[Buildroot] [git commit] Config.in: add -Ofast option
Joshua Henderson
joshua.henderson at microchip.com
Thu Apr 5 21:46:47 UTC 2018
Thomas, All,
On 03/26/2018 01:19 PM, Thomas Petazzoni wrote:
> commit: https://git.buildroot.net/buildroot/commit/?id=ed6a7e18af8f4dfddee6e6b144f20dfaf6926315
> branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/master
>
> -Ofast (introduced in GCC 4.6) It combines the existing optimization level -O3
> with options that can affect standards compliance but result in better optimized
> code. For example, -Ofast enables -ffast-math.
>
> Signed-off-by: Joshua Henderson <joshua.henderson at microchip.com>
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni at bootlin.com>
> ---
> Config.in | 11 +++++++++++
> package/Makefile.in | 3 +++
> 2 files changed, 14 insertions(+)
>
> diff --git a/Config.in b/Config.in
> index 0002df5176..037ea2265b 100644
> --- a/Config.in
> +++ b/Config.in
> @@ -527,6 +527,17 @@ config BR2_OPTIMIZE_S
> -ftree-vect-loop-version
> This is the default.
>
> +config BR2_OPTIMIZE_FAST
> + bool "optimize for fast"
> + depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_6
> + help
> + Optimize for fast. Disregard strict standards
> + compliance. -Ofast enables all -O3 optimizations. It also
> + enables optimizations that are not valid for all
> + standard-compliant programs. It turns on -ffast-math and the
> + Fortran-specific -fstack-arrays, unless -fmax-stack-var-size
> + is specified, and -fno-protect-parens.
> +
> endchoice
>
...
For reference, I just found an unfriendly package with this option.
sqlite3.c: In function ‘sqlite3IsNaN’:
sqlite3.c:28554:3: error: #error SQLite will not work correctly with the -ffast-math option of GCC.
# error SQLite will not work correctly with the -ffast-math option of GCC.
^
Makefile:541: recipe for target 'sqlite3.lo' failed
sqlite3 refuses to be built with -ffast-math (a side effect of -Ofast) when it
falls back to implementing its own isnan() function. From what I can see,
SQLITE_HAVE_ISNAN can be defined [1] to make it use the system library isnan().
But, how to tell if the system library supports a proper isnan() seems to open
up a whole new can of worms. Thoughts?
[1]: https://www.sqlite.org/compile.html
Josh
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