Performance inspector

[ralfbiedert]

Faster should have a way to hint at performance issues.

From a user's point of view it is hard to predict whether SIMD intrinsics are issued, or a fallback implementation is used. Ideally there should be a method, macro, compiler flag, ... to enable performance metrics or warnings.

In the most simple form, each fallback implementation could call something like fallback!, which in turn could be enabled or disabled with a compile feature. That macro could then emit warnings (maybe even with file names and line numbers).

As a user I could then either change my code, file an issue, or implement the missing intrinsic myself.

[AdamNiederer]

Sounds like a good way to get some drive-by commits from people who know of, say, an SSE2 polyfill for an SSE4 intrinsic, too. I think printing to stderr once per function if a certain feature is enabled is a pretty good way to go about this.

[ralfbiedert]

SIMD never looked this good:

test tests::kernel_i16 ... ok
🚄 faster is using HARDWARE acceleration here (src/arch/x86/intrin/sum.rs:168).
🚄 faster is using HARDWARE acceleration here (src/arch/x86/intrin/upcast.rs:249).
test tests::kernel_i32 ... ok
⛔ faster is using SOFTWARE emulation here (src/arch/x86/intrin/sum.rs:259).
test tests::kernel_i64 ... ok
test tests::kernel_i8 ... ok
⛔ faster is using SOFTWARE emulation here (src/arch/x86/intrin/sum.rs:259).
🚄 faster is using HARDWARE acceleration here (src/arch/x86/intrin/sum.rs:104).
test tests::kernel_u32 ... ok
test tests::kernel_u16 ... ok
test tests::kernel_u8 ... ok
test tests::kernel_u64 ... ok

[AdamNiederer]

Resolved by #52. Thanks a lot!