[PATCH] c++: Change the default dialect to C++17.
Marek Polacek
polacek@redhat.com
Sat May 16 22:34:14 GMT 2020
Since GCC 9, C++17 support is no longer experimental. It was too late
to change the default C++ dialect to C++17 in GCC 10, but I think now
it's time to pull the trigger (C++14 was made the default in GCC 6.1).
We're still missing two C++17 library features, but that shouldn't stop
us. See
<https://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html#status.iso.2017>
and
<https://gcc.gnu.org/projects/cxx-status.html#cxx17>
for the C++17 status.
I won't list all C++17 features here, but just a few heads-up:
- trigraphs were removed (hardly anyone cares, unless your keyboard is
missing the # key),
- operator++(bool) was removed (so some tests now run in C++14 and down
only),
- the keyword register was removed (some legacy code might trip on
this),
- noexcept specification is now part of the type system and C++17 does
not allow dynamic exception specifications anymore (the empty throw
specification is still available, but it is deprecated),
- the evaluation order rules are different in C++17,
- static constexpr data members are now implicitly inline (which makes
them definitions),
- C++17 requires guaranteed copy elision, meaning that a copy/move
constructor call might be elided completely. That means that if
something relied on a constructor being instantiated via e.g. copying
a function parameter, it might now fail.
Jakub, the last point is actually what I encountered in for-27.C and it
looks like an OpenMP issue, in that it wrongly depends on an implicit
instantiation. Am I mistaken?
Due to the 'register' removal, this patch depends on the regenerated
cfns.h version I posted earlier today.
I'll post an update for cxx-status.html and add a new caveat to changes.html
once this is in.
Bootstrapped/regtested on x86_64-pc-linux-gnu, aarch64-unknown-linux-gnu,
and powerpc64le-unknown-linux-gnu. Ok for trunk?
* doc/invoke.texi (C Dialect Options): Adjust -std default for C++.
* doc/standards.texi (C Language): Correct the default dialect.
(C++ Language): Update the default for C++ to gnu++17.
* c-opts.c (c_common_init_options): Default to gnu++17.
* c-c++-common/torture/vector-subscript-3.c: Remove the register
keywords.
* g++.dg/cpp1z/attributes-enum-1a.C: Update for C++17.
* g++.dg/cpp1z/fold7a.C: Likewise.
* g++.dg/cpp1z/nontype3a.C: Likewise.
* g++.dg/cpp1z/utf8-2a.C: Likewise.
* g++.dg/parse/error11.C: Use c++14_down.
* g++.dg/torture/pr34850.C: Add -Wno-attribute-warning.
* g++.dg/torture/pr49394.C: Add dg-warning.
* g++.dg/torture/pr82154.C: Use -std=c++14.
* g++.dg/ubsan/pr85029.C: Use -Wno-register.
* g++.dg/ubsan/vptr-12.C: Use -fstrong-eval-order=some.
* lib/target-supports.exp: Set to C++17.
* obj-c++.dg/try-catch-9.mm: Use -Wno-register.
* testsuite/libgomp.c++/atomic-3.C: Use -std=gnu++14.
* testsuite/libgomp.c++/for-27.C: Explicitly instantiate the
copy constructor for I<int>.
---
gcc/c-family/c-opts.c | 4 ++--
gcc/doc/invoke.texi | 2 +-
gcc/doc/standards.texi | 4 ++--
gcc/testsuite/c-c++-common/torture/vector-subscript-3.c | 6 +++---
gcc/testsuite/g++.dg/cpp1z/attributes-enum-1a.C | 4 ++--
gcc/testsuite/g++.dg/cpp1z/fold7a.C | 4 ++--
gcc/testsuite/g++.dg/cpp1z/nontype3a.C | 4 ++--
gcc/testsuite/g++.dg/cpp1z/utf8-2a.C | 4 ++--
gcc/testsuite/g++.dg/parse/error11.C | 5 +++--
gcc/testsuite/g++.dg/torture/pr34850.C | 2 +-
gcc/testsuite/g++.dg/torture/pr49394.C | 2 +-
gcc/testsuite/g++.dg/torture/pr82154.C | 3 ++-
gcc/testsuite/g++.dg/ubsan/pr85029.C | 2 +-
gcc/testsuite/g++.dg/ubsan/vptr-12.C | 2 +-
gcc/testsuite/lib/target-supports.exp | 2 +-
gcc/testsuite/obj-c++.dg/try-catch-9.mm | 2 +-
libgomp/testsuite/libgomp.c++/atomic-3.C | 3 ++-
libgomp/testsuite/libgomp.c++/for-27.C | 6 ++++++
18 files changed, 35 insertions(+), 26 deletions(-)
diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
index 7695e88c130..5b266c06f3b 100644
--- a/gcc/c-family/c-opts.c
+++ b/gcc/c-family/c-opts.c
@@ -256,9 +256,9 @@ c_common_init_options (unsigned int decoded_options_count,
}
}
- /* Set C++ standard to C++14 if not specified on the command line. */
+ /* Set C++ standard to C++17 if not specified on the command line. */
if (c_dialect_cxx ())
- set_std_cxx14 (/*ISO*/false);
+ set_std_cxx17 (/*ISO*/false);
global_dc->colorize_source_p = true;
}
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 850aeac033d..97e13421323 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -2057,7 +2057,6 @@ The name @samp{c++1y} is deprecated.
@item gnu++14
@itemx gnu++1y
GNU dialect of @option{-std=c++14}.
-This is the default for C++ code.
The name @samp{gnu++1y} is deprecated.
@item c++17
@@ -2068,6 +2067,7 @@ The name @samp{c++1z} is deprecated.
@item gnu++17
@itemx gnu++1z
GNU dialect of @option{-std=c++17}.
+This is the default for C++ code.
The name @samp{gnu++1z} is deprecated.
@item c++20
diff --git a/gcc/doc/standards.texi b/gcc/doc/standards.texi
index f39d8b378f1..fc5016028dd 100644
--- a/gcc/doc/standards.texi
+++ b/gcc/doc/standards.texi
@@ -130,7 +130,7 @@ select an extended version of the C language explicitly with
extensions).
The default, if no C language dialect options are given,
-is @option{-std=gnu11}.
+is @option{-std=gnu17}.
The ISO C standard defines (in clause 4) two classes of conforming
implementation. A @dfn{conforming hosted implementation} supports the
@@ -246,7 +246,7 @@ select an extended version of the C++ language explicitly with
@option{-std=gnu++17} (for C++17 with GNU extensions).
The default, if
-no C++ language dialect options are given, is @option{-std=gnu++14}.
+no C++ language dialect options are given, is @option{-std=gnu++17}.
@section Objective-C and Objective-C++ Languages
@cindex Objective-C
diff --git a/gcc/testsuite/c-c++-common/torture/vector-subscript-3.c b/gcc/testsuite/c-c++-common/torture/vector-subscript-3.c
index bb5c91485d7..12779af5438 100644
--- a/gcc/testsuite/c-c++-common/torture/vector-subscript-3.c
+++ b/gcc/testsuite/c-c++-common/torture/vector-subscript-3.c
@@ -12,9 +12,9 @@ struct vec_s {
int main () {
- register short vector v0 = {1,2,3,4,5,6,7};
- register myvec_t v1 = {1,2,3,4,5,6,7};
- register struct vec_s v2;
+ short vector v0 = {1,2,3,4,5,6,7};
+ myvec_t v1 = {1,2,3,4,5,6,7};
+ struct vec_s v2;
v2.member = v1;
diff --git a/gcc/testsuite/g++.dg/cpp1z/attributes-enum-1a.C b/gcc/testsuite/g++.dg/cpp1z/attributes-enum-1a.C
index aacfac875b1..4d7e547920f 100644
--- a/gcc/testsuite/g++.dg/cpp1z/attributes-enum-1a.C
+++ b/gcc/testsuite/g++.dg/cpp1z/attributes-enum-1a.C
@@ -1,5 +1,5 @@
-// This macro should not be defined without -std=c++17.
+// This macro should be defined with -std=c++17.
-#ifdef __cpp_enumerator_attributes
+#ifndef __cpp_enumerator_attributes
#error __cpp_enumerator_attributes defined
#endif
diff --git a/gcc/testsuite/g++.dg/cpp1z/fold7a.C b/gcc/testsuite/g++.dg/cpp1z/fold7a.C
index 5c782ff0969..530741d3907 100644
--- a/gcc/testsuite/g++.dg/cpp1z/fold7a.C
+++ b/gcc/testsuite/g++.dg/cpp1z/fold7a.C
@@ -1,5 +1,5 @@
-// This macro should not be defined without -std=c++17.
+// This macro should be defined with -std=c++17.
-#ifdef __cpp_fold_expressions
+#ifndef __cpp_fold_expressions
#error __cpp_fold_expressions defined
#endif
diff --git a/gcc/testsuite/g++.dg/cpp1z/nontype3a.C b/gcc/testsuite/g++.dg/cpp1z/nontype3a.C
index a704e5045b6..7b640e551b6 100644
--- a/gcc/testsuite/g++.dg/cpp1z/nontype3a.C
+++ b/gcc/testsuite/g++.dg/cpp1z/nontype3a.C
@@ -1,5 +1,5 @@
-// This macro should not be defined without -std=c++17.
+// This macro should be defined with -std=c++17.
-#ifdef __cpp_nontype_template_args
+#ifndef __cpp_nontype_template_args
#error __cpp_nontype_template_args defined
#endif
diff --git a/gcc/testsuite/g++.dg/cpp1z/utf8-2a.C b/gcc/testsuite/g++.dg/cpp1z/utf8-2a.C
index 0e243d68a75..c4a8f46fb7d 100644
--- a/gcc/testsuite/g++.dg/cpp1z/utf8-2a.C
+++ b/gcc/testsuite/g++.dg/cpp1z/utf8-2a.C
@@ -1,5 +1,5 @@
-// This macro should not be 201411 without -std=c++17.
+// This macro should be 201411 with -std=c++17.
-#if __cpp_unicode_characters == 201411
+#if __cpp_unicode_characters != 201411
#error Wrong value for __cpp_unicode_characters
#endif
diff --git a/gcc/testsuite/g++.dg/parse/error11.C b/gcc/testsuite/g++.dg/parse/error11.C
index 1a49d6edb12..4e2a7f8b75f 100644
--- a/gcc/testsuite/g++.dg/parse/error11.C
+++ b/gcc/testsuite/g++.dg/parse/error11.C
@@ -1,5 +1,6 @@
-// { dg-do compile }
-// { dg-options "-fshow-column" }"
+// { dg-do compile { target c++14_down } }
+// C++17 removed trigraphs.
+// { dg-options "-fshow-column" }
// Origin: Giovanni Bajo <giovannibajo at gcc dot gnu dot org>
// Try to find out when the digraph '<:' is used as a mistake, and parse it
// correctly to avoid cascaded errors.
diff --git a/gcc/testsuite/g++.dg/torture/pr34850.C b/gcc/testsuite/g++.dg/torture/pr34850.C
index c4d808c5a0d..59dd5dfde7d 100644
--- a/gcc/testsuite/g++.dg/torture/pr34850.C
+++ b/gcc/testsuite/g++.dg/torture/pr34850.C
@@ -1,6 +1,6 @@
/* { dg-do compile } */
/* { dg-skip-if "" { *-*-* } { "-O0" } { "" } } */
-/* { dg-options "-ffat-lto-objects -Wno-return-type" } */
+/* { dg-options "-ffat-lto-objects -Wno-return-type -Wno-attribute-warning" } */
typedef unsigned char uint8_t;
typedef unsigned int uint32_t;
diff --git a/gcc/testsuite/g++.dg/torture/pr49394.C b/gcc/testsuite/g++.dg/torture/pr49394.C
index 7bd8fd4dc72..32e1a98ce05 100644
--- a/gcc/testsuite/g++.dg/torture/pr49394.C
+++ b/gcc/testsuite/g++.dg/torture/pr49394.C
@@ -10,7 +10,7 @@ struct Mutex
#endif
{
if (locked)
- throw 0;
+ throw 0; // { dg-warning ".throw. will always call .terminate." "" { target c++17 } }
}
void lock ()
{
diff --git a/gcc/testsuite/g++.dg/torture/pr82154.C b/gcc/testsuite/g++.dg/torture/pr82154.C
index e229c3e640e..698340d8c65 100644
--- a/gcc/testsuite/g++.dg/torture/pr82154.C
+++ b/gcc/testsuite/g++.dg/torture/pr82154.C
@@ -1,5 +1,6 @@
// { dg-do compile }
-// { dg-additional-options "-Wno-deprecated" }
+// { dg-additional-options "-std=c++14 -Wno-deprecated" }
+// C++17 does not allow dynamic exception specification.
namespace a {
int b;
diff --git a/gcc/testsuite/g++.dg/ubsan/pr85029.C b/gcc/testsuite/g++.dg/ubsan/pr85029.C
index 07472af16a5..836ce69cc15 100644
--- a/gcc/testsuite/g++.dg/ubsan/pr85029.C
+++ b/gcc/testsuite/g++.dg/ubsan/pr85029.C
@@ -1,7 +1,7 @@
// PR sanitizer/85029
// { dg-do compile }
// { dg-skip-if "" { *-*-* } { "-flto -fno-fat-lto-objects" } }
-// { dg-options "-fsanitize=undefined" }
+// { dg-options "-fsanitize=undefined -Wno-register" }
struct B {
virtual B bar ();
diff --git a/gcc/testsuite/g++.dg/ubsan/vptr-12.C b/gcc/testsuite/g++.dg/ubsan/vptr-12.C
index f23bbc3fd10..ce57ba87db0 100644
--- a/gcc/testsuite/g++.dg/ubsan/vptr-12.C
+++ b/gcc/testsuite/g++.dg/ubsan/vptr-12.C
@@ -1,6 +1,6 @@
// { dg-do run }
// { dg-shouldfail "ubsan" }
-// { dg-options "-fsanitize=vptr -fno-sanitize-recover=vptr" }
+// { dg-options "-fsanitize=vptr -fno-sanitize-recover=vptr -fstrong-eval-order=some" }
struct MyClass
{
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 3e91a81dd5a..4191600fcd9 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -9018,7 +9018,7 @@ proc check_effective_target_c++ { } {
return 0
}
-set cxx_default "c++14"
+set cxx_default "c++17"
# Check whether the current active language standard supports the features
# of C++11/C++14 by checking for the presence of one of the -std flags.
# This assumes that the default for the compiler is $cxx_default, and that
diff --git a/gcc/testsuite/obj-c++.dg/try-catch-9.mm b/gcc/testsuite/obj-c++.dg/try-catch-9.mm
index 73c7c991709..b2dc61b9989 100644
--- a/gcc/testsuite/obj-c++.dg/try-catch-9.mm
+++ b/gcc/testsuite/obj-c++.dg/try-catch-9.mm
@@ -6,7 +6,7 @@
/* { dg-xfail-run-if "PR23616" { *-*-* } { "-fgnu-runtime" } { "-fnext-runtime" } } */
/* { dg-xfail-if "Needs OBJC2 ABI" { *-*-darwin* && { lp64 && { ! objc2 } } } { "-fnext-runtime" "-fgnu-runtime" } { "" } }
/* { dg-prune-output ".*internal compiler error.*" } */
-/* { dg-options "-fobjc-exceptions -O2" } */
+/* { dg-options "-fobjc-exceptions -O2 -Wno-register" } */
#include "../objc-obj-c++-shared/TestsuiteObject.m"
#include <stdlib.h>
diff --git a/libgomp/testsuite/libgomp.c++/atomic-3.C b/libgomp/testsuite/libgomp.c++/atomic-3.C
index f957b2fece5..c02532d3206 100644
--- a/libgomp/testsuite/libgomp.c++/atomic-3.C
+++ b/libgomp/testsuite/libgomp.c++/atomic-3.C
@@ -1,5 +1,6 @@
// { dg-do run }
-// { dg-options "-Wno-deprecated" }
+// C++17 forbids ++ on bool.
+// { dg-options "-Wno-deprecated -std=gnu++14" }
extern "C" void abort (void);
bool v, x1, x2, x3, x4, x5, x6;
diff --git a/libgomp/testsuite/libgomp.c++/for-27.C b/libgomp/testsuite/libgomp.c++/for-27.C
index 7dca4305f85..d286346e63a 100644
--- a/libgomp/testsuite/libgomp.c++/for-27.C
+++ b/libgomp/testsuite/libgomp.c++/for-27.C
@@ -151,6 +151,12 @@ f4 (const I<int> &x, const I<int> &y)
else if (results[i]) \
abort ()
+// FIXME: OpenMP seems to count on this being instantiated; the copy
+// constructor is called in functions fn2/fn3/fn4. But in C++17 we
+// elide this copy constructor, so it's never been instantiated. For
+// now instantiate it explicitly.
+template I<int>::I(const I<int> &);
+
int
main ()
{
base-commit: f5b461d453043c6b6dda50db0439e4c78b241f03
--
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
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