https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102037
Bug ID: 102037
Summary: False positive in -Warray-bounds
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: huntazhang at tencent dot com
Target Milestone: ---
Created attachment 51351
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51351&action=edit
test code
[root@VM-209-165-centos ~]# gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../configure --enable-language=c,c++ --prefix=/usr
--program-suffix=-12 --program-prefix=x86_64-linux-gnu --enable-plugin
--disable-multilib --build=x86_64-linux-gnu --target=x86_64-linux-gnu
--enable-vtable-verify --disable-bootstrap
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210823 (experimental) (GCC)
[root@VM-209-165-centos ~]# gcc -O2 -Wall array-bound-index.c
In function 'rdfs8',
inlined from 'main' at array-bound-index.c:13:2:
array-bound-index.c:7:9: warning: array subscript 0 is outside array bounds of
'u8[0]' {aka 'unsigned char[]'} [-Warray-bounds]
7 | asm volatile("movb %%fs:%1,%0" : "=q" (v) : "m" (*(u8 *)addr));
here is my debug log
Breakpoint 1, compute_objsize_r (ptr=0x7ffff74593a8, ostype=0,
pref=0x7fffffffd730, snlim=..., qry=0x7fffffffd5f0) at
../../gcc/pointer-query.cc:1587
1587 STRIP_NOPS (ptr);
(gdb) p debug(ptr)
1160B
$2 = void
(gdb) n
1589 const bool addr = TREE_CODE (ptr) == ADDR_EXPR;
(gdb)
1590 if (addr)
(gdb) n
1596 if (DECL_P (ptr))
(gdb) n
1621 const tree_code code = TREE_CODE (ptr);
(gdb) n
1622 range_query *const rvals = qry ? qry->rvals : NULL;
(gdb) n
1624 if (code == BIT_FIELD_REF)
(gdb)
1635 if (code == COMPONENT_REF)
(gdb) n
1702 if (code == ARRAY_REF)
(gdb)
1705 if (code == MEM_REF)
(gdb)
1708 if (code == TARGET_MEM_REF)
(gdb)
1720 if (code == INTEGER_CST)
(gdb)
1726 if (integer_zerop (ptr))
(gdb) n
1729 pref->sizrng[0] = pref->sizrng[1] = 0;
(gdb) p gimple_debug_cfg(TDF_DETAILS)
;; Function main (main, funcdef_no=1, decl_uid=1948, cgraph_uid=2,
symbol_order=1) (executed once)
;;
3 basic blocks, 2 edges, last basic block 3.
;; basic block 2, loop depth 0, count 1073741824 (estimated locally), maybe hot
;; prev block 0, next block 1, flags: (NEW, REACHABLE, VISITED)
;; pred: ENTRY [always] count:1073741824 (estimated locally)
(FALLTHRU,EXECUTABLE)
;; succ: EXIT [always] count:1073741824 (estimated locally)
(EXECUTABLE)
int main ()
{
u8 v;
;; basic block 2, loop depth 0, count 1073741824 (estimated locally), maybe
hot
;; prev block 0, next block 1, flags: (NEW, REACHABLE, VISITED)
;; pred: ENTRY [always] count:1073741824 (estimated locally)
(FALLTHRU,EXECUTABLE)
__asm__ __volatile__("movb %%fs:%1,%0" : "=q" v_2 : "m" MEM[(u8 *)1160B]);
return 0;
;; succ: EXIT [always] count:1073741824 (estimated locally)
(EXECUTABLE)
}
$3 = void
(gdb) p debug(ptr)
1160B
$4 = void
(gdb) frame 1
#1 0x000000000126212c in handle_mem_ref (mref=0x7ffff7475168, ostype=0,
pref=0x7fffffffd730, snlim=..., qry=0x7fffffffd5f0) at
../../gcc/pointer-query.cc:1551
1551 if (!compute_objsize_r (mrefop, ostype, pref, snlim, qry))
(gdb) p debug(mref)
MEM[(u8 *)1160B]
$5 = void
(gdb)
