[InstCombine] Use isKnownNeverNaN

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -2796,8 +2796,11 @@ static Instruction *foldSelectWithFCmpToFabs(SelectInst &SI,
     // Note: We require "nnan" for this fold because fcmp ignores the signbit
     //       of NAN, but IEEE-754 specifies the signbit of NAN values with
     //       fneg/fabs operations.
-    if (cast<FPMathOperator>(CondVal)->hasNoNaNs() &&
-        match(TrueVal, m_FSub(m_PosZeroFP(), m_Specific(X)))) {
+    if (match(TrueVal, m_FSub(m_PosZeroFP(), m_Specific(X))) &&
+        (cast<FPMathOperator>(CondVal)->hasNoNaNs() ||
+         isKnownNeverNaN(X, /*Depth=*/0,
+                         IC.getSimplifyQuery().getWithInstruction(
+                             cast<Instruction>(CondVal))))) {
       if (!Swap && (Pred == FCmpInst::FCMP_OLE || Pred == FCmpInst::FCMP_ULE)) {
         Value *Fabs = IC.Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, &SI);
         return IC.replaceInstUsesWith(SI, Fabs);

llvm/test/Transforms/InstCombine/fabs.ll

@@ -276,6 +276,17 @@ define double @select_fcmp_ole_zero_no_nnan(double %x) {
   ret double %fabs
 }
 
+define double @select_fcmp_ole_zero_no_nnan_input_nofpclass_nan(double nofpclass(nan) %x) {
+; CHECK-LABEL: @select_fcmp_ole_zero_no_nnan_input_nofpclass_nan(
+; CHECK-NEXT:    [[FABS:%.*]] = call double @llvm.fabs.f64(double [[X:%.*]])
+; CHECK-NEXT:    ret double [[FABS]]
+;
+  %lezero = fcmp ole double %x, 0.0
+  %negx = fsub double 0.0, %x
+  %fabs = select i1 %lezero, double %negx, double %x
+  ret double %fabs
+}
+
 define double @select_fcmp_nnan_ole_zero(double %x) {
 ; CHECK-LABEL: @select_fcmp_nnan_ole_zero(
 ; CHECK-NEXT:    [[FABS:%.*]] = call double @llvm.fabs.f64(double [[X:%.*]])