Fix compile when memory grows afterward (#126)

packages/core/src/impl.ts

@@ -636,13 +636,13 @@ interface Layout {
 const aligned = ({ size, align }: Layout): number =>
   (size + align - 1) & ~(align - 1);
 
-/** An aligned `ArrayBuffer` view, or `undefined` for zero-sized types. */
-type View = undefined | Uint8Array | Uint16Array | Uint32Array | Float64Array;
+/** An aligned `ArrayBuffer` view. */
+type View = Uint8Array | Uint16Array | Uint32Array | Float64Array;
 
 const getView = (buffer: ArrayBuffer, layout: Layout, offset: number): View => {
   // this code assumes that the layout is uniquely determined by its `size`
   const { size } = layout;
-  if (size === 0) return undefined;
+  if (size === 0) throw Error("zero-sized type");
   else if (size === 1) return new Uint8Array(buffer, offset);
   else if (size === 2) return new Uint16Array(buffer, offset);
   else if (size === 4) return new Uint32Array(buffer, offset);
@@ -660,13 +660,13 @@ interface Meta {
    *
    * The given byte offset is only used for pointer types.
    */
-  encode: (x: unknown, offset: number) => number;
+  encode: (x: unknown, pointer: number, buffer: ArrayBuffer) => number;
 
   /** Total memory cost of an object of this type, including sub-allocations. */
   cost: number;
 
   /** Return a JS value represented by the Wasm value `x`. */
-  decode: (x: number) => unknown;
+  decode: (x: number, buffer: ArrayBuffer) => unknown;
 }
 
 /**
@@ -680,7 +680,6 @@ interface Meta {
  */
 const getMeta = (
   f: Fn,
-  buffer: ArrayBuffer,
   metas: (Meta | undefined)[],
   t: number,
 ): Meta | undefined => {
@@ -724,41 +723,48 @@ const getMeta = (
     const n = func.size(func.index(t));
     const elem = aligned(layout);
     const total = aligned({ size: n * elem, align: 8 });
-    const view = getView(buffer, layout, 0);
     return {
       layout: { size: 4, align: 4 },
       encode:
-        view === undefined
-          ? (x, offset) => offset
-          : (x, offset) => {
-              let child = offset + total;
+        layout.size === 0
+          ? (x, pointer) => pointer
+          : (x, pointer, buffer) => {
+              const view = getView(buffer, layout, 0);
+              let child = pointer + total;
               for (let i = 0; i < n; ++i) {
-                view[offset / elem + i] = encode((x as unknown[])[i], child);
+                view[pointer / elem + i] = encode(
+                  (x as unknown[])[i],
+                  child,
+                  buffer,
+                );
                 child += cost;
               }
-              return offset;
+              return pointer;
             },
       cost: total + n * cost,
       decode:
-        view === undefined
-          ? () => {
+        layout.size === 0
+          ? (x, buffer) => {
               const arr: unknown[] = [];
               // this code assumes that all values of all zero-sized types can
               // be represented by zero
-              for (let i = 0; i < n; ++i) arr.push(decode(0));
+              for (let i = 0; i < n; ++i) arr.push(decode(0, buffer));
               return arr;
             }
-          : (x) => {
+          : (x, buffer) => {
+              const view = getView(buffer, layout, 0);
               const arr: unknown[] = [];
-              for (let i = 0; i < n; ++i) arr.push(decode(view[x / elem + i]));
+              for (let i = 0; i < n; ++i)
+                arr.push(decode(view[x / elem + i], buffer));
               return arr;
             },
     };
   } else if (func.isStruct(t)) {
     const keys = func.keys(t);
     const members = func.mems(t);
     const n = keys.length;
-    const mems: { key: string; meta: Meta; view?: View; child?: number }[] = [];
+    const mems: { key: string; meta: Meta; offset?: number; child?: number }[] =
+      [];
     for (let i = 0; i < n; ++i) {
       const meta = metas[members[i]];
       if (meta === undefined) return undefined;
@@ -774,38 +780,41 @@ const getMeta = (
       const { layout } = meta;
       const { size, align } = layout;
       offset = aligned({ size: offset, align });
-      mem.view = getView(buffer, layout, offset);
+      mem.offset = offset;
       offset += size;
     }
     const total = aligned({ size: offset, align: 8 });
     return {
       layout: { size: 4, align: 4 },
-      encode: (x, offset) => {
-        for (const { key, meta, view, child } of mems) {
+      encode: (x, pointer, buffer) => {
+        for (const { key, meta, offset, child } of mems) {
           // instead of mutating each element of `mems` above to add more data
           // and then still having an `if` statement in here, it would be nicer
           // to just map over `mems` above to produce an array of closures that
           // can be called directly, with the condition on `view === undefined`
           // being handled once rather than in every call to `encode` here
-          if (view !== undefined) {
-            view[offset / aligned(meta.layout)] = meta.encode(
+          if (meta.layout.size > 0) {
+            const view = getView(buffer, meta.layout, offset!);
+            view[pointer / aligned(meta.layout)] = meta.encode(
               (x as any)[key],
-              offset + total + child!,
+              pointer + total + child!,
+              buffer,
             );
           }
         }
-        return offset;
+        return pointer;
       },
       cost: total + cost,
-      decode: (x) => {
+      decode: (x, buffer) => {
         const obj: any = {};
-        for (const { key, meta, view } of mems) {
-          if (view === undefined) {
+        for (const { key, meta, offset } of mems) {
+          if (meta.layout.size === 0) {
             // this code assumes that all values of all zero-sized types can be
             // represented by zero
-            obj[key] = meta.decode(0);
+            obj[key] = meta.decode(0, buffer);
           } else {
-            obj[key] = meta.decode(view[x / aligned(meta.layout)]);
+            const view = getView(buffer, meta.layout, offset!);
+            obj[key] = meta.decode(view[x / aligned(meta.layout)], buffer);
           }
         }
         return obj;
@@ -834,9 +843,11 @@ export const compile = async <const A extends readonly any[], const R>(
   const pages = Number(res.pages);
   const imports = res.imports()!;
   res.free();
-  let memory = opts?.memory;
-  if (memory === undefined) memory = new WebAssembly.Memory({ initial: pages });
+  let memory: WebAssembly.Memory;
+  const given = opts?.memory;
+  if (given === undefined) memory = new WebAssembly.Memory({ initial: pages });
   else {
+    memory = given;
     // https://webassembly.github.io/spec/core/exec/runtime.html#page-size
     const pageSize = 65536;
     const delta = pages - memory.buffer.byteLength / pageSize;
@@ -847,11 +858,10 @@ export const compile = async <const A extends readonly any[], const R>(
     m: { "": memory },
     "": Object.fromEntries(imports.map((g, i) => [i.toString(), g])),
   });
-  const { f: g, m } = instance.exports;
+  const { f: g } = instance.exports;
   const metas: (Meta | undefined)[] = [];
   const n = func.numTypes();
-  for (let t = 0; t < n; ++t)
-    metas.push(getMeta(f, (m as WebAssembly.Memory).buffer, metas, t));
+  for (let t = 0; t < n; ++t) metas.push(getMeta(f, metas, t));
   let total = 0;
   const params = Array.from(func.paramTypes()).map((t) => {
     const { encode, cost } = metas[t]!;
@@ -861,8 +871,10 @@ export const compile = async <const A extends readonly any[], const R>(
   });
   const { decode } = metas[func.retType()]!;
   return (...args): any => {
-    const vals = params.map(({ encode, offset }, i) => encode(args[i], offset));
-    return decode((g as any)(...vals, total));
+    const vals = params.map(({ encode, offset }, i) =>
+      encode(args[i], offset, memory.buffer),
+    );
+    return decode((g as any)(...vals, total), memory.buffer);
   };
 };
 

packages/core/src/index.test.ts

@@ -643,17 +643,19 @@ describe("valid", () => {
     const memory = new WebAssembly.Memory({ initial: 0 });
     expect(memory.buffer.byteLength).toBe(0);
 
-    const f = fn([Vec(2, Real)], Real, ([x, y]) => mul(x, y));
+    const f = fn([Vec(2, Real)], Vec(2, Real), ([x, y]) => [y, x]);
     const fCompiled = await compile(f, { memory });
     expect(memory.buffer.byteLength).toBe(pageSize);
-    expect(fCompiled([2, 3])).toBe(6);
 
     const n = 10000;
     const g = fn([Vec(n, Real), Vec(n, Real)], Vec(n, Real), (a, b) =>
       vec(n, Real, (i) => mul(a[i], b[i])),
     );
     const gCompiled = await compile(g, { memory });
     expect(memory.buffer.byteLength).toBeGreaterThan(pageSize);
+
+    expect(fCompiled([2, 3])).toEqual([3, 2]);
+
     const a = [];
     const b = [];
     for (let i = 1; i <= n; ++i) {