Re: [PATCH] Append PWD to path when using -fprofile-generate=/some/path.

[Martin Sebor <msebor@gmail.com>]

On 12/20/2017 10:45 AM, Jakub Jelinek wrote:
> On Wed, Dec 20, 2017 at 10:35:44AM -0700, Martin Sebor wrote:
>> On 10/27/2017 07:17 AM, Martin Liška wrote:
>>> Hello.
>>>
>>> It's improvement that I consider still useful even though we're not
>>> going to use
>>> it for profiled bootstrap.
>>>
>>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
>>
>> For what it's worth, although it looks correct as is, I think
>> the code in the patch would be clearer and less prone to off
>> by-1 errors, while at the same time equally as efficient, if
>> it were written in terms of strcpy and strcat:
>>
>>   char *b = XNEWVEC (char,
>>                      2 + strlen (pwd)
>>                      + strlen (profile_data_prefix));
>>
>>   strcpy (b, profile_data_prefix);
>>   strcat (b, "/");
>>   strcat (b, pwd);
>
> I disagree.

Of course you do.

>  One thing is that GCC attempts to optimize even bad code;
> in many cases just can't as soon as there is some call in between etc.,
> the other is that we just shouldn't give bad examples.
> When you know the sizes, we shouldn't be lazy and rely on compiler to figure
> out what we should have written.

It's my turn to disagree now.  We most certainly should be lazy
and rely on our tools and high-level abstractions to do the work
for us.  That's what they're for.

> Though on this case we have a nice
> function for all of that,
>   char *b = concat (profile_data_prefix, "/", pwd, NULL);

Even better (unless this is being lazy ;-)

Martin