[Bug target/103124] New: PPC: "mr" instruction is unnecessary when extending DI to V1TI

[Bug target/103124] New: PPC: "mr" instruction is unnecessary when extending DI to V1TI

[guihaoc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103124

            Bug ID: 103124
           Summary: PPC: "mr" instruction is unnecessary when extending DI
                    to V1TI
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: guihaoc at gcc dot gnu.org
  Target Milestone: ---

//test.c
vector __int128 init (long long a)
{
  vector __int128 b;
  b = (vector __int128) {a};
  return b;
}

gcc -O2 -s test.c -mcpu=power9

//p9 assembly
        mr 10,3
        sradi 11,3,63
        mtvsrdd 34,11,10

The first mr is unnecessary if the last one is changed to "mtvsrdd 34,11,3".

[Bug target/103124] PPC: "mr" instruction is unnecessary when extending DI to V1TI

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103124

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug target/103124] PPC: "mr" instruction is unnecessary when extending DI to V1TI

[guihaoc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103124

--- Comment #1 from HaoChen Gui <guihaoc at gcc dot gnu.org> ---
Build command gcc -O2 -S test.c -mcpu=power9

[Bug target/103124] PPC: "mr" instruction is unnecessary when extending DI to V1TI

[guihaoc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103124

--- Comment #2 from HaoChen Gui <guihaoc at gcc dot gnu.org> ---
//lower-subreg.c
          /* If this is a cast from one mode to another, where the modes
             have the same size, and they are not tieable, then mark this
             register as non-decomposable.  If we decompose it we are
             likely to mess up whatever the backend is trying to do.  */
          if (outer_words > 1
              && outer_size == inner_size
              && !targetm.modes_tieable_p (GET_MODE (x), GET_MODE (inner)))
            {
              bitmap_set_bit (non_decomposable_context, regno);
              bitmap_set_bit (subreg_context, regno);
              iter.skip_subrtxes ();
              continue;
            }

As TI and V1TI is not tieable on powerpc, TI register 122 in the following insn
can't be decomposed. 

(insn 12 11 13 2 (set (reg:V1TI 121 [ b ])
        (subreg:V1TI (reg:TI 122) 0)) "test2.c":4:5 1167 {vsx_movv1ti_64bit}
     (nil))

[Bug target/103124] PPC: "mr" instruction is unnecessary when extending DI to V1TI

[guihaoc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103124

--- Comment #3 from HaoChen Gui <guihaoc at gcc dot gnu.org> ---
My solution is to split the move (from TI to V1TI) into one vsx_concat_v2di and
one V2DI to V1TI move. Thus, TI register 122 can be decomposed.

(insn 12 11 17 2 (set (reg:V1TI 121 [ b ])
        (subreg:V1TI (reg:TI 122 [ a ]) 0)) "test2.c":4:5 1167
{vsx_movv1ti_64bit}
     (expr_list:REG_DEAD (reg:TI 122 [ a ])
        (nil)))

//after split pass
(insn 23 11 24 2 (set (reg:V2DI 125)
        (vec_concat:V2DI (subreg:DI (reg:TI 122 [ a ]) 0)
            (subreg:DI (reg:TI 122 [ a ]) 8))) "test2.c":4:5 -1
     (nil))
(insn 24 23 17 2 (set (reg:V1TI 121 [ b ])
        (subreg:V1TI (reg:V2DI 125) 0)) "test2.c":4:5 -1
     (nil))

//after subreg pass
(insn 23 11 24 2 (set (reg:V2DI 125)
        (vec_concat:V2DI (reg:DI 126 [ a ])
            (reg:DI 127 [ a+8 ]))) "test2.c":4:5 1346 {vsx_concat_v2di}
     (nil))
(insn 24 23 17 2 (set (reg:V1TI 121 [ b ])
        (subreg:V1TI (reg:V2DI 125) 0)) "test2.c":4:5 1167 {vsx_movv1ti_64bit}
     (nil))

[Bug target/103124] PPC: "mr" instruction is unnecessary when extending DI to V1TI

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103124

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-11-10
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #4 from Segher Boessenkool <segher at gcc dot gnu.org> ---
  Skipping mode TI for zero_extend lowering.
  Splitting mode TI for ashift lowering with shift amounts = 
  Splitting mode TI for lshiftrt lowering with shift amounts = 
  Splitting mode TI for ashiftrt lowering with shift amounts = 

All these should be fixed.  But it is a red herring here, since the shift we
have is in DImode already anyway, not TImode.

Confirmed btw.

[Bug target/103124] PPC: "mr" instruction is unnecessary when extending DI to V1TI

[guihaoc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103124

--- Comment #5 from HaoChen Gui <guihaoc at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #4)
>   Skipping mode TI for zero_extend lowering.
>   Splitting mode TI for ashift lowering with shift amounts = 
>   Splitting mode TI for lshiftrt lowering with shift amounts = 
>   Splitting mode TI for ashiftrt lowering with shift amounts = 
> 
> All these should be fixed.  But it is a red herring here, since the shift we
> have is in DImode already anyway, not TImode.
> 
> Confirmed btw.

I not sure if splitting TI for zero_extend or shift is necessary. Do we
generate zero_extend:TI rtx or ashift:TI rtx? During expand, these operations
already expand to some operations on DI mode. They will be split latter if TI
copy splitting is allowed. 

zero_extend
b = (unsigned __int128) a;

(insn 7 6 8 2 (set (subreg:DI (reg:TI 119) 8)
        (const_int 0 [0])) "split1.c":5:10 -1
     (nil))


ashift
b = a << 3;

(insn 6 3 7 2 (set (reg:DI 122)
        (lshiftrt:DI (subreg:DI (reg/v:TI 119 [ a ]) 0)
            (const_int 61 [0x3d]))) "split.c":4:9 -1
     (nil))
(insn 7 6 8 2 (set (subreg:DI (reg:TI 121) 8)
        (ashift:DI (subreg:DI (reg/v:TI 119 [ a ]) 8)
            (const_int 3 [0x3]))) "split.c":4:9 -1
     (nil))
(insn 8 7 9 2 (set (subreg:DI (reg:TI 121) 8)
        (ior:DI (reg:DI 122)
            (subreg:DI (reg:TI 121) 8))) "split.c":4:9 -1
     (nil))
(insn 9 8 10 2 (set (subreg:DI (reg:TI 121) 0)
        (ashift:DI (subreg:DI (reg/v:TI 119 [ a ]) 0)
            (const_int 3 [0x3]))) "split.c":4:9 -1
     (nil))

[Bug target/103124] PPC: "mr" instruction is unnecessary when extending DI to V1TI

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103124

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by HaoChen Gui <guihaoc@gcc.gnu.org>:

https://gcc.gnu.org/g:240dd6c063b481c092c9ec406b69b400f6f033f1

commit r12-6620-g240dd6c063b481c092c9ec406b69b400f6f033f1
Author: Haochen Gui <guihaoc@gcc.gnu.org>
Date:   Mon Jan 17 11:24:20 2022 +0800

    rs6000: Split pattern for TI to V1TI move [PR103124]

    This patch defines a new split pattern for TI to V1TI move.  The pattern
concatenates two subreg:DI of a TI to a V2DI.  With the pattern, the subreg
pass can do register split for TI when there is a TI to V1TI move.

    gcc/

            PR target/103124
            * config/rs6000/vsx.md (split pattern for TI to V1TI move):
Defined.

    gcc/testsuite/

            PR target/103124
            * gcc.target/powerpc/pr103124.c: New testcase.

[Bug target/103124] PPC: "mr" instruction is unnecessary when extending DI to V1TI

[guihaoc at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103124

HaoChen Gui <guihaoc at gcc dot gnu.org> changed:

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

--- Comment #7 from HaoChen Gui <guihaoc at gcc dot gnu.org> ---
fixed by r12-6620