Update the docs of the cost model.

llvm-svn: 171016

1 files changed, 6 insertions, 3 deletions

diff --git a/llvm/lib/Analysis/CostModel.cpp b/llvm/lib/Analysis/CostModel.cpp
index 0d0a8933b35..28d6a864707 100644
--- a/llvm/lib/Analysis/CostModel.cpp
+++ b/llvm/lib/Analysis/CostModel.cpp
@@ -8,9 +8,12 @@
 //===----------------------------------------------------------------------===//
 //
 // This file defines the cost model analysis. It provides a very basic cost
-// estimation for LLVM-IR. The cost result can be thought of as cycles, but it
-// is really unit-less. The estimated cost is ment to be used for comparing
-// alternatives.
+// estimation for LLVM-IR. This analysis uses the services of the codegen
+// to approximate the cost of any IR instruction when lowered to machine
+// instructions. The cost results are unit-less and the cost number represents
+// the throughput of the machine assuming that all loads hit the cache, all
+// branches are predicted, etc. The cost numbers can be added in order to
+// compare two or more transformation alternatives.
 //
 //===----------------------------------------------------------------------===//