[llvm-branch-commits] [llvm] DAG: Call SimplifyDemandedBits on fcopysign sign value (PR #97151)

[Jay Foad via llvm-branch-commits]

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@@ -17565,6 +17565,12 @@ SDValue DAGCombiner::visitFCOPYSIGN(SDNode *N) {
   if (CanCombineFCOPYSIGN_EXTEND_ROUND(N))
     return DAG.getNode(ISD::FCOPYSIGN, SDLoc(N), VT, N0, N1.getOperand(0));
 
+  // We only take the sign bit from the sign operand.
+  EVT SignVT = N1.getValueType();
+  if (SimplifyDemandedBits(N1,
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jayfoad wrote:

I think this should be able to subsume some of the optimizations above, e.g. `copysign(x, abs(y)) -> abs(x)` would fall out if SimplifyDemandedBits knew about extracting the sign bit from `abs(x)`.

https://github.com/llvm/llvm-project/pull/97151