Support goto statement

[tobiichi3227]

Add goto and label statement support

This PR adds full support for C goto statements and labels, integrating them with the parser, IR/CFG, and SSA passes. This enables forward/backward jumps, error-handling patterns, and improves C compatibility (#280).

Changes Made

Lexer/Parser:

• Add T_goto; parse goto identifier; and identifier: labels.
• Function-scoped label table with forward-reference backpatching.
• Report unused label warning.

IR/CFG:

• Introduce OP_label; update text dump and graph dump.
• Lower goto via an if (1) wrapper to keep CFG well-formed (then: jmp label; else: fallthrough).
• Map each label to a basic-block boundary and connect jumps accordingly.

SSA/Semantics:

• Dominance-based check warns when goto crosses variable initialization (cross-initialization warning).

Notes:

• Computed goto (GNU extension) is out of scope.

Testing

• All tests pass on both Stage 0 and Stage 2

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Summary by cubic

Adds C goto and label support across the lexer/parser, IR/CFG, and SSA to enable forward/backward jumps and improve C compatibility. Also adds warnings and errors around labels and unsafe jumps.

• New Features
  • Lexer/Parser: add T_goto; parse "goto ;" and ":" labels; per-function label table with forward-reference backpatching.
  • IR/CFG: add OP_label and OP_jump; map labels to basic-block boundaries; lower goto via an if (1) wrapper to keep CFG well-formed; update text and graph dumps.
  • SSA: dominance-based check warns when a goto crosses a variable’s initialization.
  • Diagnostics: error on undefined labels and duplicate labels; warning on unused labels.
  • Tests: coverage for forward/backward jumps, label namespace, redefinition, and loop patterns.
  • Out of scope: computed goto (GNU extension).

[jserv]

Check https://github.com/sysprog21/shecc/blob/master/CONTRIBUTING.md carefully, and you must use clang-format version 18 (not later) to indent.

[cubic-dev-ai]

1 issue found across 6 files

Prompt for AI agents (all 1 issues)

Understand the root cause of the following 1 issues and fix them.


<file name="src/lexer.c">

<violation number="1" location="src/lexer.c:88">
Adding this entry expands the keyword table to 18 elements, but NUM_KEYWORDS is still 17, so the loop stops early and the last keyword (&quot;const&quot;) is never inserted into KEYWORD_MAP. Update NUM_KEYWORDS so all entries are registered.</violation>
</file>

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[jserv]

Read https://cbea.ms/git-commit/ and enforce the rules. In addition, append Close #280 at the end of git commit message.

[jserv]

Update COMPLIANCE.md once you are confident that the goto statement is supported.

[jserv]

Enforce the rules specified in How to Write a Git Commit Message:

1. Separate subject from body with a blank line
2. Limit the subject line to 50 characters
3. Capitalize the subject line
4. Do not end the subject line with a period
5. Use the imperative mood in the subject line
6. Wrap the body at 72 characters
7. Use the body to explain what and why vs. how

[jserv]

Refine git commit messages into complete English sentences that clearly describe the rationale, while supporting the 'goto' keyword.

[visitorckw]

Please resolve CI failure.
Again, please test it before pushing the remote branch for review.

[visitorckw]

Personally, I would prefer:

if (label_idx >= MAX_LABELS)

[tobiichi3227]

Oh, I referred to this.

[jserv]

Thank @tobiichi3227 for contributing!