Clarify that optimization levels -O2 and above are recommended for use of PGO.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@323902 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/docs/UsersManual.rst b/docs/UsersManual.rst
index 48ea714304b759280ce24798ce43b33a06a6426e..84dfe9fc3d733bc9a42acf54eb6f313b54090973 100644 (file)
--- a/docs/UsersManual.rst
+++ b/docs/UsersManual.rst
@@ -1375,7 +1375,8 @@ Profile Guided Optimization
 Profile information enables better optimization. For example, knowing that a
 branch is taken very frequently helps the compiler make better decisions when
 ordering basic blocks. Knowing that a function ``foo`` is called more
-frequently than another function ``bar`` helps the inliner.
+frequently than another function ``bar`` helps the inliner. Optimization
+levels ``-O2`` and above are recommended for use of profile guided optimization.
 
 Clang supports profile guided optimization with two different kinds of
 profiling. A sampling profiler can generate a profile with very low runtime