[CostModel][X86] Reduce the extra costs for ICMP complex predicates when an operand is constant

In most cases, SETCC lowering will be able to simplify/commute the comparison by adjusting the constant.

TODO: We still need to adjust ExtraCost based on CostKind

Fixes llvm#80122

Author: RKSimon

llvm/lib/Target/X86/X86TargetTransformInfo.cpp

@@ -3090,6 +3090,7 @@ InstructionCost X86TTIImpl::getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
   InstructionCost ExtraCost = 0;
   if (Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) {
     // Some vector comparison predicates cost extra instructions.
+    // TODO: Adjust ExtraCost based on CostKind?
     // TODO: Should we invert this and assume worst case cmp costs
     // and reduce for particular predicates?
     if (MTy.isVector() &&
@@ -3102,21 +3103,25 @@ InstructionCost X86TTIImpl::getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
                 Pred == CmpInst::BAD_FCMP_PREDICATE))
         Pred = cast<CmpInst>(I)->getPredicate();
 
+      bool CmpWithConstant = false;
+      if (auto *CmpInstr = dyn_cast_or_null<CmpInst>(I))
+        CmpWithConstant = isa<Constant>(CmpInstr->getOperand(1));
+
       switch (Pred) {
       case CmpInst::Predicate::ICMP_NE:
         // xor(cmpeq(x,y),-1)
-        ExtraCost = 1;
+        ExtraCost = CmpWithConstant ? 0 : 1;
         break;
       case CmpInst::Predicate::ICMP_SGE:
       case CmpInst::Predicate::ICMP_SLE:
         // xor(cmpgt(x,y),-1)
-        ExtraCost = 1;
+        ExtraCost = CmpWithConstant ? 0 : 1;
         break;
       case CmpInst::Predicate::ICMP_ULT:
       case CmpInst::Predicate::ICMP_UGT:
         // cmpgt(xor(x,signbit),xor(y,signbit))
         // xor(cmpeq(pmaxu(x,y),x),-1)
-        ExtraCost = 2;
+        ExtraCost = CmpWithConstant ? 1 : 2;
         break;
       case CmpInst::Predicate::ICMP_ULE:
       case CmpInst::Predicate::ICMP_UGE:
@@ -3127,7 +3132,7 @@ InstructionCost X86TTIImpl::getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
           ExtraCost = 1;
         } else {
           // xor(cmpgt(xor(x,signbit),xor(y,signbit)),-1)
-          ExtraCost = 3;
+          ExtraCost = CmpWithConstant ? 2 : 3;
         }
         break;
       case CmpInst::Predicate::FCMP_ONE: