[llvm] InstCombine: Clean up SimplifyDemandedFPClass use context application (PR #176886)

[Matt Arsenault via llvm-commits]

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@@ -2375,12 +2358,6 @@ Value *InstCombinerImpl::SimplifyDemandedUseFPClass(Instruction *I,
         SimplifyDemandedFPClass(I, 0, SrcDemandedMask, KnownLHS, Depth + 1))
       return I;
 
-    // Propagate nnan-ness to sources to simplify source checks.
-    if ((DemandedMask & fcNan) == fcNone) {
-      KnownLHS.knownNot(fcNan);
-      KnownRHS.knownNot(fcNan);
-    }
-
     if (FMF.noInfs()) {
       // Flag implies inputs cannot be infinity.
       KnownLHS.knownNot(fcInf);
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arsenm wrote:

Yes, the flag propgation is still needed in many cases. The demanded mask only implies the result, but the flag is stronger and implies the source for any of the operations that can overflow 

https://github.com/llvm/llvm-project/pull/176886