Richard Biener <rguent...@suse.de> writes:
> After the fix to RPO VN in loop header copying DF via RTL invariant
> motion takes 50% of the compile-time for the second testcase in
> PR46590. This is caused by the DF live problem iterating over
> all dirty blocks for the local problem which is all blocks of
> the function because while loop-invariant uses df_analyze_loop
> it always marks all blocks of the function as dirty via
> df_live_set_all_dirty. One of the possible fixes is to add
> a df_live_set_loop_dirty () function which causes the problem
> to only iterate over one loop blocks.
>
> It turns out the LIVE problem is always present so we cannot
> remove it which in turn means we have to mark blocks possibly
> not visited by invaraint motion as dirty (thus the new
> df_live_set_all_dirty at the end of move_loop_invariants).
>
> Anyhow - I'm not really into how DF should ideally work here
Me neither, but as discussed on IRC, here's alternative that seems
to give a similar speed-up.
- df_live is already present at -O2, so we only need to add it and
mark all blocks dirty for -O
- df_process_deferred_rescans should be enough to force a rescan of
blocks affected by moving invariants, but calling it in find_defs
means that we don't do any rescans for the final loop
Still testing, but posting for comments.
Thanks,
Richard
2019-04-01 Richard Sandiford <richard.sandif...@arm.com>
gcc/
PR rtl-optimization/46950
* loop-invariant.c (find_defs): Move df_remove_problem and
df_process_deferred_rescans to move_invariants.
Move df_live_add_problem and df_live_set_all_dirty calls
to move_invariants.
(move_invariants): Likewise.
(move_loop_invariants): Likewise, making the df_live calls
conditional on -O. Remove the problem again if we added it
locally.
Index: gcc/loop-invariant.c
===================================================================
--- gcc/loop-invariant.c 2019-03-08 18:15:33.704751739 +0000
+++ gcc/loop-invariant.c 2019-04-01 14:09:13.553206345 +0000
@@ -681,11 +681,7 @@ find_defs (struct loop *loop)
loop->num);
}
- df_remove_problem (df_chain);
- df_process_deferred_rescans ();
df_chain_add_problem (DF_UD_CHAIN);
- df_live_add_problem ();
- df_live_set_all_dirty ();
df_set_flags (DF_RD_PRUNE_DEAD_DEFS);
df_analyze_loop (loop);
check_invariant_table_size ();
@@ -1891,6 +1887,10 @@ move_invariants (struct loop *loop)
GENERAL_REGS, NO_REGS, GENERAL_REGS);
}
}
+ /* Remove the DF_UD_CHAIN problem added in find_defs before rescanning,
+ to save a bit of compile time. */
+ df_remove_problem (df_chain);
+ df_process_deferred_rescans ();
}
/* Initializes invariant motion data. */
@@ -2254,6 +2254,11 @@ move_loop_invariants (void)
{
struct loop *loop;
+ if (optimize == 1)
+ {
+ df_live_add_problem ();
+ df_live_set_all_dirty ();
+ }
if (flag_ira_loop_pressure)
{
df_analyze ();
@@ -2286,5 +2291,8 @@ move_loop_invariants (void)
invariant_table = NULL;
invariant_table_size = 0;
+ if (optimize == 1)
+ df_remove_problem (df_live);
+
checking_verify_flow_info ();
}
