Add a top-level comment about DAGCombiner's role in the compiler.
llvm-svn: 70052
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 72b3e36..b937eaf 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10,6 +10,10 @@
// This pass combines dag nodes to form fewer, simpler DAG nodes. It can be run
// both before and after the DAG is legalized.
//
+// This pass is not a substitute for the LLVM IR instcombine pass. This pass is
+// primarily intended to handle simplification opportunities that are implicit
+// in the LLVM IR and exposed by the various codegen lowering phases.
+//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "dagcombine"