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Re: Implement -Wimplicit-fallthrough: core (take 2)
- From: Marek Polacek <polacek at redhat dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Jason Merrill <jason at redhat dot com>, Joseph Myers <joseph at codesourcery dot com>
- Date: Wed, 27 Jul 2016 18:46:33 +0200
- Subject: Re: Implement -Wimplicit-fallthrough: core (take 2)
- Authentication-results: sourceware.org; auth=none
- References: <20160722104407.GG7007@redhat.com> <20160722110641.GL7387@tucnak.redhat.com>
On Fri, Jul 22, 2016 at 01:06:41PM +0200, Jakub Jelinek wrote:
> On Fri, Jul 22, 2016 at 12:44:07PM +0200, Marek Polacek wrote:
> > --- gcc/gcc/cp/parser.h
> > +++ gcc/gcc/cp/parser.h
> > @@ -46,7 +46,7 @@ struct GTY (()) cp_token {
> > Otherwise, this value is RID_MAX. */
> > ENUM_BITFIELD (rid) keyword : 8;
> > /* Token flags. */
> > - unsigned char flags;
> > + unsigned short flags;
> > /* True if this token is from a context where it is implicitly extern "C" */
> > BOOL_BITFIELD implicit_extern_c : 1;
> > /* True if an error has already been reported for this token, such as a
>
> I'm afraid this is really bad.
> Right now, there are 8 and 8 bit bitfields, then 8-bit char, 3 individual
> bits, 5 unused bits and 32-bit int, nicely packed into 64-bit word before a
> union with pointer members, and the C++ FE lexes everything first, so there
> are possibly millions of tokens in memory.
> Can't you just make it unsigned int flags : 11; instead? Or instead
> reshuffle the cpplib.h flags? E.g. I don't see the C++ FE to use the
> NO_EXPAND flag, so moving it to the upper byte of the short and moving the
> new flag to its bit? Perhaps that is even better for now.
Ouch, sorry, that is embarassing. I had been meaning to get back to this, but
apparently I never did. This version should be better. Another change is that
we don't warn for { something; default: return; } even in nested switches.
Another change is that I made the FEs less permissive wrt invalid code.
CCing Jason and Joseph to see what they think of the FEs part.
2016-07-27 Marek Polacek <polacek@redhat.com>
Jakub Jelinek <jakub@redhat.com>
PR c/7652
gcc/
* common.opt (Wimplicit-fallthrough): New option.
* doc/extend.texi: Document statement attributes and the fallthrough
attribute.
* doc/invoke.texi: Document -Wimplicit-fallthrough.
* gimple.h (gimple_call_internal_p): New function.
* gimplify.c (struct gimplify_ctx): Add in_switch_expr.
(struct label_entry): New struct.
(find_label_entry): New function.
(last_stmt_in_scope): New function.
(warn_implicit_fallthrough_r): New function.
(maybe_warn_implicit_fallthrough): New function.
(expand_FALLTHROUGH_r): New function.
(expand_FALLTHROUGH): New function.
(gimplify_switch_expr): Call maybe_warn_implicit_fallthrough and
expand_FALLTHROUGH for the innermost GIMPLE_SWITCH.
(gimplify_label_expr): New function.
(gimplify_case_label_expr): Set location.
(gimplify_expr): Call gimplify_label_expr.
* internal-fn.c (expand_FALLTHROUGH): New function.
* internal-fn.def (FALLTHROUGH): New internal function.
* system.h (gcc_fallthrough): Define.
* tree-core.h: Add FALLTHROUGH_LABEL_P comment.
* tree.h (FALLTHROUGH_LABEL_P): Define.
gcc/c-family/
* c-common.c (c_common_attribute_table): Add fallthrough attribute.
(handle_fallthrough_attribute): New function.
gcc/c/
* c-parser.c (struct c_token): Add flags field.
(c_lex_one_token): Pass it to c_lex_with_flags.
(c_parser_declaration_or_fndef): Turn __attribute__((fallthrough));
into IFN_FALLTHROUGH.
(c_parser_label): Set FALLTHROUGH_LABEL_P on labels.
(c_parser_statement_after_labels): Handle RID_ATTRIBUTE.
gcc/cp/
* constexpr.c (cxx_eval_internal_function): Handle IFN_FALLTHROUGH.
(potential_constant_expression_1): Likewise.
* parser.c (cp_parser_primary_expression): Handle RID_ATTRIBUTE.
(cp_parser_statement): Handle fallthrough attribute.
(cp_parser_label_for_labeled_statement): Set FALLTHROUGH_LABEL_P on
labels.
(cp_parser_std_attribute): Handle fallthrough attribute.
(cp_parser_check_std_attribute): Detect duplicated fallthrough
attribute.
gcc/testsuite/
* c-c++-common/Wimplicit-fallthrough-1.c: New test.
* c-c++-common/Wimplicit-fallthrough-10.c: New test.
* c-c++-common/Wimplicit-fallthrough-11.c: New test.
* c-c++-common/Wimplicit-fallthrough-12.c: New test.
* c-c++-common/Wimplicit-fallthrough-13.c: New test.
* c-c++-common/Wimplicit-fallthrough-14.c: New test.
* c-c++-common/Wimplicit-fallthrough-15.c: New test.
* c-c++-common/Wimplicit-fallthrough-16.c: New test.
* c-c++-common/Wimplicit-fallthrough-17.c: New test.
* c-c++-common/Wimplicit-fallthrough-2.c: New test.
* c-c++-common/Wimplicit-fallthrough-3.c: New test.
* c-c++-common/Wimplicit-fallthrough-4.c: New test.
* c-c++-common/Wimplicit-fallthrough-5.c: New test.
* c-c++-common/Wimplicit-fallthrough-6.c: New test.
* c-c++-common/Wimplicit-fallthrough-7.c: New test.
* c-c++-common/Wimplicit-fallthrough-8.c: New test.
* c-c++-common/Wimplicit-fallthrough-9.c: New test.
* c-c++-common/attr-fallthrough-1.c: New test.
* c-c++-common/attr-fallthrough-2.c: New test.
* g++.dg/cpp0x/fallthrough1.C: New test.
* g++.dg/cpp0x/fallthrough2.C: New test.
* g++.dg/cpp1z/fallthrough1.C: New test.
libcpp/
* include/cpplib.h (PREV_FALLTHROUGH): Define.
* internal.h (CPP_FALLTHRU): Define.
* lex.c (fallthrough_comment_p): New function.
(_cpp_lex_direct): Set PREV_FALLTHROUGH on tokens succeeding a falls
through comment.
diff --git gcc/gcc/c-family/c-common.c gcc/gcc/c-family/c-common.c
index 1c5974a..e33021a 100644
--- gcc/gcc/c-family/c-common.c
+++ gcc/gcc/c-family/c-common.c
@@ -392,6 +392,7 @@ static tree handle_designated_init_attribute (tree *, tree, tree, int, bool *);
static tree handle_bnd_variable_size_attribute (tree *, tree, tree, int, bool *);
static tree handle_bnd_legacy (tree *, tree, tree, int, bool *);
static tree handle_bnd_instrument (tree *, tree, tree, int, bool *);
+static tree handle_fallthrough_attribute (tree *, tree, tree, int, bool *);
static void check_nonnull_arg (void *, tree, unsigned HOST_WIDE_INT);
static bool nonnull_check_p (tree, unsigned HOST_WIDE_INT);
@@ -833,6 +834,8 @@ const struct attribute_spec c_common_attribute_table[] =
handle_bnd_legacy, false },
{ "bnd_instrument", 0, 0, true, false, false,
handle_bnd_instrument, false },
+ { "fallthrough", 0, 0, false, false, false,
+ handle_fallthrough_attribute, false },
{ NULL, 0, 0, false, false, false, NULL, false }
};
@@ -9701,6 +9704,19 @@ handle_designated_init_attribute (tree *node, tree name, tree, int,
return NULL_TREE;
}
+
+/* Handle a "fallthrough" attribute; arguments as in struct
+ attribute_spec.handler. */
+
+static tree
+handle_fallthrough_attribute (tree *, tree name, tree, int,
+ bool *no_add_attrs)
+{
+ warning (OPT_Wattributes, "%qE attribute ignored", name);
+ *no_add_attrs = true;
+ return NULL_TREE;
+}
+
/* Check for valid arguments being passed to a function with FNTYPE.
There are NARGS arguments in the array ARGARRAY. LOC should be used for
diff --git gcc/gcc/c/c-parser.c gcc/gcc/c/c-parser.c
index 8952bca..d6a0dd1 100644
--- gcc/gcc/c/c-parser.c
+++ gcc/gcc/c/c-parser.c
@@ -193,6 +193,8 @@ struct GTY (()) c_token {
location_t location;
/* The value associated with this token, if any. */
tree value;
+ /* Token flags. */
+ unsigned char flags;
source_range get_range () const
{
@@ -270,7 +272,8 @@ c_lex_one_token (c_parser *parser, c_token *token)
{
timevar_push (TV_LEX);
- token->type = c_lex_with_flags (&token->value, &token->location, NULL,
+ token->type = c_lex_with_flags (&token->value, &token->location,
+ &token->flags,
(parser->lex_untranslated_string
? C_LEX_STRING_NO_TRANSLATE : 0));
token->id_kind = C_ID_NONE;
@@ -1607,6 +1610,8 @@ static void c_finish_oacc_routine (c_parser *, tree, tree, bool, bool, bool);
declaration-specifiers declarator declaration-list[opt]
compound-statement
+ attribute ;
+
Objective-C:
attributes objc-class-definition
attributes objc-category-definition
@@ -1738,6 +1743,19 @@ c_parser_declaration_or_fndef (c_parser *parser, bool fndef_ok,
{
if (auto_type_p)
error_at (here, "%<__auto_type%> in empty declaration");
+ else if (specs->typespec_kind == ctsk_none && specs->attrs)
+ {
+ if (is_attribute_p ("fallthrough",
+ get_attribute_name (specs->attrs)))
+ {
+ tree fn = build_call_expr_internal_loc (here, IFN_FALLTHROUGH,
+ void_type_node, 0);
+ add_stmt (fn);
+ }
+ else
+ error_at (here, "only attribute %<fallthrough%> can be used "
+ "before %<;%>");
+ }
else if (empty_ok)
shadow_tag (specs);
else
@@ -4960,6 +4978,11 @@ c_parser_label (c_parser *parser)
{
location_t loc1 = c_parser_peek_token (parser)->location;
tree label = NULL_TREE;
+
+ /* Remember whether this case or a user-defined label is allowed to fall
+ through to. */
+ bool fallthrough_p = c_parser_peek_token (parser)->flags & PREV_FALLTHROUGH;
+
if (c_parser_next_token_is_keyword (parser, RID_CASE))
{
tree exp1, exp2;
@@ -5006,6 +5029,10 @@ c_parser_label (c_parser *parser)
}
if (label)
{
+ if (TREE_CODE (label) == LABEL_EXPR)
+ FALLTHROUGH_LABEL_P (LABEL_EXPR_LABEL (label)) = fallthrough_p;
+ else
+ FALLTHROUGH_LABEL_P (CASE_LABEL (label)) = fallthrough_p;
if (c_parser_next_tokens_start_declaration (parser))
{
error_at (c_parser_peek_token (parser)->location,
@@ -5059,6 +5086,9 @@ c_parser_label (c_parser *parser)
jump-statement:
goto * expression ;
+ expression-statement:
+ attributes ;
+
Objective-C:
statement:
@@ -5320,6 +5350,27 @@ c_parser_statement_after_labels (c_parser *parser, bool *if_p,
gcc_assert (c_dialect_objc ());
c_parser_objc_synchronized_statement (parser);
break;
+ case RID_ATTRIBUTE:
+ {
+ /* Allow '__attribute__((fallthrough));'. */
+ tree attrs = c_parser_attributes (parser);
+ if (attrs != NULL_TREE
+ && is_attribute_p ("fallthrough", get_attribute_name (attrs)))
+ {
+ location_t loc = c_parser_peek_token (parser)->location;
+ c_parser_require (parser, CPP_SEMICOLON, "expected %<;%>");
+ tree fn = build_call_expr_internal_loc (loc, IFN_FALLTHROUGH,
+ void_type_node, 0);
+ add_stmt (fn);
+ }
+ else if (c_parser_next_token_is (parser, CPP_SEMICOLON))
+ c_parser_error (parser, "only attribute %<fallthrough%> "
+ "can be used");
+ else
+ c_parser_error (parser, "only attribute %<fallthrough%> "
+ "followed by %<;%> can be used");
+ }
+ break;
default:
goto expr_stmt;
}
diff --git gcc/gcc/common.opt gcc/gcc/common.opt
index 8a292ed..7ba10cb 100644
--- gcc/gcc/common.opt
+++ gcc/gcc/common.opt
@@ -601,6 +601,10 @@ Whsa
Common Var(warn_hsa) Init(1) Warning
Warn when a function cannot be expanded to HSAIL.
+Wimplicit-fallthrough
+Common Var(warn_implicit_fallthrough) Warning EnabledBy(Wextra)
+Warn when a switch case falls through.
+
Winline
Common Var(warn_inline) Warning
Warn when an inlined function cannot be inlined.
diff --git gcc/gcc/cp/constexpr.c gcc/gcc/cp/constexpr.c
index 6bcb41a..e93c636 100644
--- gcc/gcc/cp/constexpr.c
+++ gcc/gcc/cp/constexpr.c
@@ -1290,6 +1290,7 @@ cxx_eval_internal_function (const constexpr_ctx *ctx, tree t,
case IFN_UBSAN_NULL:
case IFN_UBSAN_BOUNDS:
case IFN_UBSAN_VPTR:
+ case IFN_FALLTHROUGH:
return void_node;
case IFN_ADD_OVERFLOW:
@@ -4718,6 +4719,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict,
case IFN_UBSAN_NULL:
case IFN_UBSAN_BOUNDS:
case IFN_UBSAN_VPTR:
+ case IFN_FALLTHROUGH:
return true;
case IFN_ADD_OVERFLOW:
diff --git gcc/gcc/cp/parser.c gcc/gcc/cp/parser.c
index b71b9e5..84bc512 100644
--- gcc/gcc/cp/parser.c
+++ gcc/gcc/cp/parser.c
@@ -5129,6 +5129,31 @@ cp_parser_primary_expression (cp_parser *parser,
case RID_AT_SELECTOR:
return cp_parser_objc_expression (parser);
+ case RID_ATTRIBUTE:
+ {
+ /* This might be __attribute__((fallthrough));. */
+ tree attr = cp_parser_gnu_attributes_opt (parser);
+ if (attr != NULL_TREE
+ && is_attribute_p ("fallthrough", get_attribute_name (attr)))
+ {
+ tree fn = build_call_expr_internal_loc (token->location,
+ IFN_FALLTHROUGH,
+ void_type_node, 0);
+ return cp_expr (fn, token->location);
+ }
+ else if (cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON))
+ {
+ cp_parser_error (parser, "only attribute %<fallthrough%> "
+ "can be used");
+ return error_mark_node;
+ }
+ else
+ {
+ cp_parser_error (parser, "expected primary-expression");
+ return error_mark_node;
+ }
+ }
+
case RID_TEMPLATE:
if (parser->in_function_body
&& (cp_lexer_peek_nth_token (parser->lexer, 2)->type
@@ -10558,15 +10583,26 @@ cp_parser_statement (cp_parser* parser, tree in_statement_expr,
}
/* Look for an expression-statement instead. */
statement = cp_parser_expression_statement (parser, in_statement_expr);
+
+ /* Handle [[fallthrough]];. */
+ if (std_attrs != NULL_TREE
+ && is_attribute_p ("fallthrough", get_attribute_name (std_attrs))
+ && statement == NULL_TREE)
+ {
+ tree fn = build_call_expr_internal_loc (statement_location,
+ IFN_FALLTHROUGH,
+ void_type_node, 0);
+ finish_expr_stmt (fn);
+ }
}
/* Set the line number for the statement. */
if (statement && STATEMENT_CODE_P (TREE_CODE (statement)))
SET_EXPR_LOCATION (statement, statement_location);
- /* Note that for now, we don't do anything with c++11 statements
- parsed at this level. */
- if (std_attrs != NULL_TREE)
+ /* Allow "[[fallthrough]];", but warn otherwise. */
+ if (std_attrs != NULL_TREE
+ && !is_attribute_p ("fallthrough", get_attribute_name (std_attrs)))
warning_at (attrs_location,
OPT_Wattributes,
"attributes at the beginning of statement are ignored");
@@ -10601,6 +10637,10 @@ cp_parser_label_for_labeled_statement (cp_parser* parser, tree attributes)
return;
}
+ /* Remember whether this case or a user-defined label is allowed to fall
+ through to. */
+ bool fallthrough_p = token->flags & PREV_FALLTHROUGH;
+
parser->colon_corrects_to_scope_p = false;
switch (token->keyword)
{
@@ -10632,7 +10672,11 @@ cp_parser_label_for_labeled_statement (cp_parser* parser, tree attributes)
expr_hi = NULL_TREE;
if (parser->in_switch_statement_p)
- finish_case_label (token->location, expr, expr_hi);
+ {
+ tree l = finish_case_label (token->location, expr, expr_hi);
+ if (l && TREE_CODE (l) == CASE_LABEL_EXPR)
+ FALLTHROUGH_LABEL_P (CASE_LABEL (l)) = fallthrough_p;
+ }
else
error_at (token->location,
"case label %qE not within a switch statement",
@@ -10645,7 +10689,11 @@ cp_parser_label_for_labeled_statement (cp_parser* parser, tree attributes)
cp_lexer_consume_token (parser->lexer);
if (parser->in_switch_statement_p)
- finish_case_label (token->location, NULL_TREE, NULL_TREE);
+ {
+ tree l = finish_case_label (token->location, NULL_TREE, NULL_TREE);
+ if (l && TREE_CODE (l) == CASE_LABEL_EXPR)
+ FALLTHROUGH_LABEL_P (CASE_LABEL (l)) = fallthrough_p;
+ }
else
error_at (token->location, "case label not within a switch statement");
break;
@@ -10653,6 +10701,8 @@ cp_parser_label_for_labeled_statement (cp_parser* parser, tree attributes)
default:
/* Anything else must be an ordinary label. */
label = finish_label_stmt (cp_parser_identifier (parser));
+ if (label && TREE_CODE (label) == LABEL_DECL)
+ FALLTHROUGH_LABEL_P (label) = fallthrough_p;
break;
}
@@ -24024,6 +24074,16 @@ cp_parser_std_attribute (cp_parser *parser)
" use %<gnu::deprecated%>");
TREE_PURPOSE (TREE_PURPOSE (attribute)) = get_identifier ("gnu");
}
+ /* C++17 fallthrough attribute is equivalent to GNU's. */
+ else if (cxx_dialect >= cxx11
+ && is_attribute_p ("fallthrough", attr_id))
+ {
+ if (cxx_dialect < cxx1z)
+ pedwarn (token->location, OPT_Wpedantic,
+ "%<fallthrough%> is a C++17 feature;"
+ " use %<gnu::fallthrough%>");
+ TREE_PURPOSE (TREE_PURPOSE (attribute)) = get_identifier ("gnu");
+ }
/* Transactional Memory TS optimize_for_synchronized attribute is
equivalent to GNU transaction_callable. */
else if (is_attribute_p ("optimize_for_synchronized", attr_id))
@@ -24088,6 +24148,10 @@ cp_parser_check_std_attribute (tree attributes, tree attribute)
&& lookup_attribute ("deprecated", attributes))
error ("attribute deprecated can appear at most once "
"in an attribute-list");
+ else if (is_attribute_p ("fallthrough", name)
+ && lookup_attribute ("fallthrough", attributes))
+ error ("attribute fallthrough can appear at most once "
+ "in an attribute-list");
}
}
diff --git gcc/gcc/doc/extend.texi gcc/gcc/doc/extend.texi
index ad8898c..4960d57 100644
--- gcc/gcc/doc/extend.texi
+++ gcc/gcc/doc/extend.texi
@@ -60,6 +60,7 @@ extensions, accepted by GCC in C90 mode and in C++.
* Type Attributes:: Specifying attributes of types.
* Label Attributes:: Specifying attributes on labels.
* Enumerator Attributes:: Specifying attributes on enumerators.
+* Statement Attributes:: Specifying attributes on statements.
* Attribute Syntax:: Formal syntax for attributes.
* Function Prototypes:: Prototype declarations and old-style definitions.
* C++ Comments:: C++ comments are recognized.
@@ -2240,6 +2241,7 @@ GCC also supports attributes on
variable declarations (@pxref{Variable Attributes}),
labels (@pxref{Label Attributes}),
enumerators (@pxref{Enumerator Attributes}),
+statements (@pxref{Statement Attributes}),
and types (@pxref{Type Attributes}).
There is some overlap between the purposes of attributes and pragmas
@@ -5536,8 +5538,8 @@ attributes are currently defined generically for variables.
Other attributes are defined for variables on particular target
systems. Other attributes are available for functions
(@pxref{Function Attributes}), labels (@pxref{Label Attributes}),
-enumerators (@pxref{Enumerator Attributes}), and for types
-(@pxref{Type Attributes}).
+enumerators (@pxref{Enumerator Attributes}), statements
+(@pxref{Statement Attributes}), and for types (@pxref{Type Attributes}).
Other front ends might define more attributes
(@pxref{C++ Extensions,,Extensions to the C++ Language}).
@@ -6318,7 +6320,8 @@ attributes of types. Some type attributes apply only to @code{struct}
and @code{union} types, while others can apply to any type defined
via a @code{typedef} declaration. Other attributes are defined for
functions (@pxref{Function Attributes}), labels (@pxref{Label
-Attributes}), enumerators (@pxref{Enumerator Attributes}), and for
+Attributes}), enumerators (@pxref{Enumerator Attributes}),
+statements (@pxref{Statement Attributes}), and for
variables (@pxref{Variable Attributes}).
The @code{__attribute__} keyword is followed by an attribute specification
@@ -6828,7 +6831,8 @@ GCC allows attributes to be set on C labels. @xref{Attribute Syntax}, for
details of the exact syntax for using attributes. Other attributes are
available for functions (@pxref{Function Attributes}), variables
(@pxref{Variable Attributes}), enumerators (@pxref{Enumerator Attributes}),
-and for types (@pxref{Type Attributes}).
+statements (@pxref{Statement Attributes}), and for types
+(@pxref{Type Attributes}).
This example uses the @code{cold} label attribute to indicate the
@code{ErrorHandling} branch is unlikely to be taken and that the
@@ -6881,8 +6885,8 @@ with computed goto or @code{asm goto}.
GCC allows attributes to be set on enumerators. @xref{Attribute Syntax}, for
details of the exact syntax for using attributes. Other attributes are
available for functions (@pxref{Function Attributes}), variables
-(@pxref{Variable Attributes}), labels (@pxref{Label Attributes}),
-and for types (@pxref{Type Attributes}).
+(@pxref{Variable Attributes}), labels (@pxref{Label Attributes}), statements
+(@pxref{Statement Attributes}), and for types (@pxref{Type Attributes}).
This example uses the @code{deprecated} enumerator attribute to indicate the
@code{oldval} enumerator is deprecated:
@@ -6913,6 +6917,46 @@ do instead. Note that the warnings only occurs for uses.
@end table
+@node Statement Attributes
+@section Statement Attributes
+@cindex Statement Attributes
+
+GCC allows attributes to be set on null statements. @xref{Attribute Syntax},
+for details of the exact syntax for using attributes. Other attributes are
+available for functions (@pxref{Function Attributes}), variables
+(@pxref{Variable Attributes}), labels (@pxref{Label Attributes}), enumerators
+(@pxref{Enumerator Attributes}), and for types (@pxref{Type Attributes}).
+
+This example uses the @code{fallthrough} statement attribute to indicate that
+the @option{-Wimplicit-fallthrough} warning should not be emitted:
+
+@smallexample
+switch (cond)
+ @{
+ case 1:
+ bar (1);
+ __attribute__((fallthrough));
+ case 2:
+ @dots{}
+ @}
+@end smallexample
+
+@table @code
+@item fallthrough
+@cindex @code{fallthrough} statement attribute
+The @code{fallthrough} attribute with a null statement serves as a
+fallthrough statement. It hints to the compiler that a statement
+that falls through to another case label, or user-defined label
+in a switch statement is intentional and thus the
+@option{-Wimplicit-fallthrough} warning must not trigger. The
+fallthrough attribute might appear at most once in each attribute
+list, and might not be mixed with other attributes. It can only
+be used in a switch statement (the compiler will issue an error
+otherwise), after a preceding statement and before a logically
+succeeding case label, or user-defined label.
+
+@end table
+
@node Attribute Syntax
@section Attribute Syntax
@cindex attribute syntax
@@ -6940,6 +6984,8 @@ and enumerated types.
applying to labels.
@xref{Enumerator Attributes}, for details of the semantics of attributes
applying to enumerators.
+@xref{Statement Attributes}, for details of the semantics of attributes
+applying to statements.
An @dfn{attribute specifier} is of the form
@code{__attribute__ ((@var{attribute-list}))}. An @dfn{attribute list}
@@ -7005,6 +7051,10 @@ present. The optional attribute in the enumerator appertains to the
enumeration constant. It is not possible to place the attribute after
the constant expression, if present.
+@subsubheading Statement Attributes
+In GNU C, an attribute specifier list may appear as part of a null
+statement. The attribute goes before the semicolon.
+
@subsubheading Type Attributes
An attribute specifier list may appear as part of a @code{struct},
diff --git gcc/gcc/doc/invoke.texi gcc/gcc/doc/invoke.texi
index 22001f9..29052f3 100644
--- gcc/gcc/doc/invoke.texi
+++ gcc/gcc/doc/invoke.texi
@@ -272,8 +272,8 @@ Objective-C and Objective-C++ Dialects}.
-Wformat-security -Wformat-signedness -Wformat-y2k -Wframe-address @gol
-Wframe-larger-than=@var{len} -Wno-free-nonheap-object -Wjump-misses-init @gol
-Wignored-qualifiers -Wignored-attributes -Wincompatible-pointer-types @gol
--Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
--Winit-self -Winline -Wno-int-conversion @gol
+-Wimplicit -Wimplicit-fallthrough -Wimplicit-function-declaration @gol
+-Wimplicit-int -Winit-self -Winline -Wno-int-conversion @gol
-Wno-int-to-pointer-cast -Winvalid-memory-model -Wno-invalid-offsetof @gol
-Winvalid-pch -Wlarger-than=@var{len} @gol
-Wlogical-op -Wlogical-not-parentheses -Wlong-long @gol
@@ -3653,6 +3653,7 @@ name is still supported, but the newer name is more descriptive.)
@gccoptlist{-Wclobbered @gol
-Wempty-body @gol
-Wignored-qualifiers @gol
+-Wimplicit-fallthrough @gol
-Wmissing-field-initializers @gol
-Wmissing-parameter-type @r{(C only)} @gol
-Wold-style-declaration @r{(C only)} @gol
@@ -3939,6 +3940,91 @@ enabled by default and it is made into an error by
Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
This warning is enabled by @option{-Wall}.
+@item -Wimplicit-fallthrough
+@opindex Wimplicit-fallthrough
+@opindex Wno-implicit-fallthrough
+Warn when a switch case falls through. For example:
+
+@smallexample
+@group
+switch (cond)
+ @{
+ case 1:
+ a = 1;
+ break;
+ case 2:
+ a = 2;
+ case 3:
+ a = 3;
+ break;
+ @}
+@end group
+@end smallexample
+
+This warning does not warn when the last statement of a case cannot
+fall through, e.g. when there is a return statement of a function
+declared with the noreturn attribute. @option{-Wimplicit-fallthrough}
+also takes into account control flow statements, such as ifs, and only
+warns when appropriate. E.g.@:
+
+@smallexample
+@group
+switch (cond)
+ @{
+ case 1:
+ if (i > 3) @{
+ bar (5);
+ break;
+ @} else if (i < 1) @{
+ bar (0);
+ @} else
+ return;
+ default:
+ @dots{}
+ @}
+@end group
+@end smallexample
+
+Since there are occasions where a switch case fall through is desirable,
+GCC provides an attribute, @code{__attribute__ ((fallthrough))}, that is
+to be used along with a null statement to suppress this warning that
+would normally occur:
+
+@smallexample
+@group
+switch (cond)
+ @{
+ case 1:
+ bar (0);
+ __attribute__ ((fallthrough));
+ default:
+ @dots{}
+ @}
+@end group
+@end smallexample
+
+C++17 provides a standard way to suppress the @option{-Wimplicit-fallthrough}
+warning using @code{[[fallthrough]];} instead of the GNU attribute. In C++11
+or C++14 users can use @code{[[gnu::fallthrough]];}, which is a GNU extension.
+Instead of the these attributes, it is also possible to add a "falls through"
+comment to silence the warning. GCC accepts wide range of such comments, so
+e.g. all of "Falls through.", "fallthru", "FALLS-THROUGH" work.
+
+@smallexample
+@group
+switch (cond)
+ @{
+ case 1:
+ bar (0);
+ /* FALLTHRU */
+ default:
+ @dots{}
+ @}
+@end group
+@end smallexample
+
+This warning is enabled by @option{-Wextra}.
+
@item -Wignored-qualifiers @r{(C and C++ only)}
@opindex Wignored-qualifiers
@opindex Wno-ignored-qualifiers
diff --git gcc/gcc/gimple.h gcc/gcc/gimple.h
index 980bdf8..9fad15b 100644
--- gcc/gcc/gimple.h
+++ gcc/gcc/gimple.h
@@ -2921,6 +2921,16 @@ gimple_call_internal_unique_p (const gimple *gs)
return gimple_call_internal_unique_p (gc);
}
+/* Return true if GS is an internal function FN. */
+
+static inline bool
+gimple_call_internal_p (const gimple *gs, internal_fn fn)
+{
+ return (is_gimple_call (gs)
+ && gimple_call_internal_p (gs)
+ && gimple_call_internal_fn (gs) == fn);
+}
+
/* If CTRL_ALTERING_P is true, mark GIMPLE_CALL S to be a stmt
that could alter control flow. */
diff --git gcc/gcc/gimplify.c gcc/gcc/gimplify.c
index fb27dd0..7529fb2 100644
--- gcc/gcc/gimplify.c
+++ gcc/gcc/gimplify.c
@@ -160,6 +160,7 @@ struct gimplify_ctx
unsigned in_cleanup_point_expr : 1;
unsigned keep_stack : 1;
unsigned save_stack : 1;
+ unsigned in_switch_expr : 1;
};
struct gimplify_omp_ctx
@@ -1626,6 +1627,338 @@ maybe_warn_switch_unreachable (gimple_seq seq)
}
}
+
+/* A label entry that pairs label and a location. */
+struct label_entry
+{
+ tree label;
+ location_t loc;
+};
+
+/* Find LABEL in vector of label entries VEC. */
+
+static struct label_entry *
+find_label_entry (const auto_vec <struct label_entry> *vec, tree label)
+{
+ unsigned int i;
+ struct label_entry *l;
+
+ FOR_EACH_VEC_ELT (*vec, i, l)
+ if (l->label == label)
+ return l;
+ return NULL;
+}
+
+/* Find the last statement in a scope STMT. */
+
+static gimple *
+last_stmt_in_scope (gimple *stmt)
+{
+ if (!stmt)
+ return NULL;
+
+ switch (gimple_code (stmt))
+ {
+ case GIMPLE_BIND:
+ {
+ gbind *bind = as_a <gbind *> (stmt);
+ return last_stmt_in_scope (
+ gimple_seq_last_stmt (gimple_bind_body (bind)));
+ }
+
+ case GIMPLE_TRY:
+ {
+ gtry *try_stmt = as_a <gtry *> (stmt);
+ return last_stmt_in_scope (
+ gimple_seq_last_stmt (gimple_try_eval (try_stmt)));
+ }
+
+ default:
+ return stmt;
+ }
+}
+
+/* Callback for walk_gimple_seq. */
+
+static tree
+warn_implicit_fallthrough_r (gimple_stmt_iterator *gsi_p, bool *handled_ops_p,
+ struct walk_stmt_info *)
+{
+ gimple *stmt = gsi_stmt (*gsi_p);
+
+ *handled_ops_p = true;
+ switch (gimple_code (stmt))
+ {
+ case GIMPLE_TRY:
+ case GIMPLE_BIND:
+ case GIMPLE_CATCH:
+ case GIMPLE_EH_FILTER:
+ case GIMPLE_TRANSACTION:
+ /* Walk the sub-statements. */
+ *handled_ops_p = false;
+ break;
+
+ /* Find a sequence of form:
+
+ GIMPLE_LABEL
+ [...]
+ <may fallthru stmt>
+ GIMPLE_LABEL
+
+ and possibly warn. */
+ case GIMPLE_LABEL:
+ {
+ /* Found a label. Skip all immediately following labels. */
+ while (!gsi_end_p (*gsi_p)
+ && gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_LABEL)
+ gsi_next (gsi_p);
+
+ /* There might be no more statements. */
+ if (gsi_end_p (*gsi_p))
+ return integer_zero_node;
+
+ /* Next statements, if any, are non-label. */
+ gimple *prev = NULL;
+ /* Vector of labels that fall through. */
+ auto_vec <struct label_entry> labels;
+
+ do
+ {
+ if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_BIND
+ || gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_TRY)
+ {
+ /* Nested scope. Only look at the last statement of
+ the innermost scope. */
+ location_t bind_loc = gimple_location (gsi_stmt (*gsi_p));
+ gimple *last = last_stmt_in_scope (gsi_stmt (*gsi_p));
+ if (last)
+ {
+ prev = last;
+ /* It might be a label without a location. Use the
+ location of the scope then. */
+ if (!gimple_has_location (prev))
+ gimple_set_location (prev, bind_loc);
+ }
+ gsi_next (gsi_p);
+ continue;
+ }
+ /* If's are tricky. */
+ if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_COND)
+ {
+ gcond *cond_stmt = as_a <gcond *> (gsi_stmt (*gsi_p));
+ tree false_lab = gimple_cond_false_label (cond_stmt);
+ location_t if_loc = gimple_location (cond_stmt);
+
+ /* If we have e.g.
+ if (i > 1) goto <D.2259>; else goto D;
+ we can't do much with the else-branch. */
+ if (!DECL_ARTIFICIAL (false_lab))
+ break;
+
+ /* Go on until the false label, then one step back. */
+ for (; !gsi_end_p (*gsi_p); gsi_next (gsi_p))
+ {
+ stmt = gsi_stmt (*gsi_p);
+ if (gimple_code (stmt) == GIMPLE_LABEL
+ && gimple_label_label (as_a <glabel *> (stmt))
+ == false_lab)
+ break;
+ }
+
+ /* Not found? Oops. */
+ if (gsi_end_p (*gsi_p))
+ break;
+
+ {
+ struct label_entry l = { false_lab, if_loc };
+ labels.safe_push (l);
+ }
+
+ /* Go to the last statement of the then branch. */
+ gsi_prev (gsi_p);
+
+ /* if (i != 0) goto <D.1759>; else goto <D.1760>;
+ <D.1759>:
+ <stmt>;
+ goto <D.1761>;
+ <D.1760>:
+ */
+ if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_GOTO
+ && !gimple_has_location (gsi_stmt (*gsi_p)))
+ {
+ /* Look at the statement before, it might be
+ __attribute__((fallthrough)), in which case don't
+ warn. */
+ gsi_prev (gsi_p);
+ bool fallthru_before_dest
+ = gimple_call_internal_p (gsi_stmt (*gsi_p),
+ IFN_FALLTHROUGH);
+ gsi_next (gsi_p);
+ tree goto_dest = gimple_goto_dest (gsi_stmt (*gsi_p));
+ if (!fallthru_before_dest)
+ {
+ struct label_entry l = { goto_dest, if_loc };
+ labels.safe_push (l);
+ }
+ }
+ /* And move back. */
+ gsi_next (gsi_p);
+ }
+ /* Remember the last statement. Skip labels that are of no
+ interest to us. */
+ if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_LABEL)
+ {
+ tree label
+ = gimple_label_label (as_a <glabel *> (gsi_stmt (*gsi_p)));
+ if (find_label_entry (&labels, label))
+ prev = gsi_stmt (*gsi_p);
+ }
+ else
+ prev = gsi_stmt (*gsi_p);
+ gsi_next (gsi_p);
+ }
+ while (!gsi_end_p (*gsi_p)
+ /* Stop if we find a case or a user-defined label. */
+ && (gimple_code (gsi_stmt (*gsi_p)) != GIMPLE_LABEL
+ || !gimple_has_location (gsi_stmt (*gsi_p))));
+
+ /* There might be no more statements. */
+ if (gsi_end_p (*gsi_p))
+ return integer_zero_node;
+
+ gimple *next = gsi_stmt (*gsi_p);
+ tree label;
+ /* If what follows is a label, then we may have a fallthrough. */
+ if (gimple_code (next) == GIMPLE_LABEL
+ && gimple_has_location (next)
+ && (label = gimple_label_label (as_a <glabel *> (next)))
+ && !FALLTHROUGH_LABEL_P (label)
+ && prev != NULL)
+ {
+ /* Don't warn for terminated branches, i.e. when the subsequent
+ case labels immediately breaks. */
+ gimple_stmt_iterator gsi2 = *gsi_p;
+ bool fallthru_to_break_p = false;
+
+ /* Skip all immediately following labels. */
+ while (!gsi_end_p (gsi2)
+ && gimple_code (gsi_stmt (gsi2)) == GIMPLE_LABEL)
+ gsi_next (&gsi2);
+ /* { ... something; default:; } */
+ if (gsi_end_p (gsi2)
+ /* { ... something; default: break; } or
+ { ... something; default: goto L; } */
+ || gimple_code (gsi_stmt (gsi2)) == GIMPLE_GOTO
+ /* { ... something; default: return; } */
+ || gimple_code (gsi_stmt (gsi2)) == GIMPLE_RETURN)
+ fallthru_to_break_p = true;
+
+ struct label_entry *l;
+ bool warned_p = false;
+ if (fallthru_to_break_p)
+ /* Quiet. */;
+ else if (gimple_code (prev) == GIMPLE_LABEL
+ && (label = gimple_label_label (as_a <glabel *> (prev)))
+ && (l = find_label_entry (&labels, label)))
+ warned_p = warning_at (l->loc, OPT_Wimplicit_fallthrough,
+ "this statement may fall through");
+ else if (!gimple_call_internal_p (prev, IFN_FALLTHROUGH)
+ /* Try to be clever and don't warn when the statement
+ can't actually fall through. */
+ && gimple_stmt_may_fallthru (prev)
+ && gimple_has_location (prev))
+ warned_p = warning_at (gimple_location (prev),
+ OPT_Wimplicit_fallthrough,
+ "this statement may fall through");
+ if (warned_p)
+ {
+ rich_location richloc (line_table, gimple_location (next));
+ richloc.add_fixit_insert (gimple_location (next),
+ "insert '__attribute__ "
+ "((fallthrough));' to silence "
+ "this warning");
+ richloc.add_fixit_insert (gimple_location (next),
+ "insert 'break;' to avoid "
+ "fall-through");
+ inform_at_rich_loc (&richloc, "here");
+ }
+
+ /* So that next warn_implicit_fallthrough_r will start looking for
+ a new sequence starting with this label. */
+ gsi_prev (gsi_p);
+ }
+ }
+ break;
+ default:
+ break;
+ }
+ return NULL_TREE;
+}
+
+/* Warn when a switch case falls through. */
+
+static void
+maybe_warn_implicit_fallthrough (gimple_seq seq)
+{
+ if (!warn_implicit_fallthrough || lang_GNU_Fortran ())
+ return;
+
+ struct walk_stmt_info wi;
+ memset (&wi, 0, sizeof (wi));
+ walk_gimple_seq (seq, warn_implicit_fallthrough_r, NULL, &wi);
+}
+
+/* Callback for walk_gimple_seq. */
+
+static tree
+expand_FALLTHROUGH_r (gimple_stmt_iterator *gsi_p, bool *handled_ops_p,
+ struct walk_stmt_info *)
+{
+ gimple *stmt = gsi_stmt (*gsi_p);
+
+ *handled_ops_p = true;
+ switch (gimple_code (stmt))
+ {
+ case GIMPLE_TRY:
+ case GIMPLE_BIND:
+ case GIMPLE_CATCH:
+ case GIMPLE_EH_FILTER:
+ case GIMPLE_TRANSACTION:
+ /* Walk the sub-statements. */
+ *handled_ops_p = false;
+ break;
+ case GIMPLE_CALL:
+ if (gimple_call_internal_p (stmt, IFN_FALLTHROUGH))
+ {
+ gsi_remove (gsi_p, true);
+ if (gsi_end_p (*gsi_p))
+ return integer_zero_node;
+ else if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_LABEL
+ || (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_GOTO
+ && !gimple_has_location (gsi_stmt (*gsi_p))))
+ /* This usage is OK. */;
+ else
+ warning_at (gimple_location (stmt), 0,
+ "%<__attribute__ ((fallthrough))%> not preceding "
+ "a label");
+ }
+ break;
+ default:
+ break;
+ }
+ return NULL_TREE;
+}
+
+/* Expand all FALLTHROUGH () calls in SEQ. */
+
+static void
+expand_FALLTHROUGH (gimple_seq *seq_p)
+{
+ struct walk_stmt_info wi;
+ memset (&wi, 0, sizeof (wi));
+ walk_gimple_seq_mod (seq_p, expand_FALLTHROUGH_r, NULL, &wi);
+}
+
/* Gimplify a SWITCH_EXPR, and collect the vector of labels it can
branch to. */
@@ -1660,10 +1993,17 @@ gimplify_switch_expr (tree *expr_p, gimple_seq *pre_p)
labels. Save all the things from the switch body to append after. */
saved_labels = gimplify_ctxp->case_labels;
gimplify_ctxp->case_labels.create (8);
+ bool old_in_switch_expr = gimplify_ctxp->in_switch_expr;
+ gimplify_ctxp->in_switch_expr = true;
gimplify_stmt (&SWITCH_BODY (switch_expr), &switch_body_seq);
+ gimplify_ctxp->in_switch_expr = old_in_switch_expr;
maybe_warn_switch_unreachable (switch_body_seq);
+ maybe_warn_implicit_fallthrough (switch_body_seq);
+ /* Only do this for the innermost GIMPLE_SWITCH. */
+ if (!gimplify_ctxp->in_switch_expr)
+ expand_FALLTHROUGH (&switch_body_seq);
labels = gimplify_ctxp->case_labels;
gimplify_ctxp->case_labels = saved_labels;
@@ -1694,6 +2034,21 @@ gimplify_switch_expr (tree *expr_p, gimple_seq *pre_p)
return GS_ALL_DONE;
}
+/* Gimplify the LABEL_EXPR pointed to by EXPR_P. */
+
+static enum gimplify_status
+gimplify_label_expr (tree *expr_p, gimple_seq *pre_p)
+{
+ gcc_assert (decl_function_context (LABEL_EXPR_LABEL (*expr_p))
+ == current_function_decl);
+
+ glabel *label_stmt = gimple_build_label (LABEL_EXPR_LABEL (*expr_p));
+ gimple_set_location (label_stmt, EXPR_LOCATION (*expr_p));
+ gimplify_seq_add_stmt (pre_p, label_stmt);
+
+ return GS_ALL_DONE;
+}
+
/* Gimplify the CASE_LABEL_EXPR pointed to by EXPR_P. */
static enum gimplify_status
@@ -1711,6 +2066,7 @@ gimplify_case_label_expr (tree *expr_p, gimple_seq *pre_p)
break;
label_stmt = gimple_build_label (CASE_LABEL (*expr_p));
+ gimple_set_location (label_stmt, EXPR_LOCATION (*expr_p));
ctxp->case_labels.safe_push (*expr_p);
gimplify_seq_add_stmt (pre_p, label_stmt);
@@ -10704,11 +11060,7 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p,
break;
case LABEL_EXPR:
- ret = GS_ALL_DONE;
- gcc_assert (decl_function_context (LABEL_EXPR_LABEL (*expr_p))
- == current_function_decl);
- gimplify_seq_add_stmt (pre_p,
- gimple_build_label (LABEL_EXPR_LABEL (*expr_p)));
+ ret = gimplify_label_expr (expr_p, pre_p);
break;
case CASE_LABEL_EXPR:
diff --git gcc/gcc/internal-fn.c gcc/gcc/internal-fn.c
index 49f3495..358757f 100644
--- gcc/gcc/internal-fn.c
+++ gcc/gcc/internal-fn.c
@@ -243,6 +243,15 @@ expand_TSAN_FUNC_EXIT (internal_fn, gcall *)
gcc_unreachable ();
}
+/* This should get expanded in the lower pass. */
+
+static void
+expand_FALLTHROUGH (internal_fn, gcall *call)
+{
+ error_at (gimple_location (call),
+ "invalid use of %<__attribute__((fallthrough));%>");
+}
+
/* Helper function for expand_addsub_overflow. Return 1
if ARG interpreted as signed in its precision is known to be always
positive or 2 if ARG is known to be always negative, or 3 if ARG may
diff --git gcc/gcc/internal-fn.def gcc/gcc/internal-fn.def
index 6701cd9..d4fbdb2 100644
--- gcc/gcc/internal-fn.def
+++ gcc/gcc/internal-fn.def
@@ -195,6 +195,9 @@ DEF_INTERNAL_FN (ATOMIC_BIT_TEST_AND_COMPLEMENT, ECF_LEAF | ECF_NOTHROW, NULL)
DEF_INTERNAL_FN (ATOMIC_BIT_TEST_AND_RESET, ECF_LEAF | ECF_NOTHROW, NULL)
DEF_INTERNAL_FN (ATOMIC_COMPARE_EXCHANGE, ECF_LEAF | ECF_NOTHROW, NULL)
+/* To implement [[fallthrough]]. */
+DEF_INTERNAL_FN (FALLTHROUGH, ECF_LEAF | ECF_NOTHROW, NULL)
+
#undef DEF_INTERNAL_INT_FN
#undef DEF_INTERNAL_FLT_FN
#undef DEF_INTERNAL_OPTAB_FN
diff --git gcc/gcc/system.h gcc/gcc/system.h
index 78a7da6..1eba393 100644
--- gcc/gcc/system.h
+++ gcc/gcc/system.h
@@ -746,6 +746,12 @@ extern void fancy_abort (const char *, int, const char *) ATTRIBUTE_NORETURN;
#define gcc_unreachable() (fancy_abort (__FILE__, __LINE__, __FUNCTION__))
#endif
+#if GCC_VERSION >= 7000
+# define gcc_fallthrough() __attribute__((fallthrough))
+#else
+# define gcc_fallthrough()
+#endif
+
#if GCC_VERSION >= 3001
#define STATIC_CONSTANT_P(X) (__builtin_constant_p (X) && (X))
#else
diff --git gcc/gcc/tree-core.h gcc/gcc/tree-core.h
index 6e8595c..fb1cc8f 100644
--- gcc/gcc/tree-core.h
+++ gcc/gcc/tree-core.h
@@ -1043,6 +1043,9 @@ struct GTY(()) tree_base {
TRANSACTION_EXPR_RELAXED in
TRANSACTION_EXPR
+ FALLTHROUGH_LABEL_P in
+ LABEL_DECL
+
private_flag:
TREE_PRIVATE in
diff --git gcc/gcc/tree.h gcc/gcc/tree.h
index e2ffabf..52c584f 100644
--- gcc/gcc/tree.h
+++ gcc/gcc/tree.h
@@ -771,6 +771,11 @@ extern void omp_clause_range_check_failed (const_tree, const char *, int,
computed gotos. */
#define FORCED_LABEL(NODE) (LABEL_DECL_CHECK (NODE)->base.side_effects_flag)
+/* Whether a case or a user-defined label is allowed to fall through to.
+ This is used to implement -Wimplicit-fallthrough. */
+#define FALLTHROUGH_LABEL_P(NODE) \
+ (LABEL_DECL_CHECK (NODE)->base.public_flag)
+
/* Nonzero means this expression is volatile in the C sense:
its address should be of type `volatile WHATEVER *'.
In other words, the declared item is volatile qualified.
diff --git gcc/libcpp/include/cpplib.h gcc/libcpp/include/cpplib.h
index 543f3b9..550318a 100644
--- gcc/libcpp/include/cpplib.h
+++ gcc/libcpp/include/cpplib.h
@@ -185,7 +185,8 @@ struct GTY(()) cpp_string {
#define STRINGIFY_ARG (1 << 2) /* If macro argument to be stringified. */
#define PASTE_LEFT (1 << 3) /* If on LHS of a ## operator. */
#define NAMED_OP (1 << 4) /* C++ named operators. */
-#define NO_EXPAND (1 << 5) /* Do not macro-expand this token. */
+#define PREV_FALLTHROUGH (1 << 5) /* On a token preceeded by FALLTHROUGH
+ comment. */
#define BOL (1 << 6) /* Token at beginning of line. */
#define PURE_ZERO (1 << 7) /* Single 0 digit, used by the C++ frontend,
set in c-lex.c. */
@@ -193,6 +194,7 @@ struct GTY(()) cpp_string {
#define SP_PREV_WHITE (1 << 9) /* If whitespace before a ##
operator, or before this token
after a # operator. */
+#define NO_EXPAND (1 << 10) /* Do not macro-expand this token. */
/* Specify which field, if any, of the cpp_token union is used. */
diff --git gcc/libcpp/lex.c gcc/libcpp/lex.c
index 236418d..a806e6c 100644
--- gcc/libcpp/lex.c
+++ gcc/libcpp/lex.c
@@ -2031,6 +2031,94 @@ save_comment (cpp_reader *pfile, cpp_token *token, const unsigned char *from,
store_comment (pfile, token);
}
+/* Returns true if comment at COMMENT_START is a recognized FALLTHROUGH
+ comment. */
+
+static bool
+fallthrough_comment_p (cpp_reader *pfile, const unsigned char *comment_start)
+{
+ const unsigned char *from = comment_start + 1;
+ /* Whole comment contents:
+ -fallthrough
+ @fallthrough@
+ */
+ if (*from == '-' || *from == '@')
+ {
+ size_t l = sizeof "fallthrough" - 1;
+ if ((size_t) (pfile->buffer->cur - from - 1) < l)
+ return false;
+ if (memcmp (from + 1, "fallthrough", l))
+ return false;
+ if (*from == '@')
+ {
+ if (from[l + 1] != '@')
+ return false;
+ l++;
+ }
+ from += 1 + l;
+ }
+ /* Whole comment contents (regex):
+ [ \t]*FALL(S | |-)?THR(OUGH|U)\.?[ \t]*
+ [ \t]*Fall(s | |-)?[Tt]hr(ough|u)\.?[ \t]*
+ [ \t]*fall(s | |-)?thr(ough|u)\.?[ \t]*
+ */
+ else
+ {
+ while (*from == ' ' || *from == '\t')
+ from++;
+ unsigned char f = *from;
+ if (f != 'F' && f != 'f')
+ return false;
+ if ((size_t) (pfile->buffer->cur - from) < sizeof "fallthrough")
+ return false;
+ bool all_upper = false;
+ if (f == 'F' && memcmp (from + 1, "ALL", sizeof "ALL" - 1) == 0)
+ all_upper = true;
+ else if (memcmp (from + 1, "all", sizeof "all" - 1))
+ return false;
+ if (from[sizeof "fall" - 1] == (all_upper ? 'S' : 's')
+ && from[sizeof "falls" - 1] == ' ')
+ from += sizeof "falls " - 1;
+ else if (from[sizeof "fall" - 1] == ' '
+ || from[sizeof "fall" - 1] == '-')
+ from += sizeof "fall " - 1;
+ else if (from[sizeof "fall" - 1] != (all_upper ? 'T' : 't'))
+ return false;
+ else
+ from += sizeof "fall" - 1;
+ if ((f == 'f' || *from != 'T') && (all_upper || *from != 't'))
+ return false;
+ if ((size_t) (pfile->buffer->cur - from) < sizeof "thru")
+ return false;
+ if (memcmp (from + 1, all_upper ? "HRU" : "hru", sizeof "hru" - 1))
+ {
+ if ((size_t) (pfile->buffer->cur - from) < sizeof "through")
+ return false;
+ if (memcmp (from + 1, all_upper ? "HROUGH" : "hrough",
+ sizeof "hrough" - 1))
+ return false;
+ from += sizeof "through" - 1;
+ }
+ else
+ from += sizeof "thru" - 1;
+ if (*from == '.')
+ from++;
+ while (*from == ' ' || *from == '\t')
+ from++;
+ }
+ /* C block comment. */
+ if (*comment_start == '*')
+ {
+ if (*from != '*' || from[1] != '/')
+ return false;
+ }
+ /* C++ line comment. */
+ else if (*from != '\n')
+ return false;
+
+ return true;
+}
+
/* Allocate COUNT tokens for RUN. */
void
_cpp_init_tokenrun (tokenrun *run, unsigned int count)
@@ -2309,7 +2397,7 @@ _cpp_lex_direct (cpp_reader *pfile)
{
cppchar_t c;
cpp_buffer *buffer;
- const unsigned char *comment_start;
+ const unsigned char *comment_start = NULL;
cpp_token *result = pfile->cur_token++;
fresh_line:
@@ -2336,6 +2424,8 @@ _cpp_lex_direct (cpp_reader *pfile)
}
return result;
}
+ if (buffer != pfile->buffer)
+ comment_start = NULL;
if (!pfile->keep_tokens)
{
pfile->cur_run = &pfile->base_run;
@@ -2442,6 +2532,11 @@ _cpp_lex_direct (cpp_reader *pfile)
result->flags |= NAMED_OP;
result->type = (enum cpp_ttype) result->val.node.node->directive_index;
}
+
+ /* Signal FALLTHROUGH comment followed by another token. */
+ if (comment_start
+ && fallthrough_comment_p (pfile, comment_start))
+ result->flags |= PREV_FALLTHROUGH;
break;
case '\'':
@@ -2533,6 +2628,9 @@ _cpp_lex_direct (cpp_reader *pfile)
goto update_tokens_line;
}
+ if (fallthrough_comment_p (pfile, comment_start))
+ result->flags |= PREV_FALLTHROUGH;
+
/* Save the comment as a token in its own right. */
save_comment (pfile, result, comment_start, c);
break;
Marek