[llvm] [SelectionDAG] Support sign tracking trough `{S|U}INT_TO_FP` (PR #82808)

[Matt Arsenault via llvm-commits]

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@@ -4004,6 +4004,19 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
 
     break;
   }
+  case ISD::UINT_TO_FP: {
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arsenm wrote:

We used to pretend float didn't mean IEEE float layout, but I think that's behind us now

https://github.com/llvm/llvm-project/pull/82808