On Sun, Aug 07, 2016 at 10:30:48AM -0700, Andrew Pinski wrote:
> On Mon, Jun 6, 2016 at 3:19 AM, Jan Hubicka <hubi...@ucw.cz> wrote:
> > Hi,
> > while looking into profile mismatches introduced by the backward threading
> > pass
> > I noticed that the heuristics seems quite simplistics. First it should be
> > profile sensitive and disallow duplication when optimizing cold paths.
> > Second
> > it should use estimate_num_insns because gimple statement count is not
> > really
> > very realistic estimate of final code size effect and third there seems to
> > be
> > no reason to disable the pass for functions optimized for size.
> >
> > If we block duplication for more than 1 insns for size optimized paths the
> > pass
> > is able to do majority of threading decisions that are for free and improve
> > codegen.
> > The code size benefit was between 0.5% to 2.7% on testcases I tried
> > (tramp3d,
> > GCC modules, xlanancbmk and some other stuff around my hd).
> >
> > Bootstrapped/regtested x86_64-linux, seems sane?
> >
> > The pass should also avoid calling cleanup_cfg when no trheading was done
> > and i do not see why it is guarded by expensive_optimizations. What are the
> > main compile time complexity limitations?
>
> This patch caused a huge regression (~11%) on coremarks on ThunderX.
> I assume other targets too.
> Basically it looks like the path is no longer thread jumped.
This also caused:
FAIL: gcc.dg/tree-ssa/pr69270-3.c scan-tree-dump-times uncprop1 ", 1" 4
Failures:
gcc.dg/tree-ssa/pr69270-3.c
Bisected to:
Author: hubicka
Date: Sun Aug 7 10:50:16 2016 +0000
* tree-ssa-threadbackward.c: Include tree-inline.h
(profitable_jump_thread_path): Use estimate_num_insns to estimate
size of copied block; for cold paths reduce duplication.
(find_jump_threads_backwards): Remove redundant tests.
(pass_thread_jumps::gate): Enable for -Os.
* gcc.dg/tree-ssa/ssa-dom-thread-7.c: Update testcase.
svn+ssh://gcc.gnu.org/svn/gcc/trunk@239219
On my aarch64-none-linux-gnu and x86_64-none-linux-gnu automatic bisect
robots.
Thanks,
James
