When performing return slot optimization, remember to inform memdep when we're removing the memcpy.

llvm-svn: 47364

llvm/lib/Transforms/Scalar/GVN.cpp

@@ -1139,6 +1139,7 @@ bool GVN::performReturnSlotOptzn(MemCpyInst* cpy, CallInst* C,
   MD.dropInstruction(C);
   
   // Remove the memcpy
+  MD.removeInstruction(cpy);
   toErase.push_back(cpy);
   
   return true;