Re: [PATCH] middle-end/114931 - type_hash_canon and structual equality types

[Martin Uecker <uecker@tugraz.at>]

Am Freitag, dem 03.05.2024 um 14:13 +0200 schrieb Richard Biener:
> TYPE_STRUCTURAL_EQUALITY_P is part of our type system so we have
> to make sure to include that into the type unification done via
> type_hash_canon.  This requires the flag to be set before querying
> the hash which is the biggest part of the patch.

I assume this does not affect structs / unions because they
do not make this mechanism of type unification (each tagged type
is a unique type), but only derived types that end up having
TYPE_STRUCTURAL_EQUALITY_P because they are constructed from
incomplete structs / unions before TYPE_CANONICAL is set.

I do not yet understand why this change is needed. Type
identity should not be affected by setting TYPE_CANONICAL, so
why do we need to keep such types separate?  I understand that we
created some inconsistencies, but I do not see why this change
is needed to fix it.  But I also haven't understood how we ended
up with a TYPE_CANONICAL having TYPE_STRUCTURAL_EQUALITY_P in
PR 114931 ...

Martin


> 
> Bootstrapped and tested on x86_64-unknown-linux-gnu for all languages.
> 
> As said in the PR this merely makes sure to keep individual types
> consistent with themselves.  We still will have a set of types
> with TYPE_STRUCTURAL_EQUALITY_P and a set without that might be
> otherwise identical.  That could be only avoided with changes in
> the frontend.
> 
> OK for trunk?
> 
> Thanks,
> Richard.
> 
> 	PR middle-end/114931
> gcc/
> 	* tree.cc (type_hash_canon_hash): Hash TYPE_STRUCTURAL_EQUALITY_P.
> 	(type_cache_hasher::equal): Compare TYPE_STRUCTURAL_EQUALITY_P.
> 	(build_array_type_1): Set TYPE_STRUCTURAL_EQUALITY_P before
> 	probing with type_hash_canon.
> 	(build_function_type): Likewise.
> 	(build_method_type_directly): Likewise.
> 	(build_offset_type): Likewise.
> 	(build_complex_type): Likewise.
> 	* attribs.cc (build_type_attribute_qual_variant): Likewise.
> 
> gcc/c-family/
> 	* c-common.cc (complete_array_type): Set TYPE_STRUCTURAL_EQUALITY_P
> 	before probing with type_hash_canon.
> 
> gcc/testsuite/
> 	* gcc.dg/pr114931.c: New testcase.
> ---
>  gcc/attribs.cc                  | 20 +++++-----
>  gcc/c-family/c-common.cc        | 11 ++++--
>  gcc/testsuite/gcc.dg/pr114931.c | 10 +++++
>  gcc/tree.cc                     | 65 +++++++++++++++++++++++----------
>  4 files changed, 74 insertions(+), 32 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/pr114931.c
> 
> diff --git a/gcc/attribs.cc b/gcc/attribs.cc
> index 12ffc5f170a..3ab0b0fd87a 100644
> --- a/gcc/attribs.cc
> +++ b/gcc/attribs.cc
> @@ -1336,6 +1336,16 @@ build_type_attribute_qual_variant (tree otype, tree attribute, int quals)
>        tree dtype = ntype = build_distinct_type_copy (ttype);
>  
>        TYPE_ATTRIBUTES (ntype) = attribute;
> +      /* If the target-dependent attributes make NTYPE different from
> +	 its canonical type, we will need to use structural equality
> +	 checks for this type.
> +
> +	 We shouldn't get here for stripping attributes from a type;
> +	 the no-attribute type might not need structural comparison.  But
> +	 we can if was discarded from type_hash_table.  */
> +      if (TYPE_STRUCTURAL_EQUALITY_P (ttype)
> +	  || !comp_type_attributes (ntype, ttype))
> +	SET_TYPE_STRUCTURAL_EQUALITY (ntype);
>  
>        hashval_t hash = type_hash_canon_hash (ntype);
>        ntype = type_hash_canon (hash, ntype);
> @@ -1343,16 +1353,6 @@ build_type_attribute_qual_variant (tree otype, tree attribute, int quals)
>        if (ntype != dtype)
>  	/* This variant was already in the hash table, don't mess with
>  	   TYPE_CANONICAL.  */;
> -      else if (TYPE_STRUCTURAL_EQUALITY_P (ttype)
> -	       || !comp_type_attributes (ntype, ttype))
> -	/* If the target-dependent attributes make NTYPE different from
> -	   its canonical type, we will need to use structural equality
> -	   checks for this type.
> -
> -	   We shouldn't get here for stripping attributes from a type;
> -	   the no-attribute type might not need structural comparison.  But
> -	   we can if was discarded from type_hash_table.  */
> -	SET_TYPE_STRUCTURAL_EQUALITY (ntype);
>        else if (TYPE_CANONICAL (ntype) == ntype)
>  	TYPE_CANONICAL (ntype) = TYPE_CANONICAL (ttype);
>  
> diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
> index 01e3d247fc2..032dcb4b41d 100644
> --- a/gcc/c-family/c-common.cc
> +++ b/gcc/c-family/c-common.cc
> @@ -7115,6 +7115,13 @@ complete_array_type (tree *ptype, tree initial_value, bool do_default)
>    TYPE_TYPELESS_STORAGE (main_type) = TYPE_TYPELESS_STORAGE (type);
>    layout_type (main_type);
>  
> +  /* Set TYPE_STRUCTURAL_EQUALITY_P early.  */
> +  if (TYPE_STRUCTURAL_EQUALITY_P (TREE_TYPE (main_type))
> +      || TYPE_STRUCTURAL_EQUALITY_P (TYPE_DOMAIN (main_type)))
> +    SET_TYPE_STRUCTURAL_EQUALITY (main_type);
> +  else
> +    TYPE_CANONICAL (main_type) = main_type;
> +
>    /* Make sure we have the canonical MAIN_TYPE. */
>    hashval_t hashcode = type_hash_canon_hash (main_type);
>    main_type = type_hash_canon (hashcode, main_type);
> @@ -7122,7 +7129,7 @@ complete_array_type (tree *ptype, tree initial_value, bool do_default)
>    /* Fix the canonical type.  */
>    if (TYPE_STRUCTURAL_EQUALITY_P (TREE_TYPE (main_type))
>        || TYPE_STRUCTURAL_EQUALITY_P (TYPE_DOMAIN (main_type)))
> -    SET_TYPE_STRUCTURAL_EQUALITY (main_type);
> +    gcc_assert (TYPE_STRUCTURAL_EQUALITY_P (main_type));
>    else if (TYPE_CANONICAL (TREE_TYPE (main_type)) != TREE_TYPE (main_type)
>  	   || (TYPE_CANONICAL (TYPE_DOMAIN (main_type))
>  	       != TYPE_DOMAIN (main_type)))
> @@ -7130,8 +7137,6 @@ complete_array_type (tree *ptype, tree initial_value, bool do_default)
>        = build_array_type (TYPE_CANONICAL (TREE_TYPE (main_type)),
>  			  TYPE_CANONICAL (TYPE_DOMAIN (main_type)),
>  			  TYPE_TYPELESS_STORAGE (main_type));
> -  else
> -    TYPE_CANONICAL (main_type) = main_type;
>  
>    if (quals == 0)
>      type = main_type;
> diff --git a/gcc/testsuite/gcc.dg/pr114931.c b/gcc/testsuite/gcc.dg/pr114931.c
> new file mode 100644
> index 00000000000..d690ed70e52
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr114931.c
> @@ -0,0 +1,10 @@
> +/* { dg-do compile } */
> +/* { dg-options "-std=c23" } */
> +
> +struct Tcl_Obj;
> +void(Tcl_FreeInternalRepProc)(struct Tcl_Obj *);
> +typedef struct Tcl_Obj {
> +} Tcl_Obj;
> +struct {
> +  void (*tclFreeObj)(Tcl_Obj *);
> +} Tcl_InitStubs;
> diff --git a/gcc/tree.cc b/gcc/tree.cc
> index 780662549fe..6564b002dc1 100644
> --- a/gcc/tree.cc
> +++ b/gcc/tree.cc
> @@ -6012,6 +6012,8 @@ type_hash_canon_hash (tree type)
>  
>    hstate.add_int (TREE_CODE (type));
>  
> +  hstate.add_flag (TYPE_STRUCTURAL_EQUALITY_P (type));
> +
>    if (TREE_TYPE (type))
>      hstate.add_object (TYPE_HASH (TREE_TYPE (type)));
>  
> @@ -6109,6 +6111,10 @@ type_cache_hasher::equal (type_hash *a, type_hash *b)
>  	  || TYPE_MODE (a->type) != TYPE_MODE (b->type)))
>      return false;
>  
> +  if (TYPE_STRUCTURAL_EQUALITY_P (a->type)
> +      != TYPE_STRUCTURAL_EQUALITY_P (b->type))
> +    return false;
> +
>    switch (TREE_CODE (a->type))
>      {
>      case VOID_TYPE:
> @@ -7347,6 +7353,14 @@ build_array_type_1 (tree elt_type, tree index_type, bool typeless_storage,
>    TYPE_DOMAIN (t) = index_type;
>    TYPE_ADDR_SPACE (t) = TYPE_ADDR_SPACE (elt_type);
>    TYPE_TYPELESS_STORAGE (t) = typeless_storage;
> +
> +  /* Set TYPE_STRUCTURAL_EQUALITY_P.  */
> +  if (set_canonical
> +      && (TYPE_STRUCTURAL_EQUALITY_P (elt_type)
> +	  || (index_type && TYPE_STRUCTURAL_EQUALITY_P (index_type))
> +	  || in_lto_p))
> +    SET_TYPE_STRUCTURAL_EQUALITY (t);
> +
>    layout_type (t);
>  
>    if (shared)
> @@ -7363,7 +7377,7 @@ build_array_type_1 (tree elt_type, tree index_type, bool typeless_storage,
>        if (TYPE_STRUCTURAL_EQUALITY_P (elt_type)
>  	  || (index_type && TYPE_STRUCTURAL_EQUALITY_P (index_type))
>  	  || in_lto_p)
> -	SET_TYPE_STRUCTURAL_EQUALITY (t);
> +	gcc_unreachable ();
>        else if (TYPE_CANONICAL (elt_type) != elt_type
>  	       || (index_type && TYPE_CANONICAL (index_type) != index_type))
>  	TYPE_CANONICAL (t)
> @@ -7510,21 +7524,25 @@ build_function_type (tree value_type, tree arg_types,
>        TYPE_NO_NAMED_ARGS_STDARG_P (t) = 1;
>      }
>  
> -  /* If we already have such a type, use the old one.  */
> -  hashval_t hash = type_hash_canon_hash (t);
> -  tree probe_type = t;
> -  t = type_hash_canon (hash, t);
> -  if (t != probe_type)
> -    return t;
> -
>    /* Set up the canonical type. */
>    any_structural_p   = TYPE_STRUCTURAL_EQUALITY_P (value_type);
>    any_noncanonical_p = TYPE_CANONICAL (value_type) != value_type;
>    canon_argtypes = maybe_canonicalize_argtypes (arg_types,
>  						&any_structural_p,
>  						&any_noncanonical_p);
> +  /* Set TYPE_STRUCTURAL_EQUALITY_P early.  */
>    if (any_structural_p)
>      SET_TYPE_STRUCTURAL_EQUALITY (t);
> +
> +  /* If we already have such a type, use the old one.  */
> +  hashval_t hash = type_hash_canon_hash (t);
> +  tree probe_type = t;
> +  t = type_hash_canon (hash, t);
> +  if (t != probe_type)
> +    return t;
> +
> +  if (any_structural_p)
> +    gcc_assert (TYPE_STRUCTURAL_EQUALITY_P (t));
>    else if (any_noncanonical_p)
>      TYPE_CANONICAL (t) = build_function_type (TYPE_CANONICAL (value_type),
>  					      canon_argtypes);
> @@ -7667,13 +7685,6 @@ build_method_type_directly (tree basetype,
>    argtypes = tree_cons (NULL_TREE, ptype, argtypes);
>    TYPE_ARG_TYPES (t) = argtypes;
>  
> -  /* If we already have such a type, use the old one.  */
> -  hashval_t hash = type_hash_canon_hash (t);
> -  tree probe_type = t;
> -  t = type_hash_canon (hash, t);
> -  if (t != probe_type)
> -    return t;
> -
>    /* Set up the canonical type. */
>    any_structural_p
>      = (TYPE_STRUCTURAL_EQUALITY_P (basetype)
> @@ -7684,8 +7695,20 @@ build_method_type_directly (tree basetype,
>    canon_argtypes = maybe_canonicalize_argtypes (TREE_CHAIN (argtypes),
>  						&any_structural_p,
>  						&any_noncanonical_p);
> +
> +  /* Set TYPE_STRUCTURAL_EQUALITY_P early.  */
>    if (any_structural_p)
>      SET_TYPE_STRUCTURAL_EQUALITY (t);
> +
> +  /* If we already have such a type, use the old one.  */
> +  hashval_t hash = type_hash_canon_hash (t);
> +  tree probe_type = t;
> +  t = type_hash_canon (hash, t);
> +  if (t != probe_type)
> +    return t;
> +
> +  if (any_structural_p)
> +    gcc_assert (TYPE_STRUCTURAL_EQUALITY_P (t));
>    else if (any_noncanonical_p)
>      TYPE_CANONICAL (t)
>        = build_method_type_directly (TYPE_CANONICAL (basetype),
> @@ -7726,6 +7749,9 @@ build_offset_type (tree basetype, tree type)
>  
>    TYPE_OFFSET_BASETYPE (t) = TYPE_MAIN_VARIANT (basetype);
>    TREE_TYPE (t) = type;
> +  if (TYPE_STRUCTURAL_EQUALITY_P (basetype)
> +      || TYPE_STRUCTURAL_EQUALITY_P (type))
> +    SET_TYPE_STRUCTURAL_EQUALITY (t);
>  
>    /* If we already have such a type, use the old one.  */
>    hashval_t hash = type_hash_canon_hash (t);
> @@ -7741,7 +7767,7 @@ build_offset_type (tree basetype, tree type)
>      {
>        if (TYPE_STRUCTURAL_EQUALITY_P (basetype)
>  	  || TYPE_STRUCTURAL_EQUALITY_P (type))
> -	SET_TYPE_STRUCTURAL_EQUALITY (t);
> +	gcc_unreachable ();
>        else if (TYPE_CANONICAL (TYPE_MAIN_VARIANT (basetype)) != basetype
>  	       || TYPE_CANONICAL (type) != type)
>  	TYPE_CANONICAL (t)
> @@ -7770,6 +7796,8 @@ build_complex_type (tree component_type, bool named)
>    tree probe = make_node (COMPLEX_TYPE);
>  
>    TREE_TYPE (probe) = TYPE_MAIN_VARIANT (component_type);
> +  if (TYPE_STRUCTURAL_EQUALITY_P (TREE_TYPE (probe)))
> +    SET_TYPE_STRUCTURAL_EQUALITY (probe);
>  
>    /* If we already have such a type, use the old one.  */
>    hashval_t hash = type_hash_canon_hash (probe);
> @@ -7781,11 +7809,10 @@ build_complex_type (tree component_type, bool named)
>  	 out the type.  We need to check the canonicalization and
>  	 maybe set the name.  */
>        gcc_checking_assert (COMPLETE_TYPE_P (t)
> -			   && !TYPE_NAME (t)
> -			   && TYPE_CANONICAL (t) == t);
> +			   && !TYPE_NAME (t));
>  
>        if (TYPE_STRUCTURAL_EQUALITY_P (TREE_TYPE (t)))
> -	SET_TYPE_STRUCTURAL_EQUALITY (t);
> +	;
>        else if (TYPE_CANONICAL (TREE_TYPE (t)) != TREE_TYPE (t))
>  	TYPE_CANONICAL (t)
>  	  = build_complex_type (TYPE_CANONICAL (TREE_TYPE (t)), named);