From: Chris Lattner <sabre@nondot.org>
Date: Wed, 15 Dec 2010 07:28:58 +0000 (+0000)
Subject: add another overflow idiom
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=9448184b99b2bbdb9a2107ef12bf4cbff86e684f;p=oota-llvm.git

add another overflow idiom


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121854 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index e59c28697a1..5c97b8984c1 100644
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -93,6 +93,14 @@ when it would be better to generate:
 	addq	%rdi, %rbx
 	jno	LBB0_2
 
+Apparently some version of GCC knows this.  Here is a multiply idiom:
+
+unsigned int mul(unsigned int a,unsigned int b) {
+ if ((unsigned long long)a*b>0xffffffff)
+   exit(0);
+  return a*b;
+}
+
 //===---------------------------------------------------------------------===//
 
 Get the C front-end to expand hypot(x,y) -> llvm.sqrt(x*x+y*y) when errno and