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/AArch64 machines. ------------- Commit messages: - 8258010: Debug build failure with clang-10 due to -Wdeprecated-copy and -Wimplicit-int-float-conversion Changes: https://git.openjdk.java.net/jdk/pull/1874/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1874&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8258010 Stats: 6 lines in 2 files changed: 5 ins; 0 del; 1 mod Patch: https://git.openjdk.java.net/jdk/pull/1874.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/1874/head:pull/1874 PR: https://git.openjdk.java.net/jdk/pull/1874
