[PATCH] D158648: InstCombine: Introduce SimplifyDemandedUseFPClass

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

This looks conceptually fine to me.



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Comment at: llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp:1825
+    Known = computeKnownFPClass(V, DL, fcAllFlags, Depth, &TLI, &AC, CxtI, &DT);
+    if ((DemandedMask & Known.KnownFPClasses) == fcNone)
+      return PoisonValue::get(VTy);
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Should this be using getFPClassConstant() instead, just like the main code path?


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp:1846
+    case Intrinsic::fabs:
+      if (SimplifyDemandedFPClass(I, 0, llvm::fabs(DemandedMask), Known,
+                                  Depth + 1))
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It seems like this is correct, but only because `fabs(FPClassTest)` apparently does the exact opposite of what one would expect it to do. It's really `inverse_fabs()`.


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  https://reviews.llvm.org/D158648/new/

https://reviews.llvm.org/D158648