Add memoryBase compiler option

This allows having fixed-size application-specific memory in front, followed by compiler-generated static memory and the heap.

bin/asc.js

@@ -277,6 +277,7 @@ exports.main = function main(argv, options, callback) {
   assemblyscript.setNoTreeShaking(compilerOptions, !!args.noTreeShaking);
   assemblyscript.setNoAssert(compilerOptions, !!args.noAssert);
   assemblyscript.setNoMemory(compilerOptions, !!args.noMemory);
+  assemblyscript.setMemoryBase(compilerOptions, args.memoryBase >>> 0);
   assemblyscript.setSourceMap(compilerOptions, args.sourceMap != null);
 
   var module;

bin/asc.json

@@ -89,6 +89,10 @@
     "desc": "Does not set up a memory. Useful for low-level WebAssembly.",
     "type": "boolean"
   },
+  "memoryBase": {
+    "desc": "Sets the start offset of compiler-generated static memory.",
+    "type": "number"
+  },
   "noLib": {
     "desc": "Does not include the shipped standard library.",
     "type": "boolean"

src/compiler.ts

@@ -141,6 +141,8 @@ export class Options {
   noAssert: bool = false;
   /** If true, does not set up a memory. */
   noMemory: bool = false;
+  /** Static memory start offset. */
+  memoryBase: u32 = 0;
   /** Memory allocation implementation to use. */
   allocateImpl: string = "allocate_memory";
   /** Memory freeing implementation to use. */
@@ -210,7 +212,7 @@ export class Compiler extends DiagnosticEmitter {
     super(program.diagnostics);
     this.program = program;
     this.options = options ? options : new Options();
-    this.memoryOffset = i64_new(this.options.usizeType.byteSize, 0); // leave space for `null`
+    this.memoryOffset = i64_new(max(this.options.memoryBase, this.options.usizeType.byteSize), 0); // leave space for `null`
     this.module = Module.create();
   }
 

src/index.ts

@@ -97,6 +97,11 @@ export function setSourceMap(options: Options, sourceMap: bool): void {
   options.sourceMap = sourceMap;
 }
 
+/** Sets the `memoryBase` option. */
+export function setMemoryBase(options: Options, memoryBase: u32): void {
+  options.memoryBase = memoryBase;
+}
+
 /** Compiles the sources computed by the parser to a module. */
 export function compile(parser: Parser, options: Options | null = null): Module {
   var program = parser.finish();