RFR: 8341586: RISC-V: build fail with gcc9

[SendaoYan]

On Tue, 8 Oct 2024 12:12:06 GMT, Fei Yang <fyang at openjdk.org> wrote:

> It's strange that I can't reproduce the build warning/error when compiling the following test with g++-9 shipped with Ubuntu 22.04.1 LTS. Do you know why? Or maybe you can try the same g++-9 to see?

I found that, gcc-9.2.0 generate warning on riscv64, and gcc-9.3.0 doesn't generate the warning.

> ./gcc-9.2.0-binary/bin/g++ alignas-test-2.cpp -c -Wall
alignas-test-2.cpp: In function ‘uintptr_t get_addr()’:
alignas-test-2.cpp:4:29: warning: requested alignment 64 is larger than 16 [-Wattributes]
    4 |   alignas(64) char memory[64];
      |                             ^

> ./gcc-9.2.0-binary/bin/g++ -v
Using built-in specs.
COLLECT_GCC=./gcc-9.2.0-binary/bin/g++
COLLECT_LTO_WRAPPER=/home/yansendao/tone/tone-matrix-compiler/csmith/gcc-9.2.0-binary/libexec/gcc/riscv64-unknown-linux-gnu/9.2.0/lto-wrapper
Target: riscv64-unknown-linux-gnu
Configured with: configure --prefix=/home/yansendao/tone/tone-matrix-compiler/csmith/gcc-9.2.0-binary --disable-multilib --enable-languages=c,c++,objc,obj-c++,fortran,lto
Thread model: posix
gcc version 9.2.0 (GCC) 

> ./gcc-9.3.0-binary/bin/g++ alignas-test-2.cpp -c -Wall
> ./gcc-9.3.0-binary/bin/g++ -v
Using built-in specs.
COLLECT_GCC=./gcc-9.3.0-binary/bin/g++
COLLECT_LTO_WRAPPER=/home/yansendao/tone/tone-matrix-compiler/csmith/gcc-9.3.0-binary/libexec/gcc/riscv64-unknown-linux-gnu/9.3.0/lto-wrapper
Target: riscv64-unknown-linux-gnu
Configured with: configure --prefix=/home/yansendao/tone/tone-matrix-compiler/csmith/gcc-9.3.0-binary --disable-multilib --enable-languages=c,c++,objc,obj-c++,fortran,lto
Thread model: posix
gcc version 9.3.0 (GCC)

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PR Comment: https://git.openjdk.org/jdk/pull/21376#issuecomment-2401154174