On Thu, 9 Mar 2023, Qing Zhao wrote:
>
>
> > On Mar 9, 2023, at 7:20 AM, Richard Biener <rguent...@suse.de> wrote:
> >
> > On Fri, 24 Feb 2023, Qing Zhao wrote:
> >
> >> GCC extension accepts the case when a struct with a C99 flexible array
> >> member
> >> is embedded into another struct or union (possibly recursively).
> >> __builtin_object_size should treat such struct as flexible size.
> >>
> >> gcc/c/ChangeLog:
> >>
> >> PR tree-optimization/101832
> >> * c-decl.cc (finish_struct): Set TYPE_INCLUDE_FLEXARRAY for
> >> struct/union type.
> >
> > I can't really comment on the correctness of this part but since
> > only the C frontend will ever set this and you are using it from
> > addr_object_size which is also used for other C family languages
> > (at least), I wonder if you can really test
> >
> > + if (!TYPE_INCLUDE_FLEXARRAY (TREE_TYPE (v)))
> >
> > there.
>
> You mean for C++ and also other C family languages (other than C), the above
> bit cannot be set?
> Yes, that’s true. The bit is only set for C. So is the bit
> DECL_NOT_FLEXARRAY, which is only set for C too.
> So, I am wondering whether the bit DECL_NOT_FLEXARRAY should be also set in
> middle end? Or we can set DECL_NOT_FLEXARRAY in C++ FE too? And then we can
> set TYPE_INCLUDE_FLEXARRAY also in C++ FE?
> What’s your suggestion?
>
> (I personally feel that DECL_NOT_FLEXARRAY and TYPE_INCLUDE_FLEXARRAY should
> be set in the same places).
I was wondering if the above test errors on the conservative side
correctly - it will now, for all but C, cut off some thing where it
didn't before?
> >
> > Originally I was suggesting to set this flag in stor-layout.cc
> > which eventually all languages funnel their types through and
> > if there's language specific handling use a langhook (with the
> > default implementation preserving the status quo).
>
> If we decide to set the bits in stor-layout.cc, where is the best place to do
> it? I checked the star-layout.cc code, looks like “layout_type” might be the
> place where we can set these bits for RECORD_TYPE, UNION_TYPE?
Yes, it would be layout_type.
> >
> > Some more comments below ...
> >
> >> gcc/cp/ChangeLog:
> >>
> >> PR tree-optimization/101832
> >> * module.cc (trees_out::core_bools): Stream out new bit
> >> type_include_flexarray.
> >> (trees_in::core_bools): Stream in new bit type_include_flexarray.
> >>
> >> gcc/ChangeLog:
> >>
> >> PR tree-optimization/101832
> >> * print-tree.cc (print_node): Print new bit type_include_flexarray.
> >> * tree-core.h (struct tree_type_common): New bit
> >> type_include_flexarray.
> >> * tree-object-size.cc (addr_object_size): Handle structure/union type
> >> when it has flexible size.
> >> * tree-streamer-in.cc (unpack_ts_type_common_value_fields): Stream
> >> in new bit type_include_flexarray.
> >> * tree-streamer-out.cc (pack_ts_type_common_value_fields): Stream
> >> out new bit type_include_flexarray.
> >> * tree.h (TYPE_INCLUDE_FLEXARRAY): New macro
> >> TYPE_INCLUDE_FLEXARRAY.
> >>
> >> gcc/testsuite/ChangeLog:
> >>
> >> PR tree-optimization/101832
> >> * gcc.dg/builtin-object-size-pr101832.c: New test.
> >> ---
> >> gcc/c/c-decl.cc | 12 ++
> >> gcc/cp/module.cc | 2 +
> >> gcc/print-tree.cc | 5 +
> >> .../gcc.dg/builtin-object-size-pr101832.c | 134 ++++++++++++++++++
> >> gcc/tree-core.h | 4 +-
> >> gcc/tree-object-size.cc | 79 +++++++----
> >> gcc/tree-streamer-in.cc | 1 +
> >> gcc/tree-streamer-out.cc | 1 +
> >> gcc/tree.h | 6 +
> >> 9 files changed, 215 insertions(+), 29 deletions(-)
> >> create mode 100644 gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
> >>
> >> diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
> >> index 08078eadeb8..f589a2f5192 100644
> >> --- a/gcc/c/c-decl.cc
> >> +++ b/gcc/c/c-decl.cc
> >> @@ -9284,6 +9284,18 @@ finish_struct (location_t loc, tree t, tree
> >> fieldlist, tree attributes,
> >> /* Set DECL_NOT_FLEXARRAY flag for FIELD_DECL x. */
> >> DECL_NOT_FLEXARRAY (x) = !is_flexible_array_member_p (is_last_field,
> >> x);
> >>
> >> + /* Set TYPE_INCLUDE_FLEXARRAY for the context of x, t
> >> + * when x is an array. */
> >> + if (TREE_CODE (TREE_TYPE (x)) == ARRAY_TYPE)
> >> + TYPE_INCLUDE_FLEXARRAY (t) = flexible_array_member_type_p (TREE_TYPE
> >> (x)) ;
> >> + /* Recursively set TYPE_INCLUDE_FLEXARRAY for the context of x, t
> >> + when x is the last field. */
> >> + else if ((TREE_CODE (TREE_TYPE (x)) == RECORD_TYPE
> >> + || TREE_CODE (TREE_TYPE (x)) == UNION_TYPE)
> >> + && TYPE_INCLUDE_FLEXARRAY (TREE_TYPE (x))
> >> + && is_last_field)
> >> + TYPE_INCLUDE_FLEXARRAY (t) = true;
> >> +
> >> if (DECL_NAME (x)
> >> || RECORD_OR_UNION_TYPE_P (TREE_TYPE (x)))
> >> saw_named_field = true;
> >> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> >> index ac2fe66b080..c750361b704 100644
> >> --- a/gcc/cp/module.cc
> >> +++ b/gcc/cp/module.cc
> >> @@ -5371,6 +5371,7 @@ trees_out::core_bools (tree t)
> >> WB (t->type_common.lang_flag_5);
> >> WB (t->type_common.lang_flag_6);
> >> WB (t->type_common.typeless_storage);
> >> + WB (t->type_common.type_include_flexarray);
> >> }
> >>
> >> if (CODE_CONTAINS_STRUCT (code, TS_DECL_COMMON))
> >> @@ -5551,6 +5552,7 @@ trees_in::core_bools (tree t)
> >> RB (t->type_common.lang_flag_5);
> >> RB (t->type_common.lang_flag_6);
> >> RB (t->type_common.typeless_storage);
> >> + RB (t->type_common.type_include_flexarray);
> >> }
> >>
> >> if (CODE_CONTAINS_STRUCT (code, TS_DECL_COMMON))
> >> diff --git a/gcc/print-tree.cc b/gcc/print-tree.cc
> >> index 1f3afcbbc86..efacdb7686f 100644
> >> --- a/gcc/print-tree.cc
> >> +++ b/gcc/print-tree.cc
> >> @@ -631,6 +631,11 @@ print_node (FILE *file, const char *prefix, tree
> >> node, int indent,
> >> && TYPE_CXX_ODR_P (node))
> >> fputs (" cxx-odr-p", file);
> >>
> >> + if ((code == RECORD_TYPE
> >> + || code == UNION_TYPE)
> >> + && TYPE_INCLUDE_FLEXARRAY (node))
> >> + fputs (" include-flexarray", file);
> >> +
> >> /* The transparent-union flag is used for different things in
> >> different nodes. */
> >> if ((code == UNION_TYPE || code == RECORD_TYPE)
> >> diff --git a/gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
> >> b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
> >> new file mode 100644
> >> index 00000000000..60078e11634
> >> --- /dev/null
> >> +++ b/gcc/testsuite/gcc.dg/builtin-object-size-pr101832.c
> >> @@ -0,0 +1,134 @@
> >> +/* PR 101832:
> >> + GCC extension accepts the case when a struct with a C99 flexible array
> >> + member is embedded into another struct (possibly recursively).
> >> + __builtin_object_size will treat such struct as flexible size.
> >> + However, when a structure with non-C99 flexible array member, i.e,
> >> trailing
> >> + [0], [1], or [4], is embedded into anther struct, the stucture will not
> >> + be treated as flexible 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 A {
> >> + int n;
> >> + char data[];
> >> +};
> >> +
> >> +struct B {
> >> + int m;
> >> + struct A a;
> >> +};
> >> +
> >> +struct C {
> >> + int q;
> >> + struct B b;
> >> +};
> >> +
> >> +struct A0 {
> >> + int n;
> >> + char data[0];
> >> +};
> >> +
> >> +struct B0 {
> >> + int m;
> >> + struct A0 a;
> >> +};
> >> +
> >> +struct C0 {
> >> + int q;
> >> + struct B0 b;
> >> +};
> >> +
> >> +struct A1 {
> >> + int n;
> >> + char data[1];
> >> +};
> >> +
> >> +struct B1 {
> >> + int m;
> >> + struct A1 a;
> >> +};
> >> +
> >> +struct C1 {
> >> + int q;
> >> + struct B1 b;
> >> +};
> >> +
> >> +struct An {
> >> + int n;
> >> + char data[8];
> >> +};
> >> +
> >> +struct Bn {
> >> + int m;
> >> + struct An a;
> >> +};
> >> +
> >> +struct Cn {
> >> + int q;
> >> + struct Bn b;
> >> +};
> >> +
> >> +volatile void *magic1, *magic2;
> >> +
> >> +int main (int argc, char *argv[])
> >> +{
> >> + struct B *outer;
> >> + struct C *outest;
> >> +
> >> + /* Make sure optimization can't find some other object size. */
> >> + outer = (void *)magic1;
> >> + outest = (void *)magic2;
> >> +
> >> + expect (__builtin_object_size (&outer->a, 1), -1);
> >> + expect (__builtin_object_size (&outest->b, 1), -1);
> >> + expect (__builtin_object_size (&outest->b.a, 1), -1);
> >> +
> >> + struct B0 *outer0;
> >> + struct C0 *outest0;
> >> +
> >> + /* Make sure optimization can't find some other object size. */
> >> + outer0 = (void *)magic1;
> >> + outest0 = (void *)magic2;
> >> +
> >> + expect (__builtin_object_size (&outer0->a, 1), sizeof (outer0->a));
> >> + expect (__builtin_object_size (&outest0->b, 1), sizeof (outest0->b));
> >> + expect (__builtin_object_size (&outest0->b.a, 1), sizeof
> >> (outest0->b.a));
> >> +
> >> + struct B1 *outer1;
> >> + struct C1 *outest1;
> >> +
> >> + /* Make sure optimization can't find some other object size. */
> >> + outer1 = (void *)magic1;
> >> + outest1 = (void *)magic2;
> >> +
> >> + expect (__builtin_object_size (&outer1->a, 1), sizeof (outer1->a));
> >> + expect (__builtin_object_size (&outest1->b, 1), sizeof (outest1->b));
> >> + expect (__builtin_object_size (&outest1->b.a, 1), sizeof
> >> (outest1->b.a));
> >> +
> >> + struct Bn *outern;
> >> + struct Cn *outestn;
> >> +
> >> + /* Make sure optimization can't find some other object size. */
> >> + outern = (void *)magic1;
> >> + outestn = (void *)magic2;
> >> +
> >> + expect (__builtin_object_size (&outern->a, 1), sizeof (outern->a));
> >> + expect (__builtin_object_size (&outestn->b, 1), sizeof (outestn->b));
> >> + expect (__builtin_object_size (&outestn->b.a, 1), sizeof
> >> (outestn->b.a));
> >> +
> >> + DONE ();
> >> + return 0;
> >> +}
> >> diff --git a/gcc/tree-core.h b/gcc/tree-core.h
> >> index acd8deea34e..705d5702b9c 100644
> >> --- a/gcc/tree-core.h
> >> +++ b/gcc/tree-core.h
> >> @@ -1718,7 +1718,9 @@ struct GTY(()) tree_type_common {
> >> unsigned empty_flag : 1;
> >> unsigned indivisible_p : 1;
> >> RECORD_OR_UNION_CHECK
> >
> > it looks like the bit could be eventually shared with
> > no_named_args_stdarg_p (but its accessor doesn't use
> > FUNC_OR_METHOD_CHECK)
> You mean to let “type_include_flexarray” share the same bit with
> “no_named_args_stdarg_p” in order to save 1-bit space in IR?
> Then change the
>
> /* True if this is a stdarg function with no named arguments (C2x
> (...) prototype, where arguments can be accessed with va_start and
> va_arg), as opposed to an unprototyped function. */
> #define TYPE_NO_NAMED_ARGS_STDARG_P(NODE) \
> (TYPE_CHECK (NODE)->type_common.no_named_args_stdarg_p)
>
> /* True if this RECORD_TYPE or UNION_TYPE includes a flexible array member
> at the last field recursively. */
> #define TYPE_INCLUDE_FLEXARRAY(NODE) \
> (TYPE_CHECK (NODE)->type_common.type_include_flexarray)
>
> To:
>
> union {
> unsigned no_named_args_stdarg_p : 1;
> /* TYPE_INCLUDE_FLEXARRAY flag for RECORD_TYPE and UNION_TYPE. */
> unsigned int type_include_flexarray : 1;
> } shared_bit;
> unsigned spare : 15;
>
> /* True if this is a stdarg function with no named arguments (C2x
> (...) prototype, where arguments can be accessed with va_start and
> va_arg), as opposed to an unprototyped function. */
> #define TYPE_NO_NAMED_ARGS_STDARG_P(NODE) \
> (FUNC_OR_METHOD_CHECK (NODE)->type_common.shared_bit.no_named_args_stdarg_p)
>
> /* True if this RECORD_TYPE or UNION_TYPE includes a flexible array member
> at the last field recursively. */
> #define TYPE_INCLUDE_FLEXARRAY(NODE) \
> (RECORD_OR_UNION_CHECK(NODE)->type_common.shared_bit.type_include_flexarray)
No, we're just overloading bits by using the same name for different
purposes. I don't think such a union would pack nicely. We overload
by documenting the uses, in the above cases the uses are separated
by the kind of the tree node, RECORD/UNION_TYPE vs. FUNCTION/METHOD_TYPE
and the accessor macros should be updated to use the appropriate
tree check macros covering that so we don't try to inspect the
"wrong bit".
> >
> >> alias_set_type alias_set;
> >> tree pointer_to;
> >> diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
> >> index 9a936a91983..22b3c72ea6e 100644
> >> --- a/gcc/tree-object-size.cc
> >> +++ b/gcc/tree-object-size.cc
> >> @@ -633,45 +633,68 @@ addr_object_size (struct object_size_info *osi,
> >> const_tree ptr,
> >> v = NULL_TREE;
> >> break;
> >> case COMPONENT_REF:
> >> - if (TREE_CODE (TREE_TYPE (v)) != ARRAY_TYPE)
> >> + /* When the ref is not to an array, a record or a union, it
> >> + will not have flexible size, compute the object size
> >> + directly. */
> >> + if ((TREE_CODE (TREE_TYPE (v)) != ARRAY_TYPE)
> >> + && (TREE_CODE (TREE_TYPE (v)) != RECORD_TYPE)
> >> + && (TREE_CODE (TREE_TYPE (v)) != UNION_TYPE))
> >> {
> >> v = NULL_TREE;
> >> break;
> >> }
> >> - 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
> >> - && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> >> - != QUAL_UNION_TYPE)
> >> - break;
> >> - else
> >> - v = TREE_OPERAND (v, 0);
> >> - if (TREE_CODE (v) == COMPONENT_REF
> >> - && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> >> - == RECORD_TYPE)
> >> + if (TREE_CODE (TREE_TYPE (v)) == RECORD_TYPE
> >> + || TREE_CODE (TREE_TYPE (v)) == UNION_TYPE)
> >> + /* if the record or union does not include a flexible array
> >> + recursively, compute the object size directly. */
> >> {
> >> - /* compute object size only if v is not a
> >> - flexible array member. */
> >> - if (!is_flexible_array_mem_ref)
> >> + if (!TYPE_INCLUDE_FLEXARRAY (TREE_TYPE (v)))
> >> {
> >> v = NULL_TREE;
> >> break;
> >> }
> >> - v = TREE_OPERAND (v, 0);
> >> + else
> >> + v = TREE_OPERAND (v, 0);
> >> }
> >> - while (v != pt_var && TREE_CODE (v) == COMPONENT_REF)
> >> - if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> >> - != UNION_TYPE
> >> - && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> >> - != QUAL_UNION_TYPE)
> >> - break;
> >> - else
> >> - v = TREE_OPERAND (v, 0);
> >> - if (v != pt_var)
> >> - v = NULL_TREE;
> >> else
> >> - v = pt_var;
> >> + {
> >> + /* Now the ref is to an array type. */
> >> + 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
> >> + && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> >> + != QUAL_UNION_TYPE)
> >> + break;
> >> + else
> >> + v = TREE_OPERAND (v, 0);
> >> + if (TREE_CODE (v) == COMPONENT_REF
> >> + && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> >> + == RECORD_TYPE)
> >> + {
> >> + /* compute object size only if v is not a
> >> + flexible array member. */
> >> + if (!is_flexible_array_mem_ref)
> >> + {
> >> + v = NULL_TREE;
> >> + break;
> >> + }
> >> + v = TREE_OPERAND (v, 0);
> >> + }
> >> + while (v != pt_var && TREE_CODE (v) == COMPONENT_REF)
> >> + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> >> + != UNION_TYPE
> >> + && TREE_CODE (TREE_TYPE (TREE_OPERAND (v, 0)))
> >> + != QUAL_UNION_TYPE)
> >> + break;
> >> + else
> >> + v = TREE_OPERAND (v, 0);
> >> + if (v != pt_var)
> >> + v = NULL_TREE;
> >> + else
> >> + v = pt_var;
> >> + }
> >> break;
> >> default:
> >> v = pt_var;
> >> diff --git a/gcc/tree-streamer-in.cc b/gcc/tree-streamer-in.cc
> >> index d4dc30f048f..c19ede0631d 100644
> >> --- a/gcc/tree-streamer-in.cc
> >> +++ b/gcc/tree-streamer-in.cc
> >> @@ -390,6 +390,7 @@ unpack_ts_type_common_value_fields (struct bitpack_d
> >> *bp, tree expr)
> >> TYPE_TRANSPARENT_AGGR (expr) = (unsigned) bp_unpack_value (bp, 1);
> >> TYPE_FINAL_P (expr) = (unsigned) bp_unpack_value (bp, 1);
> >> TYPE_CXX_ODR_P (expr) = (unsigned) bp_unpack_value (bp, 1);
> >> + TYPE_INCLUDE_FLEXARRAY (expr) = (unsigned) bp_unpack_value (bp, 1);
> >> }
> >> else if (TREE_CODE (expr) == ARRAY_TYPE)
> >> TYPE_NONALIASED_COMPONENT (expr) = (unsigned) bp_unpack_value (bp, 1);
> >> diff --git a/gcc/tree-streamer-out.cc b/gcc/tree-streamer-out.cc
> >> index d107229da5c..73e4b4e547c 100644
> >> --- a/gcc/tree-streamer-out.cc
> >> +++ b/gcc/tree-streamer-out.cc
> >> @@ -357,6 +357,7 @@ pack_ts_type_common_value_fields (struct bitpack_d
> >> *bp, tree expr)
> >> bp_pack_value (bp, flag_wpa && TYPE_CANONICAL (expr)
> >> ? TYPE_CXX_ODR_P (TYPE_CANONICAL (expr))
> >> : TYPE_CXX_ODR_P (expr), 1);
> >> + bp_pack_value (bp, TYPE_INCLUDE_FLEXARRAY (expr), 1);
> >> }
> >> else if (TREE_CODE (expr) == ARRAY_TYPE)
> >> bp_pack_value (bp, TYPE_NONALIASED_COMPONENT (expr), 1);
> >> diff --git a/gcc/tree.h b/gcc/tree.h
> >> index 92ac0e6a214..ab1cdc3dc85 100644
> >> --- a/gcc/tree.h
> >> +++ b/gcc/tree.h
> >> @@ -778,6 +778,12 @@ extern void omp_clause_range_check_failed
> >> (const_tree, const char *, int,
> >> #define TYPE_NO_NAMED_ARGS_STDARG_P(NODE) \
> >> (TYPE_CHECK (NODE)->type_common.no_named_args_stdarg_p)
> >>
> >> +/* True if this RECORD_TYPE or UNION_TYPE includes a flexible array member
> >> + at the last field recursively. */
> >> +#define TYPE_INCLUDE_FLEXARRAY(NODE) \
> >> + (TYPE_CHECK (NODE)->type_common.type_include_flexarray)
> >
> > Please use RECORD_OR_UNION_CHECK.
> Okay.
> > The comment "at the last field"
> > doesn't seem to match implementation? (at least not obviously)
> The current implementation (in gcc/c/c-decl.cc) guarantees that it’s at the
> last field. (And recursively).
> > Given this is a generic header expanding on what a "flexible array member"
> > is to the middle-end here would be good. Especially the guarantees
> > made when the bit is _not_ set (we've evaded that with DECL_NOT_FLEXARRAY
> > vs. DECL_FLEXARRAY).
>
> The bit TYPE_INCLUDE_FLEXARRAY default is FALSE, i.e, not including a flex
> array by default.
> It’s only set to TRUE when the struct/union includes a flex array at the last
> field (and recursively). So, I think it should be correct.
> Let me know if I missed anything here.
See above - I was looking at the use (but I'm not familiar with that
code), and wondered how the change affects uses from other frontends.
Richard.
