Re: [PATCH 1/2] Change the name of array_at_struct_end_p to array_ref_flexible_size_p

[Richard Biener <rguenther@suse.de>]

On Tue, 8 Nov 2022, Qing Zhao wrote:

> The name of the utility routine "array_at_struct_end_p" is misleading
> and should be changed to a new name that more accurately reflects its
> real meaning.
> 
> The routine "array_at_struct_end_p" is used to check whether an array
> reference is to an array whose actual size might be larger than its
> upper bound implies, which includes 3 different cases:
> 
>    A. a ref to a flexible array member at the end of a structure;
>    B. a ref to an array with a different type against the original decl;
>    C. a ref to an array that was passed as a parameter;
> 
> The old name only reflects the above case A, therefore very confusing
> when reading the corresponding gcc source code.
> 
> In this patch, A new name "array_ref_flexible_size_p" is used to replace
> the old name.
> 
> All the references to the routine "array_at_struct_end_p" was replaced
> with this new name, and the corresponding comments were updated to make
> them clean and consistent.

Since you seem to feel strongly about this - OK.

Thanks,
Richard.

> gcc/ChangeLog:
> 
> 	* gimple-array-bounds.cc (trailing_array): Replace
> 	array_at_struct_end_p with new name and update comments.
> 	* gimple-fold.cc (get_range_strlen_tree): Likewise.
> 	* gimple-ssa-warn-restrict.cc (builtin_memref::builtin_memref):
> 	Likewise.
> 	* graphite-sese-to-poly.cc (bounds_are_valid): Likewise.
> 	* tree-if-conv.cc (idx_within_array_bound): Likewise.
> 	* tree-object-size.cc (addr_object_size): Likewise.
> 	* tree-ssa-alias.cc (component_ref_to_zero_sized_trailing_array_p):
> 	Likewise.
> 	(stmt_kills_ref_p): Likewise.
> 	* tree-ssa-loop-niter.cc (idx_infer_loop_bounds): Likewise.
> 	* tree-ssa-strlen.cc (maybe_set_strlen_range): Likewise.
> 	* tree.cc (array_at_struct_end_p): Rename to ...
> 	(array_ref_flexible_size_p): ... this.
> 	(component_ref_size): Replace array_at_struct_end_p with new name.
> 	* tree.h (array_at_struct_end_p): Rename to ...
> 	(array_ref_flexible_size_p): ... this.
> ---
>  gcc/gimple-array-bounds.cc      |  4 ++--
>  gcc/gimple-fold.cc              |  6 ++----
>  gcc/gimple-ssa-warn-restrict.cc |  5 +++--
>  gcc/graphite-sese-to-poly.cc    |  4 ++--
>  gcc/tree-if-conv.cc             |  7 +++----
>  gcc/tree-object-size.cc         |  2 +-
>  gcc/tree-ssa-alias.cc           |  8 ++++----
>  gcc/tree-ssa-loop-niter.cc      | 15 +++++++--------
>  gcc/tree-ssa-strlen.cc          |  2 +-
>  gcc/tree.cc                     | 11 ++++++-----
>  gcc/tree.h                      |  8 ++++----
>  11 files changed, 35 insertions(+), 37 deletions(-)
> 
> diff --git a/gcc/gimple-array-bounds.cc b/gcc/gimple-array-bounds.cc
> index e190b93aa85..fbf448e045d 100644
> --- a/gcc/gimple-array-bounds.cc
> +++ b/gcc/gimple-array-bounds.cc
> @@ -129,7 +129,7 @@ get_ref_size (tree arg, tree *pref)
>  }
>  
>  /* Return true if REF is (likely) an ARRAY_REF to a trailing array member
> -   of a struct.  It refines array_at_struct_end_p by detecting a pointer
> +   of a struct.  It refines array_ref_flexible_size_p by detecting a pointer
>     to an array and an array parameter declared using the [N] syntax (as
>     opposed to a pointer) and returning false.  Set *PREF to the decl or
>     expression REF refers to.  */
> @@ -167,7 +167,7 @@ trailing_array (tree arg, tree *pref)
>  	return false;
>      }
>  
> -  return array_at_struct_end_p (arg);
> +  return array_ref_flexible_size_p (arg);
>  }
>  
>  /* Checks one ARRAY_REF in REF, located at LOCUS. Ignores flexible
> diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
> index 9055cd8982d..cafd331ca98 100644
> --- a/gcc/gimple-fold.cc
> +++ b/gcc/gimple-fold.cc
> @@ -1690,13 +1690,11 @@ get_range_strlen_tree (tree arg, bitmap visited, strlen_range_kind rkind,
>  	  /* Handle a MEM_REF into a DECL accessing an array of integers,
>  	     being conservative about references to extern structures with
>  	     flexible array members that can be initialized to arbitrary
> -	     numbers of elements as an extension (static structs are okay).
> -	     FIXME: Make this less conservative -- see
> -	     component_ref_size in tree.cc.  */
> +	     numbers of elements as an extension (static structs are okay).  */
>  	  tree ref = TREE_OPERAND (TREE_OPERAND (arg, 0), 0);
>  	  if ((TREE_CODE (ref) == PARM_DECL || VAR_P (ref))
>  	      && (decl_binds_to_current_def_p (ref)
> -		  || !array_at_struct_end_p (arg)))
> +		  || !array_ref_flexible_size_p (arg)))
>  	    {
>  	      /* Fail if the offset is out of bounds.  Such accesses
>  		 should be diagnosed at some point.  */
> diff --git a/gcc/gimple-ssa-warn-restrict.cc b/gcc/gimple-ssa-warn-restrict.cc
> index b7ed15c8902..832456ba6fc 100644
> --- a/gcc/gimple-ssa-warn-restrict.cc
> +++ b/gcc/gimple-ssa-warn-restrict.cc
> @@ -296,8 +296,9 @@ builtin_memref::builtin_memref (pointer_query &ptrqry, gimple *stmt, tree expr,
>    tree basetype = TREE_TYPE (base);
>    if (TREE_CODE (basetype) == ARRAY_TYPE)
>      {
> -      if (ref && array_at_struct_end_p (ref))
> -	;   /* Use the maximum possible offset for last member arrays.  */
> +      if (ref && array_ref_flexible_size_p (ref))
> +	;   /* Use the maximum possible offset for an array that might
> +	       have flexible size.  */
>        else if (tree basesize = TYPE_SIZE_UNIT (basetype))
>  	if (TREE_CODE (basesize) == INTEGER_CST)
>  	  /* Size could be non-constant for a variable-length type such
> diff --git a/gcc/graphite-sese-to-poly.cc b/gcc/graphite-sese-to-poly.cc
> index 51ba3af204f..7eb24c1c991 100644
> --- a/gcc/graphite-sese-to-poly.cc
> +++ b/gcc/graphite-sese-to-poly.cc
> @@ -536,9 +536,9 @@ bounds_are_valid (tree ref, tree low, tree high)
>        || !tree_fits_shwi_p (high))
>      return false;
>  
> -  /* 1-element arrays at end of structures may extend over
> +  /* An array that has flexible size may extend over
>       their declared size.  */
> -  if (array_at_struct_end_p (ref)
> +  if (array_ref_flexible_size_p (ref)
>        && operand_equal_p (low, high, 0))
>      return false;
>  
> diff --git a/gcc/tree-if-conv.cc b/gcc/tree-if-conv.cc
> index a83b013d2ad..34bb507ff3b 100644
> --- a/gcc/tree-if-conv.cc
> +++ b/gcc/tree-if-conv.cc
> @@ -763,10 +763,9 @@ idx_within_array_bound (tree ref, tree *idx, void *dta)
>    if (TREE_CODE (ref) != ARRAY_REF)
>      return false;
>  
> -  /* For arrays at the end of the structure, we are not guaranteed that they
> -     do not really extend over their declared size.  However, for arrays of
> -     size greater than one, this is unlikely to be intended.  */
> -  if (array_at_struct_end_p (ref))
> +  /* For arrays that might have flexible sizes, it is not guaranteed that they
> +     do not extend over their declared size.  */
> +  if (array_ref_flexible_size_p (ref))
>      return false;
>  
>    ev = analyze_scalar_evolution (loop, *idx);
> diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
> index 1f04cb80fd0..2e5d267d8ce 100644
> --- a/gcc/tree-object-size.cc
> +++ b/gcc/tree-object-size.cc
> @@ -633,7 +633,7 @@ addr_object_size (struct object_size_info *osi, const_tree ptr,
>  			v = NULL_TREE;
>  			break;
>  		      }
> -		    is_flexible_array_mem_ref = array_at_struct_end_p (v);
> +		    is_flexible_array_mem_ref = array_ref_flexible_size_p (v);
>  		    while (v != pt_var && TREE_CODE (v) == COMPONENT_REF)
>  		      if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
>  			  != UNION_TYPE
> diff --git a/gcc/tree-ssa-alias.cc b/gcc/tree-ssa-alias.cc
> index b4c65da5718..d3a91b1f238 100644
> --- a/gcc/tree-ssa-alias.cc
> +++ b/gcc/tree-ssa-alias.cc
> @@ -1073,7 +1073,7 @@ component_ref_to_zero_sized_trailing_array_p (tree ref)
>  	  && TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 1))) == ARRAY_TYPE
>  	  && (!TYPE_SIZE (TREE_TYPE (TREE_OPERAND (ref, 1)))
>  	      || integer_zerop (TYPE_SIZE (TREE_TYPE (TREE_OPERAND (ref, 1)))))
> -	  && array_at_struct_end_p (ref));
> +	  && array_ref_flexible_size_p (ref));
>  }
>  
>  /* Worker for aliasing_component_refs_p. Most parameters match parameters of
> @@ -3433,10 +3433,10 @@ stmt_kills_ref_p (gimple *stmt, ao_ref *ref)
>  	    }
>  	  /* Finally check if the lhs has the same address and size as the
>  	     base candidate of the access.  Watch out if we have dropped
> -	     an array-ref that was at struct end, this means ref->ref may
> -	     be outside of the TYPE_SIZE of its base.  */
> +	     an array-ref that might have flexible size, this means ref->ref
> +	     may be outside of the TYPE_SIZE of its base.  */
>  	  if ((! innermost_dropped_array_ref
> -	       || ! array_at_struct_end_p (innermost_dropped_array_ref))
> +	       || ! array_ref_flexible_size_p (innermost_dropped_array_ref))
>  	      && (lhs == base
>  		  || (((TYPE_SIZE (TREE_TYPE (lhs))
>  			== TYPE_SIZE (TREE_TYPE (base)))
> diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
> index 4ffcef4f4ff..3fbbf4367ed 100644
> --- a/gcc/tree-ssa-loop-niter.cc
> +++ b/gcc/tree-ssa-loop-niter.cc
> @@ -3716,18 +3716,17 @@ idx_infer_loop_bounds (tree base, tree *idx, void *dta)
>    struct ilb_data *data = (struct ilb_data *) dta;
>    tree ev, init, step;
>    tree low, high, type, next;
> -  bool sign, upper = true, at_end = false;
> +  bool sign, upper = true, has_flexible_size = false;
>    class loop *loop = data->loop;
>  
>    if (TREE_CODE (base) != ARRAY_REF)
>      return true;
>  
> -  /* For arrays at the end of the structure, we are not guaranteed that they
> -     do not really extend over their declared size.  However, for arrays of
> -     size greater than one, this is unlikely to be intended.  */
> -  if (array_at_struct_end_p (base))
> +  /* For arrays that might have flexible sizes, it is not guaranteed that they
> +     do not really extend over their declared size.  */ 
> +  if (array_ref_flexible_size_p (base))
>      {
> -      at_end = true;
> +      has_flexible_size = true;
>        upper = false;
>      }
>  
> @@ -3760,9 +3759,9 @@ idx_infer_loop_bounds (tree base, tree *idx, void *dta)
>    sign = tree_int_cst_sign_bit (step);
>    type = TREE_TYPE (step);
>  
> -  /* The array of length 1 at the end of a structure most likely extends
> +  /* The array that might have flexible size most likely extends
>       beyond its bounds.  */
> -  if (at_end
> +  if (has_flexible_size
>        && operand_equal_p (low, high, 0))
>      return true;
>  
> diff --git a/gcc/tree-ssa-strlen.cc b/gcc/tree-ssa-strlen.cc
> index 5afbae1b72e..b87c7c7ce1f 100644
> --- a/gcc/tree-ssa-strlen.cc
> +++ b/gcc/tree-ssa-strlen.cc
> @@ -1987,7 +1987,7 @@ maybe_set_strlen_range (tree lhs, tree src, tree bound)
>  	 suggests if it's treated as a poor-man's flexible array member.  */
>        src = TREE_OPERAND (src, 0);
>        if (TREE_CODE (src) != MEM_REF
> -	  && !array_at_struct_end_p (src))
> +	  && !array_ref_flexible_size_p (src))
>  	{
>  	  tree type = TREE_TYPE (src);
>  	  tree size = TYPE_SIZE_UNIT (type);
> diff --git a/gcc/tree.cc b/gcc/tree.cc
> index 04603c8c902..d2b0b34a725 100644
> --- a/gcc/tree.cc
> +++ b/gcc/tree.cc
> @@ -12710,8 +12710,8 @@ array_ref_up_bound (tree exp)
>    return NULL_TREE;
>  }
>  
> -/* Returns true if REF is an array reference, component reference,
> -   or memory reference to an array whose actual size might be larger
> +/* Returns true if REF is an array reference, a component reference,
> +   or a memory reference to an array whose actual size might be larger
>     than its upper bound implies, there are multiple cases:
>     A. a ref to a flexible array member at the end of a structure;
>     B. a ref to an array with a different type against the original decl;
> @@ -12726,10 +12726,10 @@ array_ref_up_bound (tree exp)
>     int test (uint8_t *p, uint32_t t[1][1], int n) {
>     for (int i = 0; i < 4; i++, p++)
>       t[i][0] = ...;
> +*/
>  
> -   FIXME, the name of this routine need to be changed to be more accurate.  */
>  bool
> -array_at_struct_end_p (tree ref)
> +array_ref_flexible_size_p (tree ref)
>  {
>    /* the TYPE for this array referece.  */
>    tree atype = NULL_TREE;
> @@ -12862,6 +12862,7 @@ array_at_struct_end_p (tree ref)
>    return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true;
>  }
>  
> +
>  /* Return a tree representing the offset, in bytes, of the field referenced
>     by EXP.  This does not include any offset in DECL_FIELD_BIT_OFFSET.  */
>  
> @@ -12957,7 +12958,7 @@ component_ref_size (tree ref, special_array_member *sam /* = NULL */)
>  	return (tree_int_cst_equal (memsize, TYPE_SIZE_UNIT (memtype))
>  		? memsize : NULL_TREE);
>  
> -      bool trailing = array_at_struct_end_p (ref);
> +      bool trailing = array_ref_flexible_size_p (ref);
>        bool zero_length = integer_zerop (memsize);
>        if (!trailing && !zero_length)
>  	/* MEMBER is either an interior array or is an array with
> diff --git a/gcc/tree.h b/gcc/tree.h
> index a50f7b2be9d..0fcdd6b06d0 100644
> --- a/gcc/tree.h
> +++ b/gcc/tree.h
> @@ -5548,10 +5548,10 @@ extern tree array_ref_up_bound (tree);
>     EXP, an ARRAY_REF or an ARRAY_RANGE_REF.  */
>  extern tree array_ref_low_bound (tree);
>  
> -/* Returns true if REF is an array reference or a component reference
> -   to an array at the end of a structure.  If this is the case, the array
> -   may be allocated larger than its upper bound implies.  */
> -extern bool array_at_struct_end_p (tree);
> +/* Returns true if REF is an array reference, a component reference,
> +   or a memory reference to an array whose actual size might be larger
> +   than its upper bound implies.  */
> +extern bool array_ref_flexible_size_p (tree);
>  
>  /* Return a tree representing the offset, in bytes, of the field referenced
>     by EXP.  This does not include any offset in DECL_FIELD_BIT_OFFSET.  */
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)