[llvm-commits] [llvm] r122966 - /llvm/trunk/lib/Target/README.txt

[Benjamin Kramer]

Author: d0k
Date: Thu Jan  6 11:35:50 2011
New Revision: 122966

URL: http://llvm.org/viewvc/llvm-project?rev=122966&view=rev
Log:
Add a note from llvmdev, this time with more info.

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=122966&r1=122965&r2=122966&view=diff
==============================================================================
--- llvm/trunk/lib/Target/README.txt (original)
+++ llvm/trunk/lib/Target/README.txt Thu Jan  6 11:35:50 2011
@@ -2047,3 +2047,29 @@
 }
 //===---------------------------------------------------------------------===//
 
+clang -O3 currently compiles this code
+
+int g(unsigned int a) {
+  unsigned int c[100];
+  c[10] = a;
+  c[11] = a;
+  unsigned int b = c[10] + c[11];
+  if(b > a*2) a = 4;
+  else a = 8;
+  return a + 7;
+}
+
+into
+
+define i32 @g(i32 a) nounwind readnone {
+  %add = shl i32 %a, 1
+  %mul = shl i32 %a, 1
+  %cmp = icmp ugt i32 %add, %mul
+  %a.addr.0 = select i1 %cmp, i32 11, i32 15
+  ret i32 %a.addr.0
+}
+
+The icmp should fold to false. This CSE opportunity is only available
+after GVN and InstCombine have run.
+
+//===---------------------------------------------------------------------===//