[InstCombine] Fold select of ordered fcmps of fabs over NaN-scrubber selects to a single select (#192182) Fold `select (fcmp <ordered> (fabs (select isKnownNeverNaN X, X, Y)), K), ...` into a single compare/select directly on `X`. The outer fcmp is limited to ordered predicates, since only they preserve the original non-NaN behavior. fixes #143649 alive2: https://alive2.llvm.org/ce/z/G8UmjY Generalized proof (needs local alive2 build): ```alive2 declare double @llvm.fabs.f64(double) define double @src(double %x, double %y, double %k) { entry: %ord = fcmp ord double %x, 0.000000e+00 %s = select i1 %ord, double %x, double %y %a = call double @llvm.fabs.f64(double %s) %c = fcmp one double %a, %k %r = select i1 %c, double %s, double %y ret double %r } define double @tgt(double %x, double %y, double %k) { entry: %a2 = call double @llvm.fabs.f64(double %x) %c2 = fcmp one double %a2, %k %r2 = select i1 %c2, double %x, double %y ret double %r2 } ```
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