PPC: Custom lower ppcf128 is_fpclass if is_fpclass is custom (#105540)

Unfortunately expandIS_FPCLASS is called directly in SelectionDAGBuilder
depending on whether IS_FPCLASS is custom or not. This helps avoid ppc test
regressions in a future patch where the custom lowering would be bypassed.

Author: arsenm

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -1221,6 +1221,7 @@ PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM,
         setOperationAction(ISD::IS_FPCLASS, MVT::f32, Custom);
         setOperationAction(ISD::IS_FPCLASS, MVT::f64, Custom);
         setOperationAction(ISD::IS_FPCLASS, MVT::f128, Custom);
+        setOperationAction(ISD::IS_FPCLASS, MVT::ppcf128, Custom);
       }
 
       // 128 bit shifts can be accomplished via 3 instructions for SHL and
@@ -11479,6 +11480,12 @@ SDValue PPCTargetLowering::LowerIS_FPCLASS(SDValue Op,
   uint64_t RHSC = Op.getConstantOperandVal(1);
   SDLoc Dl(Op);
   FPClassTest Category = static_cast<FPClassTest>(RHSC);
+  if (LHS.getValueType() == MVT::ppcf128) {
+    // The higher part determines the value class.
+    LHS = DAG.getNode(ISD::EXTRACT_ELEMENT, Dl, MVT::f64, LHS,
+                      DAG.getConstant(1, Dl, MVT::i32));
+  }
+
   return getDataClassTest(LHS, Category, Dl, DAG, Subtarget);
 }