[Bug tree-optimization/31651] New: [4.3 Regression] FRE does not fold intermediate CCP results, FRE does no longer look through loads

[Bug tree-optimization/31651] New: [4.3 Regression] FRE does not fold intermediate CCP results, FRE does no longer look through loads

[rguenth at gcc dot gnu dot org]

Split out from PR31136.  Testcase:

struct S {
  unsigned b4:4;
  unsigned b6:6;
} s;

int main(void){
  s.b6 = 31;
  s.b4 = s.b6;
  s.b6 = s.b4;
  return s.b6 == 15 ? 0 : 1;
}

with gcc 4.2 FRE can look through s.b6 to see the 31 for the store to s.b4.
With mainline this no longer happens:

On 4.2 we have for the def_stmt

#   SFT.0D.1539_2 = V_MUST_DEF <SFT.0D.1539_1>;
sD.1526.b6D.1525 = 31

while on the trunk

# SFT.0_10 = VDEF <SFT.0_9(D)> { SFT.0 }
s.b6 = 31

and the predicate !ZERO_SSA_OPERANDS (def_stmt, SSA_OP_VIRTUAL_USES) evaluates
differently on them.  *sigh*


Also, create_value_expr_from does not fold the result even if it produces
constant arguments (generated by above look-through-loads).  This may
confuse fold (as it did in PR31136).


-- 
           Summary: [4.3 Regression] FRE does not fold intermediate CCP
                    results, FRE does no longer look through loads
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31651

[Bug tree-optimization/31651] [4.3 Regression] FRE does not fold intermediate CCP results, FRE does no longer look through loads

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2007-04-21 18:52 -------
The missed look-through-loads is a regression from 4.2.  On the branch we also
do not fold constant intermediate results.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.2.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31651

[Bug tree-optimization/31651] [4.3 Regression] FRE does not fold intermediate CCP results, FRE does no longer look through loads

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2007-04-21 18:54 -------
> and the predicate !ZERO_SSA_OPERANDS (def_stmt, SSA_OP_VIRTUAL_USES) evaluates differently on them.  *sigh*


This sounds more like this was introduced by the mem-ssa work, Diego?


-- 

pinskia at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31651

[Bug tree-optimization/31651] [4.3 Regression] FRE does not fold intermediate CCP results, FRE does no longer look through loads

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31651

[Bug tree-optimization/31651] [4.3 Regression] FRE does not fold intermediate CCP results, FRE does no longer look through loads

[amacleod at redhat dot com]

------- Comment #3 from amacleod at redhat dot com  2007-04-21 22:23 -------
I think this is actually fallout from the removal of V_MUSTDEFs, which predated
mem-ssa going in.  Although it may have been checked into mainline at the same
time as mem-ssa now that I think about it. The work was originally separate.

My guess would be that FRE was not updated at that time to deal properly with
the absence of the V_MUSTDEF.  IIRC, MUSTDEFS were considered to NOT have any
virtual operand USES, so this might now require a tuning of the
ZERO_SSA_OPERANDS conditional to check the RHS if there is one and only one
virtual def on the stmt to see whether its a relevant stmt or not.  

Since this is a missed optimization instead of a segfault or wrong code, it was
probably easy to not notice it.


-- 

amacleod at redhat dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |aldyh at gcc dot gnu dot
                   |                            |org, amacleod at redhat dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31651

[Bug tree-optimization/31651] [4.3 Regression] FRE does not fold intermediate CCP results, FRE does no longer look through loads

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2007-04-28 00:48 -------
Confirmed, I noticed this also.


-- 

pinskia 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         |2007-04-28 00:48:15
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31651

[Bug tree-optimization/31651] [4.3 Regression] FRE does not fold intermediate CCP results, FRE does no longer look through loads

[mmitchel at gcc dot gnu dot org]

-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31651

[Bug tree-optimization/31651] [4.3 Regression] FRE does not fold intermediate CCP results, FRE does no longer look through loads

[dberlin at gcc dot gnu dot org]

------- Comment #5 from dberlin at gcc dot gnu dot org  2007-06-30 14:15 -------
Subject: Bug 31651

Author: dberlin
Date: Sat Jun 30 14:15:26 2007
New Revision: 126149

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=126149
Log:
2007-06-30  Daniel Berlin  <dberlin@dberlin.org>

        Fix PR tree-optimization/32540
        Fix PR tree-optimization/31651

        * tree-ssa-sccvn.c: New file.

        * tree-ssa-sccvn.h: Ditto.

        * tree-vn.c: Include tree-ssa-sccvn.h
        (val_expr_paid_d): Removed.
        (value_table): Ditto.
        (vn_compute): Ditto.
        (val_expr_pair_hash): Ditto.
        (val_expr_pair_expr_eq): Ditto.
        (copy_vuses_from_stmt): Ditto.
        (vn_delete): Ditto.
        (vn_init): Ditto.
        (shared_vuses_from_stmt): Ditto.
        (print_creation_to_file): Moved up.
        (sort_vuses): Ditto.
        (sort_vuses_heap): Ditto.
        (set_value_handle): Make non-static.
        (make_value_handle): Ditto.
        (vn_add): Rewritten to use sccvn lookups.
        (vn_add_with_vuses): Ditto.
        (vn_lookup): Ditto (and second argument removed).
        (vn_lookup_with_vuses): Ditto.
        (vn_lookup_or_add): Ditto (and second argument removed);
        (vn_lookup_or_add_with_vuses): Ditto.
        (vn_lookup_with_stmt): New.
        (vn_lookup_or_add_with_stmt): Ditto.
        (create_value_handle_for_expr): Ditto.

        * tree-ssa-pre.c: Include tree-ssa-sccvn.h.
        (seen_during_translate): New function.
        (phi_trans_lookup): Use iterative_hash_expr, not vn_compute.
        (phi_trans_add): Ditto.
        (constant_expr_p): FIELD_DECL is always constant.
        (phi_translate_1): Renamed from phi_translate, add seen bitmap.
        Use constant_expr_p.
        Avoid infinite recursion on mutually valued expressions.
        Change callers of vn_lookup_or_add.
        (phi_translate): New function.
        (compute_antic_safe): Allow phi nodes.
        (create_component_ref_by_pieces): Update for FIELD_DECL change.
        (find_or_generate_expression): Rewrite slightly.
        (create_expression_by_pieces): Updated for vn_lookup_or_add
        change.
        Update VN_INFO for new names.
        (insert_into_preds_of_block): Update for new names.
        (add_to_exp_gen): New function.
        (add_to_sets): Use vn_lookup_or_add_with_stmt.
        (find_existing_value_expr): Rewrite to changed vn_lookup.
        (create_value_expr_from): Ditto, and use add_to_exp_gen.
        (try_look_through_load): Removed.
        (try_combine_conversion): Ditto.
        (get_sccvn_value): New function.
        (make_values_for_phi): Ditto.
        (make_values_for_stmt): Ditto.
        (compute_avail): Rewritten for vn_lookup_or_add changes and to use
        SCCVN.
        (init_pre): Update for SCCVN changes.
        (fini_pre): Ditto.
        (execute_pre): Ditto.

        * tree-flow.h (make_value_handle): Declare.
        (set_value_handle): Ditto.
        (sort_vuses_heap): Ditto.
        (vn_lookup_or_add_with_stmt): Ditto.
        (vn_lookup_with_stmt): Ditto.
        (vn_compute): Remove.
        (vn_init): Ditto.
        (vn_delete): Ditto.
        (vn_lookup): Update arguments.

        * Makefile.in (tree-ssa-pre.o): Add tree-ssa-sccvn.h
        (tree-vn.o): Ditto.
        (tree-ssa-sccvn.o): New.
        (OBJS-common): Add tree-ssa-sccvn.o



Added:
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-sccvn-1.c
      - copied unchanged from r125553,
branches/gcc-pre-vn/gcc/testsuite/gcc.dg/tree-ssa/ssa-sccvn-1.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-sccvn-2.c
      - copied unchanged from r125553,
branches/gcc-pre-vn/gcc/testsuite/gcc.dg/tree-ssa/ssa-sccvn-2.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-sccvn-3.c
      - copied unchanged from r125553,
branches/gcc-pre-vn/gcc/testsuite/gcc.dg/tree-ssa/ssa-sccvn-3.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-sccvn-4.c
      - copied unchanged from r125553,
branches/gcc-pre-vn/gcc/testsuite/gcc.dg/tree-ssa/ssa-sccvn-4.c
    trunk/gcc/tree-ssa-sccvn.c
      - copied, changed from r125553, branches/gcc-pre-vn/gcc/tree-ssa-sccvn.c
    trunk/gcc/tree-ssa-sccvn.h
      - copied, changed from r125553, branches/gcc-pre-vn/gcc/tree-ssa-sccvn.h
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/Makefile.in
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-1.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-3.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-4.c
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-5.c
    trunk/gcc/tree-flow.h
    trunk/gcc/tree-ssa-operands.h
    trunk/gcc/tree-ssa-pre.c
    trunk/gcc/tree-vn.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31651

[Bug tree-optimization/31651] [4.3 Regression] FRE does not fold intermediate CCP results, FRE does no longer look through loads

[dberlin at gcc dot gnu dot org]

------- Comment #6 from dberlin at gcc dot gnu dot org  2007-06-30 14:17 -------
Fixed


-- 

dberlin at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31651