Re: non-recursive make: is there a performance gain?

[Jim Meyering]

Jim Meyering wrote:
> Jim Meyering wrote:
> ...
>> On the subject of converting to non-recursive make in lib/,
>> I have at least one problem so far: how can I select different
>> CFLAGS depending on the directory containing the file I'm compiling?
>>
>> As you know, we currently have three different sets of warnings:
>>   - strict, for src/
>>   - less strict, for lib/
>>   - even less strict, for gnulib-tests/
>>
>> I could certainly do that with GNU make by defining
>>
>>   src_CFLAGS = ...
>>   lib_CFLAGS = ...
>>   gnulib-tests_CFLAGS = ...
>>
>> and then including $($(@D)_CFLAGS) in the generic compilation rule.
>>
>> Hmm... maybe override that default rule in cfg.mk, where only GNU make
>> will see it.  Hah!  So the act of writing this question has provided me
>> with the solution:  add these lines to cfg.mk:
>>
>>     COMPILE = $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) \
>>             $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) $($(@D)_CFLAGS)
>>
>>     src_CFLAGS = -WBOGUS
>>
>> That -WBOGUS is just to test, and I confirm that it does what I expect.
>
> Better than that, simply append to $(COMPILE).
> Here's what I'm considering, now:
>
> diff --git a/cfg.mk b/cfg.mk
> index 489f946..039c6ff 100644
> --- a/cfg.mk
> +++ b/cfg.mk
> @@ -558,3 +558,11 @@ exclude_file_name_regexp--sc_prohibit_test_backticks = \
>  # Exempt test.c, since it's nominally shared, and relatively static.
>  exclude_file_name_regexp--sc_prohibit_operator_at_end_of_line = \
>    ^src/(ptx|test|head)\.c$$
> +
> +# Augment GNU make's compilation command to include our per-directory
> +# CFLAGS options:
> +COMPILE += $($(@D)_CFLAGS)
> +
> +src_CFLAGS = $(WARN_CFLAGS)
> +lib_CFLAGS = $(GNULIB_WARN_CFLAGS)
> +gnulib-tests_CFLAGS = $(GNULIB_TEST_WARN_CFLAGS)

We could even add per-basename and per-full-file-name options:

    COMPILE += $($(@D)_CFLAGS) $($(@F)_CFLAGS) $($(@)_CFLAGS)

something I've wanted for a long time.
Of course, this works only with GNU make, so it's fine for
warnings and optimization-related things.