Thank you for working on this!
Here are a couple of comments: How is the size for an object with FAM defined? There are at least three possible choices: offset(..) + N * sizeof sizeof(..) + N * sizeof or the size of a struct with the replacement array. Or is this not relevant here? I would personally prefer an attribute which does not use a string, but uses C expressions, so that one could write something like this (although I would limit it initially to the most simple case) struct { struct bar { int n; }* ptr; int buf[] [[element_count(.ptr->n + 3)]]; }; Of course, we could still support this later even if we use a string now. Martin Am Donnerstag, dem 25.05.2023 um 16:14 +0000 schrieb Qing Zhao: > 2023-05-17 Qing Zhao <qing.z...@oracle.com> > > gcc/ChangeLog: > > PR C/108896 > * tree-object-size.cc (addr_object_size): Use the element_count > attribute info. > * tree.cc (component_ref_has_element_count_p): New function. > (component_ref_get_element_count): New function. > * tree.h (component_ref_has_element_count_p): New prototype. > (component_ref_get_element_count): New prototype. > > gcc/testsuite/ChangeLog: > > PR C/108896 > * gcc.dg/flex-array-element-count-2.c: New test. > --- > .../gcc.dg/flex-array-element-count-2.c | 56 +++++++++++ > gcc/tree-object-size.cc | 37 ++++++-- > gcc/tree.cc | 93 +++++++++++++++++++ > gcc/tree.h | 10 ++ > 4 files changed, 189 insertions(+), 7 deletions(-) > create mode 100644 gcc/testsuite/gcc.dg/flex-array-element-count-2.c > > diff --git a/gcc/testsuite/gcc.dg/flex-array-element-count-2.c > b/gcc/testsuite/gcc.dg/flex-array-element-count-2.c > new file mode 100644 > index 00000000000..5a280e8c731 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/flex-array-element-count-2.c > @@ -0,0 +1,56 @@ > +/* test the attribute element_count and its usage in > + * __builtin_dynamic_object_size. */ > +/* { dg-do run } */ > +/* { dg-options "-O2" } */ > + > +#include "builtin-object-size-common.h" > + > +#define expect(p, _v) do { \ > + size_t v = _v; \ > + if (p == v) \ > + __builtin_printf ("ok: %s == %zd\n", #p, p); \ > + else \ > + { \ > + __builtin_printf ("WAT: %s == %zd (expected %zd)\n", #p, p, v); \ > + FAIL (); \ > + } \ > +} while (0); > + > +struct flex { > + int b; > + int c[]; > +} *array_flex; > + > +struct annotated { > + int b; > + int c[] __attribute__ ((element_count ("b"))); > +} *array_annotated; > + > +void __attribute__((__noinline__)) setup (int normal_count, int attr_count) > +{ > + array_flex > + = (struct flex *)malloc (sizeof (struct flex) > + + normal_count * sizeof (int)); > + array_flex->b = normal_count; > + > + array_annotated > + = (struct annotated *)malloc (sizeof (struct annotated) > + + attr_count * sizeof (int)); > + array_annotated->b = attr_count; > + > + return; > +} > + > +void __attribute__((__noinline__)) test () > +{ > + expect(__builtin_dynamic_object_size(array_flex->c, 1), -1); > + expect(__builtin_dynamic_object_size(array_annotated->c, 1), > + array_annotated->b * sizeof (int)); > +} > + > +int main(int argc, char *argv[]) > +{ > + setup (10,10); > + test (); > + DONE (); > +} > diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc > index 9a936a91983..f9aadd59054 100644 > --- a/gcc/tree-object-size.cc > +++ b/gcc/tree-object-size.cc > @@ -585,6 +585,7 @@ addr_object_size (struct object_size_info *osi, > const_tree ptr, > if (pt_var != TREE_OPERAND (ptr, 0)) > { > tree var; > + tree element_count_ref = NULL_TREE; > > > if (object_size_type & OST_SUBOBJECT) > { > @@ -600,11 +601,12 @@ addr_object_size (struct object_size_info *osi, > const_tree ptr, > var = TREE_OPERAND (var, 0); > if (var != pt_var && TREE_CODE (var) == ARRAY_REF) > var = TREE_OPERAND (var, 0); > - if (! TYPE_SIZE_UNIT (TREE_TYPE (var)) > + if (! component_ref_has_element_count_p (var) > + && ((! TYPE_SIZE_UNIT (TREE_TYPE (var)) > || ! tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (var))) > || (pt_var_size && TREE_CODE (pt_var_size) == INTEGER_CST > && tree_int_cst_lt (pt_var_size, > - TYPE_SIZE_UNIT (TREE_TYPE (var))))) > + TYPE_SIZE_UNIT (TREE_TYPE (var))))))) > var = pt_var; > else if (var != pt_var && TREE_CODE (pt_var) == MEM_REF) > { > @@ -612,6 +614,7 @@ addr_object_size (struct object_size_info *osi, > const_tree ptr, > /* For &X->fld, compute object size if fld isn't a flexible array > member. */ > bool is_flexible_array_mem_ref = false; > + > while (v && v != pt_var) > switch (TREE_CODE (v)) > { > @@ -639,6 +642,8 @@ addr_object_size (struct object_size_info *osi, > const_tree ptr, > break; > } > is_flexible_array_mem_ref = array_ref_flexible_size_p (v); > + element_count_ref = component_ref_get_element_count (v); > + > while (v != pt_var && TREE_CODE (v) == COMPONENT_REF) > if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0))) > != UNION_TYPE > @@ -652,8 +657,11 @@ addr_object_size (struct object_size_info *osi, > const_tree ptr, > == RECORD_TYPE) > { > /* compute object size only if v is not a > - flexible array member. */ > - if (!is_flexible_array_mem_ref) > + flexible array member or the flexible array member > + has a known element count indicated by the user > + through attribute element_count. */ > + if (!is_flexible_array_mem_ref > + || element_count_ref) > { > v = NULL_TREE; > break; > @@ -686,9 +694,24 @@ addr_object_size (struct object_size_info *osi, > const_tree ptr, > > > if (var != pt_var) > { > - var_size = TYPE_SIZE_UNIT (TREE_TYPE (var)); > - if (!TREE_CONSTANT (var_size)) > - var_size = get_or_create_ssa_default_def (cfun, var_size); > + if (!element_count_ref) > + { > + var_size = TYPE_SIZE_UNIT (TREE_TYPE (var)); > + if (!TREE_CONSTANT (var_size)) > + var_size = get_or_create_ssa_default_def (cfun, var_size); > + } > + else > + { > + gcc_assert (TREE_CODE (var) == COMPONENT_REF > + && TREE_CODE (TREE_TYPE (var)) == ARRAY_TYPE); > + tree element_size = TYPE_SIZE_UNIT (TREE_TYPE (TREE_TYPE (var))); > + var_size > + = size_binop (MULT_EXPR, > + fold_convert (sizetype, element_count_ref), > + fold_convert (sizetype, element_size)); > + if (!todo) > + todo = TODO_update_ssa_only_virtuals; > + } > if (!var_size) > return false; > } > diff --git a/gcc/tree.cc b/gcc/tree.cc > index 7e6de288886..48753b94f2c 100644 > --- a/gcc/tree.cc > +++ b/gcc/tree.cc > @@ -12745,6 +12745,99 @@ array_ref_element_size (tree exp) > return SUBSTITUTE_PLACEHOLDER_IN_EXPR (TYPE_SIZE_UNIT (elmt_type), exp); > } > > > +/* For a component_ref that has an array type ARRAY_REF, return TRUE when > + an element_count attribute attached to the corresponding FIELD_DECL. > + return FALSE otherwise. */ > +bool > +component_ref_has_element_count_p (tree array_ref) > +{ > + if (TREE_CODE (array_ref) != COMPONENT_REF) > + return false; > + > + if (TREE_CODE (TREE_TYPE (array_ref)) != ARRAY_TYPE) > + return false; > + > + tree struct_object = TREE_OPERAND (array_ref, 0); > + tree struct_type = TREE_TYPE (struct_object); > + > + if (!RECORD_OR_UNION_TYPE_P (struct_type)) > + return false; > + tree field_decl = TREE_OPERAND (array_ref, 1); > + tree attr_element_count = lookup_attribute ("element_count", > + DECL_ATTRIBUTES (field_decl)); > + > + if (!attr_element_count) > + return false; > + return true; > +} > + > + > +/* For a component_ref that has an array type ARRAY_REF, get the object that > + represents its element_count per the attribute element_count attached to > + the corresponding FIELD_DECL. return NULL_TREE when cannot find such > + object. > + For example, if: > + > + struct P { > + int k; > + int x[] __attribute__ ((element_count ("k"))); > + } *p; > + > + for the following reference: > + > + p->x[b] > + > + the object that represents its element count will be: > + > + p->k > + > + So, when component_ref_get_element_count (p->x[b]) is called, p->k > should be > + returned. > +*/ > + > +tree > +component_ref_get_element_count (tree array_ref) > +{ > + if (! component_ref_has_element_count_p (array_ref)) > + return NULL_TREE; > + > + tree struct_object = TREE_OPERAND (array_ref, 0); > + tree struct_type = TREE_TYPE (struct_object); > + tree field_decl = TREE_OPERAND (array_ref, 1); > + tree attr_element_count = lookup_attribute ("element_count", > + DECL_ATTRIBUTES (field_decl)); > + gcc_assert (attr_element_count); > + > + /* If there is an element_count attribute attached to the field, > + get the field that maps to the element_count. */ > + > + const char *fieldname > + = TREE_STRING_POINTER (TREE_VALUE (TREE_VALUE (attr_element_count))); > + > + tree element_count_field = NULL_TREE; > + for (tree field = TYPE_FIELDS (struct_type); field; > + field = DECL_CHAIN (field)) > + if (TREE_CODE (field) == FIELD_DECL > + && DECL_NAME (field) != NULL > + && strcmp (IDENTIFIER_POINTER (DECL_NAME (field)), fieldname) == 0) > + { > + element_count_field = field; > + break; > + } > + > + gcc_assert (element_count_field); > + > + /* generate the tree node that represent the element_count of this array > + ref. This is a COMPONENT_REF to the element_count_field of the > + containing structure. */ > + > + tree element_count_ref = build3 (COMPONENT_REF, > + TREE_TYPE (element_count_field), > + struct_object, element_count_field, > + NULL_TREE); > + return element_count_ref; > +} > + > /* Return a tree representing the lower bound of the array mentioned in > EXP, an ARRAY_REF or an ARRAY_RANGE_REF. */ > > > diff --git a/gcc/tree.h b/gcc/tree.h > index 0b72663e6a1..8f36370a02d 100644 > --- a/gcc/tree.h > +++ b/gcc/tree.h > @@ -5582,6 +5582,16 @@ extern tree get_base_address (tree t); > of EXP, an ARRAY_REF or an ARRAY_RANGE_REF. */ > extern tree array_ref_element_size (tree); > > > +/* Give a component_ref that has an array type, return true when an > + attribute element_count attached to the corresponding FIELD_DECL. */ > +extern bool component_ref_has_element_count_p (tree); > + > +/* Give a component_ref that has an array type, return the object that > + represents its element_count per the attribute element_count attached to > + the corresponding FIELD_DECL. return NULL_TREE when cannot find such > + object. */ > +extern tree component_ref_get_element_count (tree); > + > /* Return a typenode for the "standard" C type with a given name. */ > extern tree get_typenode_from_name (const char *); > >