diff mbox series

[v2,2/3] doc: -falign-functions is ignored under -Os

Message ID 20221011210156.7710-3-palmer@rivosinc.com
State New
Headers
Series doc: -falign-functions improvements |

Commit Message

Palmer Dabbelt Oct. 11, 2022, 9:01 p.m. UTC 
  This is implicitly mentioned in the docs, but there were some questions
in a recent patch.  This makes it more exlicit that -falign-functions is
meant to be ignored under -Os.

gcc/doc/ChangeLog

	* invoke.texi (-falign-functions): Mention -Os
---
 gcc/doc/invoke.texi | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Eric Gallager Oct. 11, 2022, 10:15 p.m. UTC | #1 
On Tue, Oct 11, 2022 at 5:03 PM Palmer Dabbelt <palmer@rivosinc.com> wrote:
>
> This is implicitly mentioned in the docs, but there were some questions
> in a recent patch.  This makes it more exlicit that -falign-functions is
> meant to be ignored under -Os.
>
> gcc/doc/ChangeLog
>
>         * invoke.texi (-falign-functions): Mention -Os

Since there's -Oz now, too, should that be mentioned as well?

> ---
>  gcc/doc/invoke.texi | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 8326a60dcf1..a24798d5029 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -13164,7 +13164,8 @@ equivalent and mean that functions are not aligned.
>  If @var{n} is not specified or is zero, use a machine-dependent default.
>  The maximum allowed @var{n} option value is 65536.
>
> -Enabled at levels @option{-O2}, @option{-O3}.
> +Enabled at levels @option{-O2}, @option{-O3}.  This has no behavior under under
> +@option{-Os}.
>
>  @item -flimit-function-alignment
>  If this option is enabled, the compiler tries to avoid unnecessarily
> --
> 2.34.1
>
Jan Hubicka Oct. 12, 2022, 7:24 a.m. UTC | #2 
> This is implicitly mentioned in the docs, but there were some questions
> in a recent patch.  This makes it more exlicit that -falign-functions is
> meant to be ignored under -Os.
> 
> gcc/doc/ChangeLog
> 
> 	* invoke.texi (-falign-functions): Mention -Os
> ---
>  gcc/doc/invoke.texi | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 8326a60dcf1..a24798d5029 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -13164,7 +13164,8 @@ equivalent and mean that functions are not aligned.
>  If @var{n} is not specified or is zero, use a machine-dependent default.
>  The maximum allowed @var{n} option value is 65536.
>  
> -Enabled at levels @option{-O2}, @option{-O3}.
> +Enabled at levels @option{-O2}, @option{-O3}.  This has no behavior under under
> +@option{-Os}.

Maybe we could instead say that the function alignment is included for
functions optimized for size.

This can happen by -Os, -Oz, cold attribute
or because we auto-detect function as cold (i.e. it unavoidably leads to
abort or is only called on such paths)

It would be also nice to mention that for other alignment options (align
jumps, loops and labels are ignored when given jump, loop or label is
optimized for size).

Honza
>  
>  @item -flimit-function-alignment
>  If this option is enabled, the compiler tries to avoid unnecessarily
> -- 
> 2.34.1
>
diff mbox series

Patch

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 8326a60dcf1..a24798d5029 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -13164,7 +13164,8 @@  equivalent and mean that functions are not aligned.
 If @var{n} is not specified or is zero, use a machine-dependent default.
 The maximum allowed @var{n} option value is 65536.
 
-Enabled at levels @option{-O2}, @option{-O3}.
+Enabled at levels @option{-O2}, @option{-O3}.  This has no behavior under under
+@option{-Os}.
 
 @item -flimit-function-alignment
 If this option is enabled, the compiler tries to avoid unnecessarily