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[Docs][llvm-exegesis] Clarify AArch64 support #114989

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Nov 7, 2024
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[Docs][llvm-exegesis] Clarify AArch64 support #114989

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21 changes: 16 additions & 5 deletions llvm/docs/CommandGuide/llvm-exegesis.rst
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Expand Up @@ -33,11 +33,22 @@ snippets.
SUPPORTED PLATFORMS
-------------------

:program:`llvm-exegesis` currently only supports X86 (64-bit only), ARM (AArch64
only), MIPS, and PowerPC (PowerPC64LE only) on Linux for benchmarking. Not all
benchmarking functionality is guaranteed to work on every platform.
:program:`llvm-exegesis` also has a separate analysis mode that is supported
on every platform that LLVM is.
:program:`llvm-exegesis` currently only supports X86 (64-bit only), ARM
(AArch64 only, snippet generation is sparse), MIPS, and PowerPC (PowerPC64LE
only) on Linux for benchmarking. Not all benchmarking functionality is
guaranteed to work on every platform. :program:`llvm-exegesis` also has a
separate analysis mode that is supported on every platform that LLVM is.

To enable benchmarking in llvm-exegesis, LLVM must be configured and built with
`LLVM_ENABLE_LIBPFM` enabled, as :program:`llvm-exegesis` depends on libpfm4
for accessing performance counters. Benchmarking may fail if the target CPU is
unsupported by libpfm. This can be verified by setting `LIBPFM_VERBOSE` and
`LIBPFM_DEBUG` environment variables to enable verbose or debug mode for
libpfm. If libpfm is installed in a non-standard directory, LLVM can be
configured to locate the necessary library and header files by setting
`LIBRARY_PATH`, `C_INCLUDE_PATH`, and `CPLUS_INCLUDE_PATH` environment
variables. Additionally, `LD_LIBRARY_PATH` should be set so that
:program:`llvm-exegesis` can locate the libpfm library during execution.

SNIPPET ANNOTATIONS
-------------------
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7 changes: 4 additions & 3 deletions llvm/tools/llvm-exegesis/README.md
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Expand Up @@ -13,8 +13,8 @@ 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.
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
Expand All @@ -28,7 +28,8 @@ architectures:
* 64-bit only due to this being the only implemented calling convention
in `llvm-exegesis` currently.
* ARM
* AArch64 only
* 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)

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