add a note

llvm-svn: 45377

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/lib/Target/README.txt b/llvm/lib/Target/README.txt
index 37c0a359a2b..b94bdeac94e 100644
--- a/llvm/lib/Target/README.txt
+++ b/llvm/lib/Target/README.txt
@@ -464,3 +464,22 @@ entry:
 }
 
 //===---------------------------------------------------------------------===//
+
+"basicaa" should know how to look through "or" instructions that act like add
+instructions.  For example in this code, the x*4+1 is turned into x*4 | 1, and
+basicaa can't analyze the array subscript, leading to duplicated loads in the
+generated code:
+
+void test(int X, int Y, int a[]) {
+int i;
+  for (i=2; i<1000; i+=4) {
+  a[i+0] = a[i-1+0]*a[i-2+0];
+  a[i+1] = a[i-1+1]*a[i-2+1];
+  a[i+2] = a[i-1+2]*a[i-2+2];
+  a[i+3] = a[i-1+3]*a[i-2+3];
+  }
+}
+
+
+
+//===---------------------------------------------------------------------===//