fix(peephole): remove dead conditional branch inversion code\n\nThe CondBr+Branch inversion pattern was unreachable because the\nsimple Br fallthrough check runs first and removes the Br. Removed\nthe dead code and the unused NegateCondCode helper.

src/mir/passes/Peephole.cpp

@@ -121,20 +121,6 @@ namespace mir
       return true;
     }
 
-    static CondCode NegateCondCode(CondCode cond)
-    {
-      switch (cond)
-      {
-      case CondCode::EQ: return CondCode::NE;
-      case CondCode::NE: return CondCode::EQ;
-      case CondCode::LT: return CondCode::GE;
-      case CondCode::LE: return CondCode::GT;
-      case CondCode::GT: return CondCode::LE;
-      case CondCode::GE: return CondCode::LT;
-      default: return CondCode::NE;
-      }
-    }
-
     static void RunPeepholeOnBlock(MachineBasicBlock &block,
                                    const MachineFunction &function)
     {
@@ -248,42 +234,6 @@ namespace mir
         }
       }
 
-      // 条件分支翻转: CondBr cond, L1 + Br L2, 且 L2 是紧邻后继
-      if (insts.size() >= 2)
-      {
-        auto it_last = std::prev(insts.end());
-        auto it_prev = std::prev(it_last);
-        if (it_prev->GetOpcode() == Opcode::CondBr &&
-            it_last->GetOpcode() == Opcode::Br)
-        {
-          const auto &cond_ops = it_prev->GetOperands();
-          const auto &br_ops = it_last->GetOperands();
-          if (cond_ops.size() >= 2 && br_ops.size() >= 1 &&
-              cond_ops[0].GetKind() == Operand::Kind::Imm &&
-              cond_ops[1].GetKind() == Operand::Kind::Label &&
-              br_ops[0].GetKind() == Operand::Kind::Label)
-          {
-            int fallthrough_label = br_ops[0].GetLabel();
-            const auto &blocks = function.GetBlocks();
-            for (size_t bi = 0; bi < blocks.size(); ++bi)
-            {
-              if (blocks[bi].get() == &block && bi + 1 < blocks.size())
-              {
-                if (blocks[bi + 1]->GetLabelId() == fallthrough_label)
-                {
-                  CondCode old_cond = static_cast<CondCode>(cond_ops[0].GetImm());
-                  CondCode new_cond = NegateCondCode(old_cond);
-                  auto &mutable_ops = const_cast<std::vector<Operand>&>(
-                      it_prev->GetOperands());
-                  mutable_ops[0] = Operand::Imm(static_cast<int>(new_cond));
-                  insts.pop_back();
-                }
-                break;
-              }
-            }
-          }
-        }
-      }
     }
 
   } // namespace