PGO: Clarify the testing README

<rdar://problem/16276448>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203593 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/test/Profile/README b/test/Profile/README
index 8cf13c062ff676855a146ab9c2492769fff22840..3b66765711f214a04cdb9d17a7c6935af03420af 100644 (file)
--- a/test/Profile/README
+++ b/test/Profile/README
@@ -1,8 +1,16 @@
-These are tests for instrumentation based profiling. This specifically
-means the -fprofile-instr-generate and -fprofile-instr-use driver flags.
-
-Tests in this directory should test both the generation of profile
-data, and the use of that same data. As such, the input source file
-should include a main function such that building with -use and
-running the resulting program would generate the input data that is
-consumed in the -generate case.
+These are tests for instrumentation based profiling.  This specifically means
+the -fprofile-instr-generate and -fprofile-instr-use driver flags.
+
+Tests in this directory should usually test both:
+
+  - the generation of instrumentation (-fprofile-instr-generate), and
+  - the use of profile data from instrumented runs (-fprofile-instr-use).
+
+In order to test -fprofile-instr-use without actually running an instrumented
+program, .profdata files are checked into Inputs/.
+
+The input source files must include a main function such that building with
+-fprofile-instr-generate and running the resulting program generates the same
+.profdata file that is consumed by the tests for -fprofile-instr-use.  Even
+tests that only check -fprofile-instr-use should include such a main function,
+so that profile data can be regenerated as the .profdata file format evolves.