Re: [PATCH 0/8] gitlab: speed up msys windows jobs with GCC

[Thomas Huth <thuth@redhat.com>]

On 01/08/2023 16.35, Daniel P. Berrangé wrote:
> On Tue, Aug 01, 2023 at 03:53:22PM +0200, Markus Armbruster wrote:
>> Daniel P. Berrangé <berrange@redhat.com> writes:
>>
>>> This is an alternative and/or complementary to Thomas' proposal
>>> to use CLang with msys:
>>>
>>>    https://lists.gnu.org/archive/html/qemu-devel/2023-07/msg05402.html
>>>
>>> First of all, the current msys installer we're using is over 12
>>> months out of date. Thus after running the install, pacman then
>>> replaces most of what we've just installed with new downloaded
>>> content. Using the most update installer cuts 3+1/2 minutes off
>>> the msys install time - 7 minutes becomes 3+1/2.
>>>
>>> Secondly, QEMU defaults to compiling with -O2 and this is more
>>> computationally expensive for GCC. Switching to -O0 drops the
>>> build time from 60 minutes down to 45 minutes.
>>
>>  From the fine manual[*]: "The effectiveness of some warnings depends on
>> optimizations also being enabled.  For example '-Wsuggest-final-types'
>> is more effective with link-time optimization and some instances of
>> other warnings may not be issued at all unless optimization is enabled.
>> While optimization in general improves the efficacy of control and data
>> flow sensitive warnings, in some cases it may also cause false
>> positives."  Do we care?
> 
> In general, yes, we do care.
> 
> In this specific case though, we're battling to figure out the lesser
> of multiple evils.

I agree. Additionally, we also test compiling for Windows with the MinGW 
cross compiler suite in a Fedora container, and we still use the default 
optimization there, so we should have that covered.

  Thomas