Continue refactor and rewrite comparison operator compilation

README.md

@@ -137,34 +137,96 @@ The compiler always checks types on the fly, so there is no need for a separate
 
 ### Instructions
 
-Dust's virtual machine is register-based and uses 64-bit instructions, which encode ten pieces of
+Dust's virtual machine uses 32-bit instructions, which encode seven pieces of information:
-information:
 
 Bit   | Description
 ----- | -----------
-0-5   | Operation code
+0-4   | Operation code
-6-8   | Unused, reserved in case more operation codes are needed
+5     | Flag indicating if the B argument is a constant
-9     | Flag indicating that A is a local
+6     | Flag indicating if the C argument is a constant
-10    | Flag indicating that B is a constant
+7     | D field (boolean)
-11    | Flag indicating that B is a local
+8-15  | A field (unsigned 8-bit integer)
-12    | Flag indicating that C is a constant
+16-23 | B field (unsigned 8-bit integer)
-13    | Flag indicating that C is a local
+24-31 | C field (unsigned 8-bit integer)
-14    | D Argument (boolean value)
-15-16 | Unused
-17-32 | A argument (unsigned 16-bit integer)
-33-48 | B argument (unsigned 16-bit integer)
-49-63 | C argument (unsigned 16-bit integer)
 
-Because the instructions are 64 bits, the maximum number of registers is 2^16, which is more than
+#### Operations
-enough, even for programs that are very large. This also means that chunks can store up to 2^16
+
-constants and locals.
+Five bits are used for the operation, which allows for up to 32 operations.
+
+##### Stack manipulation
+
+- MOVE: Makes a register's value available in another register by using a pointer. This avoids
+  copying the value or invalidating the original register.
+- CLOSE: Sets a range of registers to the "empty" state.
+
+##### Value loaders
+
+- LOAD_BOOLEAN: Loads a boolean, the value of which is encoded in the instruction, to a register.
+- LOAD_CONSTANT: Loads a constant from the constant list to a register.
+- LOAD_LIST: Creates a list abstraction from a range of registers and loads it to a register.
+- LOAD_MAP: Creates a map abstraction from a range of registers and loads it to a register.
+- LOAD_SELF: Creates an abstraction that represents the current function and loads it to a register.
+
+##### Variable operations
+
+- GET_LOCAL: Loads a variable's value to a register by using a pointer to point to the variable's
+  canonical register (i.e. the register whose index is stored in the locals list).
+- SET_LOCAL: Changes a variable's register to a pointer to another register, effectively changing
+  the variable's value.
+
+##### Arithmetic
+
+Arithmetic instructions use every field except for D. The A field is the destination register, the B
+and C fields are the arguments, and the flags indicate whether the arguments are constants.
+
+- ADD: Adds two values and stores the result in a register. Unlike the other arithmetic operations,
+  the ADD instruction can also be used to concatenate strings and characters.
+- SUBTRACT: Subtracts one argument from another and stores the result in a register.
+- MULTIPLY: Multiplies two arguments and stores the result in a register.
+- DIVIDE: Divides one value by another and stores the result in a register.
+- MODULO: Calculates the division remainder of two values and stores the result in a register.
+- POWER: Raises one value to the power of another and stores the result in a register.
+
+##### Logic
+
+Logic instructions work differently from arithmetic and comparison instructions, but they are still
+essentially binary operations with a left and a right argument. Rather than performing some
+calculation and storing a result, the logic instructions perform a check on the left-hand argument
+and, based on the result, either skip the right-hand argument or allow it to be executed. A `TEST`
+is always followed by a `JUMP`. If the left argument passes the test (a boolean equality check), the
+`JUMP` instruction is skipped and the right argument is executed. If the left argument fails the
+test, the `JUMP` is not skipped and it jumps past the right argument.
+
+- TEST
+- TEST_SET
+
+##### Comparison
+
+- EQUAL
+- LESS
+- LESS_EQUAL
+
+##### Unary operations
+
+- NEGATE
+- NOT
+
+##### Execution
+
+- CALL
+- CALL_NATIVE
+- JUMP
+- RETURN
+
+
+The A, B, and C
+fields are used for usually used as indexes into the constant list or stack, but they can also hold
+other information, like the number of arguments for a function call.
 
 ### Virtual Machine
 
 The virtual machine is simple and efficient. It uses a stack of registers, which can hold values or
-pointers. Pointers can point to values in the constant list, locals list, or the stack itself. If it
+pointers. Pointers can point to values in the constant list, locals list, or the stack itself.
-points to a local, the VM must consult its local definitions to find which register hold's the
-value. Those local defintions are stored as a simple list of register indexes.
 
 While the compiler has multiple responsibilities that warrant more complexity, the VM is simple
 enough to use a very straightforward design. The VM's `run` function uses a simple `while` loop with

dust-lang/src/chunk/disassembler.rs

@@ -13,30 +13,30 @@
 //! # Output
 //!
 //! The output of [Disassembler::disassemble] is a string that can be printed to the console or
-//! written to a file. Below is an example of the disassembly for a simple "Hello, world!" program.
+//! written to a file. Below is an example of the disassembly for a simple "Hello world!" program.
 //!
 //! ```text
-//! ┌──────────────────────────────────────────────────────────────────────────────┐
+//! ┌───────────────────────────────────────────────────────────────┐
 //! │                             dust                              │
 //! │                                                               │
-//! │                          write_line("hello_world")                           │
+//! │                  write_line("Hello world!")                   │
 //! │                                                               │
 //! │      3 instructions, 1 constants, 0 locals, returns none      │
 //! │                                                               │
 //! │                         Instructions                          │
 //! │                         ------------                          │
-//! │  i   POSITION    OPERATION        TYPE                    INFO               │
+//! │  i   POSITION    OPERATION                 INFO               │
-//! │ --- ---------- ------------- -------------- -------------------------------- │
+//! │ --- ---------- ------------- -------------------------------- │
-//! │  0   (11, 24)  LOAD_CONSTANT      str                   R0 = C0              │
+//! │  0   (11, 25)  LOAD_CONSTANT             R0 = C0              │
-//! │  1   (0, 25)   CALL_NATIVE        none             write_line(R0..R1)        │
+//! │  1   (0, 26)   CALL_NATIVE          write_line(R0..R1)        │
-//! │  2   (25, 25)  RETURN             none                                       │
+//! │  2   (26, 26)  RETURN                                         │
-//! │┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈│
+//! │┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈│
 //! │                           Constants                           │
 //! │                           ---------                           │
 //! │             i        TYPE             VALUE                   │
 //! │            --- ---------------- -----------------             │
-//! │                     0        str           hello_world                       │
+//! │             0        str          Hello world!                │
-//! └──────────────────────────────────────────────────────────────────────────────┘
+//! └───────────────────────────────────────────────────────────────┘
 //! ```
 use std::env::current_exe;
 

dust-lang/src/chunk/mod.rs

@@ -3,6 +3,9 @@
 //! A chunk consists of a sequence of instructions and their positions, a list of constants, and a
 //! list of locals that can be executed by the Dust virtual machine. Chunks have a name when they
 //! belong to a named function.
+mod disassembler;
+
+pub use disassembler::Disassembler;
 
 use std::fmt::{self, Debug, Display, Write};
 
@@ -10,7 +13,7 @@ use serde::{Deserialize, Serialize};
 use smallvec::SmallVec;
 use smartstring::alias::String;
 
-use crate::{ConcreteValue, Disassembler, FunctionType, Instruction, Scope, Span, Type};
+use crate::{ConcreteValue, FunctionType, Instruction, Scope, Span, Type};
 
 /// In-memory representation of a Dust program or function.
 ///

dust-lang/src/compiler/mod.rs

@@ -13,7 +13,10 @@ use std::{
 };
 
 use colored::Colorize;
-use optimize::{optimize_control_flow, optimize_set_local};
+use optimize::{
+    condense_set_local_to_math, optimize_test_with_explicit_booleans,
+    optimize_test_with_loader_arguments,
+};
 use smallvec::{smallvec, SmallVec};
 
 use crate::{
@@ -1003,7 +1006,7 @@ impl<'src> Compiler<'src> {
             });
 
             self.emit_instruction(set_local, Type::None, start_position);
-            optimize_set_local(self)?;
+            condense_set_local_to_math(self)?;
 
             return Ok(());
         }
@@ -1209,9 +1212,8 @@ impl<'src> Compiler<'src> {
         self.instructions
             .insert(if_block_start, (jump, Type::None, if_block_start_position));
 
-        if self.instructions.len() >= 4 {
+        optimize_test_with_explicit_booleans(self);
-            optimize_control_flow(&mut self.instructions);
+        optimize_test_with_loader_arguments(self);
-        }
 
         let else_last_register = self.next_register().saturating_sub(1);
         let r#move = Instruction::from(Move {
@@ -1385,13 +1387,24 @@ impl<'src> Compiler<'src> {
 
             self.emit_instruction(r#return, Type::None, self.current_position);
         } else {
-            let previous_expression_type = self.get_last_instruction_type();
+            let previous_expression_type = self
-            let should_return_value = previous_expression_type != Type::None;
+                .instructions
+                .iter()
+                .rev()
+                .find_map(|(instruction, r#type, _)| {
+                    if instruction.yields_value() {
+                        Some(r#type)
+                    } else {
+                        None
+                    }
+                })
+                .unwrap_or(&Type::None);
+            let should_return_value = previous_expression_type != &Type::None;
             let r#return = Instruction::from(Return {
                 should_return_value,
             });
 
-            self.update_return_type(previous_expression_type)?;
+            self.update_return_type(previous_expression_type.clone())?;
             self.emit_instruction(r#return, Type::None, self.current_position);
         }
 

dust-lang/src/compiler/optimize.rs

@@ -1,29 +1,14 @@
 //! Tools used by the compiler to optimize a chunk's bytecode.
 
-use crate::{instruction::SetLocal, CompileError, Compiler, Instruction, Operation, Span, Type};
+use crate::{instruction::SetLocal, CompileError, Compiler, Operation};
 
-fn get_last_operations<const COUNT: usize>(
+/// Optimizes a control flow pattern by removing redundant instructions.
-    instructions: &[(Instruction, Type, Span)],
+///
-) -> Option<[Operation; COUNT]> {
+/// If a comparison instruction is followed by a test instruction, the test instruction may be
-    let mut n_operations = [Operation::Return; COUNT];
+/// redundant because the comparison instruction already sets the correct value. If the test's
-
+/// arguments (i.e. the boolean loaders) are `true` and `false` (in that order) then the boolean
-    for (nth, operation) in n_operations.iter_mut().rev().zip(
+/// loaders, jump and test instructions are removed, leaving a single comparison instruction.
-        instructions
-            .iter()
-            .rev()
-            .map(|(instruction, _, _)| instruction.operation()),
-    ) {
-        *nth = operation;
-    }
-
-    Some(n_operations)
-}
-
-/// Optimizes a short control flow pattern.
 ///
-/// Comparison and test instructions (which are always followed by a JUMP) can be optimized when
-/// the next instructions are two constant or boolean loaders. The first loader is set to skip
-/// an instruction if it is run while the second loader is modified to use the first's register.
 /// This makes the following two code snippets compile to the same bytecode:
 ///
 /// ```dust
@@ -35,15 +20,55 @@ fn get_last_operations<const COUNT: usize>(
 /// ```
 ///
 /// The instructions must be in the following order:
-///     - `Equal`, `Less`, `LessEqual` or `Test`
+///     - `Equal`, `Less` or `LessEqual`
+///     - `Test`
+///     - `Jump`
+///     - `LoadBoolean`
+///     - `LoadBoolean`
+pub fn optimize_test_with_explicit_booleans(compiler: &mut Compiler) {
+    if matches!(
+        compiler.get_last_operations(),
+        Some([
+            Operation::Equal | Operation::Less | Operation::LessEqual,
+            Operation::Test,
+            Operation::Jump,
+            Operation::LoadBoolean,
+            Operation::LoadBoolean,
+        ])
+    ) {
+        log::debug!("Removing redundant test, jump and boolean loaders after comparison");
+
+        let first_loader = compiler.instructions.iter().nth_back(1).unwrap();
+        let second_loader = compiler.instructions.last().unwrap();
+        let first_boolean = first_loader.0.b != 0;
+        let second_boolean = second_loader.0.b != 0;
+
+        if first_boolean && !second_boolean {
+            compiler.instructions.pop();
+            compiler.instructions.pop();
+            compiler.instructions.pop();
+            compiler.instructions.pop();
+        }
+    }
+}
+
+/// Optimizes a control flow pattern.
+///
+/// Test instructions (which are always followed by a jump) can be optimized when the next
+/// instructions are two constant or boolean loaders. The first loader is set to skip an instruction
+/// if it is run while the second loader is modified to use the first's register. This foregoes the
+/// use of a jump instruction and uses one fewer register.
+///
+/// The instructions must be in the following order:
+///     - `Test`
 ///     - `Jump`
 ///     - `LoadBoolean` or `LoadConstant`
 ///     - `LoadBoolean` or `LoadConstant`
-pub fn optimize_control_flow(instructions: &mut [(Instruction, Type, Span)]) {
+pub fn optimize_test_with_loader_arguments(compiler: &mut Compiler) {
     if !matches!(
-        get_last_operations(instructions),
+        compiler.get_last_operations(),
         Some([
-            Operation::Equal | Operation::Less | Operation::LessEqual | Operation::Test,
+            Operation::Test,
             Operation::Jump,
             Operation::LoadBoolean | Operation::LoadConstant,
             Operation::LoadBoolean | Operation::LoadConstant,
@@ -54,17 +79,17 @@ pub fn optimize_control_flow(instructions: &mut [(Instruction, Type, Span)]) {
 
     log::debug!("Consolidating registers for control flow optimization");
 
-    let first_loader = &mut instructions.iter_mut().nth_back(1).unwrap().0;
+    let first_loader = &mut compiler.instructions.iter_mut().nth_back(1).unwrap().0;
 
     first_loader.c = true as u8;
 
     let first_loader_destination = first_loader.a;
-    let second_loader = &mut instructions.last_mut().unwrap().0;
+    let second_loader = &mut compiler.instructions.last_mut().unwrap().0;
 
     second_loader.a = first_loader_destination;
 }
 
-/// Optimizes a math instruction followed by a SetLocal instruction.
+/// Optimizes a math assignment pattern.
 ///
 /// The SetLocal instruction is removed and the math instruction is modified to use the local as
 /// its destination. This makes the following two code snippets compile to the same bytecode:
@@ -82,7 +107,7 @@ pub fn optimize_control_flow(instructions: &mut [(Instruction, Type, Span)]) {
 /// The instructions must be in the following order:
 ///     - `Add`, `Subtract`, `Multiply`, `Divide` or `Modulo`
 ///     - `SetLocal`
-pub fn optimize_set_local(compiler: &mut Compiler) -> Result<(), CompileError> {
+pub fn condense_set_local_to_math(compiler: &mut Compiler) -> Result<(), CompileError> {
     if !matches!(
         compiler.get_last_operations(),
         Some([

dust-lang/src/instruction/mod.rs

@@ -365,6 +365,9 @@ impl Instruction {
             | Operation::Multiply
             | Operation::Divide
             | Operation::Modulo
+            | Operation::Equal
+            | Operation::Less
+            | Operation::LessEqual
             | Operation::Negate
             | Operation::Not
             | Operation::Call

dust-lang/src/lib.rs

@@ -30,7 +30,6 @@
 
 pub mod chunk;
 pub mod compiler;
-pub mod disassembler;
 pub mod dust_error;
 pub mod instruction;
 pub mod lexer;
@@ -41,9 +40,8 @@ pub mod r#type;
 pub mod value;
 pub mod vm;
 
-pub use crate::chunk::{Chunk, Local};
+pub use crate::chunk::{Chunk, Disassembler, Local};
 pub use crate::compiler::{compile, CompileError, Compiler};
-pub use crate::disassembler::Disassembler;
 pub use crate::dust_error::{AnnotatedError, DustError};
 pub use crate::instruction::{Argument, Instruction, Operation};
 pub use crate::lexer::{lex, LexError, Lexer};