[cpunion]

Protect the existing #2704 fix for #3020 in the ordinary -O3 -lto=full release profile:

//go:noinline
func convert(p *item) reader { return p }
// Load a static itab; no NewItab lookup or interface box.

Build the shared test/go case with full LTO, check frontend conversion IR before optimization, and execute checksum, identity and typed-nil assertions. Add conversion and preconstructed-interface benchmarks. The IR assertion guards frontend lowering; executing the final binary checks full-LTO semantics. No compiler/runtime implementation change is needed on current main.

Validation: the new regression fails on reported commit 3571c25 with a NewItab call and passes on main 96331c1. Regular and dev-tag host tests, standard Go, native LLGo and WASI checks pass; the dev-tag test explicitly uses ordinary release settings.

Fixes #3020.

[fennoai]

Review summary

This PR only adds tests. The runtime fixture in test/go/static_itab_test.go looks correct. Both checksums are right: 45000 in the test, and the closed form in checkStaticItabBenchmark. The typed-nil case is a good addition.

The main problem is in internal/build/static_itab_test.go. The IR assertions run on the per-package IR before O3 or LTO runs, so only the runBinary step actually covers the full-LTO build. I also left a few smaller notes inline.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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