Add clear instruction

compiler/lib/terror/generator.rb

@@ -6,7 +6,7 @@ module Terror
   class Generator
     include Instructions
     include Branching
-    attr_reader :literals, :scope, :ip, :parent
+    attr_reader :literals, :scope, :ip, :parent, :stack_size
     attr_accessor :children
 
     def initialize(parent=nil)
@@ -21,8 +21,9 @@ def initialize(parent=nil)
         @scope = Scope.new
       end
 
-      @literals  = []
-      @ip        = 0
+      @stack_size = 0
+      @literals   = []
+      @ip         = 0
     end
 
     def disassemble
@@ -50,13 +51,19 @@ def setline(line)
     end
 
     def push(value)
+      inc
       @ip += 2
       _push literal(value)
     end
 
-    def pop
-      @ip += 1
-      _pop
+    def pop(count)
+      @ip += 2
+      _pop count
+    end
+
+    def clear(count)
+      @ip += 2
+      _clear count
     end
 
     def pushtrue
@@ -81,28 +88,33 @@ def jmp(label)
     end
 
     def jif(label)
+      dec
       @ip += 2
       label.start!
       _jif label
     end
 
     def jit(label)
+      dec
       @ip += 2
       label.start!
       _jit label
     end
 
     def pushself
+      inc
       @ip += 1
       _pushself
     end
 
     def pushlobby
+      inc
       @ip += 1
       _pushlobby
     end
 
     def pushlocal(name)
+      inc
       l = local(name)
       if l.depth > 0
         @ip += 3
@@ -130,21 +142,25 @@ def getslot(name)
     end
 
     def setslot(name)
+      dec
       @ip += 2
       _setslot literal(name)
     end
 
     def send_message(msg, argc)
+      argc.times { dec }
       @ip += 3
       _send literal(msg), argc
     end
 
     def defn(name)
+      inc
       @ip += 2
       _defn literal(name)
     end
 
     def makevec(count)
+      (count-1).times { dec }
       @ip += 2
       _makevec count
     end
@@ -154,8 +170,22 @@ def ret
       _ret
     end
 
+    def clear_stack
+      extra = @stack_size - 1
+      @stack_size = 1
+      clear extra
+    end
+
     private
 
+    def inc
+      @stack_size += 1
+    end
+
+    def dec
+      @stack_size -= 1
+    end
+
     def local name
       @scope.search_local(name)
     end

compiler/lib/terror/instructions.rb

@@ -130,9 +130,10 @@ def emit(instruction)
     op :getslot,   0x40, 1
     op :setslot,   0x41, 1
 
-    op :pop,       0x42, 0
+    op :pop,       0x42, 1
     op :defn,      0x43, 1
     op :makevec,   0x44, 1
+    op :clear,     0x45, 1
 
     op :send,      0x80, 2
     op :ret,       0x90, 0

compiler/lib/terror/visitor.rb

@@ -229,6 +229,7 @@ def or(node, parent)
     end
 
     def finalize(name)
+      g.clear_stack
       out = g.encode(name)
       fns = @fns.map { |fn| fn.finalize(fn.name) }
       [out, fns].flatten.join("\n")

compiler/test/terror/generator_test.rb

@@ -136,6 +136,18 @@ module Terror
       end
     end
 
+    describe '#pop' do
+      it 'pops n elements off the stack' do
+        @g.pop 3
+      end
+    end
+
+    describe '#clear' do
+      it 'clears n elements right below the top of the stack' do
+        @g.clear 3
+      end
+    end
+
     describe '#ret' do
       it 'returns from the active call frame' do
         @g.ret

compiler/test/terror/instructions_test.rb

@@ -23,7 +23,7 @@ module Terror
     end
 
     describe 'instructions with 1 operand' do
-      %w(setline push pushlocal setlocal jmp jif jit getslot setslot makevec).each do |instruction|
+      %w(setline push pushlocal setlocal jmp jif jit getslot pop setslot makevec).each do |instruction|
         describe instruction do
           it "#{instruction} is encoded correctly" do
             inst = @g.__send__ "_#{instruction}", 2
@@ -37,7 +37,7 @@ module Terror
     end
 
     describe 'instructions with no operands' do
-      %w(noop pushself pushlobby pushtrue pushfalse pushnil pop ret dump).each do |instruction|
+      %w(noop pushself pushlobby pushtrue pushfalse pushnil ret dump).each do |instruction|
         describe instruction do
           it "#{instruction} is encoded correctly" do
             inst = @g.__send__ :"_#{instruction}"