[llvm] [ValueTracking] Merge `cannotBeOrderedLessThanZeroImpl` into `computeKnownFPClass` (PR #76360)

[Matt Arsenault via llvm-commits]

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@@ -5740,9 +5740,9 @@ static Value *simplifyFMAFMul(Value *Op0, Value *Op1, FastMathFlags FMF,
       return ConstantFP::getZero(Op0->getType());
 
     // +normal number * (-)0.0 --> (-)0.0
-    if (isKnownNeverInfOrNaN(Op0, Q.DL, Q.TLI, 0, Q.AC, Q.CxtI, Q.DT) &&
-        // TODO: Check SignBit from computeKnownFPClass when it's more complete.
-        SignBitMustBeZero(Op0, Q.DL, Q.TLI))
+    KnownFPClass Known = computeKnownFPClass(
+        Op0, FMF, Q.DL, fcInf | fcNan, /*Depth*/ 0, Q.TLI, Q.AC, Q.CxtI, Q.DT);
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arsenm wrote:

/*Depth=/* so clang-format recognizes it 

https://github.com/llvm/llvm-project/pull/76360