From 2889780436ebc7feccb81aa11117e8a0a4de42ed Mon Sep 17 00:00:00 2001
From: Daniel Dunbar <daniel@zuster.org>
Date: Wed, 12 Nov 2008 12:31:28 +0000
Subject: [PATCH] Start a README.txt of possible optimizations to do in IRgen.

llvm-svn: 59130
---
 clang/lib/CodeGen/README.txt | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 clang/lib/CodeGen/README.txt

diff --git a/clang/lib/CodeGen/README.txt b/clang/lib/CodeGen/README.txt
new file mode 100644
index 000000000000..33fbfdb744ad
--- /dev/null
+++ b/clang/lib/CodeGen/README.txt
@@ -0,0 +1,24 @@
+IRgen optimization opportunities.
+
+//===---------------------------------------------------------------------===//
+
+The common pattern of
+--
+short x; // or char, etc
+(x == 10)
+--
+generates an zext/sext of x which can easily be avoided.
+
+//===---------------------------------------------------------------------===//
+
+Bitfields accesses can be shifted to simplify masking and sign
+extension. For example, if the bitfield width is 8 and it is
+appropriately aligned then is is a lot shorter to just load the char
+directly.
+
+//===---------------------------------------------------------------------===//
+
+Bitfields should not reload the stored value just to return the
+correct result.
+
+//===---------------------------------------------------------------------===//