> -----Original Message-----
> From: Richard Biener <rguent...@suse.de>
> Sent: Wednesday, August 21, 2024 5:09 PM
> To: Prathamesh Kulkarni <prathame...@nvidia.com>
> Cc: Richard Sandiford <richard.sandif...@arm.com>; Thomas Schwinge
> <tschwi...@baylibre.com>; gcc-patches@gcc.gnu.org
> Subject: RE: Re-compute TYPE_MODE and DECL_MODE while streaming in for
> accelerator
>
> External email: Use caution opening links or attachments
>
>
> On Wed, 21 Aug 2024, Prathamesh Kulkarni wrote:
>
> >
> >
> > > -----Original Message-----
> > > From: Richard Biener <rguent...@suse.de>
> > > Sent: Tuesday, August 20, 2024 10:36 AM
> > > To: Richard Sandiford <richard.sandif...@arm.com>
> > > Cc: Prathamesh Kulkarni <prathame...@nvidia.com>; Thomas Schwinge
> > > <tschwi...@baylibre.com>; gcc-patches@gcc.gnu.org
> > > Subject: Re: Re-compute TYPE_MODE and DECL_MODE while streaming in
> > > for accelerator
> > >
> > > External email: Use caution opening links or attachments
> > >
> > >
> > > > Am 19.08.2024 um 20:56 schrieb Richard Sandiford
> > > <richard.sandif...@arm.com>:
> > > >
> > > > Prathamesh Kulkarni <prathame...@nvidia.com> writes:
> > > >> diff --git a/gcc/lto-streamer-in.cc b/gcc/lto-streamer-in.cc
> > > >> index
> > > >> cbf6041fd68..0420183faf8 100644
> > > >> --- a/gcc/lto-streamer-in.cc
> > > >> +++ b/gcc/lto-streamer-in.cc
> > > >> @@ -44,6 +44,7 @@ along with GCC; see the file COPYING3. If
> not
> > > see
> > > >> #include "debug.h"
> > > >> #include "alloc-pool.h"
> > > >> #include "toplev.h"
> > > >> +#include "stor-layout.h"
> > > >>
> > > >> /* Allocator used to hold string slot entries for line map
> > > streaming.
> > > >> */ static struct object_allocator<struct string_slot>
> > > >> *string_slot_allocator; @@ -1752,6 +1753,17 @@ lto_read_tree_1
> > > (class lto_input_block *ib, class data_in *data_in, tree expr)
> > > >> with -g1, see for example PR113488. */
> > > >> else if (DECL_P (expr) && DECL_ABSTRACT_ORIGIN (expr) ==
> > > expr)
> > > >> DECL_ABSTRACT_ORIGIN (expr) = NULL_TREE;
> > > >> +
> > > >> +#ifdef ACCEL_COMPILER
> > > >> + /* For decl with aggregate type, host streams out
> VOIDmode.
> > > >> + Compute the correct DECL_MODE by calling relayout_decl.
> */
> > > >> + if ((VAR_P (expr)
> > > >> + || TREE_CODE (expr) == PARM_DECL
> > > >> + || TREE_CODE (expr) == FIELD_DECL)
> > > >> + && AGGREGATE_TYPE_P (TREE_TYPE (expr))
> > > >> + && DECL_MODE (expr) == VOIDmode)
> > > >> + relayout_decl (expr);
> > > >> +#endif
> > > >
> > > > Genuine question, but: is relayout_decl safe in this context?
> It
> > > does
> > > > a lot more than just reset the mode. It also applies the target
> > > ABI's
> > > > preferences wrt alignment, padding, and so on, rather than
> > > preserving
> > > > those of the host's.
> > >
> > > It would be better to just recompute the mode here.
> > Hi,
> > The attached patch sets DECL_MODE (expr) to TYPE_MODE (TREE_TYPE
> (expr)) in lto_read_tree_1 instead of calling relayout_decl (expr).
> > I checked layout_decl_type does the same thing for setting decl
> mode,
> > except for bit fields. Since bit-fields cannot have aggregate type,
> I am assuming setting DECL_MODE (expr) to TYPE_MODE (TREE_TYPE (expr))
> would be OK in this case ?
>
> Yep, that should work.
Thanks, I have committed the patch in:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=792adb8d222d0d1d16b182871e105f47823b8e72
after verifying it passes bootstrap+test on aarch64-linux-gnu,
and libgomp testing (without GPU) for aarch64->nvptx and x86_64->nvptx.
>
> > Sorry if this sounds like a silly ques -- Why would it be unsafe to
> > call relayout_decl for variables that are mapped to accelerator even
> > if it'd not preserve host's properties ? I assumed we want to assign
> accel's ABI properties for mapped decls (mode being one of them), or
> am I misunderstanding ?
>
> Structure layout need not be compatible but we are preserving that of
> the host instead of re-layouting in target context. Likewise type <->
> mode mapping doesn't have to agree.
Ah OK, thanks for clarifying. So IIUC, in future, we might need to change that
if
(in theory), host's structure layout for a decl is incompatible with a
particular accel's ABI
and will need to relayout in accel's context ?
Thanks,
Prathamesh
>
> Richard.
>
> > Signed-off-by: Prathamesh Kulkarni <prathame...@nvidia.com>
> >
> > Thanks,
> > Prathamesh
> > >
> > > Richard
> > >
> > > > Thanks,
> > > > Richard
> > > >
> > > >
> > > >> }
> > > >> }
> > > >>
> > > >> diff --git a/gcc/stor-layout.cc b/gcc/stor-layout.cc index
> > > >> 10c0809914c..0ff8bd1171e 100644
> > > >> --- a/gcc/stor-layout.cc
> > > >> +++ b/gcc/stor-layout.cc
> > > >> @@ -2396,6 +2396,32 @@ finish_builtin_struct (tree type, const
> > > >> char
> > > *name, tree fields,
> > > >> layout_decl (TYPE_NAME (type), 0); }
> > > >>
> > > >> +/* Compute TYPE_MODE for TYPE (which is ARRAY_TYPE). */
> > > >> +
> > > >> +void compute_array_mode (tree type) {
> > > >> + gcc_assert (TREE_CODE (type) == ARRAY_TYPE);
> > > >> +
> > > >> + SET_TYPE_MODE (type, BLKmode); if (TYPE_SIZE (type) != 0
> > > >> + && ! targetm.member_type_forces_blk (type, VOIDmode)
> > > >> + /* BLKmode elements force BLKmode aggregate;
> > > >> + else extract/store fields may lose. */
> > > >> + && (TYPE_MODE (TREE_TYPE (type)) != BLKmode
> > > >> + || TYPE_NO_FORCE_BLK (TREE_TYPE (type))))
> > > >> + {
> > > >> + SET_TYPE_MODE (type, mode_for_array (TREE_TYPE (type),
> > > >> + TYPE_SIZE (type)));
> > > >> + if (TYPE_MODE (type) != BLKmode
> > > >> + && STRICT_ALIGNMENT && TYPE_ALIGN (type) <
> BIGGEST_ALIGNMENT
> > > >> + && TYPE_ALIGN (type) < GET_MODE_ALIGNMENT (TYPE_MODE
> > > (type)))
> > > >> + {
> > > >> + TYPE_NO_FORCE_BLK (type) = 1;
> > > >> + SET_TYPE_MODE (type, BLKmode);
> > > >> + }
> > > >> + }
> > > >> +}
> > > >> +
> > > >> /* Calculate the mode, size, and alignment for TYPE.
> > > >> For an array type, calculate the element separation as well.
> > > >> Record TYPE on the chain of permanent or temporary types @@
> > > >> -2709,24 +2735,7 @@ layout_type (tree type)
> > > >> align = MAX (align, BITS_PER_UNIT); #endif
> > > >> SET_TYPE_ALIGN (type, align);
> > > >> - SET_TYPE_MODE (type, BLKmode);
> > > >> - if (TYPE_SIZE (type) != 0
> > > >> - && ! targetm.member_type_forces_blk (type, VOIDmode)
> > > >> - /* BLKmode elements force BLKmode aggregate;
> > > >> - else extract/store fields may lose. */
> > > >> - && (TYPE_MODE (TREE_TYPE (type)) != BLKmode
> > > >> - || TYPE_NO_FORCE_BLK (TREE_TYPE (type))))
> > > >> - {
> > > >> - SET_TYPE_MODE (type, mode_for_array (TREE_TYPE (type),
> > > >> - TYPE_SIZE (type)));
> > > >> - if (TYPE_MODE (type) != BLKmode
> > > >> - && STRICT_ALIGNMENT && TYPE_ALIGN (type) <
> > > BIGGEST_ALIGNMENT
> > > >> - && TYPE_ALIGN (type) < GET_MODE_ALIGNMENT (TYPE_MODE
> > > (type)))
> > > >> - {
> > > >> - TYPE_NO_FORCE_BLK (type) = 1;
> > > >> - SET_TYPE_MODE (type, BLKmode);
> > > >> - }
> > > >> - }
> > > >> + compute_array_mode (type);
> > > >> if (AGGREGATE_TYPE_P (element))
> > > >> TYPE_TYPELESS_STORAGE (type) = TYPE_TYPELESS_STORAGE
> > > (element);
> > > >> /* When the element size is constant, check that it is at
> > > >> least
> > > as
> > > >> diff --git a/gcc/stor-layout.h b/gcc/stor-layout.h index
> > > >> 096ca811762..9d9b8c385f6 100644
> > > >> --- a/gcc/stor-layout.h
> > > >> +++ b/gcc/stor-layout.h
> > > >> @@ -34,6 +34,7 @@ extern tree rli_size_so_far
> > > >> (record_layout_info); extern void normalize_rli
> > > >> (record_layout_info); extern void place_field
> > > >> (record_layout_info, tree); extern void compute_record_mode
> > > >> (tree);
> > > >> +extern void compute_array_mode (tree);
> > > >> extern void finish_bitfield_layout (tree); extern void
> > > >> finish_record_layout (record_layout_info, int); extern void
> > > >> finalize_size_functions (void); diff --git a/gcc/tree-streamer-
> > > in.cc
> > > >> b/gcc/tree-streamer-in.cc index 40029437199..329d218e7d4 100644
> > > >> --- a/gcc/tree-streamer-in.cc
> > > >> +++ b/gcc/tree-streamer-in.cc
> > > >> @@ -35,6 +35,7 @@ along with GCC; see the file COPYING3. If
> not
> > > see
> > > >> #include "attribs.h"
> > > >> #include "asan.h"
> > > >> #include "opts.h"
> > > >> +#include "stor-layout.h"
> > > >>
> > > >>
> > > >> /* Read a STRING_CST from the string table in DATA_IN using
> input
> > > @@
> > > >> -395,6 +396,17 @@ unpack_ts_type_common_value_fields (struct
> > > >> bitpack_d *bp, tree expr) #ifdef ACCEL_COMPILER
> > > >> if (TYPE_ALIGN (expr) > targetm.absolute_biggest_alignment)
> > > >> SET_TYPE_ALIGN (expr, targetm.absolute_biggest_alignment);
> > > >> +
> > > >> + /* Host streams out VOIDmode for aggregate type. */ if
> > > >> + (AGGREGATE_TYPE_P (expr) && TYPE_MODE (expr) == VOIDmode)
> > > >> + {
> > > >> + if (TREE_CODE (expr) == ARRAY_TYPE)
> > > >> + compute_array_mode (expr);
> > > >> + else if (RECORD_OR_UNION_TYPE_P (expr))
> > > >> + compute_record_mode (expr);
> > > >> + else
> > > >> + gcc_unreachable ();
> > > >> + }
> > > >> #endif
> > > >> }
> > > >>
> > > >> diff --git a/gcc/tree-streamer-out.cc b/gcc/tree-streamer-
> out.cc
> > > >> index b7205287ffb..7de4447a1b5 100644
> > > >> --- a/gcc/tree-streamer-out.cc
> > > >> +++ b/gcc/tree-streamer-out.cc
> > > >> @@ -187,7 +187,17 @@ pack_ts_fixed_cst_value_fields (struct
> > > bitpack_d
> > > >> *bp, tree expr) static void pack_ts_decl_common_value_fields
> > > (struct
> > > >> bitpack_d *bp, tree expr) {
> > > >> - bp_pack_machine_mode (bp, DECL_MODE (expr));
> > > >> + /* Similar to TYPE_MODE, avoid streaming out host-specific
> > > DECL_MODE
> > > >> + for aggregate type with offloading enabled, and while
> > > streaming-in
> > > >> + recompute appropriate DECL_MODE for accelerator. */ if
> > > >> + (lto_stream_offload_p
> > > >> + && (VAR_P (expr)
> > > >> + || TREE_CODE (expr) == PARM_DECL
> > > >> + || TREE_CODE (expr) == FIELD_DECL)
> > > >> + && AGGREGATE_TYPE_P (TREE_TYPE (expr)))
> > > >> + bp_pack_machine_mode (bp, VOIDmode); else
> > > >> + bp_pack_machine_mode (bp, DECL_MODE (expr));
> > > >> bp_pack_value (bp, DECL_NONLOCAL (expr), 1);
> > > >> bp_pack_value (bp, DECL_VIRTUAL_P (expr), 1);
> > > >> bp_pack_value (bp, DECL_IGNORED_P (expr), 1); @@ -317,10
> > > >> +327,18
> > > @@
> > > >> pack_ts_function_decl_value_fields (struct bitpack_d *bp, tree
> > > expr)
> > > >> static void pack_ts_type_common_value_fields (struct bitpack_d
> > > >> *bp, tree expr) {
> > > >> + /* For offloading, avoid streaming out TYPE_MODE for
> aggregate
> > > type since
> > > >> + it may be host-specific. For eg, aarch64 uses OImode for
> > > ARRAY_TYPE
> > > >> + whose size is 256-bits, which is not representable on
> > > accelerator.
> > > >> + Instead stream out VOIDmode, and while streaming-in,
> > > recompute
> > > >> + appropriate TYPE_MODE for accelerator. */ if
> > > >> + (lto_stream_offload_p && AGGREGATE_TYPE_P (expr))
> > > >> + bp_pack_machine_mode (bp, VOIDmode);
> > > >> /* for VECTOR_TYPE, TYPE_MODE reevaluates the mode using
> > > target_flags
> > > >> not necessary valid in a global context.
> > > >> Use the raw value previously set by layout_type. */
> > > >> - bp_pack_machine_mode (bp, TYPE_MODE_RAW (expr));
> > > >> + else
> > > >> + bp_pack_machine_mode (bp, TYPE_MODE_RAW (expr));
> > > >> /* TYPE_NO_FORCE_BLK is private to stor-layout and need
> > > >> no streaming. */
> > > >> bp_pack_value (bp, TYPE_PACKED (expr), 1);
> >
>
> --
> Richard Biener <rguent...@suse.de>
> SUSE Software Solutions Germany GmbH,
> Frankenstrasse 146, 90461 Nuernberg, Germany;
> GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG
> Nuernberg)
