[llvm] [Reassociate] Preserve NSW flags after expr tree rewriting (PR #93105)

[Yingwei Zheng via llvm-commits]

================
@@ -648,6 +651,9 @@ static bool LinearizeExprTree(Instruction *I,
     // Ensure the leaf is only output once.
     It->second = 0;
     Ops.push_back(std::make_pair(V, Weight));
+    if (Opcode == Instruction::Add && Flags.AllKnownNonNegative) {
----------------
dtcxzyw wrote:

```suggestion
    if (Opcode == Instruction::Add && Flags.AllKnownNonNegative && Flags.HasNSW) {
```
Can we avoid computing this when `HasNSW` is false?


https://github.com/llvm/llvm-project/pull/93105