diff options
author | Laurent Pinchart <laurent.pinchart@ideasonboard.com> | 2023-05-01 05:57:11 +0300 |
---|---|---|
committer | Kieran Bingham <kieran.bingham@ideasonboard.com> | 2023-05-01 11:17:36 +0100 |
commit | af7d6a4c2df6c836ecc704ea44b39ea07418d832 (patch) | |
tree | 21c24709f04e6879909cafb5b3a0fc8f368185d1 | |
parent | 36435e2aeac66dcba3255c62622154579cc38cd4 (diff) |
meson: Ignore -Wredundant-move with gcc-13 and newer
Starting from 13.1, gcc implements the C++23 version of automatic move
from local variables in return statements (see
https://en.cppreference.com/w/cpp/language/return). As a result, some
previously required explicit `std::move()` in return statements generate
warnings. This is the case when a function returns an object whose type
is a class derived from the class type the function returns:
struct U { };
struct T : U { };
U f()
{
T t;
return t;
}
Up to C++20, the automatic move from local variables selects the move
constructor of class U, which is not the move constructor of the
expression. Overload resolution is then performed a second time, with t
considered as an lvalue. An explicit `std::move(t)` is needed in the
return statement to select the U move constructor.
Starting from C++23, `t` is treated as an xvalue, and the U move
constructor is selected without the need for an explicit `std::move(t)`.
An explicit `std:move()` then generates a redundant-move warning, as in
the valueOrTuple() function in src/py/libcamera/py_helpers.cpp.
Omitting the `std::move()` silences the warning, but selects the copy
constructor of U with older gcc versions and with clang, which
negatively impacts performance.
The easiest fix is to disable the warning. With -Wpessimizing-move
enabled, the compiler will still warn of pessimizing moves, only the
redundant but not pessimizing moves will be ignored.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
-rw-r--r-- | meson.build | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/meson.build b/meson.build index 8628e6ac..6e363a90 100644 --- a/meson.build +++ b/meson.build @@ -136,6 +136,21 @@ if cc.get_id() == 'gcc' ] endif + # gcc 13 implements the C++23 version of automatic move from local + # variables in return statements (see + # https://en.cppreference.com/w/cpp/language/return). As a result, some + # previously required explicit std::move() in return statements generate + # warnings. Those moves can't be removed as older compiler versions could + # use copy constructors instead of move constructors. The easiest fix is to + # disable the warning. With -Wpessimizing-move enabled, the compiler will + # still warn of pessimizing moves, only the redundant but not pessimizing + # moves will be ignored. + if cc.version().version_compare('>=13') + cpp_arguments += [ + '-Wno-redundant-move', + ] + endif + # gcc 7.1 introduced processor-specific ABI breakages related to parameter # passing on ARM platforms. This generates a large number of messages # during compilation. Silence them. |