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Jun 16, 2015
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Stop inlining all the things #2

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339 changes: 194 additions & 145 deletions lib/code_writer.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ class CodeWriter
def initialize(output)
@output = AssemblyWriter.new(output)
@counter = 0
@implementations_cache = {}
end

def set_file_name(filename)
Expand All @@ -20,74 +21,80 @@ def write_init
end

def write_arithmetic(command)
case command
when 'add', 'sub', 'and', 'or'
output.puts <<-EOF
@SP
// SP--
MD=M-1
// Load M[SP]
A=M
D=M
// Load M[SP-1]
A=A-1
// Add M[SP] to M[SP-1]
M=M#{operand(command)}D
EOF
when 'neg', 'not'
output.puts <<-EOF
@SP
A=M-1
M=#{operand(command)}M
EOF
when 'eq', 'gt', 'lt'
true_label, end_label = 2.times.map { generate_label }
output.puts <<-EOF
@SP
// SP--
MD=M-1
// Load M[SP]
A=M
D=M
// Load M[SP-1]
A=A-1
// Subtract M[SP-1] from M[SP]
D=M-D
// If the result satisfies command then jump to (TRUE)
@#{true_label}
D;J#{command.upcase}
// Load M[SP]
@SP
A=M-1
// M[SP-1] = 0
M=0
EOF
output.jump_to(end_label)

output.define_label(true_label)
output.puts <<-EOF
// Load M[SP]
@SP
A=M-1
// M[SP-1] = -1
M=-1
EOF
output.define_label(end_label)
cache_implementation(command) do
case command
when 'add', 'sub', 'and', 'or'
output.puts <<-EOF
@SP
// SP--
MD=M-1
// Load M[SP]
A=M
D=M
// Load M[SP-1]
A=A-1
// Add M[SP] to M[SP-1]
M=M#{operand(command)}D
EOF
when 'neg', 'not'
output.puts <<-EOF
@SP
A=M-1
M=#{operand(command)}M
EOF
when 'eq', 'gt', 'lt'
true_label, end_label = 2.times.map { generate_label }
output.puts <<-EOF
@SP
// SP--
MD=M-1
// Load M[SP]
A=M
D=M
// Load M[SP-1]
A=A-1
// Subtract M[SP-1] from M[SP]
D=M-D
// If the result satisfies command then jump to (TRUE)
@#{true_label}
D;J#{command.upcase}
// Load M[SP]
@SP
A=M-1
// M[SP-1] = 0
M=0
EOF
output.jump_to(end_label)

output.define_label(true_label)
output.puts <<-EOF
// Load M[SP]
@SP
A=M-1
// M[SP-1] = -1
M=-1
EOF
output.define_label(end_label)
end
end
end

def write_push_pop(command, segment, index)
case command
when Parser::C_PUSH
write_push(segment, index)
cache_implementation("push_#{filename}_#{segment}_#{index}") do
write_push(segment, index)
end
when Parser::C_POP
load_base_address_into_r13(segment, index)
output.pop_register_d
output.puts <<-EOF
@R13
A=M
M=D
EOF
cache_implementation("pop_#{filename}_#{segment}_#{index}") do
load_base_address_into_r13(segment, index)
output.pop_register_d
output.puts <<-EOF
@R13
A=M
M=D
EOF
end
end
end

Expand All @@ -111,108 +118,115 @@ def write_if(label)
def write_function(function_name, num_locals)
@function_name = function_name
output.puts "(#{function_name})"
num_locals.times do
write_push 'constant', 0

cache_implementation("push_locals_#{num_locals}") do
num_locals.times do
write_push 'constant', 0
end
end
end

def write_call(function_name, num_args)
return_label = generate_label
output.push_value(return_label)

%w(LCL ARG THIS THAT).each do |label|
output.push_value_at(label)
end
cache_implementation("call_#{num_args}") do
%w(LCL ARG THIS THAT).each do |label|
output.push_value_at(label)
end

output.puts <<-EOF
// ARG = SP - num_args - 5
@SP
D=M
@#{num_args + 5}
D=D-A
@ARG
M=D
EOF
output.puts <<-EOF
// ARG = SP - num_args - 5
@SP
D=M
@#{num_args + 5}
D=D-A
@ARG
M=D
EOF

output.copy(from: 'SP', to: 'LCL')
output.copy(from: 'SP', to: 'LCL')
end

output.jump_to(function_name)
output.define_label(return_label)
end

def write_return
output.puts <<-EOF
// FRAME = LCL
@LCL
D=M // D=RAM[LCL]
@FRAME
M=D // RAM[FRAME]=D=RAM[LCL]

// RET = *(FRAME - 5)
@5
A=D-A // A=RAM[FRAME]-5
D=M // D=RAM[RAM[FRAME]-5]
@RET
M=D // RAM[RET]=RAM[RAM[FRAME]-5]
EOF
cache_implementation("return") do
output.puts <<-EOF
// FRAME = LCL
@LCL
D=M // D=RAM[LCL]
@FRAME
M=D // RAM[FRAME]=D=RAM[LCL]

// RET = *(FRAME - 5)
@5
A=D-A // A=RAM[FRAME]-5
D=M // D=RAM[RAM[FRAME]-5]
@RET
M=D // RAM[RET]=RAM[RAM[FRAME]-5]
EOF

# *ARG = pop()
output.pop_register_d
output.puts <<-EOF
@ARG
A=M // A=RAM[ARG]
M=D // RAM[RAM[ARG]] = pop()

// SP = ARG+1
@ARG
D=M+1
@SP
M=D

// THAT = *(FRAME - 1)
@FRAME
A=M-1 // A=RAM[FRAME-1]
D=M // D=RAM[RAM[FRAME-1]]
@THAT
M=D // RAM[THAT]=RAM[RAM[FRAME-1]]

// THIS = *(FRAME - 2)
@FRAME
A=M-1
A=A-1
D=M
@THIS
M=D

// ARG = *(FRAME - 3)
@FRAME
A=M-1
A=A-1
A=A-1
D=M
@ARG
M=D

// LCL = *(FRAME - 4)
@FRAME
A=M-1
A=A-1
A=A-1
A=A-1
D=M
@LCL
M=D

// goto RET
@RET
A=M
0;JMP
EOF
# *ARG = pop()
output.pop_register_d
output.puts <<-EOF
@ARG
A=M // A=RAM[ARG]
M=D // RAM[RAM[ARG]] = pop()

// SP = ARG+1
@ARG
D=M+1
@SP
M=D

// THAT = *(FRAME - 1)
@FRAME
A=M-1 // A=RAM[FRAME-1]
D=M // D=RAM[RAM[FRAME-1]]
@THAT
M=D // RAM[THAT]=RAM[RAM[FRAME-1]]

// THIS = *(FRAME - 2)
@FRAME
A=M-1
A=A-1
D=M
@THIS
M=D

// ARG = *(FRAME - 3)
@FRAME
A=M-1
A=A-1
A=A-1
D=M
@ARG
M=D

// LCL = *(FRAME - 4)
@FRAME
A=M-1
A=A-1
A=A-1
A=A-1
D=M
@LCL
M=D

// goto RET
@RET
A=M
0;JMP
EOF
end
end

private

attr_reader :output, :filename, :function_name
attr_reader :output, :filename, :function_name, :implementations_cache

def write_push(segment, index)
case segment
Expand Down Expand Up @@ -298,8 +312,43 @@ def base_address(segment)
}.fetch(segment)
end

def generate_label
def generate_label(text = "LABEL")
@counter += 1
"LABEL.#{@counter}"
"#{text}.#{@counter}"
end

# Only output code for an implementation subroutine once, otherwise we
# are inlining everything and the code bloats enough to not fit the ROM
def cache_implementation(name)
return_label = generate_label("RETURN_#{name.upcase}")
function_label = "__INTERNAL__#{name.upcase}"

output.puts <<-EOF
@#{return_label}
D=A
EOF

output.jump_to(function_label)

implementations_cache[name] ||= begin
output.define_label(function_label)
# Using R14 rather than some static memory as it interferes with the test assumptions >_<
output.puts <<-EOF
// Save return address
@R14
M=D
EOF

yield

output.puts <<-EOF
@R14
A=M;JMP
EOF

true # Only once! \o/
end

output.define_label(return_label)
end
end