[llvm] [InstSimplify] `A == MIN_INT ? B != MIN_INT : A < B` to `A < B` (PR #120177)

[Nikita Popov via llvm-commits]

================
@@ -4608,6 +4608,45 @@ static Value *simplifySelectWithEquivalence(Value *CmpLHS, Value *CmpRHS,
   return nullptr;
 }
 
+/// `A == MIN_INT ? B != MIN_INT : A < B` --> `A < B`
+/// `A == MAX_INT ? B != MAX_INT : A > B` --> `A > B`
+static Value *foldSelectWithExtremeEqCond(Value *CmpLHS, Value *CmpRHS,
+                                          Value *TrueVal, Value *FalseVal) {
+  CmpPredicate Pred;
+  Value *A, *B;
+
+  if (!match(FalseVal, m_ICmp(Pred, m_Value(A), m_Value(B))))
+    return nullptr;
+
+  // make sure `CmpLHS` is on the LHS of `FalseVal`.
+  if (match(CmpLHS, m_Specific(B))) {
----------------
nikic wrote:

```suggestion
  if (CmpLHS == B) {
```
etc

https://github.com/llvm/llvm-project/pull/120177