diff --git a/lib/CodeGen/SimpleRegisterCoalescing.h b/lib/CodeGen/SimpleRegisterCoalescing.h
index 7823ba0df4b..fa63159d1c8 100644
--- a/lib/CodeGen/SimpleRegisterCoalescing.h
+++ b/lib/CodeGen/SimpleRegisterCoalescing.h
@@ -223,6 +223,8 @@ namespace llvm {
     /// subregister.
     void UpdateRegDefsUses(unsigned SrcReg, unsigned DstReg, unsigned SubIdx);
 
+    /// RemoveDeadImpDef - Remove implicit_def instructions which are
+    /// "re-defining" registers due to insert_subreg coalescing. e.g.
     void RemoveDeadImpDef(unsigned Reg, LiveInterval &LI);
 
     /// RemoveUnnecessaryKills - Remove kill markers that are no longer accurate