Why does march=native not work on Apple M1?

Clang Frontend Using Clang
#1

Whenever I try to compile any C++ program with march=native on a Macbook with a M1 chip, I get the following error when using clang:

clang: error: the clang compiler does not support '-march=native'

However, it used to work on an older Macbook with an Intel CPU. Does clang not support this architecture (yet)?

clang --version gives:

Apple clang version 12.0.0 (clang-1200.0.32.29)
Target: arm64-apple-darwin20.2.0
#2

I see the same behaviour, and I see that this works with apple clang 13 on x64, so they must have made a decision to not support this (for some reason).

#3

I’m not familiar with the code, or specifics about this, but it looks to me like this special case of native just isn’t implemented for arm64 like it is for x86_64. Here’s the x86_64 handling

And the relevant arm64 handling happens here llvm-project/AArch64.cpp at 4465c299069f3ff5b93ba648edf699faf7f39e79 · llvm/llvm-project · GitHub

Which ends up checking what you pass against this switch llvm-project/AArch64TargetParser.cpp at 4465c299069f3ff5b93ba648edf699faf7f39e79 · llvm/llvm-project · GitHub

You could probably submit a change handling native if you have a good use case and I imagine some more folks might see it

#4

I submitted ⚙ D119788 [AArch64] Add support for -march=native for Apple M1 CPU for this