runtime: attribute panic caller lines

[cpunion]

Summary

• build on the caller-frame metadata path from runtime: track caller frames for LLGo metadata #1884 and update caller line attribution immediately before panic-prone SSA operations
• preserve the caller-frame snapshot captured at panic time so deferred runtime.Caller(2) can report the panic site
• add LLGo-run test/go coverage for explicit panic, nil field panic, bounds panic CallersFrames, and deferred return caller lines
• remove verified darwin/arm64 xfails for bug347.go, bug348.go, issue14646.go, issue29504.go, issue4562.go, and issue5856.go

Scope

• Left issue27201.go xfailed: it depends on runtime.Stack line output, which is covered by the separate lineinfo/runtime.Stack work.
• Left issue33724.go xfailed: it currently fails because the promoted-method nil access does not panic, which is nil/method semantics rather than caller-line attribution.
• This branch is stacked on the already-open caller-frame metadata PR runtime: track caller frames for LLGo metadata #1884; the final commit is the panic-line attribution delta.

Tests

• go test ./test/go -run TestRuntimePanicCallerLineAttribution -count=1 -timeout=10m
• go test ./test/go -run 'TestRuntime(Caller|Callers|PanicCaller)' -count=1 -timeout=10m
• go test ./test/goroot -run TestGoRootRunCases -count=1 -timeout=15m -args -goroot /opt/homebrew/Cellar/go@1.24/1.24.11/libexec -dirs fixedbugs -case '^(fixedbugs/(bug347|bug348|issue14646|issue29504|issue4562|issue5856)\\.go)$' -xfail /dev/null -run-timeout 2m -build-timeout 5m
• go test ./test/goroot -run TestGoRootRunCases -count=1 -timeout=15m -args -goroot /opt/homebrew/Cellar/go@1.24/1.24.11/libexec -dirs fixedbugs -case '^(fixedbugs/(bug347|bug348|issue14646|issue29504|issue4562|issue5856)\\.go)$' -run-timeout 2m -build-timeout 5m
• go test ./test/goroot -run TestGoRootRunCases -count=1 -timeout=15m -args -goroot /opt/homebrew/Cellar/go@1.24/1.24.11/libexec -dirs fixedbugs -case '^(fixedbugs/(bug347|bug348|issue14646|issue27201|issue29504|issue33724|issue4562|issue5856)\\.go)$' -run-timeout 2m -build-timeout 5m
• go test ./ssa -count=1 -timeout=15m
• go test ./cl -count=1 -timeout=15m
• (cd runtime && go test ./... -count=1 -timeout=15m)
• git diff --check

[codecov-commenter]

Codecov Report

❌ Patch coverage is 97.59036% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cl/compile.go	93.75%	4 Missing ⚠️

📢 Thoughts on this report? Let us know!

[cpunion]

Added focused package-level coverage for the panic caller-line instrumentation paths.

Changes:

• Added cl tests for caller-frame tracking guards, runtime caller import forms, frame name normalization, and compiled IR insertion of PushCallerFrame / SetCallerLine / PopCallerFrame for panic-line operations.
• Added an ssa test for the exported RuntimeFunc wrapper used by the compiler instrumentation.

Local verification:

• go test -timeout 30m -coverprofile=/tmp/pr1925-cl-ssa-current.cover ./cl ./ssa
  • cl: 94.1% statements
  • ssa: 87.9% statements
• Local patch-coverage estimate for the previously reported source files: 190/195 executable added lines covered (97.4%).
• go test ./test/go -run TestRuntimePanicCallerLineAttribution -count=1
• go test ./test/goroot -run TestGoRoot -goroot "$(go env GOROOT)" -dirs=fixedbugs -case="fixedbugs/(bug347|bug348|issue14646|issue29504|issue4562|issue5856)\\.go$" -count=1 -timeout=30m
• git diff --check

Pushed commit: 5f4113ff2260d056dc9e3bbfe13d00701f91008a.

CI/Codecov are now rerunning on the updated PR head.

[cpunion]

Merged latest xgo-dev/main and fixed the CI build failure from duplicate runtime.Func.FileLine definitions in runtime/internal/lib/runtime/symtab.go.

The single remaining FileLine implementation keeps the panic/caller-line rtdebug.FrameForPC path first, preserves the main-branch clitedebug.Addrinfo file fallback, and removes the duplicate method body. No print/exponent changes were made.

Local verification:

• go test ./cl ./ssa -run 'Test.*Caller|Test.*Panic|Test.*FileLine|TestDoesNotExist' -count=1
• go test ./test/go -run TestRuntimePanicCallerLineAttribution -count=1
• go test ./test/goroot -run TestGoRootRunCases -count=1 -timeout=15m -args -goroot /opt/homebrew/Cellar/go@1.24/1.24.11/libexec -dirs fixedbugs -case '^(fixedbugs/(bug347|bug348|issue14646|issue29504|issue4562|issue5856)\\.go)$' -xfail /dev/null -run-timeout 2m -build-timeout 5m
• git diff --check

Pushed commit: f203cff2db8f664efd454ad23367bd65667c85e6.