On Wed, 23 Dec 2020 01:45:58 GMT, Hao Sun <github.com+16932759+shqk...@openjdk.org> wrote:
> 1. '-Wdeprecated-copy' > As specified in C++11 [1], "the generation of the implicitly-defined > copy constructor is deprecated if T has a user-defined destructor or > user-defined copy assignment operator". The rationale behind is the > well-known Rule of Three [2]. > > Introduced since gcc-9 [3] and clang-10 [4], flag '-Wdeprecated-copy' > warns about the C++11 deprecation of implicitly declared copy > constructor and assignment operator if one of them is user-provided. > Defining an explicit copy constructor would suppress this warning. > > The main reason why debug build with gcc-9 or higher succeeds lies in > the inconsistent warning behaviors between gcc and clang. See the > reduced code example [5]. We suspect it might be return value > optimization/copy elision [6] that drives gcc not to declare implicit > copy constructor for this case. > > Note that flag '-Wdeprecated' in clang-8 and clang-9 would also raise > warnings for deprecated defintions of copy constructors. However, > '-Wdeprecated' is not enabled by '-Wall' or '-Wextra'. Hence, clang-8 > and clang-9 are not affected. > > ~~2. '-Wimplicit-int-float-conversion'~~ > ~~Making the conversion explicit would fix it.~~ > > ~~Flag '-Wimplicit-int-float-conversion' is first introduced in clang-10.~~ > ~~Therefore clang-8 and clang-9 are not affected. The flag with similar~~ > ~~functionality in gcc is '-Wfloat-conversion', but it is not enabled by~~ > ~~'-Wall' or '-Wextra'. That's why this warning does not apprear when~~ > ~~building with gcc.~~ > > [1] https://en.cppreference.com/w/cpp/language/copy_constructor > [2] https://en.cppreference.com/w/cpp/language/rule_of_three > [3] https://www.gnu.org/software/gcc/gcc-9/changes.html > [4] https://releases.llvm.org/10.0.0/tools/clang/docs/ReleaseNotes.html > [5] https://godbolt.org/z/err4jM > [6] https://en.wikipedia.org/wiki/Copy_elision#Return_value_optimization > > > Note that we have tested with this patch, debug build succeeded with clang-10 > on Linux X86-64/AArch64 machines. > Note that '--with-extra-cxxflags=-Wno-implicit-int-float-conversion' should > be added when configuration. It's another issue (See JDK-8259288) This pull request has now been integrated. Changeset: 5513f989 Author: Hao Sun <hao....@arm.com> Committer: Ningsheng Jian <nj...@openjdk.org> URL: https://git.openjdk.java.net/jdk/commit/5513f989 Stats: 11 lines in 1 file changed: 8 ins; 1 del; 2 mod 8258010: Debug build failure with clang-10 due to -Wdeprecated-copy Reviewed-by: xliu, kvn, kbarrett ------------- PR: https://git.openjdk.java.net/jdk/pull/1874
