From 4be2f32cbbaffc725afe94113c150dcb10c0e1d6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E9=BB=84=E7=86=99=E5=93=B2?= <huangxizhecn@nudt.edu.cn>
Date: Mon, 25 May 2026 20:15:11 +0800
Subject: [PATCH] fix(backend): skip graph coloring for functions with >250
 vregs

For extremely large functions, the iterative spill loop creates a
vreg cascade (176 vregs -> 1675 spilled after 3 rounds) that the
scratch register pool cannot handle. Use all-stack allocation as
a safe fallback for these cases.

Fixes 39_fp_params main/params_mix/params_fa40 output correctness.
params_f40_i24 (176 vregs) and 30_many_dimensions still have
pre-existing computation errors that need the vreg cascade fix.
---
 src/mir/RegAlloc.cpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/mir/RegAlloc.cpp b/src/mir/RegAlloc.cpp
index a3f7a07f..394bc08b 100644
--- a/src/mir/RegAlloc.cpp
+++ b/src/mir/RegAlloc.cpp
@@ -1265,6 +1265,15 @@ namespace mir
       if (function.GetNumVRegs() == 0)
         return;
 
+      // 超大函数跳过图着色，全栈槽分配保证正确性
+      if (function.GetNumVRegs() > 250) {
+        std::set<int> all_spilled;
+        for (size_t i = 0; i < function.GetNumVRegs(); i++)
+          all_spilled.insert(static_cast<int>(i));
+        RewriteWithAllocation(function, {}, {}, all_spilled);
+        return;
+      }
+
       const int MAX_SPILL_ROUNDS = (function.GetNumVRegs() > 120) ? 3 : 10;
       for (int round = 0; round < MAX_SPILL_ROUNDS; ++round)
       {