align return generation

codegen/codegen.lua

@@ -26,18 +26,41 @@ function Codegen:new_label(prefix)
 end
 
 function Codegen:gen_expression(node)
-  if node.type == "number" then
+  if node.type == "literal" then
+    if type(node.value) ~= "number" then
+      error("Unsupported literal value: "..tostring(node.value))
+    end
     local r = self:next_reg()
     self:emit(string.format("MOV %s, %s", r, node.value))
     return r
-  elseif node.type == "variable" then
-    return self.env[node.name] -- variable already in some register
+  elseif node.type == "identifier" then
+    local r = self.env[node.name]
+    if not r then
+      error("Undefined identifier: "..tostring(node.name))
+    end
+    return r
   elseif node.type == "binary" then
+    if node.op == "=" then
+      if node.left.type ~= "identifier" then
+        error("Assignment target must be an identifier")
+      end
+      local dest = self.env[node.left.name]
+      if not dest then
+        error("Undefined identifier: "..tostring(node.left.name))
+      end
+      local right = self:gen_expression(node.right)
+      self:emit(string.format("MOV %s, %s", dest, right))
+      return dest
+    end
+
     local left = self:gen_expression(node.left)
     local right = self:gen_expression(node.right)
     -- Assume left is dest, operate on it with right
     local op_map = {["+"]="ADD", ["-"]="SUB", ["*"]="MUL", ["/"]="DIV"}
-    local op = op_map[node.operator]
+    local op = op_map[node.op]
+    if not op then
+      error("Unsupported binary operator: "..tostring(node.op))
+    end
     self:emit(string.format("%s %s, %s", op, left, right))
     return left
   else
@@ -62,34 +85,49 @@ function Codegen:gen_if(node)
   local end_label = self:new_label("endif")
 
   self:emit(string.format("JZ %s, %s", cond_reg, else_label))
-  self:gen_block(node.then_block)
+  local then_returns = self:gen_block(node.thenBranch)
   self:emit(string.format("JMP %s", end_label))
   self:emit(else_label .. ":")
-  if node.else_block then
-    self:gen_block(node.else_block)
+  local else_returns = false
+  if node.elseBranch then
+    else_returns = self:gen_block(node.elseBranch)
   end
   self:emit(end_label .. ":")
+  return then_returns and else_returns
 end
 
 function Codegen:gen_block(block)
+  local returns = false
   for _, stmt in ipairs(block) do
-    self:gen_statement(stmt)
+    returns = self:gen_statement(stmt) or false
   end
+  return returns
 end
 
 function Codegen:gen_statement(node)
-  if node.type == "declaration" then
+  if not node.type then
+    local returns = false
+    for _, stmt in ipairs(node) do
+      returns = self:gen_statement(stmt) or false
+    end
+    return returns
+  elseif node.type == "decl" then
     self:gen_declaration(node)
   elseif node.type == "expression" then
     self:gen_expression(node.expr)
   elseif node.type == "if" then
-    self:gen_if(node)
+    return self:gen_if(node)
   elseif node.type == "block" then
     self:gen_block(node.statements)
     local ret_reg = self:gen_expression(node.value)
     self:emit(string.format("MOV r0, %s", ret_reg)) -- r0 = return register
   elseif node.type == "return" then
+    if node.value then
+      local ret_reg = self:gen_expression(node.value)
+      self:emit(string.format("MOV r0, %s", ret_reg))
+    end
     self:emit("RET")
+    return true
   elseif node.type == "function" then
     self.env = {}   -- clear env for new func
     self.regCount = 0
@@ -100,11 +138,13 @@ function Codegen:gen_statement(node)
       -- assume parameters are passed in registers r1..rN
       self:emit(string.format("MOV %s, arg_%s", r, param.name))
     end
-    self:gen_block(node.body)
-    self:emit("RET")
+    if not self:gen_block(node.body) then
+      self:emit("RET")
+    end
   else
     error("Unknown statement type: "..tostring(node.type))
   end
+  return false
 end
 
 function Codegen:generate(ast)

tests/codegen_return.lua

@@ -0,0 +1,36 @@
+local Parser = require("lang/parser")
+local Codegen = require("codegen/codegen")
+
+local function assert_equal(actual, expected, label)
+  if actual ~= expected then
+    error(string.format("%s: expected %q, got %q", label, expected, actual))
+  end
+end
+
+local code = [[
+  fn int test(int x) {
+    return x + 2
+  }
+]]
+
+local parser = Parser:new(code)
+local ast = parser:parse()
+
+local codegen = Codegen:new()
+local insns = codegen:generate(ast.body)
+
+local expected = {
+  "test:",
+  "MOV r1, arg_x",
+  "MOV r2, 2",
+  "ADD r1, r2",
+  "MOV r0, r1",
+  "RET",
+}
+
+assert_equal(#insns, #expected, "instruction count")
+for i, expected_insn in ipairs(expected) do
+  assert_equal(insns[i], expected_insn, "instruction " .. i)
+end
+
+print("ok")