[Bug tree-optimization/45122] New: [4.6 Regression] -funsafe-loop-optimizations causes FAIL: gcc.c-torture/execute/pr27285.c execution

[Bug tree-optimization/45122] New: [4.6 Regression] -funsafe-loop-optimizations causes FAIL: gcc.c-torture/execute/pr27285.c execution

[zsojka at seznam dot cz]

With -funsafe-loop-optimizations in flags, pr27285.c FAILs:
FAIL: gcc.c-torture/execute/pr27285.c execution,  -O1 
FAIL: gcc.c-torture/execute/pr27285.c execution,  -O2 
FAIL: gcc.c-torture/execute/pr27285.c execution,  -O3 -fomit-frame-pointer 
FAIL: gcc.c-torture/execute/pr27285.c execution,  -O3 -fomit-frame-pointer
-funroll-loops 
FAIL: gcc.c-torture/execute/pr27285.c execution,  -O3 -fomit-frame-pointer
-funroll-all-loops -finline-functions 
FAIL: gcc.c-torture/execute/pr27285.c execution,  -O3 -g 
FAIL: gcc.c-torture/execute/pr27285.c execution,  -O2 -flto 
FAIL: gcc.c-torture/execute/pr27285.c execution,  -O2 -fwhopr 

Output:
$ gcc -O -funsafe-loop-optimizations pr27285.i -Wunsafe-loop-optimizations
/mnt/svn/gcc-trunk/gcc/testsuite/gcc.c-torture/execute/pr27285.c: In function
'foo':
/mnt/svn/gcc-trunk/gcc/testsuite/gcc.c-torture/execute/pr27285.c:19:10:
warning: assuming that the loop counter does not overflow
[-Wunsafe-loop-optimizations]
/mnt/svn/gcc-trunk/gcc/testsuite/gcc.c-torture/execute/pr27285.c:17:9: warning:
assuming that the loop counter does not overflow [-Wunsafe-loop-optimizations]
$ ./a.out 
Aborted

There is no overflow in the loop.

When compiled with -funsafe-loop-optimizations, the loop is exited when 'b' has
value 1 (that is, e[a] = d[a] & c; is not executed when b == 0). 'b' has values
of 25,17,19,1 (and then the loop ends) - without -funsafe-loop-optimizations,
it has values 25,17,19,1,0.

Even though -funsafe-loop-optimizations is expected to be unsafe, this
behaviour makes it unusable. The loop is finite and the counter doesn't
overflow, so this is a wrong code generated.

Tested revisions:
r162653 - fail
r162456 - OK


-- 
           Summary: [4.6 Regression] -funsafe-loop-optimizations causes
                    FAIL: gcc.c-torture/execute/pr27285.c execution
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: zsojka at seznam dot cz
  GCC host triplet: x86_64-pc-linux-gnu
GCC target triplet: x86_64-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45122

[Bug tree-optimization/45122] [4.6 Regression] -funsafe-loop-optimizations causes FAIL: gcc.c-torture/execute/pr27285.c execution

[zsojka at seznam dot cz]

------- Comment #1 from zsojka at seznam dot cz  2010-07-29 01:24 -------
"25,17,19,1" should have been "25,17,9,1"


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45122

[Bug tree-optimization/45122] [4.6 Regression] -funsafe-loop-optimizations causes FAIL: gcc.c-torture/execute/pr27285.c execution

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2010-07-29 01:28 -------
IV-OPTS is choosing b-8 as the IV which seems wrong anyways as that produces
worse code as far as I can tell.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.6.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45122

[Bug tree-optimization/45122] [4.6 Regression] -funsafe-loop-optimizations causes FAIL: gcc.c-torture/execute/pr27285.c execution

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2010-07-29 09:40 -------
Confirmed.  In the original code b doesn't overflow.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-07-29 09:40:17
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45122

[Bug tree-optimization/45122] [4.6 Regression] -funsafe-loop-optimizations causes FAIL: gcc.c-torture/execute/pr27285.c execution

[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=45122