[go] cmd/compile: treat singly-assigned func vars as static in escape analysis

0 views

Skip to first unread message

Keith Randall (Gerrit)

unread,

May 15, 2026, 12:50:00 PM (16 hours ago) May 15

to Keith Randall, Jake Bailey, goph...@pubsubhelper.golang.org, golang-...@googlegroups.com, Dmitri Shuralyov, Dmitri Shuralyov, Keith Randall, golang...@luci-project-accounts.iam.gserviceaccount.com, Mateusz Poliwczak, Alan Donovan, David Chase, t hepudds, golang-co...@googlegroups.com

Keith Randall submitted the change

Change information

Commit message:

cmd/compile: treat singly-assigned func vars as static in escape analysis

When a function variable is declared without an initializer and then
assigned exactly once, escape analysis cannot identify the callee:

    var f func(*int)
    f = func(p *int) {}  // callee not visible to StaticValue
    f(new(int))          // new(int) conservatively escapes

This pattern is common for recursive closures:

    var visit func(*Node)
    visit = func(n *Node) {
        for _, child := range n.Children {
            visit(child)
        }
    }
    visit(root)

There is a trick we can use here: a nil func cannot be called, because
it panics, and a panic cannot cause anything to escape. So for
variables declared without an initializer and assigned exactly once, we
can treat that single assignment as the static value for escape
analysis purposes, since the only other possible value (nil) is a dead
end.

Add ir.FuncSingleAssignment to find such singly-assigned func variables,
and use it as a fallback in escape analysis when StaticCalleeName fails.
This is restricted to func-typed variables only: tracking all local
variables is too expensive, and only func-typed variables benefit from
callee resolution. A future CL will instead do this in the "oracle",
but I am splitting that up as I think it is wasteful to do that and
then not use it to replace StaticValue, but apparently that has its
own issues.

This optimization resolves callees 7 times in std, 100 times in cmd,
51 times in github.com/microsoft/typescript-go, 276 times in x/tools,
and 547 times in x/tools/gopls. Most resolutions improve parameter
escape precision; of those, 5 heap allocations are eliminated in
std/cmd, 6 in x/tools, 5 in x/tools/gopls, and 16 in typescript-go.

compilebench results (this CL vs parent):

                         │         sec/op          │     sec/op      vs base              │
Template                              157.8m ±  6%     157.9m ± 10%       ~ (p=0.699 n=6)
Unicode                               121.7m ± 12%     122.1m ±  4%       ~ (p=0.589 n=6)
GoTypes                               897.4m ±  5%     902.5m ±  3%       ~ (p=0.937 n=6)
Compiler                              163.1m ±  5%     162.4m ±  2%       ~ (p=0.818 n=6)
SSA                                    7.269 ±  2%      7.177 ±  1%       ~ (p=0.699 n=6)
Flate                                 167.6m ±  5%     167.7m ± 14%       ~ (p=1.000 n=6)
GoParser                              180.5m ±  5%     179.1m ±  5%       ~ (p=1.000 n=6)
Reflect                               399.5m ±  2%     411.2m ±  7%       ~ (p=0.310 n=6)
Tar                                   172.2m ±  7%     180.0m ±  9%       ~ (p=0.699 n=6)
XML                                   201.1m ±  6%     197.4m ±  4%       ~ (p=0.699 n=6)
LinkCompiler                          675.7m ±  2%     672.7m ±  2%       ~ (p=0.485 n=6)
ExternalLinkCompiler                   2.313 ±  2%      2.330 ±  1%       ~ (p=0.394 n=6)
LinkWithoutDebugCompiler              430.5m ±  3%     430.9m ±  6%       ~ (p=0.818 n=6)
StdCmd                                 30.43 ±  5%      30.31 ±  2%       ~ (p=0.699 n=6)
geomean                               539.1m           540.6m        +0.28%

Updates #59708
Fixes #70171

Change-Id: I6b701748f05f62376a46bc811181698d8ef76d47

Reviewed-on: https://go-review.googlesource.com/c/go/+/771160

Reviewed-by: Keith Randall <k...@golang.org>

Reviewed-by: Keith Randall <k...@google.com>

Reviewed-by: Mateusz Poliwczak <mpoliw...@gmail.com>

Reviewed-by: Dmitri Shuralyov <dmit...@google.com>

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

Files:

M src/cmd/compile/internal/escape/call.go
M src/cmd/compile/internal/ir/expr.go
M test/escape_closure.go

Change size: M

Delta: 3 files changed, 204 insertions(+), 0 deletions(-)

Branch: refs/heads/master

Submit Requirements:

Code-Review: +1 by Mateusz Poliwczak, +2 by Keith Randall, +1 by Keith Randall, +1 by Dmitri Shuralyov
TryBots-Pass: LUCI-TryBot-Result+1 by golang...@luci-project-accounts.iam.gserviceaccount.com

Open in Gerrit

Inspect html for hidden footers to help with email filtering. To unsubscribe visit settings.

Gerrit

open

diffy

satisfied_requirement

Reply all

Reply to author

Forward

0 new messages