gir/optimizations.md

Gir has three optimization passes.

joinAdjacentOps

consumes | commands without offsets produces | commands without offsets unknown commands | passed through unmodified acts on | moveHead, add

joinAdjacentOps joins adjacent moveHeads and adds together. Normally parse joins runs of <> or +- into one command, but if the runs are interrupted by another character two commands get generated. moveHeads are joined first, before the pass goes over the generated commands again and joins adds.

transformClearLoops

consumes | commands without offsets produces | commands without offsets unknown commands | passed through unmodified acts on | loop with one command, which is add 1 or add -1

transformClearLoops changes loops of the form [-] or [+] into a single clear command.

addOffsetProperties

consumes | commands without offsets produces | commands with offsets unknown commands | raise UnknownIRError acts on | moveHead, add, clear, writeByte, readByte, loop

addOffsetProperties adds an offset property to add, clear, writeByte, and readByte. The offset tells the offset at which from the current tape head location the operations are performed. It also adds an isBalanced property to loops. This property tells if execution of loop body ends at the same cell where it began, which is useful for performing further optimizations.