I am porting a project from x86 to ARM64 and I have been struggling with poor performance for some time. Recently I tested switching from GCC to LLVM. To my surprise, I got a massive performance boost. In some cases code execution is several times faster. I experimented with all sorts of optimization flags but I can't get GCC to generate fast enough code. I suspect that vectorization doesn't work. When I compile a random source code file with the --verbose flag, LLVM reports +neon while GCC doesn't report SIMD features. I tried on different ARM64 cores and operating systems and the result is the same.
Any suggestions on how to enable vectorization with GCC on ARM64?
Somehow this has to do with the combination of ARM64 + Linux. GCC performs better than Clang on Intel and AMD hardware. I tested it on Apple M1 under macOS - GCC was significantly better.Ignore this. I tested single-threaded on M1.