perf(mir): CMP常量lhs交换——mov+cmp优化为cmp#imm+条件翻转

src/mir/Lowering.cpp

@@ -344,13 +344,30 @@ namespace mir
                                 scalar_slots, array_slots, block);
 
           // 立即数折叠：常量 rhs 直接用 CmpImm
+          // 常量 lhs 则交换并翻转条件
           int cmp_imm = 0;
+          CondCode cond = GetCondCodeForCompareOpcode(bin->GetOpcode());
           if (TryGetConstantInt(bin->GetRhs(), cmp_imm) && static_cast<unsigned int>(cmp_imm) <= 4095)
           {
             block.Append(Opcode::CmpImm,
                          {Operand::VReg(lhs, VRegClass::Int),
                           Operand::Imm(cmp_imm)});
           }
+          else if (TryGetConstantInt(bin->GetLhs(), cmp_imm) && static_cast<unsigned int>(cmp_imm) <= 4095)
+          {
+            // 交换：cmp rhs, #lhs 并翻转条件
+            block.Append(Opcode::CmpImm,
+                         {Operand::VReg(rhs, VRegClass::Int),
+                          Operand::Imm(cmp_imm)});
+            switch (cond)
+            {
+            case CondCode::LT: cond = CondCode::GT; break;
+            case CondCode::LE: cond = CondCode::GE; break;
+            case CondCode::GT: cond = CondCode::LT; break;
+            case CondCode::GE: cond = CondCode::LE; break;
+            default: break;
+            }
+          }
           else
           {
             block.Append(Opcode::CmpRR,
@@ -359,7 +376,7 @@ namespace mir
           int dst = function.CreateVReg(VRegClass::Int);
           block.Append(Opcode::CSet,
                        {Operand::VReg(dst, VRegClass::Int),
-                        Operand::Imm(static_cast<int>(GetCondCodeForCompareOpcode(bin->GetOpcode())))});
+                        Operand::Imm(static_cast<int>(cond))});
           value_vregs[value] = dst;
           return dst;
         }