DAG: Fix asserting in error case for frexp softening (#147236)

Author: arsenm

llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp

@@ -761,20 +761,21 @@ SDValue DAGTypeLegalizer::SoftenFloatRes_FFREXP(SDNode *N) {
   EVT VT0 = N->getValueType(0);
   EVT VT1 = N->getValueType(1);
   RTLIB::Libcall LC = RTLIB::getFREXP(VT0);
+  EVT NVT0 = TLI.getTypeToTransformTo(*DAG.getContext(), VT0);
+  SDLoc DL(N);
 
   if (DAG.getLibInfo().getIntSize() != VT1.getSizeInBits()) {
     // If the exponent does not match with sizeof(int) a libcall would use the
     // wrong type for the argument.
     // TODO: Should be able to handle mismatches.
     DAG.getContext()->emitError("ffrexp exponent does not match sizeof(int)");
-    return DAG.getUNDEF(N->getValueType(0));
+    SDValue PoisonExp = DAG.getPOISON(VT1);
+    ReplaceValueWith(SDValue(N, 1), PoisonExp);
+    return DAG.getMergeValues({DAG.getPOISON(NVT0), PoisonExp}, DL);
   }
 
-  EVT NVT0 = TLI.getTypeToTransformTo(*DAG.getContext(), VT0);
   SDValue StackSlot = DAG.CreateStackTemporary(VT1);
 
-  SDLoc DL(N);
-
   auto PointerTy = PointerType::getUnqual(*DAG.getContext());
   TargetLowering::MakeLibCallOptions CallOptions;
   SDValue Ops[2] = {GetSoftenedFloat(N->getOperand(0)), StackSlot};

llvm/test/CodeGen/ARM/frexp-soften-libcall-error.ll

@@ -0,0 +1,8 @@
+; RUN: not llc -mtriple arm-linux-gnu -float-abi=soft -filetype=null %s 2>&1 | FileCheck %s
+
+; FIXME: This should not fail but isn't implemented
+; CHECK: error: ffrexp exponent does not match sizeof(int)
+define { float, i64 } @soften_frexp_error(float %x) {
+  %frexp = call { float, i64 } @llvm.frexp.f32.i64(float %x)
+  ret { float, i64 } %frexp
+}