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[Bug middle-end/48267] incorrect signed overflow warning when a pointer cannot possibly overflow
- From: "rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 24 Mar 2011 12:14:52 -0000
- Subject: [Bug middle-end/48267] incorrect signed overflow warning when a pointer cannot possibly overflow
- Auto-submitted: auto-generated
- References: <bug-48267-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48267
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic
Status|UNCONFIRMED |NEW
Last reconfirmed| |2011.03.24 12:14:46
Component|c |middle-end
Ever Confirmed|0 |1
Known to fail| |4.5.2, 4.7.0
--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-03-24 12:14:46 UTC ---
Confirmed. Happens from
#1 0x00000000007307e7 in fold_undefer_overflow_warnings (issue=1 '\001',
stmt=0x7ffff5b373c0, code=2)
at /space/rguenther/src/svn/trunk/gcc/fold-const.c:281
281 warning_at (locus, OPT_Wstrict_overflow, "%s", warnmsg);
(gdb)
#2 0x0000000000afdfdf in evaluate_stmt (stmt=0x7ffff5b373c0)
at /space/rguenther/src/svn/trunk/gcc/tree-ssa-ccp.c:2117
2117 fold_undefer_overflow_warnings (is_constant, stmt, 0);
(gdb)
#3 0x0000000000aff7c5 in visit_cond_stmt (stmt=0x7ffff5b373c0,
taken_edge_p=0x7fffffffda48)
at /space/rguenther/src/svn/trunk/gcc/tree-ssa-ccp.c:2443
2443 val = evaluate_stmt (stmt);
(gdb)
#4 0x0000000000aff8f8 in ccp_visit_stmt (stmt=0x7ffff5b373c0,
taken_edge_p=0x7fffffffda48, output_p=0x7fffffffda40)
at /space/rguenther/src/svn/trunk/gcc/tree-ssa-ccp.c:2501
2501 return visit_cond_stmt (stmt, taken_edge_p);
(gdb) call debug_gimple_stmt (stmt)
if (p_1 < &head_table[1])
which calls fold_binary with &head_table < &head_table[1] and in the end warns
here:
8688 if (code != EQ_EXPR
8689 && code != NE_EXPR
8690 && bitpos0 != bitpos1
8691 && (pointer_may_wrap_p (base0, offset0, bitpos0)
8692 || pointer_may_wrap_p (base1, offset1, bitpos1)))
8693 fold_overflow_warning (("assuming pointer wraparound
does not "
8694 "occur when comparing P +- C1
with "
8695 "P +- C2"),
8696
WARN_STRICT_OVERFLOW_CONDITIONAL)
because we call pointer_may_wrap_p with base0 which isn't an address
but an object which is bogus. It's argument has to depend on
indirect_base in which case we stripped an ADDR_EXPR.