[Docs][llvm-exegesis] Specify platform support for different modes

[aidengrossman]

Summary

llvm-exegesis has both a capture mode and an analysis mode that can be
used independently of each other. This patch makes it clear that
analysis mode will work on other platforms that LLVM supports in the
documentation which was unclear before.

[aidengrossman]

Definitely an oversight on my part. Updates documentation on supported platforms (noting the platform support differences between the modes) based on a comment from @RKSimon in D149378.

[courbet]

llvm/docs/CommandGuide/llvm-exegesis.rst

37–40

This is called "benchmarking" elsewhere. Let's use that for consistency.

40

[nit] "on which LLVM is" ?

llvm/tools/llvm-exegesis/README.md

10–11

typo

12

on which

[aidengrossman]

Address reviewer feedback

[courbet]

llvm/tools/llvm-exegesis/README.md

15–17

missing one

31

missing one

llvm/docs/CommandGuide/llvm-exegesis.rst

 
 :program:`llvm-exegesis` can also benchmark arbitrary user-provided code
 snippets.
 
 SUPPORTED PLATFORMS
 -------------------
 
 :program:`llvm-exegesis` currently only supports X86 (64-bit only), ARM (AArch64
-only), MIPS, and PowerPC (PowerPC64LE only) on Linux. Not all functionality is
-guaranteed to work on every platform.
+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 on which LLVM is.
 
 SNIPPET ANNOTATIONS
 -------------------
 
 :program:`llvm-exegesis` supports benchmarking arbitrary snippets of assembly.
 However, benchmarking these snippets often requires some setup so that they
 can execute properly. :program:`llvm-exegesis` has two annotations and some
 additional utilities to help with setup so that snippets can be benchmarked

llvm/tools/llvm-exegesis/README.md

 # 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.
+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
+#### Currently Supported Operating Systems for Benchmarking
 
-Currently, `llvm-exegesis` only supports Linux. This is mainly due to a
-dependency on the Linux perf subsystem for reading performance counters.
+Currently, `llvm-exegesis`  only supports benchmarking on Linux. This is mainly
+due to a dependency on the Linux perf subsystem for reading performance
+counters.
 
-##### Currently Supported Architectures
-
-Currently, `llvm-exegesis` supports the following architectures:
+#### 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 all functionality is guaranteed to work on all architectures.
+Note that not benchmarking functionality is guaranteed to work on all platforms.