r323902 - Clarify that optimization levels -O2 and above are recommended for use of PGO.

[Eric Christopher via cfe-commits]

Author: echristo
Date: Wed Jan 31 11:52:58 2018
New Revision: 323902

URL: http://llvm.org/viewvc/llvm-project?rev=323902&view=rev
Log:
Clarify that optimization levels -O2 and above are recommended for use of PGO.

Modified:
    cfe/trunk/docs/UsersManual.rst

Modified: cfe/trunk/docs/UsersManual.rst
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/UsersManual.rst?rev=323902&r1=323901&r2=323902&view=diff
==============================================================================
--- cfe/trunk/docs/UsersManual.rst (original)
+++ cfe/trunk/docs/UsersManual.rst Wed Jan 31 11:52:58 2018
@@ -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