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.
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);
--
2.30.2
