Re: Re: [PATCH V3] VECT: Support loop len control on EXTRACT_LAST vectorization

[Richard Biener <rguenther@suse.de>]

On Fri, 11 Aug 2023, juzhe.zhong@rivai.ai wrote:

> Hi, Richi.
> 
> > 1. Target is using loop MASK as the partial vector loop control.
> >> I don't think it checks for this?
> 
> I am not sure whether I understand EXTRACT_LAST correctly.
> But if target doesn't use loop MASK for partial vector loop control, how does target use EXTRACT_LAST?
> Since EXTRACT_LAST is always extracting the last element of the vector according to MASK operand.
> 
> > But we don't really know this at this point?  The only thing we know
> > is that nothing set LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P to false.
> 
> Yes. So I am try to use 'get_len_load_store' to check whether target support LEN loop control.
> 
> Well, I admit it's not a good idea.
> 
> 
> > I think it should work to change the direct_internal_fn_supported_p
> > check for IFN_EXTRACT_LAST to a "poitive" one guarding
> 
> >               gcc_assert (ncopies == 1 && !slp_node);
> >               vect_record_loop_mask (loop_vinfo,
> >                                      &LOOP_VINFO_MASKS (loop_vinfo),
> >                                      1, vectype, NULL);
> 
> > and in the else branch check for VEC_EXTRACT support and if present
> > record a loop len.  Just in this case this particular order would
> > be important.
> 
> Do you mean change the codes as follows :?
> 
> -         if (!direct_internal_fn_supported_p (IFN_EXTRACT_LAST, vectype,
> -                                              OPTIMIZE_FOR_SPEED))
> -           {
> -             if (dump_enabled_p ())
> -               dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> -                                "can't operate on partial vectors "
> -                                "because the target doesn't support extract "
> -                                "last reduction.\n");
> -             LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P (loop_vinfo) = false;
> -           }
> -         else if (slp_node)
>           if (slp_node)
>             {
>               if (dump_enabled_p ())
>                 dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
>                                  "can't operate on partial vectors "
>                                  "because an SLP statement is live after "
>                                  "the loop.\n");
>               LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P (loop_vinfo) = false;
>             }
>           else if (ncopies > 1)
>             {
>               if (dump_enabled_p ())
>                 dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
>                                  "can't operate on partial vectors "
>                                  "because ncopies is greater than 1.\n");
>               LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P (loop_vinfo) = false;
>             }
>           else
>             {
>               gcc_assert (ncopies == 1 && !slp_node);
>               if (direct_internal_fn_supported_p (IFN_EXTRACT_LAST, vectype,
>                                                   OPTIMIZE_FOR_SPEED))
>                 vect_record_loop_mask (loop_vinfo,
>                                        &LOOP_VINFO_MASKS (loop_vinfo),
>                                        1, vectype, NULL);
>               else

check here the target supports VEC_EXTRACT

>                 vect_record_loop_len (loop_vinfo,
>                                       &LOOP_VINFO_LENS (loop_vinfo),
>                                       1, vectype, 1);

else set LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P to false with a
diagnostic.

>             }
> 
> 
> Thanks.
> 
> 
> juzhe.zhong@rivai.ai
>  
> From: Richard Biener
> Date: 2023-08-11 18:21
> To: juzhe.zhong@rivai.ai
> CC: gcc-patches; richard.sandiford; linkw; krebbel
> Subject: Re: Re: [PATCH V3] VECT: Support loop len control on EXTRACT_LAST vectorization
> On Fri, 11 Aug 2023, juzhe.zhong@rivai.ai wrote:
>  
> > Hi, Richi.
> > 
> > >> So how can we resolve the issue when a non-VL operation like
> > >> .VEC_EXTRACT is used for _len support?
> > 
> > Do you mean non-VL extract last operation (I am sorry that not sure whether I understand your question correctly)? 
> > If yes, the answer is for RVV, we are reusing the same flow as ARM SVE (BIT_FILED_REF approach), see the example below:
> > 
> > https://godbolt.org/z/cqrWrY8q4 
> > 
> > #define EXTRACT_LAST(TYPE)          \
> >   TYPE __attribute__ ((noinline, noclone))  \
> >   test_##TYPE (TYPE *x, int n, TYPE value)  \
> >   {                     \
> >     TYPE last;                  \
> >     for (int j = 0; j < 64; ++j)            \
> >       {                     \
> >     last = x[j];                \
> >     x[j] = last * value;            \
> >       }                     \
> >     return last;                \
> >   }
> > 
> > #define TEST_ALL(T)             \
> >   T (uint8_t)                   \
> > 
> > TEST_ALL (EXTRACT_LAST)
> > 
> >   vect_cst__22 = {value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D), value_12(D)};
> >   vect_last_11.6_3 = MEM <vector(64) unsigned char> [(uint8_t *)x_10(D)];
> >   vect__4.7_23 = vect_last_11.6_3 * vect_cst__22;
> >   MEM <vector(64) unsigned char> [(uint8_t *)x_10(D)] = vect__4.7_23;
> >   _21 = BIT_FIELD_REF <vect_last_11.6_3, 8, 504>;
> > 
> > This approach works perfectly for both RVV and ARM SVE for non-VL and non-MASK EXTRACT_LAST operation.
> > 
> > >> So, why do we test for get_len_load_store_mode and not just for
> > >> VEC_EXTRACT?
> > 
> > Before answer this question, let me first elaborate how ARM SVE is doing with MASK EXTRACT_LAST.
> > 
> > Here is the example:
> > https://godbolt.org/z/8cTv1jqMb 
> > 
> > ARM SVE IR:
> > 
> >   <bb 4> [local count: 955630224]:
> >   # ivtmp_31 = PHI <ivtmp_32(4), 0(3)>
> > 
> >   # loop_mask_22 = PHI <next_mask_35(4), max_mask_34(3)> -----> For RVV, we want this to be loop_len = SELECT_VL;
> > 
> >   _7 = &MEM <vector([16,16]) unsigned char> [(uint8_t *)x_11(D) + ivtmp_31 * 1];
> >   vect_last_12.8_23 = .MASK_LOAD (_7, 8B, loop_mask_22);
> >   vect__4.9_27 = vect_last_12.8_23 * vect_cst__26;
> >   .MASK_STORE (_7, 8B, loop_mask_22, vect__4.9_27);
> >   ivtmp_32 = ivtmp_31 + POLY_INT_CST [16, 16];
> >   _1 = (unsigned int) ivtmp_32;
> > 
> >   next_mask_35 = .WHILE_ULT (_1, bnd.5_6, { 0, ... });
> > 
> >   if (next_mask_35 != { 0, ... })
> >     goto <bb 4>; [89.00%]
> >   else
> >     goto <bb 5>; [11.00%]
> > 
> >   <bb 5> [local count: 105119324]:
> > 
> >   _25 = .EXTRACT_LAST (loop_mask_22, vect_last_12.8_23); [tail call] ----> Use the last mask generated in BB 4, so for RVV, we are using the loop_len.
> > 
> > So this patch is trying to optimize the codegen with simulating same flow as ARM SVE but with replacing 'loop_mask_22' (This is generated in BB4) into 'loop_len'.
> > 
> > For ARM SVE, they only check whether target support EXTRACT_LAST pattern, this pattern is supported means:
> > 
> > 1. Target is using loop MASK as the partial vector loop control.
>  
> I don't think it checks for this?
>  
> > 2. extract_last optab is enabled in the backend.
> > 
> > So for RVV, we are also checking same conditions:
> > 
> > 1. Target is using loop LEN as the partial vector loop control (I use get_len_load_store_mode to check whether target is using loop LEN as the partial vector loop control).
>  
> But we don't really know this at this point?  The only thing we know
> is that nothing set LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P to false.
>  
> > 2. vec_extract optab is enabled in the backend.
> > 
> > An alternative approach is that we can adding EXTRACT_LAST_LEN internal FN, then we can only check this like ARM SVE only check EXTRACT_LAST.
>  
> I think it should work to change the direct_internal_fn_supported_p
> check for IFN_EXTRACT_LAST to a "poitive" one guarding
>  
>               gcc_assert (ncopies == 1 && !slp_node);
>               vect_record_loop_mask (loop_vinfo,
>                                      &LOOP_VINFO_MASKS (loop_vinfo),
>                                      1, vectype, NULL);
>  
> and in the else branch check for VEC_EXTRACT support and if present
> record a loop len.  Just in this case this particular order would
> be important.
>  
> > >> can we double-check this on powerpc and s390?
> > 
> > Sure, I hope it can be beneficial to powerpc and s390.
> > And, I think Richard's comments are also very important so I am gonna wait for it.
>  
> Yeah, just to double-check the bias stuff works correctly.
>  
> Richard.
>  
> > Thanks.
> > 
> > 
> > juzhe.zhong@rivai.ai
> >  
> > From: Richard Biener
> > Date: 2023-08-11 15:01
> > To: Ju-Zhe Zhong
> > CC: gcc-patches; richard.sandiford; linkw; krebbel
> > Subject: Re: [PATCH V3] VECT: Support loop len control on EXTRACT_LAST vectorization
> > On Fri, 11 Aug 2023, juzhe.zhong@rivai.ai wrote:
> >  
> > > From: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
> > > 
> > > Hi, Richard and Richi.
> > > 
> > > This patch add support live vectorization by VEC_EXTRACT for LEN loop control.
> > > 
> > > Consider this following case:
> > > 
> > > #include <stdint.h>
> > > 
> > > #define EXTRACT_LAST(TYPE) \
> > >   TYPE __attribute__ ((noinline, noclone)) \
> > >   test_##TYPE (TYPE *x, int n, TYPE value) \
> > >   { \
> > >     TYPE last; \
> > >     for (int j = 0; j < n; ++j) \
> > >       { \
> > > last = x[j]; \
> > > x[j] = last * value; \
> > >       } \
> > >     return last; \
> > >   }
> > > 
> > > #define TEST_ALL(T) \
> > >   T (uint8_t) \
> > > 
> > > TEST_ALL (EXTRACT_LAST)
> > > 
> > > ARM SVE IR:
> > > 
> > > Preheader:
> > >   max_mask_34 = .WHILE_ULT (0, bnd.5_6, { 0, ... });
> > > 
> > > Loop:
> > >   ...
> > >   # loop_mask_22 = PHI <next_mask_35(4), max_mask_34(3)>
> > >   ...
> > >   vect_last_12.8_23 = .MASK_LOAD (_7, 8B, loop_mask_22);
> > >   vect__4.9_27 = vect_last_12.8_23 * vect_cst__26;
> > >   .MASK_STORE (_7, 8B, loop_mask_22, vect__4.9_27);
> > >   ...
> > >   next_mask_35 = .WHILE_ULT (_1, bnd.5_6, { 0, ... });
> > >   ...
> > > 
> > > Epilogue:
> > >   _25 = .EXTRACT_LAST (loop_mask_22, vect_last_12.8_23);
> > > 
> > > For RVV since we prefer len in loop control, after this patch for RVV:
> > > 
> > > Loop:
> > >   ...
> > >   loop_len_22 = SELECT_VL;
> > >   vect_last_12.8_23 = .MASK_LOAD (_7, 8B, loop_len_22);
> > >   vect__4.9_27 = vect_last_12.8_23 * vect_cst__26;
> > >   .MASK_STORE (_7, 8B, loop_len_22, vect__4.9_27);
> > >   ...
> > > 
> > > Epilogue:
> > >   _25 = .VEC_EXTRACT (loop_len_22 + bias - 1, vect_last_12.8_23);
> > > 
> > > Details of this approach:
> > > 
> > > 1. Step 1 - Add 'vect_can_vectorize_extract_last_with_len_p'  to enable live vectorization
> > >             for LEN loop control.
> > >    
> > >    This function we check whether target support:
> > >     - Use LEN as the loop control.
> > >     - Support VEC_EXTRACT optab.
> > > 
> > > 2. Step 2 - Record LEN for loop control if 'vect_can_vectorize_extract_last_with_len_p' is true.
> > > 
> > > 3. Step 3 - Gerenate VEC_EXTRACT (v, LEN + BIAS - 1).
> > > 
> > > The only difference between mask and len is that len is using length generated by SELECT_VL and
> > > use VEC_EXTRACT pattern. The rest of the live vectorization is totally the same ARM SVE.
> > > 
> > > Bootstrap and Regression on X86 passed.
> > > 
> > > Tested on ARM QEMU.
> > > 
> > > Ok for trunk?
> > > 
> > > gcc/ChangeLog:
> > > 
> > > * tree-vect-loop.cc (vect_can_vectorize_extract_last_with_len_p): New function.
> > > (vectorizable_live_operation): Add loop len control.
> > > 
> > > ---
> > >  gcc/tree-vect-loop.cc | 76 +++++++++++++++++++++++++++++++++++++++----
> > >  1 file changed, 70 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> > > index bf8d677b584..809b73b966c 100644
> > > --- a/gcc/tree-vect-loop.cc
> > > +++ b/gcc/tree-vect-loop.cc
> > > @@ -8963,6 +8963,27 @@ vect_can_vectorize_without_simd_p (code_helper code)
> > >    && vect_can_vectorize_without_simd_p (tree_code (code)));
> > >  }
> > >  
> > > +/* Return true if target supports extract last vectorization with LEN.  */
> > > +
> > > +static bool
> > > +vect_can_vectorize_extract_last_with_len_p (tree vectype)
> > > +{
> > > +  /* Return false if target doesn't support LEN in loop control.  */
> > > +  machine_mode vmode;
> > > +  machine_mode vec_mode = TYPE_MODE (vectype);
> > > +  if (!VECTOR_MODE_P (vec_mode))
> > > +    return false;
> > > +  if (!get_len_load_store_mode (vec_mode, true).exists (&vmode)
> > > +      || !get_len_load_store_mode (vec_mode, false).exists (&vmode))
> > > +    return false;
> >  
> > So this "hidden" bit in the end decides whether to ...
> >  
> > > +  /* Target need to support VEC_EXTRACT to extract the last active element.  */
> > > +  return convert_optab_handler (vec_extract_optab,
> > > + vec_mode,
> > > + TYPE_MODE (TREE_TYPE (vectype)))
> > > + != CODE_FOR_nothing;
> > > +}
> > > +
> > >  /* Create vector init for vectorized iv.  */
> > >  static tree
> > >  vect_create_nonlinear_iv_init (gimple_seq* stmts, tree init_expr,
> > > @@ -10279,7 +10300,8 @@ vectorizable_live_operation (vec_info *vinfo, stmt_vec_info stmt_info,
> > >        if (loop_vinfo && LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P (loop_vinfo))
> > >  {
> > >    if (!direct_internal_fn_supported_p (IFN_EXTRACT_LAST, vectype,
> > > -        OPTIMIZE_FOR_SPEED))
> > > +        OPTIMIZE_FOR_SPEED)
> > > +       && !vect_can_vectorize_extract_last_with_len_p (vectype))
> > >      {
> > >        if (dump_enabled_p ())
> > >  dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> > > @@ -10308,9 +10330,14 @@ vectorizable_live_operation (vec_info *vinfo, stmt_vec_info stmt_info,
> > >    else
> > >      {
> > >        gcc_assert (ncopies == 1 && !slp_node);
> > > -       vect_record_loop_mask (loop_vinfo,
> > > -      &LOOP_VINFO_MASKS (loop_vinfo),
> > > -      1, vectype, NULL);
> > > +       if (vect_can_vectorize_extract_last_with_len_p (vectype))
> > > + vect_record_loop_len (loop_vinfo,
> > > +       &LOOP_VINFO_LENS (loop_vinfo),
> > > +       1, vectype, 1);
> >  
> > .. record a loop_len here.  I think powerpc at least has .VEC_EXTRACT as 
> > well but of course .VEC_EXTRACT support itself doesn't have anything to
> > do with 'len' support.
> >  
> > x86 has .VEC_SET but not yet .VEC_EXTRACT, if it gets .VEC_EXTRACT
> > its partial vector support still wants masks, not lens (and once
> > we record both we fail).
> >  
> > So how can we resolve the issue when a non-VL operation like
> > .VEC_EXTRACT is used for _len support?
> >  
> > Note x86 doens't yet support IFN_EXTRACT_LAST either.
> >  
> > So, why do we test for get_len_load_store_mode and not just for
> > VEC_EXTRACT?
> >  
> > > +       else
> > > + vect_record_loop_mask (loop_vinfo,
> > > +        &LOOP_VINFO_MASKS (loop_vinfo),
> > > +        1, vectype, NULL);
> > >      }
> > >  }
> > >        /* ???  Enable for loop costing as well.  */
> > > @@ -10336,7 +10363,9 @@ vectorizable_live_operation (vec_info *vinfo, stmt_vec_info stmt_info,
> > >    gimple *vec_stmt;
> > >    if (slp_node)
> > >      {
> > > -      gcc_assert (!loop_vinfo || !LOOP_VINFO_FULLY_MASKED_P (loop_vinfo));
> > > +      gcc_assert (!loop_vinfo
> > > +   || (!LOOP_VINFO_FULLY_MASKED_P (loop_vinfo)
> > > +       && !LOOP_VINFO_FULLY_WITH_LENGTH_P (loop_vinfo)));
> > >  
> > >        /* Get the correct slp vectorized stmt.  */
> > >        vec_lhs = SLP_TREE_VEC_DEFS (slp_node)[vec_entry];
> > > @@ -10380,7 +10409,42 @@ vectorizable_live_operation (vec_info *vinfo, stmt_vec_info stmt_info,
> > >  
> > >        gimple_seq stmts = NULL;
> > >        tree new_tree;
> > > -      if (LOOP_VINFO_FULLY_MASKED_P (loop_vinfo))
> > > +      if (LOOP_VINFO_FULLY_WITH_LENGTH_P (loop_vinfo))
> > > + {
> > > +   /* Emit:
> > > +
> > > +        SCALAR_RES = VEC_EXTRACT <VEC_LHS, LEN + BIAS - 1>
> > > +
> > > +      where VEC_LHS is the vectorized live-out result and MASK is
> > > +      the loop mask for the final iteration.  */
> > > +   gcc_assert (ncopies == 1 && !slp_node);
> > > +   gimple_seq tem = NULL;
> > > +   gimple_stmt_iterator gsi = gsi_last (tem);
> > > +   tree len
> > > +     = vect_get_loop_len (loop_vinfo, &gsi,
> > > + &LOOP_VINFO_LENS (loop_vinfo),
> > > + 1, vectype, 0, 0);
> > > +
> > > +   /* BIAS - 1.  */
> > > +   signed char biasval = LOOP_VINFO_PARTIAL_LOAD_STORE_BIAS (loop_vinfo);
> > > +   tree bias_minus_one
> > > +     = int_const_binop (MINUS_EXPR,
> > > +        build_int_cst (TREE_TYPE (len), biasval),
> > > +        build_one_cst (TREE_TYPE (len)));
> > > +
> > > +   /* LAST_INDEX = LEN + (BIAS - 1).  */
> > > +   tree last_index = gimple_build (&stmts, PLUS_EXPR, TREE_TYPE (len),
> > > +   len, bias_minus_one);
> > > +
> > > +   /* SCALAR_RES = VEC_EXTRACT <VEC_LHS, LEN + BIAS - 1>.  */
> > > +   tree scalar_res
> > > +     = gimple_build (&stmts, CFN_VEC_EXTRACT, TREE_TYPE (vectype),
> > > +     vec_lhs_phi, last_index);
> > > +
> >  
> > can we double-check this on powerpc and s390?
> >  
> > Thanks,
> > Richard.
> >  
> > > +   /* Convert the extracted vector element to the scalar type.  */
> > > +   new_tree = gimple_convert (&stmts, lhs_type, scalar_res);
> > > + }
> > > +      else if (LOOP_VINFO_FULLY_MASKED_P (loop_vinfo))
> > >  {
> > >    /* Emit:
> > >  
> >  
> > 
>  
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)