[llvm] [ValueTracking] Add support for `sub` in `isKnownNonEqual` (PR #87704)

[via llvm-commits]

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@@ -3134,6 +3135,36 @@ static bool isNonEqualShl(const Value *V1, const Value *V2, unsigned Depth,
   return false;
 }
 
+/// Return true if V1 == V2 - X or V1 == X - V2 implies V2 != V1
+static bool isNonEqualSub(const Value *V1, const Value *V2, unsigned Depth,
+                          const SimplifyQuery &Q) {
+  const BinaryOperator *BO = dyn_cast<BinaryOperator>(V1);
+  if (!BO || BO->getOpcode() != Instruction::Sub)
+    return false;
+
+  // -V2 != V2 iff V2 != 0 and V2 != INT_MIN
+  if (match(BO, m_Sub(m_Zero(), m_Specific(V2)))) {
+    const OverflowingBinaryOperator *OBO = cast<OverflowingBinaryOperator>(V1);
+    // nsw implies no INT_MIN case.
+    if (OBO->hasNoSignedWrap())
+      return isKnownNonZero(V2, Depth + 1, Q);
+    // Otherwise check for INT_MIN case directly.
+    KnownBits V2Known = computeKnownBits(V2, Depth + 1, Q);
+    if (V2Known.isNonNegative() ||
+        (!V2Known.One.isZero() && !V2Known.One.isMinSignedValue()))
+      return V2Known.isNonZero() || isKnownNonZero(V2, Depth + 1, Q);
+  }
+
+  // X - V2 != V2 if X != 0
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goldsteinn wrote:

Fixed + updated proofs / commit / tests.

https://github.com/llvm/llvm-project/pull/87704