[Bug c/29274] New: 4.1, 4.2 (possibly 4.0?) not using mulsidi3

[Bug c/29274] New: 4.1, 4.2 (possibly 4.0?) not using mulsidi3

[eplondke at gmail dot com]

GCC 4.x tree optimization decides to put int values into long long int
temporaries.  When RTL expansion comes around, the expander sees only a DImode
multiply and so generates three SImode multiplies to deal with the problem.

GCC 3.x sees that the source values are SImode and uses mulsidi3 to generate
32x32->64 multiplies, which are much more efficient.  It also picks up the
accumulation.

(using -O3 for all compilations)

GCC 3.4 has an 84-byte stack frame, and a body of 372 instructions.
GCC 4.1 has a 1416-byte stack frame, and a body of 1668 instructions.
GCC 4.2 has a 1320-byte stack frame, and a body of 1565 instructions.


-- 
           Summary: 4.1, 4.2 (possibly 4.0?) not using mulsidi3
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: eplondke at gmail dot com
  GCC host triplet: x86_64-suse-linux
GCC target triplet: arm-unkown-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug c/29274] 4.1, 4.2 (possibly 4.0?) not using mulsidi3

[eplondke at gmail dot com]

------- Comment #1 from eplondke at gmail dot com  2006-09-28 16:45 -------
Created an attachment (id=12351)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12351&action=view)
Test case showing mulsidi problem

Multimedia processing

It's not self-running, but you can see plainly from the assembly output.

If you want a self-running test I can modify it a bit.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug c/29274] 4.1, 4.2 (possibly 4.0?) not using mulsidi3

[eplondke at gmail dot com]

------- Comment #2 from eplondke at gmail dot com  2006-09-28 16:46 -------
Forgot to say: I'm seeing this on an ARM cross-compilation.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug target/29274] 4.1, 4.2 (possibly 4.0?) not using mulsidi3

[ramana at gcc dot gnu dot org]

------- Comment #3 from ramana at gcc dot gnu dot org  2009-03-27 17:12 -------
I can see this with trunk as well as 4.3 branch today.



-- 

ramana 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         |2009-03-27 17:12:32
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.2/4.3/4.4 Regression] not using mulsidi3

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2009-03-27 17:26 -------
The issue is that TER does not build large trees for the multiplications as
the factors are used multiple times (and come from memory).  Thus the expander
does not see the widened multiplication and appearantly combine / lower-subreg
is not able to optimize this.

I think with expand-from-SSA we could enable this optimization during expand.

Simplified testcase:

long long foo (int i, int j)
{
   return (long long)i * (long long)j * (long long)i;
}

because we CSE (long long)i we don't optimize this case.  Disabling tree-level
CSE re-enables the optimizations: -fno-tree-fre -fno-tree-pre 
-fno-tree-dominator-opts


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|target                      |middle-end
 GCC target triplet|arm-unkown-elf              |arm-unkown-elf, i?86-*-*
           Keywords|                            |missed-optimization
            Summary|4.1, 4.2 (possibly 4.0?) not|[4.2/4.3/4.4 Regression] not
                   |using mulsidi3              |using mulsidi3
   Target Milestone|---                         |4.2.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.2/4.3/4.4 Regression] not using mulsidi3

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2009-03-27 17:27 -------
CC'ing micha.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |matz at suse dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.2/4.3/4.4/4.5 Regression] not using mulsidi3

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.3/4.4/4.5 Regression] not using mulsidi3

[jsm28 at gcc dot gnu dot org]

------- Comment #6 from jsm28 at gcc dot gnu dot org  2009-03-31 19:46 -------
Closing 4.2 branch.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.2/4.3/4.4/4.5 Regression]|[4.3/4.4/4.5 Regression] not
                   |not using mulsidi3          |using mulsidi3
   Target Milestone|4.2.5                       |4.3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.3/4.4/4.5 Regression] not using mulsidi3

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2009-08-04 12:27 -------
GCC 4.3.4 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.4                       |4.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.3/4.4/4.5 Regression] not using mulsidi3

[froydnj at gcc dot gnu dot org]

------- Comment #8 from froydnj at gcc dot gnu dot org  2009-08-26 15:50 -------
Even if the problems in expand are fixed, reassoc is still going to cause
problems with the original testcase.  From the dse1 dump:

  D.2474_14 = (long long int) vLo_11;
  D.2475_15 = (long long int) c1_6;
  D.2476_16 = D.2474_14 * D.2475_15;
  D.2477_19 = (long long int) c2_8;
  D.2478_20 = D.2474_14 * D.2477_19;

>From the reassoc1 dump right after:

  D.2474_14 = (long long int) vLo_11;
  D.2475_15 = (long long int) c1_6;
  D.2477_19 = (long long int) c2_8;
  D.2495_16 = D.2477_19 + D.2475_15;
  D.2495_20 = D.2495_16 * D.2474_14;

So we've traded a multiplication for an addition, but we've also made it
difficult to see that we could have used mulsidi3.


-- 

froydnj at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.3/4.4/4.5 Regression] not using mulsidi3

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2009-08-26 18:35 -------
Note that even for

  (long long)i * (long long)j * (long long)i

we can only use one mulsidi3, so promoting parts of the multiplications to
additions should be still beneficial.

I suppose we should detect widening multiply on the tree level before
re-association where it is beneficial (if the target doesn't have a native
wide multiplication).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.3/4.4/4.5 Regression] not using mulsidi3

[ramana at gcc dot gnu dot org]

------- Comment #10 from ramana at gcc dot gnu dot org  2009-12-29 23:21 -------
*** Bug 42498 has been marked as a duplicate of this bug. ***


-- 

ramana at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |carrot at google dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.3/4.4/4.5/4.6 Regression] not using mulsidi3

[bernds at gcc dot gnu dot org]

------- Comment #11 from bernds at gcc dot gnu dot org  2010-04-22 09:31 -------
Subject: Bug 29274

Author: bernds
Date: Thu Apr 22 09:30:27 2010
New Revision: 158633

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=158633
Log:
gcc/
        PR middle-end/29274
        * optabs.h (expand_widening_mult): Declare.
        * tree-pass.h (pass_optimize_widening_mul): Declare.
        * tree-ssa-math-opts.c (execute_optimize_widening_mul,
        gate_optimize_widening_mul): New static functions.
        (pass_optimize_widening_mul): New.
        * expr.c (expand_expr_real_2) <case WIDEN_MULT_EXPR>: New
        case.
        <case MULT_EXPR>: Remove support for widening multiplies.
        * tree.def (WIDEN_MULT_EXPR): Tweak comment.
        * cfgexpand.c (expand_debug_expr) <case WIDEN_MULT_EXPR>: Use
        simplify_gen_unary rather than directly building extensions.
        * tree-cfg.c (verify_gimple_assign_binary): Add tests for
        WIDEN_MULT_EXPR.
        * expmed.c (expand_widening_mult): New function.
        * passes.c (init_optimization_passes): Add pass_optimize_widening_mul.

gcc/testsuite/
        PR middle-end/29274
        * gcc.target/i386/wmul-1.c: New test.
        * gcc.target/i386/wmul-2.c: New test.
        * gcc.target/bfin/wmul-1.c: New test.
        * gcc.target/bfin/wmul-2.c: New test.


Added:
    trunk/gcc/testsuite/gcc.target/bfin/wmul-1.c
    trunk/gcc/testsuite/gcc.target/bfin/wmul-2.c
    trunk/gcc/testsuite/gcc.target/i386/wmul-1.c
    trunk/gcc/testsuite/gcc.target/i386/wmul-2.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/cfgexpand.c
    trunk/gcc/expmed.c
    trunk/gcc/expr.c
    trunk/gcc/passes.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-cfg.c
    trunk/gcc/tree-pass.h
    trunk/gcc/tree-ssa-math-opts.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.3/4.4/4.5 Regression] not using mulsidi3

[rguenth at gcc dot gnu dot org]

------- Comment #12 from rguenth at gcc dot gnu dot org  2010-04-22 10:11 -------
Fixed for 4.6.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|3.4.2                       |3.4.2 4.6.0
            Summary|[4.3/4.4/4.5/4.6 Regression]|[4.3/4.4/4.5 Regression] not
                   |not using mulsidi3          |using mulsidi3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.3/4.4/4.5 Regression] not using mulsidi3

[bernds at gcc dot gnu dot org]

------- Comment #13 from bernds at gcc dot gnu dot org  2010-04-22 11:26 -------
Subject: Bug 29274

Author: bernds
Date: Thu Apr 22 11:25:44 2010
New Revision: 158642

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=158642
Log:
        PR middle-end/29274
        * gcc.target/arm/wmul-1.c: New test.
        * gcc.target/arm/wmul-2.c: New test.


Added:
    trunk/gcc/testsuite/gcc.target/arm/wmul-1.c
    trunk/gcc/testsuite/gcc.target/arm/wmul-2.c
Modified:
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274

[Bug middle-end/29274] [4.3/4.4/4.5 Regression] not using mulsidi3

[rguenth at gcc dot gnu dot org]

------- Comment #14 from rguenth at gcc dot gnu dot org  2010-05-22 18:11 -------
GCC 4.3.5 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.5                       |4.3.6


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274