On Mon, 10 Feb 2025, Richard Biener wrote:
> On Mon, 10 Feb 2025, Richard Biener wrote:
>
> > The following addresses the fact that we keep an excessive amount of
> > redundant DEBUG BEGIN_STMTs - in the testcase it sums up to 99.999%
> > of all stmts, sucking up compile-time in IL walks. The patch amends
> > the GIMPLE DCE code that elides redundant DEBUG BIND stmts, also
> > pruning uninterrupted sequences of DEBUG BEGIN_STMTs, keeping only
> > the last one.
> >
> > Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
> >
> > For the testcase this brings down compile-time to 150% of -g0 levels
> > (and only 215 out of originally 1981380 DEBUG BEGIN_STMTs kept).
> >
> > OK for trunk and possibly backports?
>
> It regresses a few guality checks (and progresses one), I've looked
> only into one, g++.dg/guality/pr67192.C, where we now see
> FAIL: g++.dg/guality/pr67192.C -O[123sg] line 54 cnt == 15
> because the breakpoint happens in the wrong place. But this shows
> it "works" only by accident. The testcase is
>
> __attribute__((noinline, noclone)) static void
> f4 (void)
> {
> while (1) /* { dg-final { gdb-test 54 "cnt" "15" } } */
> if (last ())
> break;
> else
> do_it ();
> do_it (); /* { dg-final { gdb-test 59 "cnt" "20" } } */
> }
>
> and we have two BEGIN_STMTs for line 54(!) originally:
>
> [/space/rguenther/src/gcc/gcc/testsuite/g++.dg/guality/pr67192.C:54:3] #
> DEBUG BEGIN_STMT
> <D.2884>:
> [/space/rguenther/src/gcc/gcc/testsuite/g++.dg/guality/pr67192.C:55:5] #
> DEBUG BEGIN_STMT
> ...
> [/space/rguenther/src/gcc/gcc/testsuite/g++.dg/guality/pr67192.C:54:3] #
> DEBUG BEGIN_STMT
> [/space/rguenther/src/gcc/gcc/testsuite/g++.dg/guality/pr67192.C:55:5]
> goto <D.2884>;
>
> and special code in make_blocks() moves the first BEGIN_STMT after
> the label, altering when we reach a breakpoint on the line.
>
> You can see that with the first BEGIN_STMT moved the patch will elide it,
> and gdb will find the second location.
>
> With removing only repeating BEGIN_STMT with exactly
> the same location (unfortunately with uint64_t a bitmap no longer
> works), we're "only" down to 996 BEGIN_STMTs for the testcase.
>
> So I'm retesting the following.
Bootstrapped and tested on x86_64-unknown-linux-gnu without
regressions this time.
Alex, is this OK for trunk?
Thanks,
Richard.
> Richard.
>
> From 38d49d3e2c0bf98e9e2a46e251ae0454b084cc8d Mon Sep 17 00:00:00 2001
> From: Richard Biener <rguent...@suse.de>
> Date: Mon, 10 Feb 2025 10:23:45 +0100
> Subject: [PATCH] middle-end/118801 - excessive redundant DEBUG BEGIN_STMT
> To: gcc-patches@gcc.gnu.org
>
> The following addresses the fact that we keep an excessive amount of
> redundant DEBUG BEGIN_STMTs - in the testcase it sums up to 99.999%
> of all stmts, sucking up compile-time in IL walks. The patch amends
> the GIMPLE DCE code that elides redundant DEBUG BIND stmts, also
> pruning uninterrupted sequences of DEBUG BEGIN_STMTs, keeping only
> the last of each set of DEBUG BEGIN_STMT with unique location.
>
> PR middle-end/118801
> * tree-ssa-dce.cc (eliminate_unnecessary_stmts): Prune
> sequences of uninterrupted DEBUG BEGIN_STMTs, keeping only
> the last of a set with unique location.
> ---
> gcc/tree-ssa-dce.cc | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
> index be21a2d0b50..461283ba858 100644
> --- a/gcc/tree-ssa-dce.cc
> +++ b/gcc/tree-ssa-dce.cc
> @@ -1508,6 +1508,7 @@ eliminate_unnecessary_stmts (bool aggressive)
>
> /* Remove dead statements. */
> auto_bitmap debug_seen;
> + hash_set<int_hash <location_t, 0>> locs_seen;
> for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi = psi)
> {
> stmt = gsi_stmt (gsi);
> @@ -1670,6 +1671,15 @@ eliminate_unnecessary_stmts (bool aggressive)
> remove_dead_stmt (&gsi, bb, to_remove_edges);
> continue;
> }
> + else if (gimple_debug_begin_stmt_p (stmt))
> + {
> + /* We are only keeping the last debug-begin in a series of
> + debug-begin stmts. */
> + if (locs_seen.add (gimple_location (stmt)))
> + remove_dead_stmt (&gsi, bb, to_remove_edges);
> + continue;
> + }
> + locs_seen.empty ();
> bitmap_clear (debug_seen);
> }
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
