Re: PROPOSAL: Extend inline asm syntax with size spec

[Richard Biener]

On Tue, 9 Oct 2018, Segher Boessenkool wrote:

> On Mon, Oct 08, 2018 at 11:07:46AM +0200, Richard Biener wrote:
> > On Mon, 8 Oct 2018, Segher Boessenkool wrote:
> > > On Sun, Oct 07, 2018 at 03:53:26PM +0000, Michael Matz wrote:
> > > > On Sun, 7 Oct 2018, Segher Boessenkool wrote:
> > > > > On Sun, Oct 07, 2018 at 11:18:06AM +0200, Borislav Petkov wrote:
> > > > > > Now, Richard suggested doing something like:
> > > > > > 
> > > > > >  1) inline asm ("...")
> > > > > 
> > > > > What would the semantics of this be?
> > > > 
> > > > The size of the inline asm wouldn't be counted towards the inliner size 
> > > > limits (or be counted as "1").
> > > 
> > > That sounds like a good option.
> > 
> > Yes, I also like it for simplicity.  It also avoids the requirement
> > of translating the number (in bytes?) given by the user to
> > "number of GIMPLE instructions" as needed by the inliner.
> 
> This patch implements this, for C only so far.  And the syntax is
> "asm inline", which is more in line with other syntax.
> 
> How does this look?

Looks good.  A few nits - you need to document this in extend.texi, the
tree flag use needs documenting in tree-core.h, and we need a testcase
(I'd suggest one that shows we inline a function with "large" asm inline 
() even at -Os).

Oh, and I don't think we want C and C++ to diverge - so you need to
cook up C++ support as well.

Can kernel folks give this a second and third thought please so we
don't implement sth that in the end won't satisfy you guys?

Thanks for doing this,
Richard.

> 
> Segher
> 
> 
> 
> diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
> index 1f173fc..94b1d41 100644
> --- a/gcc/c/c-parser.c
> +++ b/gcc/c/c-parser.c
> @@ -6287,7 +6287,7 @@ static tree
>  c_parser_asm_statement (c_parser *parser)
>  {
>    tree quals, str, outputs, inputs, clobbers, labels, ret;
> -  bool simple, is_goto;
> +  bool simple, is_goto, is_inline;
>    location_t asm_loc = c_parser_peek_token (parser)->location;
>    int section, nsections;
>  
> @@ -6318,6 +6318,13 @@ c_parser_asm_statement (c_parser *parser)
>        is_goto = true;
>      }
>  
> +  is_inline = false;
> +  if (c_parser_next_token_is_keyword (parser, RID_INLINE))
> +    {
> +      c_parser_consume_token (parser);
> +      is_inline = true;
> +    }
> +
>    /* ??? Follow the C++ parser rather than using the
>       lex_untranslated_string kludge.  */
>    parser->lex_untranslated_string = true;
> @@ -6393,7 +6400,8 @@ c_parser_asm_statement (c_parser *parser)
>      c_parser_skip_to_end_of_block_or_statement (parser);
>  
>    ret = build_asm_stmt (quals, build_asm_expr (asm_loc, str, outputs, inputs,
> -					       clobbers, labels, simple));
> +					       clobbers, labels, simple,
> +					       is_inline));
>  
>   error:
>    parser->lex_untranslated_string = false;
> diff --git a/gcc/c/c-tree.h b/gcc/c/c-tree.h
> index 017c01c..f5629300 100644
> --- a/gcc/c/c-tree.h
> +++ b/gcc/c/c-tree.h
> @@ -677,7 +677,8 @@ extern tree build_compound_literal (location_t, tree, tree, bool,
>  extern void check_compound_literal_type (location_t, struct c_type_name *);
>  extern tree c_start_case (location_t, location_t, tree, bool);
>  extern void c_finish_case (tree, tree);
> -extern tree build_asm_expr (location_t, tree, tree, tree, tree, tree, bool);
> +extern tree build_asm_expr (location_t, tree, tree, tree, tree, tree, bool,
> +			    bool);
>  extern tree build_asm_stmt (tree, tree);
>  extern int c_types_compatible_p (tree, tree);
>  extern tree c_begin_compound_stmt (bool);
> diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
> index 9d09b8d..e013100 100644
> --- a/gcc/c/c-typeck.c
> +++ b/gcc/c/c-typeck.c
> @@ -10064,7 +10064,7 @@ build_asm_stmt (tree cv_qualifier, tree args)
>     are subtly different.  We use a ASM_EXPR node to represent this.  */
>  tree
>  build_asm_expr (location_t loc, tree string, tree outputs, tree inputs,
> -		tree clobbers, tree labels, bool simple)
> +		tree clobbers, tree labels, bool simple, bool is_inline)
>  {
>    tree tail;
>    tree args;
> @@ -10182,6 +10182,7 @@ build_asm_expr (location_t loc, tree string, tree outputs, tree inputs,
>       as volatile.  */
>    ASM_INPUT_P (args) = simple;
>    ASM_VOLATILE_P (args) = (noutputs == 0);
> +  ASM_INLINE_P (args) = is_inline;
>  
>    return args;
>  }
> diff --git a/gcc/gimple-pretty-print.c b/gcc/gimple-pretty-print.c
> index 83e2273..1a00fa3 100644
> --- a/gcc/gimple-pretty-print.c
> +++ b/gcc/gimple-pretty-print.c
> @@ -2019,6 +2019,8 @@ dump_gimple_asm (pretty_printer *buffer, gasm *gs, int spc, dump_flags_t flags)
>        pp_string (buffer, "__asm__");
>        if (gimple_asm_volatile_p (gs))
>  	pp_string (buffer, " __volatile__");
> +      if (gimple_asm_inline_p (gs))
> +	pp_string (buffer, " __inline__");
>        if (gimple_asm_nlabels (gs))
>  	pp_string (buffer, " goto");
>        pp_string (buffer, "(\"");
> diff --git a/gcc/gimple.h b/gcc/gimple.h
> index a5dda93..8a58e07 100644
> --- a/gcc/gimple.h
> +++ b/gcc/gimple.h
> @@ -137,6 +137,7 @@ enum gimple_rhs_class
>  enum gf_mask {
>      GF_ASM_INPUT		= 1 << 0,
>      GF_ASM_VOLATILE		= 1 << 1,
> +    GF_ASM_INLINE		= 1 << 2,
>      GF_CALL_FROM_THUNK		= 1 << 0,
>      GF_CALL_RETURN_SLOT_OPT	= 1 << 1,
>      GF_CALL_TAILCALL		= 1 << 2,
> @@ -3911,7 +3912,7 @@ gimple_asm_volatile_p (const gasm *asm_stmt)
>  }
>  
>  
> -/* If VOLATLE_P is true, mark asm statement ASM_STMT as volatile.  */
> +/* If VOLATILE_P is true, mark asm statement ASM_STMT as volatile.  */
>  
>  static inline void
>  gimple_asm_set_volatile (gasm *asm_stmt, bool volatile_p)
> @@ -3923,6 +3924,27 @@ gimple_asm_set_volatile (gasm *asm_stmt, bool volatile_p)
>  }
>  
>  
> +/* Return true ASM_STMT ASM_STMT is an asm statement marked inline.  */
> +
> +static inline bool
> +gimple_asm_inline_p (const gasm *asm_stmt)
> +{
> +  return (asm_stmt->subcode & GF_ASM_INLINE) != 0;
> +}
> +
> +
> +/* If INLINE_P is true, mark asm statement ASM_STMT as inline.  */
> +
> +static inline void
> +gimple_asm_set_inline (gasm *asm_stmt, bool inline_p)
> +{
> +  if (inline_p)
> +    asm_stmt->subcode |= GF_ASM_INLINE;
> +  else
> +    asm_stmt->subcode &= ~GF_ASM_INLINE;
> +}
> +
> +
>  /* If INPUT_P is true, mark asm ASM_STMT as an ASM_INPUT.  */
>  
>  static inline void
> diff --git a/gcc/gimplify.c b/gcc/gimplify.c
> index 509fc2f..10b80f2 100644
> --- a/gcc/gimplify.c
> +++ b/gcc/gimplify.c
> @@ -6315,6 +6315,7 @@ gimplify_asm_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
>  
>        gimple_asm_set_volatile (stmt, ASM_VOLATILE_P (expr) || noutputs == 0);
>        gimple_asm_set_input (stmt, ASM_INPUT_P (expr));
> +      gimple_asm_set_inline (stmt, ASM_INLINE_P (expr));
>  
>        gimplify_seq_add_stmt (pre_p, stmt);
>      }
> diff --git a/gcc/ipa-icf-gimple.c b/gcc/ipa-icf-gimple.c
> index ba39ea3..5361139 100644
> --- a/gcc/ipa-icf-gimple.c
> +++ b/gcc/ipa-icf-gimple.c
> @@ -993,6 +993,9 @@ func_checker::compare_gimple_asm (const gasm *g1, const gasm *g2)
>    if (gimple_asm_input_p (g1) != gimple_asm_input_p (g2))
>      return false;
>  
> +  if (gimple_asm_inline_p (g1) != gimple_asm_inline_p (g2))
> +    return false;
> +
>    if (gimple_asm_ninputs (g1) != gimple_asm_ninputs (g2))
>      return false;
>  
> diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
> index 9134253..6b1d2ea 100644
> --- a/gcc/tree-inline.c
> +++ b/gcc/tree-inline.c
> @@ -4108,6 +4108,8 @@ estimate_num_insns (gimple *stmt, eni_weights *weights)
>  	   with very long asm statements.  */
>  	if (count > 1000)
>  	  count = 1000;
> +	if (gimple_asm_inline_p (as_a <gasm *> (stmt)))
> +	  count = !!count;
>  	return MAX (1, count);
>        }
>  
> diff --git a/gcc/tree.h b/gcc/tree.h
> index 2e45f9d..160b3a7 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -1245,6 +1245,9 @@ extern tree maybe_wrap_with_location (tree, location_t);
>     ASM_OPERAND with no operands.  */
>  #define ASM_INPUT_P(NODE) (ASM_EXPR_CHECK (NODE)->base.static_flag)
>  #define ASM_VOLATILE_P(NODE) (ASM_EXPR_CHECK (NODE)->base.public_flag)
> +/* Nonzero if we want to consider this asm as minimum length and cost
> +   for inlining decisions.  */
> +#define ASM_INLINE_P(NODE) (ASM_EXPR_CHECK (NODE)->base.protected_flag)
>  
>  /* COND_EXPR accessors.  */
>  #define COND_EXPR_COND(NODE)	(TREE_OPERAND (COND_EXPR_CHECK (NODE), 0))
> 
> 

-- 
Richard Biener <rguenther@xxxxxxx>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)