[Bug rtl-optimization/35404] New: ra-conflict does not handle subregs optimally

[Bug rtl-optimization/35404] New: ra-conflict does not handle subregs optimally

[ian at airs dot com]

I'm reporting this as an enhancement request to record a case where libcalls
are still used in the compiler.

Consider this test case:

extern long long bar();
long long foo () { return bar () | bar (); }

Compile it with -O2 -fno-wide-types.  I'm using -fno-wide-types to permit using
a simple test case; without that option, the same issue would arise for more
complicated cases.

In the .lreg dump I see this:

(insn:HI 9 8 10 2 /home/iant/foo4.c:2 (parallel [
            (set (subreg:SI (reg:DI 61) 0)
                (ior:SI (subreg:SI (reg:DI 58 [ D.1180 ]) 0)
                    (subreg:SI (reg:DI 59 [ D.1179 ]) 0)))
            (clobber (reg:CC 17 flags))
        ]) 253 {*iorsi_1} (expr_list:REG_UNUSED (reg:CC 17 flags)
        (insn_list:REG_LIBCALL 12 (expr_list:REG_NO_CONFLICT (reg:DI 58 [
D.1180 ])
                (expr_list:REG_NO_CONFLICT (reg:DI 59 [ D.1179 ])
                    (nil))))))

(insn:HI 10 9 12 2 /home/iant/foo4.c:2 (parallel [
            (set (subreg:SI (reg:DI 61) 4)
                (ior:SI (subreg:SI (reg:DI 58 [ D.1180 ]) 4)
                    (subreg:SI (reg:DI 59 [ D.1179 ]) 4)))
            (clobber (reg:CC 17 flags))
        ]) 253 {*iorsi_1} (expr_list:REG_DEAD (reg:DI 59 [ D.1179 ])
        (expr_list:REG_DEAD (reg:DI 58 [ D.1180 ])
            (expr_list:REG_UNUSED (reg:CC 17 flags)
                (expr_list:REG_NO_CONFLICT (reg:DI 58 [ D.1180 ])
                    (expr_list:REG_NO_CONFLICT (reg:DI 59 [ D.1179 ])
                        (nil)))))))

(insn:HI 12 10 17 2 /home/iant/foo4.c:2 (set (reg:DI 61)
        (reg:DI 61)) 63 {*movdi_2} (insn_list:REG_RETVAL 9 (expr_list:REG_EQUAL
(ior:DI (reg:DI 58 [ D.1180 ])
                (reg:DI 59 [ D.1179 ]))
            (nil))))

This is a libcall sequence which represent a no-conflict block.  It was created
by emit_no_conflict_block.  It means that register 61 does not conflict with
either register 58 or 59.

It is desirable to detect this fact in some other way.  If we can do that, then
we have eliminated one case where we use libcalls.

If we can track subreg lifetimes, then we can detect that there is no
conflicts.  Register 58 and 59 dies in insn 10.  Insn 10 does not refer to
subreg 0 of either register.  Therefore, subreg 0 of both registers die in insn
9.  Therefore we can know that there is no conflict between register 61 and
either register 58 or 59.

The code in ra-conflict.c tries to track subreg lifetimes.  However, it does
not detect this case.  In the greg dump file, I see this:

;; 58 conflicts: 61 59 0 1 3
;; 59 conflicts: 61 58 0 1 3
;; 61 conflicts: 58 59 1 3 4

Ideally this should be

;; 58 conflicts: 59 0 1 3
;; 59 conflicts: 58 0 1 3
;; 61 conflicts: 1 3 4

I will attach an old patch I have which was able to make this sort of
determination.  This patch is pre-DF, pre-ra-conflict, and is certainly not
applicable today.


-- 
           Summary: ra-conflict does not handle subregs optimally
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ian at airs dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35404

[Bug rtl-optimization/35404] ra-conflict does not handle subregs optimally

[ian at airs dot com]

------- Comment #1 from ian at airs dot com  2008-02-28 22:59 -------
Created an attachment (id=15244)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15244&action=view)
Old patch for this issue


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35404

[Bug rtl-optimization/35404] ra-conflict does not handle subregs optimally

[ian at airs dot com]

------- Comment #2 from ian at airs dot com  2008-02-29 18:43 -------
Whoops, you have to use to -fno-split-wide-types, not -fno-wide-types.  Sorry.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35404

[Bug rtl-optimization/35404] ra-conflict does not handle subregs optimally

[steven at gcc dot gnu dot org]

------- Comment #3 from steven at gcc dot gnu dot org  2008-03-10 21:48 -------
IRA does not handle this either with -fno-split-wide-types.  Left is IRA as-is
with -O2 -fomit-frame-pointer.  Right is same options + -fno-split-wide-types.

        .file   "t.c"                           .file   "t.c"
        .text                                   .text
        .p2align 4,,15                          .p2align 4,,15
.globl _foo                             .globl _foo
        .def    _foo;   .scl    2;              .def    _foo;   .scl    2;
_foo:                                   _foo:
        subl    $12, %esp                       subl    $12, %esp
        movl    %ebx, 4(%esp)         |         movl    %ebx, (%esp)
        movl    %esi, 8(%esp)         |         movl    %esi, 4(%esp)
                                      >         movl    %edi, 8(%esp)
                                      >         call    _bar
                                      >         movl    %eax, %esi
                                      >         movl    %edx, %edi
        call    _bar                            call    _bar
        movl    %eax, %ebx                      movl    %eax, %ebx
                                      >         orl     %esi, %ebx
        movl    %edx, %esi                      movl    %edx, %esi
        call    _bar                  |         orl     %edi, %esi
        orl     %ebx, %eax            |         movl    %ebx, %eax
        orl     %esi, %edx            |         movl    8(%esp), %edi
        movl    4(%esp), %ebx         |         movl    %esi, %edx
        movl    8(%esp), %esi         |         movl    (%esp), %ebx
                                      >         movl    4(%esp), %esi
        addl    $12, %esp                       addl    $12, %esp
        ret                                     ret
        .def    _bar;   .scl    2;              .def    _bar;   .scl    2;


-- 

steven 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         |2008-03-10 21:48:33
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35404

[Bug rtl-optimization/35404] ra-conflict does not handle subregs optimally

[hutchinsonandy at gcc dot gnu dot org]

------- Comment #4 from hutchinsonandy at gcc dot gnu dot org  2008-04-13 19:15 -------
Please look at PR35860. I believe this is same problem noted here.
subreg-lowering triggering the regression due to worsened conflicts.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35860


-- 

hutchinsonandy at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35404

[Bug rtl-optimization/35404] ra-conflict does not handle subregs optimally

[zadeck at naturalbridge dot com]

------- Comment #5 from zadeck at naturalbridge dot com  2008-04-13 19:31 -------
Subject: Re:  ra-conflict does not handle subregs
 optimally

hutchinsonandy at gcc dot gnu dot org wrote:
> ------- Comment #4 from hutchinsonandy at gcc dot gnu dot org  2008-04-13 19:15 -------
> Please look at PR35860. I believe this is same problem noted here.
> subreg-lowering triggering the regression due to worsened conflicts.
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35860
>
>
>   
In a couple of days i will have a patch ready for public examination 
that will fix the 35404 issue.
It does so by doing a more precise conflict building so that multiword 
registers can be packed on top of one another if they the "pieces" do 
not ever conflict.  

This is the info that is encoded in REG_NO_CONFLICT notes, but i have 
discovered that I find pairs of these even in places where no such 
notes/blocks were ever created.

I am in the testing process now on the part that makes global understand 
the info my conflict builder is building.  

Stevenb is working on a patch that takes local-alloc out of the loop and 
that will help also.    That is a more complex patch in that there are 
things in local that still have to be done.   

I have cc'ed my self and steven on this bugzilla and i will forward the 
patches to you as they become available and we can see if this solves 
your problems.

kenny


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35404

[Bug rtl-optimization/35404] ra-conflict does not handle subregs optimally

[hutchinsonandy at gcc dot gnu dot org]

------- Comment #6 from hutchinsonandy at gcc dot gnu dot org  2008-04-13 19:47 -------
That sounds great - it was one bug I was struggling with.

I can turn around a complete  test for AVR on mingw and Debian as soon as are
ready.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35404

[Bug rtl-optimization/35404] ra-conflict does not handle subregs optimally

[zadeck at naturalbridge dot com]

------- Comment #7 from zadeck at naturalbridge dot com  2008-04-25 21:34 -------
any regressions, if any exist at all, must be addressed by vlad's new register
allocator.


-- 

zadeck at naturalbridge dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vmakarov at gcc dot gnu dot
                   |                            |org
         AssignedTo|zadeck at naturalbridge dot |vmakarov at gcc dot gnu dot
                   |com                         |org
             Status|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35404

[Bug rtl-optimization/35404] ra-conflict does not handle subregs optimally

[aldot at gcc dot gnu dot org]

------- Comment #8 from aldot at gcc dot gnu dot org  2009-08-27 20:28 -------
(In reply to comment #7)
> any regressions, if any exist at all, must be addressed by vlad's new register
> allocator.
> 
IRA is now on trunk, is this fixed on >4.4.x ?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35404