Re: [Buildroot] [PATCH 04/16 v2] package/infras: do not conditionally set empty variables

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

On Sat, 13 Nov 2021 14:28:15 +0100
"Yann E. MORIN" <yann.morin.1998@free.fr> wrote:

> Setting an unset variable to an empty value is useless in make; an unset
> variable just expands to an empty string anyway. So what we do currently
> has no side effect:
> 
>     variable set and not empty   -> variable not modified
>     variable set and empty       -> variable not modified
>     variable unset               -> set to an empty string
> 
> However, additional variables do have an impact on the parsing time of
> the Makefiles, and the more variables, the more collisions in the hash
> table used internally by make, which slows down the parsing.
> 
> By dropping those conditionally-set-empty variables, we gain about 3%:
> 
>     Run     Before  After
>     1       5.572   5.325
>     2       5.434   5.354
>     3       5.490   5.320
>     4       5.525   5.330
>     5       5.476   5.330
>     6       5.511   5.434
>     7       5.498   5.388
>     8       5.524   5.371
>     9       5.479   5.346
>     10      5.637   5.324
>     Mean:   5.515   5.352
> 
> Yeah, 0.163s does not look like much, and this does not make
> autocompletion any more usable. Still, that 3% gain is not to be
> ashamed of either.
> 
> Note that there are 3 others case where we do set empty variables, but
> those are unconditional and serve other purposes:
> 
>   - pkg-virtual: this is done on purpose to avoid a bug when the
>     environment may have TOOLCHAIN_VERSION or _SOURCE set, and we really
>     want those to be empty, so the assignment is not conditional;
> 
>   - pkg-python: the reason for setting those to empty is dubious at
>     best; it's been there since the inception of the python infra, back
>     in 2013; still, the case is different than this patch addresses;
> 
>   - pkg-toolchain-external: this is the case for a toolchain already
>     installed, so indeed we want to set _SOURCE and _VERSION to empty.
> 
> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
> Cc: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
> Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
> ---
>  package/pkg-autotools.mk |  4 ----
>  package/pkg-cmake.mk     |  4 ----
>  package/pkg-generic.mk   | 27 ---------------------------
>  package/pkg-kconfig.mk   |  3 ---
>  package/pkg-meson.mk     |  4 ----
>  package/pkg-python.mk    |  4 ----
>  package/pkg-qmake.mk     |  4 ----
>  package/pkg-waf.mk       |  5 -----
>  8 files changed, 55 deletions(-)

Applied to master, thanks.

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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