CodeGen: Default overflow operations to expand so we don't have to assume targets are lying

[jvesely]

Summary

we shouldn't lie, getOperationAction should match the legalizer action

[ab]

This makes sense; I did some archeology and didn't find any good reason either. I assume no target actually marked this as Legal?

[jvesely]

Couple of targets (aarch64, arm x86, sparc) mark those as custom. I didn't find any that would set it to legal. I also grepped for patterns/instructions in .td and did not find any.

llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

void SelectionDAGLegalize::LegalizeOp(SDNode *Node) {
   case ISD::CALLSEQ_END:
     // FIXME: This shouldn't be necessary.  These nodes have special properties
     // dealing with the recursive nature of legalization.  Removing this
     // special case should be done as part of making LegalizeDAG non-recursive.
     SimpleFinishLegalizing = false;
     break;
   case ISD::EXTRACT_ELEMENT:
   case ISD::FLT_ROUNDS_:
-  case ISD::SADDO:
-  case ISD::SSUBO:
-  case ISD::UADDO:
-  case ISD::USUBO:
-  case ISD::SMULO:
-  case ISD::UMULO:
   case ISD::FPOWI:
   case ISD::MERGE_VALUES:
   case ISD::EH_RETURN:
   case ISD::FRAME_TO_ARGS_OFFSET:
   case ISD::EH_SJLJ_SETJMP:
   case ISD::EH_SJLJ_LONGJMP:
     // These operations lie about being legal: when they claim to be legal,
     // they should actually be expanded.

llvm/trunk/lib/CodeGen/TargetLoweringBase.cpp

for (MVT VT : MVT::all_valuetypes()) {
 
     // These operations default to expand.
     setOperationAction(ISD::FGETSIGN, VT, Expand);
     setOperationAction(ISD::CONCAT_VECTORS, VT, Expand);
     setOperationAction(ISD::FMINNUM, VT, Expand);
     setOperationAction(ISD::FMAXNUM, VT, Expand);
     setOperationAction(ISD::FMAD, VT, Expand);
 
+    // Overflow operations default to expand
+    setOperationAction(ISD::SADDO, VT, Expand);
+    setOperationAction(ISD::SSUBO, VT, Expand);
+    setOperationAction(ISD::UADDO, VT, Expand);
+    setOperationAction(ISD::USUBO, VT, Expand);
+    setOperationAction(ISD::SMULO, VT, Expand);
+    setOperationAction(ISD::UMULO, VT, Expand);
+
     // These library functions default to expand.
     setOperationAction(ISD::FROUND, VT, Expand);
 
     // These operations default to expand for vector types.
     if (VT.isVector()) {
       setOperationAction(ISD::FCOPYSIGN, VT, Expand);
       setOperationAction(ISD::ANY_EXTEND_VECTOR_INREG, VT, Expand);
       setOperationAction(ISD::SIGN_EXTEND_VECTOR_INREG, VT, Expand);