[PATCH] D139319: ValueTracking: Teach isKnownNeverInfinity about llvm.log*

[Matt Arsenault via Phabricator via llvm-commits]

arsenm planned changes to this revision.
arsenm added inline comments.


================
Comment at: llvm/lib/Analysis/ValueTracking.cpp:3844
+      return isKnownNeverInfinity(Inst->getOperand(0), TLI, Depth + 1) &&
+             cannotBeOrderedLessThanZeroImpl(Inst->getOperand(0), TLI,
+                                             /*SignBitOnly=*/false, Depth + 1);
----------------
spatel wrote:
> Don't we need to check that the input is non-zero to guard against log(0) --> -inf?
> 
> This should not fold?
> 
> 
> ```
> define i1 @isKnownNeverNegInfinity_log(double %x) {
>   %a = call ninf double @llvm.sqrt.f64(double %x) ; could be 0.0
>   %e = call double @llvm.log.f64(double %a) ; log(0.0) --> -inf
>   %r = fcmp une double %e, 0xfff0000000000000
>   ret i1 %r
> }
> 
> ```
> 
Yes, I was thinking cannotBeOrderedLessThanZeroImpl would catch it but we're missing the known-never-0 API. I want to merge all of these into one knownFPClass API which would help catch this


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  https://reviews.llvm.org/D139319/new/

https://reviews.llvm.org/D139319