Class: Optimize::Passes::IdentityElimPass

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

Overview

Strip arithmetic identities: x * 1, 1 * x, x + 0, 0 + x, x - 0, x / 1. See docs/superpowers/specs/2026-04-21-pass-identity-elim-design.md.

Constant Summary collapse

IDENTITY_OPS = 
{
  opt_plus:  { identity: 0, sides: :either },
  opt_mult:  { identity: 1, sides: :either },
  opt_minus: { identity: 0, sides: :right  },
  opt_div:   { identity: 1, sides: :right  },
}.freeze
SAFE_PRODUCER_OPCODES =

Non-literal side must be in this whitelist. Shared with ArithReassocPass: any producer with observable side effects (send, invokesuper, …) is absent here so that eliding the op never elides a side effect.

ArithReassocPass::SINGLE_PUSH_OPERAND_OPCODES

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/identity_elim_pass.rb', line 25

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

  loop do
    eliminated_any = false
    i = 0
    while i <= insts.size - 3
      a  = insts[i]
      b  = insts[i + 1]
      op = insts[i + 2]
      entry = IDENTITY_OPS[op.opcode]
      if entry && SAFE_PRODUCER_OPCODES.include?(a.opcode) && SAFE_PRODUCER_OPCODES.include?(b.opcode)
        keep = try_eliminate(a, b, entry, object_table)
        if keep
          function.splice_instructions!(i..(i + 2), [keep])
          log.rewrite(pass: :identity_elim, reason: :identity_eliminated,
                      file: function.path, line: (op.line || a.line || function.first_lineno))
          eliminated_any = true
          i = i - 1 if i.positive?
          next
        end
      end
      i += 1
    end
    break unless eliminated_any
  end
end

#name ⇒ Object 



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# File 'lib/optimize/passes/identity_elim_pass.rb', line 23

def name = :identity_elim