[llvm] [SROA] Propagate no-signed-zeros(nsz) fast-math flag on the phi node using function attribute (PR #83381)

[Matt Arsenault via llvm-commits]

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@@ -1113,6 +1114,17 @@ void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
         for (unsigned i = 0; i != NumEdges; ++i)
           APN->addIncoming(IncomingVals[AllocaNo], Pred);
 
+        // For the  sequence `return X > 0.0 ? X : -X`, it is expected that this
+        // results in fabs intrinsic. However, without no-signed-zeros(nsz) flag
+        // on the phi node generated at this stage, fabs folding does not
+        // happen. So, we try to infer nsz flag from the function attributes to
+        // enable this fabs folding.
+        if (APN->isComplete() && isa<FPMathOperator>(APN) &&
+            APN->getFunction()
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arsenm wrote:

```suggestion
            BB->getParent()
```

https://github.com/llvm/llvm-project/pull/83381