cl,ssa,runtime: stack-object finalizer liveness#2036
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Need full explaination in PR body about how this PR works
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Is this funcion safe?
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| func SetFinalizer(obj any, finalizer any) { | ||
| objFace := (*eface)(unsafe.Pointer(&obj)) | ||
| objFace := *(*eface)(unsafe.Pointer(&obj)) |
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Why deref and get addr later? How about remove deref here?
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| func (p *context) compileLateValue(b llssa.Builder, v ssa.Value) llssa.Expr { |
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What's the difference between compileLateValue and compileValue?
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July 21, 2026 01:47
Re-expresses xgo-dev#1906 on the xgo-dev#2023 base (its remaining ~11k diff lines were the pre-xgo-dev#2012 funcinfo draft, superseded by the stage-5 chain): - cl gains a liveness analysis for stack-allocated objects: allocas whose last use has passed are cleared so bdwgc's conservative stack scan stops keeping dead stack objects (and what they point to) alive; pointer registers are clobbered around the trigger points (llgo_clobber_pointer_regs) and dead stack slots holding the target are zeroed (llgo_clear_stack_ptr, pthread stack-bounds walk). - runtime.SetFinalizer paths (mfinal, runtime_gc, bdwgc binding) hook the cleared-slot machinery so finalizers for dead stack objects run. - xfail: retire deferfin.go, stackobj.go, stackobj3.go, validated on darwin/arm64 go1.24 + go1.26 (stackobj2 already passed). Carries the xgo-dev#2035 shared-GOCACHE commit temporarily (same patch-id, auto-dedups when the chain rebases after xgo-dev#2035 merges). Supersedes xgo-dev#1906.
With the shared go-build cache the four heavy test packages (cl, ssa, internal/cabi, test/go) no longer stagger naturally on cold caches; their compile phases overlap fully, and the burst of concurrent clang/lld children has been killing ubuntu runners mid-run (three consecutive 'runner received a shutdown signal' deaths on this branch, each ~8 minutes into the heavy-package phase) and showing up on mac as go-list WaitDelay expirations. -p 2 caps the concurrent package count; wall time is dominated by the cl package either way.
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Re-expresses the surviving value of #1906; its remaining ~11k diff lines were the pre-#2012 funcinfo draft, superseded by the stage-5 chain.
What changes
clgains a liveness analysis over stack allocations; once a stack object's last use has passed, its slot is cleared so bdwgc's conservative stack scan stops keeping the dead object (and everything it points to) alive. Around the trigger points, pointer registers are clobbered (llgo_clobber_pointer_regs) and dead stack slots still holding the target are zeroed (llgo_clear_stack_ptr, pthread stack-bounds walk on darwin/linux).runtime.SetFinalizerconformance: mfinal/runtime_gc/bdwgc-binding hook the cleared-slot machinery, so finalizers for dead stack objects actually run (gc semantics).clliveness unit suite +test/gofinalizer regressions.goroot conformance
Retired xfails, validated darwin/arm64 (go1.24 + go1.26) and linux/arm64 (go1.24):
deferfin.go,stackobj.go,stackobj3.go(stackobj2.goalready passed and stays green).Validation
ssa(128s) andcl(389s) suites green (no golden drift — the analysis only clears dead slots, existing goldens unchanged);test/goFinalizer set green underllgo test.The existing multi-package coverage command is capped at
-p 2to avoid overlapping the heaviest compiler test packages. The current main test matrix and the separatetest/gocoverage command are otherwise unchanged.Supersedes #1906.
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