1 files changed, 12 insertions, 2 deletions
diff --git a/site/docs/bazel-user-manual.html b/site/docs/bazel-user-manual.html
index df28a6dbd5..17b8725ea0 100644
--- a/site/docs/bazel-user-manual.html
+++ b/site/docs/bazel-user-manual.html
@@ -1372,7 +1372,7 @@ $ bazel fetch //...
 <p>
   The <code class='flag'>--fdo_instrument</code> option enables the generation of
   FDO (feedback directed optimization) profile output when the
-  built C/C++ binary is executed. The argument provided is used as a
+  built C/C++ binary is executed. For GCC, the argument provided is used as a
   directory prefix for a per-object file directory tree of .gcda files
   containing profile information for each .o file.
 </p>
@@ -1384,6 +1384,11 @@ $ bazel fetch //...
 
 </p>
 <p>
+  For the LLVM compiler the argument instead is the path to the raw LLVM profile
+  output file to generate, e.g.
+  <code class='flag'>--fdo_instrument=<var>/path/to/profile.profraw</var></code>.
+</p>
+<p>
   The options <code class='flag'>--fdo_instrument</code> and <code class='flag'>--fdo_optimize</code>
   cannot be used at the same time.
 </p>
@@ -1392,7 +1397,7 @@ $ bazel fetch //...
 <p>
   The <code class='flag'>--fdo_optimize</code> option enables the use of the
   per-object file profile information to perform FDO (feedback
-  directed optimization) optimizations when compiling. The argument
+  directed optimization) optimizations when compiling. For GCC, the argument
   provided is the zip file containing the previously-generated file tree
   of .gcda files containing profile information for each .o file.
 </p>
@@ -1407,6 +1412,11 @@ $ bazel fetch //...
   make the file visible to Bazel.
 </p>
 <p>
+  For the LLVM compiler the argument provided should point to the indexed LLVM
+  profile output file prepared by the llvm-profdata tool, and should have a .profdata
+  extension.
+</p>
+<p>
   The options <code class='flag'>--fdo_instrument</code> and <code class='flag'>
   --fdo_optimize</code> cannot be used at the same time.
 </p>