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go/doc/next/5-toolchain.md
David Chase 1028d973d2 doc: add release notes for hot block alignment
This is for the changes in CL 577935.

Change-Id: I8f70dd36c89aaede11a37744c0f279439e01eb13
Reviewed-on: https://go-review.googlesource.com/c/go/+/586895
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
2024-05-20 20:23:04 +00:00

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## 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
accessed in disjoint regions of a function, which reduces stack usage
for Go applications.
<!-- https://go.dev/cl/577935 -->
For 386 and amd64, the compiler will use information from PGO to align certain
hot blocks in loops. This improves performance an additional 1-1.5% at
a cost of an additional 0.1% text and binary size. This is currently only implemented
on 386 and amd64 because it has not shown an improvement on other platforms.
Hot block alignment can be disabled with `-gcflags=[<packages>=]-d=alignhot=0`
## Assembler {#assembler}
## Linker {#linker}