[llvm] [DAG] computeKnownFPClass - add ISD::SQRT handling + test coverage (PR #195405)

[Matt Arsenault via llvm-commits]

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@@ -6075,6 +6073,34 @@ 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);
+
+    DenormalMode Mode = DenormalMode::getDynamic();
+
+    bool HasNSZ = Op->getFlags().hasNoSignedZeros();
+    bool nnan = Op->getFlags().hasNoNaNs();
+
+    if (!HasNSZ) {
+      const fltSemantics &FltSem =
+          Op.getValueType().getScalarType().getFltSemantics();
+      Mode = getMachineFunction().getDenormalMode(FltSem);
+    }
+
+    Known = KnownFPClass::sqrt(KnownSrc, Mode);
+
+    if (HasNSZ)
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arsenm wrote:

Can't promote nsz into a poison returning value. I'm surprised we handle it this way in the IR Version, but that has the additional special predicate in the InstrInfoQuery 

https://github.com/llvm/llvm-project/pull/195405