Re: [PATCH] Use C++ RAII to clear currently_expanding_gimple_stmt

[Richard Biener <rguenther@suse.de>]

On Tue, 1 Mar 2022, H.J. Lu wrote:

> Use C++ RAII with make_temp_override in the C++ FE to automatically clear
> currently_expanding_gimple_stmt.

Hmm, the temp-override isn't really a good fit since we only want to
have the cleanup part and that should always "restore" to nullptr.

Richard.


> gcc/
> 
> 	PR middle-end/104721
> 	* cfgexpand.cc (expand_gimple_basic_block): Use make_temp_override
> 	to clear currently_expanding_gimple_stmt automatically.
> 	* tree.h (temp_override): Moved from cp/cp-tree.h.
> 	(type_identity_t): Likewise.
> 	make_temp_override(): Likewise.
> 
> gcc/cp/
> 
> 	PR middle-end/104721
> 	* cp-tree.h (temp_override): Moved to ../tree.h.
> 	(type_identity_t): Likewise.
> 	make_temp_override(): Likewise.
> ---
>  gcc/cfgexpand.cc | 15 +++++---------
>  gcc/cp/cp-tree.h | 51 ------------------------------------------------
>  gcc/tree.h       | 51 ++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 56 insertions(+), 61 deletions(-)
> 
> diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc
> index 87536ec7ccd..3d656113df5 100644
> --- a/gcc/cfgexpand.cc
> +++ b/gcc/cfgexpand.cc
> @@ -5817,6 +5817,9 @@ expand_gimple_basic_block (basic_block bb, bool disable_tail_calls)
>    if (note)
>      NOTE_BASIC_BLOCK (note) = bb;
>  
> +  auto cleanup = make_temp_override (currently_expanding_gimple_stmt,
> +				     nullptr);
> +
>    for (; !gsi_end_p (gsi); gsi_next (&gsi))
>      {
>        basic_block new_bb;
> @@ -5927,10 +5930,7 @@ expand_gimple_basic_block (basic_block bb, bool disable_tail_calls)
>  	{
>  	  new_bb = expand_gimple_cond (bb, as_a <gcond *> (stmt));
>  	  if (new_bb)
> -	    {
> -	      currently_expanding_gimple_stmt = NULL;
> -	      return new_bb;
> -	    }
> +	    return new_bb;
>  	}
>        else if (is_gimple_debug (stmt))
>  	{
> @@ -6052,10 +6052,7 @@ expand_gimple_basic_block (basic_block bb, bool disable_tail_calls)
>  		  if (can_fallthru)
>  		    bb = new_bb;
>  		  else
> -		    {
> -		      currently_expanding_gimple_stmt = NULL;
> -		      return new_bb;
> -		    }
> +		    return new_bb;
>  		}
>  	    }
>  	  else
> @@ -6078,8 +6075,6 @@ expand_gimple_basic_block (basic_block bb, bool disable_tail_calls)
>  	}
>      }
>  
> -  currently_expanding_gimple_stmt = NULL;
> -
>    /* Expand implicit goto and convert goto_locus.  */
>    FOR_EACH_EDGE (e, ei, bb->succs)
>      {
> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index 80994e94793..0a55588dc5d 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -1961,57 +1961,6 @@ public:
>    }
>  };
>  
> -/* RAII sentinel that saves the value of a variable, optionally
> -   overrides it right away, and restores its value when the sentinel
> -   id destructed.  */
> -
> -template <typename T>
> -class temp_override
> -{
> -  T& overridden_variable;
> -  T saved_value;
> -public:
> -  temp_override(T& var) : overridden_variable (var), saved_value (var) {}
> -  temp_override(T& var, T overrider)
> -    : overridden_variable (var), saved_value (var)
> -  {
> -    overridden_variable = overrider;
> -  }
> -  ~temp_override() { overridden_variable = saved_value; }
> -};
> -
> -/* Wrapping a template parameter in type_identity_t hides it from template
> -   argument deduction.  */
> -#if __cpp_lib_type_identity
> -using std::type_identity_t;
> -#else
> -template <typename T>
> -struct type_identity { typedef T type; };
> -template <typename T>
> -using type_identity_t = typename type_identity<T>::type;
> -#endif
> -
> -/* Object generator function for temp_override, so you don't need to write the
> -   type of the object as a template argument.
> -
> -   Use as auto x = make_temp_override (flag); */
> -
> -template <typename T>
> -inline temp_override<T>
> -make_temp_override (T& var)
> -{
> -  return { var };
> -}
> -
> -/* Likewise, but use as auto x = make_temp_override (flag, value); */
> -
> -template <typename T>
> -inline temp_override<T>
> -make_temp_override (T& var, type_identity_t<T> overrider)
> -{
> -  return { var, overrider };
> -}
> -
>  /* The cached class binding level, from the most recently exited
>     class, or NULL if none.  */
>  
> diff --git a/gcc/tree.h b/gcc/tree.h
> index 36ceed57064..32d610474d2 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -6581,4 +6581,55 @@ extern tree get_attr_nonstring_decl (tree, tree * = NULL);
>  
>  extern int get_target_clone_attr_len (tree);
>  
> +/* RAII sentinel that saves the value of a variable, optionally
> +   overrides it right away, and restores its value when the sentinel
> +   id destructed.  */
> +
> +template <typename T>
> +class temp_override
> +{
> +  T& overridden_variable;
> +  T saved_value;
> +public:
> +  temp_override(T& var) : overridden_variable (var), saved_value (var) {}
> +  temp_override(T& var, T overrider)
> +    : overridden_variable (var), saved_value (var)
> +  {
> +    overridden_variable = overrider;
> +  }
> +  ~temp_override() { overridden_variable = saved_value; }
> +};
> +
> +/* Wrapping a template parameter in type_identity_t hides it from template
> +   argument deduction.  */
> +#if __cpp_lib_type_identity
> +using std::type_identity_t;
> +#else
> +template <typename T>
> +struct type_identity { typedef T type; };
> +template <typename T>
> +using type_identity_t = typename type_identity<T>::type;
> +#endif
> +
> +/* Object generator function for temp_override, so you don't need to write the
> +   type of the object as a template argument.
> +
> +   Use as auto x = make_temp_override (flag); */
> +
> +template <typename T>
> +inline temp_override<T>
> +make_temp_override (T& var)
> +{
> +  return { var };
> +}
> +
> +/* Likewise, but use as auto x = make_temp_override (flag, value); */
> +
> +template <typename T>
> +inline temp_override<T>
> +make_temp_override (T& var, type_identity_t<T> overrider)
> +{
> +  return { var, overrider };
> +}
> +
>  #endif  /* GCC_TREE_H  */
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)