[vm] Add dup instructions.

`Dup` will duplicate the value at the top of the stack, while `DupN` will duplicate the top `n` values on the stack.

Author: faultyserver

BYTECODE_REFERENCE.md

@@ -12,6 +12,8 @@ Myst bytecode is a binary stream of instructions for the Myst Virtual Machine to
 |            | setlocal     | 0x02   | name   | value |         |
 | stack      | push         | 0x10   | value  |       | value   |
 |            | pop          | 0x11   |        | value |         |
+|            | dup          | 0x12   |        | val   | val,val |
+|            | dupn         | 0x13   | n      | *n    | *n,*n   |
 | math       | add          | 0x20   |        | b,a   | a+b     |
 |            | subtract     | 0x21   |        | b,a   | a-b     |
 |            | multiply     | 0x22   |        | b,a   | a*b     |

src/bytecode_generator.cr

@@ -3,10 +3,20 @@ require "./myst/vm"
 include Myst::VM
 
 iseq = InstructionSequence.new
-iseq.add_instruction(Instruction::Push.new(MTValue.new("Hello,")))
-iseq.add_instruction(Instruction::Push.new(MTValue.new(" world!")))
+iseq.add_instruction(Instruction::Push.new(MTValue.new(1_i64)))
+iseq.add_instruction(Instruction::SetLocal.new(MTValue.new("n_2")))
+iseq.add_instruction(Instruction::Push.new(MTValue.new(1_i64)))
+iseq.add_instruction(Instruction::SetLocal.new(MTValue.new("n_1")))
+iseq.add_instruction(Instruction::Label.new(MTValue.new("loop")))
+iseq.add_instruction(Instruction::GetLocal.new(MTValue.new("n_1")))
+iseq.add_instruction(Instruction::GetLocal.new(MTValue.new("n_2")))
 iseq.add_instruction(Instruction::Add.new)
+iseq.add_instruction(Instruction::Dup.new)
 iseq.add_instruction(Instruction::Write.new)
+iseq.add_instruction(Instruction::GetLocal.new(MTValue.new("n_1")))
+iseq.add_instruction(Instruction::SetLocal.new(MTValue.new("n_2")))
+iseq.add_instruction(Instruction::SetLocal.new(MTValue.new("n_1")))
+iseq.add_instruction(Instruction::Jump.new(MTValue.new("loop")))
 
 File.open("./generated_bytecode.mtc", "w") do |io|
   iseq.to_bytecode(io)

src/myst/vm/instruction.cr

@@ -15,6 +15,9 @@ module Myst
       def_instruction Push,         0x10,
         value : MTValue
       def_instruction Pop,          0x11
+      def_instruction Dup,          0x12
+      def_instruction DupN,         0x13,
+        size : MTValue
 
       # Math
       def_instruction Add,          0x20