[Bug tree-optimization/59413] New: wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[Bug tree-optimization/59413] New: wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

            Bug ID: 59413
           Summary: wrong code at -Os on x86_64-linux-gnu in both 32-bit
                    and 64-bit modes
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk miscompiles the following code on x86_64-linux at -Os
(but not at the other optimization levels) in both 32-bit and 64-bit modes. 

It is interesting that the typedef appears necessary to trigger the
miscompilation. 

This is a regression from 4.8.x.

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 4.9.0 20131206 (experimental) [trunk revision 205734] (GCC) 
$ 
$ gcc-trunk -O1 small.c; a.out
7
$ gcc-trunk -O2 small.c; a.out
7
$ gcc-4.8 -Os small.c; a.out
7
$ 
$ gcc-trunk -Os small.c; a.out
2
$ 


--------------------------------


int printf (const char *, ...);

typedef unsigned int uint32_t;

uint32_t a;
int b;

int
main ()
{
  uint32_t c;
  for (a = 7; a <= 1; a++)
    {
      char d = a;
      c = d;
      b = a == c;
    }
  printf ("%d\n", a);
  return 0;
}

[Bug tree-optimization/59413] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I can't reproduce this one with gcc version 4.9.0 20131217.

[Bug tree-optimization/59413] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I couldn't reproduce this either, neither -m32/-m64 helps, tried also r205733
and various other snapshots, everything prints 7.

[Bug tree-optimization/59413] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

--- Comment #3 from Zhendong Su <su at cs dot ucdavis.edu> ---
(In reply to Jakub Jelinek from comment #2)
> I couldn't reproduce this either, neither -m32/-m64 helps, tried also
> r205733 and various other snapshots, everything prints 7.

I rebuilt r205734 with the same config

    configure --prefix=/usr/local/gcc-trunk --enable-languages=c,c++
--disable-werror --enable-multilib

and 

    make bootstrap-lean

It still fails for me at -Os: 

$ ./gcc -Os small.c; a.out
2
$ cat small.c
int printf (const char *, ...);

typedef unsigned int uint32_t;

uint32_t a;
int b;

int
main ()
{
  uint32_t c;
  for (a = 7; a <= 1; a++)
    {
      char d = a;
      c = d;
      b = a == c;
    }
  printf ("%d\n", a);
  return 0;
}

[Bug tree-optimization/59413] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

--- Comment #4 from Zhendong Su <su at cs dot ucdavis.edu> ---
(In reply to Jakub Jelinek from comment #2)
> I couldn't reproduce this either, neither -m32/-m64 helps, tried also
> r205733 and various other snapshots, everything prints 7.

But it doesn't appear to fail with the latest trunk revision (r206135): 

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++,lto --disable-werror --enable-multilib
Thread model: posix
gcc version 4.9.0 20131219 (experimental) [trunk revision 206135] (GCC) 
$     
$ gcc-trunk -Os small.c; a.out
7
$

[Bug tree-optimization/59413] [4.9 Regression] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-12-20
   Target Milestone|---                         |4.9.0
            Summary|wrong code at -Os on        |[4.9 Regression] wrong code
                   |x86_64-linux-gnu in both    |at -Os on x86_64-linux-gnu
                   |32-bit and 64-bit modes     |in both 32-bit and 64-bit
                   |                            |modes
     Ever confirmed|0                           |1

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
It is fixed by r205884.  We can add the testcase and close it.

[Bug tree-optimization/59413] [4.9 Regression] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Weird, I still get exactly the same code (except for gcc version string)
between pre-r205884 and post-r205884.  So, what exact differences are you
seeing on the testcase, and with -fdump-tree-all -da starting with what pass? 
Tried both a non-bootstrap gcc in my bisecting tree and 12 freshly built gcc
x86_64 bootstraps from around Dec 5 till now.
Because when I'm not able to reproduce it, I'm hesistant to adding the
testcase...

[Bug tree-optimization/59413] [4.9 Regression] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com

--- Comment #7 from H.J. Lu <hjl.tools at gmail dot com> ---
[hjl@gnu-mic-2 gcc-regression]$ cat pr59413.c
typedef unsigned int uint32_t;

uint32_t a;
int b;

int
main ()
{
  uint32_t c;
  for (a = 7; a <= 1; a++)
    {
      char d = a;
      c = d;
      b = a == c;
    }
  if (a != 7)
    __builtin_abort ();
  return 0;
}
[hjl@gnu-mic-2 gcc-regression]$
/export/project/git/gcc-regression/master/205883/usr/bin/gcc -S pr59413.c -Os
-o bad.s
[hjl@gnu-mic-2 gcc-regression]$
/export/project/git/gcc-regression/master/205887/usr/bin/gcc -S pr59413.c -Os
-o good.s
[hjl@gnu-mic-2 gcc-regression]$ diff -up bad.s good.s
--- bad.s    2013-12-20 04:38:57.810620352 -0800
+++ good.s    2013-12-20 04:39:12.476337299 -0800
@@ -8,20 +8,9 @@
 main:
 .LFB0:
     .cfi_startproc
-    movl    b(%rip), %edx
-    movl    $7, %eax
-.L2:
-    incl    %eax
-    cmpl    $3, %eax
-    je    .L6
-    movl    $1, %edx
-    jmp    .L2
-.L6:
-    pushq    %rax
-    .cfi_def_cfa_offset 16
-    movl    %edx, b(%rip)
-    movl    $2, a(%rip)
-    call    abort
+    movl    $7, a(%rip)
+    xorl    %eax, %eax
+    ret
     .cfi_endproc
 .LFE0:
     .size    main, .-main
@@ -31,5 +20,5 @@ main:
 .LHOTE0:
     .comm    b,4,4
     .comm    a,4,4
-    .ident    "GCC: (GNU) 4.9.0 20131211 (experimental) [trunk revision
205883]"
+    .ident    "GCC: (GNU) 4.9.0 20131211 (experimental) [trunk revision
205887]"
     .section    .note.GNU-stack,"",@progbits
[hjl@gnu-mic-2 gcc-regression]$

[Bug tree-optimization/59413] [4.9 Regression] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Ah, my fault then, terribly sorry, I've simplified the testcase a little bit
(removed the typedef and used unsigned int instead).  Apparently for the
reproduction it is important that the c variable uses some typedef to unsigned
int rather than that type directly.

[Bug tree-optimization/59413] [4.9 Regression] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

--- Comment #9 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to H.J. Lu from comment #5)
> It is fixed by r205884.  We can add the testcase and close it.

FWIW, it is also introduced by r204516.

[Bug tree-optimization/59413] [4.9 Regression] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Fri Dec 20 13:07:10 2013
New Revision: 206147

URL: http://gcc.gnu.org/viewcvs?rev=206147&root=gcc&view=rev
Log:
    PR tree-optimization/59413
    * gcc.c-torture/execute/pr59413.c: New test.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr59413.c
Modified:
    trunk/gcc/testsuite/ChangeLog

[Bug tree-optimization/59413] [4.9 Regression] wrong code at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59413

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Thanks, testcase committed, so we are all set now.