[llvm-commits] [llvm] r128107 - /llvm/trunk/lib/Target/README.txt

[Eli Friedman]

Author: efriedma
Date: Tue Mar 22 15:49:53 2011
New Revision: 128107

URL: http://llvm.org/viewvc/llvm-project?rev=128107&view=rev
Log:
A bit more analysis of a memset-related README entry.


Modified:
    llvm/trunk/lib/Target/README.txt

Modified: llvm/trunk/lib/Target/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=128107&r1=128106&r2=128107&view=diff
==============================================================================
--- llvm/trunk/lib/Target/README.txt (original)
+++ llvm/trunk/lib/Target/README.txt Tue Mar 22 15:49:53 2011
@@ -2074,11 +2074,12 @@
 }
 
 This shouldn't need the ((zext (%n - 1)) + 1) game, and it should ideally fold
-the two memset's together. The issue with %n seems to stem from poor handling
-of the original loop.
+the two memset's together.
 
-To simplify this, we need SCEV to know that "n != 0" because of the dominating
-conditional.  That would turn the second memset into a simple memset of 'n'.
+The issue with the addition only occurs in 64-bit mode, and appears to be at
+least partially caused by Scalar Evolution not keeping its cache updated: it
+returns the "wrong" result immediately after indvars runs, but figures out the
+expected result if it is run from scratch on IR resulting from running indvars.
 
 //===---------------------------------------------------------------------===//