Re: [PATCH v2] MIPS: add speculation_barrier support

[Richard Sandiford <richard.sandiford@arm.com>]

YunQiang Su <yunqiang.su@cipunited.com> writes:
> speculation_barrier for MIPS needs sync+jr.hb (r2+),
> so we implement __speculation_barrier in libgcc, like arm32 does.

Looks reasonable, but do you have a source for the fallback
pre-r2 handling?  (Thanks for adding that btw, since I realise
it's not your focus here.)

Nit: the copyright for the new files should start with this year,
unless you're copying something significant from an existing file.

Thanks,
Richard

>
> gcc/ChangeLog:
> 	* config/mips/mips-protos.h (mips_emit_speculation_barrier): New
>         prototype.
> 	* config/mips/mips.cc (speculation_barrier_libfunc): New static
>         variable.
> 	(mips_init_libfuncs): Initialize it.
> 	(mips_emit_speculation_barrier): New function.
> 	* config/mips/mips.md (speculation_barrier): Call
>         mips_emit_speculation_barrier.
>
> libgcc/ChangeLog:
> 	* config/mips/lib1funcs.S: New file.
> 	define __speculation_barrier and include mips16.S.
> 	* config/mips/t-mips: define LIB1ASMSRC as mips/lib1funcs.S.
> 	define LIB1ASMFUNCS as _speculation_barrier.
> 	set version info for __speculation_barrier.
> 	* config/mips/libgcc-mips.ver: New file.
> 	* config/mips/t-mips16: don't define LIB1ASMSRC as mips16.S is
> 	included in lib1funcs.S now.
> ---
>  gcc/config/mips/mips-protos.h      |  2 +
>  gcc/config/mips/mips.cc            | 13 +++++++
>  gcc/config/mips/mips.md            | 12 ++++++
>  libgcc/config/mips/lib1funcs.S     | 60 ++++++++++++++++++++++++++++++
>  libgcc/config/mips/libgcc-mips.ver | 21 +++++++++++
>  libgcc/config/mips/t-mips          |  7 ++++
>  libgcc/config/mips/t-mips16        |  3 +-
>  7 files changed, 116 insertions(+), 2 deletions(-)
>  create mode 100644 libgcc/config/mips/lib1funcs.S
>  create mode 100644 libgcc/config/mips/libgcc-mips.ver
>
> diff --git a/gcc/config/mips/mips-protos.h b/gcc/config/mips/mips-protos.h
> index 20483469105..da7902c235b 100644
> --- a/gcc/config/mips/mips-protos.h
> +++ b/gcc/config/mips/mips-protos.h
> @@ -388,4 +388,6 @@ extern void mips_register_frame_header_opt (void);
>  extern void mips_expand_vec_cond_expr (machine_mode, machine_mode, rtx *);
>  extern void mips_expand_vec_cmp_expr (rtx *);
>  
> +extern void mips_emit_speculation_barrier_function (void);
> +
>  #endif /* ! GCC_MIPS_PROTOS_H */
> diff --git a/gcc/config/mips/mips.cc b/gcc/config/mips/mips.cc
> index ca822758b41..139707fda34 100644
> --- a/gcc/config/mips/mips.cc
> +++ b/gcc/config/mips/mips.cc
> @@ -13611,6 +13611,9 @@ mips_autovectorize_vector_modes (vector_modes *modes, bool)
>    return 0;
>  }
>  
> +
> +static GTY(()) rtx speculation_barrier_libfunc;
> +
>  /* Implement TARGET_INIT_LIBFUNCS.  */
>  
>  static void
> @@ -13680,6 +13683,7 @@ mips_init_libfuncs (void)
>        synchronize_libfunc = init_one_libfunc ("__sync_synchronize");
>        init_sync_libfuncs (UNITS_PER_WORD);
>      }
> +  speculation_barrier_libfunc = init_one_libfunc ("__speculation_barrier");
>  }
>  
>  /* Build up a multi-insn sequence that loads label TARGET into $AT.  */
> @@ -19092,6 +19096,15 @@ mips_avoid_hazard (rtx_insn *after, rtx_insn *insn, int *hilo_delay,
>        }
>  }
>  
> +/* Emit a speculation barrier.
> +   JR.HB is needed, so we need to put
> +   speculation_barrier_libfunc in libgcc */
> +void
> +mips_emit_speculation_barrier_function ()
> +{
> +  emit_library_call (speculation_barrier_libfunc, LCT_NORMAL, VOIDmode);
> +}
> +
>  /* A SEQUENCE is breakable iff the branch inside it has a compact form
>     and the target has compact branches.  */
>  
> diff --git a/gcc/config/mips/mips.md b/gcc/config/mips/mips.md
> index ac1d77afc7d..5d04ac566dd 100644
> --- a/gcc/config/mips/mips.md
> +++ b/gcc/config/mips/mips.md
> @@ -160,6 +160,8 @@
>    ;; The `.insn' pseudo-op.
>    UNSPEC_INSN_PSEUDO
>    UNSPEC_JRHB
> +
> +  VUNSPEC_SPECULATION_BARRIER
>  ])
>  
>  (define_constants
> @@ -7455,6 +7457,16 @@
>    mips_expand_conditional_move (operands);
>    DONE;
>  })
> +
> +(define_expand "speculation_barrier"
> +  [(unspec_volatile [(const_int 0)] VUNSPEC_SPECULATION_BARRIER)]
> +  ""
> +  "
> +  mips_emit_speculation_barrier_function ();
> +  DONE;
> +  "
> +)
> +
>  \f
>  ;;
>  ;;  ....................
> diff --git a/libgcc/config/mips/lib1funcs.S b/libgcc/config/mips/lib1funcs.S
> new file mode 100644
> index 00000000000..45d74e2e762
> --- /dev/null
> +++ b/libgcc/config/mips/lib1funcs.S
> @@ -0,0 +1,60 @@
> +/* Copyright (C) 1995-2023 Free Software Foundation, Inc.
> +
> +This file is free software; you can redistribute it and/or modify it
> +under the terms of the GNU General Public License as published by the
> +Free Software Foundation; either version 3, or (at your option) any
> +later version.
> +
> +This file is distributed in the hope that it will be useful, but
> +WITHOUT ANY WARRANTY; without even the implied warranty of
> +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +General Public License for more details.
> +
> +Under Section 7 of GPL version 3, you are granted additional
> +permissions described in the GCC Runtime Library Exception, version
> +3.1, as published by the Free Software Foundation.
> +
> +You should have received a copy of the GNU General Public License and
> +a copy of the GCC Runtime Library Exception along with this program;
> +see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
> +<http://www.gnu.org/licenses/>.  */
> +
> +#include "mips16.S"
> +
> +#ifdef L_speculation_barrier
> +
> +/* MIPS16e1 has no sync/jr.hb instructions, and MIPS16e2 lacks of jr.hb.
> +   So, we use normal MIPS code here, just like what we do for __sync_* */
> +	.set nomips16
> +
> +	.set noreorder
> +	.globl	__speculation_barrier
> +	.ent	__speculation_barrier
> +
> +__speculation_barrier:
> +	.set	push
> +/* MIPS1 has no sync, and in fact it doesn't need it at all.
> +   We wish that all newer CPUs should run software with MIPS2+ */
> +#if __mips >= 2
> +	sync /* complementation barrier for memory */
> +#endif
> +#if __mips_isa_rev >= 2
> +/* MIPSr2+: sync+jr.hb is enough */
> +	jr.hb	$ra /* Jump with instruction hazard barrier */
> +#else
> +/* Make ssnop available, ssnop only recognized by GAS since mips32,
> +   however it's actually available since R5500,
> +   and it will be decoded as nop on earlier processors */
> +	.set mips32
> +/* MIPS1 to MIPSr1: R10000 have 7 stage pipeline,
> +   so 8 ssnop is sufficient to block all speculation on all CPUs */
> +	.rept 8
> +	ssnop
> +	.endr
> +	jr	$ra
> +#endif
> +	.set	pop
> +	.end	__speculation_barrier
> +
> +	.set reorder
> +#endif
> diff --git a/libgcc/config/mips/libgcc-mips.ver b/libgcc/config/mips/libgcc-mips.ver
> new file mode 100644
> index 00000000000..f0e9fc54965
> --- /dev/null
> +++ b/libgcc/config/mips/libgcc-mips.ver
> @@ -0,0 +1,21 @@
> +# Copyright (C) 2008-2023 Free Software Foundation, Inc.
> +#
> +# This file is part of GCC.
> +#
> +# GCC is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3, or (at your option)
> +# any later version.
> +#
> +# GCC is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with GCC; see the file COPYING3.  If not see
> +# <http://www.gnu.org/licenses/>.
> +
> +GCC_14.0 {
> +  __speculation_barrier
> +}
> diff --git a/libgcc/config/mips/t-mips b/libgcc/config/mips/t-mips
> index 4fb8e136217..d05ef7cbf74 100644
> --- a/libgcc/config/mips/t-mips
> +++ b/libgcc/config/mips/t-mips
> @@ -7,3 +7,10 @@ softfp_truncations :=
>  softfp_exclude_libgcc2 := n
>  
>  LIB2ADD_ST += $(srcdir)/config/mips/lib2funcs.c
> +
> +
> +LIB1ASMSRC = mips/lib1funcs.S
> +LIB1ASMFUNCS = _speculation_barrier
> +
> +# Version these symbols if building libgcc.so.
> +SHLIB_MAPFILES += $(srcdir)/config/mips/libgcc-mips.ver
> diff --git a/libgcc/config/mips/t-mips16 b/libgcc/config/mips/t-mips16
> index 2bad5119d51..5fd9d60d7a3 100644
> --- a/libgcc/config/mips/t-mips16
> +++ b/libgcc/config/mips/t-mips16
> @@ -16,8 +16,7 @@
>  # along with GCC; see the file COPYING3.  If not see
>  # <http://www.gnu.org/licenses/>.
>  
> -LIB1ASMSRC = mips/mips16.S
> -LIB1ASMFUNCS = _m16addsf3 _m16subsf3 _m16mulsf3 _m16divsf3 \
> +LIB1ASMFUNCS += _m16addsf3 _m16subsf3 _m16mulsf3 _m16divsf3 \
>  	_m16eqsf2 _m16nesf2 _m16gtsf2 _m16gesf2 _m16lesf2 _m16ltsf2 \
>  	_m16unordsf2 \
>  	_m16fltsisf _m16fix_truncsfsi _m16fltunsisf \