From 2e33985300d5d0e5a46af12dc081db98744927fb Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Wed, 15 Dec 2010 07:25:55 +0000
Subject: [PATCH] add a note about overflow idiom recognition.

llvm-svn: 121853
---
 llvm/lib/Target/README.txt | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Target/README.txt b/llvm/lib/Target/README.txt
index 17617ad54735..e59c28697a19 100644
--- a/llvm/lib/Target/README.txt
+++ b/llvm/lib/Target/README.txt
@@ -73,7 +73,25 @@ This has a number of uses:
 
 //===---------------------------------------------------------------------===//
 
-Make the PPC branch selector target independant
+We should recognized various "overflow detection" idioms and translate them into
+llvm.uadd.with.overflow and similar intrinsics.  For example, we compile this:
+
+size_t add(size_t a,size_t b) {
+ if (a+b<a)
+   exit(0);
+ return a+b;
+}
+
+into:
+
+	addq	%rdi, %rbx
+	cmpq	%rdi, %rbx
+	jae	LBB0_2
+
+when it would be better to generate:
+
+	addq	%rdi, %rbx
+	jno	LBB0_2
 
 //===---------------------------------------------------------------------===//