[Bug c/42952] New: possible integer wrong code bug

[Bug c/42952] New: possible integer wrong code bug

[regehr at cs dot utah dot edu]

The program below looks to me like it should print "0".

regehr@john-home:~$ current-gcc -O small.c -o small
regehr@john-home:~$ ./small
1
regehr@john-home:~$ cat small.c
extern int printf (__const char *__restrict __format, ...);

static int g_16[1];

static int *g_135 = &g_16[0];
static int *l_15 = &g_16[0];

static void foo (void)
{
  g_16[0] = 1;
  *g_135 = 0;
  *g_135 = *l_15;
  printf("%d\n", g_16[0]);
}

int main(void)
{
   foo();
   return 0;
} 
regehr@john-home:~$ current-gcc -v
Using built-in specs.
COLLECT_GCC=current-gcc
COLLECT_LTO_WRAPPER=/home/regehr/z/tmp/gcc-r156486-install/libexec/gcc/i686-pc-linux-gnu/4.5.0/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ../configure --with-libelf=/usr/local --enable-lto
--prefix=/home/regehr/z/tmp/gcc-r156486-install --program-prefix=r156486-
--enable-languages=c,c++
Thread model: posix
gcc version 4.5.0 20100204 (experimental) (GCC)


-- 
           Summary: possible integer wrong code bug
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: regehr at cs dot utah dot edu
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug middle-end/42952] [4.5 Regression] possible integer wrong code bug

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c                           |middle-end
           Keywords|                            |wrong-code
            Summary|possible integer wrong code |[4.5 Regression] possible
                   |bug                         |integer wrong code bug
   Target Milestone|---                         |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.5 Regression] possible integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2010-02-04 10:03 -------
Confirmed.  Fails with -O -fno-tree-pta as well.

extern void abort (void);

static int g[1];

static int *p = &g[0];
static int *q = &g[0];

int main(void)
{
  g[0] = 1;
  *p = 0;
  *p = *q;
  if (g[0] != 0)
    abort ();
  return 0;
}


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|middle-end                  |rtl-optimization
     Ever Confirmed|0                           |1
  GCC build triplet|i686-pc-linux-gnu           |
   GCC host triplet|i686-pc-linux-gnu           |
 GCC target triplet|i686-pc-linux-gnu           |i?86-*-* x86_64-*-*
           Priority|P3                          |P1
   Last reconfirmed|0000-00-00 00:00:00         |2010-02-04 10:03:02
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.5 Regression] possible integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2010-02-04 10:11 -------
dse1 deletes insn 7 in

(insn 7 6 8 2 t.c:11 (set (mem:SI (reg/f:DI 58 [ p.0 ]) [0 S4 A32])
        (const_int 0 [0x0])) 47 {*movsi_1} (nil))

(insn 8 7 9 2 t.c:12 (set (reg/f:DI 63 [ q ])
        (mem/u/f/c/i:DI (symbol_ref:DI ("q") [flags 0x2]  <var_decl
0x7ffff5ae7140 q>) [0 q+0 S8 A64])) 89 {*movdi_1_rex64} (nil))

(insn 9 8 10 2 t.c:12 (set (reg:SI 64)
        (mem:SI (reg/f:DI 63 [ q ]) [0 S4 A32])) 47 {*movsi_1}
(expr_list:REG_DEAD (reg/f:DI 63 [ q ])
        (nil)))

(insn 10 9 11 2 t.c:12 (set (mem:SI (reg/f:DI 58 [ p.0 ]) [0 S4 A32])
        (reg:SI 64)) 47 {*movsi_1} (expr_list:REG_DEAD (reg:SI 64)
        (expr_list:REG_DEAD (reg/f:DI 58 [ p.0 ])
            (nil))))

The two canonical RTXen that are not detected as conflicting are

(mem/u/f/c/i:DI (symbol_ref:DI ("q") [flags 0x2]  <var_decl 0x7ffff5ae7140 q>)
[0 q+0 S8 A64])

(mem/u/f/c/i:DI (symbol_ref:DI ("p") [flags 0x2]  <var_decl 0x7ffff5ae70a0 p>)
[0 p+0 S8 A64])

I will have a look.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2010-02-04 10:03:02         |2010-02-04 10:11:02
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.5 Regression] possible integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2010-02-04 10:33 -------
Well, dse puts

(mem/u/f/c/i:DI (symbol_ref:DI ("q") [flags 0x2]  <var_decl 0x7ffff5ae7140 q>)
[0 q+0 S8 A64])

(mem/u/f/c/i:DI (symbol_ref:DI ("p") [flags 0x2]  <var_decl 0x7ffff5ae70a0 p>)
[0 p+0 S8 A64])

into different groups:

**scanning insn=9
cselib value 2 0x10f8e58 (reg/f:DI 63 [ q ])

cselib lookup (reg/f:DI 63 [ q ]) => 2
  mem: (reg/f:DI 63 [ q ])

   after canon_rtx address: (mem/u/f/c/i:DI (symbol_ref:DI ("q") [flags 0x2] 
<var_decl 0x7ffff5ae7140 q>) [0 q+0 S8 A64])
  gid=2 offset=0
 processing const load gid=2[0..4)
mems_found = 0, cannot_delete = true
cselib lookup (mem:SI (reg/f:DI 63 [ q ]) [0 S4 A32]) => 0

**scanning insn=10
cselib lookup (reg/f:DI 58 [ p.0 ]) => 1
  mem: (reg/f:DI 58 [ p.0 ])

   after canon_rtx address: (mem/u/f/c/i:DI (symbol_ref:DI ("p") [flags 0x2] 
<var_decl 0x7ffff5ae70a0 p>) [0 p+0 S8 A64])
  gid=1 offset=0
 processing const base store gid=1[0..4)
    trying store in insn=7 gid=1[0..4)


just because the addresses are MEM_READONLY_P.  But that obviously does not
mean they do not point to the same thing - no idea what implementor had
in mind here.  Kenny?

The following fixes this for me:

Index: dse.c
===================================================================
--- dse.c       (revision 156468)
+++ dse.c       (working copy)
@@ -1015,9 +1015,6 @@ const_or_frame_p (rtx x)
 {
   switch (GET_CODE (x))
     {
-    case MEM:
-      return MEM_READONLY_P (x);
-
     case CONST:
     case CONST_INT:
     case CONST_DOUBLE:


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |zadeck at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.5 Regression] possible integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2010-02-04 10:36 -------
The only addresses treated as the dse "constant" kind should be symbol-refs.
Or we need to lookup the constant initializer the constant mem refers to
and use that (but I have no idea if that's easily possible on RTL).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.5 Regression] possible integer wrong code bug

[zadeck at naturalbridge dot com]

------- Comment #5 from zadeck at naturalbridge dot com  2010-02-04 14:57 -------
Richi, you are, of course, correct.   

kenny


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.5 Regression] possible integer wrong code bug

[matz at gcc dot gnu dot org]

------- Comment #6 from matz at gcc dot gnu dot org  2010-02-04 15:03 -------
Re comment #4, there are two possibilities to fix this:
1) as you say, don't regard MEM addresses (i.e. used in double indirection)
   as const_or_frame_p, because that would put different (but runtime-same)
   bases into different groups, or
2) fix this marvel in check_mem_read_rtx:
     if (group_id == store_info->group_id)
       ...
     /* else
        The else case that is missing here is that the
        bases are constant but different.  There is nothing
        to do here because there is no overlap.  */

Clearly the comment is wrong, base addresses can be constant, different for
rtx_equal purposes, but still be the same at runtime.

When going the (2) way we would need to ask the oracle, which most of the time
would probably say "don't know" anyway, and be slow.  Hence not regarding
such base addresses as interesting for the global problem seems to be the
better fix.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.3/4.4/4.5 Regression] possible integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2010-02-04 15:22 -------
Also fails with 4.3.4 and 4.4.2 if you do -fno-tree-ccp -fno-tree-fre
(I have a fix for the CCP optimization regression as well).


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P1                          |P2
            Summary|[4.5 Regression] possible   |[4.3/4.4/4.5 Regression]
                   |integer wrong code bug      |possible integer wrong code
                   |                            |bug
   Target Milestone|4.5.0                       |4.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.3/4.4/4.5 Regression] possible integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2010-02-04 16:14 -------
Subject: Bug 42952

Author: rguenth
Date: Thu Feb  4 16:14:17 2010
New Revision: 156494

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=156494
Log:
2010-02-04  Richard Guenther  <rguenther@suse.de>

        PR rtl-optimization/42952
        * dse.c (const_or_frame_p): Remove MEM handling.

        * gcc.dg/torture/pr42952.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/pr42952.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/dse.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.3/4.4/4.5 Regression] possible integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2010-02-04 16:18 -------
Subject: Bug 42952

Author: rguenth
Date: Thu Feb  4 16:18:01 2010
New Revision: 156495

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=156495
Log:
2010-02-04  Richard Guenther  <rguenther@suse.de>

        PR rtl-optimization/42952
        * dse.c (const_or_frame_p): Remove MEM handling.

        * gcc.dg/torture/pr42952.c: New testcase.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/gcc.dg/torture/pr42952.c
Modified:
    branches/gcc-4_4-branch/gcc/ChangeLog
    branches/gcc-4_4-branch/gcc/dse.c
    branches/gcc-4_4-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.3/4.4/4.5 Regression] possible integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #11 from rguenth at gcc dot gnu dot org  2010-02-04 16:22 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to fail|                            |4.3.4 4.4.3
      Known to work|                            |4.3.5 4.4.4 4.5.0
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952

[Bug rtl-optimization/42952] [4.3/4.4/4.5 Regression] possible integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2010-02-04 16:22 -------
Subject: Bug 42952

Author: rguenth
Date: Thu Feb  4 16:21:47 2010
New Revision: 156496

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=156496
Log:
2010-02-04  Richard Guenther  <rguenther@suse.de>

        PR rtl-optimization/42952
        * dse.c (const_or_frame_p): Remove MEM handling.

        * gcc.dg/torture/pr42952.c: New testcase.

Added:
    branches/gcc-4_3-branch/gcc/testsuite/gcc.dg/torture/pr42952.c
Modified:
    branches/gcc-4_3-branch/gcc/ChangeLog
    branches/gcc-4_3-branch/gcc/dse.c
    branches/gcc-4_3-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42952