[llvm] [ValueTracking] Fix crash in PR175590 (PR #180355)

[Kshitij Paranjape via llvm-commits]

================
@@ -9248,6 +9289,40 @@ static bool matchTwoInputRecurrence(const PHINode *PN, InstTy *&Inst,
   return false;
 }
 
+template <typename InstTy>
+static bool matchThreeInputRecurrence(const PHINode *PN, InstTy *&Inst,
+                                      Value *&Init, Value *&OtherOp0,
+                                      Value *&OtherOp1) {
+  if (PN->getNumIncomingValues() != 2)
+    return false;
+
+  for (unsigned I = 0; I != 2; ++I) {
+    if (auto *Operation = dyn_cast<InstTy>(PN->getIncomingValue(I));
+        Operation) {
----------------
kshitijvp wrote:

Is that the reason for the crash, although I can't understand how.
Because `matchThreeInputRecurrence` is being called only through `matchSimpleTernaryIntrinsicRecurrence` where the arguments are checked as:
```
  if (I->arg_size() != 3 || I->getType() != I->getArgOperand(0)->getType() ||
      I->getType() != I->getArgOperand(1)->getType() ||
      I->getType() != I->getArgOperand(2)->getType())
    return false;
```

https://github.com/llvm/llvm-project/pull/180355