[PATCH] D142345: [X86] Transform `(icmp eq/ne Abs(A), Pow2)` -> `(and/or (icmp eq/ne A,Pow2), (icmp eq/ne A,-Pow2))`

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:53411
+
+      // With C as a power of 2 and C != 0 and C != INT_MIN:
+      //    icmp eq Abs(X) C ->
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goldstein.w.n wrote:
> pengfei wrote:
> > Seems for `0` and `INT_MIN`, we can simply transform to `icmp eq/ne A, C`. Should we do it together given we already got the constant, or a follow?
> We can although I don't that that IR ever really reaches the backend as the middle-end would clean up that pattern.
> My thought it strange IR shouldn't cause broken transforms, but its fine for it to cause missed optimizations.
> 
> Although can add those two cases if you'd like, dont really have strong opinions on the matter.
The general rule of thumb is that DAGCombiner should only copy IR folds if the pattern appears as a result of legalization of canonical IR.


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  https://reviews.llvm.org/D142345/new/

https://reviews.llvm.org/D142345