Add transformMultiplyLoops optimization pass and switch to using Maps

README.md

@@ -21,9 +21,8 @@ TODO
 ----
 ### gir.js
 * Implement `:;#`
-* Optimization pass to turn multiply loops into commands that do `x += y * c`
-* Make VM use a Proxied object that gives out 0 for nonexistent elements for
-  its memory
+* Make VM and transformMultiplyLoops use a Proxied object that gives out 0
+  for nonexistent elements for tape
 * Keep a cache of compiled programs in `run()`
 * Support for other types of EOF?
 

gir.js

@@ -26,6 +26,9 @@ const loop = Symbol('loop');
 // Can have offset property
 const clear = Symbol('clear');
 
+// [>+>++<<-] → {type: move, changes: Map { 0 → -1, 1 → 1, 2 → 2 }}
+const multiply = Symbol('multiply');
+
 // {type: jumpIfZero, target: 5}
 const jumpIfZero = Symbol('jumpIfZero');
 // {type: jumpIfNonZero, target: 2}
@@ -205,6 +208,13 @@ function prettifyIR(parsed) {
 					line += ` (${command.offset})`;
 				}
 				lines.push(line);
+			} else if(command.type == multiply) {
+				let changes = [];
+				for(let [offset, value] of command.changes.entries()) {
+					changes.push(`${offset}: ${value}`);
+				}
+				line += `multiply ${changes.join(', ')}`;
+				lines.push(line);
 			} else if(command.type == jumpIfZero) {
 				line += `jumpIfZero ${command.target}`;
 				lines.push(line);
@@ -212,7 +222,7 @@ function prettifyIR(parsed) {
 				line += `jumpIfNonZero ${command.target}`;
 				lines.push(line);
 			} else {
-				line += `unknown ${command.type}`;
+				line += `unknown ${command.type.toString()}`;
 				lines.push(line);
 			}
 		}
@@ -349,7 +359,8 @@ function addOffsetProperties(parsed) {
 				// our isBalanced, which will be forced to
 				// false if any inner loop is not balanced
 			} else {
-				throw new UnknownIRError();
+				throw new UnknownIRError(
+					`Unknown command ${command.type.toString()}`);
 			}
 		}
 
@@ -370,7 +381,68 @@ function addOffsetProperties(parsed) {
 	return worker(parsed).offsetted;
 }
 
-// TODO: Optimization pass to turn copy loops into copy commands
+// ([offsetCommandObjects]) → [offsetCommandObjects]
+function transformMultiplyLoops(offsetted) {
+	let optimized = [];
+
+	for(let command of offsetted) {
+		let isMultiplyLoop = false;
+		// Not necessarily a multiply loop, since multiply loops,
+		// in addition to being balanced loops with only adds,
+		// also decrement / increment the cell under tape head
+		// by one. However, these are loops we can run through the
+		// next processing step, and we can drop unfit ones after
+		// that
+		let maybeMultiplyLoop = command.type == loop &&
+			command.isBalanced &&
+			command.contents.every(x => x.type == add);
+
+		// TODO: Change this to use a Proxy thingie
+		let changes = new Map();
+		if(maybeMultiplyLoop) {
+			for(let addition of command.contents) {
+				// We already know all of these are adds
+				if(!changes.has(addition.offset)) {
+					changes.set(addition.offset, 0);
+				}
+
+				let current = changes.get(addition.offset);
+				changes.set(addition.offset,
+					current + addition.value);
+			}
+
+			// Did we actually have a multiply loop?
+			isMultiplyLoop = changes.has(0) &&
+				(changes.get(0) == 1 ||
+					changes.get(0) == -1);
+		}
+
+		if(isMultiplyLoop) {
+			// If changes[0] is 1, we are dealing with
+			// a loop of the type [>-<+], which is
+			// (except for run time) same as [>+<-].
+			// Transform former into latter
+			if(changes.get(0) == 1) {
+				for(let [offset, value] of changes.entries()) {
+					changes.set(offset, -value);
+				}
+			}
+
+			optimized.push({type: multiply,
+				changes: changes});
+		} else if(command.type == loop) {
+			// Recurse
+			optimized.push({type: loop,
+				contents: transformMultiplyLoops(command.contents),
+				balanced: command.balanced});
+		} else {
+			// Pass through
+			optimized.push(command);
+		}
+	}
+
+	return optimized;
+}
 
 // ([offsetCommandObjects]) → [flatCommandObjects]
 function flattenLoops(offsetted) {
@@ -432,6 +504,7 @@ function optimize(parsed) {
 		joinAdjacentOps,
 		transformClearLoops,
 		addOffsetProperties,
+		transformMultiplyLoops,
 		flattenLoops
 	]
 	return optimizations.reduce((IR, optimization) =>
@@ -449,7 +522,7 @@ function newVM(program, input) {
 		program: program,
 		ip: 0,
 
-		memory: Object.create(null),
+		memory: new Map(),
 		tapeHead: 0,
 
 		input: input,
@@ -468,10 +541,7 @@ function runVM(state, maxCycles = null) {
 	// Create a copy of the memory, since we're going to modify it
 	// TODO: Make memory into a Proxied thing that returns 0 if it
 	// doesn't have the requested cell
-	let memory = Object.create(null);
-	for(let key in state.memory) {
-		memory[key] = state.memory[key];
-	}
+	let memory = new Map(state.memory.entries());
 	let tapeHead = state.tapeHead;
 
 	// Create copies of input and output, since we might modify them
@@ -502,32 +572,32 @@ function runVM(state, maxCycles = null) {
 				// These have an offset property, add it
 				index += command.offset;
 				// Fall through
+			case multiply:
 			case jumpIfZero:
 			case jumpIfNonZero:
 				// Ensure the cell exists
-				if(!(index in memory)) {
-					memory[index] = 0;
+				if(!memory.has(index)) {
+					memory.set(index, 0);
 				}
 		}
 
 		// Run the command
 		switch(command.type) {
 			case add:
-				if(!(index in memory)) memory[index] = 0;
-				memory[index] += command.value;
-				// Implement wraparound
-				memory[index] = memory[index] & 0xFF;
+				let old = memory.get(index);
+				memory.set(index, (command.value + old) & 0xFF);
+
 				ip++;
 				break;
 
 			case moveHead:
 				tapeHead += command.value;
+
 				ip++;
 				break;
 
 			case writeByte:
-				if(!(index in memory)) memory[index] = 0;
-				output.push(memory[index]);
+				output.push(memory.get(index));
 				ip++;
 				break;
 
@@ -535,22 +605,42 @@ function runVM(state, maxCycles = null) {
 				// Have we reached EOF?
 				if(input.length == 0) {
 					// Yes, return 0
-					memory[index] = 0;
+					memory.set(index, 0);
 				} else {
 					// No, return character
-					memory[index] = input.shift();
+					memory.set(index, input.shift());
 				}
 				ip++;
 				break;
 
 			case clear:
-				memory[index] = 0;
+				memory.set(index, 0);
+				ip++;
+				break;
+
+			case multiply:
+				if(command.changes.get(0) != -1) {
+					throw new UnknownIRError(
+						`multiply where change for 0 is ${command.changes.get(0)}`);
+				}
+
+				let multiplier = memory.get(index);
+
+				for(let [offset, change] of command.changes.entries()) {
+					let index = tapeHead + offset;
+					if(!memory.has(index)) {
+						memory.set(index, 0);
+					}
+					let old = memory.get(index);
+					memory.set(index, old +
+						multiplier * change);
+				}
+
 				ip++;
 				break;
 
 			case jumpIfZero:
-				if(!(index in memory)) memory[index] = 0;
-				if(memory[index] == 0) {
+				if(memory.get(index) == 0) {
 					ip = command.target;
 				} else {
 					ip++;
@@ -558,8 +648,7 @@ function runVM(state, maxCycles = null) {
 				break;
 
 			case jumpIfNonZero:
-				if(!(index in memory)) memory[index] = 0;
-				if(memory[index] != 0) {
+				if(memory.get(index) != 0) {
 					ip = command.target;
 				} else {
 					ip++;
@@ -568,7 +657,8 @@ function runVM(state, maxCycles = null) {
 
 			default:
 				// Unknown command type
-				throw new UnknownIRError();
+				throw new UnknownIRError(
+					`Unknown command ${command.type.toString()}`);
 		}
 	}