Sea of nodes optimizations and convenience functions

lib/syntax_tree/yarv/control_flow_graph.rb

@@ -203,6 +203,10 @@ def to_dfg
         DataFlowGraph.compile(self)
       end
 
+      def to_son
+        to_dfg.to_son
+      end
+
       def to_mermaid
         output = StringIO.new
         output.puts("flowchart TD")

lib/syntax_tree/yarv/instruction_sequence.rb

@@ -273,6 +273,14 @@ def to_cfg
         ControlFlowGraph.compile(self)
       end
 
+      def to_dfg
+        to_cfg.to_dfg
+      end
+
+      def to_son
+        to_dfg.to_son
+      end
+
       def disasm
         fmt = Disassembler.new
         fmt.enqueue(self)

lib/syntax_tree/yarv/sea_of_nodes.rb

@@ -118,7 +118,8 @@ def compile
 
           connect_local_graphs_control(local_graphs)
           connect_local_graphs_data(local_graphs)
-          cleanup
+          cleanup_phi_nodes
+          cleanup_insn_nodes
 
           SeaOfNodes.new(dfg, nodes, local_graphs).tap(&:verify)
         end
@@ -311,23 +312,13 @@ def connect_local_graphs_data(local_graphs)
         # We don't always build things in an optimal way. Go back and fix up
         # some mess we left. Ideally we wouldn't create these problems in the
         # first place.
-        def cleanup
+        def cleanup_phi_nodes
           nodes.dup.each do |node| # dup because we're mutating
             next unless node.is_a?(PhiNode)
 
             if node.inputs.size == 1
               # Remove phi nodes with a single input.
-              node.inputs.each do |producer_edge|
-                node.outputs.each do |consumer_edge|
-                  connect(
-                    producer_edge.from,
-                    consumer_edge.to,
-                    producer_edge.type,
-                    consumer_edge.label
-                  )
-                end
-              end
-
+              connect_over(node)
               remove(node)
             elsif node.inputs.map(&:from).uniq.size == 1
               # Remove phi nodes where all inputs are the same.
@@ -344,6 +335,66 @@ def cleanup
           end
         end
 
+        # Eliminate as many unnecessary nodes as we can.
+        def cleanup_insn_nodes
+          nodes.dup.each do |node|
+            next unless node.is_a?(InsnNode)
+
+            case node.insn
+            when AdjustStack
+              # If there are any inputs to the adjust stack that are immediately
+              # discarded, we can remove them from the input list.
+              number = node.insn.number
+
+              node.inputs.dup.each do |input_edge|
+                next if input_edge.type != :data
+
+                from = input_edge.from
+                next unless from.is_a?(InsnNode)
+
+                if from.inputs.empty? && from.outputs.size == 1
+                  number -= 1
+                  remove(input_edge.from)
+                elsif from.insn.is_a?(Dup)
+                  number -= 1
+                  connect_over(from)
+                  remove(from)
+
+                  new_edge = node.inputs.last
+                  new_edge.from.outputs.delete(new_edge)
+                  node.inputs.delete(new_edge)
+                end
+              end
+
+              if number == 0
+                connect_over(node)
+                remove(node)
+              else
+                next_node =
+                  if number == 1
+                    InsnNode.new(Pop.new, node.offset)
+                  else
+                    InsnNode.new(AdjustStack.new(number), node.offset)
+                  end
+
+                next_node.inputs.concat(node.inputs)
+                next_node.outputs.concat(node.outputs)
+
+                # Dynamically finding the index of the node in the nodes array
+                # because we're mutating the array as we go.
+                nodes[nodes.index(node)] = next_node
+              end
+            when Jump
+              # When you have a jump instruction that only has one input and one
+              # output, you can just connect over top of it and remove it.
+              if node.inputs.size == 1 && node.outputs.size == 1
+                connect_over(node)
+                remove(node)
+              end
+            end
+          end
+        end
+
         # Connect one node to another.
         def connect(from, to, type, label = nil)
           raise if from == to
@@ -354,6 +405,20 @@ def connect(from, to, type, label = nil)
           to.inputs << edge
         end
 
+        # Connect all of the inputs to all of the outputs of a node.
+        def connect_over(node)
+          node.inputs.each do |producer_edge|
+            node.outputs.each do |consumer_edge|
+              connect(
+                producer_edge.from,
+                consumer_edge.to,
+                producer_edge.type,
+                producer_edge.label
+              )
+            end
+          end
+        end
+
         # Remove a node from the graph.
         def remove(node)
           node.inputs.each do |producer_edge|

test/yarv_test.rb

@@ -302,7 +302,7 @@ def test_cfg
       iseq = SyntaxTree::YARV::InstructionSequence.from(iseq.to_a)
       cfg = SyntaxTree::YARV::ControlFlowGraph.compile(iseq)
 
-      assert_equal(<<~CFG, cfg.disasm)
+      assert_equal(<<~DISASM, cfg.disasm)
         == cfg: #<ISeq:<compiled>@<compiled>:1 (1,0)-(1,0)>
         block_0
             0000 putobject                              100
@@ -325,7 +325,7 @@ def test_cfg
             0014 opt_plus                               <calldata!mid:+, argc:1, ARGS_SIMPLE>
             0016 leave
             == to: leaves
-      CFG
+      DISASM
     end
 
     def test_dfg
@@ -334,7 +334,7 @@ def test_dfg
       cfg = SyntaxTree::YARV::ControlFlowGraph.compile(iseq)
       dfg = SyntaxTree::YARV::DataFlowGraph.compile(cfg)
 
-      assert_equal(<<~DFG, dfg.disasm)
+      assert_equal(<<~DISASM, dfg.disasm)
         == dfg: #<ISeq:<compiled>@<compiled>:1 (1,0)-(1,0)>
         block_0
             0000 putobject                              100 # out: out_0
@@ -363,7 +363,7 @@ def test_dfg
             0014 opt_plus                               <calldata!mid:+, argc:1, ARGS_SIMPLE> # in: in_0, in_1; out: 16
             0016 leave # in: 14
             == to: leaves
-      DFG
+      DISASM
     end
 
     def test_son
@@ -373,14 +373,13 @@ def test_son
       dfg = SyntaxTree::YARV::DataFlowGraph.compile(cfg)
       son = SyntaxTree::YARV::SeaOfNodes.compile(dfg)
 
-      assert_equal(<<~SON, son.to_mermaid)
+      assert_equal(<<~MERMAID, son.to_mermaid)
         flowchart TD
           node_0("0000 putobject 14")
           node_2("0002 putobject_INT2FIX_0_")
           node_3("0003 opt_lt &lt;calldata!mid:&lt;, argc:1, ARGS_SIMPLE&gt;")
           node_5("0005 branchunless 0011")
           node_7("0007 putobject -1")
-          node_9("0009 jump 0012")
           node_11("0011 putobject_INT2FIX_1_")
           node_12("0012 putobject 100")
           node_14("0014 opt_plus &lt;calldata!mid:+, argc:1, ARGS_SIMPLE&gt;")
@@ -397,28 +396,26 @@ def test_son
           linkStyle 3 stroke:green;
           node_5 --> |branch0| node_11
           linkStyle 4 stroke:red;
-          node_5 --> |fallthrough| node_9
+          node_5 --> |fallthrough| node_1000
           linkStyle 5 stroke:red;
           node_7 --> |0009| node_1001
           linkStyle 6 stroke:green;
-          node_9 --> |branch0| node_1000
-          linkStyle 7 stroke:red;
           node_11 --> |branch0| node_1000
-          linkStyle 8 stroke:red;
+          linkStyle 7 stroke:red;
           node_11 --> |0011| node_1001
-          linkStyle 9 stroke:green;
+          linkStyle 8 stroke:green;
           node_12 --> |1| node_14
-          linkStyle 10 stroke:green;
+          linkStyle 9 stroke:green;
           node_14 --> node_16
-          linkStyle 11 stroke:red;
+          linkStyle 10 stroke:red;
           node_14 --> |0| node_16
-          linkStyle 12 stroke:green;
+          linkStyle 11 stroke:green;
           node_1000 --> node_14
-          linkStyle 13 stroke:red;
+          linkStyle 12 stroke:red;
           node_1001 -.-> node_1000
           node_1001 --> |0| node_14
-          linkStyle 15 stroke:green;
-      SON
+          linkStyle 14 stroke:green;
+      MERMAID
     end
 
     def test_son_indirect_basic_block_argument
@@ -428,15 +425,14 @@ def test_son_indirect_basic_block_argument
       dfg = SyntaxTree::YARV::DataFlowGraph.compile(cfg)
       son = SyntaxTree::YARV::SeaOfNodes.compile(dfg)
 
-      assert_equal(<<~SON, son.to_mermaid)
+      assert_equal(<<~MERMAID, son.to_mermaid)
         flowchart TD
           node_0("0000 putobject 100")
           node_2("0002 putobject 14")
           node_4("0004 putobject_INT2FIX_0_")
           node_5("0005 opt_lt &lt;calldata!mid:&lt;, argc:1, ARGS_SIMPLE&gt;")
           node_7("0007 branchunless 0013")
           node_9("0009 putobject -1")
-          node_11("0011 jump 0014")
           node_13("0013 putobject_INT2FIX_1_")
           node_14("0014 opt_plus &lt;calldata!mid:+, argc:1, ARGS_SIMPLE&gt;")
           node_16("0016 leave")
@@ -454,26 +450,24 @@ def test_son_indirect_basic_block_argument
           linkStyle 4 stroke:green;
           node_7 --> |branch0| node_13
           linkStyle 5 stroke:red;
-          node_7 --> |fallthrough| node_11
+          node_7 --> |fallthrough| node_1002
           linkStyle 6 stroke:red;
           node_9 --> |0011| node_1004
           linkStyle 7 stroke:green;
-          node_11 --> |branch0| node_1002
-          linkStyle 8 stroke:red;
           node_13 --> |branch0| node_1002
-          linkStyle 9 stroke:red;
+          linkStyle 8 stroke:red;
           node_13 --> |0013| node_1004
-          linkStyle 10 stroke:green;
+          linkStyle 9 stroke:green;
           node_14 --> node_16
-          linkStyle 11 stroke:red;
+          linkStyle 10 stroke:red;
           node_14 --> |0| node_16
-          linkStyle 12 stroke:green;
+          linkStyle 11 stroke:green;
           node_1002 --> node_14
-          linkStyle 13 stroke:red;
+          linkStyle 12 stroke:red;
           node_1004 -.-> node_1002
           node_1004 --> |1| node_14
-          linkStyle 15 stroke:green;
-      SON
+          linkStyle 14 stroke:green;
+      MERMAID
     end
 
     private