[llvm] [ValueTracking] Fix frexp exponent range for nan/inf inputs (PR #202447)

[Matt Arsenault via llvm-commits]

================
@@ -10447,21 +10434,23 @@ ConstantRange llvm::computeConstantRange(const Value *V, bool ForSigned,
       // It should be possible to implement this for any type, but this logic
       // only computes the range assuming standard subnormal handling.
       if (APFloat::isIEEELikeFP(FltSem)) {
-        KnownFPClass KnownSrc =
-            computeKnownFPClass(FrexpSrc, fcSubnormal, SQ, Depth + 1);
-
-        // Exponent result is (src == 0) ? 0 : ilogb(src) + 1, and unspecified
-        // for inf/nan.
-        int MinExp = APFloat::semanticsMinExponent(FltSem) + 1;
-
-        // Offset to find the true minimum exponent value for a denormal.
-        if (!KnownSrc.isKnownNeverSubnormal())
-          MinExp -= (APFloat::semanticsPrecision(FltSem) - 1);
-
-        int MaxExp = APFloat::semanticsMaxExponent(FltSem) + 1;
-        CR = ConstantRange::getNonEmpty(
-            APInt(BitWidth, MinExp, /*isSigned=*/true),
-            APInt(BitWidth, MaxExp + 1, /*isSigned=*/true));
+        KnownFPClass KnownSrc = computeKnownFPClass(
+            FrexpSrc, fcSubnormal | fcNan | fcInf, SQ, Depth + 1);
+
+        // The exponent of frexp(NaN) and frexp(Inf) is unspecified. Only
+        // constrain its range when the source can be neither.
+        if (KnownSrc.isKnownNeverNaN() && KnownSrc.isKnownNeverInfinity()) {
----------------
arsenm wrote:

```suggestion
        if (KnownSrc.isKnownNeverInfOrNaN()) {
```

https://github.com/llvm/llvm-project/pull/202447