Re: Bison 3.0 updates

On 2013-07-29 08:02:49 -0400, Tom Lane wrote:
> Andres Freund <andres@2ndquadrant.com> writes:
> > On 2013-07-29 07:11:13 -0400, Stephen Frost wrote:
> >> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
> >>> The bottom line was:
> >>> It looks like our choices are (1) teach configure to enable
> >>> -fno-aggressive-loop-optimizations if the compiler recognizes it,
> >>> or (2) back-port commit 8137f2c32322c624e0431fac1621e8e9315202f9.
> >>> 
> >>> I am in favor of fixing the back branches via (1), because it's less
> >>> work and much less likely to break third-party extensions.  Some other
> >>> people argued for (2), but I've not seen any patch emerge from them,
> >>> and you can bet I'm not going to do it.
> 
> >> Yea, just passing -fno-aggressive-loop-optimizations seems like the
> >> safest and best option to me also..
> 
> > I think we need to do both. There very well might be other optimizations
> > made based on the unreachability information.
> 
> If we turn off the optimization, that will fix any other cases as well,
> no?  So why would we risk breaking third-party code by back-porting the
> struct declaration changes?

The -fno-agressive-loop thingie afaics only controls the optimization
with regard to loopey constructs, not in general. I *think* there are
independent hazards with general unreachability detection. Not sure
whether they trigger at -O2 or only at -O3 though.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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