From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Thu, 6 Jan 2011 17:35:50 +0000 (+0000)
Subject: Add a note from llvmdev, this time with more info.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=fa366800766d71e00ac1cc3adf623bef06800d0d;p=oota-llvm.git

Add a note from llvmdev, this time with more info.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122966 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index 29bd10949e5..bedc893fbb1 100644
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -2047,3 +2047,29 @@ entry:
 }
 //===---------------------------------------------------------------------===//
 
+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.
+
+//===---------------------------------------------------------------------===//