| Message ID | 56ABA2BA.3030705@redhat.com |
|---|---|
| State | New |
| Headers | show |
On January 29, 2016 6:34:50 PM GMT+01:00, Bernd Schmidt <bschmidt@redhat.com> wrote: >So PR57193 has an example of sub-optimal code generation, with some >unnecessary register moves left after LRA. These seem to be difficult >to >prevent, but last year Robert Suchanek made some modifications to >regrename that allow it to clean up such cases. Enabling >-frename-registers removes one of the two unnecessary copies, and I'm >pretty sure I could make it eliminate the other one as well with a bit >more work. > >Hence, this patch. The renamer has seen a lot of fixes over the years >and should be in pretty good shape IMO. Still, I won't deny that this >is >a bit riskier than the usual bugfix patch at this stage. > >Bootstrapped and tested on x86_64-linux, with my earlier patch to fix >some i386 tests. Thoughts? Should we do this for gcc-7 at least? I don't think it's appropriate at this stage. Richard. > >Bernd
On 01/29/2016 10:34 AM, Bernd Schmidt wrote: > So PR57193 has an example of sub-optimal code generation, with some > unnecessary register moves left after LRA. These seem to be difficult to > prevent, but last year Robert Suchanek made some modifications to > regrename that allow it to clean up such cases. Enabling > -frename-registers removes one of the two unnecessary copies, and I'm > pretty sure I could make it eliminate the other one as well with a bit > more work. > > Hence, this patch. The renamer has seen a lot of fixes over the years > and should be in pretty good shape IMO. Still, I won't deny that this is > a bit riskier than the usual bugfix patch at this stage. > > Bootstrapped and tested on x86_64-linux, with my earlier patch to fix > some i386 tests. Thoughts? Should we do this for gcc-7 at least? invoke.texi has an independent list (probably incomplete! ;( of all the things that -O2 enables. Make sure to add -frename-registers to that list and this is Ok for the trunk (gcc-7). jeff
PR rtl-optimization/57193 * opts.c (default_options_table): Add OPT_frename_registers at -O2 and above. * doc/invoke.texi (-frename-registers): Update documentation. Index: gcc/opts.c =================================================================== --- gcc/opts.c (revision 232689) +++ gcc/opts.c (working copy) @@ -498,6 +498,7 @@ static const struct default_options defa { OPT_LEVELS_2_PLUS, OPT_fstrict_overflow, NULL, 1 }, { OPT_LEVELS_2_PLUS_SPEED_ONLY, OPT_freorder_blocks_algorithm_, NULL, REORDER_BLOCKS_ALGORITHM_STC }, + { OPT_LEVELS_2_PLUS, OPT_frename_registers, NULL, 1 }, { OPT_LEVELS_2_PLUS, OPT_freorder_functions, NULL, 1 }, { OPT_LEVELS_2_PLUS, OPT_ftree_vrp, NULL, 1 }, { OPT_LEVELS_2_PLUS, OPT_ftree_pre, NULL, 1 }, Index: gcc/doc/invoke.texi =================================================================== --- gcc/doc/invoke.texi (revision 232689) +++ gcc/doc/invoke.texi (working copy) @@ -8467,7 +8467,8 @@ debug information format adopted by the make debugging impossible, since variables no longer stay in a ``home register''. -Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}. +Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}, +and also enabled at levels @option{-O2} and @option{-O3}. @item -fschedule-fusion @opindex fschedule-fusion