# llvm-exegesis

`llvm-exegesis` is a benchmarking tool that accepts or assembles a snippet and
can measure characteristics of that snippet by executing it while keeping track
of performance counters.

### Currently Supported Platforms

`llvm-exegesis` is quite platform-dependent and currently only supports a couple
platform configurations for benchmarking. The limitations are listed below.
Analysis mode in `llvm-exegesis` is supported on all platforms on which LLVM is.

#### Currently Supported Operating Systems for Benchmarking

Currently, `llvm-exegesis`  only supports benchmarking on Linux. This is mainly
due to a dependency on the Linux perf subsystem for reading performance
counters.

The subprocess execution mode and memory annotations currently only supports
Linux due to a heavy reliance on many Linux specific syscalls/syscall
implementations.

#### Currently Supported Architectures for Benchmarking

Currently, using `llvm-exegesis` for benchmarking is supported on the following
architectures:
* x86
  * 64-bit only due to this being the only implemented calling convention
    in `llvm-exegesis` currently.
* ARM
  * AArch64 only
* MIPS
* PowerPC (PowerPC64LE only)

Note that not benchmarking functionality is guaranteed to work on all platforms.

Memory annotations are currently only supported on 64-bit X86. There is no
inherent limitations for porting memory annotations to other architectures, but
parts of the test harness are implemented as MCJITed assembly that is generated
in `./lib/X86/Target.cpp` that would need to be implemented on other architectures
to bring up support.