[llvm] [ValueTracking] isNonEqual Pointers with with a recursive GEP (PR #70459)

[Nikita Popov via llvm-commits]

================
@@ -3141,6 +3141,73 @@ static bool isNonEqualSelect(const Value *V1, const Value *V2, unsigned Depth,
          isKnownNonEqual(SI1->getFalseValue(), V2, Depth + 1, Q);
 }
 
+static bool isNonEqualPointersWithRecursiveGEP(const Value *A, const Value *B,
+                                               unsigned Depth,
+                                               const SimplifyQuery &Q) {
+  // Where A is a recursive GEP for an incoming value of PHI indicating a
+  // loop. B can be a ptr/GEP.
+  // If the PHI has 2 incoming values, one of it being the recursive GEP A
+  // and other a ptr at same base and at an same/higher offset than B we are
+  // only incrementing the pointer further in loop if offset of recursive GEP is
+  // greater than 0.
+  if (!A->getType()->isPointerTy() || !B->getType()->isPointerTy())
+    return false;
+
+  auto *GEPA = dyn_cast<GEPOperator>(A);
+  // Make sure GEPA pointer operand is a PHI.
+  if (!GEPA || !isa<PHINode>(GEPA->getPointerOperand()))
+    return false;
+
+  // Handle 2 incoming PHI values with one being a recursive GEP.
+  auto *PN = dyn_cast<PHINode>(GEPA->getPointerOperand());
+  if (PN->getNumIncomingValues() != 2)
----------------
nikic wrote:

```suggestion
  if (!GEPA)
    return false;

  // Handle 2 incoming PHI values with one being a recursive GEP.
  auto *PN = dyn_cast<PHINode>(GEPA->getPointerOperand());
  if (PN && PN->getNumIncomingValues() != 2)
```

https://github.com/llvm/llvm-project/pull/70459