[llvm] expandFMINIMUMNUM_FMAXIMUMNUM: Improve compare between zeros (PR #140193)

[Matt Arsenault via llvm-commits]

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@@ -8866,13 +8867,19 @@ SDValue TargetLowering::expandFMINIMUMNUM_FMAXIMUMNUM(SDNode *Node,
       DAG.getTargetConstant(IsMax ? fcPosZero : fcNegZero, DL, MVT::i32);
   SDValue IsZero = DAG.getSetCC(DL, CCVT, MinMax,
                                 DAG.getConstantFP(0.0, DL, VT), ISD::SETEQ);
-  SDValue LCmp = DAG.getSelect(
-      DL, VT, DAG.getNode(ISD::IS_FPCLASS, DL, CCVT, LHS, TestZero), LHS,
+  EVT IntVT = VT.changeTypeToInteger();
+  EVT FloatVT = VT.changeElementType(MVT::f32);
+  SDValue LHSTrunc = LHS;
+  if (!isTypeLegal(IntVT) && !isOperationLegal(ISD::IS_FPCLASS, VT)) {
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arsenm wrote:

This is a pretty x86 specific hack, for hacking around the DAG's annoying phased legalization. 

https://github.com/llvm/llvm-project/pull/140193