On 10/5/22 14:04, Jørgen Kvalsvik via Gcc-patches wrote:
> Edges with locus are candidates for splitting so that the edge with
> locus is the only edge out of a basic block, except when the locuses
> match. The test checks the last (non-debug) statement in a basic block,
> but this causes an unnecessary split when the edge locus go to a block
> which coincidentally has an unrelated label. Comparing the first
> statement of the destination block is the same check but does not get
> tripped up by labels.
>
> An example with source/edge/dest locus when an edge is split:
>
> 1 int fn (int a, int b, int c) {
> 2 int x = 0;
> 3 if (a && b) {
> 4 x = a;
> 5 } else {
> 6 a_:
> 7 x = (a - b);
> 8 }
> 9
> 10 return x;
> 11 }
>
> block file line col stmt
>
> src t.c 3 10 if (a_3(D) != 0)
> edge t.c 6 1
> dest t.c 6 1 a_:
>
> src t.c 3 13 if (b_4(D) != 0)
> edge t.c 6 1
> dst t.c 6 1 a_:
>
> With label removed:
>
> 1 int fn (int a, int b, int c) {
> 2 int x = 0;
> 3 if (a && b) {
> 4 x = a;
> 5 } else {
> 6 // a_: <- label removed
> 7 x = (a - b);
> 8 }
> 9
> 10 return x;
> 11
>
> block file line col stmt
>
> src t.c 3 10 if (a_3(D) != 0)
> edge (null) 0 0
> dest t.c 6 1 a_:
>
> src t.c 3 13 if (b_4(D) != 0)
> edge (null) 0 0
> dst t.c 6 1 a_:
>
> and this is extract from gcov-4b.c which *should* split:
>
> 205 int
> 206 test_switch (int i, int j)
> 207 {
> 208 int result = 0;
> 209
> 210 switch (i) /* branch(80 25) */
> 211 /* branch(end) */
> 212 {
> 213 case 1:
> 214 result = do_something (2);
> 215 break;
> 216 case 2:
> 217 result = do_something (1024);
> 218 break;
> 219 case 3:
> 220 case 4:
> 221 if (j == 2) /* branch(67) */
> 222 /* branch(end) */
> 223 return do_something (4);
> 224 result = do_something (8);
> 225 break;
> 226 default:
> 227 result = do_something (32);
> 228 switch_m++;
> 229 break;
> 230 }
> 231 return result;
> 231 }
>
> block file line col stmt
>
> src 4b.c 214 18 result_18 = do_something (2);
> edge 4b.c 215 9
> dst 4b.c 231 10 _22 = result_3;
>
> src 4b.c 217 18 result_16 = do_something (1024);
> edge 4b.c 218 9
> dst 4b.c 231 10 _22 = result_3;
>
> src 4b.c 224 18 result_12 = do_something (8);
> edge 4b.c 225 9
> dst 4b.c 231 10 _22 = result_3;
>
> Note that the behaviour of comparison is preserved for the (switch) edge
> splitting case. The former case now fails the check (even though
> e->goto_locus is no longer a reserved location) because the dest matches
> the e->locus.
It's fine, please install it.
I verified tramp3d coverage output is the same as before the patch.
Martin
>
> gcc/ChangeLog:
>
> * profile.cc (branch_prob): Compare edge locus to dest, not src.
> ---
> gcc/profile.cc | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/gcc/profile.cc b/gcc/profile.cc
> index 96121d60711..c13a79a84c2 100644
> --- a/gcc/profile.cc
> +++ b/gcc/profile.cc
> @@ -1208,17 +1208,17 @@ branch_prob (bool thunk)
> FOR_EACH_EDGE (e, ei, bb->succs)
> {
> gimple_stmt_iterator gsi;
> - gimple *last = NULL;
> + gimple *dest = NULL;
>
> /* It may happen that there are compiler generated statements
> without a locus at all. Go through the basic block from the
> last to the first statement looking for a locus. */
> - for (gsi = gsi_last_nondebug_bb (bb);
> + for (gsi = gsi_start_nondebug_bb (bb);
> !gsi_end_p (gsi);
> - gsi_prev_nondebug (&gsi))
> + gsi_next_nondebug (&gsi))
> {
> - last = gsi_stmt (gsi);
> - if (!RESERVED_LOCATION_P (gimple_location (last)))
> + dest = gsi_stmt (gsi);
> + if (!RESERVED_LOCATION_P (gimple_location (dest)))
> break;
> }
>
> @@ -1227,14 +1227,14 @@ branch_prob (bool thunk)
> Don't do that when the locuses match, so
> if (blah) goto something;
> is not computed twice. */
> - if (last
> - && gimple_has_location (last)
> + if (dest
> + && gimple_has_location (dest)
> && !RESERVED_LOCATION_P (e->goto_locus)
> && !single_succ_p (bb)
> && (LOCATION_FILE (e->goto_locus)
> - != LOCATION_FILE (gimple_location (last))
> + != LOCATION_FILE (gimple_location (dest))
> || (LOCATION_LINE (e->goto_locus)
> - != LOCATION_LINE (gimple_location (last)))))
> + != LOCATION_LINE (gimple_location (dest)))))
> {
> basic_block new_bb = split_edge (e);
> edge ne = single_succ_edge (new_bb);
