[llvm] [KnownFPClass] Fix `KnownFPClass::log` deductions for ppcf128 (PR #223296)

[Eric Ross via llvm-commits]

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@@ -3188,7 +3200,7 @@ Value *InstCombinerImpl::SimplifyDemandedUseFPClass(Instruction *I,
       if (DemandedMask & fcNegInf) {
         DemandedSrcMask |= fcZero;
 
-        // No value produces subnormal result.
+        // Subnormals may be treated as logical zero.
         if (Mode.inputsMayBeZero())
           DemandedSrcMask |= fcSubnormal;
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ZERICO2005 wrote:

The correction I made to this comment is unrelated to this PR.

https://github.com/llvm/llvm-project/pull/223296