> 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)
Hao Sun has updated the pull request incrementally with one additional commit since the last revision: Split the PR, addressing -Wdeprecated-copy only As suggested by kimbarrett, we should focus on warnings produced by '-Wdeprecated-copy' in this PR. Because JDK-8259288 is a very different problem and might be reviewed by folks from different teams. Will create a new PR to address JDK-8259288. Change-Id: I1b9f434ab6fcdf2763a46870eaed91641984fd76 CustomizedGitHooks: yes ------------- Changes: - all: https://git.openjdk.java.net/jdk/pull/1874/files - new: https://git.openjdk.java.net/jdk/pull/1874/files/d0f5d7d5..4cc18217 Webrevs: - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1874&range=03 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1874&range=02-03 Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 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
