether an AggValueSlot is potentially aliased, and do not

emit call results into potentially aliased slots.  This allows us
to properly mark indirect return slots as noalias, at the cost
of requiring an extra memcpy when assigning an aggregate call
result into a l-value.  It also brings us into compliance with
the x86-64 ABI.

llvm-svn: 138599

1 files changed, 1 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index dc3e702d6a3..846e1aa3934 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -907,6 +907,7 @@ void CodeGenFunction::EmitFunctionProlog(const CGFunctionInfo &FI,
   // Name the struct return argument.
   if (CGM.ReturnTypeUsesSRet(FI)) {
     AI->setName("agg.result");
+    AI->addAttr(llvm::Attribute::NoAlias);
     ++AI;
   }