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- (** Peephole optimisation on generated assembly. *)
- (** This is a final optimisation round that makes use of optimised VM
- instructions and common optimisable constructions in generated assembly
- code.
- There are two optimisations on branch instructions: if the branch is never
- taken, remove it. If the branch is always taken, replace it with a jump
- instruction:
- {v bloadc_t
- branch_t label
- OR
- bloadc_f
- branch_f label v}
- becomes [jump label].
- {v bloadc_f
- branch_t label
- OR
- bloadc_t
- branch_f label v}
- is removed.
- The last performed optimisation is somewhat more complex, namely the
- conversion of addition or subtraction of an integer variable by a constant
- value, to specialised [iinc|idec] instructions:
- {v iload L | iload L
- iloadc[_ ]C | iloadc_1
- i{add,sub} | i{add,sub}
- istore L | istore L
- | |
- v v
- i{inc,dec} L C | i{inc,dec}_1 L v}
- Note that the [iload] and [iloadc] may also be in reverse order, which in
- CiviC code is the difference between [i = i + 1;] and [i = 1 + i;]. Both
- orders of succession are supported by the implementation.
- *)
- (** Main phase function, called by {!Main}. *)
- val phase : Main.phase_func
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