Add constant propagation pass.

lib/furnace-avm2/abc/metadata/method_body_info.rb

@@ -33,11 +33,17 @@ def code_to_cfg(options={})
           Furnace::AVM2::Transform::DataflowInvariantCodeMotion.new,
           Furnace::AVM2::Transform::PartialEvaluation.new,
           Furnace::AVM2::Transform::SSAOptimize.new,
+
+          Furnace::AVM2::Transform::LivenessAnalysis.new,
           Furnace::AVM2::Transform::FoldBooleanShortcuts.new,
           Furnace::AVM2::Transform::FoldTernaryOperators.new,
           Furnace::AVM2::Transform::FoldIncrementDecrement.new,
+          Furnace::AVM2::Transform::SSAOptimize.new,
         ]),
 
+        Furnace::AVM2::Transform::LivenessAnalysis.new(idempotent: true),
+        Furnace::AVM2::Transform::PropagateConstants.new,
+
         Furnace::AVM2::Transform::UpdateExceptionVariables.new,
         Furnace::AVM2::Transform::FoldPassthroughAssignments.new,
       ])

lib/furnace-avm2/transform.rb

@@ -13,6 +13,7 @@ module Furnace::AVM2::Transform
 require_relative "transform/liveness_analysis"
 require_relative "transform/dataflow_invariant_code_motion"
 require_relative "transform/partial_evaluation"
+require_relative "transform/propagate_constants"
 require_relative "transform/fold_ternary_operators"
 require_relative "transform/fold_boolean_shortcuts"
 require_relative "transform/fold_passthrough_assignments"

lib/furnace-avm2/transform/liveness_analysis.rb

@@ -4,6 +4,10 @@ class LivenessAnalysis
       # Avoid creating too much literals.
       EMPTY_SET = Set[]
 
+      def initialize(options={})
+        @idempotent = options[:idempotent] || false
+      end
+
       def transform(cfg)
         dom   = cfg.dominators
         loops = cfg.identify_loops
@@ -83,7 +87,7 @@ def transform(cfg)
 
         # This transform does not change CFG in any way,
         # it just rebuilds the metadata.
-        nil
+        cfg if @idempotent
       end
     end
   end

lib/furnace-avm2/transform/propagate_constants.rb

@@ -4,6 +4,26 @@ class PropagateConstants
       include SubgraphOperations
 
       def transform(cfg)
+        changed = false
+
+        evaluator = Evaluator.new
+
+        cfg.nodes.each do |block|
+          block.metadata.sets.each do |id|
+            set = block.metadata.set_map[id]
+            _, set_value = set.children
+
+            # TODO add options for folding complex constants
+            if evaluator.immediate?(set_value)
+              replace_r_nodes(cfg, block, id, set_value)
+              block.metadata.remove_set(id)
+              block.insns.delete set
+
+              changed = true
+            end
+          end
+        end
+
         cfg
       end
     end

lib/furnace-avm2/transform/subgraph_operations.rb

@@ -1,7 +1,7 @@
 module Furnace::AVM2
   module Transform
     module SubgraphOperations
-      def walk_live_nodes(cfg, root)
+      def walk_live_nodes(cfg, root, id)
         worklist = Set[ root ]
         visited  = Set[]
 
@@ -13,15 +13,15 @@ def walk_live_nodes(cfg, root)
           yield block
 
           block.targets.each do |target|
-            if target.metadata.live.include? target_id
+            if target.metadata.live.include? id
               worklist.add target unless visited.include? target
             end
           end
         end
       end
 
       def reduce_phi_nodes(cfg, root, target_id, supplementary_id)
-        walk_live_nodes(cfg, root) do |block|
+        walk_live_nodes(cfg, root, target_id) do |block|
           gets = block.metadata.gets_map[target_id]
           gets.each do |get|
             if get.children.include? supplementary_id
@@ -32,7 +32,7 @@ def reduce_phi_nodes(cfg, root, target_id, supplementary_id)
       end
 
       def replace_r_nodes(cfg, root, target_id, replacement)
-        walk_live_nodes(cfg, root) do |block|
+        walk_live_nodes(cfg, root, target_id) do |block|
           gets = block.metadata.gets_map[target_id]
           gets.each do |get|
             get.update(replacement.type,