From: Daniel Dunbar <daniel@zuster.org>
Date: Wed, 12 Nov 2008 12:31:28 +0000 (+0000)
Subject: Start a README.txt of possible optimizations to do in IRgen.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=8787530df554f1ff5643b342b03de95a108fe97c;p=clang

Start a README.txt of possible optimizations to do in IRgen.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59130 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/README.txt b/lib/CodeGen/README.txt
new file mode 100644
index 0000000000..33fbfdb744
--- /dev/null
+++ b/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.
+
+//===---------------------------------------------------------------------===//