[llvm] [InstCombine] Optimize x * !x to 0 for vector #84608 (PR #84792)

[Yingwei Zheng via llvm-commits]

================
@@ -198,6 +198,20 @@ Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) {
   if (SimplifyAssociativeOrCommutative(I))
     return &I;
 
+  // mul (sext X)), Y -> select X, -Y, 0
+  // mul Y, (sext X)) -> select X, -Y, 0
----------------
dtcxzyw wrote:

```suggestion
  // mul (sext X), Y -> select X, -Y, 0
  // mul Y, (sext X) -> select X, -Y, 0
```

https://github.com/llvm/llvm-project/pull/84792