On Tue, 5 Dec 2023 11:19:00 GMT, Magnus Ihse Bursie <i...@openjdk.org> wrote:
>> Hi Marcus (@magicus), please see the updated code which added guards to
>> check for GCC version >= 7.5 in
>> `src/java.base/linux/native/libsimdsort/{avx2-linux-qsort.cpp,
>> avx512-linux-qsort.cpp}`. GCC >= 7.5 is needed to compile libsimdsort using
>> C++17 features. Made sure that OpenJDK builds without errors using both GCC
>> 7.5 and GCC 6.4.
>
> That sounds weird. You can't check for if compiler options should be enabled
> or not inside source code files.
>
> Are you saying that when compiling with GCC 6, it will just silently ignore
> `-std=c++17`? I'd have assumed that it printed a warning or error about an
> unknown or invalid option, if C++17 is not supported.
Hi Magnus (@magicus),
> Are you saying that when compiling with GCC 6, it will just silently ignore
> `-std=c++17`? I'd have assumed that it printed a warning or error about an
> unknown or invalid option, if C++17 is not supported.
The GCC complier for versions 6 (and even 5) silently ignores the flag
`-std=c++17`. It does not print any warning or error. I tested it with a toy
C++ program and also by building OpenJDK using GCC 6.
> You can't check for if compiler options should be enabled or not inside
> source code files.
what I meant was, there are #ifdef guards using predefined macros in the C++
source code to check for GCC version and make the simdsort code available for
compilation or not based on the GCC version
// src/java.base/linux/native/libsimdsort/simdsort-support.hpp
#if defined(_LP64) && (defined(__GNUC__) && ((__GNUC__ > 7) || ((__GNUC__ == 7)
&& (__GNUC_MINOR__ >= 5))))
#define __SIMDSORT_SUPPORTED_LINUX
#endif
//src/java.base/linux/native/libsimdsort/avx2-linux-qsort.cpp
#include "simdsort-support.hpp"
#ifdef __SIMDSORT_SUPPORTED_LINUX
<simdsort functions>
#endif
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PR Review Comment: https://git.openjdk.org/jdk/pull/16534#discussion_r1416037340
