[Bug tree-optimization/51062] New: SLP vectorization of dot (inner) product

[Bug tree-optimization/51062] New: SLP vectorization of dot (inner) product

[vincenzo.innocente at cern dot ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51062

             Bug #: 51062
           Summary: SLP vectorization of dot (inner) product
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vincenzo.innocente@cern.ch


SLP is working nicely in 4.7
the most needed missing bit is the ability to vectorize a dot product (using
for instance _mm_dp_ps for sse4)

Any chance to get this any time soon?

small test here
cat dot.cc 
struct V {
  float x,y,z,w;
};

V a;
V b;

float dot() {
  return a.x*b.x+a.y*b.y+a.z*b.z+a.w*b.w;
}

V sum() {
  V v=a;
  v.x+=b.x; v.y+=b.y; v.z+=b.z; v.w+=b.w;
  return v; 
}

c++ -Ofast -c dot.cc -march=corei7
otool -X -t -v -V dot.o | c++filt
dot():
    movss    _b+0x00000004(%rip),%xmm0
    movss    _b(%rip),%xmm1
    mulss    _a+0x00000004(%rip),%xmm0
    mulss    _a(%rip),%xmm1
    addss    %xmm1,%xmm0
    movss    _b+0x00000008(%rip),%xmm1
    mulss    _a+0x00000008(%rip),%xmm1
    addss    %xmm1,%xmm0
    movss    _b+0x0000000c(%rip),%xmm1
    mulss    _a+0x0000000c(%rip),%xmm1
    addss    %xmm1,%xmm0
    ret
    nopl    (%rax)
sum():
    movaps    _b(%rip),%xmm0
    addps    _a(%rip),%xmm0
    movaps    %xmm0,0xc8(%rsp)
    movq    0xc8(%rsp),%rax
    movaps    %xmm0,0xe8(%rsp)
    movq    _a(%rsp),%xmm1
    movd    %rax,%xmm0
    ret

[Bug tree-optimization/51062] SLP vectorization of dot (inner) product

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51062

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-11-09
                 CC|                            |irar at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-11-09 14:58:42 UTC ---
I think we do not perform pattern detection in SLP mode.  Ira?

[Bug tree-optimization/51062] SLP vectorization of dot (inner) product

[irar at il dot ibm.com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51062

Ira Rosen <irar at il dot ibm.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |irar at il dot ibm.com

--- Comment #2 from Ira Rosen <irar at il dot ibm.com> 2011-11-09 16:13:08 UTC ---
(In reply to comment #1)
> I think we do not perform pattern detection in SLP mode.  Ira?

Right. I actually had a patch for pattern detection in SLP ready couple of
hours after Stage 1 was over. But this patch doesn't handle dot product (and
widen-sum), since these patterns look for reduction, i.e., loop, so it will
need some additional work.

[Bug tree-optimization/51062] SLP vectorization of dot (inner) product

[vincenzo.innocente at cern dot ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51062

vincenzo Innocente <vincenzo.innocente at cern dot ch> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|4.7.0                       |4.8.0

--- Comment #3 from vincenzo Innocente <vincenzo.innocente at cern dot ch> 2012-11-30 13:53:41 UTC ---
in 4.8 using 
typedef float __attribute__( ( vector_size( 16 ) ) ) float32x4_t;
typedef double __attribute__( ( vector_size( 32 ) ) ) float64x4_t;
the scalar product works well IF WRITTEN as a loop!

in the following 
dot_product2 produces exactly the code I would have expected to be emitted by
"dot_product"..
would be nice to have also the reduction of a single vector to emit
horizonal-sum…


float dot_product(float32x4_t x, float32x4_t y) {
  float32x4_t res = x*y;
  float ret=0;
  for (int i=0;i!=4;++i) ret+=res[i];
  return ret;
}

float dot_product2(float32x4_t x, float32x4_t y) {
  float ret=0;
  for (int i=0;i!=4;++i) ret+=x[i]*y[i];
  return ret;
}


double dot_product(float64x4_t x, float64x4_t y) {
  float64x4_t res = x*y;
  double ret=0;
  for (int i=0;i!=4;++i) ret+=res[i];
  return ret;
}

double dot_product2(float64x4_t x, float64x4_t y) {
  double ret=0;
  for (int i=0;i!=4;++i) ret+=x[i]*y[i];
  return ret;
}

c++ -Ofast -ftree-vectorizer-verbose=2 -S cross.cc  -march=corei7-avx; cat
cross.s | c++filt
dot_product(float __vector, float __vector):
LFB2:
    vmulps    %xmm1, %xmm0, %xmm1
    vmovaps    %xmm1, %xmm0
    vshufps    $85, %xmm1, %xmm1, %xmm2
    vaddss    %xmm0, %xmm2, %xmm0
    vunpckhps    %xmm1, %xmm1, %xmm2
    vshufps    $255, %xmm1, %xmm1, %xmm1
    vaddss    %xmm2, %xmm0, %xmm0
    vaddss    %xmm1, %xmm0, %xmm0
    ret
LFE2:
    .align 4,0x90
    .globl dot_product2(float __vector, float __vector)
dot_product2(float __vector, float __vector):
LFB3:
    vmulps    %xmm0, %xmm1, %xmm1
    vhaddps    %xmm1, %xmm1, %xmm0
    vhaddps    %xmm0, %xmm0, %xmm0
    ret
LFE3:
    .align 4,0x90
    .globl dot_product(double __vector, double __vector)
dot_product(double __vector, double __vector):
LFB4:
    vmulpd    %ymm1, %ymm0, %ymm1
    vmovapd    %xmm1, %xmm0
    vextractf128    $0x1, %ymm1, %xmm1
    vhaddpd    %xmm0, %xmm0, %xmm0
    vmovapd    %xmm1, %xmm2
    vunpckhpd    %xmm1, %xmm1, %xmm1
    vaddsd    %xmm2, %xmm0, %xmm0
    vaddsd    %xmm1, %xmm0, %xmm0
    vzeroupper
    ret
LFE4:
    .align 4,0x90
    .globl dot_product2(double __vector, double __vector)
dot_product2(double __vector, double __vector):
LFB5:
    vmulpd    %ymm0, %ymm1, %ymm1
    vhaddpd    %ymm1, %ymm1, %ymm1
    pushq    %rbp
LCFI0:
    movq    %rsp, %rbp
LCFI1:
    andq    $-32, %rsp
    addq    $16, %rsp
    vperm2f128    $1, %ymm1, %ymm1, %ymm0
    vaddpd    %ymm0, %ymm1, %ymm1
    vmovapd    %xmm1, %xmm0
    vzeroupper
    leave
LCFI2:
    ret