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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug ipa/65270] [5 regression] ICF needs to match TYPE attributes on memory accesses Date: Thu, 05 Mar 2015 09:40:00 -0000 [thread overview] Message-ID: <bug-65270-4-C4KIDXOIzQ@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-65270-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65270 --- Comment #21 from rguenther at suse dot de <rguenther at suse dot de> --- On Wed, 4 Mar 2015, hubicka at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65270 > > --- Comment #16 from Jan Hubicka <hubicka at gcc dot gnu.org> --- > Richard, > thanks, I also think alias trick makes gloal vars safe for merging across > RESTRICT flags. > > One however needs to consider merging of items referring restricted vars. > > const restrict int *a=&var; > const int *b = &var; > > const int **ptrs1={&a}; > const int **ptrs2=[&b}; > > with -fmerge-all-constants we may merge ptrs1 and ptrs2 and, in the late > compilation, in turn fold expression "ptrs2[0]" into a restricted pointer to > var? So we merge a and b with introducing an alias which is why we can merge ptrs1 and ptrs2, correct? But still with introducing an alias. But folding ptrs1[0] and ptrs2[0] will now return the same (but random?) value. Note that it's not folding that can introduce issues but points-to analysis and what it computes for the globals ptrs1 and ptrs2 and thus for code that reads from them. We are not really parsing constructors fully in PTA - at least I see ptrs1 = NONLOCAL ptrs1.0_2 = ptrs1 _3 = *ptrs1.0_2 _4 = *_3 only for int var; const int * restrict a=&var; const int *b = &var; const int * const *ptrs1={&a}; const int * const *ptrs2={&b}; int main() { return *(ptrs1[0]); } IPA PTA does sth funny though: ptrs2 = NONLOCAL b = NONLOCAL var = NONLOCAL b = &var ESCAPED = &var ptrs2 = &b ESCAPED = &b ptrs1 = NONLOCAL a = &GLOBAL_RESTRICT GLOBAL_RESTRICT = NONLOCAL ptrs1 = &a ESCAPED = &a but obviously we don't seem to merge ptrs1/ptrs2. But IPA PTA needs quite some thoughts with respect to aliases I think (and in other ways as well...). > If this case is legit, the correct place to match RESTRICT flags is > compare_cgraph_references. We can also go with your patch that will make A and > B considered to be different and thus prevent merging PTRS1&PTRS2. That would certainly be a safe thing to do. Even with -flto -fmerge-all-constants we don't get ptrs1 and ptrs2 merged it seems (with -fwhole-program we fold stuff too early). Richard.
next prev parent reply other threads:[~2015-03-05 9:40 UTC|newest] Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-03-02 0:49 [Bug ipa/65270] New: " hubicka at gcc dot gnu.org 2015-03-02 8:58 ` [Bug ipa/65270] " rguenth at gcc dot gnu.org 2015-03-02 11:50 ` rguenth at gcc dot gnu.org 2015-03-02 14:32 ` rguenth at gcc dot gnu.org 2015-03-02 14:51 ` rguenth at gcc dot gnu.org 2015-03-02 18:25 ` hubicka at gcc dot gnu.org 2015-03-03 14:57 ` rguenther at suse dot de 2015-03-03 15:08 ` howarth at bromo dot med.uc.edu 2015-03-03 17:24 ` rguenther at suse dot de 2015-03-03 18:23 ` hubicka at gcc dot gnu.org 2015-03-03 20:38 ` hubicka at gcc dot gnu.org 2015-03-04 9:26 ` rguenth at gcc dot gnu.org 2015-03-04 9:45 ` rguenther at suse dot de 2015-03-04 10:35 ` rguenth at gcc dot gnu.org 2015-03-04 11:52 ` rguenth at gcc dot gnu.org 2015-03-04 11:57 ` rguenth at gcc dot gnu.org 2015-03-04 18:21 ` hubicka at gcc dot gnu.org 2015-03-05 0:11 ` hubicka at gcc dot gnu.org 2015-03-05 0:21 ` hubicka at gcc dot gnu.org 2015-03-05 0:42 ` hubicka at gcc dot gnu.org 2015-03-05 8:43 ` rguenth at gcc dot gnu.org 2015-03-05 9:40 ` rguenther at suse dot de [this message] 2015-03-05 9:42 ` rguenther at suse dot de 2015-03-05 9:45 ` rguenther at suse dot de 2015-03-05 11:30 ` marxin at gcc dot gnu.org 2015-03-05 19:47 ` [Bug ipa/65270] issues with merging memory accesses from different code paths hubicka at gcc dot gnu.org 2015-03-05 19:59 ` hubicka at gcc dot gnu.org 2015-03-05 20:11 ` hubicka at gcc dot gnu.org 2015-03-05 21:18 ` hubicka at gcc dot gnu.org 2015-03-06 8:32 ` rguenther at suse dot de 2015-03-06 15:41 ` hubicka at gcc dot gnu.org 2015-03-06 18:03 ` [Bug ipa/65270] [5 regression] " hubicka at gcc dot gnu.org 2015-03-09 11:11 ` rguenth at gcc dot gnu.org 2015-03-09 13:55 ` rguenth at gcc dot gnu.org 2015-03-09 13:55 ` rguenth at gcc dot gnu.org 2015-03-12 13:03 ` rguenth at gcc dot gnu.org
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