[Bug c/41497] New: apparent integer wrong code bug

[Bug c/41497] New: apparent integer wrong code bug

[regehr at cs dot utah dot edu]

It looks wrong at -Os.  The compiler is valgrind-clean at that level.

regehr@john-home:~/volatile/tmp200$ current-gcc -O small.c -o small
regehr@john-home:~/volatile/tmp200$ ./small
checksum = -13

regehr@john-home:~/volatile/tmp200$ current-gcc -Os small.c -o small
regehr@john-home:~/volatile/tmp200$ ./small
checksum = 65523

regehr@john-home:~/volatile/tmp200$ current-gcc -v

Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../configure --prefix=/home/regehr/z/tmp/gcc-r152261-install
--program-prefix=r152261- --enable-languages=c,c++
Thread model: posix
gcc version 4.5.0 20090929 (experimental) (GCC) 

regehr@john-home:~/volatile/tmp200$ cat small.c

#include <stdint.h>
#include <stdio.h>

static uint16_t add (uint16_t ui1, uint16_t ui2)
{
  return ui1 + ui2;
}

uint32_t g_108;
uint8_t f3;
uint8_t f0;

void func_1 (void);
void func_1 (void)
{
  for (f3 = 0; f3 <= 0; f3 = 1) {
    for (g_108 = -13; g_108 == 0; g_108 = add (g_108, 0)) {
      f0 = 1;
    }
  }
}

int
main (void)
{
  func_1 ();
  printf ("checksum = %d\n", g_108);
  return 0;
}


-- 
           Summary: apparent integer wrong code bug
           Product: gcc
           Version: unknown
            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=41497

[Bug c/41497] apparent integer wrong code bug

[jakub at gcc dot gnu dot org]

------- Comment #1 from jakub at gcc dot gnu dot org  2009-09-29 07:23 -------
Fails on x86_64-linux too, the bug first appears in sccp.
extern void abort (void);

static unsigned short
bar (unsigned short x, unsigned short y)
{
  return x + y;
}

unsigned int a;
unsigned char b, c;

void
foo (void)
{
  for (b = 0; b <= 0; b = 1)
    for (a = -13; a == 0; a = bar (a, 0))
      c = 1;
}

int
main ()
{
  foo ();
  if (a != -13)
    abort ();
  return 0;
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2009-09-29 09:51 -------
Thus, confirmed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|c                           |tree-optimization
     Ever Confirmed|0                           |1
           Keywords|                            |wrong-code
      Known to work|                            |4.3.4 4.4.1
   Last reconfirmed|0000-00-00 00:00:00         |2009-09-29 09:51:50
               date|                            |
            Summary|apparent integer wrong code |[4.5 Regression] apparent
                   |bug                         |integer wrong code bug
   Target Milestone|---                         |4.5.0
            Version|unknown                     |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2009-10-11 11:56 -------
The key is IMHO that the inner loop does not have its loop header copied.
This confuses SCEV enough to think that a = (unsigned short)a is always
executed.  LIM is necessary to promote all the memory to SSA names, the
interesting CHREC that gets wrong is

<bb 3>:
..
  a_lsm.6_18 = 0x0fffffff3;
  goto <bb 5>;

<bb 4>:
...
  a.1_2 = a_lsm.6_15;
  D.2006_3 = (short unsigned int) a.1_2;
  a.2_4 = (unsigned int) D.2006_3;
  a_lsm.6_20 = a.2_4;

<bb 5>:
  # a_lsm.6_15 = PHI <a_lsm.6_18(3), a_lsm.6_20(4)>
...
  a.1_1 = a_lsm.6_15;
  if (a.1_1 == 0)
    goto <bb 4>;
  else
    goto <bb 6>;

 <bb 6>:
...
-  # a_lsm.6_27 = PHI <a_lsm.6_15(5)>


 <bb 8>:
-  # a_lsm.6_28 = PHI <a_lsm.6_27(6)>
-  a = a_lsm.6_28;
+  a = 65523;

where interestingly a_lsm.6_15 isn't computed wrong.


Testcase, fails at -Os:

extern void abort (void);

unsigned int a;
int b, c;

void
foo (void)
{
  b = 0;
  do {
    for (a = -13; a == 0; a = (unsigned short)a)
      c = 1;
    b++;
  } while (b == 0);
}

int
main ()
{
  foo ();
  if (a != -13)
    abort ();
  return 0;
}


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2009-10-11 11:56 -------
Sebastian, can you have a look?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[hjl dot tools at gmail dot com]

------- Comment #5 from hjl dot tools at gmail dot com  2009-10-11 16:59 -------
Revision 147714 is OK and revision 147717 is bad.


-- 

hjl dot tools at gmail dot com changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[hjl dot tools at gmail dot com]

------- Comment #6 from hjl dot tools at gmail dot com  2009-10-11 19:34 -------
It is caused by revision 147716:

http://gcc.gnu.org/ml/gcc-cvs/2009-05/msg00693.html


-- 

hjl dot tools at gmail dot com changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[ebotcazou at gcc dot gnu dot org]

------- Comment #7 from ebotcazou at gcc dot gnu dot org  2009-10-12 17:59 -------
> It is caused by revision 147716:
> 
> http://gcc.gnu.org/ml/gcc-cvs/2009-05/msg00693.html

Yep, but it's Richard's fault. ;-)  The bug is exposed by the change requested
in http://gcc.gnu.org/ml/gcc-patches/2009-05/msg01227.html so I won't go beyond
suggesting the following partial reversion

Index: tree-scalar-evolution.c
===================================================================
--- tree-scalar-evolution.c     (revision 152647)
+++ tree-scalar-evolution.c     (working copy)
@@ -1159,7 +1159,7 @@ follow_ssa_edge_expr (struct loop *loop,

   switch (code)
     {
-    CASE_CONVERT:
+    case NOP_EXPR:
       /* This assignment is under the form "a_1 = (cast) rhs.  */
       res = follow_ssa_edge_expr (loop, at_stmt, TREE_OPERAND (expr, 0),
                                  halting_phi, evolution_of_loop, limit);
@@ -1222,7 +1222,7 @@ follow_ssa_edge_in_rhs (struct loop *loo

   switch (code)
     {
-    CASE_CONVERT:
+    case NOP_EXPR:
       /* This assignment is under the form "a_1 = (cast) rhs.  */
       res = follow_ssa_edge_expr (loop, stmt, gimple_assign_rhs1 (stmt),
                                  halting_phi, evolution_of_loop, limit);

But I also think that the real problem is elsewhere.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2009-10-12 20:23 -------
Eh, indeed if that fixes it the bug is elsewhere.  I suggest to not apply this
partial reversion until we know better.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2009-10-12 20:24 -------
The problem is that we follow SSA edges into loops that may not be executed.
Sebastian - how are we supposed to deal with this case?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[spop at gcc dot gnu dot org]

------- Comment #10 from spop at gcc dot gnu dot org  2009-10-20 21:53 -------
Subject: Re:  [4.5 Regression] apparent integer 
        wrong code bug

> The problem is that we follow SSA edges into loops that may not be executed.

It is correct to follow SSA edges in loops that may not execute, as we
compute a symbolic expression of the evolution.

The error is that we are not careful enough in the use of this
symbolic information: in analyze_evolution_in_loop we are given the
loop_phi_node: a_lsm.6_15 = PHI <a_lsm.6_18(3), a_lsm.6_20(4)> and its
initial value init_cond: a_lsm.6_18.

follow_ssa_edge returns an evolution function ev_fn that could be
incompatible with the initial value:

(unsigned int) (short unsigned int) a_lsm.6_18;

The attached patch fixes the problem by returning "don't know" when
init_cond is not equal to ev_fn when no_evolution_in_loop_p manages to
prove that ev_fn is invariant in the loop.

Sebastian


------- Comment #11 from spop at gcc dot gnu dot org  2009-10-20 21:53 -------
Created an attachment (id=18847)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18847&action=view)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[spop at gcc dot gnu dot org]

------- Comment #12 from spop at gcc dot gnu dot org  2009-10-21 23:05 -------
Subject: Bug 41497

Author: spop
Date: Wed Oct 21 23:05:39 2009
New Revision: 153441

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=153441
Log:
        PR tree-optimization/41497
        * tree-scalar-evolution.c (analyze_evolution_in_loop): Return
        chrec_dont_know if the evolution function returned by follow_ssa_edge
        is constant in the analyzed loop and is not compatible with the
        initial value before the loop.
        * tree-chrec.h (no_evolution_in_loop_p): Call STRIP_NOPS.

        * gcc.dg/tree-ssa/pr41497.c: New.


Added:
    trunk/gcc/testsuite/gcc.dg/tree-ssa/pr41497.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-chrec.h
    trunk/gcc/tree-scalar-evolution.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[spop at gcc dot gnu dot org]

------- Comment #13 from spop at gcc dot gnu dot org  2009-10-21 23:10 -------
Fixed.

This bug is potentially latent in older branches.
Should I test it in the 4.4 branch as well?


-- 

spop at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497

[Bug tree-optimization/41497] [4.5 Regression] apparent integer wrong code bug

[hjl at gcc dot gnu dot org]

------- Comment #14 from hjl at gcc dot gnu dot org  2009-10-30 16:05 -------
Subject: Bug 41497

Author: hjl
Date: Fri Oct 30 16:04:41 2009
New Revision: 153759

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=153759
Log:
2009-10-30  H.J. Lu  <hongjiu.lu@intel.com>

        Backport from mainline:
        2009-10-30  Dodji Seketeli  <dodji@redhat.com>

        PR c++/41863
        * g++.dg/template/sizeof12.C: New test.

        2009-10-29  Martin Jambor  <mjambor@suse.cz>

        PR tree-optimization/41775
        * g++.dg/torture/pr41775.C: New testcase.

        2009-10-28  Jakub Jelinek  <jakub@redhat.com>

        PR debug/41801
        * g++.dg/ext/sync-3.C: New test.

        2009-10-27  Jakub Jelinek  <jakub@redhat.com>

        PR c++/41020
        * g++.dg/lookup/extern-c-redecl5.C: Fix up regexp.

        2009-10-26  Jakub Jelinek  <jakub@redhat.com>

        PR bootstrap/41345
        * gcc.dg/pr41345.c: New test.

        2009-10-26  Dodji Seketeli  <dodji@redhat.com>

        PR c++/41785
        * g++.dg/cpp0x/variadic96.C: New test.

        2009-10-26  Dodji Seketeli  <dodji@redhat.com>

        PR c++/41020
        * g++.dg/lookup/extern-c-redecl2.C: New test.
        * g++.dg/lookup/extern-c-redecl3.C: Likewise.
        * g++.dg/lookup/extern-c-redecl4.C: Likewise.
        * g++.dg/lookup/extern-c-redecl5.C: Likewise.

        2009-10-23  Joseph Myers  <joseph@codesourcery.com>

        PR c/40033
        * gcc.dg/noncompile/pr40033-1.c: New test.

        2009-10-23  Joseph Myers  <joseph@codesourcery.com>

        PR c/41673
        * gcc.dg/Wstrict-aliasing-bogus-vla-1.c: New test.

        2009-10-21  Sebastian Pop  <sebastian.pop@amd.com>

        PR tree-optimization/41497
        * gcc.dg/tree-ssa/pr41497.c: New.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/g++.dg/cpp0x/variadic96.C
      - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/cpp0x/variadic96.C
    branches/gcc-4_4-branch/gcc/testsuite/g++.dg/ext/sync-3.C
      - copied unchanged from r153757, trunk/gcc/testsuite/g++.dg/ext/sync-3.C
    branches/gcc-4_4-branch/gcc/testsuite/g++.dg/lookup/extern-c-redecl2.C
      - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/lookup/extern-c-redecl2.C
    branches/gcc-4_4-branch/gcc/testsuite/g++.dg/lookup/extern-c-redecl3.C
      - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/lookup/extern-c-redecl3.C
    branches/gcc-4_4-branch/gcc/testsuite/g++.dg/lookup/extern-c-redecl4.C
      - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/lookup/extern-c-redecl4.C
    branches/gcc-4_4-branch/gcc/testsuite/g++.dg/lookup/extern-c-redecl5.C
      - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/lookup/extern-c-redecl5.C
    branches/gcc-4_4-branch/gcc/testsuite/g++.dg/template/sizeof12.C
      - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/template/sizeof12.C
    branches/gcc-4_4-branch/gcc/testsuite/g++.dg/torture/pr41775.C
      - copied unchanged from r153757,
trunk/gcc/testsuite/g++.dg/torture/pr41775.C
    branches/gcc-4_4-branch/gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-vla-1.c
      - copied unchanged from r153758,
trunk/gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-vla-1.c
    branches/gcc-4_4-branch/gcc/testsuite/gcc.dg/noncompile/pr40033-1.c
      - copied unchanged from r153758,
trunk/gcc/testsuite/gcc.dg/noncompile/pr40033-1.c
    branches/gcc-4_4-branch/gcc/testsuite/gcc.dg/pr41345.c
      - copied unchanged from r153757, trunk/gcc/testsuite/gcc.dg/pr41345.c
    branches/gcc-4_4-branch/gcc/testsuite/gcc.dg/tree-ssa/pr41497.c
      - copied unchanged from r153758,
trunk/gcc/testsuite/gcc.dg/tree-ssa/pr41497.c
Modified:
    branches/gcc-4_4-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41497