Attempt to outwit overly smart compiler.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115251 91177308-0d34-0410-b5e6-96231b3b80d8

lib/VMCore/Instructions.cpp

@@ -2462,6 +2462,7 @@ CastInst::getCastOpcode(
     if (const VectorType *SrcPTy = dyn_cast<VectorType>(SrcTy)) {
       assert(SrcPTy->getBitWidth()==64 &&
              "Casting vector of wrong width to X86_MMX");
+      SrcPTy = NULL;      // inhibit compiler warning
       return BitCast;                               // 64-bit vector to MMX
     } else {
       assert(!"Illegal cast to X86_MMX");