add a note

llvm-svn: 27360

llvm/lib/Target/PowerPC/README.txt

@@ -551,3 +551,12 @@ void func(unsigned int *ret, float dx, float dy, float dz, float dw) {
 
 ===-------------------------------------------------------------------------===
 
+extract_vector_elt of an arbitrary constant vector can be done with the 
+following instructions:
+
+vTemp = vec_splat(v0,2);    // 2 is the element the src is in.
+vec_ste(&destloc,0,vTemp);
+
+We can do an arbitrary non-constant value by using lvsr/perm/ste.
+
+===-------------------------------------------------------------------------===