ssa,test: lower builtin panic in defer paths

[zhouguangyuan0718]

Summary

• lower builtin panic calls through Builder.Panic during SSA lowering
• add cl/_testdata/deferpanic coverage for panic raised from a deferred call
• verify the deferred recover() path prints the expected output

Testing

• not run

[fennoai]

Review Summary

Clean, well-scoped change that correctly routes the panic builtin through Builder.Panic when it appears as a deferred builtin call (e.g., defer panic("msg")). Without this fix, such calls would fall through to panic("todo: " + fn), crashing the compiler.

The test uses both CHECK directives for IR verification and expect.txt for runtime output verification, which is good.

Two minor nits below.

[fennoai]

Nit: This accesses args[0] without a length guard. Other void-returning builtins in this switch (delete, close, clear) use guards like if len(args) == 1. Since the Go type checker guarantees panic always has exactly one argument, this is safe — and other fixed-arity builtins (complex, real, imag) also skip the guard. Still, adding if len(args) == 1 { would be defensive and self-documenting about the expected arity.

Not a bug, just a consistency observation.

[fennoai]

Nit: This blank line was not present before and is inconsistent with the original formatting (the closing } of the switch was immediately followed by panic("todo: " + fn) with no blank line).

[gemini-code-assist]

Code Review

This pull request implements support for the panic built-in function within the SSA builder and includes a new test case to verify its behavior. The feedback suggests adding an argument count validation for the panic built-in to ensure robustness and consistency with other built-in function implementations in the SSA builder.

[gemini-code-assist]

For robustness, it's good practice to validate the number of arguments for built-in functions. The panic function expects exactly one argument. While the frontend should enforce this, adding a check here would make the SSA builder more resilient to potential issues in earlier compilation stages. Other built-ins like len, cap, and close in this file already have similar checks.

		if len(args) != 1 {
			panic("ssa: builtin panic expects 1 argument")
		}
		b.Panic(args[0])

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.50%. Comparing base (1196550) to head (7b18956).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1839   +/-   ##
=======================================
  Coverage   88.50%   88.50%           
=======================================
  Files          50       50           
  Lines       14426    14429    +3     
=======================================
+ Hits        12768    12771    +3     
  Misses       1438     1438           
  Partials      220      220           

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