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* [Bug tree-optimization/29708] New: Alias can go funny with pointer addition @ 2006-11-04 9:13 pinskia at gcc dot gnu dot org 2006-11-04 17:21 ` [Bug tree-optimization/29708] " rguenth at gcc dot gnu dot org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: pinskia at gcc dot gnu dot org @ 2006-11-04 9:13 UTC (permalink / raw) To: gcc-bugs With the following testcase: int a[100], b[100], d[100]; void link_error (void); int g(int i, int j) { int *c; int t; c = i?a:b; c++; d[j] = 1; c[j] = 2; if (d[j] != 1) link_error (); return 0; } ---- May-alias should figure out that c can only pointer to a or b but it gets confused as we get: j.2_11 = (unsigned int) j_7; D.1537_12 = j.2_11 * 4; D.1538_13 = (int *) D.1537_12; D.1539_14 = D.1538_13 + c_6; *D.1539_14 = 2; as may-alias only looks at the left hand side of a PLUS expression, we get the following result: D.1538_13 = &ANYTHING D.1539_14 = D.1538_13 Note 4.1 optimzed this testcase but I think that was by accident and is not actually getting it correct. If we add PTR_PLUS_EXPR we get the correct answer all the time unless someone does some real weird tricks by doing something like: size_t t = (size_t)a; int *c = (int*)(size_t)j; *(c+t) = 2; -- Summary: Alias can go funny with pointer addition Product: gcc Version: 4.3.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: tree-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: pinskia at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29708 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/29708] Alias can go funny with pointer addition 2006-11-04 9:13 [Bug tree-optimization/29708] New: Alias can go funny with pointer addition pinskia at gcc dot gnu dot org @ 2006-11-04 17:21 ` rguenth at gcc dot gnu dot org 2007-05-22 0:52 ` pinskia at gcc dot gnu dot org 2007-06-16 5:50 ` pinskia at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu dot org @ 2006-11-04 17:21 UTC (permalink / raw) To: gcc-bugs ------- Comment #1 from rguenth at gcc dot gnu dot org 2006-11-04 17:21 ------- Confirmed. -- rguenth at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |rguenth at gcc dot gnu dot | |org Status|UNCONFIRMED |NEW Ever Confirmed|0 |1 Last reconfirmed|0000-00-00 00:00:00 |2006-11-04 17:21:20 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29708 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/29708] Alias can go funny with pointer addition 2006-11-04 9:13 [Bug tree-optimization/29708] New: Alias can go funny with pointer addition pinskia at gcc dot gnu dot org 2006-11-04 17:21 ` [Bug tree-optimization/29708] " rguenth at gcc dot gnu dot org @ 2007-05-22 0:52 ` pinskia at gcc dot gnu dot org 2007-06-16 5:50 ` pinskia at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu dot org @ 2007-05-22 0:52 UTC (permalink / raw) To: gcc-bugs ------- Comment #2 from pinskia at gcc dot gnu dot org 2007-05-22 01:51 ------- Mine, we always get the correct answer on the pointer plus branch. On the trunk: ANYTHING = &ANYTHING READONLY = &ANYTHING INTEGER = &ANYTHING a = &ANYTHING c_1 = &a b = &ANYTHING c_1 = &b c_6 = c_1 + 32 D.1639_11 = &ANYTHING D.1640_12 = D.1639_11 D.1640_12 = c_6 *D.1640_12 = 2; While on the branch: ANYTHING = &ANYTHING READONLY = &ANYTHING INTEGER = &ANYTHING a = &ANYTHING c_1 = &a b = &ANYTHING c_1 = &b c_6 = c_1 + 32 D.1639_11 = c_6 *D.1639_11 = 2; So there is no extra Constraint for the store to &ANYTHING. -- pinskia at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- AssignedTo|unassigned at gcc dot gnu |pinskia at gcc dot gnu dot |dot org |org Status|NEW |ASSIGNED http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29708 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/29708] Alias can go funny with pointer addition 2006-11-04 9:13 [Bug tree-optimization/29708] New: Alias can go funny with pointer addition pinskia at gcc dot gnu dot org 2006-11-04 17:21 ` [Bug tree-optimization/29708] " rguenth at gcc dot gnu dot org 2007-05-22 0:52 ` pinskia at gcc dot gnu dot org @ 2007-06-16 5:50 ` pinskia at gcc dot gnu dot org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu dot org @ 2007-06-16 5:50 UTC (permalink / raw) To: gcc-bugs ------- Comment #3 from pinskia at gcc dot gnu dot org 2007-06-16 05:50 ------- Fixed at revision 125755. -- pinskia at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- Status|ASSIGNED |RESOLVED Resolution| |FIXED Target Milestone|--- |4.3.0 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29708 ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2007-06-16 5:50 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2006-11-04 9:13 [Bug tree-optimization/29708] New: Alias can go funny with pointer addition pinskia at gcc dot gnu dot org 2006-11-04 17:21 ` [Bug tree-optimization/29708] " rguenth at gcc dot gnu dot org 2007-05-22 0:52 ` pinskia at gcc dot gnu dot org 2007-06-16 5:50 ` pinskia at gcc dot gnu dot org
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