sync: align Cond with stdlib to fix interface nil comparisons

[cpunion]

Fixes #1493

Root cause: llgo’s sync.Cond diverged from the stdlib layout. It stored a *sync.Mutex and didn’t expose Cond.L, so code that accessed Cond.L (an interface) loaded a pointer instead. Comparisons like p.c.L == nil or nil == p.c.L then produced invalid LLVM IR (icmp between pointer and interface).

Changes:

• Add L gosync.Locker to sync.Cond and store it in NewCond.
• Use Cond.L in Wait (validate *Mutex and ensure init).
• Use cond.Signal/Broadcast directly (remove pthread linkname calls).
• Add http2pipe interface comparison tests/demos covering both operand orders.

[gemini-code-assist]

Summary of Changes

Hello @cpunion, 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 addresses a critical bug in the SSA generation process that led to the creation of malformed LLVM IR when comparing an interface value with a non-interface value. The core change ensures that such comparisons are correctly handled by explicitly converting the non-interface operand to an interface, thereby aligning the generated IR with Go's runtime semantics for interface equality and preventing runtime errors or unexpected behavior.

Highlights

• Bug Fix: Resolved an issue where comparing a non-interface value with an interface value generated invalid LLVM IR, specifically icmp eq ptr ... instead of proper interface equality checks.
• Type Conversion: Implemented logic in the BinOp function to detect mixed interface/non-interface comparisons and automatically convert the non-interface operand to an interface type using MakeInterface.
• New Test Case: Added a new test file, interface_cmp_test.go, to specifically verify the fix for mixed interface comparisons, drawing inspiration from sync.Cond usage in net/http.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a bug that caused invalid LLVM IR generation for comparisons between interface and non-interface types. The approach of converting the non-interface operand to an interface before comparison is sound. The added test case effectively covers the failing scenario. I have a couple of suggestions to improve code readability and maintainability in both the fix and the new test file.

[xgopilot]

Code Review Summary

Great work on fixing the invalid LLVM IR generation for mixed interface/pointer comparisons! The approach is sound, but there's a critical bug that needs to be fixed.

Critical Issue:

• Missing kind = y.kind in the second conversion branch (line 554). This will cause incorrect comparison logic when the right operand is converted.

Important Improvements:

• Add inline comments explaining the interface conversion logic
• Expand test coverage to validate both conversion branches
• Add test documentation referencing issue Compiler error: Invalid LLVM IR instruction for nil pointer comparison with interface #1493

Security & Performance: No concerns. The code is type-safe and the interface conversion overhead is acceptable for correctness.

Please address the critical bug before merging.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.58%. Comparing base (5627fb3) to head (26e43bb).
⚠️ Report is 18 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1494   +/-   ##
=======================================
  Coverage   90.58%   90.58%           
=======================================
  Files          43       43           
  Lines       11429    11429           
=======================================
  Hits        10353    10353           
  Misses        914      914           
  Partials      162      162           

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