Re: [7606] shell builtin "test" not invoked if appears alone

[kabe]

address@hidden sed in <address@hidden>:

>> %% <address@hidden> writes:
>> 
>>   >>> any other special character that would cause make to kick the command 
>> to
>>   >>> the slow path?
>> 
>>   k> BTW Solaris /bin/test is a shellscript which is merly `basename $0`
>>   k> "$@" so on platforms like this, the slow path (sh -c test) should
>>   k> be faster.
>> 
>> Why faster?  This means make invokes a shell, which invokes a shell,
>> which invokes basename.

On a builtin "test" platform,
"sh -c test" invokes builtin "test", never the /bin/test script.
exec()ing a shellscript /bin/test will invoke "sh /bin/test" inside exec(),
read the /bin/test script, then basename, so a bit slower actually.
(sh -c /bin/test will be the slowest path as you point out)


Even if binary /bin/test is provided, modern shells having builtin "test"
will actually gain a bit by "sh -c test", given /bin/sh is 
likely live in the cache. /bin/test is never consulted here.

The only case the patch will degrade performance is ancient platforms
which doesn't have "test" as a builtin and needs /bin/test binary,
or the binary /bin/test is way faster than shell builtin and
bare "test" is used a lot. (unlikely)


I could be overlooking something; feel free for corrections.

>> Speed isn't a premium for bare "test", but over the lifetime of a large
>> build you can get noticeable savings by avoiding shell invocations where
>> possible.  A large build without a fast path can involve many thousands
>> of extra shells being invoked.
>> 
>> It's quite obviously not worth doing anything gross like figuring out
>> whether the command is "test", whether "test" exists on the PATH, or
>> whether it's a shell script, or anything like that.

I don't think the fix will penalize in Real World, because
- As you thought, bare "test" is rare
- Real World Makefiles will have ||, &&, if - fi whatever after it
  because you usually want to do something according to "test" result.
  It had been fallbacking to slow path anyway.
-- 
kabe