[libvirt] [PATCH] tests: improve build time for qemuxml2argvtest

[Daniel P. Berrangé]

On Thu, Nov 28, 2019 at 11:06:12AM +0100, Michal Privoznik wrote:
> On 11/27/19 8:38 PM, Ján Tomko wrote:
> > On Wed, Nov 27, 2019 at 04:22:42PM +0000, Daniel P. Berrangé wrote:
> > > On Fedora 31 with GCC 9.2.1, compiling qemuxml2argvtest takes
> > > about 36 seconds since
> > > 
> > >  commit 30c6d99209cd36bba8e14795622f658827698522
> > >  Author: Jiri Denemark <jdenemar at redhat.com>
> > >  Date:   Thu Oct 24 17:51:42 2019 +0200
> > > 
> > >    qemuxml2argvtest: Update host arch for DO_TEST*ARCH* tests
> > > 
> > > The optimizer is hitting some pathelogical performance behaviour due to
> > 
> > *pathological
> > 
> > > the high number of branches in the mymain() method.
> > > 
> > 
> > Missing bugzilla link:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58479
> > 
> > > Pushing the branch tests down into the testCompareXMLToArgv method
> > > brings the compile time down to 3 seconds.
> > > 
> > 
> > -fno-var-tracking-assignments brings it down even more for me
> > 
> > Can we turn the flag off for tests?
> 
> Don't that hurt us when trying to debug tests?

That seems to be the implication from the info pages on this
option

     Annotate assignments to user variables early in the compilation and
     attempt to carry the annotations over throughout the compilation
     all the way to the end, in an attempt to improve debug information
     while optimizing.  Use of '-gdwarf-4' is recommended along with it.

Even with this enabled by default it is quite painful debugging due
to variables being optimized out, so I'm loathe to make it worse
just to shave off a few seconds.

Regards,
Daniel
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