[llvm] [DAG] Add ISD::FSQRT handling to computeKnownFPClass (PR #213620)

[Matt Arsenault via llvm-commits]

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@@ -6191,6 +6191,25 @@ KnownFPClass SelectionDAG::computeKnownFPClass(SDValue Op,
     Known.fneg();
     break;
   }
+  case ISD::FSQRT: {
+    FPClassTest InterestedSrcs = InterestedClasses;
+    if (InterestedClasses & fcNan)
+      InterestedSrcs |= KnownFPClass::OrderedLessThanZeroMask;
+
+    KnownFPClass KnownSrc = computeKnownFPClass(Op.getOperand(0), DemandedElts,
+                                                InterestedSrcs, Depth + 1);
+
+    const fltSemantics &FltSem =
+        Op.getValueType().getScalarType().getFltSemantics();
+    DenormalMode Mode = getMachineFunction().getDenormalMode(FltSem);
+
+    Known = KnownFPClass::sqrt(KnownSrc, Mode);
+
+    if (Op->getFlags().hasNoNaNs())
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arsenm wrote:

This should be applied automatically in context. If that doesn't already happen, this should follow what the IR version does with the scope_exit 

https://github.com/llvm/llvm-project/pull/213620