[llvm] DAG: Call SimplifyDemandedBits on copysign value operand (PR #97180)

[Jay Foad via llvm-commits]

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@@ -17571,6 +17571,11 @@ SDValue DAGCombiner::visitFCOPYSIGN(SDNode *N) {
                            APInt::getSignMask(SignVT.getScalarSizeInBits())))
     return SDValue(N, 0);
 
+  // We only take the non-sign bits from the value operand
+  if (SimplifyDemandedBits(N0,
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jayfoad wrote:

This looks like it could subsume all these optimizations from above:
```
  // copysign(fabs(x), y) -> copysign(x, y)
  // copysign(fneg(x), y) -> copysign(x, y)
  // copysign(copysign(x,z), y) -> copysign(x, y)
```

https://github.com/llvm/llvm-project/pull/97180