fix(cl): fill cross-package unexported method Ifn/Tfn so itab is complete

[luoliwoshang]

Fixed #1559

Summary

• Fix itab construction when a type embeds a cross-package type with unexported methods: previously the emitted method metadata set Ifn/Tfn to nil for those promoted unexported methods, leaving the itab with fun[0]=0 and causing interface calls to jump to a null pointer. Now
  Ifn/Tfn are always emitted, so the itab is complete.
• Keep method names fully qualified for unexported methods (package path included) to match interface requirements, but never skip generating function pointers.
• Add regression demo _demo/go/ifaceprom-1599 (self-contained foo package) that embeds a foreign Game and asserts it implements the foreign interface, covering the crash path.
• Regenerate cl/_testgo/abimethod/out.ll to align with the corrected method metadata (no skipped Ifn/Tfn).

Root Cause

• A embeds cross-package B and gains promoted unexported methods.
• During A’s metadata emission (abiUncommonMethods), for unexported methods from another package, skipfn set Ifn/Tfn to nil. The method name/type still matched the interface, but the pointer was nil.
• NewItab matched the method but received a nil Ifn, set fun[0]=0, and marked the itab as “not implemented”; interface calls then dereferenced a null pointer and crashed.

Fix

• Remove the skip-on-cross-package-unexported behavior: always emit Ifn/Tfn using the concrete type’s package; do not write nil pointers.
• Preserve name selection: exported methods use the type’s package for names, unexported methods use the defining package’s fully qualified name; only the function pointers needed correction.
• Ensure both Ifn (interface-call wrapper) and Tfn (direct-call wrapper) are present for promoted methods so itab stays valid.

Tests

• _demo/go: llgo run ./ifaceprom-1599

[gemini-code-assist]

Summary of Changes

Hello @luoliwoshang, 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 introduces two significant compiler fixes: one addressing a nil pointer dereference when calling interface methods on types with promoted, cross-package unexported embedded methods, and another correcting float32 to unsigned integer conversions to match Go's specification. These changes enhance the correctness and stability of the compiler's type system and numerical operations, accompanied by new regression tests and detailed documentation for clarity.

Highlights

• Interface Method Table (itab) Fix: Resolved a runtime panic where promoted, cross-package unexported methods in embedded types resulted in nil function pointers in interface method tables. The fix ensures correct wrapper function pointer emission from the concrete type's package.
• Float-to-Unsigned Integer Conversion Fix: Addressed an issue (Issue 1538) where llgo incorrectly handled float32 to uint8/uint32 conversions, leading to incorrect values and test failures. The compiler now aligns with Go's specification by performing a two-step conversion (float to 64-bit int, then truncate).
• Regression Tests & Documentation: Comprehensive regression tests have been added for both fixes, including _demo/go/ifaceprom for the itab issue and _demo/go/issue1538-floatcvtuint-over for the float conversion. Detailed documentation explaining the root cause and fix strategy for both issues is also included.

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[gemini-code-assist]

Code Review

This pull request contains two main changes: a fix for itab generation for promoted embedded methods, and a fix for a float-to-uint conversion issue (issue #1538). The itab generation fix is well-implemented, and the associated refactoring of the ABI type system in ssa/abitype.go is a significant improvement. The regression test is also comprehensive. However, bundling the unrelated fix for issue #1538 makes this pull request difficult to review and understand. It's a strong convention to have one pull request address one concern. This helps with reviewability, testing, and maintaining a clean commit history. I highly recommend splitting this PR into two separate ones. My review comments are focused on the current state of the code.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.01%. Comparing base (f6337d4) to head (d2adf5d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1560      +/-   ##
==========================================
- Coverage   91.01%   91.01%   -0.01%     
==========================================
  Files          45       45              
  Lines       11971    11960      -11     
==========================================
- Hits        10896    10885      -11     
  Misses        899      899              
  Partials      176      176              

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[xgopilot]

Code Review Summary

This PR correctly fixes the itab generation bug for promoted embedded methods. The fix is well-targeted: removing the flawed skipfn path and always emitting function pointers from the concrete type's package.

Strengths:

• Clean removal of buggy conditional logic
• Proper separation of concerns: method name uses defining package (mPkg), function pointer uses concrete type's package (fnPkg)
• Demo adequately demonstrates the regression scenario

Minor suggestions:

• The fnPkg := pkg variable could be eliminated since it's never modified
• Demo file would benefit from comments explaining the test case

Overall, this is a correct and focused bug fix.

[visualfc]

对于 Go 官方编译器，结构体的嵌入类型如果位于不同包，未导出的的 method ifn/tfn 始终为 -1 。这块可以分析一下是否还有其他实现原因。