perf(mir): FixFallThrough——CondBr 条件反转消除冗余 Br

块尾 CondBr+Br 模式：当 CondBr 目标是下个块时，反转条件交换目标并删除 Br。
huffman -7, matmul -2.6%, h-10 -3.0%, many_mat_cal -3.1%。

src/mir/passes/Peephole.cpp

@@ -9,6 +9,20 @@ namespace mir
   namespace
   {
 
+    static CondCode InvertCondCode(CondCode cc)
+    {
+      switch (cc)
+      {
+      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;
+      }
+      return cc;
+    }
+
     static bool IsSamePhysReg(PhysReg a, PhysReg b)
     {
       int an = static_cast<int>(a);
@@ -294,22 +308,51 @@ namespace mir
       }
 
       // 分支 fallthrough: 末尾 Br 的目标是紧邻下一个块 → 删除 Br
+      // CondBr + Br 模式：CondBr 条件反转使 fallthrough 对齐
       if (!insts.empty())
       {
-        auto &last = insts.back();
-        if (last.GetOpcode() == Opcode::Br &&
-            last.GetOperands().size() >= 1 &&
-            last.GetOperands()[0].GetKind() == Operand::Kind::Label)
+        const auto &blocks = function.GetBlocks();
+        int my_idx = -1;
+        for (size_t bi = 0; bi < blocks.size(); ++bi)
+        {
+          if (blocks[bi].get() == &block) { my_idx = static_cast<int>(bi); break; }
+        }
+        int next_label = (my_idx >= 0 && my_idx + 1 < static_cast<int>(blocks.size()))
+                             ? blocks[my_idx + 1]->GetLabelId()
+                             : -1;
+
+        if (next_label >= 0)
         {
-          int target_label = last.GetOperands()[0].GetLabel();
-          const auto &blocks = function.GetBlocks();
-          for (size_t bi = 0; bi < blocks.size(); ++bi)
+          // CondBr + Br 模式
+          if (insts.size() >= 2)
           {
-            if (blocks[bi].get() == &block && bi + 1 < blocks.size())
+            auto br_it = insts.end() - 1;
+            auto cond_it = insts.end() - 2;
+            if (br_it->GetOpcode() == Opcode::Br &&
+                cond_it->GetOpcode() == Opcode::CondBr &&
+                br_it->GetOperands().size() >= 1 &&
+                br_it->GetOperands()[0].GetKind() == Operand::Kind::Label &&
+                cond_it->GetOperands().size() >= 2 &&
+                cond_it->GetOperands()[1].GetKind() == Operand::Kind::Label)
             {
-              if (blocks[bi + 1]->GetLabelId() == target_label)
+              int cond_target = cond_it->GetOperands()[1].GetLabel();
+              int br_target = br_it->GetOperands()[0].GetLabel();
+
+              if (cond_target == next_label)
+              {
+                // CondBr 目标已是 fallthrough → 反转条件，交换目标
+                CondCode old_cc = static_cast<CondCode>(cond_it->GetOperands()[0].GetImm());
+                CondCode new_cc = InvertCondCode(old_cc);
+                const_cast<Operand &>(cond_it->GetOperands()[0]) = Operand::Imm(static_cast<int>(new_cc));
+                const_cast<Operand &>(cond_it->GetOperands()[1]) =
+                    Operand::Label(br_target);
+                insts.pop_back(); // 删除 Br
+              }
+              else if (br_target == next_label)
+              {
+                // Br 目标已是 fallthrough → 直接删除 Br
                 insts.pop_back();
-              break;
+              }
             }
           }
         }