Support multiple branch targets per instruction

Author: kddnewton

lib/syntax_tree/yarv/control_flow_graph.rb

@@ -105,7 +105,7 @@ def initialize(block_start, insns)
         # checks that the only instruction in this basic block that branches is
         # the last instruction.
         def verify
-          insns[0...-1].each { |insn| raise if insn.branches? }
+          insns[0...-1].each { |insn| raise unless insn.branch_targets.empty? }
         end
 
         def last
@@ -157,8 +157,13 @@ def find_basic_block_starts
           block_starts = Set.new([0])
 
           insns.each_with_index do |insn, index|
-            if insn.branches?
-              block_starts.add(labels[insn.label]) if insn.respond_to?(:label)
+            branch_targets = insn.branch_targets
+
+            if branch_targets.any?
+              branch_targets.each do |branch_target|
+                block_starts.add(labels[branch_target])
+              end
+
               block_starts.add(index + 1) if insn.falls_through?
             end
           end
@@ -186,11 +191,11 @@ def connect_basic_blocks(blocks)
           blocks.each do |block_start, block|
             insn = block.last
 
-            if insn.branches? && insn.respond_to?(:label)
-              block.successors << blocks.fetch(labels[insn.label])
+            insn.branch_targets.each do |branch_target|
+              block.successors << blocks.fetch(labels[branch_target])
             end
 
-            if (!insn.branches? && !insn.leaves?) || insn.falls_through?
+            if (insn.branch_targets.empty? && !insn.leaves?) || insn.falls_through?
               block.successors << blocks.fetch(block_start + block.insns.length)
             end
 

lib/syntax_tree/yarv/instructions.rb

@@ -90,9 +90,9 @@ def pops
         0
       end
 
-      # Whether or not this instruction is a branch instruction.
-      def branches?
-        false
+      # This returns an array of labels.
+      def branch_targets
+        []
       end
 
       # Whether or not this instruction leaves the current frame.
@@ -261,8 +261,8 @@ def call(vm)
         vm.jump(label) if vm.pop
       end
 
-      def branches?
-        true
+      def branch_targets
+        [label]
       end
 
       def falls_through?
@@ -322,8 +322,8 @@ def call(vm)
         vm.jump(label) if vm.pop.nil?
       end
 
-      def branches?
-        true
+      def branch_targets
+        [label]
       end
 
       def falls_through?
@@ -382,8 +382,8 @@ def call(vm)
         vm.jump(label) unless vm.pop
       end
 
-      def branches?
-        true
+      def branch_targets
+        [label]
       end
 
       def falls_through?
@@ -2237,8 +2237,8 @@ def call(vm)
         vm.jump(label)
       end
 
-      def branches?
-        true
+      def branch_targets
+        [label]
       end
     end
 
@@ -2283,10 +2283,6 @@ def call(vm)
         vm.leave
       end
 
-      def branches?
-        true
-      end
-
       def leaves?
         true
       end
@@ -2998,8 +2994,8 @@ def call(vm)
         vm.jump(case_dispatch_hash.fetch(vm.pop, else_label))
       end
 
-      def branches?
-        true
+      def branch_targets
+        case_dispatch_hash.values.push(else_label)
       end
 
       def falls_through?

lib/syntax_tree/yarv/legacy.rb

@@ -115,8 +115,8 @@ def call(vm)
           vm.push(nil)
         end
 
-        def branches?
-          true
+        def branch_targets
+          [label]
         end
 
         def falls_through?