[Bug tree-optimization/101080] New: wrong code with "-O3"

[Bug tree-optimization/101080] New: wrong code with "-O3"

[suochenyao at 163 dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101080

            Bug ID: 101080
           Summary: wrong code with "-O3"
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: suochenyao at 163 dot com
  Target Milestone: ---

*******************************************************************************
OS and Platform:
CentOS Linux release 7.8.2003 (Core), x86_64 GNU/Linux
*******************************************************************************
Program:
struct a {
  unsigned b : 3;
} const c;
char d;
int e;
long f;
void g(const struct a h) {
  for (; d != 20; d = d + 4) {
    int i = h.b;
    e = h.b;
    f = h.b || 0;
  }
}
int main() { g(c); }
*******************************************************************************
gcc version:
$ gcc -v
Using built-in specs.
COLLECT_GCC=/data/bin/gcc-dev/bin/gcc
COLLECT_LTO_WRAPPER=/data/bin/gcc-dev/libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/data/bin/gcc-dev --disable-multilib
--enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210614 (experimental) (GCC)


git version: f9598d89a9f5a327ecdfa6f6978a0cfbe4447111
*******************************************************************************
Command Lines:
$ gcc a.c -o a1.out
$ gcc -O3 -Wall -Wextra -fno-strict-aliasing -fwrapv  a.c -o a2.out
a.c: In function ‘g’:
a.c:9:9: warning: unused variable ‘i’ [-Wunused-variable]
    9 |     int i = h.b;
      |         ^
$ ./a1.out
$ ./a2.out
Segmentation fault (core dumped)

[Bug tree-optimization/101080] wrong code with "-O3"

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101080

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |wrong-code
   Last reconfirmed|                            |2021-06-16
     Ever confirmed|0                           |1
                 CC|                            |jamborm at gcc dot gnu.org

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Also happens with -O3 -fno-tree-vectorize which produces

Program received signal SIGSEGV, Segmentation fault.
0x00000000004003b7 in main ()
(gdb) disassemble
Dump of assembler code for function main:
   0x00000000004003a0 <+0>:     movzbl 0x200c95(%rip),%eax        # 0x60103c
<d>
   0x00000000004003a7 <+7>:     cmp    $0x14,%al
   0x00000000004003a9 <+9>:     je     0x4003da <main+58>
   0x00000000004003ab <+11>:    nopl   0x0(%rax,%rax,1)
   0x00000000004003b0 <+16>:    add    $0x4,%eax
   0x00000000004003b3 <+19>:    cmp    $0x14,%al
   0x00000000004003b5 <+21>:    jne    0x4003b0 <main+16>
=> 0x00000000004003b7 <+23>:    andb   $0xf8,0x186(%rip)        # 0x400544 <c>
   0x00000000004003be <+30>:    movl   $0x0,0x200c70(%rip)        # 0x601038
<e>
   0x00000000004003c8 <+40>:    movq   $0x0,0x200c5d(%rip)        # 0x601030
<f>
   0x00000000004003d3 <+51>:    movb   $0x14,0x200c62(%rip)        # 0x60103c
<d>
   0x00000000004003da <+58>:    xor    %eax,%eax
   0x00000000004003dc <+60>:    ret    

simpler IL testcase (elide g) - note the inlining is critical.

struct a {
  unsigned b : 3;
} const c;
char d;
int e;
long f;
static void g(const struct a h)
{
  for (; d != 20; d = d + 4) {
      int i = h.b;
      e = h.b;
      f = h.b || 0;
  }
}
int main()
{
  g(c);
}

so the issue is we store to 'c' which resides in .rodata - suspect this is
a dup of the pending SRA issue.  -fno-tree-sra fixes it.

But it's a nice testcase.

[Bug tree-optimization/101080] wrong code with "-O3"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101080

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|NEW                         |RESOLVED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It is a dup of the other SRA issue.
PR 100453

*** This bug has been marked as a duplicate of bug 100453 ***

[Bug tree-optimization/101080] wrong code with "-O3"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101080

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #1) 
> But it's a nice testcase.

The other PR has basically the same testcase even already and about the same
size.