https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105368
--- Comment #2 from Zdenek Sojka <zsojka at seznam dot cz> ---
(gdb) disas
Dump of assembler code for function powi_cost(long):
0x0000000001538160 <+0>: push %r14
0x0000000001538162 <+2>: mov $0x20,%ecx
0x0000000001538167 <+7>: push %r13
0x0000000001538169 <+9>: push %r12
0x000000000153816b <+11>: push %rbp
0x000000000153816c <+12>: push %rbx
0x000000000153816d <+13>: mov %rdi,%rbx
0x0000000001538170 <+16>: sub $0x100,%rsp
0x0000000001538177 <+23>: neg %rbx
0x000000000153817a <+26>: cmovs %rdi,%rbx
0x000000000153817e <+30>: mov %rsp,%r13
0x0000000001538181 <+33>: xor %eax,%eax
0x0000000001538183 <+35>: xor %r12d,%r12d
0x0000000001538186 <+38>: mov %r13,%rdi
0x0000000001538189 <+41>: rep stos %rax,%es:(%rdi)
0x000000000153818c <+44>: movb $0x1,0x1(%rsp)
=> 0x0000000001538191 <+49>: cmp $0xff,%rbx
0x0000000001538198 <+56>: jg 0x15381b0 <powi_cost(long)+80>
0x000000000153819a <+58>: jmp 0x1538207 <powi_cost(long)+167>
1463
1464 /* Ignore the reciprocal when calculating the cost. */
1465 val = (n < 0) ? -n : n;
0x000000000153816d <+13>: mov %rdi,%rbx
1454 powi_cost (HOST_WIDE_INT n)
0x0000000001538170 <+16>: sub $0x100,%rsp
1455 {
1456 bool cache[POWI_TABLE_SIZE];
1457 unsigned HOST_WIDE_INT digit;
1458 unsigned HOST_WIDE_INT val;
1459 int result;
1460
1461 if (n == 0)
1462 return 0;
--Type <RET> for more, q to quit, c to continue without paging--
1463
1464 /* Ignore the reciprocal when calculating the cost. */
1465 val = (n < 0) ? -n : n;
0x0000000001538177 <+23>: neg %rbx
0x000000000153817a <+26>: cmovs %rdi,%rbx
...
/repo/gcc-trunk/gcc/tree-ssa-math-opts.cc:
1469 cache[1] = true;
0x000000000153818c <+44>: movb $0x1,0x1(%rsp)
1472
1473 while (val >= POWI_TABLE_SIZE)
=> 0x0000000001538191 <+49>: cmp $0xff,%rbx
0x0000000001538198 <+56>: jg 0x15381b0 <powi_cost(long)+80>
0x000000000153819a <+58>: jmp 0x1538207 <powi_cost(long)+167>
(gdb) p/x n
$19 = 0x8000000000000000
(gdb) p/x val
$20 = 0x8000000000000000
(gdb) p/x $rbx
$22 = 0x8000000000000000
The "while (val >= POWI_TABLE_SIZE)" check seems to be done in signed
arithmetics ("jg" conditional jump), so the value is not reduced and cache[i]
accesses out of bounds.
This happens with both boostrapped and non-bootstrapped compiler (using host
gcc-11.3.0)
