[llvm-branch-commits] [llvm] ValueTracking: Improve handling of exp intrinsic for overflow (PR #173430)

[Yingwei Zheng via llvm-branch-commits]

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@@ -5362,6 +5362,22 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
         Known.signBitMustBeZero();
       }
 
+      if (KnownSrc.cannotBeOrderedLessThanZero()) {
+        // If the source is positive, and cannot be ~0, this cannot underflow.
+        Known.knownNot(fcPosZero);
+
+        // Cannot introduce new denormal values.
+        if (KnownSrc.isKnownNever(fcPosSubnormal))
+          Known.knownNot(fcPosSubnormal);
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dtcxzyw wrote:

`x >= 0` implies `exp(x) >= 1`. It should never introduce denormal values.

https://github.com/llvm/llvm-project/pull/173430