# build succeeds without PGO when default.pgo file is absent
go build -n -pgo=auto -o nopgo.exe ./nopgo
stderr 'compile.*nopgo.go'
! stderr 'compile.*-pgoprofile'

# check that pgo doesn't appear in build info
! stderr 'build\\t-pgo='

# other build-related commands
go install -a -n -pgo=auto ./a/a1
stderr 'compile.*-pgoprofile=.*a1.go'

go run -a -n -pgo=auto ./a/a1
stderr 'compile.*-pgoprofile=.*a1.go'

# Test go build -pgo=auto flag with multiple main packages.

go install -a -n -pgo=auto ./a ./b ./nopgo

# a/default.pgo and b/default.pgo are both preprocessed
stderr 'preprofile.*-i.*a(/|\\\\)default\.pgo'
stderr 'preprofile.*-i.*b(/|\\\\)default\.pgo'

# a and b built once each with PGO.
# Ideally we would check that the passed profile is the expected profile (here
# and for dependencies). Unfortunately there is no nice way to map the expected

# Test that pgo properly splits off the Imports field so that list doesn't alias
# the non-pgo variant's slice when it modifies the pgo variant's Imports field to
# add the [.ForMain] suffix.

go list -f 'ImportPath: "{{.ImportPath}}", Imports: "{{.Imports}}", ImportMap: "{{.ImportMap}}"' m/a m/b
cmp stdout want

-- want --
ImportPath: "m/a", Imports: "[m/b [m/a]]", ImportMap: "map[m/b:m/b [m/a]]"
ImportPath: "m/b", Imports: "[m/c]", ImportMap: "map[]"

# Test go build -pgo flag.
# Specifically, the build cache handles profile content correctly.

[short] skip 'compiles and links executables'

# Set up fresh GOCACHE.
env GOCACHE=$WORK/gocache
mkdir $GOCACHE

# build without PGO
go build triv.go

# build with PGO, should trigger rebuild
# starting with an empty profile (the compiler accepts it)
go build -x -pgo=prof -o triv.exe triv.go
stderr 'preprofile.*-i.*prof'

mkdir $GOCACHE

# Building trivial non-main package should run preprofile the first time.
go build -x -pgo=default.pgo lib.go
stderr 'preprofile.*default\.pgo'

# ... but not again ...
go build -x -pgo=default.pgo lib.go
! stderr 'preprofile.*default\.pgo'

# ... unless we use -a.
go build -a -x -pgo=default.pgo lib.go
stderr 'preprofile.*default\.pgo'

# ... building a different package should not run preprofile again, instead

## Compiler {#compiler}

The build time overhead to building with [Profile Guided Optimization](/doc/pgo) has been reduced significantly.
Previously, large builds could see 100%+ build time increase from enabling PGO.
In Go 1.23, overhead should be in the single digit percentages.

<!-- https://go.dev/issue/62737 , https://golang.org/cl/576681,  https://golang.org/cl/577615 -->
The compiler in Go 1.23 can now overlap the stack frame slots of local variables

// during PGO in the compiler. This transformation depends only on the profile
// itself and is thus wasteful to perform in every invocation of the compiler.
//
// Usage:
//
//	go tool preprofile [-v] [-o output] -i input
//
//

package main

import (
	"bufio"
	"cmd/internal/objabi"
	"cmd/internal/pgo"
	"cmd/internal/telemetry"
	"flag"
	"fmt"
	"log"
	"os"

// Also ignore test files.
var ignoreSuffixes = []string{
	"_test.s",
	"_test.go",
	// Skip PGO profile. No need to build toolchain1 compiler
	// with PGO. And as it is not a text file the import path
	// rewrite will break it.
	".pgo",
	// Skip editor backup files.
	"~",
}

var tryDirs = []string{
	"sdk/go1.17",
	"go1.17",
}

	HotPgo                           // By PGO-based heuristics, this block occurs in a hot loop

	HotNot                 = 0
	HotInitialNotFlowIn    = HotInitial | HotNotFlowIn          // typically first block of a rotated loop, loop is entered with a branch (not to this block).  No PGO

	return b.build(ctx, a)
}

// pgoActionID computes the action ID for a preprocess PGO action.
func (b *Builder) pgoActionID(input string) cache.ActionID {
	h := cache.NewHash("preprocess PGO profile " + input)

	fmt.Fprintf(h, "preprocess PGO profile\n")
	fmt.Fprintf(h, "preprofile %s\n", b.toolID("preprofile"))
	fmt.Fprintf(h, "input %q\n", b.fileHash(input))

	return h.Sum()