Re: GDB 8.2 release 2018-08-21 status update

[Pedro Alves <palves@redhat.com>]

On 08/24/2018 08:14 PM, Simon Marchi wrote:
> On 2018-08-24 14:35, Pedro Alves wrote:

>> Unless I'm wrong that
>> -freorder-blocks-and-partition is on by default in GCC 8 already?
> 
> Looking at gcc/doc/invoke.texi, apparently it's been enabled for -O2/-O3 for some time and more recently -Os.  You can check whether it is enabled with:
> 
>   gcc -Q -v --help 2>/dev/null | grep reorder-blocks-and-partition
> 
> I see it as disabled by default and enabled if I add -O2, with different gcc versions between 5.4.0 and 8.2.0.  So it doesn't seem to have changed recently.  Maybe what changed is that gcc 8 partitions more aggressively?  Or it's just that gcc developers tend to debug -O2 builds?  I have no idea.

Here's what Jakub Jelinek had to say about it:

 <palves> is -freorder-blocks-and-partition on by default in any gcc release yet?
 <jakub_> palves: yes, in gcc 8
 <jakub_> palves: for older releases I believe it has been enabled, but due to a bug actually disabled later on, unless -fprofile-use was used
 <jakub_> palves: "-freorder-blocks-and-partition, a pass splitting function bodies into hot and cold regions, is now enabled by default at -O2 and higher for x86 and x86-64." is in gcc.gnu.org/gcc-8/changes.html
 <jakub_> palves: it was added for -fprofile-use initially, and its test coverage was using usually explicit -freorder-blocks-and-partition

Thanks,
Pedro Alves