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

[Matt Arsenault via llvm-commits]

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@@ -2408,19 +2408,19 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
   }
   case Intrinsic::copysign: {
     Value *Mag = II->getArgOperand(0), *Sign = II->getArgOperand(1);
-    if (SignBitMustBeZero(Sign, DL, &TLI)) {
-      // If we know that the sign argument is positive, reduce to FABS:
-      // copysign Mag, +Sign --> fabs Mag
-      Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, Mag, II);
-      return replaceInstUsesWith(*II, Fabs);
-    }
-    // TODO: There should be a ValueTracking sibling like SignBitMustBeOne.
-    const APFloat *C;
-    if (match(Sign, m_APFloat(C)) && C->isNegative()) {
-      // If we know that the sign argument is negative, reduce to FNABS:
-      // copysign Mag, -Sign --> fneg (fabs Mag)
-      Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, Mag, II);
-      return replaceInstUsesWith(*II, Builder.CreateFNegFMF(Fabs, II));
+    if (std::optional<bool> KnownSignBit = computeKnownFPSignBit(
+            Sign, getDataLayout(), &TLI, /*Depth*/ 0, &AC, II, &DT)) {
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arsenm wrote:

/*Depth=*/

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