[docs] Coverage: Document the profile merge pool specifier
llvm-svn: 272604
diff --git a/clang/docs/SourceBasedCodeCoverage.rst b/clang/docs/SourceBasedCodeCoverage.rst
index ff43c93..95b2eb6 100644
--- a/clang/docs/SourceBasedCodeCoverage.rst
+++ b/clang/docs/SourceBasedCodeCoverage.rst
@@ -78,6 +78,14 @@
* "%h" expands out to the hostname of the machine running the program.
+* "%Nm" expands out to the instrumented binary's signature. When this pattern
+ is specified, the runtime creates a pool of N raw profiles which are used for
+ on-line profile merging. The runtime takes care of selecting a raw profile
+ from the pool, locking it, and updating it before the program exits. If N is
+ not specified (i.e the pattern is "%m"), it's assumed that ``N = 1``. N must
+ be between 1 and 9. The merge pool specifier can only occur once per filename
+ pattern.
+
.. code-block:: console
# Step 2: Run the program.