> Ah, no you're right, those would end up wrong for saturation. Arg.. Sorry
> should have
> though it through more.
Never mind, but you enlighten me for even more optimize with some restrictions.
I revisited the pattern, for example as below.
uint16_t a, b;
uint8_t result = (uint8_t)(a >= b ? a - b : 0);
=> result = (char unsigned).SAT_SUB (a, b)
If a has a def like below
uint8_t other = 0x1f;
a = (uint8_t)other
then we can safely convert result = (char unsigned).SAT_SUB (a, b) to
result = .SAT_SUB ((char unsigned)a, (char unsigned).b)
Then we may have better vectorized code if a is limited to char unsigned. Of
course we can do that based on this patch.
Pan
-----Original Message-----
From: Tamar Christina <tamar.christ...@arm.com>
Sent: Tuesday, June 25, 2024 12:01 PM
To: Li, Pan2 <pan2...@intel.com>; gcc-patches@gcc.gnu.org
Cc: juzhe.zh...@rivai.ai; kito.ch...@gmail.com; richard.guent...@gmail.com;
jeffreya...@gmail.com; pins...@gmail.com
Subject: RE: [PATCH v2] Vect: Support truncate after .SAT_SUB pattern in zip
> -----Original Message-----
> From: Li, Pan2 <pan2...@intel.com>
> Sent: Tuesday, June 25, 2024 3:25 AM
> To: Tamar Christina <tamar.christ...@arm.com>; gcc-patches@gcc.gnu.org
> Cc: juzhe.zh...@rivai.ai; kito.ch...@gmail.com; richard.guent...@gmail.com;
> jeffreya...@gmail.com; pins...@gmail.com
> Subject: RE: [PATCH v2] Vect: Support truncate after .SAT_SUB pattern in zip
>
> Thanks Tamar for comments. It indeed benefits the vectorized code, for
> example in
> RISC-V, we may eliminate some vsetvel insn in loop for widen here.
>
> > iftmp.0_5 = .SAT_SUB ((short unsigned int) a_11, (short unsigned int)
> > b_12(D));
> > is cheaper than
> > iftmp.0_5 = (short unsigned int).SAT_SUB (a_11, b_12(D));
>
> I am not sure if it has any correctness problem for this transform, take
> uint16_t to
> uint8_t as example.
>
> uint16_t a, b;
> uint8_t result = (uint8_t)(a >= b ? a - b : 0);
>
> Given a = 0x100; // 256
> b = 0xff; // 255
> For iftmp.0_5 = .SAT_SUB ((char unsigned) a, (char unsigned) b) = .SAT_SUB (0,
> 255) = 0
> For iftmp.0_5 = (char unsigned).SAT_SUB (a, b) = (char unsigned).SAT_SUB (256,
> 255) = 1
>
> Please help to correct me if any misunderstanding, thanks again for
> enlightening.
Ah, no you're right, those would end up wrong for saturation. Arg.. Sorry
should have
though it through more.
Tamar.
>
> Pan
>
> -----Original Message-----
> From: Tamar Christina <tamar.christ...@arm.com>
> Sent: Tuesday, June 25, 2024 4:00 AM
> To: Li, Pan2 <pan2...@intel.com>; gcc-patches@gcc.gnu.org
> Cc: juzhe.zh...@rivai.ai; kito.ch...@gmail.com; richard.guent...@gmail.com;
> jeffreya...@gmail.com; pins...@gmail.com
> Subject: RE: [PATCH v2] Vect: Support truncate after .SAT_SUB pattern in zip
>
> Hi,
>
> > -----Original Message-----
> > From: pan2...@intel.com <pan2...@intel.com>
> > Sent: Monday, June 24, 2024 2:55 PM
> > To: gcc-patches@gcc.gnu.org
> > Cc: juzhe.zh...@rivai.ai; kito.ch...@gmail.com; richard.guent...@gmail.com;
> > jeffreya...@gmail.com; pins...@gmail.com; Pan Li <pan2...@intel.com>
> > Subject: [PATCH v2] Vect: Support truncate after .SAT_SUB pattern in zip
> >
> > From: Pan Li <pan2...@intel.com>
> >
> > The zip benchmark of coremark-pro have one SAT_SUB like pattern but
> > truncated as below:
> >
> > void test (uint16_t *x, unsigned b, unsigned n)
> > {
> > unsigned a = 0;
> > register uint16_t *p = x;
> >
> > do {
> > a = *--p;
> > *p = (uint16_t)(a >= b ? a - b : 0); // Truncate after .SAT_SUB
> > } while (--n);
> > }
> >
> > It will have gimple before vect pass, it cannot hit any pattern of
> > SAT_SUB and then cannot vectorize to SAT_SUB.
> >
> > _2 = a_11 - b_12(D);
> > iftmp.0_13 = (short unsigned int) _2;
> > _18 = a_11 >= b_12(D);
> > iftmp.0_5 = _18 ? iftmp.0_13 : 0;
> >
> > This patch would like to improve the pattern match to recog above
> > as truncate after .SAT_SUB pattern. Then we will have the pattern
> > similar to below, as well as eliminate the first 3 dead stmt.
> >
> > _2 = a_11 - b_12(D);
> > iftmp.0_13 = (short unsigned int) _2;
> > _18 = a_11 >= b_12(D);
> > iftmp.0_5 = (short unsigned int).SAT_SUB (a_11, b_12(D));
> >
>
> I guess this is because one branch of the cond is a constant so the
> convert is folded in. I was wondering though, can't we just push
> in the truncate in this case?
>
> i.e. in this case we know both types are unsigned and the difference
> positive and max value is the max value of the truncate type.
>
> It seems like folding as a general rule
>
> _1 = *p_10;
> a_11 = (unsigned int) _1;
> _2 = a_11 - b_12(D);
> iftmp.0_13 = (short unsigned int) _2;
> _18 = a_11 >= b_12(D);
> iftmp.0_5 = _18 ? iftmp.0_13 : 0;
> *p_10 = iftmp.0_5;
>
> Into
>
> _1 = *p_10;
> a_11 = (unsigned int) _1;
> _2 = ((short unsigned int) a_11) - ((short unsigned int) b_12(D));
> iftmp.0_13 = _2;
> _18 = a_11 >= b_12(D);
> iftmp.0_5 = _18 ? iftmp.0_13 : 0;
> *p_10 = iftmp.0_5;
>
> Is valid (though might have missed something). This would negate the need for
> this change to the vectorizer and saturation detection
> but also should generate better vector code. This is what we do in the
> general case
> https://godbolt.org/z/dfoj6fWdv
> I think here we're just not seeing through the cond.
>
> Typically lots of architectures have cheap truncation operations, so
> truncating
> before saturation means you do the cheap
> operation first rather than doing the complex operation on the wider type.
>
> That is,
>
> _2 = a_11 - b_12(D);
> iftmp.0_13 = (short unsigned int) _2;
> _18 = a_11 >= b_12(D);
> iftmp.0_5 = .SAT_SUB ((short unsigned int) a_11, (short unsigned int)
> b_12(D));
>
> is cheaper than
>
> _2 = a_11 - b_12(D);
> iftmp.0_13 = (short unsigned int) _2;
> _18 = a_11 >= b_12(D);
> iftmp.0_5 = (short unsigned int).SAT_SUB (a_11, b_12(D));
>
> after vectorization. Normally the vectorizer will try to do this through
> over-
> widening detection as well,
> but we haven't taught ranger about the ranges of these new IFNs (probably
> should at some point).
>
> Cheers,
> Tamar
>
> > The below tests are passed for this patch.
> > 1. The rv64gcv fully regression tests.
> > 2. The rv64gcv build with glibc.
> > 3. The x86 bootstrap tests.
> > 4. The x86 fully regression tests.
> >
> > gcc/ChangeLog:
> >
> > * match.pd: Add convert description for minus and capture.
> > * tree-vect-patterns.cc (vect_recog_build_binary_gimple_call): Add
> > new logic to handle in_type is incompatibile with out_type, as
> > well as rename from.
> > (vect_recog_build_binary_gimple_stmt): Rename to.
> > (vect_recog_sat_add_pattern): Leverage above renamed func.
> > (vect_recog_sat_sub_pattern): Ditto.
> >
> > Signed-off-by: Pan Li <pan2...@intel.com>
> > ---
> > gcc/match.pd | 4 +--
> > gcc/tree-vect-patterns.cc | 51 ++++++++++++++++++++++++---------------
> > 2 files changed, 33 insertions(+), 22 deletions(-)
> >
> > diff --git a/gcc/match.pd b/gcc/match.pd
> > index 3d0689c9312..4a4b0b2e72f 100644
> > --- a/gcc/match.pd
> > +++ b/gcc/match.pd
> > @@ -3164,9 +3164,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> > /* Unsigned saturation sub, case 2 (branch with ge):
> > SAT_U_SUB = X >= Y ? X - Y : 0. */
> > (match (unsigned_integer_sat_sub @0 @1)
> > - (cond^ (ge @0 @1) (minus @0 @1) integer_zerop)
> > + (cond^ (ge @0 @1) (convert? (minus (convert1? @0) (convert1? @1)))
> > integer_zerop)
> > (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
> > - && types_match (type, @0, @1))))
> > + && TYPE_UNSIGNED (TREE_TYPE (@0)) && types_match (@0, @1))))
> >
> > /* Unsigned saturation sub, case 3 (branchless with gt):
> > SAT_U_SUB = (X - Y) * (X > Y). */
> > diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
> > index cef901808eb..3d887d36050 100644
> > --- a/gcc/tree-vect-patterns.cc
> > +++ b/gcc/tree-vect-patterns.cc
> > @@ -4490,26 +4490,37 @@ vect_recog_mult_pattern (vec_info *vinfo,
> > extern bool gimple_unsigned_integer_sat_add (tree, tree*, tree (*)(tree));
> > extern bool gimple_unsigned_integer_sat_sub (tree, tree*, tree (*)(tree));
> >
> > -static gcall *
> > -vect_recog_build_binary_gimple_call (vec_info *vinfo, gimple *stmt,
> > +static gimple *
> > +vect_recog_build_binary_gimple_stmt (vec_info *vinfo, stmt_vec_info
> stmt_info,
> > internal_fn fn, tree *type_out,
> > - tree op_0, tree op_1)
> > + tree lhs, tree op_0, tree op_1)
> > {
> > tree itype = TREE_TYPE (op_0);
> > - tree vtype = get_vectype_for_scalar_type (vinfo, itype);
> > + tree otype = TREE_TYPE (lhs);
> > + tree v_itype = get_vectype_for_scalar_type (vinfo, itype);
> > + tree v_otype = get_vectype_for_scalar_type (vinfo, otype);
> >
> > - if (vtype != NULL_TREE
> > - && direct_internal_fn_supported_p (fn, vtype, OPTIMIZE_FOR_BOTH))
> > + if (v_itype != NULL_TREE && v_otype != NULL_TREE
> > + && direct_internal_fn_supported_p (fn, v_itype, OPTIMIZE_FOR_BOTH))
> > {
> > gcall *call = gimple_build_call_internal (fn, 2, op_0, op_1);
> > + tree in_ssa = vect_recog_temp_ssa_var (itype, NULL);
> >
> > - gimple_call_set_lhs (call, vect_recog_temp_ssa_var (itype, NULL));
> > + gimple_call_set_lhs (call, in_ssa);
> > gimple_call_set_nothrow (call, /* nothrow_p */ false);
> > - gimple_set_location (call, gimple_location (stmt));
> > + gimple_set_location (call, gimple_location (STMT_VINFO_STMT
> (stmt_info)));
> > +
> > + *type_out = v_otype;
> >
> > - *type_out = vtype;
> > + if (types_compatible_p (itype, otype))
> > + return call;
> > + else
> > + {
> > + append_pattern_def_seq (vinfo, stmt_info, call, v_itype);
> > + tree out_ssa = vect_recog_temp_ssa_var (otype, NULL);
> >
> > - return call;
> > + return gimple_build_assign (out_ssa, CONVERT_EXPR, in_ssa);
> > + }
> > }
> >
> > return NULL;
> > @@ -4541,13 +4552,13 @@ vect_recog_sat_add_pattern (vec_info *vinfo,
> > stmt_vec_info stmt_vinfo,
> >
> > if (gimple_unsigned_integer_sat_add (lhs, ops, NULL))
> > {
> > - gcall *call = vect_recog_build_binary_gimple_call (vinfo, last_stmt,
> > - IFN_SAT_ADD, type_out,
> > - ops[0], ops[1]);
> > - if (call)
> > + gimple *stmt = vect_recog_build_binary_gimple_stmt (vinfo,
> > stmt_vinfo,
> > + IFN_SAT_ADD, type_out,
> > + lhs, ops[0], ops[1]);
> > + if (stmt)
> > {
> > vect_pattern_detected ("vect_recog_sat_add_pattern", last_stmt);
> > - return call;
> > + return stmt;
> > }
> > }
> >
> > @@ -4579,13 +4590,13 @@ vect_recog_sat_sub_pattern (vec_info *vinfo,
> > stmt_vec_info stmt_vinfo,
> >
> > if (gimple_unsigned_integer_sat_sub (lhs, ops, NULL))
> > {
> > - gcall *call = vect_recog_build_binary_gimple_call (vinfo, last_stmt,
> > - IFN_SAT_SUB, type_out,
> > - ops[0], ops[1]);
> > - if (call)
> > + gimple *stmt = vect_recog_build_binary_gimple_stmt (vinfo,
> > stmt_vinfo,
> > + IFN_SAT_SUB, type_out,
> > + lhs, ops[0], ops[1]);
> > + if (stmt)
> > {
> > vect_pattern_detected ("vect_recog_sat_sub_pattern", last_stmt);
> > - return call;
> > + return stmt;
> > }
> > }
> >
> > --
> > 2.34.1
