Update documentation

README.md

@@ -16,6 +16,7 @@ Gir supports following optimizations:
 * Turn runs of +- or <> into one command
 * Turn [-] or [+] into one command
 * Add offsets to commands that modify tape, to reduce moving tape head
+* Turn multiply loops into one command
 
 TODO
 ----

ir.md

@@ -95,6 +95,12 @@ property | value
 type     | `clear`
 offset   | The location of the cell relative to current tape position
 
+### multiply
+property | value
+---------|------
+type     | `multiply`
+changes  | Map of offsets to the number that should be added to those cells multiplies by the current cell
+
 
 Flattened
 ---------

optimizations.md

@@ -1,4 +1,4 @@
-Gir has four optimization passes.
+Gir has five optimization passes.
 
 joinAdjacentOps
 ---------------
@@ -39,6 +39,16 @@ current tape head location the operations are performed. It also adds an
 body ends at the same cell where it began, which is useful for performing
 further optimizations.
 
+transformMultiplyLoops
+----------------------
+* *consumed*: commands with offsets
+* *unknown commands*: passed through unmodified
+* *acts on*: balanced `loop`s that only have adds and where adds at offset 0 are together 1 or -1
+* *other known commands*: `loop` (recurses)
+
+`transformMultiplyLoops` changes loops of the form `[>+>++<<-]` into a
+single `multiply` command.
+
 flattenLoops
 ------------
 * *consumes*: commands with offsets