Correctly handle a one-word struct passed byval on x86_64.
rdar://problem/6920088


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132105 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CallingConvLower.cpp b/lib/CodeGen/CallingConvLower.cpp
index bfb6ba1..d9cadf0 100644
--- a/lib/CodeGen/CallingConvLower.cpp
+++ b/lib/CodeGen/CallingConvLower.cpp
@@ -48,8 +48,13 @@
   if (MinAlign > (int)Align)
     Align = MinAlign;
   TM.getTargetLowering()->HandleByVal(const_cast<CCState*>(this), Size);
-  unsigned Offset = AllocateStack(Size, Align);
-  addLoc(CCValAssign::getMem(ValNo, ValVT, Offset, LocVT, LocInfo));
+  if (Size) {
+    unsigned Offset = AllocateStack(Size, Align);
+    addLoc(CCValAssign::getMem(ValNo, ValVT, Offset, LocVT, LocInfo));
+  } else {
+    addLoc(CCValAssign::getReg(ValNo, ValVT, getFirstByValReg(), LocVT,
+                               LocInfo));
+  }
 }
 
 /// MarkAllocated - Mark a register and all of its aliases as allocated.