Sounds like we could just use !tune_param->slow_unaligned_access for
TARGET_OVERLAP_OP_BY_PIECES_P?
since it improves both performance and code size if we have cheap
unaligned accesses.
On Thu, Jul 22, 2021 at 5:23 PM Christoph Müllner via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Thu, Jul 22, 2021 at 10:53 AM Kito Cheng <kito.ch...@gmail.com> wrote:
> >
> > It's my first time seeing this hook :p Did you mind describing when we
> > need to set it to true?
> > I mean when a CPU has some feature then we can/should set it to true?
>
> The by-pieces infrastructure allows to inline builtins quite well and
> uses slow_unaligned_access and overlap_op_by_pieces to tune the
> emitted instruction sequence.
>
> In case unaligned accesses are fast, then overlap_op_by_pieces can reduce
> the number of instructions (emitted by by-pieces for e.g. memset) for the cost
> of overlapping memory accesses.
>
> E.g. you want to clear 15-bytes with memset (and cheap unaligned accesses):
> Without overlap_op_by_pieces you will get:
> 8e: 00053023 sd zero,0(a0)
> 92: 00052423 sw zero,8(a0)
> 96: 00051623 sh zero,12(a0)
> 9a: 00050723 sb zero,14(a0)
> With overlap_op_by_pieces you will get:
> 7e: 00053023 sd zero,0(a0)
> 82: 000533a3 sd zero,7(a0)
>
> BR
> Christoph
>
> >
> >
> > On Thu, Jul 22, 2021 at 7:33 AM Christoph Muellner via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> > >
> > > This patch adds the field overlap_op_by_pieces to the struct
> > > riscv_tune_param, which allows to enable the overlap_op_by_pieces
> > > feature of the by-pieces infrastructure.
> > >
> > > gcc/ChangeLog:
> > >
> > > * config/riscv/riscv.c (struct riscv_tune_param): New field.
> > > (riscv_overlap_op_by_pieces): New function.
> > > (TARGET_OVERLAP_OP_BY_PIECES_P): Connect to
> > > riscv_overlap_op_by_pieces.
> > >
> > > Signed-off-by: Christoph Muellner <cmuell...@gcc.gnu.org>
> > > ---
> > > gcc/config/riscv/riscv.c | 14 ++++++++++++++
> > > 1 file changed, 14 insertions(+)
> > >
> > > diff --git a/gcc/config/riscv/riscv.c b/gcc/config/riscv/riscv.c
> > > index 576960bb37c..824e930ef05 100644
> > > --- a/gcc/config/riscv/riscv.c
> > > +++ b/gcc/config/riscv/riscv.c
> > > @@ -220,6 +220,7 @@ struct riscv_tune_param
> > > unsigned short branch_cost;
> > > unsigned short memory_cost;
> > > bool slow_unaligned_access;
> > > + bool overlap_op_by_pieces;
> > > };
> > >
> > > /* Information about one micro-arch we know about. */
> > > @@ -285,6 +286,7 @@ static const struct riscv_tune_param rocket_tune_info
> > > = {
> > > 3, /* branch_cost */
> > > 5, /* memory_cost */
> > > true, /*
> > > slow_unaligned_access */
> > > + false, /* overlap_op_by_pieces */
> > > };
> > >
> > > /* Costs to use when optimizing for Sifive 7 Series. */
> > > @@ -298,6 +300,7 @@ static const struct riscv_tune_param
> > > sifive_7_tune_info = {
> > > 4, /* branch_cost */
> > > 3, /* memory_cost */
> > > true, /*
> > > slow_unaligned_access */
> > > + false, /* overlap_op_by_pieces */
> > > };
> > >
> > > /* Costs to use when optimizing for T-HEAD c906. */
> > > @@ -311,6 +314,7 @@ static const struct riscv_tune_param
> > > thead_c906_tune_info = {
> > > 3, /* branch_cost */
> > > 5, /* memory_cost */
> > > false, /* slow_unaligned_access */
> > > + false, /* overlap_op_by_pieces */
> > > };
> > >
> > > /* Costs to use when optimizing for size. */
> > > @@ -324,6 +328,7 @@ static const struct riscv_tune_param
> > > optimize_size_tune_info = {
> > > 1, /* branch_cost */
> > > 2, /* memory_cost */
> > > false, /* slow_unaligned_access
> > > */
> > > + false, /* overlap_op_by_pieces */
> > > };
> > >
> > > static tree riscv_handle_fndecl_attribute (tree *, tree, tree, int, bool
> > > *);
> > > @@ -5201,6 +5206,12 @@ riscv_slow_unaligned_access (machine_mode,
> > > unsigned int)
> > > return riscv_slow_unaligned_access_p;
> > > }
> > >
> > > +static bool
> > > +riscv_overlap_op_by_pieces (void)
> > > +{
> > > + return tune_param->overlap_op_by_pieces;
> > > +}
> > > +
> > > /* Implement TARGET_CAN_CHANGE_MODE_CLASS. */
> > >
> > > static bool
> > > @@ -5525,6 +5536,9 @@ riscv_asan_shadow_offset (void)
> > > #undef TARGET_SLOW_UNALIGNED_ACCESS
> > > #define TARGET_SLOW_UNALIGNED_ACCESS riscv_slow_unaligned_access
> > >
> > > +#undef TARGET_OVERLAP_OP_BY_PIECES_P
> > > +#define TARGET_OVERLAP_OP_BY_PIECES_P riscv_overlap_op_by_pieces
> > > +
> > > #undef TARGET_SECONDARY_MEMORY_NEEDED
> > > #define TARGET_SECONDARY_MEMORY_NEEDED riscv_secondary_memory_needed
> > >
> > > --
> > > 2.31.1
> > >
