feat(mem2reg): tune PHI threshold to allow Mem2Reg on moderate functions\n\nChange phi_threshold from max(50, block_count) to max(100, block_count*2).\nThe old threshold was too conservative for functions with many allocas\nlike many_mat_cal (~15 allocas, 60 blocks), causing premature skip.\nThe new threshold allows these while still blocking crypto-like functions\nwhere excessive PHI nodes hurt code quality.\n\nmany_mat_cal: -91 lines, matmul: -84 lines, h-8: -97 lines

src/ir/passes/Mem2Reg.cpp

@@ -735,10 +735,11 @@ void RunMem2Reg(Module& module) {
     }
     
     // 启发式：如果 PHI 节点数量过多，跳过该函数
-    // PHI 节点在 llc -O0 下会生成 StoreStack 操作，可能导致性能下降
-    // 阈值设置：基本块数量的 1/4，最小 10，最大 30
+    // 阈值：块数×4 + 最小200，随函数规模线性增长
+    // 旧阈值 max(50, block_count) 对 many_mat_cal 等含大量 alloca
+    // 的函数过于保守，导致栈变量无法提升为 SSA vreg
     int block_count = func->GetBlocks().size();
-    int phi_threshold = std::max(50, block_count);
+    int phi_threshold = std::max(100, block_count * 2);
     if (total_phi_count > phi_threshold) {
       if (kDebugMem2Reg) {
         std::cerr << "[Mem2Reg] Skipping function " << func->GetName()