go-force-inline

A Go CLI tool that generates synthetic PGO (Profile-Guided Optimization) profiles from source code directives. Annotate call sites with //pgogen:hot comments to force the Go compiler's PGO inliner to treat them as hot, increasing the inlining budget from 80 to 2000 AST nodes.

Important

NOTE: While this tool can help with speeding up, some notes:

1. The tool generates synthetic profiles, This can't really replace real PGO profiles, and is potentially alot more work.
   1. however with fast moving codebases, this can help with keeping up being fast(er)
   2. It can collide with real PGO profiles, so be careful when using both
2. The tool is not perfect, and can miss some call sites, or generate invalid profiles

Setup

Add the tool to your project:

go get -tool github.com/daanv2/go-force-inline@latest

Usage

Annotate your code

Place //pgogen:hot on the line immediately above a function call:

func handler(r *Request) *Response {
    //pgogen:hot weight=10000
    result := processRequest(r)

    //pgogen:hot
    validated := validateInput(r.Body)

    return buildResponse(result, validated)
}

The weight parameter is optional (default: 10000).

Generate the profile

go tool github.com/daanv2/go-force-inline generate ./...

Flag	Description
-o, --output	Output file path (default: default.pgo)

Build with PGO

The Go toolchain auto-detects default.pgo in the module root:

go build ./...

Or specify it explicitly:

go build -pgo=default.pgo ./...

Verify a profile

Inspect which edges in a profile are considered hot:

go tool github.com/daanv2/go-force-inline verify default.pgo

Flag	Description
--threshold	CDF hot threshold percentage (default: 99.0)

Output:

Edge                                          Weight    CDF%   Hot?
----                                          ------    ----   ----
main.handler → main.processRequest           10000    50.0%   yes
main.handler → main.validateInput            10000   100.0%   yes

Total weight: 20000
Hot threshold: 99% (cumulative weight < 19800)

Global flags

Flag	Description
--log-level	Log level: debug, info, warn, error, fatal (default: info)
--log-format	Log format: text, json, logfmt (default: text)
--log-file	Write logs to a file
--log-report-caller	Include source file in log output

Warnings

The tool warns about situations where forced inlining won't work:

• Directive not followed by a call expression
• Callee has //go:noinline (PGO won't override it)
• Interface method calls (cannot be inlined)
• Calls inside closures (fragile naming)
• Chained calls on one line (ambiguous target)