Improve pass documentation and comments.

Patch by Matthijs Kooijman!

llvm-svn: 50861

2 files changed, 15 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/IPO/StripDeadPrototypes.cpp b/llvm/lib/Transforms/IPO/StripDeadPrototypes.cpp
index fd22fdb37f8..ca8a436844a 100644
--- a/llvm/lib/Transforms/IPO/StripDeadPrototypes.cpp
+++ b/llvm/lib/Transforms/IPO/StripDeadPrototypes.cpp
@@ -1,4 +1,4 @@
-//===-- StripDeadPrototypes.cpp - Removed unused function declarations ----===//
+//===-- StripDeadPrototypes.cpp - Remove unused function declarations ----===//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -8,7 +8,9 @@
 //===----------------------------------------------------------------------===//
 //
 // This pass loops over all of the functions in the input module, looking for 
-// dead declarations and removes them.
+// dead declarations and removes them. Dead declarations are declarations of
+// functions for which no implementation is available (i.e., declarations for
+// unused library functions).
 //
 //===----------------------------------------------------------------------===//
 
diff --git a/llvm/lib/Transforms/IPO/StructRetPromotion.cpp b/llvm/lib/Transforms/IPO/StructRetPromotion.cpp
index 77a35b42875..83ceb0dd0eb 100644
--- a/llvm/lib/Transforms/IPO/StructRetPromotion.cpp
+++ b/llvm/lib/Transforms/IPO/StructRetPromotion.cpp
@@ -1,4 +1,4 @@
-//===-- StructRetPromotion.cpp - Promote sret arguments -000000------------===//
+//===-- StructRetPromotion.cpp - Promote sret arguments ------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -7,7 +7,16 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// TODO : Describe this pass.
+// This pass finds functions that return a struct (using a pointer to the struct
+// as the first argument of the function, marked with the 'sret' attribute) and
+// replaces them with a new function that simply returns each of the elements of
+// that struct (using multiple return values).
+//
+// This pass works under a number of conditions:
+//  1. The returned struct must not contain other structs
+//  2. The returned struct must only be used to load values from
+//  3. The placeholder struct passed in is the result of an alloca
+//
 //===----------------------------------------------------------------------===//
 
 #define DEBUG_TYPE "sretpromotion"