extern void abort (void); extern void *memset (void *s, int c, __SIZE_TYPE__ n); struct S { int i[16]; }; struct S *p; void __attribute__((noinline)) foo(struct S *a, struct S *b) { a->i[0] = -1; p = b; } void test (void) { struct S a, b; memset (&a.i[0], '\0', sizeof (a.i)); memset (&b.i[0], '\0', sizeof (b.i)); foo (&a, &b); *p = a; *p = b; if (b.i[0] != -1) abort (); } int main() { test(); return 0; } tree DSE removes the *p = a store wrongly. Non-executable testcase: struct S { int i[16]; }; struct S *p; void foo(struct S *, struct S *); void test (void) { struct S a, b; foo (&a, &b); *p = a; *p = b; }
We have # VUSE <p_7> p.0_1 = p; # a_11 = VDEF <a_8> # b_12 = VDEF <b_9> # SMT.5_13 = VDEF <SMT.5_10> *p.0_1 = a; # a_14 = VDEF <a_11> # b_15 = VDEF <b_12> # SMT.5_16 = VDEF <SMT.5_13> *p.0_1 = b; This is actually a case of PR34459 and it is its testcase that actually fails with the fix for PR27799.
Patch in testing.
Fixed on the trunk, waiting for 4.3.1.
Subject: Bug 35472 Author: rguenth Date: Wed Mar 5 16:13:04 2008 New Revision: 132899 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=132899 Log: 2008-03-05 Richard Guenther <rguenther@suse.de> PR tree-optimization/35472 * tree-ssa-dse.c (dse_optimize_stmt): Do not delete a store whose single use_stmt has a overlapping set of loaded and stored symbols as that use_stmt might be a noop assignment then. * gcc.c-torture/execute/pr35472.c: New testcase. Added: trunk/gcc/testsuite/gcc.c-torture/execute/pr35472.c Modified: trunk/gcc/ChangeLog trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-ssa-dse.c
Subject: Bug 35472 Author: rguenth Date: Fri Mar 7 09:47:06 2008 New Revision: 133004 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=133004 Log: 2008-03-07 Richard Guenther <rguenther@suse.de> PR tree-optimization/35472 * tree-ssa-dse.c (dse_optimize_stmt): Do not delete a store whose single use_stmt has a overlapping set of loaded and stored symbols as that use_stmt might be a noop assignment then. * gcc.c-torture/execute/pr35472.c: New testcase. Added: branches/gcc-4_3-branch/gcc/testsuite/gcc.c-torture/execute/pr35472.c - copied unchanged from r132899, trunk/gcc/testsuite/gcc.c-torture/execute/pr35472.c Modified: branches/gcc-4_3-branch/gcc/ChangeLog branches/gcc-4_3-branch/gcc/testsuite/ChangeLog branches/gcc-4_3-branch/gcc/tree-ssa-dse.c
Fixed.