[Bug tree-optimization/18137] arguments being gimple registers cause redundant memory loads

[Bug tree-optimization/18137] arguments being gimple registers cause redundant memory loads

[hubicka at gcc dot gnu dot org]

------- Additional Comments From hubicka at gcc dot gnu dot org  2004-10-25 00:51 -------
Created an attachment (id=7407)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=7407&action=view)
testcase


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug tree-optimization/18137] New: arguments being gimple registers cause redundant memory loads

[hubicka at gcc dot gnu dot org]

Since the arguments are gimple registers, gimple optimizers are happy to create many references to it.
While lowering them to RTL these however compile to memory loads causing number of redundant loads.
The attached quicksort loop on when compiled with -O2 -fno-loop-optimize (the other being needed only for clarity of the testcase) produces such a funny sequence:
        movl    8(%ebp), %eax   # 143   *movsi_1/1      [length = 3]
        movl    8(%ebp), %edx   # 171   *movsi_1/1      [length = 3]
        movl    8(%ebp), %ebx   # 145   *movsi_1/1      [length = 3]
These are comming from:
  median = data[start];
  pos.22 = start + 1;
  if (end - start <= 1) goto <L6>; else goto <L25>;
where each of these compiles into RTL expression that looks different to CSE:
(insn 16 15 18 1 (set (reg/v:SI 66 [ median ])
        (mem/s:SI (plus:SI (mult:SI (reg/v:SI 68 [ start ])
                    (const_int 4 [0x4]))
                (reg/f:SI 70)) [3 data S4 A32])) -1 (nil)
    (nil))

(insn 18 16 20 1 (parallel [
            (set (reg/v:SI 60 [ pos.22 ])
                (plus:SI (reg/v:SI 68 [ start ])
                    (const_int 1 [0x1])))
            (clobber (reg:CC 17 flags))
        ]) -1 (nil)
    (nil))

(insn 20 18 21 1 (parallel [
            (set (reg:SI 71)
                (minus:SI (reg/v:SI 69 [ end ])
                    (reg/v:SI 68 [ start ])))
            (clobber (reg:CC 17 flags))
        ]) -1 (nil)
    (nil))

(insn 21 20 22 1 (set (reg:CCGC 17 flags)
        (compare:CCGC (reg:SI 71)
            (const_int 1 [0x1]))) -1 (nil)
    (nil))
Similarly we get redudnant loads inside the loop itself.

Not sure about sollution - making arguments nongimple registers does not lead optimizers to deal with them very nicely, forcing
expander to load memory operands to register in prologue would lead to unnecesarly long lifetimes...
forcing memory operands to registers in RTL generation is something we want to avoid ;)
Ideas?

-- 
           Summary: arguments being gimple registers cause redundant memory
                    loads
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hubicka at gcc dot gnu dot org
                CC: dnovillo at redhat dot com,gcc-bugs at gcc dot gnu dot
                    org,rth at redhat dot com,stevenb at suse dot de
GCC target triplet: i686-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug tree-optimization/18137] arguments being gimple registers cause redundant memory loads

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-10-25 01:03 -------


*** This bug has been marked as a duplicate of 18136 ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug tree-optimization/18137] arguments being gimple registers cause redundant memory loads

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-10-25 01:08 -------
Lets reopen this one as this is the one with the testcase.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|DUPLICATE                   |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug tree-optimization/18137] arguments being gimple registers cause redundant memory loads

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-10-25 01:09 -------
*** Bug 18136 has been marked as a duplicate of this bug. ***

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug tree-optimization/18137] arguments being gimple registers cause redundant memory loads

[pinskia at gcc dot gnu dot org]

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug tree-optimization/18137] arguments being gimple registers cause redundant memory loads

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug rtl-optimization/18137] arguments being gimple registers cause redundant memory loads

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-10-25 03:33 -------
This is really a rtl problem, the problem comes from greg. before that we have:
(insn:HI 7 11 8 0 (set (reg/v:SI 68 [ start ])
        (mem/i:SI (reg/f:SI 16 argp) [3 start+0 S4 A32])) 44 {*movsi_1} (nil)
    (expr_list:REG_EQUIV (mem/i:SI (reg/f:SI 16 argp) [3 start+0 S4 A32])
        (nil)))

(insn:HI 16 9 18 0 (set (reg/v:SI 66 [ median ])
        (mem/s:SI (plus:SI (mult:SI (reg/v:SI 68 [ start ])
                    (const_int 4 [0x4]))
                (symbol_ref:SI ("data") <var_decl 0x416db6c8 data>)) [3 data S4 A32])) 44 {*movsi_1} 
(insn_list:REG_DEP_TRUE 7 (nil))
    (nil))

(insn:HI 18 16 20 0 (parallel [
            (set (reg/v:SI 60 [ pos.22 ])
                (plus:SI (reg/v:SI 68 [ start ])
                    (const_int 1 [0x1])))
            (clobber (reg:CC 17 flags))
        ]) 200 {*addsi_1} (nil)
    (expr_list:REG_UNUSED (reg:CC 17 flags)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

(insn:HI 20 18 21 0 (parallel [
            (set (reg:SI 71)
                (minus:SI (reg/v:SI 69 [ end ])
                    (reg/v:SI 68 [ start ])))
            (clobber (reg:CC 17 flags))
        ]) 233 {*subsi_1} (insn_list:REG_DEP_TRUE 8 (nil))
    (expr_list:REG_UNUSED (reg:CC 17 flags)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))


but after that we get:
(insn 153 9 16 0 (set (reg:SI 0 ax)
        (mem/i:SI (plus:SI (reg/f:SI 6 bp)
                (const_int 8 [0x8])) [3 start+0 S4 A32])) 44 {*movsi_1} (nil)
    (nil))

(insn:HI 16 153 154 0 (set (reg:SI 0 ax)
        (mem/s:SI (plus:SI (mult:SI (reg:SI 0 ax)
                    (const_int 4 [0x4]))
                (symbol_ref:SI ("data") <var_decl 0x416db6c8 data>)) [3 data S4 A32])) 44 {*movsi_1} 
(insn_list:REG_DEP_TRUE 7 (nil))
    (nil))

(insn 154 16 155 0 (set (mem:SI (plus:SI (reg/f:SI 6 bp)
                (const_int -16 [0xfffffffffffffff0])) [4 median+0 S4 A8])
        (reg:SI 0 ax)) 44 {*movsi_1} (nil)
    (nil))

(insn 155 154 18 0 (set (reg/v:SI 3 bx [orig:60 pos.22 ] [60])
        (mem/i:SI (plus:SI (reg/f:SI 6 bp)
                (const_int 8 [0x8])) [3 start+0 S4 A32])) 44 {*movsi_1} (nil)
    (nil))


Oh why is reload doing this.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|tree-optimization           |rtl-optimization
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-10-25 03:33:34
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug rtl-optimization/18137] arguments being gimple registers cause redundant memory loads

[hubicka at ucw dot cz]

------- Additional Comments From hubicka at ucw dot cz  2004-10-25 09:20 -------
Subject: Re:  arguments being gimple registers cause redundant memory loads

> 
> ------- Additional Comments From pinskia at gcc dot gnu dot org  2004-10-25 03:33 -------
> This is really a rtl problem, the problem comes from greg. before that we have:
> (insn:HI 7 11 8 0 (set (reg/v:SI 68 [ start ])
>         (mem/i:SI (reg/f:SI 16 argp) [3 start+0 S4 A32])) 44 {*movsi_1} (nil)
>     (expr_list:REG_EQUIV (mem/i:SI (reg/f:SI 16 argp) [3 start+0 S4 A32])
>         (nil)))
> 
> (insn:HI 16 9 18 0 (set (reg/v:SI 66 [ median ])
>         (mem/s:SI (plus:SI (mult:SI (reg/v:SI 68 [ start ])
>                     (const_int 4 [0x4]))
>                 (symbol_ref:SI ("data") <var_decl 0x416db6c8 data>)) [3 data S4 A32])) 44 {*movsi_1} 
> (insn_list:REG_DEP_TRUE 7 (nil))
>     (nil))
> 
> (insn:HI 18 16 20 0 (parallel [
>             (set (reg/v:SI 60 [ pos.22 ])
>                 (plus:SI (reg/v:SI 68 [ start ])
>                     (const_int 1 [0x1])))
>             (clobber (reg:CC 17 flags))
>         ]) 200 {*addsi_1} (nil)
>     (expr_list:REG_UNUSED (reg:CC 17 flags)
>         (expr_list:REG_UNUSED (reg:CC 17 flags)
>             (nil))))
> 
> (insn:HI 20 18 21 0 (parallel [
>             (set (reg:SI 71)
>                 (minus:SI (reg/v:SI 69 [ end ])
>                     (reg/v:SI 68 [ start ])))
>             (clobber (reg:CC 17 flags))
>         ]) 233 {*subsi_1} (insn_list:REG_DEP_TRUE 8 (nil))
>     (expr_list:REG_UNUSED (reg:CC 17 flags)
>         (expr_list:REG_UNUSED (reg:CC 17 flags)
>             (nil))))

Yep, I was sleepy enought to missread the patterns and mess up the bug
entry, sorry for that.  Hmm, this does not look that bad after all, but
still the 20% slowdown in the loop is interesting, I will look into it
deeper later today.

Honza


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug rtl-optimization/18137] [4.0 Regression] arguments being gimple registers cause redundant memory loads

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-11-25 23:54 -------
A simpler exampler which shows the problem.
Compile with -O1 -fno-ivopts:
void 
fcpy(float *restrict a,  float *restrict b, 
     float *restrict aa, float *restrict bb, int n) 
{ 
        int i; 
        for(i = 0; i < n; i++) { 
                aa[i]=a[i]; 
                bb[i]=b[i]; 
        } 
} 

You will see that we pull the load to aa into the loop which is wrong.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|arguments being gimple      |[4.0 Regression] arguments
                   |registers cause redundant   |being gimple registers cause
                   |memory loads                |redundant memory loads
   Target Milestone|---                         |4.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug rtl-optimization/18137] [4.0 Regression] arguments being gimple registers cause redundant memory loads

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-11-26 05:13 -------
Note the small example is wrong as not related at all, we just don't have enough registers so we use the 
agrument's location.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137

[Bug rtl-optimization/18137] [4.0 Regression] arguments being gimple registers cause redundant memory loads

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-11-26 05:30 -------
Fixed, at least it looks to be.
Most likely by:
2004-11-25  Andrew Pinski <pinskia@physics.uc.edu>

        parts of PR rtl-opt/18463, rtl-opt/17647
        * cse.c (canon_for_address): New function.
        (find_best_addr): Call canon_for_address before getting the
        address's cost when checking if we should take that address.

But I don't know for sure.

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18137