[polly] r201887 - DCE: Update description

[Tobias Grosser]

Author: grosser
Date: Fri Feb 21 14:51:40 2014
New Revision: 201887

URL: http://llvm.org/viewvc/llvm-project?rev=201887&view=rev
Log:
DCE: Update description

Modified:
    polly/trunk/lib/DeadCodeElimination.cpp

Modified: polly/trunk/lib/DeadCodeElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/DeadCodeElimination.cpp?rev=201887&r1=201886&r2=201887&view=diff
==============================================================================
--- polly/trunk/lib/DeadCodeElimination.cpp (original)
+++ polly/trunk/lib/DeadCodeElimination.cpp Fri Feb 21 14:51:40 2014
@@ -7,15 +7,28 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This is a skeleton that is meant to contain a dead code elimination pass
-// later on.
+// The polyhedral dead code elimination pass analyses a SCoP to eliminate
+// statement instances that can be proven dead.
+// As a consequence, the code generated for this SCoP may execute a statement
+// less often. This means, a statement may be executed only in certain loop
+// iterations or it may not even be part of the generated code at all.
 //
-// The idea of this pass is to loop over all statements and to remove statement
-// iterations that do not calculate any value that is read later on. We need to
-// make sure to forward RAR and WAR dependences.
+// This code:
 //
-// A case where this pass might be useful is
-// http://llvm.org/bugs/show_bug.cgi?id=5117
+//    for (i = 0; i < N; i++)
+//        arr[i] = 0;
+//    for (i = 0; i < N; i++)
+//        arr[i] = 10;
+//    for (i = 0; i < N; i++)
+//        arr[i] = i;
+//
+// is e.g. simplified to:
+//
+//    for (i = 0; i < N; i++)
+//        arr[i] = i;
+//
+// The idea and the algorithm used was first implemented by Sven Verdoolaege in
+// the 'ppcg' tool.
 //
 //===----------------------------------------------------------------------===//