[llvm] [InstCombine] Extend bitmask mul combine to handle independent operands (PR #142503)

[Yingwei Zheng via llvm-commits]

================
@@ -3602,6 +3603,11 @@ struct DecomposedBitMaskMul {
   APInt Mask;
   bool NUW;
   bool NSW;
+
+  bool isCombineableWith(DecomposedBitMaskMul Other) {
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dtcxzyw wrote:

```suggestion
  bool isCombineableWith(const DecomposedBitMaskMul &Other) {
```

https://github.com/llvm/llvm-project/pull/142503