## 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.

## Assembler {#assembler}

// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package cgotest

import (
	"io"
	"os"
	"path/filepath"
	"strings"
)

// OverlayDir makes a minimal-overhead copy of srcRoot in which new files may be added.
func OverlayDir(dstRoot, srcRoot string) error {
	dstRoot = filepath.Clean(dstRoot)
	if err := os.MkdirAll(dstRoot, 0777); err != nil {
		return err
	}

	return &Arena{a: runtime_arena_newArena()}
}

// Free frees the arena (and all objects allocated from the arena) so that
// memory backing the arena can be reused fairly quickly without garbage
// collection overhead. Applications must not call any method on this
// arena after it has been freed.
func (a *Arena) Free() {
	runtime_arena_arena_Free(a.a)
	a.a = nil
}

pkg crypto/cipher, func NewGCM(Block) (AEAD, error)
pkg crypto/cipher, type AEAD interface { NonceSize, Open, Overhead, Seal }
pkg crypto/cipher, type AEAD interface, NonceSize() int
pkg crypto/cipher, type AEAD interface, Open([]uint8, []uint8, []uint8, []uint8) ([]uint8, error)
pkg crypto/cipher, type AEAD interface, Overhead() int
pkg crypto/cipher, type AEAD interface, Seal([]uint8, []uint8, []uint8, []uint8) []uint8

setting](/pkg/crypto/tls/#ConnectionState.ExportKeyingMaterial).

Go 1.22 changed how the runtime interacts with transparent huge pages on Linux.
In particular, a common default Linux kernel configuration can result in
significant memory overheads, and Go 1.22 no longer works around this default.
To work around this issue without adjusting kernel settings, transparent huge
pages can be disabled for Go memory with the

<p>
it can happen that <code>g</code> prints <code>2</code> and then <code>0</code>.
</p>

<p>
This fact invalidates a few common idioms.
</p>

<p>
Double-checked locking is an attempt to avoid the overhead of synchronization.
For example, the <code>twoprint</code> program might be
incorrectly written as:
</p>

<pre>
var a string
var done bool

func setup() {
	a = "hello, world"
	done = true

  The runtime now keeps type-based garbage collection metadata nearer to each
  heap object, improving the CPU performance (latency or throughput) of Go programs
  by 1–3%.
  This change also reduces the memory overhead of the majority Go programs by
  approximately 1% by deduplicating redundant metadata.
  Some programs may see a smaller improvement because this change adjusts the size