[Bug lto/106274] New: Loss of macro tracking information with -flto
lhyatt at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Tue Jul 12 19:51:32 GMT 2022
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106274
Bug ID: 106274
Summary: Loss of macro tracking information with -flto
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: lhyatt at gcc dot gnu.org
CC: marxin at gcc dot gnu.org
Target Milestone: ---
This is related to PR101551 but easier to demonstrate a testcase for:
=======
#define X(p) p == 0
int f(void *) __attribute__((nonnull));
int f(void *p) {
return X(p);
}
========
When compiled without -flto, there is information on the macro expansion in the
diagnostics:
$ gcc -c t5.c -Wnonnull-compare
/home/lewis/t5.c: In function ‘f’:
/home/lewis/t5.c:1:16: warning: nonnull argument ‘p’ compared to NULL
[-Wnonnull-compare]
1 | #define X(p) p == 0
| ^
/home/lewis/t5.c:4:12: note: in expansion of macro ‘X’
4 | return X(p);
| ^
However, if you add -flto, you don't get the extra information:
$ gcc -c t5.c -Wnonnull-compare -flto
/home/lewis/t5.c: In function ‘f’:
/home/lewis/t5.c:1:16: warning: nonnull argument ‘p’ compared to NULL
[-Wnonnull-compare]
1 | #define X(p) p == 0
| ^
The reason is that this warning is generated after the ipa_free_lang_data pass,
and that does this:
========
/* If we are the LTO frontend we have freed lang-specific data already. */
if (in_lto_p
|| (!flag_generate_lto && !flag_generate_offload))
{
/* Rebuild type inheritance graph even when not doing LTO to get
consistent profile data. */
rebuild_type_inheritance_graph ();
return 0;
}
...
/* Reset diagnostic machinery. */
tree_diagnostics_defaults (global_dc);
========
With -flto, flag_generate_lto is true, so it doesn't return early, and proceeds
to the last line, which resets the diagnostic finalizer to
default_diagnostic_finalizer, which is not aware of virtual locations.
PR101551 is about more or less the same thing except it's the other case that
prevents this function from returning early (flag_generate_offload == true). I
am not sure to what extent they are otherwise related.
Is it possible to avoid resetting the diagnostics machinery in either of these
cases? Thanks...
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