Re: [PATCH] bpf: Use enum for resolved overloaded builtins

["Jose E. Marchesi" <jose.marchesi@oracle.com>]

Hi David.

> Change several places in the eBPF backend dealing with overloaded
> built-in functions to consistently use the enum bpf_builtins type,
> rather than variously using integer constants or booleans. The result is
> eaiser to read and extend.
>
> Tested on bpf-unknown-none, no known regressions.
> OK to push?

OK.
Thanks for the patch.

>
> Thanks.
>
> gcc/
>
> 	* config/bpf/bpf.cc (struct core_walk_data): Add field `which'...
> 	(bpf_resolve_overloaded_builtin): ... set it here. Use values of enum
> 	bpf_builtins for error checks.
> 	(bpf_core_walk): Use values of enum bpf_builtins.
> 	(bpf_core_newdecl): Likewise.
> 	(bpf_expand_builtin): Likewise.
> ---
>  gcc/config/bpf/bpf.cc | 106 +++++++++++++++++++++++-------------------
>  1 file changed, 59 insertions(+), 47 deletions(-)
>
> diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
> index fd4003c2bfc..16af2412bf6 100644
> --- a/gcc/config/bpf/bpf.cc
> +++ b/gcc/config/bpf/bpf.cc
> @@ -1222,7 +1222,7 @@ bpf_expand_builtin (tree exp, rtx target ATTRIBUTE_UNUSED,
>        return gen_rtx_REG (ops[0].mode, BPF_R0);
>      }
>  
> -  else if (code == -1)
> +  else if (code == -BPF_BUILTIN_PRESERVE_ACCESS_INDEX)
>      {
>        /* A resolved overloaded __builtin_preserve_access_index.  */
>        tree arg = CALL_EXPR_ARG (exp, 0);
> @@ -1249,7 +1249,7 @@ bpf_expand_builtin (tree exp, rtx target ATTRIBUTE_UNUSED,
>        return expand_normal (arg);
>      }
>  
> -  else if (code == -2)
> +  else if (code == -BPF_BUILTIN_PRESERVE_FIELD_INFO)
>      {
>        /* A resolved overloaded __builtin_preserve_field_info.  */
>        tree src = CALL_EXPR_ARG (exp, 0);
> @@ -1444,28 +1444,37 @@ bpf_core_get_index (const tree node)
>     __builtin_preserve_access_index.  */
>  
>  static tree
> -bpf_core_newdecl (tree type, bool is_pai)
> +bpf_core_newdecl (tree type, enum bpf_builtins which)
>  {
>    tree rettype;
>    char name[80];
>    static unsigned long pai_count = 0;
>    static unsigned long pfi_count = 0;
>  
> -  if (is_pai)
> +  switch (which)
>      {
> -      rettype = build_function_type_list (type, type, NULL);
> -      int len = snprintf (name, sizeof (name), "%s", "__builtin_pai_");
> -      len = snprintf (name + len, sizeof (name) - len, "%lu", pai_count++);
> -    }
> -  else
> -    {
> -      rettype = build_function_type_list (unsigned_type_node, type,
> -					  unsigned_type_node, NULL);
> -      int len = snprintf (name, sizeof (name), "%s", "__builtin_pfi_");
> -      len = snprintf (name + len, sizeof (name) - len, "%lu", pfi_count++);
> +    case BPF_BUILTIN_PRESERVE_ACCESS_INDEX:
> +      {
> +	rettype = build_function_type_list (type, type, NULL);
> +	int len = snprintf (name, sizeof (name), "%s", "__builtin_pai_");
> +	len = snprintf (name + len, sizeof (name) - len, "%lu", pai_count++);
> +      }
> +      break;
> +
> +    case BPF_BUILTIN_PRESERVE_FIELD_INFO:
> +      {
> +	rettype = build_function_type_list (unsigned_type_node, type,
> +					    unsigned_type_node, NULL);
> +	int len = snprintf (name, sizeof (name), "%s", "__builtin_pfi_");
> +	len = snprintf (name + len, sizeof (name) - len, "%lu", pfi_count++);
> +      }
> +      break;
> +
> +    default:
> +      gcc_unreachable ();
>      }
>  
> -  return add_builtin_function_ext_scope (name, rettype, is_pai ? -1 : -2,
> +  return add_builtin_function_ext_scope (name, rettype, -which,
>  					 BUILT_IN_MD, NULL, NULL_TREE);
>  }
>  
> @@ -1492,6 +1501,7 @@ bpf_core_is_maybe_aggregate_access (tree expr)
>  
>  struct core_walk_data {
>    location_t loc;
> +  enum bpf_builtins which;
>    tree arg;
>  };
>  
> @@ -1501,7 +1511,6 @@ static tree
>  bpf_core_walk (tree *tp, int *walk_subtrees, void *data)
>  {
>    struct core_walk_data *dat = (struct core_walk_data *) data;
> -  bool is_pai = dat->arg == NULL_TREE;
>  
>    /* If this is a type, don't do anything. */
>    if (TYPE_P (*tp))
> @@ -1510,19 +1519,21 @@ bpf_core_walk (tree *tp, int *walk_subtrees, void *data)
>        return NULL_TREE;
>      }
>  
> -  /* Build a new function call to a resolved builtin for the desired operation.
> -     If this is a preserve_field_info call, pass along the argument to the
> -     resolved builtin call. */
> -  if (bpf_core_is_maybe_aggregate_access (*tp))
> -    {
> -      tree newdecl = bpf_core_newdecl (TREE_TYPE (*tp), is_pai);
> -      tree newcall;
> -      if (is_pai)
> -	newcall = build_call_expr_loc (dat->loc, newdecl, 1, *tp);
> -      else
> -	newcall = build_call_expr_loc (dat->loc, newdecl, 2, *tp, dat->arg);
> +  /* Build a new function call to a type-resolved temporary builtin for the
> +     desired operation, and pass along args as necessary.  */
> +  tree newdecl = bpf_core_newdecl (TREE_TYPE (*tp), dat->which);
>  
> -      *tp = newcall;
> +  if (dat->which == BPF_BUILTIN_PRESERVE_ACCESS_INDEX)
> +    {
> +      if (bpf_core_is_maybe_aggregate_access (*tp))
> +	{
> +	  *tp = build_call_expr_loc (dat->loc, newdecl, 1, *tp);
> +	  *walk_subtrees = 0;
> +	}
> +    }
> +  else
> +    {
> +      *tp = build_call_expr_loc (dat->loc, newdecl, 2, *tp, dat->arg);
>        *walk_subtrees = 0;
>      }
>  
> @@ -1572,32 +1583,26 @@ bpf_is_valid_preserve_field_info_arg (tree expr)
>  
>  /* Implement TARGET_RESOLVE_OVERLOADED_BUILTIN (see gccint manual section
>     Target Macros::Misc.).
> -   We use this for the __builtin_preserve_access_index builtin for CO-RE
> -   support.
> +   Used for CO-RE support builtins such as __builtin_preserve_access_index
> +   and __builtin_preserve_field_info.
>  
>     FNDECL is the declaration of the builtin, and ARGLIST is the list of
> -   arguments passed to it, and is really a vec<tree,_> *.
> -
> -   In this case, the 'operation' implemented by the builtin is a no-op;
> -   the builtin is just a marker. So, the result is simply the argument.  */
> +   arguments passed to it, and is really a vec<tree,_> *.  */
>  
>  static tree
>  bpf_resolve_overloaded_builtin (location_t loc, tree fndecl, void *arglist)
>  {
> -  bool is_pai = DECL_MD_FUNCTION_CODE (fndecl)
> -    == BPF_BUILTIN_PRESERVE_ACCESS_INDEX;
> -  bool is_pfi = DECL_MD_FUNCTION_CODE (fndecl)
> -    == BPF_BUILTIN_PRESERVE_FIELD_INFO;
> +  enum bpf_builtins which = (enum bpf_builtins) DECL_MD_FUNCTION_CODE (fndecl);
>  
> -  if (!is_pai && !is_pfi)
> +  if (which < BPF_BUILTIN_PRESERVE_ACCESS_INDEX
> +      || which >= BPF_BUILTIN_MAX)
>      return NULL_TREE;
>  
> -  /* We only expect one argument, but it may be an arbitrarily-complicated
> -     statement-expression. */
>    vec<tree, va_gc> *params = static_cast<vec<tree, va_gc> *> (arglist);
>    unsigned n_params = params ? params->length() : 0;
>  
> -  if ((is_pai && n_params != 1) || (is_pfi && n_params != 2))
> +  if (!(which == BPF_BUILTIN_PRESERVE_ACCESS_INDEX && n_params == 1)
> +      && n_params != 2)
>      {
>        error_at (loc, "wrong number of arguments");
>        return error_mark_node;
> @@ -1605,12 +1610,15 @@ bpf_resolve_overloaded_builtin (location_t loc, tree fndecl, void *arglist)
>  
>    tree param = (*params)[0];
>  
> -  /* If not generating BPF_CORE information, preserve_access_index does nothing,
> -     and simply "resolves to" the argument.  */
> -  if (!TARGET_BPF_CORE && is_pai)
> +  /* If not generating BPF_CORE information, preserve_access_index does
> +     nothing, and simply "resolves to" the argument.  */
> +  if (which == BPF_BUILTIN_PRESERVE_ACCESS_INDEX && !TARGET_BPF_CORE)
>      return param;
>  
> -  if (is_pfi && !bpf_is_valid_preserve_field_info_arg (param))
> +  /* For __builtin_preserve_field_info, enforce that the parameter is exactly a
> +     field access and not a more complex expression.  */
> +  else if (which == BPF_BUILTIN_PRESERVE_FIELD_INFO
> +	   && !bpf_is_valid_preserve_field_info_arg (param))
>      {
>        error_at (EXPR_LOC_OR_LOC (param, loc),
>  		"argument is not a field access");
> @@ -1642,7 +1650,11 @@ bpf_resolve_overloaded_builtin (location_t loc, tree fndecl, void *arglist)
>  
>    struct core_walk_data data;
>    data.loc = loc;
> -  data.arg = is_pai ? NULL_TREE : (*params)[1];
> +  data.which = which;
> +  if (which == BPF_BUILTIN_PRESERVE_ACCESS_INDEX)
> +    data.arg = NULL_TREE;
> +  else
> +    data.arg = (*params)[1];
>  
>    walk_tree (&param, bpf_core_walk, (void *) &data, NULL);