[doc] Add optimization ideas

Author: titzer

doc/allopts.txt

@@ -1,6 +1,11 @@
 || All optimizations
 =======================
 
+IR-construction time
+    only create phis for variables referenced after a join point
+    run all local misc optimizations per-BB
+  * run loop optimizations immediately after AST translation
+
 local check eliminations
   * shift check
   * divide check
@@ -27,7 +32,7 @@ local misc
     fold pointer arithmetic
     boilerplate object copy for large mostly constant arrays
     strength-reduce {ADT == k} to check only one tag
-    combine adjacent loads/stores
+    combine adjacent byte loads/stores into words
     byteswap recognition
     reorder bounds checks of a[0], a[1], a[2]...
     ordering of strength-reduction and direct call recording (inlining)
@@ -147,6 +152,8 @@ whole-program
     code layout
     data layout
     field packing across hierarchy
+    specialize class to field's type
+    pull methods down--specialize to this
     escape analysis
     region inference--stack allocation
     purity analysis