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

[Stefano Lattarini]

On 09/08/2012 07:46 PM, Jim Meyering wrote:
> Stefano Lattarini wrote:
>> On 09/08/2012 03:29 PM, Jim Meyering wrote:
>>>
>>> But, ... surprise!  So far there is *no* improvement, and in fact a small
>>> penalty in this very worst case:
>>>
>> My wild guess is that the culprit for this might be the Automake-generated
>> recursive make invocation in the handling of $(BUILT_SOURCES):
>>
>>     all: $(BUILT_SOURCES)
>>             $(MAKE) $(AM_MAKEFLAGS) all-am
>>
>> What happens if, after the first build, you substitute the rule above in
>> your Makefile with simply:
>>
>>     all: all-am
>>
>> ? Is there any improvement?
> 
> Good call!  Yes:
> 
> [SNIP]
>
Unfortunately, the extra recursive invocation involving $(BUILT_SOURCES) is
truly needed in order to have correct semantics, because $(BUILT_SOURCES) must
be built before *any* other (direct or indirect) prerequisite of 'all'.
Automake-NG plays dirty tricks to maintain this semantics while avoiding that
recursion, but I haven't been able to come up with a similar trick working also
for portable make.

Regards,
  Stefano