[llvm] [KnownFPClass] Add KnownFPClass deductions for `pow` (PR #215592)

[Matt Arsenault via llvm-commits]

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@@ -5562,6 +5562,34 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
 
       break;
     }
+    case Intrinsic::pow: {
+      if ((InterestedClasses & (fcNan | fcNegative)) == fcNone)
+        break;
+
+      FPClassTest InterestedLHS = fcNone;
+      FPClassTest InterestedRHS = fcNone;
+      if (InterestedClasses & fcNan) {
+        // pow may return NaN if one of the arguments is NaN. NaN may be
+        // produced from a non-zero-finite-negative base and a non-integer
+        // exponent.
+        InterestedLHS |= fcNan | fcNegNormal | fcNegSubnormal;
+        InterestedRHS |= fcNan;
+      }
+      if (InterestedClasses & fcNegative) {
+        // A negative result requires both a negative base and an odd integer
+        // exponent. Only normal values can be odd integers.
+        InterestedLHS |= fcNegative;
+        InterestedRHS |= fcNormal;
+      }
+
+      KnownFPClass KnownLHS, KnownRHS;
+      computeKnownFPClass(II->getArgOperand(0), DemandedElts, InterestedLHS,
+                          KnownLHS, Q, Depth + 1);
+      computeKnownFPClass(II->getArgOperand(1), DemandedElts, InterestedRHS,
+                          KnownRHS, Q, Depth + 1);
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arsenm wrote:

Try RHS and early out if it's unknown?

https://github.com/llvm/llvm-project/pull/215592