ssa: fix types named cycle

[visualfc]

fix build types named cycle type stateFn func(*counter) stateFn

[gemini-code-assist]

Summary of Changes

Hello @visualfc, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request primarily addresses and fixes potential issues related to type cycles within the SSA package's handling of named types, particularly structs. It refines the internal type representation by transitioning from direct LLVM type usage to a custom Type interface/struct for named types. The core of the fix involves restructuring the toNamed and toLLVMNamedStruct functions to correctly identify and handle previously encountered named types, thereby preventing infinite loops during type resolution. Additionally, a new demo file demonstrating a state machine pattern in Go has been introduced.

Highlights

• Type System Refinement: The internal representation for named types within the aProgram struct has been updated from map[string]llvm.Type to map[string]Type, indicating a move towards a more integrated and controlled type system within the SSA package.
• Cycle Handling in Named Types: The toNamed function now includes an early check for already processed named types, leveraging the p.named map. This crucial change prevents infinite recursion when encountering type cycles during type resolution.
• Refactored Named Struct Conversion: The toLLVMNamedStruct function's signature and implementation have been revised to accept more specific arguments (*types.Named, *types.Struct, valueKind) and directly return the custom Type, allowing for more precise type construction and registration.
• New Demo/Example: A new Go program (_demo/go/statefn/main.go) has been added, showcasing a state machine pattern implemented using function types.

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[gemini-code-assist]

Code Review

This pull request aims to fix cyclic dependencies in type definitions by refactoring how named types are handled, particularly for structs. The changes correctly move the caching logic for named structs to break recursion. However, the fix is incomplete as it doesn't handle recursive named types that are not structs, such as the function type stateFn introduced in the new demo file. This will lead to a stack overflow. I've left a comment with details on the specific location of the issue.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.66%. Comparing base (0233891) to head (b3c5e67).
⚠️ Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1439      +/-   ##
==========================================
+ Coverage   90.63%   90.66%   +0.03%     
==========================================
  Files          43       43              
  Lines       11400    11402       +2     
==========================================
+ Hits        10332    10338       +6     
+ Misses        907      903       -4     
  Partials      161      161              

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[xgopilot]

Code Review Summary

This PR effectively resolves a critical compiler bug involving recursive named types. The implementation is sound with proper cycle detection through early type registration.

Key strengths:

• Correct cycle breaking by registering types before processing fields
• Maintains type system consistency with dual-map caching strategy
• Minimal, targeted changes with no backward compatibility issues
• Clear reproduction case in demo

Minor suggestion: Consider adding a formal test case to cl/_testgo/ to ensure long-term regression protection alongside the demo.

Verdict: Approved - high quality fix with no security, performance, or correctness concerns.