[llvm] Reland "[ValueTracking] Compute knownbits from known fp classes" (PR #92084)

[Matt Arsenault via llvm-commits]

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@@ -1118,6 +1118,42 @@ static void computeKnownBitsFromOperator(const Operator *I,
       break;
     }
 
+    const Value *V;
+    // Handle bitcast from floating point to integer.
+    if (match(I, m_ElementWiseBitCast(m_Value(V))) &&
+        V->getType()->isFPOrFPVectorTy()) {
+      Type *FPType = V->getType()->getScalarType();
+      KnownFPClass Result = computeKnownFPClass(V, fcAllFlags, Depth + 1, Q);
+      FPClassTest FPClasses = Result.KnownFPClasses;
+
+      if (Result.isKnownNever(fcNormal | fcSubnormal | fcNan)) {
+        Known.Zero.setAllBits();
+        Known.One.setAllBits();
+
+        if (FPClasses & fcInf)
+          Known = Known.intersectWith(KnownBits::makeConstant(
+              APFloat::getInf(FPType->getFltSemantics()).bitcastToAPInt()));
+
+        if (FPClasses & fcZero)
+          Known = Known.intersectWith(KnownBits::makeConstant(
+              APInt::getZero(FPType->getScalarSizeInBits())));
+
+        Known.Zero.clearSignBit();
+        Known.One.clearSignBit();
+      }
+
+      if (Result.SignBit) {
+        if (*Result.SignBit)
+          Known.makeNegative();
+        else
+          Known.makeNonNegative();
+      }
+
+      assert(!Known.hasConflict() && "Bits known to be one AND zero?");
+
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arsenm wrote:

Delete blank this blank line 

https://github.com/llvm/llvm-project/pull/92084