Re: [PATCH] builtins: Commonise default handling of nonlocal_goto

[Richard Biener <richard.guenther@gmail.com>]

On Sun, Nov 13, 2022 at 10:33 AM Richard Sandiford via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> expand_builtin_longjmp and expand_builtin_nonlocal_goto both
> emit nonlocal gotos.  They first try to use a target-provided
> pattern and fall back to generic code otherwise.  These pieces
> of generic code are almost identical, and having them inline
> like this makes it difficult to define a nonlocal_goto pattern
> that only wants to add extra steps, not change the default ones.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?

OK.

> Richard
>
> gcc/
>         * builtins.h (emit_standard_nonlocal_goto): Declare.
>         * builtins.cc (emit_standard_nonlocal_goto): New function,
>         commonizing code from...
>         (expand_builtin_longjmp, expand_builtin_nonlocal_goto): ...here.
>         * genemit.cc (main): Emit an include of builtins.h.
> ---
>  gcc/builtins.cc | 103 +++++++++++++++++++++---------------------------
>  gcc/builtins.h  |   1 +
>  gcc/genemit.cc  |   1 +
>  3 files changed, 47 insertions(+), 58 deletions(-)
>
> diff --git a/gcc/builtins.cc b/gcc/builtins.cc
> index 4dc1ca672b2..2507745c17a 100644
> --- a/gcc/builtins.cc
> +++ b/gcc/builtins.cc
> @@ -998,6 +998,49 @@ expand_builtin_setjmp_receiver (rtx receiver_label)
>    emit_insn (gen_blockage ());
>  }
>
> +/* Emit the standard sequence for a nonlocal_goto.  The arguments are
> +   the operands to the .md pattern.  */
> +
> +void
> +emit_standard_nonlocal_goto (rtx value, rtx label, rtx stack, rtx fp)
> +{
> +  emit_clobber (gen_rtx_MEM (BLKmode, gen_rtx_SCRATCH (VOIDmode)));
> +  emit_clobber (gen_rtx_MEM (BLKmode, hard_frame_pointer_rtx));
> +
> +  label = copy_to_reg (label);
> +
> +  /* Restore the frame pointer and stack pointer.  We must use a
> +     temporary since the setjmp buffer may be a local.  */
> +  fp = copy_to_reg (fp);
> +  emit_stack_restore (SAVE_NONLOCAL, stack);
> +
> +  /* Ensure the frame pointer move is not optimized.  */
> +  emit_insn (gen_blockage ());
> +  emit_clobber (hard_frame_pointer_rtx);
> +  emit_clobber (frame_pointer_rtx);
> +  emit_move_insn (hard_frame_pointer_rtx, fp);
> +
> +  /* USE of hard_frame_pointer_rtx added for consistency;
> +     not clear if really needed.  */
> +  emit_use (hard_frame_pointer_rtx);
> +  emit_use (stack_pointer_rtx);
> +
> +  /* If the architecture is using a GP register, we must
> +     conservatively assume that the target function makes use of it.
> +     The prologue of functions with nonlocal gotos must therefore
> +     initialize the GP register to the appropriate value, and we
> +     must then make sure that this value is live at the point
> +     of the jump.  (Note that this doesn't necessarily apply
> +     to targets with a nonlocal_goto pattern; they are free
> +     to implement it in their own way.  Note also that this is
> +     a no-op if the GP register is a global invariant.)  */
> +  unsigned regnum = PIC_OFFSET_TABLE_REGNUM;
> +  if (value == const0_rtx && regnum != INVALID_REGNUM && fixed_regs[regnum])
> +    emit_use (pic_offset_table_rtx);
> +
> +  emit_indirect_jump (label);
> +}
> +
>  /* __builtin_longjmp is passed a pointer to an array of five words (not
>     all will be used on all machines).  It operates similarly to the C
>     library function of the same name, but is more efficient.  Much of
> @@ -1049,27 +1092,7 @@ expand_builtin_longjmp (rtx buf_addr, rtx value)
>            what that value is, because builtin_setjmp does not use it.  */
>         emit_insn (targetm.gen_nonlocal_goto (value, lab, stack, fp));
>        else
> -       {
> -         emit_clobber (gen_rtx_MEM (BLKmode, gen_rtx_SCRATCH (VOIDmode)));
> -         emit_clobber (gen_rtx_MEM (BLKmode, hard_frame_pointer_rtx));
> -
> -         lab = copy_to_reg (lab);
> -
> -         /* Restore the frame pointer and stack pointer.  We must use a
> -            temporary since the setjmp buffer may be a local.  */
> -         fp = copy_to_reg (fp);
> -         emit_stack_restore (SAVE_NONLOCAL, stack);
> -
> -         /* Ensure the frame pointer move is not optimized.  */
> -         emit_insn (gen_blockage ());
> -         emit_clobber (hard_frame_pointer_rtx);
> -         emit_clobber (frame_pointer_rtx);
> -         emit_move_insn (hard_frame_pointer_rtx, fp);
> -
> -         emit_use (hard_frame_pointer_rtx);
> -         emit_use (stack_pointer_rtx);
> -         emit_indirect_jump (lab);
> -       }
> +       emit_standard_nonlocal_goto (value, lab, stack, fp);
>      }
>
>    /* Search backwards and mark the jump insn as a non-local goto.
> @@ -1201,43 +1224,7 @@ expand_builtin_nonlocal_goto (tree exp)
>    if (targetm.have_nonlocal_goto ())
>      emit_insn (targetm.gen_nonlocal_goto (const0_rtx, r_label, r_sp, r_fp));
>    else
> -    {
> -      emit_clobber (gen_rtx_MEM (BLKmode, gen_rtx_SCRATCH (VOIDmode)));
> -      emit_clobber (gen_rtx_MEM (BLKmode, hard_frame_pointer_rtx));
> -
> -      r_label = copy_to_reg (r_label);
> -
> -      /* Restore the frame pointer and stack pointer.  We must use a
> -        temporary since the setjmp buffer may be a local.  */
> -      r_fp = copy_to_reg (r_fp);
> -      emit_stack_restore (SAVE_NONLOCAL, r_sp);
> -
> -      /* Ensure the frame pointer move is not optimized.  */
> -      emit_insn (gen_blockage ());
> -      emit_clobber (hard_frame_pointer_rtx);
> -      emit_clobber (frame_pointer_rtx);
> -      emit_move_insn (hard_frame_pointer_rtx, r_fp);
> -
> -      /* USE of hard_frame_pointer_rtx added for consistency;
> -        not clear if really needed.  */
> -      emit_use (hard_frame_pointer_rtx);
> -      emit_use (stack_pointer_rtx);
> -
> -      /* If the architecture is using a GP register, we must
> -        conservatively assume that the target function makes use of it.
> -        The prologue of functions with nonlocal gotos must therefore
> -        initialize the GP register to the appropriate value, and we
> -        must then make sure that this value is live at the point
> -        of the jump.  (Note that this doesn't necessarily apply
> -        to targets with a nonlocal_goto pattern; they are free
> -        to implement it in their own way.  Note also that this is
> -        a no-op if the GP register is a global invariant.)  */
> -      unsigned regnum = PIC_OFFSET_TABLE_REGNUM;
> -      if (regnum != INVALID_REGNUM && fixed_regs[regnum])
> -       emit_use (pic_offset_table_rtx);
> -
> -      emit_indirect_jump (r_label);
> -    }
> +    emit_standard_nonlocal_goto (const0_rtx, r_label, r_sp, r_fp);
>
>    /* Search backwards to the jump insn and mark it as a
>       non-local goto.  */
> diff --git a/gcc/builtins.h b/gcc/builtins.h
> index 5ad830c9fbf..5c86b241fea 100644
> --- a/gcc/builtins.h
> +++ b/gcc/builtins.h
> @@ -150,6 +150,7 @@ extern char target_percent_c[3];
>  extern char target_percent_s_newline[4];
>  extern bool target_char_cst_p (tree t, char *p);
>  extern rtx get_memory_rtx (tree exp, tree len);
> +extern void emit_standard_nonlocal_goto (rtx, rtx, rtx, rtx);
>
>  extern internal_fn associated_internal_fn (combined_fn, tree);
>  extern internal_fn associated_internal_fn (tree);
> diff --git a/gcc/genemit.cc b/gcc/genemit.cc
> index 909ac89a16b..c3e2152a491 100644
> --- a/gcc/genemit.cc
> +++ b/gcc/genemit.cc
> @@ -905,6 +905,7 @@ from the machine description file `md'.  */\n\n");
>    printf ("#include \"tm-constrs.h\"\n");
>    printf ("#include \"ggc.h\"\n");
>    printf ("#include \"target.h\"\n\n");
> +  printf ("#include \"builtins.h\"\n\n");
>
>    /* Read the machine description.  */
>
> --
> 2.25.1
>