[llvm-dev] GCC 5 and -Wstrict-aliasing in JSON.h

[Leslie Zhai via llvm-dev]

Hi Sam,

Thanks for your response!

Please review it, thanks a lot!

A patch by Loongson!

diff --git a/include/llvm/Support/JSON.h b/include/llvm/Support/JSON.h
index da3c5ea..fd60b40 100644
--- a/include/llvm/Support/JSON.h
+++ b/include/llvm/Support/JSON.h
@@ -452,7 +452,10 @@ private:
      new (reinterpret_cast<T *>(Union.buffer)) T(std::forward<U>(V)...);
    }
    template <typename T> T &as() const {
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wstrict-aliasing"
      return *reinterpret_cast<T *>(Union.buffer);
+#pragma GCC diagnostic pop
    }

    template <typename Indenter>


在 2018年08月09日 19:25, Sam McCall 写道:
> Author of the problematic code here. Thanks everyone, and sorry to 
> have caused difficulty!
>
> Obviously if there really is something illegal here we should fix it 
> in LLVM, but it looks like this warning is a false positive (anyone 
> disagree?)
False positive!

>
> Still if there's a simple source-level workaround, or we can suppress 
> the warning with a #pragma, I'd be happy to do that. GCC 4.9.3 is a 
> supported compiler for LLVM and the more configurations we build 
> cleanly in, the better.
>
> If this is a useful direction, could someone with an affected 
> environment send me a small patch? I don't have the right setup to 
> verify myself.
I test it for mips64el built with gcc-4-branch:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/mips64el-redhat-linux/4.9.3/lto-wrapper
Target: mips64el-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man 
--infodir=/usr/share/info 
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap 
--enable-shared --enable-threads=posix --enable-checking=release 
--enable-multilib --with-system-zlib --enable-__cxa_atexit 
--disable-libunwind-exceptions --enable-gnu-unique-object 
--enable-linker-build-id --with-arch=loongson3a 
--enable-languages=c,c++,objc,obj-c++,fortran,go,lto --enable-plugin 
--disable-libgcj 
--with-isl=/builddir/build/BUILD/gcc-4.9.3/obj-mips64el-redhat-linux/isl-install 
--with-cloog=/builddir/build/BUILD/gcc-4.9.3/obj-mips64el-redhat-linux/cloog-install 
--enable-gnu-indirect-function --with-long-double-128 
--build=mips64el-redhat-linux
Thread model: posix
gcc version 4.9.3 20150626 (Red Hat 4.9.3-8) (GCC)

>
> Cheers, Sam

-- 
Regards,
Leslie Zhai