On Wed, Jul 29, 2020 at 03:30:07PM -0400, Jason Merrill via Gcc-patches wrote:
> On 7/14/20 4:50 AM, Jakub Jelinek wrote:
> > For C++11 we already emit an error if a constexpr function doesn't contain
> > a return statement, because in C++11 that is the only thing it needs to
> > contain, but for C++14 we would normally issue a -Wreturn-type warning.
> >
> > As mentioned by Jonathan, such constexpr functions are invalid, no
> > diagnostics required, because there doesn't exist any arguments for
> > which it would result in valid constant expression.
> >
> > This raises it to an error in such cases. The !LAMBDA_TYPE_P case
> > is to avoid error on g++.dg/pr81194.C where the user didn't write
> > constexpr anywhere and the operator() is compiler generated.
>
> We set DECL_DECLARED_CONSTEXPR_P on lambdas earlier in finish_function if
> suitable; can we move this diagnostic up before that?
That works too. Bootstrapped/regtested on x86_64-linux and i686-linux, ok
for trunk then?
2020-07-31 Jakub Jelinek <ja...@redhat.com>
PR c++/96182
* decl.c (finish_function): In constexpr functions use for C++14 and
later error instead of warning if no return statement is present and
diagnose it regardless of warn_return_type. Move the warn_return_type
diagnostics earlier in the function.
* g++.dg/cpp1y/constexpr-96182.C: New test.
* g++.dg/other/error35.C (S<T>::g()): Add return statement.
* g++.dg/cpp1y/pr63996.C (foo): Likewise.
* g++.dg/cpp1y/constexpr-return2.C (f): Likewise.
* g++.dg/cpp1y/var-templ44.C (make_array): Add throw 1.
--- gcc/cp/decl.c.jj 2020-07-29 11:57:23.340517489 +0200
+++ gcc/cp/decl.c 2020-07-30 20:44:33.634951396 +0200
@@ -17112,6 +17112,51 @@ finish_function (bool inline_p)
DECL_ATTRIBUTES (fndecl)))
omp_declare_variant_finalize (fndecl, attr);
+ /* Complain if there's just no return statement. */
+ if ((warn_return_type
+ || (cxx_dialect >= cxx14
+ && DECL_DECLARED_CONSTEXPR_P (fndecl)))
+ && !VOID_TYPE_P (TREE_TYPE (fntype))
+ && !dependent_type_p (TREE_TYPE (fntype))
+ && !current_function_returns_value && !current_function_returns_null
+ /* Don't complain if we abort or throw. */
+ && !current_function_returns_abnormally
+ /* Don't complain if there's an infinite loop. */
+ && !current_function_infinite_loop
+ /* Don't complain if we are declared noreturn. */
+ && !TREE_THIS_VOLATILE (fndecl)
+ && !DECL_NAME (DECL_RESULT (fndecl))
+ && !TREE_NO_WARNING (fndecl)
+ /* Structor return values (if any) are set by the compiler. */
+ && !DECL_CONSTRUCTOR_P (fndecl)
+ && !DECL_DESTRUCTOR_P (fndecl)
+ && targetm.warn_func_return (fndecl))
+ {
+ gcc_rich_location richloc (input_location);
+ /* Potentially add a "return *this;" fix-it hint for
+ assignment operators. */
+ if (IDENTIFIER_ASSIGN_OP_P (DECL_NAME (fndecl)))
+ {
+ tree valtype = TREE_TYPE (DECL_RESULT (fndecl));
+ if (TREE_CODE (valtype) == REFERENCE_TYPE
+ && current_class_ref
+ && same_type_ignoring_top_level_qualifiers_p
+ (TREE_TYPE (valtype), TREE_TYPE (current_class_ref))
+ && global_dc->option_enabled (OPT_Wreturn_type,
+ global_dc->lang_mask,
+ global_dc->option_state))
+ add_return_star_this_fixit (&richloc, fndecl);
+ }
+ if (cxx_dialect >= cxx14
+ && DECL_DECLARED_CONSTEXPR_P (fndecl))
+ error_at (&richloc, "no return statement in %<constexpr%> function "
+ "returning non-void");
+ else if (warning_at (&richloc, OPT_Wreturn_type,
+ "no return statement in function returning "
+ "non-void"))
+ TREE_NO_WARNING (fndecl) = 1;
+ }
+
/* Lambda closure members are implicitly constexpr if possible. */
if (cxx_dialect >= cxx17
&& LAMBDA_TYPE_P (CP_DECL_CONTEXT (fndecl)))
@@ -17163,44 +17208,6 @@ finish_function (bool inline_p)
to the FUNCTION_DECL node itself. */
BLOCK_SUPERCONTEXT (DECL_INITIAL (fndecl)) = fndecl;
- /* Complain if there's just no return statement. */
- if (warn_return_type
- && !VOID_TYPE_P (TREE_TYPE (fntype))
- && !dependent_type_p (TREE_TYPE (fntype))
- && !current_function_returns_value && !current_function_returns_null
- /* Don't complain if we abort or throw. */
- && !current_function_returns_abnormally
- /* Don't complain if there's an infinite loop. */
- && !current_function_infinite_loop
- /* Don't complain if we are declared noreturn. */
- && !TREE_THIS_VOLATILE (fndecl)
- && !DECL_NAME (DECL_RESULT (fndecl))
- && !TREE_NO_WARNING (fndecl)
- /* Structor return values (if any) are set by the compiler. */
- && !DECL_CONSTRUCTOR_P (fndecl)
- && !DECL_DESTRUCTOR_P (fndecl)
- && targetm.warn_func_return (fndecl))
- {
- gcc_rich_location richloc (input_location);
- /* Potentially add a "return *this;" fix-it hint for
- assignment operators. */
- if (IDENTIFIER_ASSIGN_OP_P (DECL_NAME (fndecl)))
- {
- tree valtype = TREE_TYPE (DECL_RESULT (fndecl));
- if (TREE_CODE (valtype) == REFERENCE_TYPE
- && current_class_ref
- && same_type_ignoring_top_level_qualifiers_p
- (TREE_TYPE (valtype), TREE_TYPE (current_class_ref))
- && global_dc->option_enabled (OPT_Wreturn_type,
- global_dc->lang_mask,
- global_dc->option_state))
- add_return_star_this_fixit (&richloc, fndecl);
- }
- if (warning_at (&richloc, OPT_Wreturn_type,
- "no return statement in function returning non-void"))
- TREE_NO_WARNING (fndecl) = 1;
- }
-
/* Store the end of the function, so that we get good line number
info for the epilogue. */
cfun->function_end_locus = input_location;
--- gcc/testsuite/g++.dg/other/error35.C.jj 2020-01-12 11:54:37.214401324
+0100
+++ gcc/testsuite/g++.dg/other/error35.C 2020-07-13 22:35:55.359228614
+0200
@@ -9,6 +9,6 @@ template <typename> struct S {
enum S<char>::E;
template <typename T> enum S<T>::E : int { b };
template <typename T>
-constexpr int S<T>::g() const { b; } // { dg-error "not declared" }
+constexpr int S<T>::g() const { b; if (false) return 0; } // { dg-error "not
declared" }
static_assert(S<char>().g() == 1, ""); // { dg-error "" }
// { dg-message "in .constexpr. expansion of" "" { target *-*-* } .-1 }
--- gcc/testsuite/g++.dg/cpp1y/pr63996.C.jj 2020-01-12 11:54:37.000000000
+0100
+++ gcc/testsuite/g++.dg/cpp1y/pr63996.C 2020-07-13 22:17:39.034004329
+0200
@@ -5,6 +5,7 @@ constexpr int
foo (int i)
{
int a[i] = { }; // { dg-error "7:ISO C\\+\\+ forbids variable length array
.a" }
+ if (i == 23) return 0;
}
constexpr int j = foo (1); // { dg-error "flows off the end|in .constexpr.
expansion of" }
--- gcc/testsuite/g++.dg/cpp1y/constexpr-96182.C.jj 2020-07-13
19:16:42.742936492 +0200
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-96182.C 2020-07-13
19:16:12.264357640 +0200
@@ -0,0 +1,6 @@
+// PR c++/96182
+// { dg-do compile { target c++11 } }
+
+constexpr int foo () {} // { dg-error "no return statement in 'constexpr'
function returning non-void" "" { target c++14 } }
+// { dg-error "body of 'constexpr' function 'constexpr int foo\\\(\\\)' not a
return-statement" "" { target c++11_only } .-1 }
+// { dg-warning "no return statement in function returning non-void" "" {
target c++11_only } .-2 }
--- gcc/testsuite/g++.dg/cpp1y/constexpr-return2.C.jj 2020-01-12
11:54:37.115402818 +0100
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-return2.C 2020-07-13
22:17:03.582513397 +0200
@@ -3,6 +3,7 @@
constexpr int f (int i)
{
+ if (i == -1) return 0;
}
constexpr int i = f(42); // { dg-error "flows off the end|in .constexpr.
expansion of " }
--- gcc/testsuite/g++.dg/cpp1y/var-templ44.C.jj 2020-01-12 11:54:37.123402697
+0100
+++ gcc/testsuite/g++.dg/cpp1y/var-templ44.C 2020-07-13 22:35:03.322980157
+0200
@@ -26,5 +26,6 @@ constexpr auto make_array()
-> array<conditional_t<is_void_v<_Dest>, common_type_t<>, _Dest>,
sizeof...(_Types)> {
static_assert(__or_<__not_<is_void<_Dest>>, __and_<>>::value, ""); // {
dg-error "static assert" }
+ throw 1;
}
auto d = make_array();
Jakub
