On Fri, May 17, 2024 at 11:05 AM Tamar Christina
<tamar.christ...@arm.com> wrote:
>
> > -----Original Message-----
> > From: Richard Biener <richard.guent...@gmail.com>
> > Sent: Friday, May 17, 2024 6:51 AM
> > To: Victor Do Nascimento <victor.donascime...@arm.com>
> > Cc: gcc-patches@gcc.gnu.org; Richard Sandiford <richard.sandif...@arm.com>;
> > Richard Earnshaw <richard.earns...@arm.com>; Victor Do Nascimento
> > <vicdo...@e133397.arm.com>
> > Subject: Re: [PATCH] middle-end: Expand {u|s}dot product support in
> > autovectorizer
> >
> > On Thu, May 16, 2024 at 4:40 PM Victor Do Nascimento
> > <victor.donascime...@arm.com> wrote:
> > >
> > > From: Victor Do Nascimento <vicdo...@e133397.arm.com>
> > >
> > > At present, the compiler offers the `{u|s|us}dot_prod_optab' direct
> > > optabs for dealing with vectorizable dot product code sequences. The
> > > consequence of using a direct optab for this is that backend-pattern
> > > selection is only ever able to match against one datatype - Either
> > > that of the operands or of the accumulated value, never both.
> > >
> > > With the introduction of the 2-way (un)signed dot-product insn [1][2]
> > > in AArch64 SVE2, the existing direct opcode approach is no longer
> > > sufficient for full specification of all the possible dot product
> > > machine instructions to be matched to the code sequence; a dot product
> > > resulting in VNx4SI may result from either dot products on VNx16QI or
> > > VNx8HI values for the 4- and 2-way dot product operations, respectively.
> > >
> > > This means that the following example fails autovectorization:
> > >
> > > uint32_t foo(int n, uint16_t* data) {
> > > uint32_t sum = 0;
> > > for (int i=0; i<n; i+=1) {
> > > sum += data[i] * data[i];
> > > }
> > > return sum;
> > > }
> > >
> > > To remedy the issue a new optab is added, tentatively named
> > > `udot_prod_twoway_optab', whose selection is dependent upon checking
> > > of both input and output types involved in the operation.
> >
> > I don't like this too much. I'll note we document dot_prod as
> >
> > @cindex @code{sdot_prod@var{m}} instruction pattern
> > @item @samp{sdot_prod@var{m}}
> >
> > Compute the sum of the products of two signed elements.
> > Operand 1 and operand 2 are of the same mode. Their
> > product, which is of a wider mode, is computed and added to operand 3.
> > Operand 3 is of a mode equal or wider than the mode of the product. The
> > result is placed in operand 0, which is of the same mode as operand 3.
> > @var{m} is the mode of operand 1 and operand 2.
> >
> > with no restriction on the wider mode but we don't specify it which is
> > bad design. This should have been a convert optab with two modes
> > from the start - adding a _twoway variant is just a hack.
>
> We did discuss this at the time we started implementing it. There was two
> options, one was indeed to change it to a convert dot_prod optab, but doing
> this means we have to update every target that uses it.
>
> Now that means 3 ISAs for AArch64, Arm, Arc, c6x, 2 for x86, loongson and
> altivec.
>
> Which sure could be possible, but there's also every use in the backends that
> need
> to be updated, and tested, which for some targets we don't even know how to
> begin.
>
> So it seems very hard to correct dotprod to a convert optab now.
It's still the correct way to go. At _least_ your new pattern should
have been this,
otherwise what do you do when you have two-way, four-way and eight-way variants?
Add yet another optab?
Another thing is that when you do it your way you should fix the existing optab
to be two-way by documenting how the second mode derives from the first.
And sure, it's not the only optab suffering from this issue.
Richard.
> Tamar
>
> >
> > Richard.
> >
> > > In order to minimize changes to the existing codebase,
> > > `optab_for_tree_code' is renamed `optab_for_tree_code_1' and a new
> > > argument is added to its signature - `const_tree otype', allowing type
> > > information to be specified for both input and output types. The
> > > existing nterface is retained by defining a new `optab_for_tree_code',
> > > which serves as a shim to `optab_for_tree_code_1', passing old
> > > parameters as-is and setting the new `optype' argument to `NULL_TREE'.
> > >
> > > For DOT_PROD_EXPR tree codes, we can call `optab_for_tree_code_1'
> > > directly, passing it both types, adding the internal logic to the
> > > function to distinguish between competing optabs.
> > >
> > > Finally, necessary changes are made to `expand_widen_pattern_expr' to
> > > ensure the new icode can be correctly selected, given the new optab.
> > >
> > > [1] https://developer.arm.com/documentation/ddi0602/2024-03/SVE-
> > Instructions/UDOT--2-way--vectors---Unsigned-integer-dot-product-
> > > [2] https://developer.arm.com/documentation/ddi0602/2024-03/SVE-
> > Instructions/SDOT--2-way--vectors---Signed-integer-dot-product-
> > >
> > > gcc/ChangeLog:
> > >
> > > * config/aarch64/aarch64-sve2.md
> > > (@aarch64_sve_<sur>dotvnx4sivnx8hi):
> > > renamed to `<sur>dot_prod_twoway_vnx8hi'.
> > > * config/aarch64/aarch64-sve-builtins-base.cc (svdot_impl.expand):
> > > update icodes used in line with above rename.
> > > * optabs-tree.cc (optab_for_tree_code_1): Renamed
> > > `optab_for_tree_code' and added new argument.
> > > (optab_for_tree_code): Now a call to `optab_for_tree_code_1'.
> > > * optabs-tree.h (optab_for_tree_code_1): New.
> > > * optabs.cc (expand_widen_pattern_expr): Expand support for
> > > DOT_PROD_EXPR patterns.
> > > * optabs.def (udot_prod_twoway_optab): New.
> > > (sdot_prod_twoway_optab): Likewise.
> > > * tree-vect-patterns.cc (vect_supportable_direct_optab_p): Add
> > > support for misc optabs that use two modes.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > > * gcc.dg/vect/vect-dotprod-twoway.c: New.
> > > ---
> > > .../aarch64/aarch64-sve-builtins-base.cc | 4 ++--
> > > gcc/config/aarch64/aarch64-sve2.md | 2 +-
> > > gcc/optabs-tree.cc | 23 ++++++++++++++++--
> > > gcc/optabs-tree.h | 2 ++
> > > gcc/optabs.cc | 2 +-
> > > gcc/optabs.def | 2 ++
> > > .../gcc.dg/vect/vect-dotprod-twoway.c | 24 +++++++++++++++++++
> > > gcc/tree-vect-patterns.cc | 2 +-
> > > 8 files changed, 54 insertions(+), 7 deletions(-)
> > > create mode 100644 gcc/testsuite/gcc.dg/vect/vect-dotprod-twoway.c
> > >
> > > diff --git a/gcc/config/aarch64/aarch64-sve-builtins-base.cc
> > b/gcc/config/aarch64/aarch64-sve-builtins-base.cc
> > > index 0d2edf3f19e..e457db09f66 100644
> > > --- a/gcc/config/aarch64/aarch64-sve-builtins-base.cc
> > > +++ b/gcc/config/aarch64/aarch64-sve-builtins-base.cc
> > > @@ -764,8 +764,8 @@ public:
> > > icode = (e.type_suffix (0).float_p
> > > ? CODE_FOR_aarch64_sve_fdotvnx4sfvnx8hf
> > > : e.type_suffix (0).unsigned_p
> > > - ? CODE_FOR_aarch64_sve_udotvnx4sivnx8hi
> > > - : CODE_FOR_aarch64_sve_sdotvnx4sivnx8hi);
> > > + ? CODE_FOR_udot_prod_twoway_vnx8hi
> > > + : CODE_FOR_sdot_prod_twoway_vnx8hi);
> > > return e.use_unpred_insn (icode);
> > > }
> > > };
> > > diff --git a/gcc/config/aarch64/aarch64-sve2.md
> > b/gcc/config/aarch64/aarch64-sve2.md
> > > index 934e57055d3..5677de7108d 100644
> > > --- a/gcc/config/aarch64/aarch64-sve2.md
> > > +++ b/gcc/config/aarch64/aarch64-sve2.md
> > > @@ -2021,7 +2021,7 @@ (define_insn
> > "@aarch64_sve_qsub_<sve_int_op>_lane_<mode>"
> > > )
> > >
> > > ;; Two-way dot-product.
> > > -(define_insn "@aarch64_sve_<sur>dotvnx4sivnx8hi"
> > > +(define_insn "<sur>dot_prod_twoway_vnx8hi"
> > > [(set (match_operand:VNx4SI 0 "register_operand")
> > > (plus:VNx4SI
> > > (unspec:VNx4SI
> > > diff --git a/gcc/optabs-tree.cc b/gcc/optabs-tree.cc
> > > index b69a5bc3676..e3c5a618ea2 100644
> > > --- a/gcc/optabs-tree.cc
> > > +++ b/gcc/optabs-tree.cc
> > > @@ -35,8 +35,8 @@ along with GCC; see the file COPYING3. If not see
> > > cannot give complete results for multiplication or division) but
> > > probably
> > > ought to be relied on more widely throughout the expander. */
> > > optab
> > > -optab_for_tree_code (enum tree_code code, const_tree type,
> > > - enum optab_subtype subtype)
> > > +optab_for_tree_code_1 (enum tree_code code, const_tree type,
> > > + const_tree otype, enum optab_subtype subtype)
> > > {
> > > bool trapv;
> > > switch (code)
> > > @@ -149,6 +149,14 @@ optab_for_tree_code (enum tree_code code,
> > const_tree type,
> > >
> > > case DOT_PROD_EXPR:
> > > {
> > > + if (otype && (TYPE_PRECISION (TREE_TYPE (type)) * 2
> > > + == TYPE_PRECISION (TREE_TYPE (otype))))
> > > + {
> > > + if (TYPE_UNSIGNED (type) && TYPE_UNSIGNED (otype))
> > > + return udot_prod_twoway_optab;
> > > + if (!TYPE_UNSIGNED (type) && !TYPE_UNSIGNED (otype))
> > > + return sdot_prod_twoway_optab;
> > > + }
> > > if (subtype == optab_vector_mixed_sign)
> > > return usdot_prod_optab;
> > >
> > > @@ -285,6 +293,17 @@ optab_for_tree_code (enum tree_code code,
> > const_tree type,
> > > }
> > > }
> > >
> > > +/* Return the optab used for computing the operation given by the tree
> > > code,
> > > + CODE and the tree EXP. This function is not always usable (for
> > > example, it
> > > + cannot give complete results for multiplication or division) but
> > > probably
> > > + ought to be relied on more widely throughout the expander. */
> > > +optab
> > > +optab_for_tree_code (enum tree_code code, const_tree type,
> > > + enum optab_subtype subtype)
> > > +{
> > > + return optab_for_tree_code_1 (code, type, NULL_TREE, subtype);
> > > +}
> > > +
> > > /* Check whether an operation represented by CODE is a 'half' widening
> > operation
> > > in which the input vector type has half the number of bits of the
> > > output
> > > vector type e.g. V8QI->V8HI.
> > > diff --git a/gcc/optabs-tree.h b/gcc/optabs-tree.h
> > > index f2b49991462..13ff7ca2e4b 100644
> > > --- a/gcc/optabs-tree.h
> > > +++ b/gcc/optabs-tree.h
> > > @@ -36,6 +36,8 @@ enum optab_subtype
> > > /* Return the optab used for computing the given operation on the type
> > > given
> > by
> > > the second argument. The third argument distinguishes between the
> > > types of
> > > vector shifts and rotates. */
> > > +optab optab_for_tree_code_1 (enum tree_code, const_tree, const_tree
> > __attribute__((unused)),
> > > + enum optab_subtype );
> > > optab optab_for_tree_code (enum tree_code, const_tree, enum
> > optab_subtype);
> > > bool
> > > supportable_half_widening_operation (enum tree_code, tree, tree,
> > > diff --git a/gcc/optabs.cc b/gcc/optabs.cc
> > > index ce91f94ed43..3a1c6c7b90e 100644
> > > --- a/gcc/optabs.cc
> > > +++ b/gcc/optabs.cc
> > > @@ -311,7 +311,7 @@ expand_widen_pattern_expr (sepops ops, rtx op0, rtx
> > op1, rtx wide_op,
> > > gcc_unreachable ();
> > >
> > > widen_pattern_optab
> > > - = optab_for_tree_code (ops->code, TREE_TYPE (oprnd0), subtype);
> > > + = optab_for_tree_code_1 (ops->code, TREE_TYPE (oprnd0), TREE_TYPE
> > (oprnd2), subtype);
> > > }
> > > else
> > > widen_pattern_optab
> > > diff --git a/gcc/optabs.def b/gcc/optabs.def
> > > index ad14f9328b9..cf1a6e7a7dc 100644
> > > --- a/gcc/optabs.def
> > > +++ b/gcc/optabs.def
> > > @@ -408,6 +408,8 @@ OPTAB_D (sdot_prod_optab, "sdot_prod$I$a")
> > > OPTAB_D (ssum_widen_optab, "widen_ssum$I$a3")
> > > OPTAB_D (udot_prod_optab, "udot_prod$I$a")
> > > OPTAB_D (usdot_prod_optab, "usdot_prod$I$a")
> > > +OPTAB_D (sdot_prod_twoway_optab, "sdot_prod_twoway_$I$a")
> > > +OPTAB_D (udot_prod_twoway_optab, "udot_prod_twoway_$I$a")
> > > OPTAB_D (usum_widen_optab, "widen_usum$I$a3")
> > > OPTAB_D (usad_optab, "usad$I$a")
> > > OPTAB_D (ssad_optab, "ssad$I$a")
> > > diff --git a/gcc/testsuite/gcc.dg/vect/vect-dotprod-twoway.c
> > b/gcc/testsuite/gcc.dg/vect/vect-dotprod-twoway.c
> > > new file mode 100644
> > > index 00000000000..cba2aadbec8
> > > --- /dev/null
> > > +++ b/gcc/testsuite/gcc.dg/vect/vect-dotprod-twoway.c
> > > @@ -0,0 +1,24 @@
> > > +/* { dg-do compile { target { aarch64*-*-* } } } */
> > > +/* { dg-additional-options "-march=-O3 -march=armv9.2-a+sme2 -fdump-tree-
> > vect-details" { target { aarch64*-*-* } } } */
> > > +
> > > +#include <stdint.h>
> > > +
> > > +uint32_t udot2(int n, uint16_t* data) {
> > > + uint32_t sum = 0;
> > > + for (int i=0; i<n; i+=1) {
> > > + sum += data[i] * data[i];
> > > + }
> > > + return sum;
> > > +}
> > > +
> > > +int32_t sdot2(int n, int16_t* data) {
> > > + int32_t sum = 0;
> > > + for (int i=0; i<n; i+=1) {
> > > + sum += data[i] * data[i];
> > > + }
> > > + return sum;
> > > +}
> > > +
> > > +/* { dg-final { scan-tree-dump-times "vect_recog_dot_prod_pattern:
> > > detected:"
> > 2 "vect" } } */
> > > +/* { dg-final { scan-tree-dump-times "vect_recog_widen_mult_pattern:
> > detected" 4 "vect" } } */
> > > +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 2 "vect" } } */
> > > diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
> > > index dfb7d800526..0760f25d94d 100644
> > > --- a/gcc/tree-vect-patterns.cc
> > > +++ b/gcc/tree-vect-patterns.cc
> > > @@ -233,7 +233,7 @@ vect_supportable_direct_optab_p (vec_info *vinfo, tree
> > otype, tree_code code,
> > > if (!vecotype)
> > > return false;
> > >
> > > - optab optab = optab_for_tree_code (code, vecitype, subtype);
> > > + optab optab = optab_for_tree_code_1 (code, vecitype, vecotype,
> > > subtype);
> > > if (!optab)
> > > return false;
> > >
> > > --
> > > 2.34.1
> > >
