[llvm-commits] [llvm] r121854 - /llvm/trunk/lib/Target/README.txt

[Chris Lattner]

Author: lattner
Date: Wed Dec 15 01:28:58 2010
New Revision: 121854

URL: http://llvm.org/viewvc/llvm-project?rev=121854&view=rev
Log:
add another overflow idiom

Modified:
    llvm/trunk/lib/Target/README.txt

Modified: llvm/trunk/lib/Target/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=121854&r1=121853&r2=121854&view=diff
==============================================================================
--- llvm/trunk/lib/Target/README.txt (original)
+++ llvm/trunk/lib/Target/README.txt Wed Dec 15 01:28:58 2010
@@ -93,6 +93,14 @@
 	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