[PATCH] D139130: InstCombine: Fold and (fcmp), (is.fpclass) into is.fpclass

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp:829-843
+  if (Mask == fcNan && !IsStrict) {
+    // Equivalent of isnan. Replace with standard fcmp if we don't care about FP
+    // exceptions.
+    Value *FCmp = Builder.CreateIsNaN(Src0);
+    FCmp->takeName(&II);
+    return replaceInstUsesWith(II, FCmp);
+  }
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sepavloff wrote:
> Replacement of `llvm.is_fpclass` with comparison hides class checks and make analysis of code passes harder. Does it have any benefit over creation of the comparison in selector?
Using fcmp makes analysis easier. fcmp has fewer constraints, and will always be better understood by generic passes than a special case intrinsic. It's a better canonical form; otherwise every single place that considers compares would have to perform the exact same checks for a class that performs a compare.

I also just noticed when I rebased I attached the wrong patch here.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D139130/new/

https://reviews.llvm.org/D139130