[llvm] [InstCombine] Generalize fold of `fcmp + copysign` (PR #86387)

[Andy Kaylor via llvm-commits]

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@@ -8101,22 +8101,22 @@ Instruction *InstCombinerImpl::visitFCmpInst(FCmpInst &I) {
   }
 
   // Convert a sign-bit test of an FP value into a cast and integer compare.
-  // TODO: Simplify if the copysign constant is 0.0 or NaN.
-  // TODO: Handle non-zero compare constants.
-  // TODO: Handle other predicates.
   if (match(Op0, m_OneUse(m_Intrinsic<Intrinsic::copysign>(m_APFloat(C),
                                                            m_Value(X)))) &&
-      match(Op1, m_AnyZeroFP()) && !C->isZero() && !C->isNaN()) {
+      match(Op1, m_ImmConstant(RHSC))) {
     Type *IntType = Builder.getIntNTy(X->getType()->getScalarSizeInBits());
     if (auto *VecTy = dyn_cast<VectorType>(OpType))
       IntType = VectorType::get(IntType, VecTy->getElementCount());
 
-    // copysign(non-zero constant, X) < 0.0 --> (bitcast X) < 0
-    if (Pred == FCmpInst::FCMP_OLT) {
-      Value *IntX = Builder.CreateBitCast(X, IntType);
-      return new ICmpInst(ICmpInst::ICMP_SLT, IntX,
-                          ConstantInt::getNullValue(IntType));
-    }
+    APFloat PosC = abs(*C);
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andykaylor wrote:

Can you add a description of this transformation as a comment? Something like:

`copysign(C1, X) pred C2 --> signbit(X) ? ABS(C1) pred C2 : -ABS(C1) pred C2`


https://github.com/llvm/llvm-project/pull/86387