[PATCH] Add emulated gather capability to the vectorizer

Kewen.Lin linkw@linux.ibm.com
Mon Aug 2 08:35:35 GMT 2021


on 2021/8/2 下午3:09, Richard Biener wrote:
> On Mon, 2 Aug 2021, Kewen.Lin wrote:
> 
>> on 2021/7/30 下午10:04, Kewen.Lin via Gcc-patches wrote:
>>> Hi Richi,
>>>
>>> on 2021/7/30 下午7:34, Richard Biener wrote:
>>>> This adds a gather vectorization capability to the vectorizer
>>>> without target support by decomposing the offset vector, doing
>>>> sclar loads and then building a vector from the result.  This
>>>> is aimed mainly at cases where vectorizing the rest of the loop
>>>> offsets the cost of vectorizing the gather.
>>>>
>>>> Note it's difficult to avoid vectorizing the offset load, but in
>>>> some cases later passes can turn the vector load + extract into
>>>> scalar loads, see the followup patch.
>>>>
>>>> On SPEC CPU 2017 510.parest_r this improves runtime from 250s
>>>> to 219s on a Zen2 CPU which has its native gather instructions
>>>> disabled (using those the runtime instead increases to 254s)
>>>> using -Ofast -march=znver2 [-flto].  It turns out the critical
>>>> loops in this benchmark all perform gather operations.
>>>>
>>>
>>> Wow, it sounds promising!
>>>
>>>> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>>>>
>>>> Any comments?  I still plan to run this over full SPEC and
>>>> I have to apply TLC to the followup patch before I can post it.
>>>>
>>>> I think neither power nor z has gather so I'm curious if the
>>>> patch helps 510.parest_r there, I'm unsure about neon/advsimd.
>>>
>>> Yes, Power (latest Power10) doesn't support gather load.
>>> I just measured 510.parest_r with this patch on Power9 at option
>>> -Ofast -mcpu=power9 {,-funroll-loops}, both are neutral.
>>>
>>> It fails to vectorize the loop in vect-gather-1.c:
>>>
>>> vect-gather.c:12:28: missed:  failed: evolution of base is not affine.
>>> vect-gather.c:11:46: missed:   not vectorized: data ref analysis failed _6 = *_5;
>>> vect-gather.c:12:28: missed:   not vectorized: data ref analysis failed: _6 = *_5;
>>> vect-gather.c:11:46: missed:  bad data references.
>>> vect-gather.c:11:46: missed: couldn't vectorize loop
>>>
>>
>> By further investigation, it's due to that rs6000 fails to make
>> maybe_gather true in:
>>
>> 	  bool maybe_gather
>> 	    = DR_IS_READ (dr)
>> 	      && !TREE_THIS_VOLATILE (DR_REF (dr))
>> 	      && (targetm.vectorize.builtin_gather != NULL
>> 		  || supports_vec_gather_load_p ());
>>
>> With the hacking defining TARGET_VECTORIZE_BUILTIN_GATHER (as
>> well as TARGET_VECTORIZE_BUILTIN_SCATTER) for rs6000, the
>> case gets vectorized as expected.
> 
> Ah, yeah - this check needs to be elided.  Checking with a cross
> that's indeed what is missing.
> 
>> But re-evaluated 510.parest_r with this extra hacking, the
>> runtime performance doesn't have any changes.
> 
> OK, it likely needs the followup as well then.  For the added
> testcase I end up with
> 
> .L4:
>         lwz %r10,8(%r9)
>         lwz %r31,12(%r9)
>         addi %r8,%r8,32
>         addi %r9,%r9,16
>         lwz %r7,-16(%r9)
>         lwz %r0,-12(%r9)
>         lxv %vs10,-16(%r8)
>         lxv %vs12,-32(%r8)
>         extswsli %r10,%r10,3
>         extswsli %r31,%r31,3
>         extswsli %r7,%r7,3
>         extswsli %r0,%r0,3
>         ldx %r10,%r6,%r10
>         ldx %r31,%r6,%r31
>         ldx %r7,%r6,%r7
>         ldx %r12,%r6,%r0
>         mtvsrdd %vs0,%r31,%r10
>         mtvsrdd %vs11,%r12,%r7
>         xvmuldp %vs0,%vs0,%vs10
>         xvmaddadp %vs0,%vs12,%vs11
>         xvadddp %vs32,%vs32,%vs0
>         bdnz .L4
> 
> as the inner vectorized loop.  Looks like power doesn't have
> extending SI->DImode loads?  Otherwise the code looks

You meant one instruction for both left shifting and loads?
It doesn't if so.  btw, the above code sequence looks nice!
> straight-forward (I've used -mcpu=power10), but eventually
> the whole gather, which I think boils down to
> 
>         lwz %r10,8(%r9)
>         lwz %r31,12(%r9)
>         addi %r9,%r9,16
>         lwz %r7,-16(%r9)
>         lwz %r0,-12(%r9)
>         extswsli %r10,%r10,3
>         extswsli %r31,%r31,3
>         extswsli %r7,%r7,3
>         extswsli %r0,%r0,3
>         ldx %r10,%r6,%r10
>         ldx %r31,%r6,%r31
>         ldx %r7,%r6,%r7
>         ldx %r12,%r6,%r0
>         mtvsrdd %vs0,%r31,%r10
>         mtvsrdd %vs11,%r12,%r7
> 
> is too difficult for the integer/load side of the pipeline.  It's
> of course the same in the scalar loop but there the FP ops only
> need to wait for one lane to complete.  Note the above is with
> the followup patch.
> 

Good point!  Will check the actual effect after this and its follow-up
are landed, may need some cost tweaking on it.

BR,
Kewen

> Richard.
> 
>> BR,
>> Kewen
>>
>>>> Both might need the followup patch - I was surprised about
>>>> the speedup without it on Zen (the followup improves runtime
>>>> to 198s there).
>>>>
>>>> Thanks,
>>>> Richard.
>>>>
>>>> 2021-07-30  Richard Biener  <rguenther@suse.de>
>>>>
>>>> 	* tree-vect-data-refs.c (vect_check_gather_scatter):
>>>> 	Include widening conversions only when the result is
>>>> 	still handed by native gather or the current offset
>>>> 	size not already matches the data size.
>>>> 	Also succeed analysis in case there's no native support,
>>>> 	noted by a IFN_LAST ifn and a NULL decl.
>>>> 	* tree-vect-patterns.c (vect_recog_gather_scatter_pattern):
>>>> 	Test for no IFN gather rather than decl gather.
>>>> 	* tree-vect-stmts.c (vect_model_load_cost): Pass in the
>>>> 	gather-scatter info and cost emulated gathers accordingly.
>>>> 	(vect_truncate_gather_scatter_offset): Properly test for
>>>> 	no IFN gather.
>>>> 	(vect_use_strided_gather_scatters_p): Likewise.
>>>> 	(get_load_store_type): Handle emulated gathers and its
>>>> 	restrictions.
>>>> 	(vectorizable_load): Likewise.  Emulate them by extracting
>>>>         scalar offsets, doing scalar loads and a vector construct.
>>>>
>>>> 	* gcc.target/i386/vect-gather-1.c: New testcase.
>>>> 	* gfortran.dg/vect/vect-8.f90: Adjust.
>>>> ---
>>>>  gcc/testsuite/gcc.target/i386/vect-gather-1.c |  18 ++++
>>>>  gcc/testsuite/gfortran.dg/vect/vect-8.f90     |   2 +-
>>>>  gcc/tree-vect-data-refs.c                     |  29 +++--
>>>>  gcc/tree-vect-patterns.c                      |   2 +-
>>>>  gcc/tree-vect-stmts.c                         | 100 ++++++++++++++++--
>>>>  5 files changed, 136 insertions(+), 15 deletions(-)
>>>>  create mode 100644 gcc/testsuite/gcc.target/i386/vect-gather-1.c
>>>>
>>>> diff --git a/gcc/testsuite/gcc.target/i386/vect-gather-1.c b/gcc/testsuite/gcc.target/i386/vect-gather-1.c
>>>> new file mode 100644
>>>> index 00000000000..134aef39666
>>>> --- /dev/null
>>>> +++ b/gcc/testsuite/gcc.target/i386/vect-gather-1.c
>>>> @@ -0,0 +1,18 @@
>>>> +/* { dg-do compile } */
>>>> +/* { dg-options "-Ofast -msse2 -fdump-tree-vect-details" } */
>>>> +
>>>> +#ifndef INDEXTYPE
>>>> +#define INDEXTYPE int
>>>> +#endif
>>>> +double vmul(INDEXTYPE *rowstart, INDEXTYPE *rowend,
>>>> +	    double *luval, double *dst)
>>>> +{
>>>> +  double res = 0;
>>>> +  for (const INDEXTYPE * col = rowstart; col != rowend; ++col, ++luval)
>>>> +        res += *luval * dst[*col];
>>>> +  return res;
>>>> +}
>>>> +
>>>> +/* With gather emulation this should be profitable to vectorize
>>>> +   even with plain SSE2.  */
>>>> +/* { dg-final { scan-tree-dump "loop vectorized" "vect" } } */
>>>> diff --git a/gcc/testsuite/gfortran.dg/vect/vect-8.f90 b/gcc/testsuite/gfortran.dg/vect/vect-8.f90
>>>> index 9994805d77f..cc1aebfbd84 100644
>>>> --- a/gcc/testsuite/gfortran.dg/vect/vect-8.f90
>>>> +++ b/gcc/testsuite/gfortran.dg/vect/vect-8.f90
>>>> @@ -706,5 +706,5 @@ END SUBROUTINE kernel
>>>>  
>>>>  ! { dg-final { scan-tree-dump-times "vectorized 24 loops" 1 "vect" { target aarch64_sve } } }
>>>>  ! { dg-final { scan-tree-dump-times "vectorized 23 loops" 1 "vect" { target { aarch64*-*-* && { ! aarch64_sve } } } } }
>>>> -! { dg-final { scan-tree-dump-times "vectorized 2\[23\] loops" 1 "vect" { target { vect_intdouble_cvt && { ! aarch64*-*-* } } } } }
>>>> +! { dg-final { scan-tree-dump-times "vectorized 2\[234\] loops" 1 "vect" { target { vect_intdouble_cvt && { ! aarch64*-*-* } } } } }
>>>>  ! { dg-final { scan-tree-dump-times "vectorized 17 loops" 1 "vect" { target { { ! vect_intdouble_cvt } && { ! aarch64*-*-* } } } } }
>>>> diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
>>>> index 6995efba899..0279e75fa8e 100644
>>>> --- a/gcc/tree-vect-data-refs.c
>>>> +++ b/gcc/tree-vect-data-refs.c
>>>> @@ -4007,8 +4007,26 @@ vect_check_gather_scatter (stmt_vec_info stmt_info, loop_vec_info loop_vinfo,
>>>>  	      continue;
>>>>  	    }
>>>>  
>>>> -	  if (TYPE_PRECISION (TREE_TYPE (op0))
>>>> -	      < TYPE_PRECISION (TREE_TYPE (off)))
>>>> +	  /* Include the conversion if it is widening and we're using
>>>> +	     the IFN path or the target can handle the converted from
>>>> +	     offset or the current size is not already the same as the
>>>> +	     data vector element size.  */
>>>> +	  if ((TYPE_PRECISION (TREE_TYPE (op0))
>>>> +	       < TYPE_PRECISION (TREE_TYPE (off)))
>>>> +	      && ((!use_ifn_p
>>>> +		   && (DR_IS_READ (dr)
>>>> +		       ? (targetm.vectorize.builtin_gather
>>>> +			  && targetm.vectorize.builtin_gather (vectype,
>>>> +							       TREE_TYPE (op0),
>>>> +							       scale))
>>>> +		       : (targetm.vectorize.builtin_scatter
>>>> +			  && targetm.vectorize.builtin_scatter (vectype,
>>>> +								TREE_TYPE (op0),
>>>> +								scale))))
>>>> +		  || (!use_ifn_p
>>>> +		      && !operand_equal_p (TYPE_SIZE (TREE_TYPE (off)),
>>>> +					   TYPE_SIZE (TREE_TYPE (vectype)),
>>>> +					   0))))
>>>>  	    {
>>>>  	      off = op0;
>>>>  	      offtype = TREE_TYPE (off);
>>>> @@ -4036,7 +4054,8 @@ vect_check_gather_scatter (stmt_vec_info stmt_info, loop_vec_info loop_vinfo,
>>>>        if (!vect_gather_scatter_fn_p (loop_vinfo, DR_IS_READ (dr), masked_p,
>>>>  				     vectype, memory_type, offtype, scale,
>>>>  				     &ifn, &offset_vectype))
>>>> -	return false;
>>>> +	ifn = IFN_LAST;
>>>> +      decl = NULL_TREE;
>>>>      }
>>>>    else
>>>>      {
>>>> @@ -4050,10 +4069,6 @@ vect_check_gather_scatter (stmt_vec_info stmt_info, loop_vec_info loop_vinfo,
>>>>  	  if (targetm.vectorize.builtin_scatter)
>>>>  	    decl = targetm.vectorize.builtin_scatter (vectype, offtype, scale);
>>>>  	}
>>>> -
>>>> -      if (!decl)
>>>> -	return false;
>>>> -
>>>>        ifn = IFN_LAST;
>>>>        /* The offset vector type will be read from DECL when needed.  */
>>>>        offset_vectype = NULL_TREE;
>>>> diff --git a/gcc/tree-vect-patterns.c b/gcc/tree-vect-patterns.c
>>>> index 743fd3f5414..25de97bd9b0 100644
>>>> --- a/gcc/tree-vect-patterns.c
>>>> +++ b/gcc/tree-vect-patterns.c
>>>> @@ -4811,7 +4811,7 @@ vect_recog_gather_scatter_pattern (vec_info *vinfo,
>>>>       function for the gather/scatter operation.  */
>>>>    gather_scatter_info gs_info;
>>>>    if (!vect_check_gather_scatter (stmt_info, loop_vinfo, &gs_info)
>>>> -      || gs_info.decl)
>>>> +      || gs_info.ifn == IFN_LAST)
>>>>      return NULL;
>>>>  
>>>>    /* Convert the mask to the right form.  */
>>>> diff --git a/gcc/tree-vect-stmts.c b/gcc/tree-vect-stmts.c
>>>> index 05085e1b110..9d51b476db6 100644
>>>> --- a/gcc/tree-vect-stmts.c
>>>> +++ b/gcc/tree-vect-stmts.c
>>>> @@ -1084,6 +1084,7 @@ static void
>>>>  vect_model_load_cost (vec_info *vinfo,
>>>>  		      stmt_vec_info stmt_info, unsigned ncopies, poly_uint64 vf,
>>>>  		      vect_memory_access_type memory_access_type,
>>>> +		      gather_scatter_info *gs_info,
>>>>  		      slp_tree slp_node,
>>>>  		      stmt_vector_for_cost *cost_vec)
>>>>  {
>>>> @@ -1172,9 +1173,17 @@ vect_model_load_cost (vec_info *vinfo,
>>>>    if (memory_access_type == VMAT_ELEMENTWISE
>>>>        || memory_access_type == VMAT_GATHER_SCATTER)
>>>>      {
>>>> -      /* N scalar loads plus gathering them into a vector.  */
>>>>        tree vectype = STMT_VINFO_VECTYPE (stmt_info);
>>>>        unsigned int assumed_nunits = vect_nunits_for_cost (vectype);
>>>> +      if (memory_access_type == VMAT_GATHER_SCATTER
>>>> +	  && gs_info->ifn == IFN_LAST && !gs_info->decl)
>>>> +	/* For emulated gathers N offset vector element extracts
>>>> +	   (we assume the scalar scaling and ptr + offset add is consumed by
>>>> +	   the load).  */
>>>> +	inside_cost += record_stmt_cost (cost_vec, ncopies * assumed_nunits,
>>>> +					 vec_to_scalar, stmt_info, 0,
>>>> +					 vect_body);
>>>> +      /* N scalar loads plus gathering them into a vector.  */
>>>>        inside_cost += record_stmt_cost (cost_vec,
>>>>  				       ncopies * assumed_nunits,
>>>>  				       scalar_load, stmt_info, 0, vect_body);
>>>> @@ -1184,7 +1193,9 @@ vect_model_load_cost (vec_info *vinfo,
>>>>  			&inside_cost, &prologue_cost, 
>>>>  			cost_vec, cost_vec, true);
>>>>    if (memory_access_type == VMAT_ELEMENTWISE
>>>> -      || memory_access_type == VMAT_STRIDED_SLP)
>>>> +      || memory_access_type == VMAT_STRIDED_SLP
>>>> +      || (memory_access_type == VMAT_GATHER_SCATTER
>>>> +	  && gs_info->ifn == IFN_LAST && !gs_info->decl))
>>>>      inside_cost += record_stmt_cost (cost_vec, ncopies, vec_construct,
>>>>  				     stmt_info, 0, vect_body);
>>>>  
>>>> @@ -1866,7 +1877,8 @@ vect_truncate_gather_scatter_offset (stmt_vec_info stmt_info,
>>>>        tree memory_type = TREE_TYPE (DR_REF (dr));
>>>>        if (!vect_gather_scatter_fn_p (loop_vinfo, DR_IS_READ (dr), masked_p,
>>>>  				     vectype, memory_type, offset_type, scale,
>>>> -				     &gs_info->ifn, &gs_info->offset_vectype))
>>>> +				     &gs_info->ifn, &gs_info->offset_vectype)
>>>> +	  || gs_info->ifn == IFN_LAST)
>>>>  	continue;
>>>>  
>>>>        gs_info->decl = NULL_TREE;
>>>> @@ -1901,7 +1913,7 @@ vect_use_strided_gather_scatters_p (stmt_vec_info stmt_info,
>>>>  				    gather_scatter_info *gs_info)
>>>>  {
>>>>    if (!vect_check_gather_scatter (stmt_info, loop_vinfo, gs_info)
>>>> -      || gs_info->decl)
>>>> +      || gs_info->ifn == IFN_LAST)
>>>>      return vect_truncate_gather_scatter_offset (stmt_info, loop_vinfo,
>>>>  						masked_p, gs_info);
>>>>  
>>>> @@ -2355,6 +2367,27 @@ get_load_store_type (vec_info  *vinfo, stmt_vec_info stmt_info,
>>>>  			     vls_type == VLS_LOAD ? "gather" : "scatter");
>>>>  	  return false;
>>>>  	}
>>>> +      else if (gs_info->ifn == IFN_LAST && !gs_info->decl)
>>>> +	{
>>>> +	  if (vls_type != VLS_LOAD)
>>>> +	    {
>>>> +	      if (dump_enabled_p ())
>>>> +		dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
>>>> +				 "unsupported emulated scatter.\n");
>>>> +	      return false;
>>>> +	    }
>>>> +	  else if (!TYPE_VECTOR_SUBPARTS (vectype).is_constant ()
>>>> +		   || !known_eq (TYPE_VECTOR_SUBPARTS (vectype),
>>>> +				 TYPE_VECTOR_SUBPARTS
>>>> +				   (gs_info->offset_vectype)))
>>>> +	    {
>>>> +	      if (dump_enabled_p ())
>>>> +		dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
>>>> +				 "unsupported vector types for emulated "
>>>> +				 "gather.\n");
>>>> +	      return false;
>>>> +	    }
>>>> +	}
>>>>        /* Gather-scatter accesses perform only component accesses, alignment
>>>>  	 is irrelevant for them.  */
>>>>        *alignment_support_scheme = dr_unaligned_supported;
>>>> @@ -8692,6 +8725,15 @@ vectorizable_load (vec_info *vinfo,
>>>>  			     "unsupported access type for masked load.\n");
>>>>  	  return false;
>>>>  	}
>>>> +      else if (memory_access_type == VMAT_GATHER_SCATTER
>>>> +	       && gs_info.ifn == IFN_LAST
>>>> +	       && !gs_info.decl)
>>>> +	{
>>>> +	  if (dump_enabled_p ())
>>>> +	    dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
>>>> +			     "unsupported masked emulated gather.\n");
>>>> +	  return false;
>>>> +	}
>>>>      }
>>>>  
>>>>    if (!vec_stmt) /* transformation not required.  */
>>>> @@ -8725,7 +8767,7 @@ vectorizable_load (vec_info *vinfo,
>>>>  
>>>>        STMT_VINFO_TYPE (orig_stmt_info) = load_vec_info_type;
>>>>        vect_model_load_cost (vinfo, stmt_info, ncopies, vf, memory_access_type,
>>>> -			    slp_node, cost_vec);
>>>> +			    &gs_info, slp_node, cost_vec);
>>>>        return true;
>>>>      }
>>>>  
>>>> @@ -9438,7 +9480,8 @@ vectorizable_load (vec_info *vinfo,
>>>>  		    unsigned int misalign;
>>>>  		    unsigned HOST_WIDE_INT align;
>>>>  
>>>> -		    if (memory_access_type == VMAT_GATHER_SCATTER)
>>>> +		    if (memory_access_type == VMAT_GATHER_SCATTER
>>>> +			&& gs_info.ifn != IFN_LAST)
>>>>  		      {
>>>>  			tree zero = build_zero_cst (vectype);
>>>>  			tree scale = size_int (gs_info.scale);
>>>> @@ -9456,6 +9499,51 @@ vectorizable_load (vec_info *vinfo,
>>>>  			data_ref = NULL_TREE;
>>>>  			break;
>>>>  		      }
>>>> +		    else if (memory_access_type == VMAT_GATHER_SCATTER)
>>>> +		      {
>>>> +			/* Emulated gather-scatter.  */
>>>> +			gcc_assert (!final_mask);
>>>> +			unsigned HOST_WIDE_INT const_nunits
>>>> +			  = nunits.to_constant ();
>>>> +			vec<constructor_elt, va_gc> *ctor_elts;
>>>> +			vec_alloc (ctor_elts, const_nunits);
>>>> +			gimple_seq stmts = NULL;
>>>> +			tree idx_type = TREE_TYPE (TREE_TYPE (vec_offset));
>>>> +			tree scale = size_int (gs_info.scale);
>>>> +			align
>>>> +			  = get_object_alignment (DR_REF (first_dr_info->dr));
>>>> +			tree ltype = build_aligned_type (TREE_TYPE (vectype),
>>>> +							 align);
>>>> +			for (unsigned k = 0; k < const_nunits; ++k)
>>>> +			  {
>>>> +			    tree boff = size_binop (MULT_EXPR,
>>>> +						    TYPE_SIZE (idx_type),
>>>> +						    bitsize_int (k));
>>>> +			    tree idx = gimple_build (&stmts, BIT_FIELD_REF,
>>>> +						     idx_type, vec_offset,
>>>> +						     TYPE_SIZE (idx_type),
>>>> +						     boff);
>>>> +			    idx = gimple_convert (&stmts, sizetype, idx);
>>>> +			    idx = gimple_build (&stmts, MULT_EXPR,
>>>> +						sizetype, idx, scale);
>>>> +			    tree ptr = gimple_build (&stmts, PLUS_EXPR,
>>>> +						     TREE_TYPE (dataref_ptr),
>>>> +						     dataref_ptr, idx);
>>>> +			    ptr = gimple_convert (&stmts, ptr_type_node, ptr);
>>>> +			    tree elt = make_ssa_name (TREE_TYPE (vectype));
>>>> +			    tree ref = build2 (MEM_REF, ltype, ptr,
>>>> +					       build_int_cst (ref_type, 0));
>>>> +			    new_stmt = gimple_build_assign (elt, ref);
>>>> +			    gimple_seq_add_stmt (&stmts, new_stmt);
>>>> +			    CONSTRUCTOR_APPEND_ELT (ctor_elts, NULL_TREE, elt);
>>>> +			  }
>>>> +			gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
>>>> +			new_stmt = gimple_build_assign (NULL_TREE,
>>>> +							build_constructor
>>>> +							  (vectype, ctor_elts));
>>>> +			data_ref = NULL_TREE;
>>>> +			break;
>>>> +		      }
>>>>  
>>>>  		    align =
>>>>  		      known_alignment (DR_TARGET_ALIGNMENT (first_dr_info));
>>>>
>>>
>>
> 


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