[Bug target/22076] New: Strange code for MMX register moves

[Bug target/22076] New: Strange code for MMX register moves

[uros at kss-loka dot si]

This testcase:
#include <mmintrin.h>

__m64 test() {
   __m64 a;

   return a;
}

results in quite strange code when compiled with '-O2 -mmmx':

test:
	pushl	%ebp
	movl	%esp, %ebp
	subl	$8, %esp
	movl	%eax, -8(%ebp)   <<<<
	movl	%edx, -4(%ebp)   <<<<
	movq	-8(%ebp), %mm0
	leave
	ret

If xmm registers are used (change __m64 into __m128), asm code is OK.
It looks there are some problems with register costs, from _.22.lreg:

Pass 0

  Register 58 costs: AD_REGS:13000 Q_REGS:13000 NON_Q_REGS:13000 
INDEX_REGS:13000 LEGACY_REGS:13000 GENERAL_REGS:13000 MMX_REGS:24000 
FLOAT_INT_REGS:30000 INT_SSE_REGS:30000 FLOAT_INT_SSE_REGS:30000 ALL_REGS:30000 
MEM:20000

  Register 58 pref GENERAL_REGS or none


Pass 1

  Register 58 costs: AD_REGS:13000 Q_REGS:13000 NON_Q_REGS:13000 
INDEX_REGS:13000 LEGACY_REGS:13000 GENERAL_REGS:13000 MMX_REGS:24000 
FLOAT_INT_REGS:30000 INT_SSE_REGS:30000 FLOAT_INT_SSE_REGS:30000 ALL_REGS:30000 
MEM:20000

...

(insn:HI 16 28 22 1 (set (reg/i:V2SI 29 mm0 [ <result> ])
        (reg/v:V2SI 58 [ a ])) 768 {*movv2si_internal} (nil)
    (expr_list:REG_DEAD (reg/v:V2SI 58 [ a ])
        (nil)))
...

The instructions, marked with '<<<<' are then produced by reload.

-- 
           Summary: Strange code for MMX register moves
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: ssemmx
          Severity: normal
          Priority: P2
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: uros at kss-loka dot si
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22076

[Bug target/22076] Strange code for MMX register moves

[falk at debian dot org]

------- Additional Comments From falk at debian dot org  2005-06-15 12:56 -------
(In reply to comment #0)
> This testcase:
> #include <mmintrin.h>
> 
> __m64 test() {
>    __m64 a;
> 
>    return a;
> }

Well, this is invalid code, so it's not really important what the code
looks like. If it also occurs in valid code, it might be related to PR 7061.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22076

[Bug target/22076] Strange code for MMX register moves

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-06-15 17:35 -------
a is uninitialized so what do you expect?

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22076

[Bug target/22076] Strange code for MMX register moves

[uros at kss-loka dot si]

------- Additional Comments From uros at kss-loka dot si  2005-06-21 12:04 -------
New testcase (everything is initialized this time):

--cut here--
#include <mmintrin.h>

__v8qi test ()
{
  __v8qi mm0 = {1,2,3,4,5,6,7,8};
  __v8qi mm1 = {11,22,33,44,55,66,77,88};
  volatile __m64 x;

  x = _mm_add_pi8 (mm0, mm1);

  return x;
}
--cut here--


Pass 0

  Register 67 costs: AD_REGS:4000 Q_REGS:4000 NON_Q_REGS:4000 INDEX_REGS:4000 
LEGACY_REGS:4000 GENERAL_REGS:4000 MMX_REGS:46000 INT_SSE_REGS:38000 MEM:16000

  Register 67 pref GENERAL_REGS or none


Pass 1

  Register 67 costs: AD_REGS:4000 Q_REGS:4000 NON_Q_REGS:4000 INDEX_REGS:4000 
LEGACY_REGS:4000 GENERAL_REGS:4000 MMX_REGS:46000 INT_SSE_REGS:38000 MEM:16000

69 registers.

...

(insn:HI 18 45 22 1 (set (reg:V8QI 67)
        (mem/u/i:V8QI (symbol_ref/u:SI ("*.LC2") [flags 0x2]) [0 S8 A64])) 766 
{*movv8qi_internal} (nil)
    (expr_list:REG_EQUIV (const_vector:V8QI [
                (const_int 12 [0xc])
                (const_int 24 [0x18])
                (const_int 36 [0x24])
                (const_int 48 [0x30])
                (const_int 60 [0x3c])
                (const_int 72 [0x48])
                (const_int 84 [0x54])
                (const_int 96 [0x60])
            ])
        (nil)))

...

test:
	pushl	%ebp
	movl	%esp, %ebp
	subl	$24, %esp
	movl	$807671820, %eax
	movl	$1616136252, %edx
	movl	%eax, -8(%ebp)
	movl	%edx, -4(%ebp)
	movl	-8(%ebp), %eax
	movl	-4(%ebp), %edx
	movl	%eax, -24(%ebp)
	movl	%edx, -20(%ebp)
	movq	-24(%ebp), %mm1
	leave
	movq	%mm1, %mm0
	ret



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22076

[Bug target/22076] Strange code for MMX register moves

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-06-21 13:06 -------
I think this is more related to PR 14552 which was shown by me that we regressed because we did not 
output emms at all before so not emmiting mmx instructions without use of the functions in 
mmintrin.h

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22076

[Bug target/22076] Strange code for MMX register moves

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |22152
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22076

[Bug target/22076] Strange code for MMX register moves

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-06-22 20:27 -------
Confirmed.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2005-06-22 20:27:37
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22076

[Bug target/22076] Strange code for MMX register moves

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-31 19:18 -------
*** Bug 23660 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vahur dot sinijarv at
                   |                            |cydonia dot ee


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22076

[Bug target/22076] Strange code for MMX register moves

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2005-08-31 20:34 -------
In the discussion on the duplicate PR 23660, rth explained part of this here: 
  http://gcc.gnu.org/ml/gcc/2005-08/msg00934.html 
 
W. 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22076