[tools] go/ssa: avoid allocations on the MethodValue hit path

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Gopher Robot (Gerrit)

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Sep 25, 2026, 4:19:16 PMSep 25

to Hung Chuang, Gerrit Bot, goph...@pubsubhelper.golang.org, golang-...@googlegroups.com, golang...@luci-project-accounts.iam.gserviceaccount.com, Alex Putman, Alan Donovan, golang-co...@googlegroups.com

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Commit message:

go/ssa: avoid allocations on the MethodValue hit path

MethodValue is called once per (call site, concrete type) pair by RTA
and VTA, and nearly every call finds a Function it already created.
Three things still allocated on that path.

A builder was declared before the critical section and captured by
the closure, so it escaped to the heap on every call. The closure now
returns a builder only when it created a Function; a hit returns nil
and allocates nothing.

waitForSharedFunction allocated a task and a channel before checking
whether the function was already built, and iterate then closed and
waited on them. It now checks first.

The method table was keyed by Id(), which builds a new string for
every unexported method. Key it by (package path, name) instead,
which is the same equivalence without the concatenation. LookupMethod
uses the same key, so its fast path stops allocating too.

TestMethodValueNoAlloc checks with testing.AllocsPerRun that neither
MethodValue nor LookupMethod allocates once the method exists, for an
exported method, an unexported one, and a wrapper.

Updates golang/go#81308

Change-Id: Ib2dbbec10561672166436a882d555ba9a078fe6a

GitHub-Last-Rev: e40b3b08dd2140f864fe105f72b808a0aedc078e

GitHub-Pull-Request: golang/tools#687

Reviewed-on: https://go-review.googlesource.com/c/tools/+/836845

Reviewed-by: Alan Donovan <adon...@google.com>

Reviewed-by: Alex Putman <apu...@golang.org>

Auto-Submit: Alan Donovan <adon...@google.com>

LUCI-TryBot-Result: golang...@luci-project-accounts.iam.gserviceaccount.com <golang...@luci-project-accounts.iam.gserviceaccount.com>

Files:

M go/ssa/builder.go
M go/ssa/methods.go
M go/ssa/methods_test.go

Change size: M

Delta: 3 files changed, 132 insertions(+), 37 deletions(-)

Branch: refs/heads/master

Submit Requirements:

Code-Review: +2 by Alan Donovan, +2 by Alex Putman
Review-Enforcement: Code-Review+2 by Alan Donovan, Code-Review+2 by Alex Putman
TryBots-Pass: LUCI-TryBot-Result+1 by golang...@luci-project-accounts.iam.gserviceaccount.com

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