[llvm] [compiler-rt] [docs][IRPGO]Document two binary formats for IRPGO profiles (PR #76105)

[David Li via llvm-commits]

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+=====================
+IRPGO Profile Format
+=====================
+
+.. contents::
+   :local:
+
+
+Overview
+==========
+
+IR-based instrumentation (IRPGO) and its context-sensitive variant (CS-IRPGO)
+inserts `llvm.instrprof.*` `code generator intrinsics <https://llvm.org/docs/LangRef.html#code-generator-intrinsics>`_
+in LLVM IR to generate profiles. This document describes two binary profile
+formats (raw and indexed) used by IR-based instrumentation.
+
+.. note::
+
+  Both the compiler-rt profiling infrastructure and profile format are general
+  and could support other use cases (e.g., coverage and temporal profiling).
+  This document will focus on IRPGO while briefly introducing other use cases
+  with pointers.
+
+Raw PGO Profile Format
+========================
+
+The raw PGO profile is generated by running the instrumented binary. It is a
+memory dump of the profile data.
+
+Two kinds of frequently used profile information are function's basic block
+counters and its (various flavors of) value profiles. A function's profiled
----------------
david-xl wrote:

The profile data for a function can span ..

https://github.com/llvm/llvm-project/pull/76105