[PowerPC][CodeGen] Expand ISD::AssertNoFPClass for ppc_fp128

780054d added support for `ISD::AssertNoFPClass`.

This ISD node can be used with the `ppc_fp128` type, which is really just two
`f64s` and requires expanding when used with `ISD::AssertNoFPClass`. Without the
support for expanding the result, we get an assertion because the legalizer
does not know how to expand the results of `ppc_fp128` with `ISD::AssertNoFPClass`.
```
ExpandFloatResult #0: t7: ppcf128 = AssertNoFPClass t5, TargetConstant:i32<3>

LLVM ERROR: Do not know how to expand the result of this operator!
```
Thus, this patch aims to add support for the expand so we no longer assert.

This fixes #151375.

Author: amy-kwan

llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp

@@ -1551,6 +1551,7 @@ void DAGTypeLegalizer::ExpandFloatResult(SDNode *N, unsigned ResNo) {
   case ISD::VAARG:              ExpandRes_VAARG(N, Lo, Hi); break;
 
   case ISD::ConstantFP: ExpandFloatRes_ConstantFP(N, Lo, Hi); break;
+  case ISD::AssertNoFPClass: ExpandFloatRes_AssertNoFPClass(N, Lo, Hi); break;
   case ISD::FABS:       ExpandFloatRes_FABS(N, Lo, Hi); break;
   case ISD::STRICT_FMINNUM:
   case ISD::FMINNUM:    ExpandFloatRes_FMINNUM(N, Lo, Hi); break;
@@ -1966,6 +1967,14 @@ void DAGTypeLegalizer::ExpandFloatRes_FNEG(SDNode *N, SDValue &Lo,
   Hi = DAG.getNode(ISD::FNEG, dl, Hi.getValueType(), Hi);
 }
 
+void DAGTypeLegalizer::ExpandFloatRes_AssertNoFPClass(SDNode *N, SDValue &Lo,
+                                                      SDValue &Hi) {
+  SDLoc dl(N);
+  GetExpandedFloat(N->getOperand(0), Lo, Hi);
+  Lo = DAG.getNode(ISD::AssertNoFPClass, dl, Lo.getValueType(), Lo);
+  Hi = DAG.getNode(ISD::AssertNoFPClass, dl, Hi.getValueType(), Hi);
+}
+
 void DAGTypeLegalizer::ExpandFloatRes_FP_EXTEND(SDNode *N, SDValue &Lo,
                                                 SDValue &Hi) {
   EVT NVT = TLI.getTypeToTransformTo(*DAG.getContext(), N->getValueType(0));

llvm/lib/CodeGen/SelectionDAG/LegalizeTypes.h

@@ -681,6 +681,7 @@ class LLVM_LIBRARY_VISIBILITY DAGTypeLegalizer {
       SDNode *N, RTLIB::Libcall LC, std::optional<unsigned> CallRetResNo = {});
 
   // clang-format off
+  void ExpandFloatRes_AssertNoFPClass(SDNode *N, SDValue &Lo, SDValue &Hi);
   void ExpandFloatRes_FABS      (SDNode *N, SDValue &Lo, SDValue &Hi);
   void ExpandFloatRes_FACOS     (SDNode *N, SDValue &Lo, SDValue &Hi);
   void ExpandFloatRes_FASIN     (SDNode *N, SDValue &Lo, SDValue &Hi);

llvm/test/CodeGen/PowerPC/nofpclass.ll

@@ -0,0 +1,13 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -verify-machineinstrs  -mtriple=powerpc64le-unknown-linux-gnu < %s \
+; RUN:   | FileCheck %s
+; RUN: llc -verify-machineinstrs  -mtriple=powerpc64-ibm-aix-xcoff < %s \
+; RUN:   | FileCheck %s
+
+define ppc_fp128 @f(ppc_fp128 nofpclass(nan) %s) {
+; CHECK-LABEL: f:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    blr
+entry:
+  ret ppc_fp128 %s
+}