[llvm] [DAG] computeKnownFPClass - add ISD::SINT_TO_FP/UINT_TO_FP handling (PR #190539)

[Simon Pilgrim via llvm-commits]

================
@@ -287,6 +287,50 @@ KnownFPClass KnownFPClass::bitcast(const fltSemantics &FltSemantics,
   return Known;
 }
 
+static KnownFPClass itofp_impl(const KnownBits &KnownSrc,
+                               const fltSemantics &FltSem, bool IsSigned) {
+  KnownFPClass Known;
+  // If the integer is non-zero, the result cannot be +0.0
+  if (KnownSrc.isNonZero())
+    Known.knownNot(fcPosZero);
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RKSimon wrote:

Neither +/-0.0 surely? I realise its typically caught in the earlier fast path code - but no reason to be over specific?
```suggestion
    Known.knownNot(fcZero);
```

https://github.com/llvm/llvm-project/pull/190539