Re: [patch 2/7] enable unit-at-a-time optimisations for gcc4

Jeff Garzik
2006-01-06T17:18:52Z

Arjan van de Ven wrote:
> Subject: allow gcc4 to optimize unit-at-a-time
>
>
> From: Ingo Molnar <mingo@elte.hu>
>
> allow gcc4 compilers to optimize unit-at-a-time.
>
> This flag enables gcc to "see" the entire C file before making optimisation
> decisions such as inline, which results in gcc making better decisions. One
> of the immediate effects of this is that static functions that are used only
> once now get inlined.
>
> gcc 3.4 has this flag as well, however gcc 3.x have a problem with inlining
> and stacks and as a result, enabling this flag there would cause excessive
> and unacceptable stack use. This problem is fixed in the gcc 4.x series.
> The x86-64 architecture already enables this feature so it's well tested
> already.
>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> Signed-off-by: Arjan van de Ven <arjan@infradead.org>

ACK, with a note: gcc also supports limited program-at-a-time -- you
pass multiple .c files on the same command line, and specify a single
output on the command line.

It would be nice to update kbuild to do this for single directory
modules....

Jeff