# llvm-exegesis

`llvm-exegesis` is a benchmarking tool that accepts or generates snippets and
can measure characteristics of those snippets 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
  * Very experimental AArch64 support only: most opcodes probably won't work as
    e.g. pseudo instructions and most register classes are not supported.
* MIPS
* PowerPC (PowerPC64LE only)
* RISC-V
  * RV64I/E, RV32I/E and extensions supported by LLVM's RISC-V backend with
    some limitations.

Note that not all 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.
