[GlobalIsel] Fix undefined behavior if Action not set (release), it aslo crashing in debug mode.

Differential Revision: https://reviews.llvm.org/D34978

llvm-svn: 311272

llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h

@@ -162,6 +162,9 @@ public:
   /// on Ty until we find a legal type for this operation.
   Optional<LLT> findLegalizableSize(const InstrAspect &Aspect,
                                     function_ref<LLT(LLT)> NextType) const {
+    if (Aspect.Idx >= Actions[Aspect.Opcode - FirstOp].size())
+      return None;
+
     LegalizeAction Action;
     const TypeMap &Map = Actions[Aspect.Opcode - FirstOp][Aspect.Idx];
     LLT Ty = Aspect.Type;