The resolution of C11 DR#423, apart from doing things with the types
of expressions cast to qualified types which are only in standard
terms observable with _Generic and which agree with how GCC has
implemented _Generic all along, also specifies that qualifiers are
discarded from function return types: "derived-declarator-type-list
function returning T" becomes "derived-declarator-type-list function
returning the unqualified version of T" in the rules giving types for
function declarators. This means that declarations of a function with
both qualified and unqualified return types are now compatible,
similar to how different declarations can vary in whether a function
argument is declared with a qualifier or unqualified type.
This patch implements this resolution. Since the motivation for the
change was _Generic, the resolution is restricted to C11 mode; there's
no reason to consider there to be a defect in this regard in older
standard versions. Some less-obvious issues are handled as follows:
* As usual, and as with function arguments, _Atomic is not considered
a qualifier for this purpose; that is, function declarations must
agree regarding whether the return type is atomic.
* By 6.9.1#2, a function definition cannot return qualified void. But
with this change, specifying "const void" in the declaration
produces the type "function returning void", which is perfectly
valid, so "const void f (void) {}" is no longer an error.
* The application to restrict is less clear. The way I am
interpreting it in this patch is that "unqualified version of T" is
not valid if T is not valid, as in the case where T is a
restrict-qualified version of a type that cannot be restrict
qualified (non-pointer, or pointer-to-function). But it's possible
to argue the other way from the wording.
Bootstrapped with no regressions on x86_64-pc-linux-gnu. Applied to
mainline.
gcc/c:
2016-05-13 Joseph Myers <jos...@codesourcery.com>
* c-decl.c (grokdeclarator): For C11, discard qualifiers on
function return type.
gcc/testsuite:
2016-05-13 Joseph Myers <jos...@codesourcery.com>
* gcc.dg/qual-return-5.c, gcc.dg/qual-return-6.c: New tests.
* gcc.dg/call-diag-2.c, gcc.dg/qual-return-2.c ,
gcc.dg/qual-return-3.c, gcc.dg/qual-return-4.c: Use -std=gnu99.
Index: gcc/c/c-decl.c
===================================================================
--- gcc/c/c-decl.c (revision 236213)
+++ gcc/c/c-decl.c (working copy)
@@ -6106,13 +6106,19 @@ grokdeclarator (const struct c_declarator *declara
qualify the return type, not the function type. */
if (type_quals)
{
+ int quals_used = type_quals;
/* Type qualifiers on a function return type are
normally permitted by the standard but have no
effect, so give a warning at -Wreturn-type.
Qualifiers on a void return type are banned on
function definitions in ISO C; GCC used to used
- them for noreturn functions. */
- if (VOID_TYPE_P (type) && really_funcdef)
+ them for noreturn functions. The resolution of C11
+ DR#423 means qualifiers (other than _Atomic) are
+ actually removed from the return type when
+ determining the function type. */
+ if (flag_isoc11)
+ quals_used &= TYPE_QUAL_ATOMIC;
+ if (quals_used && VOID_TYPE_P (type) && really_funcdef)
pedwarn (loc, 0,
"function definition has qualified void return
type");
else
@@ -6119,7 +6125,16 @@ grokdeclarator (const struct c_declarator *declara
warning_at (loc, OPT_Wignored_qualifiers,
"type qualifiers ignored on function return type");
- type = c_build_qualified_type (type, type_quals);
+ /* Ensure an error for restrict on invalid types; the
+ DR#423 resolution is not entirely clear about
+ this. */
+ if (flag_isoc11
+ && (type_quals & TYPE_QUAL_RESTRICT)
+ && (!POINTER_TYPE_P (type)
+ || !C_TYPE_OBJECT_OR_INCOMPLETE_P (TREE_TYPE (type))))
+ error_at (loc, "invalid use of %<restrict%>");
+ if (quals_used)
+ type = c_build_qualified_type (type, quals_used);
}
type_quals = TYPE_UNQUALIFIED;
Index: gcc/testsuite/gcc.dg/call-diag-2.c
===================================================================
--- gcc/testsuite/gcc.dg/call-diag-2.c (revision 236213)
+++ gcc/testsuite/gcc.dg/call-diag-2.c (working copy)
@@ -1,7 +1,7 @@
/* Test diagnostics for calling function returning qualified void or
other incomplete type other than void. PR 35210. */
/* { dg-do compile } */
-/* { dg-options "-pedantic-errors" } */
+/* { dg-options "-std=gnu99 -pedantic-errors" } */
const void f_cv (void);
struct s f_s (void);
Index: gcc/testsuite/gcc.dg/qual-return-2.c
===================================================================
--- gcc/testsuite/gcc.dg/qual-return-2.c (revision 236213)
+++ gcc/testsuite/gcc.dg/qual-return-2.c (working copy)
@@ -1,7 +1,7 @@
/* Test for warnings for qualified function return types. -pedantic test. */
/* Origin: Joseph Myers <js...@cam.ac.uk> */
/* { dg-do compile } */
-/* { dg-options "-pedantic" } */
+/* { dg-options "-pedantic -std=gnu99" } */
/* Qualifying a function return type makes no sense. */
Index: gcc/testsuite/gcc.dg/qual-return-3.c
===================================================================
--- gcc/testsuite/gcc.dg/qual-return-3.c (revision 236213)
+++ gcc/testsuite/gcc.dg/qual-return-3.c (working copy)
@@ -4,7 +4,7 @@
/* Origin: Joseph Myers <j...@polyomino.org.uk> */
/* { dg-do compile } */
-/* { dg-options "" } */
+/* { dg-options "-std=gnu99" } */
int foo (); /* { dg-message "note: previous declaration" "different
qualifiers" } */
const int foo () { return 0; } /* { dg-error "conflicting types" "different
qualifiers" } */
Index: gcc/testsuite/gcc.dg/qual-return-4.c
===================================================================
--- gcc/testsuite/gcc.dg/qual-return-4.c (revision 236213)
+++ gcc/testsuite/gcc.dg/qual-return-4.c (working copy)
@@ -3,7 +3,7 @@
types, not other such types within the definition. */
/* Origin: Joseph Myers <j...@polyomino.org.uk> */
/* { dg-do compile } */
-/* { dg-options "-pedantic" } */
+/* { dg-options "-pedantic -std=gnu99" } */
volatile void (*y)(int);
Index: gcc/testsuite/gcc.dg/qual-return-5.c
===================================================================
--- gcc/testsuite/gcc.dg/qual-return-5.c (nonexistent)
+++ gcc/testsuite/gcc.dg/qual-return-5.c (working copy)
@@ -0,0 +1,32 @@
+/* Test qualifiers on function return types after DR#423: those
+ qualifiers are now ignored for all purposes (but _Atomic is not,
+ for this purpose, a qualifier). */
+/* { dg-do compile } */
+/* { dg-options "-std=c11 -pedantic-errors" } */
+
+int f1 (void);
+const int f1 (void);
+volatile int f1 (void) { return 0; }
+
+int *restrict f2 (void) { return 0; }
+int *f2 (void);
+
+const volatile long f3 (void);
+long f3 (void);
+
+const volatile void f4 (void) { }
+void f4 (void);
+
+_Atomic int f5 (void); /* { dg-message "previous declaration" } */
+int f5 (void); /* { dg-error "conflicting" } */
+
+int f6 (void); /* { dg-message "previous declaration" } */
+_Atomic int f6 (void) { return 0; } /* { dg-error "conflicting" } */
+
+/* The standard seems unclear regarding the case where restrict is
+ applied to a function return type that may not be
+ restrict-qualified; assume here that it is disallowed. */
+restrict int f7 (void); /* { dg-error "restrict" } */
+
+typedef void FT (void);
+FT *restrict f8 (void); /* { dg-error "restrict" } */
Index: gcc/testsuite/gcc.dg/qual-return-6.c
===================================================================
--- gcc/testsuite/gcc.dg/qual-return-6.c (nonexistent)
+++ gcc/testsuite/gcc.dg/qual-return-6.c (working copy)
@@ -0,0 +1,12 @@
+/* Test qualifiers on function return types after DR#423: those
+ qualifiers are now ignored for all purposes (except that _Atomic
+ still affects the type), but should still get warnings. */
+/* { dg-do compile } */
+/* { dg-options "-std=c11 -Wignored-qualifiers" } */
+
+const int f1 (void); /* { dg-warning "qualifiers ignored" } */
+volatile int f2 (void) { return 0; } /* { dg-warning "qualifiers ignored" } */
+const volatile void f3 (void) { } /* { dg-warning "qualifiers ignored" } */
+const void f4 (void); /* { dg-warning "qualifiers ignored" } */
+_Atomic int f5 (void); /* { dg-warning "qualifiers ignored" } */
+_Atomic int f6 (void) { return 0; } /* { dg-warning "qualifiers ignored" } */
--
Joseph S. Myers
jos...@codesourcery.com
