[llvm] r212570 - DominanceInfo is strongly preferred over RegionInfo

Tobias Grosser tobias at grosser.es
Tue Jul 8 15:51:03 PDT 2014

Author: grosser
Date: Tue Jul  8 17:51:03 2014
New Revision: 212570

URL: http://llvm.org/viewvc/llvm-project?rev=212570&view=rev
DominanceInfo is strongly preferred over RegionInfo

This is and always was strong community consensus. Make this clear in the header
in case newcomers may not be aware.


Modified: llvm/trunk/include/llvm/Analysis/RegionInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/RegionInfo.h?rev=212570&r1=212569&r2=212570&view=diff
--- llvm/trunk/include/llvm/Analysis/RegionInfo.h (original)
+++ llvm/trunk/include/llvm/Analysis/RegionInfo.h Tue Jul  8 17:51:03 2014
@@ -22,6 +22,16 @@
 // itself is not, but in practice runtime seems to be in the order of magnitude
 // of dominance tree calculation.
+// WARNING: LLVM is generally very concerned about compile time such that
+//          the use of additional analysis passes in the default
+//          optimization sequence is avoided as much as possible.
+//          Specifically, if you do not need the RegionInfo, but dominance
+//          information could be sufficient please base your work only on
+//          the dominator tree. Most passes maintain it, such that using
+//          it has often near zero cost. In contrast RegionInfo is by
+//          default not available, is not maintained by existing
+//          transformations and there is no intention to do so.

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