[ValueTracking] Handle shl pair in isKnownNonEqual()

Handle (x << s) != (y << s) where x != y and the shifts are
non-wrapping. Once again, this establishes parity with the
corresponing mul fold that already exists. The shift case is
more powerful because we don't need to guard against multiplies
by zero.

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 6f89ba9..39d8f9b 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2655,6 +2655,20 @@ static bool isKnownNonEqual(const Value *V1, const Value *V2, unsigned Depth,
                                Depth + 1, Q);
       break;
     }
+    case Instruction::Shl: {
+      // Same as multiplies, with the difference that we don't need to check
+      // for a non-zero multiply. Shifts always multiply by non-zero.
+      auto *OBO1 = cast<OverflowingBinaryOperator>(O1);
+      auto *OBO2 = cast<OverflowingBinaryOperator>(O2);
+      if ((!OBO1->hasNoUnsignedWrap() || !OBO2->hasNoUnsignedWrap()) &&
+          (!OBO1->hasNoSignedWrap() || !OBO2->hasNoSignedWrap()))
+        break;
+
+      if (O1->getOperand(1) == O2->getOperand(1))
+        return isKnownNonEqual(O1->getOperand(0), O2->getOperand(0),
+                               Depth + 1, Q);
+      break;
+    }
     case Instruction::SExt:
     case Instruction::ZExt:
       if (O1->getOperand(0)->getType() == O2->getOperand(0)->getType())