https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120938
Bug ID: 120938
Summary: discriminators are not useful in statements doing
multiple calls
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: hubicka at gcc dot gnu.org
Target Milestone: ---
jh@shroud:~> cat d.C
#include <stdio.h>
volatile int a;
static int dead ()
{
return 0;
}
static void inc(int b)
{
a++;
}
static void
inline_me (int l)
{
for (int i = 0; i < 100000000; i++)
{dead();inc(dead ());inc(dead ());}
if (!l)
inline_me (l+1);
printf ("block tail recursion\n");
}
int main ()
{
inline_me (0);
return 0;
}
jh@shroud:~> cat afdo-test
~/trunk-install-new7/bin/gcc -O3 -g $* -o train -g -flto
-fdump-tree-all-details-lineno || exit
perf record -e ex_ret_brn_tkn:Pu -c100003 -b ./train || exit
create_gcov --binary train --gcov_version 2 --use_discriminator_encoding
--debug_dump perf.data --gcov a.gcov | tee gcov-debug
~/trunk-install-new7/bin/gcc -O3 -g -fauto-profile=a.gcov -Wauto-profile
-fdump-tree-all-details-lineno -fdump-ipa-all-details -o trained $* || exit
jh@shroud:~> sh afdo-test d.C
gives
d.C:16:14: warning: auto-profile contains inlined function with symbol name inc
instead of symbol name _ZL4deadv [-Wauto-profile]
16 | {dead();inc(dead ());inc(dead ());}
| ~~~~^~
d.C:13:1: warning: auto-profile of ‘void inline_me(int)’ contains extra
callsites [-Wauto-profile]
13 | inline_me (int l)
| ^~~~~~~~~
d.C:13:1: note: call of inc with relative location +3, discriminator 0
d.C:16:14: warning: auto-profile contains inlined function with symbol name inc
instead of symbol name _ZL4deadv [-Wauto-profile]
16 | {dead();inc(dead ());inc(dead ());}
| ~~~~^~
d.C:13:1: warning: auto-profile of ‘void inline_me(int)’ contains extra
callsites [-Wauto-profile]
13 | inline_me (int l)
| ^~~~~~~~~
d.C:13:1: note: call of inc with relative location +3, discriminator 0
The problem here is in the profile info:
_ZL9inline_mei total:27945 head:0
1: 0
2.1: 9315
4: 0
6: 0
7: 0
3.2: inc total:9315
2: 9315
3.4: inc total:9315
2: 9315
5: inline_me total:0
2.1: 0
6: 0
3: inc total:0
2: 0
main total:18780 head:0
1: 0
4: 0
2: inline_me total:18780
2.1: 9390
5: 0
6: 0
3: inc total:9390
2: 9390
Notice that _ZL9inline_mei in offline version correctly records two calls of
"inc" with discriminators 2 and 4. Inline versions in main and inline_me
(which is dead) has only one call with discriminator 0 that gets confused with
call to dead() function...
