Fix PTOAS warning build failures

[FangRui0]

修复 macOS/Clang 和gitcode/gcc下 ninja -C build install 的 -Werror 构建失败。

主要清理了几处会被 Clang 视为错误的编译告警：

1. 去掉已覆盖全部枚举值的 switch 中多余的 default 分支，并补充必要的兜底返回
2. 补全 AddressSpace 的 Zero / GM 分支映射，消除未处理枚举告警
3. 删除 PTOToEmitC 中未使用的 lambda capture
4. 将当前未使用但保留设计意图的字段、常量和辅助函数显式标记为 [[maybe_unused]]

[gemini-code-assist]

Code Review

This pull request introduces several code cleanups and robustness improvements, including the addition of [[maybe_unused]] attributes to suppress compiler warnings, the removal of unnecessary lambda captures, and the refactoring of switch statements to move default return values outside the blocks. Additionally, stringifyLocFromMemorySpace was updated with a null check and new address space mappings. Feedback was provided regarding the mapping of AddressSpace::Zero to "illegal", which may cause issues with IR round-tripping since it is treated as a valid memory space elsewhere in the codebase.

[gemini-code-assist]

在 stringifyLocFromMemorySpace 中将 AddressSpace::Zero 映射为 "illegal" 可能会导致 IR 在序列化后无法正确解析回原始状态（Round-tripping）。由于 PTOToEmitC.cpp 中将 AddressSpace::Zero 处理为有效的全局内存空间（映射到 __gm__），建议为其提供一个有效的字符串表示（如 "gm" 或 "zero"），除非该值仅作为内部哨兵使用且不应出现在序列化后的 IR 中。

[reedhecre]

Codex Review

该评论由 review 机器人自动更新。

• PR: Fix PTOAS warning build failures #675 Fix PTOAS Clang warning build failures
• Author: FangRui0
• Base/Head: main / fix_compile_warning
• Head SHA: bb0da65a150a
• Trigger: PR 有新提交
• Generated At: 2026-05-19T04:41:34Z
• Previous Head SHA: 5aca246a8656
• Status: completed

Summary

未检查到 PR #675 存在问题

Findings

No issues found.

[reedhecre]

A5 板测成功

• 触发方式：merged
• 源码提交：72e314460b54
• 结果汇总：OK 17 / FAIL 0 / SKIP 0
• 日志：/root/ptoas-board-monitor-a5/logs/20260519_153405_merged_pr675.log
• 结果 TSV：/root/ptoas-board-monitor-a5/logs/20260519_153405_merged_pr675.tsv

[reedhecre]

A3 板测完成（有跳过）

• 触发方式：merged
• 源码提交：72e314460b54
• 结果汇总：OK 212 / FAIL 0 / SKIP 2
• 日志：/home/zhongxuan/ptoas-board-monitor/runtime/logs/20260519_154905_merged_pr675.log
• 结果 TSV：/home/zhongxuan/ptoas-board-monitor/runtime/logs/20260519_154905_merged_pr675.tsv