Class: Optimize::Passes::ConstFoldPass

Inherits:
Optimize::Pass show all
Defined in:
lib/optimize/passes/const_fold_pass.rb

Constant Summary collapse

FOLDABLE_OPS = 
{
  opt_plus:  :+,
  opt_minus: :-,
  opt_mult:  :*,
  opt_div:   :/,
  opt_mod:   :%,
  opt_lt:    :<,
  opt_le:    :<=,
  opt_gt:    :>,
  opt_ge:    :>=,
  opt_eq:    :==,
  opt_neq:   :"!=",
}.freeze

Instance Method Summary collapse

Methods inherited from Optimize::Pass

#one_shot?

Instance Method Details

#apply(function, type_env:, log:, object_table: nil, **_extras) ⇒ Object 



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# File 'lib/optimize/passes/const_fold_pass.rb', line 22

def apply(function, type_env:, log:, object_table: nil, **_extras)
  _ = type_env
  return unless object_table
  insts = function.instructions
  return unless insts

  # Outer fixpoint loop: defense-in-depth around the inner step-back
  # scan. The step-back already catches the common left-associative
  # chain shape (`putobject N; putobject N; opt_plus` after one fold),
  # but the outer loop makes the "fold to a fixed point" invariant
  # explicit and covers any triple-shape the step-back misses.
  # Termination: each iteration either folds (strictly decreasing
  # `insts.size` by 2) or sets `folded_any = false` and breaks.
  loop do
    folded_any = false
    i = 0
    while i <= insts.size - 3
      a  = insts[i]
      b  = insts[i + 1]
      op = insts[i + 2]
      new_inst = try_fold_triple(a, b, op, function, log, object_table)
      if new_inst
        # Safe: the two removed instructions are `putobject`-family literal
        # producers — neither is ever a branch target. splice_instructions!
        # adjusts absolute indices for any branches targeting past the splice.
        function.splice_instructions!(i..(i + 2), [new_inst])
        folded_any = true
        # Step back so we recheck at `i-1` in case the previous
        # instruction is now the first of a new foldable triple.
        i = i - 1 if i.positive?
      else
        i += 1
      end
    end
    break unless folded_any
  end
end

#name ⇒ Object 



60
 
# File 'lib/optimize/passes/const_fold_pass.rb', line 60

def name = :const_fold