[llvm] [BOLT] Add profile format documentation (PR #186685)

[Amir Ayupov via llvm-commits]

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@@ -0,0 +1,212 @@
+# BOLT Profile Formats
+
+BOLT accepts profile data in several formats. This document describes each
+format, how to generate it, and how BOLT consumes it.
+
+The general recommended workflow is to convert unsymbolized profiles (perf.data
+or pre-aggregated) into symbolized (fdata or YAML):
+
+```
+$ perf2bolt executable \
+# perf.data is consumed directly:
+  -p perf.data
+# OR pre-aggregated requires `--pa` switch:
+  -p preagg --pa
+# fdata is the default output format, OR YAML is emitted using `-w` flag:
+  -o perf.fdata [-w perf.yaml]
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aaupov wrote:

Correct. Let me rephrase this snippet

https://github.com/llvm/llvm-project/pull/186685