[llvm] r211268 - Updated comments as suggested by Rafael. Thanks.

[Dinesh Dwivedi]

Author: dinesh
Date: Thu Jun 19 09:11:53 2014
New Revision: 211268

URL: http://llvm.org/viewvc/llvm-project?rev=211268&view=rev
Log:
Updated comments as suggested by Rafael. Thanks.


Modified:
    llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=211268&r1=211267&r2=211268&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Thu Jun 19 09:11:53 2014
@@ -158,7 +158,13 @@ bool JumpThreading::runOnFunction(Functi
   TLI = &getAnalysis<TargetLibraryInfo>();
   LVI = &getAnalysis<LazyValueInfo>();
 
-  // Remove unreachable blocks from function as they may result in infinite loop.
+  // Remove unreachable blocks from function as they may result in infinite
+  // loop. We do threading if we found something profitable. Jump threading a
+  // branch can create other opportunities. If these opportunities form a cycle
+  // i.e. if any jump treading is undoing previous threading in the path, then
+  // we will loop forever. We take care of this issue by not jump threading for
+  // back edges. This works for normal cases but not for unreachable blocks as
+  // they may have cycle with no back edge.
   removeUnreachableBlocks(F);
 
   FindLoopHeaders(F);