Preserve asm.js code (#3362)

* Preserve asm.js code

* Actually TEST what we want to fix, and fix the implementation. Note: If we add "initial values" to instance variables in TypeScript, they are assigned AFTER the constructor is done, while "initialise" is done DURING the constructor call

src/ast/nodes/BlockStatement.ts

@@ -5,13 +5,17 @@ import BlockScope from '../scopes/BlockScope';
 import ChildScope from '../scopes/ChildScope';
 import Scope from '../scopes/Scope';
 import { UNKNOWN_EXPRESSION } from '../values';
+import ExpressionStatement from './ExpressionStatement';
 import * as NodeType from './NodeType';
 import { IncludeChildren, Node, StatementBase, StatementNode } from './shared/Node';
 
 export default class BlockStatement extends StatementBase {
 	body!: StatementNode[];
 	type!: NodeType.tBlockStatement;
 
+	private deoptimizeBody!: boolean;
+	private directlyIncluded = false;
+
 	addImplicitReturnExpressionToScope() {
 		const lastStatement = this.body[this.body.length - 1];
 		if (!lastStatement || lastStatement.type !== NodeType.ReturnStatement) {
@@ -26,6 +30,7 @@ export default class BlockStatement extends StatementBase {
 	}
 
 	hasEffects(context: HasEffectsContext) {
+		if (this.deoptimizeBody) return true;
 		for (const node of this.body) {
 			if (node.hasEffects(context)) return true;
 			if (context.brokenFlow) break;
@@ -34,13 +39,24 @@ export default class BlockStatement extends StatementBase {
 	}
 
 	include(context: InclusionContext, includeChildrenRecursively: IncludeChildren) {
-		this.included = true;
-		for (const node of this.body) {
-			if (includeChildrenRecursively || node.shouldBeIncluded(context))
-				node.include(context, includeChildrenRecursively);
+		if (!this.deoptimizeBody || !this.directlyIncluded) {
+			this.included = true;
+			this.directlyIncluded = true;
+			if (this.deoptimizeBody) includeChildrenRecursively = true;
+			for (const node of this.body) {
+				if (includeChildrenRecursively || node.shouldBeIncluded(context))
+					node.include(context, includeChildrenRecursively);
+			}
 		}
 	}
 
+	initialise() {
+		const firstBodyStatement = this.body[0];
+		this.deoptimizeBody =
+			firstBodyStatement instanceof ExpressionStatement &&
+			firstBodyStatement.directive === 'use asm';
+	}
+
 	render(code: MagicString, options: RenderOptions) {
 		if (this.body.length) {
 			renderStatementList(this.body, code, this.start + 1, this.end - 1, options);

test/form/samples/preserve-asm-js/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'Preserves asm.js code (#3360)'
+};

test/form/samples/preserve-asm-js/_expected.js

@@ -0,0 +1,34 @@
+function asmjs_included_1() {
+	'use asm';
+
+	function noop(e) {
+		// this is crucial
+		e = e | 0;
+	}
+
+	return { noop: noop };
+}
+
+function asmjs_included_2() {
+	'use asm';
+
+	function noop(e) {
+		e = e | 0;
+
+		switch (e | 0) {
+			case 10:
+				return 10;
+
+			default:
+				return e | 0;
+		}
+
+		// this is crucial
+		return e | 0;
+	}
+
+	return { noop: noop };
+}
+
+console.log(asmjs_included_1().noop(3));
+console.log(asmjs_included_2().noop(3));

test/form/samples/preserve-asm-js/main.js

@@ -0,0 +1,44 @@
+function asmjs_included_1() {
+	'use asm';
+
+	function noop(e) {
+		// this is crucial
+		e = e | 0;
+	}
+
+	return { noop: noop };
+}
+
+function asmjs_included_2() {
+	'use asm';
+
+	function noop(e) {
+		e = e | 0;
+
+		switch (e | 0) {
+			case 10:
+				return 10;
+
+			default:
+				return e | 0;
+		}
+
+		// this is crucial
+		return e | 0;
+	}
+
+	return { noop: noop };
+}
+
+function asmjs_removed() {
+	'use asm';
+
+	function noop(e) {
+		e = e | 0;
+	}
+
+	return { noop: noop };
+}
+
+console.log(asmjs_included_1().noop(3));
+console.log(asmjs_included_2().noop(3));