ValueTracking: Handle powi in computeKnownFPClass

Extract the handling from cannotBeOrderedLessThanZeroImpl and
avoid the mentioned -0 bug.

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index cc3f672..fa5c214 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4693,6 +4693,36 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
 
         break;
       }
+      case Intrinsic::powi: {
+        if ((InterestedClasses & fcNegative) == fcNone)
+          break;
+
+        const Value *Exp = II->getArgOperand(1);
+        unsigned BitWidth =
+            Exp->getType()->getScalarType()->getIntegerBitWidth();
+        KnownBits ExponentKnownBits(BitWidth);
+        computeKnownBits(Exp, DemandedElts, ExponentKnownBits, Depth + 1, Q);
+
+        if (ExponentKnownBits.Zero[0]) { // Is even
+          Known.knownNot(fcNegative);
+          break;
+        }
+
+        // Given that exp is an integer, here are the
+        // ways that pow can return a negative value:
+        //
+        //   pow(-x, exp)   --> negative if exp is odd and x is negative.
+        //   pow(-0, exp)   --> -inf if exp is negative odd.
+        //   pow(-0, exp)   --> -0 if exp is positive odd.
+        //   pow(-inf, exp) --> -0 if exp is negative odd.
+        //   pow(-inf, exp) --> -inf if exp is positive odd.
+        KnownFPClass KnownSrc;
+        computeKnownFPClass(II->getArgOperand(0), DemandedElts, fcNegative,
+                            KnownSrc, Depth + 1, Q, TLI);
+        if (KnownSrc.isKnownNever(fcNegative))
+          Known.knownNot(fcNegative);
+        break;
+      }
       case Intrinsic::arithmetic_fence: {
         computeKnownFPClass(II->getArgOperand(0), DemandedElts,
                             InterestedClasses, Known, Depth + 1, Q, TLI);