From: Chris Lattner <sabre@nondot.org>
Date: Thu, 20 Apr 2006 18:49:28 +0000 (+0000)
Subject: add a note
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=879acefed5e710764eef6018d843107a8092dfd0;p=oota-llvm.git

add a note


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27907 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index 23503517c07..fd862fe63a9 100644
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -172,3 +172,21 @@ information in the constant folder, so we don't know the endianness of the
 target!
 
 //===---------------------------------------------------------------------===//
+
+Consider this:
+
+unsigned short swap_16(unsigned short v) { return (v>>8) | (v<<8); }
+
+Compiled with the ppc backend:
+
+_swap_16:
+        slwi r2, r3, 8
+        srwi r3, r3, 8
+        or r2, r3, r2
+        rlwinm r3, r2, 0, 16, 31
+        blr
+
+The rlwinm (an and by 65535) is dead.  The dag combiner should propagate bits
+better than that to see this.
+
+//===---------------------------------------------------------------------===//