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Re: [PATCH] Adding _Dependent_ptr type qualifier in C part 1/3


Good points!

On the type-qualifier interactions, here is an initial list.  Thoughts?

							Thanx, Paul

_Alignas: Dependency-breaking optimizations would be avoided, and the
variable would be aligned as specified.

_Atomic: Dependency-breaking optimizations would be avoided, and the
variable would be accessed using C11 atomics.

const: This is not particularly useful for variables with static storage
duration because compile-time initialization does not require dependency
ordering, but then again, use of _Dependent_ptr on such variables is
suspect to begin with.  Otherwise, the const _Dependent_ptr variable
would normally be initialized from another _Dependent_ptr variable or
from a memory_order_consume load.  The variable would disallow further
stores and avoid breaking dependencies.

extern: Dependency-breaking optimizations would be avoided, and the
variable would be usable within other translation units.  This is
also an unusual addition to a _Dependent_ptr unless also accompanied by
_Thread_local because there are no known non-suspect multi-threaded-access
use cases for _Dependent_ptr.

register: Dependency-breaking optimizations would be avoided, and the
compiler would be given a hint to keep the variable in a register.

restrict: Dependency-breaking optimizations would be avoided, and the
compiler may assume that the pointed-to object is only accessed through
this pointer and through pointers derived from it.

static: Dependency-breaking optimizations would be avoided, and the
variable would be static.  This is also an unusual addition to a
_Dependent_ptr unless also accompanied by _Thread_local because there are
no known non-suspect multi-threaded-access use cases for _Dependent_ptr.

_Thread_local: The dependency-carrying variable is thread-local, and
avoids dependency-breaking optimizations.

volatile: All accesses would be executed as per the abstract machine,
and dependency-breaking optimizations would be avoided.

On Fri, Aug 02, 2019 at 08:30:49PM -0600, Martin Sebor wrote:
> On 8/1/19 9:26 AM, Paul McKenney wrote:
> >Excellent point, this discussion needs to be made official.
> >Please see attached for an initial draft of a working paper.
> >
> >Thoughts?
> 
> The draft is a start but it (obviously) needs a lot of work to cover
> the constraints and semantics so I'll just comment on the patch in
> a bit more detail.
> 
> Since the feature is being (or will be) proposed to WG14 and could
> change I would expect it to be only available under -std=c2x and
> disabled otherwise, so that code that makes use of it does so with
> the understanding that it's only experimental.  (I just noticed
> Akshat email with a tweak to the patch.  I'm not sure that issuing
> a pedantic warning and having the name in the implementation namepace
> is enough but others (the C FE maintainers) will know better.)
> 
> Other than that, I would also expect to see more extensive test
> coverage, at a minimum to exercise error detection (invalid uses,
> conversions, etc.).  For example, I see the code that rejects it
> but no tests for declaring, say, a _Dependent_ptr-qualified integer.
> What I don't think I see is code that rejects _Dependent_ptr-qualified
> function pointers (AFAIK, POINTER_TYPE_P evaluates to nonzero for both).
> Is that intended?  (And if so, what does it mean?)    I also see that
> the new tests look for warnings but it's not clear to me that that's
> their intent or that the dg-warning directives are being used to
> "suppress" warnings for issues in the tests.  For instance, this
> is common:
> 
>   rcu_assign_pointer (gp,p);		/* { dg-warning
> "\\\[-Wincompatible-pointer-types]" } */
> 
> but neither gp nor p is a  _Dependent_ptr.  (I may be missing
> the purpose of the compile-only tests.  E.g., the only thing
> p0190r4_fig10.c seems to be exercising besides that the _Dependent_ptr
> qualifier is accepted is a couple of warnings, one of which is the one
> above.)  I would suggest to look at tests for other qualifiers for
> examples and model the new ones after those.
> 
> I'm also wondering how the new qualifier interacts with others like
> const.  Should all combinations of qualifiers be accepted and do
> they affect the semantics in any interesting way?  This is probably
> something to cover in the proposal.
> 
> Martin
> 
> >
> >                                          Thanx, Paul
> >
> >On Tue, Jul 30, 2019 at 12:46 PM Martin Sebor <msebor@gmail.com> wrote:
> >>
> >>On 7/30/19 1:13 AM, Akshat Garg wrote:
> >>>Hi,
> >>>This patch includes C front-end code for a type qualifier _Dependent_ptr.
> >>
> >>Just some very high-level comments/questions.  I only followed
> >>the _Dependent_ptr discussion from a distance and I'm likely
> >>missing some context so the first thing I looked for in this
> >>patch is documentation of the new qualifier.  Unless it's
> >>a proposed C2x feature that I missed I would expect to find it
> >>in section 6 - Extensions to the C Language Family of the manual.
> >>I saw the references to WG21's p0190r4 in the tests but the paper
> >>doesn't mention _Dependent_ptr, and I found no references to a C
> >>paper that does.  If it has been proposed for C2X as well can
> >>you point to it?  (In that case, or if a proposal is planned,
> >>the feature should probably either only be available with
> >>-std=c2x and -std=gnu2x or a pedantic warning should be issued
> >>for its use in earlier modes similarly to how uses of _Atomic
> >>are diagnosed in pre-C11 modes.)
> >>
> >>Martin
> >>
> >>>The patch has been tested using the following
> >>>make bootstrap -j 4
> >>>make -k check -j 4
> >>>
> >>>on x86_64-linux-gnu.
> >>>
> >>>Thanks,
> >>>Akshat
> >>>
> >>>gcc/ChangeLog:
> >>>
> >>>2019-07-30  Akshat Garg <xkspr7@gmail.com>
> >>>
> >>>          * c-family/c-common.c (struct c_common_resword c_common_reswords):
> >>>Add "_Dependent_ptr".
> >>>          (c_apply_type_quals_to_decl): Set the flag for _Dependent_ptr if
> >>>qualified.
> >>>          (keyword_is_type_qualifier): Add RID_DEPENDENT_PTR.
> >>>          * c-family/c-common.h (enum rid): Add RID_DEPENDENT_PTR.
> >>>          * c-family/c-format.c (check_format_types): Add dependent pointer
> >>>as a qualifier check.
> >>>          * c-family/c-pretty-print.c (pp_c_cv_qualifiers): Handle dependent
> >>>pointer qualifier.
> >>>          * c/c-aux-info.c (gen_type): Handle dependent pointer qualifier.
> >>>          (gen_decl): Handle dependent pointer qualifier.
> >>>          * c/c-decl.c (merge_decls): Set old declaration as having dependent
> >>>pointer qualification if new declaration has one.
> >>>          (shadow_tag_warned): Add dependent_ptr_p to declspecs check.
> >>>          (quals_from_declspecs): Add dependent_ptr_p to declspecs check.
> >>>          (grokdeclarator): Add checks for dependent pointer qualifier and
> >>>warn of duplicate or errors. Allow dependent pointer for pointer types only.
> >>>          * c/c-parser.c (c_keyword_starts_typename, c_token_is_qualifier,
> >>>c_token_starts_declspecs): Add RID_DEPENDENT_PTR.
> >>>          (c_parser_static_assert_declaration_no_semi): Add _Dependent_ptr
> >>>qualifier in comments.
> >>>          (c_parser_declspecs, c_parser_attribute_any_word): Add
> >>>RID_DEPENDENT_PTR.
> >>>          * c/c-tree.h (C_TYPE_FIELDS_DEPENDENT_PTR): New macro to mark
> >>>dependent pointer.
> >>>          (enum c_declspec_word): Add cdw_dependent_ptr.
> >>>          (struct c_declspecs): Add dependent_ptr_p field.
> >>>          * print-tree.c (print_node): Print dependent_ptr qualifier.
> >>>          * tree-core.hi (enum cv_qualifier): Add TYPE_QUAL_DEPENDENT_PTR.
> >>>          (enum tree_index): Add TI_DEPENDENT_PTR_TYPE.
> >>>          (struct tree_base): Add dependent_ptr_flag field.
> >>>          * tree-pretty-print.c (dump_generic_node): Print dependent pointer
> >>>type qualifier.
> >>>          * tree.c (fld_type_variant, set_type_quals): Set TYPE_DEPENDENT_PTR.
> >>>          * tree.h (TREE_THIS_DEPENDENT_PTR): New macro. To access
> >>>dependent_ptr_flag field in tree_base.
> >>>          (TYPE_DEPENDENT_PTR): New accessor macro.
> >>>          (TYPE_QUALS, TYPE_QUALS_NO_ADDR_SPACE): Add TYPE_QUAL_DEPENDENT_PTR.
> >>>          (dependent_ptrTI_type_node): Add new type node.
> >>>
> >>>gcc/testsuite/ChangeLog:
> >>>
> >>>2019-07-30  Akshat Garg <xkspr7@gmail.com>
> >>>
> >>>          * gcc.dg/c11-dependent_ptr-test-1.c: New test for _Dependent_ptr
> >>>qualifier.
> >>>          * gcc.dg/{p0190r4_fig8, p0190r4_fig9, p0190r4_fig10, p0190r4_fig11,
> >>>p0190r4_fig12, p0190r4_fig13}.c: New tests from document P0190R4 for
> >>>_Dependent_ptr qualifier.
> >>>
> >>>diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
> >>>index cb92710..4f09037 100644
> >>>--- a/gcc/c-family/c-common.c
> >>>+++ b/gcc/c-family/c-common.c
> >>>@@ -345,6 +345,7 @@ const struct c_common_resword c_common_reswords[] =
> >>>     { "_Alignas", RID_ALIGNAS,   D_CONLY },
> >>>     { "_Alignof", RID_ALIGNOF,   D_CONLY },
> >>>     { "_Atomic", RID_ATOMIC,    D_CONLY },
> >>>+ { "_Dependent_ptr",   RID_DEPENDENT_PTR,  0 },
> >>>     { "_Bool", RID_BOOL,      D_CONLY },
> >>>     { "_Complex", RID_COMPLEX, 0 },
> >>>     { "_Imaginary", RID_IMAGINARY, D_CONLY },
> >>>@@ -3546,6 +3547,11 @@ c_apply_type_quals_to_decl (int type_quals, tree
> >>>decl)
> >>>         TREE_SIDE_EFFECTS (decl) = 1;
> >>>         TREE_THIS_VOLATILE (decl) = 1;
> >>>       }
> >>>+  if (type_quals & TYPE_QUAL_DEPENDENT_PTR)
> >>>+    {
> >>>+      TREE_SIDE_EFFECTS (decl) = 1;
> >>>+      TREE_THIS_DEPENDENT_PTR (decl) = 1;
> >>>+    }
> >>>     if (type_quals & TYPE_QUAL_RESTRICT)
> >>>       {
> >>>         while (type && TREE_CODE (type) == ARRAY_TYPE)
> >>>@@ -7851,6 +7857,7 @@ keyword_is_type_qualifier (enum rid keyword)
> >>>       case RID_VOLATILE:
> >>>       case RID_RESTRICT:
> >>>       case RID_ATOMIC:
> >>>+    case RID_DEPENDENT_PTR:
> >>>         return true;
> >>>       default:
> >>>         return false;
> >>>diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
> >>>index 117d729..ab55882 100644
> >>>--- a/gcc/c-family/c-common.h
> >>>+++ b/gcc/c-family/c-common.h
> >>>@@ -68,7 +68,7 @@ enum rid
> >>>     RID_UNSIGNED, RID_LONG,    RID_CONST, RID_EXTERN,
> >>>     RID_REGISTER, RID_TYPEDEF, RID_SHORT, RID_INLINE,
> >>>     RID_VOLATILE, RID_SIGNED,  RID_AUTO,  RID_RESTRICT,
> >>>-  RID_NORETURN, RID_ATOMIC,
> >>>+  RID_NORETURN, RID_ATOMIC, RID_DEPENDENT_PTR,
> >>>
> >>>     /* C extensions */
> >>>     RID_COMPLEX, RID_THREAD, RID_SAT,
> >>>diff --git a/gcc/c-family/c-format.c b/gcc/c-family/c-format.c
> >>>index d134116..00769bb 100644
> >>>--- a/gcc/c-family/c-format.c
> >>>+++ b/gcc/c-family/c-format.c
> >>>@@ -4172,6 +4172,7 @@ check_format_types (const substring_loc &fmt_loc,
> >>>     && (TYPE_READONLY (cur_type)
> >>>         || TYPE_VOLATILE (cur_type)
> >>>         || TYPE_ATOMIC (cur_type)
> >>>+      || TYPE_DEPENDENT_PTR (cur_type)
> >>>         || TYPE_RESTRICT (cur_type)))
> >>>    warning (OPT_Wformat_, "extra type qualifiers in format "
> >>>    "argument (argument %d)",
> >>>diff --git a/gcc/c-family/c-pretty-print.c b/gcc/c-family/c-pretty-print.c
> >>>index 3e25624..e034a8f 100644
> >>>--- a/gcc/c-family/c-pretty-print.c
> >>>+++ b/gcc/c-family/c-pretty-print.c
> >>>@@ -181,6 +181,8 @@ pp_c_cv_qualifiers (c_pretty_printer *pp, int
> >>>qualifiers, bool func_type)
> >>>
> >>>     if (qualifiers & TYPE_QUAL_ATOMIC)
> >>>       pp_c_ws_string (pp, "_Atomic");
> >>>+  if (qualifiers & TYPE_QUAL_DEPENDENT_PTR)
> >>>+    pp_c_ws_string (pp, "_Dependent_ptr");
> >>>     if (qualifiers & TYPE_QUAL_CONST)
> >>>       pp_c_ws_string (pp, func_type ? "__attribute__((const))" : "const");
> >>>     if (qualifiers & TYPE_QUAL_VOLATILE)
> >>>diff --git a/gcc/c/c-aux-info.c b/gcc/c/c-aux-info.c
> >>>index 96bb2e2..514093c 100644
> >>>--- a/gcc/c/c-aux-info.c
> >>>+++ b/gcc/c/c-aux-info.c
> >>>@@ -284,6 +284,8 @@ gen_type (const char *ret_val, tree t, formals_style
> >>>style)
> >>>    case POINTER_TYPE:
> >>>     if (TYPE_ATOMIC (t))
> >>>       ret_val = concat ("_Atomic ", ret_val, NULL);
> >>>+  if (TYPE_DEPENDENT_PTR (t))
> >>>+    ret_val = concat ("_Dependent_ptr ", ret_val, NULL);
> >>>     if (TYPE_READONLY (t))
> >>>       ret_val = concat ("const ", ret_val, NULL);
> >>>     if (TYPE_VOLATILE (t))
> >>>@@ -427,6 +429,8 @@ gen_type (const char *ret_val, tree t, formals_style
> >>>style)
> >>>       }
> >>>     if (TYPE_ATOMIC (t))
> >>>       ret_val = concat ("_Atomic ", ret_val, NULL);
> >>>+  if (TYPE_DEPENDENT_PTR (t))
> >>>+    ret_val = concat ("_Dependent_ptr ", ret_val, NULL);
> >>>     if (TYPE_READONLY (t))
> >>>       ret_val = concat ("const ", ret_val, NULL);
> >>>     if (TYPE_VOLATILE (t))
> >>>@@ -474,6 +478,8 @@ gen_decl (tree decl, int is_func_definition,
> >>>formals_style style)
> >>>       ret_val = concat ("volatile ", ret_val, NULL);
> >>>     if (TREE_READONLY (decl))
> >>>       ret_val = concat ("const ", ret_val, NULL);
> >>>+  if (TREE_THIS_DEPENDENT_PTR (decl))
> >>>+    ret_val = concat ("dependent_ptr ", ret_val, NULL);
> >>>
> >>>     data_type = "";
> >>>
> >>>diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
> >>>index f85f481..2047575 100644
> >>>--- a/gcc/c/c-decl.c
> >>>+++ b/gcc/c/c-decl.c
> >>>@@ -2587,6 +2587,9 @@ merge_decls (tree newdecl, tree olddecl, tree
> >>>newtype, tree oldtype)
> >>>     if (TREE_THIS_VOLATILE (newdecl))
> >>>       TREE_THIS_VOLATILE (olddecl) = 1;
> >>>
> >>>+  if (TREE_THIS_DEPENDENT_PTR (newdecl))
> >>>+    TREE_THIS_DEPENDENT_PTR (olddecl) = 1;
> >>>+
> >>>     /* Merge deprecatedness.  */
> >>>     if (TREE_DEPRECATED (newdecl))
> >>>       TREE_DEPRECATED (olddecl) = 1;
> >>>@@ -2638,6 +2641,7 @@ merge_decls (tree newdecl, tree olddecl, tree
> >>>newtype, tree oldtype)
> >>>     DECL_NO_INSTRUMENT_FUNCTION_ENTRY_EXIT (newdecl)
> >>>       |= DECL_NO_INSTRUMENT_FUNCTION_ENTRY_EXIT (olddecl);
> >>>     TREE_THIS_VOLATILE (newdecl) |= TREE_THIS_VOLATILE (olddecl);
> >>>+  TREE_THIS_DEPENDENT_PTR (newdecl) |= TREE_THIS_DEPENDENT_PTR (olddecl);
> >>>     DECL_IS_MALLOC (newdecl) |= DECL_IS_MALLOC (olddecl);
> >>>     if (DECL_IS_OPERATOR_NEW_P (olddecl))
> >>>       DECL_SET_IS_OPERATOR_NEW (newdecl, true);
> >>>@@ -4544,6 +4548,7 @@ shadow_tag_warned (const struct c_declspecs
> >>>*declspecs, int warned)
> >>>      && (declspecs->const_p
> >>>          || declspecs->volatile_p
> >>>          || declspecs->atomic_p
> >>>+       || declspecs->dependent_ptr_p
> >>>          || declspecs->restrict_p
> >>>          || declspecs->address_space))
> >>>       {
> >>>@@ -4672,6 +4677,7 @@ quals_from_declspecs (const struct c_declspecs *specs)
> >>>          | (specs->volatile_p ? TYPE_QUAL_VOLATILE : 0)
> >>>          | (specs->restrict_p ? TYPE_QUAL_RESTRICT : 0)
> >>>          | (specs->atomic_p ? TYPE_QUAL_ATOMIC : 0)
> >>>+       | (specs->dependent_ptr_p ? TYPE_QUAL_DEPENDENT_PTR : 0)
> >>>          | (ENCODE_QUAL_ADDR_SPACE (specs->address_space)));
> >>>     gcc_assert (!specs->type
> >>>         && !specs->decl_attr
> >>>@@ -5837,6 +5843,7 @@ grokdeclarator (const struct c_declarator *declarator,
> >>>     int restrictp;
> >>>     int volatilep;
> >>>     int atomicp;
> >>>+  int dependent_ptrp;
> >>>     int type_quals = TYPE_UNQUALIFIED;
> >>>     tree name = NULL_TREE;
> >>>     bool funcdef_flag = false;
> >>>@@ -6003,6 +6010,7 @@ grokdeclarator (const struct c_declarator *declarator,
> >>>     restrictp = declspecs->restrict_p + TYPE_RESTRICT (element_type);
> >>>     volatilep = declspecs->volatile_p + TYPE_VOLATILE (element_type);
> >>>     atomicp = declspecs->atomic_p + TYPE_ATOMIC (element_type);
> >>>+  dependent_ptrp = declspecs->dependent_ptr_p + TYPE_DEPENDENT_PTR
> >>>(element_type);
> >>>     as1 = declspecs->address_space;
> >>>     as2 = TYPE_ADDR_SPACE (element_type);
> >>>     address_space = ADDR_SPACE_GENERIC_P (as1)? as2 : as1;
> >>>@@ -6015,6 +6023,8 @@ grokdeclarator (const struct c_declarator *declarator,
> >>>       pedwarn_c90 (loc, OPT_Wpedantic, "duplicate %<volatile%>");
> >>>     if (atomicp > 1)
> >>>       pedwarn_c90 (loc, OPT_Wpedantic, "duplicate %<_Atomic%>");
> >>>+  if (dependent_ptrp > 1)
> >>>+    pedwarn_c90 (loc, OPT_Wpedantic, "duplicate %<_Dependent_ptr%>");
> >>>
> >>>     if (!ADDR_SPACE_GENERIC_P (as1) && !ADDR_SPACE_GENERIC_P (as2) && as1 !=
> >>>as2)
> >>>       error_at (loc, "conflicting named address spaces (%s vs %s)",
> >>>@@ -6031,6 +6041,7 @@ grokdeclarator (const struct c_declarator *declarator,
> >>>    | (restrictp ? TYPE_QUAL_RESTRICT : 0)
> >>>    | (volatilep ? TYPE_QUAL_VOLATILE : 0)
> >>>    | (atomicp ? TYPE_QUAL_ATOMIC : 0)
> >>>+ | (dependent_ptrp ? TYPE_QUAL_DEPENDENT_PTR : 0)
> >>>    | ENCODE_QUAL_ADDR_SPACE (address_space));
> >>>     if (type_quals != TYPE_QUALS (element_type))
> >>>       orig_qual_type = NULL_TREE;
> >>>@@ -6042,6 +6053,13 @@ grokdeclarator (const struct c_declarator
> >>>*declarator,
> >>>     if (declspecs->atomic_p && TREE_CODE (type) == ARRAY_TYPE)
> >>>       error_at (loc, "%<_Atomic%>-qualified array type");
> >>>
> >>>+  /* Applying the _Dependent_ptr qualifier to an array type (through
> >>>+     the use of typedefs or typeof) must be detected here.  If the
> >>>+     qualifier is introduced later, any appearance of applying it to
> >>>+     an array is actually applying it to an element of that array.  */
> >>>+  if (declspecs->dependent_ptr_p && TREE_CODE (type) == ARRAY_TYPE)
> >>>+    error_at (loc, "%<_Dependent_ptr%>-qualified array type");
> >>>+
> >>>     /* Warn about storage classes that are invalid for certain
> >>>        kinds of declarations (parameters, typenames, etc.).  */
> >>>
> >>>@@ -7214,6 +7232,10 @@ grokdeclarator (const struct c_declarator
> >>>*declarator,
> >>>    /* An uninitialized decl with `extern' is a reference.  */
> >>>    int extern_ref = !initialized && storage_class == csc_extern;
> >>>
> >>>+ /* _Dependent_ptr qualifier only reserved for pointer type variable */
> >>>+ if ((type_quals & TYPE_QUAL_DEPENDENT_PTR) && (!POINTER_TYPE_P (type)))
> >>>+  error_at (loc, "invalid use of %<_Dependent_ptr%>");
> >>>+
> >>>    type = c_build_qualified_type (type, type_quals, orig_qual_type,
> >>>          orig_qual_indirect);
> >>>
> >>>@@ -7294,7 +7316,7 @@ grokdeclarator (const struct c_declarator *declarator,
> >>>    DECL_REGISTER (decl) = 1;
> >>>         }
> >>>
> >>>-    /* Record constancy and volatility.  */
> >>>+    /* Record constancy, data dependency and volatility.  */
> >>>       c_apply_type_quals_to_decl (type_quals, decl);
> >>>
> >>>       /* Apply _Alignas specifiers.  */
> >>>@@ -8258,6 +8280,11 @@ finish_struct (location_t loc, tree t, tree
> >>>fieldlist, tree attributes,
> >>>         if (TREE_THIS_VOLATILE (x))
> >>>    C_TYPE_FIELDS_VOLATILE (t) = 1;
> >>>
> >>>+      /* Any field that is a dependent pointer means variables of this
> >>>+ type must be treated in some ways as dependent pointer.  */
> >>>+      if (TREE_THIS_DEPENDENT_PTR (x))
> >>>+ C_TYPE_FIELDS_DEPENDENT_PTR (t) = 1;
> >>>+
> >>>         /* Any field of nominal variable size implies structure is too.  */
> >>>         if (C_DECL_VARIABLE_SIZE (x))
> >>>    C_TYPE_VARIABLE_SIZE (t) = 1;
> >>>@@ -10177,6 +10204,12 @@ declspecs_add_qual (location_t loc,
> >>>         prev_loc = specs->locations[cdw_atomic];
> >>>         specs->locations[cdw_atomic] = loc;
> >>>         break;
> >>>+    case RID_DEPENDENT_PTR:
> >>>+      dupe = specs->dependent_ptr_p;
> >>>+      specs->dependent_ptr_p = true;
> >>>+      prev_loc = specs->locations[cdw_dependent_ptr];
> >>>+      specs->locations[cdw_dependent_ptr] = loc;
> >>>+      break;
> >>>       default:
> >>>         gcc_unreachable ();
> >>>       }
> >>>diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
> >>>index 6721049..35e25bb 100644
> >>>--- a/gcc/c/c-parser.c
> >>>+++ b/gcc/c/c-parser.c
> >>>@@ -503,6 +503,7 @@ c_keyword_starts_typename (enum rid keyword)
> >>>       case RID_TYPEOF:
> >>>       case RID_CONST:
> >>>       case RID_ATOMIC:
> >>>+    case RID_DEPENDENT_PTR:
> >>>       case RID_VOLATILE:
> >>>       case RID_RESTRICT:
> >>>       case RID_ATTRIBUTE:
> >>>@@ -606,6 +607,7 @@ c_token_is_qualifier (c_token *token)
> >>>    case RID_RESTRICT:
> >>>    case RID_ATTRIBUTE:
> >>>    case RID_ATOMIC:
> >>>+ case RID_DEPENDENT_PTR:
> >>>     return true;
> >>>    default:
> >>>     return false;
> >>>@@ -687,6 +689,7 @@ c_token_starts_declspecs (c_token *token)
> >>>    case RID_SAT:
> >>>    case RID_ALIGNAS:
> >>>    case RID_ATOMIC:
> >>>+ case RID_DEPENDENT_PTR:
> >>>    case RID_AUTO_TYPE:
> >>>     return true;
> >>>    default:
> >>>@@ -2575,6 +2578,7 @@ c_parser_static_assert_declaration_no_semi (c_parser
> >>>*parser)
> >>>        volatile
> >>>        address-space-qualifier
> >>>        _Atomic
> >>>+     _Dependent_ptr
> >>>
> >>>      (restrict is new in C99.)
> >>>      (_Atomic is new in C11.)
> >>>@@ -2865,6 +2869,11 @@ c_parser_declspecs (c_parser *parser, struct
> >>>c_declspecs *specs,
> >>>     else
> >>>       declspecs_add_qual (loc, specs, value);
> >>>     break;
> >>>+ case RID_DEPENDENT_PTR:
> >>>+  attrs_ok = true;
> >>>+  declspecs_add_qual (loc, specs, c_parser_peek_token (parser)->value);
> >>>+  c_parser_consume_token (parser);
> >>>+  break;
> >>>    case RID_CONST:
> >>>    case RID_VOLATILE:
> >>>    case RID_RESTRICT:
> >>>@@ -4275,6 +4284,7 @@ c_parser_attribute_any_word (c_parser *parser)
> >>>    case RID_TRANSACTION_ATOMIC:
> >>>    case RID_TRANSACTION_CANCEL:
> >>>    case RID_ATOMIC:
> >>>+ case RID_DEPENDENT_PTR:
> >>>    case RID_AUTO_TYPE:
> >>>    case RID_INT_N_0:
> >>>    case RID_INT_N_1:
> >>>diff --git a/gcc/c/c-tree.h b/gcc/c/c-tree.h
> >>>index dae2979..0e416f2 100644
> >>>--- a/gcc/c/c-tree.h
> >>>+++ b/gcc/c/c-tree.h
> >>>@@ -34,6 +34,9 @@ along with GCC; see the file COPYING3.  If not see
> >>>   /* In a RECORD_TYPE or UNION_TYPE, nonzero if any component is volatile.
> >>>   */
> >>>   #define C_TYPE_FIELDS_VOLATILE(TYPE) TREE_LANG_FLAG_2 (TYPE)
> >>>
> >>>+/* In a RECORD_TYPE or UNION_TYPE, nonzero if any component is dependent
> >>>pointer.  */
> >>>+#define C_TYPE_FIELDS_DEPENDENT_PTR(TYPE) TREE_LANG_FLAG_3 (TYPE)
> >>>+
> >>>   /* In a RECORD_TYPE or UNION_TYPE or ENUMERAL_TYPE
> >>>      nonzero if the definition of the type has already started.  */
> >>>   #define C_TYPE_BEING_DEFINED(TYPE) TYPE_LANG_FLAG_0 (TYPE)
> >>>@@ -279,6 +282,7 @@ enum c_declspec_word {
> >>>     cdw_volatile,
> >>>     cdw_restrict,
> >>>     cdw_atomic,
> >>>+  cdw_dependent_ptr,
> >>>     cdw_saturating,
> >>>     cdw_alignas,
> >>>     cdw_address_space,
> >>>@@ -387,6 +391,8 @@ struct c_declspecs {
> >>>     BOOL_BITFIELD restrict_p : 1;
> >>>     /* Whether "_Atomic" was specified.  */
> >>>     BOOL_BITFIELD atomic_p : 1;
> >>>+  /* Whether "_Dependent_ptr" was specified.  */
> >>>+  BOOL_BITFIELD dependent_ptr_p : 1;
> >>>     /* Whether "_Sat" was specified.  */
> >>>     BOOL_BITFIELD saturating_p : 1;
> >>>     /* Whether any alignment specifier (even with zero alignment) was
> >>>diff --git a/gcc/print-tree.c b/gcc/print-tree.c
> >>>index debea2b..ec4e3db 100644
> >>>--- a/gcc/print-tree.c
> >>>+++ b/gcc/print-tree.c
> >>>@@ -348,6 +348,8 @@ print_node (FILE *file, const char *prefix, tree node,
> >>>int indent,
> >>>       fputs (" addressable", file);
> >>>     if (TREE_THIS_VOLATILE (node))
> >>>       fputs (" volatile", file);
> >>>+  if (TREE_THIS_DEPENDENT_PTR (node))
> >>>+    fputs (" dependent_ptr", file);
> >>>     if (TREE_ASM_WRITTEN (node))
> >>>       fputs (" asm_written", file);
> >>>     if (TREE_USED (node))
> >>>diff --git a/gcc/tree-core.h b/gcc/tree-core.h
> >>>index 60d8c68..3f3e682 100644
> >>>--- a/gcc/tree-core.h
> >>>+++ b/gcc/tree-core.h
> >>>@@ -567,7 +567,8 @@ enum cv_qualifier {
> >>>     TYPE_QUAL_CONST    = 0x1,
> >>>     TYPE_QUAL_VOLATILE = 0x2,
> >>>     TYPE_QUAL_RESTRICT = 0x4,
> >>>-  TYPE_QUAL_ATOMIC   = 0x8
> >>>+  TYPE_QUAL_ATOMIC   = 0x8,
> >>>+  TYPE_QUAL_DEPENDENT_PTR = 0x10
> >>>   };
> >>>
> >>>   /* Standard named or nameless data types of the C compiler.  */
> >>>@@ -591,6 +592,8 @@ enum tree_index {
> >>>     TI_ATOMICDI_TYPE,
> >>>     TI_ATOMICTI_TYPE,
> >>>
> >>>+  TI_DEPENDENT_PTR_TYPE,
> >>>+
> >>>     TI_UINT16_TYPE,
> >>>     TI_UINT32_TYPE,
> >>>     TI_UINT64_TYPE,
> >>>@@ -969,6 +972,7 @@ struct GTY(()) tree_base {
> >>>     unsigned asm_written_flag: 1;
> >>>     unsigned nowarning_flag : 1;
> >>>     unsigned visited : 1;
> >>>+  unsigned dependent_ptr_flag : 1;
> >>>
> >>>     unsigned used_flag : 1;
> >>>     unsigned nothrow_flag : 1;
> >>>diff --git a/gcc/tree-pretty-print.c b/gcc/tree-pretty-print.c
> >>>index 9bea132..ae59cea 100644
> >>>--- a/gcc/tree-pretty-print.c
> >>>+++ b/gcc/tree-pretty-print.c
> >>>@@ -1622,6 +1622,8 @@ dump_generic_node (pretty_printer *pp, tree node, int
> >>>spc, dump_flags_t flags,
> >>>     pp_string (pp, "atomic ");
> >>>    if (quals & TYPE_QUAL_CONST)
> >>>     pp_string (pp, "const ");
> >>>+ if (quals & TYPE_QUAL_DEPENDENT_PTR)
> >>>+  pp_string (pp, "dependent_ptr ");
> >>>    else if (quals & TYPE_QUAL_VOLATILE)
> >>>     pp_string (pp, "volatile ");
> >>>    else if (quals & TYPE_QUAL_RESTRICT)
> >>>@@ -1768,6 +1770,8 @@ dump_generic_node (pretty_printer *pp, tree node, int
> >>>spc, dump_flags_t flags,
> >>>       pp_string (pp, " volatile");
> >>>     if (quals & TYPE_QUAL_RESTRICT)
> >>>       pp_string (pp, " restrict");
> >>>+  if (quals & TYPE_QUAL_DEPENDENT_PTR)
> >>>+    pp_string (pp, " dependent_ptr");
> >>>
> >>>     if (!ADDR_SPACE_GENERIC_P (TYPE_ADDR_SPACE (node)))
> >>>       {
> >>>@@ -1871,6 +1875,8 @@ dump_generic_node (pretty_printer *pp, tree node, int
> >>>spc, dump_flags_t flags,
> >>>
> >>>    if (quals & TYPE_QUAL_ATOMIC)
> >>>     pp_string (pp, "atomic ");
> >>>+ if (quals & TYPE_QUAL_DEPENDENT_PTR)
> >>>+  pp_string (pp, "dependent_ptr ");
> >>>    if (quals & TYPE_QUAL_CONST)
> >>>     pp_string (pp, "const ");
> >>>    if (quals & TYPE_QUAL_VOLATILE)
> >>>diff --git a/gcc/tree.c b/gcc/tree.c
> >>>index 8cf75f2..b4dff8d 100644
> >>>--- a/gcc/tree.c
> >>>+++ b/gcc/tree.c
> >>>@@ -5213,6 +5213,7 @@ fld_type_variant (tree first, tree t, class
> >>>free_lang_data_d *fld,
> >>>     TYPE_READONLY (v) = TYPE_READONLY (t);
> >>>     TYPE_VOLATILE (v) = TYPE_VOLATILE (t);
> >>>     TYPE_ATOMIC (v) = TYPE_ATOMIC (t);
> >>>+  TYPE_DEPENDENT_PTR (v) = TYPE_DEPENDENT_PTR (t);
> >>>     TYPE_RESTRICT (v) = TYPE_RESTRICT (t);
> >>>     TYPE_ADDR_SPACE (v) = TYPE_ADDR_SPACE (t);
> >>>     TYPE_NAME (v) = TYPE_NAME (t);
> >>>@@ -6348,6 +6349,7 @@ set_type_quals (tree type, int type_quals)
> >>>     TYPE_VOLATILE (type) = (type_quals & TYPE_QUAL_VOLATILE) != 0;
> >>>     TYPE_RESTRICT (type) = (type_quals & TYPE_QUAL_RESTRICT) != 0;
> >>>     TYPE_ATOMIC (type) = (type_quals & TYPE_QUAL_ATOMIC) != 0;
> >>>+  TYPE_DEPENDENT_PTR (type) = (type_quals & TYPE_QUAL_DEPENDENT_PTR) != 0;
> >>>     TYPE_ADDR_SPACE (type) = DECODE_QUAL_ADDR_SPACE (type_quals);
> >>>   }
> >>>
> >>>diff --git a/gcc/tree.h b/gcc/tree.h
> >>>index 4aa2c4a..0c2f192 100644
> >>>--- a/gcc/tree.h
> >>>+++ b/gcc/tree.h
> >>>@@ -789,6 +789,9 @@ extern void omp_clause_range_check_failed (const_tree,
> >>>const char *, int,
> >>>      If this bit is set in an expression, so is TREE_SIDE_EFFECTS.  */
> >>>   #define TREE_THIS_VOLATILE(NODE) ((NODE)->base.volatile_flag)
> >>>
> >>>+/* Nonzero means this expression is involved in some data dependency.  */
> >>>+#define TREE_THIS_DEPENDENT_PTR(NODE) ((NODE)->base.dependent_ptr_flag)
> >>>+
> >>>   /* Nonzero means this node will not trap.  In an INDIRECT_REF, means
> >>>      accessing the memory pointed to won't generate a trap.  However,
> >>>      this only applies to an object when used appropriately: it doesn't
> >>>@@ -2070,6 +2073,9 @@ extern machine_mode vector_type_mode (const_tree);
> >>>   /* Nonzero in a type considered atomic as a whole.  */
> >>>   #define TYPE_ATOMIC(NODE) (TYPE_CHECK (NODE)->base.u.bits.atomic_flag)
> >>>
> >>>+/* Nonzero in a type considered dependent_ptr as a whole.  */
> >>>+#define TYPE_DEPENDENT_PTR(NODE) (TYPE_CHECK
> >>>(NODE)->base.dependent_ptr_flag)
> >>>+
> >>>   /* Means this type is const-qualified.  */
> >>>   #define TYPE_READONLY(NODE) (TYPE_CHECK (NODE)->base.readonly_flag)
> >>>
> >>>@@ -2100,6 +2106,7 @@ extern machine_mode vector_type_mode (const_tree);
> >>>     ((int) ((TYPE_READONLY (NODE) * TYPE_QUAL_CONST) \
> >>>     | (TYPE_VOLATILE (NODE) * TYPE_QUAL_VOLATILE) \
> >>>     | (TYPE_ATOMIC (NODE) * TYPE_QUAL_ATOMIC) \
> >>>+  | (TYPE_DEPENDENT_PTR (NODE) * TYPE_QUAL_DEPENDENT_PTR)   \
> >>>     | (TYPE_RESTRICT (NODE) * TYPE_QUAL_RESTRICT) \
> >>>     | (ENCODE_QUAL_ADDR_SPACE (TYPE_ADDR_SPACE (NODE)))))
> >>>
> >>>@@ -2108,6 +2115,7 @@ extern machine_mode vector_type_mode (const_tree);
> >>>     ((int) ((TYPE_READONLY (NODE) * TYPE_QUAL_CONST) \
> >>>     | (TYPE_VOLATILE (NODE) * TYPE_QUAL_VOLATILE) \
> >>>     | (TYPE_ATOMIC (NODE) * TYPE_QUAL_ATOMIC) \
> >>>+  | (TYPE_DEPENDENT_PTR (NODE) * TYPE_QUAL_DEPENDENT_PTR)   \
> >>>     | (TYPE_RESTRICT (NODE) * TYPE_QUAL_RESTRICT)))
> >>>
> >>>   /* The same as TYPE_QUALS without the address space and atomic
> >>>@@ -3940,6 +3948,8 @@ tree_strip_any_location_wrapper (tree exp)
> >>>   #define atomicDI_type_node global_trees[TI_ATOMICDI_TYPE]
> >>>   #define atomicTI_type_node global_trees[TI_ATOMICTI_TYPE]
> >>>
> >>>+#define dependent_ptrTI_type_node global_trees[TI_DEPENDENT_PTR_TYPE]
> >>>+
> >>>   #define uint16_type_node global_trees[TI_UINT16_TYPE]
> >>>   #define uint32_type_node global_trees[TI_UINT32_TYPE]
> >>>   #define uint64_type_node global_trees[TI_UINT64_TYPE]
> >>>diff --git a/gcc/testsuite/gcc.dg/c11-dependent_ptr-test-1.c
> >>>b/gcc/testsuite/gcc.dg/c11-dependent_ptr-test-1.c
> >>>new file mode 100644
> >>>index 0000000..8a70733
> >>>--- /dev/null
> >>>+++ b/gcc/testsuite/gcc.dg/c11-dependent_ptr-test-1.c
> >>>@@ -0,0 +1,62 @@
> >>>+/* Test for _Dependent_ptr. _Dependent_ptr qualified pointer
> >>>initialization tests. */
> >>>+/* { dg-do run } */
> >>>+/* { dg-options "-std=c11 -pedantic-errors" } */
> >>>+
> >>>+typedef __SIZE_TYPE__ size_t;
> >>>+extern void abort (void);
> >>>+extern void exit (int);
> >>>+extern void *malloc (size_t);
> >>>+
> >>>+#define TEST_SIMPLE_ASSIGN(TYPE)           \
> >>>+  do                   \
> >>>+    {                 \
> >>>+      static volatile _Atomic (TYPE) * _Dependent_ptr a;     \
> >>>+      static volatile _Atomic (TYPE) b;         \
> >>>+      a = &b;               \
> >>>+      if (a != &b)               \
> >>>+   abort();               \
> >>>+    }                                                             \
> >>>+  while (0)
> >>>+
> >>>+#define TEST_SIMPLE_ASSIGN_POINTER()           \
> >>>+  do                                                               \
> >>>+    {                                                             \
> >>>+      TEST_SIMPLE_ASSIGN (_Bool);         \
> >>>+      TEST_SIMPLE_ASSIGN (char);           \
> >>>+      TEST_SIMPLE_ASSIGN (signed char);         \
> >>>+      TEST_SIMPLE_ASSIGN (unsigned char);       \
> >>>+      TEST_SIMPLE_ASSIGN (signed short);         \
> >>>+      TEST_SIMPLE_ASSIGN (unsigned short);         \
> >>>+      TEST_SIMPLE_ASSIGN (signed int);           \
> >>>+      TEST_SIMPLE_ASSIGN (unsigned int);         \
> >>>+      TEST_SIMPLE_ASSIGN (signed long);         \
> >>>+      TEST_SIMPLE_ASSIGN (unsigned long);       \
> >>>+      TEST_SIMPLE_ASSIGN (signed long long);         \
> >>>+      TEST_SIMPLE_ASSIGN (unsigned long long);         \
> >>>+      TEST_SIMPLE_ASSIGN (float);         \
> >>>+      TEST_SIMPLE_ASSIGN (double);           \
> >>>+      TEST_SIMPLE_ASSIGN (long double);         \
> >>>+      TEST_SIMPLE_ASSIGN (_Complex float);         \
> >>>+      TEST_SIMPLE_ASSIGN (_Complex double);       \
> >>>+      TEST_SIMPLE_ASSIGN (_Complex long double);       \
> >>>+      struct new_struct { struct new_struct * _Dependent_ptr next; };   \
> >>>+      struct new_struct * _Dependent_ptr s;         \
> >>>+      s = malloc (sizeof (struct new_struct));         \
> >>>+      struct new_struct t;             \
> >>>+      s->next = &t;             \
> >>>+      if (s->next != &t)             \
> >>>+        abort();               \
> >>>+    }                 \
> >>>+  while (0)
> >>>+
> >>>+static void
> >>>+test_simple_assign (void)
> >>>+{
> >>>+  TEST_SIMPLE_ASSIGN_POINTER ();
> >>>+}
> >>>+
> >>>+int main (void)
> >>>+{
> >>>+  test_simple_assign ();
> >>>+  exit (0);
> >>>+}
> >>>diff --git a/gcc/testsuite/gcc.dg/p0190r4_fig10.c
> >>>b/gcc/testsuite/gcc.dg/p0190r4_fig10.c
> >>>new file mode 100644
> >>>index 0000000..057c2ba
> >>>--- /dev/null
> >>>+++ b/gcc/testsuite/gcc.dg/p0190r4_fig10.c
> >>>@@ -0,0 +1,46 @@
> >>>+/* Test for _Dependent_ptr. _Dependent_ptr test for checking dependency
> >>>through non-local storage. Refer figure 10 in document p0190r4 (
> >>>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0190r4.pdf). */
> >>>+/* { dg-do compile } */
> >>>+/* { dg-options "-std=c11 -pedantic" } */
> >>>+
> >>>+#include <stdatomic.h>
> >>>+
> >>>+typedef __SIZE_TYPE__ size_t;
> >>>+extern void abort (void);
> >>>+extern void exit (int);
> >>>+extern void *malloc (size_t);
> >>>+extern int assert ();
> >>>+
> >>>+struct rcutest
> >>>+{
> >>>+  int a;
> >>>+  int b;
> >>>+  int c;
> >>>+};
> >>>+
> >>>+_Atomic struct rcutest *gp;
> >>>+struct rcutest *gslp;
> >>>+
> >>>+#define rcu_assign_pointer(p,v) \
> >>>+  atomic_store_explicit(&(p), (v), memory_order_release);
> >>>+
> >>>+#define rcu_dereference(p) \
> >>>+  atomic_load_explicit(&(p), memory_order_consume);
> >>>+
> >>>+void thread0 ()
> >>>+{
> >>>+  struct rcutest *p;
> >>>+
> >>>+  p = (struct rcutest *)malloc (sizeof (*p));
> >>>+  assert (p);
> >>>+  p->a = 42;
> >>>+  rcu_assign_pointer (gp,p); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+}
> >>>+
> >>>+void thread1 ()
> >>>+{
> >>>+  struct rcutest *_Dependent_ptr p = rcu_dereference (gp); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+  gslp = p;
> >>>+  p = gslp;
> >>>+  if (p)
> >>>+    assert (p->a = 42);
> >>>+}
> >>>diff --git a/gcc/testsuite/gcc.dg/p0190r4_fig11.c
> >>>b/gcc/testsuite/gcc.dg/p0190r4_fig11.c
> >>>new file mode 100644
> >>>index 0000000..39c4b61
> >>>--- /dev/null
> >>>+++ b/gcc/testsuite/gcc.dg/p0190r4_fig11.c
> >>>@@ -0,0 +1,51 @@
> >>>+/* Test for _Dependent_ptr. _Dependent_ptr test in which reload kills
> >>>dependency. Refer figure 11 in document p0190r4 (
> >>>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0190r4.pdf). */
> >>>+/* { dg-do compile } */
> >>>+/* { dg-options "-std=c11 -pedantic" } */
> >>>+
> >>>+#include <stdatomic.h>
> >>>+
> >>>+typedef __SIZE_TYPE__ size_t;
> >>>+extern void abort (void);
> >>>+extern void exit (int);
> >>>+extern void *malloc (size_t);
> >>>+extern int assert ();
> >>>+struct rcutest
> >>>+{
> >>>+  int a;
> >>>+  int b;
> >>>+  int c;
> >>>+};
> >>>+
> >>>+_Atomic struct rcutest *gp;
> >>>+_Atomic struct rcutest *gsgp;
> >>>+
> >>>+#define rcu_assign_pointer(p,v) \
> >>>+  atomic_store_explicit(&(p), (v), memory_order_release);
> >>>+
> >>>+#define rcu_dereference(p) \
> >>>+  atomic_load_explicit(&(p), memory_order_consume);
> >>>+
> >>>+void thread0 ()
> >>>+{
> >>>+  struct rcutest *p;
> >>>+
> >>>+  p = (struct rcutest *)malloc (sizeof (*p));
> >>>+  assert (p);
> >>>+  p->a = 42;
> >>>+  rcu_assign_pointer (gp,p); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+}
> >>>+
> >>>+void thread1 ()
> >>>+{
> >>>+  struct rcutest * _Dependent_ptr p = rcu_dereference (gp); /* {
> >>>dg-warning "\\\[-Wincompatible-pointer-types]" } */
> >>>+  atomic_store_explicit(&gsgp, p, memory_order_relaxed); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+}
> >>>+
> >>>+void thread2 ()
> >>>+{
> >>>+  struct rcutest *p;
> >>>+
> >>>+  p = atomic_load_explicit(&gsgp, memory_order_relaxed); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+  if (p)
> >>>+    assert(p->a == 42);
> >>>+}
> >>>diff --git a/gcc/testsuite/gcc.dg/p0190r4_fig12.c
> >>>b/gcc/testsuite/gcc.dg/p0190r4_fig12.c
> >>>new file mode 100644
> >>>index 0000000..4f7fcd3
> >>>--- /dev/null
> >>>+++ b/gcc/testsuite/gcc.dg/p0190r4_fig12.c
> >>>@@ -0,0 +1,53 @@
> >>>+/* Test for _Dependent_ptr. _Dependent_ptr test when casting a dependency
> >>>pointer to another pointer type which in turn reserves the dependency.
> >>>Refer figure 12 in document p0190r4 (
> >>>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0190r4.pdf). */
> >>>+/* { dg-do compile } */
> >>>+/* { dg-options "-std=c11 -pedantic" } */
> >>>+
> >>>+#include <stdatomic.h>
> >>>+
> >>>+typedef __SIZE_TYPE__ size_t;
> >>>+extern void abort (void);
> >>>+extern void exit (int);
> >>>+extern void *malloc (size_t);
> >>>+extern int assert ();
> >>>+
> >>>+struct rcutest
> >>>+{
> >>>+  int a;
> >>>+  int b;
> >>>+  int c;
> >>>+};
> >>>+
> >>>+struct rcutest1
> >>>+{
> >>>+  int a;
> >>>+  struct rcutest rt;
> >>>+};
> >>>+
> >>>+_Atomic struct rcutest *gp;
> >>>+
> >>>+#define rcu_assign_pointer(p,v) \
> >>>+  atomic_store_explicit(&(p), (v), memory_order_release);
> >>>+
> >>>+#define rcu_dereference(p) \
> >>>+  atomic_load_explicit(&(p), memory_order_consume);
> >>>+
> >>>+void thread0 ()
> >>>+{
> >>>+  struct rcutest *p;
> >>>+
> >>>+  p = (struct rcutest *)malloc (sizeof (*p));
> >>>+  assert (p);
> >>>+  p->a = 42;
> >>>+  rcu_assign_pointer (gp,p); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+}
> >>>+
> >>>+void thread1 ()
> >>>+{
> >>>+  struct rcutest * _Dependent_ptr p;
> >>>+  struct rcutest1 *_Dependent_ptr q;
> >>>+
> >>>+  p = rcu_dereference (gp); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+  q = p;                /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+  if (q)
> >>>+    assert(q->a == 42);
> >>>+}
> >>>diff --git a/gcc/testsuite/gcc.dg/p0190r4_fig13.c
> >>>b/gcc/testsuite/gcc.dg/p0190r4_fig13.c
> >>>new file mode 100644
> >>>index 0000000..b4010fc
> >>>--- /dev/null
> >>>+++ b/gcc/testsuite/gcc.dg/p0190r4_fig13.c
> >>>@@ -0,0 +1,48 @@
> >>>+/* Test for _Dependent_ptr. _Dependent_ptr test: casting to non-pointer
> >>>kills dependency. Refer figure 13 in document p0190r4 (
> >>>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0190r4.pdf). */
> >>>+/* { dg-do compile } */
> >>>+/* { dg-options "-std=c11 -pedantic" } */
> >>>+
> >>>+#include <stdatomic.h>
> >>>+
> >>>+typedef __SIZE_TYPE__ size_t;
> >>>+extern void abort (void);
> >>>+extern void exit (int);
> >>>+extern void *malloc (size_t);
> >>>+extern int assert ();
> >>>+
> >>>+struct rcutest
> >>>+{
> >>>+  int a;
> >>>+  int b;
> >>>+  int c;
> >>>+};
> >>>+
> >>>+_Atomic struct rcutest *gp;
> >>>+
> >>>+#define rcu_assign_pointer(p,v) \
> >>>+  atomic_store_explicit(&(p), (v), memory_order_release);
> >>>+
> >>>+#define rcu_dereference(p) \
> >>>+  atomic_load_explicit(&(p), memory_order_consume);
> >>>+
> >>>+void thread0 ()
> >>>+{
> >>>+  struct rcutest *p;
> >>>+
> >>>+  p = (struct rcutest *)malloc (sizeof (*p));
> >>>+  assert (p);
> >>>+  p->a = 42;
> >>>+  rcu_assign_pointer (gp,p); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+}
> >>>+
> >>>+void thread1 ()
> >>>+{
> >>>+  struct rcutest * _Dependent_ptr p;
> >>>+  long int q;
> >>>+
> >>>+  p = rcu_dereference (gp); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+  q = (long int)(p);
> >>>+  p = (_Dependent_ptr struct rcutest *)q;
> >>>+  if (p)
> >>>+    assert(p->a == 42);
> >>>+}
> >>>diff --git a/gcc/testsuite/gcc.dg/p0190r4_fig8.c
> >>>b/gcc/testsuite/gcc.dg/p0190r4_fig8.c
> >>>new file mode 100644
> >>>index 0000000..e706a9b
> >>>--- /dev/null
> >>>+++ b/gcc/testsuite/gcc.dg/p0190r4_fig8.c
> >>>@@ -0,0 +1,44 @@
> >>>+/* Test for _Dependent_ptr. _Dependent_ptr test for checking simple
> >>>left-hand side dependency. Refer figure 8 in document p0190r4 (
> >>>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0190r4.pdf). */
> >>>+/* { dg-do compile } */
> >>>+/* { dg-options "-std=c11 -pedantic" } */
> >>>+
> >>>+#include <stdatomic.h>
> >>>+
> >>>+typedef __SIZE_TYPE__ size_t;
> >>>+extern void abort (void);
> >>>+extern void exit (int);
> >>>+extern void *malloc (size_t);
> >>>+extern int assert ();
> >>>+
> >>>+struct rcutest
> >>>+{
> >>>+  int a;
> >>>+  int b;
> >>>+  int c;
> >>>+};
> >>>+
> >>>+_Atomic struct rcutest *gp;
> >>>+
> >>>+#define rcu_assign_pointer(p,v) \
> >>>+  atomic_store_explicit(&(p), (v), memory_order_release);
> >>>+
> >>>+#define rcu_dereference(p) \
> >>>+  atomic_load_explicit(&(p), memory_order_consume);
> >>>+
> >>>+void thread0 ()
> >>>+{
> >>>+  struct rcutest *p;
> >>>+
> >>>+  p = (struct rcutest *)malloc (sizeof (*p));
> >>>+  assert (p);
> >>>+  p->a = 42;
> >>>+  assert (p->a != 43);
> >>>+  rcu_assign_pointer (gp,p); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+}
> >>>+
> >>>+void thread1 ()
> >>>+{
> >>>+  struct rcutest * _Dependent_ptr p = rcu_dereference (gp); /* {
> >>>dg-warning "\\\[-Wincompatible-pointer-types]" } */
> >>>+  if (p)
> >>>+    p->a = 43;
> >>>+}
> >>>diff --git a/gcc/testsuite/gcc.dg/p0190r4_fig9.c
> >>>b/gcc/testsuite/gcc.dg/p0190r4_fig9.c
> >>>new file mode 100644
> >>>index 0000000..32f67b3
> >>>--- /dev/null
> >>>+++ b/gcc/testsuite/gcc.dg/p0190r4_fig9.c
> >>>@@ -0,0 +1,43 @@
> >>>+/* Test for _Dependent_ptr. _Dependent_ptr test for checking simple
> >>>right-hand side dependency. Refer figure 9 in document p0190r4 (
> >>>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0190r4.pdf). */
> >>>+/* { dg-do compile } */
> >>>+/* { dg-options "-std=c11 -pedantic" } */
> >>>+
> >>>+#include <stdatomic.h>
> >>>+
> >>>+typedef __SIZE_TYPE__ size_t;
> >>>+extern void abort (void);
> >>>+extern void exit (int);
> >>>+extern void *malloc (size_t);
> >>>+extern int assert ();
> >>>+
> >>>+struct rcutest
> >>>+{
> >>>+  int a;
> >>>+  int b;
> >>>+  int c;
> >>>+};
> >>>+
> >>>+_Atomic struct rcutest *gp;
> >>>+
> >>>+#define rcu_assign_pointer(p,v) \
> >>>+  atomic_store_explicit(&(p), (v), memory_order_release);
> >>>+
> >>>+#define rcu_dereference(p) \
> >>>+  atomic_load_explicit(&(p), memory_order_consume);
> >>>+
> >>>+void thread0 ()
> >>>+{
> >>>+  struct rcutest *p;
> >>>+
> >>>+  p = (struct rcutest *)malloc (sizeof (*p));
> >>>+  assert (p);
> >>>+  p->a = 42;
> >>>+  rcu_assign_pointer (gp,p); /* { dg-warning
> >>>"\\\[-Wincompatible-pointer-types]" } */
> >>>+}
> >>>+
> >>>+void thread1 ()
> >>>+{
> >>>+  struct rcutest * _Dependent_ptr p = rcu_dereference (gp); /* {
> >>>dg-warning "\\\[-Wincompatible-pointer-types]" } */
> >>>+  if (p)
> >>>+    assert (p->a = 42);
> >>>+}
> >>>
> >>
> 


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