| Summary: | [4.2 Regression] Wrong aliasing with global var grouping during call clobbering | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Richard Biener <rguenth> |
| Component: | tree-optimization | Assignee: | Diego Novillo <dnovillo> |
| Status: | RESOLVED FIXED | ||
| Severity: | blocker | CC: | dberlin, gcc-bugs, mueller, pinskia |
| Priority: | P3 | Keywords: | alias, wrong-code |
| Version: | 4.2.0 | ||
| Target Milestone: | 4.2.0 | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2006-07-17 13:30:56 | |
Oh - build with -O2 --param global-var-threshold=1 Runnable testcase:
extern void abort(void);
struct Bar { int p; };
struct Foo { struct Bar *p; };
struct Bar p0 = { 0 };
struct Bar p1 = { 1 };
void bar(struct Foo *f)
{
f->p = &p0;
}
int foo(struct Foo *f)
{
f->p->p = 1;
bar(f);
return f->p->p;
}
int main()
{
struct Foo f;
f.p = &p1;
if (foo(&f) != 0)
abort ();
return 0;
}
Testing patch. The bug was in the alias pruning code. We need to handle .GLOBAL_VAR in access_can_touch_variable. A memory reference that uses a call-clobbered memory tag should always be considered to touch .GLOBAL_VAR. Subject: Re: [4.2 Regression] Wrong aliasing
with global var grouping during call clobbering
dnovillo at gcc dot gnu dot org wrote:
> ------- Comment #3 from dnovillo at gcc dot gnu dot org 2006-07-18 13:25 -------
>
> Testing patch. The bug was in the alias pruning code. We need to handle
> .GLOBAL_VAR in access_can_touch_variable. A memory reference that uses a
> call-clobbered memory tag should always be considered to touch .GLOBAL_VAR.
Yay for random invariants!
Subject: Bug 28410 Author: dnovillo Date: Tue Jul 18 17:27:57 2006 New Revision: 115564 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=115564 Log: PR 28410 * tree-ssa-operands.c (access_can_touch_variable): Update comment. Return true if ALIAS is .GLOBAL_VAR. testsuite/ChangeLog PR 28410 * gcc.dg/tree-ssa/pr28410.c: New test. Added: trunk/gcc/testsuite/gcc.dg/tree-ssa/pr28410.c Modified: trunk/gcc/ChangeLog trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-ssa-operands.c |
struct Bar { int p; }; struct Foo { struct Bar *p; }; int foo(struct Foo *f) { f->p->p = 1; bar(f); return f->p->p; } .alias1: # VUSE <SMT.4_6>; D.1528_2 = f_1->p; # SMT.5_8 = V_MAY_DEF <SMT.5_7>; D.1528_2->p = 1; # .GLOBAL_VAR_10 = V_MAY_DEF <.GLOBAL_VAR_9>; bar (f_1); # VUSE <SMT.4_6>; D.1528_3 = f_1->p; # VUSE <SMT.5_8>; D.1529_4 = D.1528_3->p; return D.1529_4; and fre then does: # VUSE <SMT.4_6>; D.1528_2 = f_1->p; # SMT.5_8 = V_MAY_DEF <SMT.5_7>; D.1528_2->p = 1; # .GLOBAL_VAR_10 = V_MAY_DEF <.GLOBAL_VAR_9>; bar (f_1); D.1528_3 = D.1528_2; # VUSE <SMT.5_8>; D.1529_4 = D.1528_3->p; return D.1529_4; miscompiles kde4.