uncomment CopyOnce return

Author: folkertdev

llvm/lib/Target/X86/X86ISelLoweringCall.cpp

@@ -2047,15 +2047,12 @@ X86TargetLowering::ByValCopyKind X86TargetLowering::ByValNeedsCopyForTailCall(
   int64_t SrcOffset = MFI.getObjectOffset(SrcFI);
   int64_t DstOffset = MFI.getObjectOffset(DstFI);
 
-  // FIXME:
-
-  //  // If the source is in the local frame, then the copy to the argument
-  //  memory
-  //  // is always valid.
-  //  bool FixedSrc = MFI.isFixedObjectIndex(SrcFI);
-  //  if (!FixedSrc ||
-  //      (FixedSrc && SrcOffset < -(int64_t)AFI->getArgRegsSaveSize()))
-  //    return CopyOnce;
+
+  // If the source is in the local frame, then the copy to the argument
+  // memory is always valid.
+  bool FixedSrc = MFI.isFixedObjectIndex(SrcFI);
+  if (!FixedSrc || (FixedSrc && SrcOffset < 0))
+    return CopyOnce;
 
   // In the case of byval arguments split between registers and the stack,
   // computeAddrForCallArg returns a FrameIndex which corresponds only to the