[Bug tree-optimization/47770] New: wrong code -O2 -ftree-loop-if-convert-stores -fno-tree-reassoc

[Bug tree-optimization/47770] New: wrong code -O2 -ftree-loop-if-convert-stores -fno-tree-reassoc

[zsojka at seznam dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47770

           Summary: wrong code -O2 -ftree-loop-if-convert-stores
                    -fno-tree-reassoc
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zsojka@seznam.cz
                CC: spop@gcc.gnu.org
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu


Created attachment 23365
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23365
reduced testcase

Output:
$ gcc -O2 -ftree-loop-if-convert-stores -fno-tree-reassoc testcase.c
$ ./a.out
Aborted

By looking that the dumps testcase.c.110t.ifcvt is "binary equal" to
testcase.c.109t.ivcanon, but with -ftree-loop-if-convert-stores, 
testcase.c.126t.cddce2 removes most of code of foo(). Dumps with and without
-ftree-loop-if-convert-stores are the same up to that point.

[Bug tree-optimization/47770] wrong code -O2 -ftree-loop-if-convert-stores -fno-tree-reassoc

[zsojka at seznam dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47770

--- Comment #1 from Zdenek Sojka <zsojka at seznam dot cz> 2011-02-16 22:36:17 UTC ---
"-ftree-loop-if-convert -fno-tree-reassoc -fno-tree-vectorize" gives about 316
exec failures on current trunk. I should try the fix for PR46029 from
http://gcc.gnu.org/ml/gcc-patches/2010-11/msg01613.html, but I am failing to
apply it (I can't find the revision it applies to, and the mentioned
0001-Fix-PR46029-reimplement-if-convert-stores.patch in general).

[Bug tree-optimization/47770] wrong code -O2 -ftree-loop-if-convert-stores -fno-tree-reassoc

[spop at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47770

Sebastian Pop <spop at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011.02.17 00:36:38
         AssignedTo|unassigned at gcc dot       |spop at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #2 from Sebastian Pop <spop at gcc dot gnu.org> 2011-02-17 00:36:38 UTC ---
I do not think that 0001-Fix-PR46029-reimplement-if-convert-stores.patch
is the right way to fix this: I discussed with Ira Rosen about the
vectorization
of the code produced by this patch and we ended up realizing that the
vectorizer would have to answer the same hard questions (memory accesses
out of bounds and writes into read-only memory) that are now analyzed in
-ftree-loop-if-convert-stores.

I will look at how to fix these miscompiles.

[Bug tree-optimization/47770] wrong code -O2 -ftree-loop-if-convert-stores -fno-tree-reassoc

[zsojka at seznam dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47770

--- Comment #3 from Zdenek Sojka <zsojka at seznam dot cz> 2011-02-24 02:20:56 UTC ---
It seems most of the exec failures disappeared between r170436 and r170443 -
that is, probably by the fix for PR47849.

Running testsuite (languages=c,c++,lto,fortran) with 
RUNTESTFLAGS="--target_board=unix/-ftree-loop-if-convert-stores/-fno-tree-reassoc/-fno-tree-vectorize"
gives only one ICE - PR47738 and two exec failures:

ext/pb_ds/example/tree_intervals.cc (PR46029)
gfortran.dg/allocate_deferred_char_scalar_1.f03 (fails even with no
optimisation flags)

Also, the attachment in comment #0 doesn't fail anymore.

[Bug tree-optimization/47770] wrong code -O2 -ftree-loop-if-convert-stores -fno-tree-reassoc

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47770

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

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