[Bug rtl-optimization/59811] [4.8/4.9 Regression] Huge increase in memory usage and compile time in combine

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59811

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r190594 which apparently made big changes in some of the GIMPLE
passes, e.g. the optimized dump linecount went down from 65782 lines (r190593)
to 52107 lines (r190594).  But, for some reason that change results in
uncomparably more log links and combiner opportunities.
In -fdump-rtl-combine-details dump, 'Successfully match' matches went up from
9742 up to 3921927, and 'Failed to match' matches went up from 53193 to
22538586.
So, the combiner success rate is approximately the same, around 17.5%, just on
400 times more opportunities.
For GIMPLE passes, looking just at the sizes of the gimple dumps, until esra
the sizes are the same, from fre1 the dump with r190594 is slightly to
significantly larger than corresponding r190593 dump until crited, and then
surprisingly the pre dump is on the other side half the size of r190593 dump
and from sink till optimized the dump sizes roughly match the 65782 to 52107
lines.