[Bug fortran/48636] Enable more inlining with -O2 and higher

["jamborm at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48636

--- Comment #15 from Martin Jambor <jamborm at gcc dot gnu.org> 2012-07-03 17:43:35 UTC ---
Hi,

(In reply to comment #12)
> Hi,
> I discussed some of the issues today with Martin.  For the array descriptor
> testcase, we really want ipa-cp to be propagate the constant array bounds
> instead of making Inliner to blindly inline enough in all cases.
> For that we need
> 
>   1) Make ipa-prop to work on aggregates.  For aggregates passed by value we
> can have jump functions that define known constants at known offsets

I have posted a patch implementing this yesterday:
http://gcc.gnu.org/ml/gcc-patches/2012-07/msg00039.html

>   2) Make ipa-inline-analysis to produce predicates on constantness of
> aggregate fields in the same format

I have posted a patch implementing this yesterday too:
http://gcc.gnu.org/ml/gcc-patches/2012-07/msg00041.html

With this patch, the test case from comment #4 is inlined at -O3
without any parameter tweaking.  It is in fact a testcase in that
patch.  However, functions in real benchmarks are bigger.  We will see
to what extent IPA-CP can help with them.

>   3) Array descriptors are passed by reference, rather than by value.  This
> need further work, since need to be sure that the value passed does not change
> by aliasing.  IPA-SRA would help here if it was really SRA and we had
> -fwhole-program, but that is weak. We would need IPA-PTA to solve this in
> general. Perhaps frontend could help us here since the descriptors are probably
> constant after they are initialized, or is there way to change existing
> descriptor?

At the moment I'm relying on a slightly sophisticated intra-PTA and
TBAA.  I'll try to investigate where this does not work in Fortran and
perhaps will have some suggestions afterwards.

>   4) Make ipa-inline-analysis to understand that determining loop bounds is
> very cool to do.

Yep, knowing what constants should get a profitability "boost" would
be indeed very beneficial.

Meanwhile, the following patch also helps ipa-inline-analysis.c with
cases like fatigue2:
http://gcc.gnu.org/ml/gcc-patches/2012-07/msg00052.html