Experimental: add ahead-of-time compilation via weval and PBL.

This PR pulls in my work to use "weval", the WebAssembly partial
evaluator, to perform ahead-of-time compilation of JavaScript using the
PBL interpreter we previously contributed to SpiderMonkey. This work has
been merged into the BA fork of SpiderMonkey in
bytecodealliance/gecko-dev#45,  bytecodealliance/gecko-dev#46,
bytecodealliance/gecko-dev#47, bytecodealliance/gecko-dev#48,
bytecodealliance/gecko-dev#51, bytecodealliance/gecko-dev#52,
bytecodealliance/gecko-dev#53, bytecodealliance/gecko-dev#54,
bytecodealliance/gecko-dev#55, and then integrated into StarlingMonkey
in bytecodealliance/StarlingMonkey#91.

The feature is off by default; it requires a `--enable-experimental-aot`
flag to be passed to `js-compute-runtime-cli.js`. This requires a
separate build of the engine Wasm module to be used when the flag is
passed.

This should still be considered experimental until it is tested more
widely. The PBL+weval combination passes all jit-tests and jstests in
SpiderMonkey, and all integration tests in StarlingMonkey; however, it
has not yet been widely tested in real-world scenarios.

Initial speedups we are seeing on Octane (CPU-intensive JS benchmarks)
are in the 3x-5x range. This is roughly equivalent to the speedup that a
native JS engine's "baseline JIT" compiler tier gets over its
interpreter, and it uses the same basic techniques -- compiling all
polymorphic operations (all basic JS operators) to inline-cache sites
that dispatch to stubs depending on types. Further speedups can be
obtained eventually by inlining stubs from warmed-up IC chains, but that
requires warmup.

Important to note is that this compilation approach is *fully
ahead-of-time*: it requires no profiling or observation or warmup of
user code, and compiles the JS directly to Wasm that does not do any
further codegen/JIT at runtime. Thus, it is suitable for the per-request
isolation model (new Wasm instance for each request, with no shared
state).

.github/workflows/main.yml

@@ -394,7 +394,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        profile: [debug, release]
+        profile: [debug, release, weval]
     steps:
     - uses: actions/checkout@v3
       with:
@@ -409,10 +409,18 @@ jobs:
     - name: Build
       if: ${{ matrix.profile == 'debug' }}
       run: npm run build:starlingmonkey:debug
+    - name: Build
+      if: ${{ matrix.profile == 'weval' }}
+      run: npm run build:starlingmonkey:weval
     - uses: actions/upload-artifact@v3
       with:
         name: starling-${{ matrix.profile }}
         path: starling.wasm
+    - uses: actions/upload-artifact@v3
+      if: ${{ matrix.profile == 'weval' }}
+      with:
+        name: starling-${{ matrix.profile }}-ic-cache
+        path: starling-ics.wevalcache
 
   starlingmonkey-run_wpt:
     concurrency:

js-compute-runtime-cli.js

@@ -7,6 +7,8 @@ import { addSdkMetadataField } from "./src/addSdkMetadataField.js";
 
 const {
   enablePBL,
+  enableAOT,
+  aotCache,
   enableExperimentalHighResolutionTimeMethods,
   enableExperimentalTopLevelAwait,
   starlingMonkey,
@@ -38,7 +40,9 @@ if (version) {
     enableExperimentalHighResolutionTimeMethods,
     enablePBL,
     enableExperimentalTopLevelAwait,
-    starlingMonkey
+    starlingMonkey,
+    enableAOT,
+    aotCache,
   );
   await addSdkMetadataField(output, enablePBL, starlingMonkey);
 }

package.json

@@ -36,6 +36,7 @@
     "build:debug": "DEBUG=true make -j8 -C runtime/js-compute-runtime && cp runtime/js-compute-runtime/js-compute-runtime.wasm .",
     "build:starlingmonkey": "./runtime/fastly/build-release.sh",
     "build:starlingmonkey:debug": "./runtime/fastly/build-debug.sh",
+    "build:starlingmonkey:weval": "./runtime/fastly/build-release-weval.sh",
     "format-changelog": "node ci/format-changelog.js CHANGELOG.md"
   },
   "devDependencies": {
@@ -52,6 +53,7 @@
   "dependencies": {
     "@bytecodealliance/jco": "^1.3.1",
     "@bytecodealliance/wizer": "^3.0.1",
+    "@cfallin/weval": "^0.2.7",
     "acorn": "^8.12.1",
     "acorn-walk": "^8.3.3",
     "esbuild": "^0.23.0",

runtime/fastly/build-release-weval.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+cd "$(dirname "$0")" || exit 1
+RUNTIME_VERSION=$(npm pkg get version --json --prefix=../../ | jq -r)
+HOST_API=$(realpath host-api) cmake -B build-release-weval -DCMAKE_BUILD_TYPE=Release -DENABLE_BUILTIN_WEB_FETCH=0 -DENABLE_BUILTIN_WEB_FETCH_FETCH_EVENT=0 -DRUNTIME_VERSION="\"$RUNTIME_VERSION\"" -DWEVAL=ON
+cmake --build build-release-weval --parallel 8
+mv build-release-weval/starling.wasm/starling.wasm ../../starling-weval.wasm
+mv build-release-weval/starling.wasm/starling-ics.wevalcache ../../

src/compileApplicationToWasm.js

@@ -6,6 +6,7 @@ import { rmSync } from "node:fs";
 import { isFile } from "./isFile.js";
 import { isFileOrDoesNotExist } from "./isFileOrDoesNotExist.js";
 import wizer from "@bytecodealliance/wizer";
+import weval from "@cfallin/weval";
 import { precompile } from "./precompile.js";
 import { enableTopLevelAwait } from "./enableTopLevelAwait.js";
 import { bundle } from "./bundle.js";
@@ -21,7 +22,9 @@ export async function compileApplicationToWasm(
   enableExperimentalHighResolutionTimeMethods = false,
   enablePBL = false,
   enableExperimentalTopLevelAwait = false,
-  starlingMonkey = false
+  starlingMonkey = false,
+  enableAOT = false,
+  aotCache = '',
 ) {
   try {
     if (!(await isFile(input))) {
@@ -121,35 +124,68 @@ export async function compileApplicationToWasm(
   }
 
   try {
-    let wizerProcess = spawnSync(
-      `"${wizer}"`,
-      [
-        "--inherit-env=true",
-        "--allow-wasi",
-        "--dir=.",
-        ...starlingMonkey ? [`--dir=${dirname(wizerInput)}`] : [],
-        `--wasm-bulk-memory=true`,
-        "-r _start=wizer.resume",
-        `-o="${output}"`,
-        `"${wasmEngine}"`,
-      ],
-      {
-        stdio: [null, process.stdout, process.stderr],
-        input: wizerInput,
-        shell: true,
-        encoding: "utf-8",
-        env: {
-          ENABLE_EXPERIMENTAL_HIGH_RESOLUTION_TIME_METHODS:
-            enableExperimentalHighResolutionTimeMethods ? "1" : "0",
-          ENABLE_PBL: enablePBL ? "1" : "0",
-          ...process.env,
-        },
+    if (enableAOT) {
+      const wevalBin = await weval();
+
+      let wevalProcess = spawnSync(
+        `"${wevalBin}"`,
+        [
+          "weval",
+          ...aotCache ? [`--cache-ro ${aotCache}`] : [],
+          "--dir .",
+          ...starlingMonkey ? [`--dir ${dirname(wizerInput)}`] : [],
+          "-w",
+          `-i "${wasmEngine}"`,
+          `-o "${output}"`,
+        ],
+        {
+          stdio: [null, process.stdout, process.stderr],
+          input: wizerInput,
+          shell: true,
+          encoding: "utf-8",
+          env: {
+            ENABLE_EXPERIMENTAL_HIGH_RESOLUTION_TIME_METHODS:
+              enableExperimentalHighResolutionTimeMethods ? "1" : "0",
+            ENABLE_PBL: enablePBL ? "1" : "0",
+            ...process.env,
+          },
+        }
+      );
+      if (wevalProcess.status !== 0) {
+        throw new Error(`Weval initialization failure`);
       }
-    );
-    if (wizerProcess.status !== 0) {
-      throw new Error(`Wizer initialization failure`);
+      process.exitCode = wevalProcess.status;
+    } else {
+      let wizerProcess = spawnSync(
+        `"${wizer}"`,
+        [
+          "--inherit-env=true",
+          "--allow-wasi",
+          "--dir=.",
+          ...starlingMonkey ? [`--dir=${dirname(wizerInput)}`] : [],
+          `--wasm-bulk-memory=true`,
+          "-r _start=wizer.resume",
+          `-o="${output}"`,
+          `"${wasmEngine}"`,
+        ],
+        {
+          stdio: [null, process.stdout, process.stderr],
+          input: wizerInput,
+          shell: true,
+          encoding: "utf-8",
+          env: {
+            ENABLE_EXPERIMENTAL_HIGH_RESOLUTION_TIME_METHODS:
+              enableExperimentalHighResolutionTimeMethods ? "1" : "0",
+            ENABLE_PBL: enablePBL ? "1" : "0",
+            ...process.env,
+          },
+        }
+      );
+      if (wizerProcess.status !== 0) {
+        throw new Error(`Wizer initialization failure`);
+      }
+      process.exitCode = wizerProcess.status;
     }
-    process.exitCode = wizerProcess.status;
   } catch (error) {
     console.error(
       `Error: Failed to compile JavaScript to Wasm: `,

src/parseInputs.js

@@ -10,8 +10,10 @@ export async function parseInputs(cliInputs) {
   let enableExperimentalTopLevelAwait = false;
   let starlingMonkey = true;
   let enablePBL = false;
+  let enableAOT = false;
   let customEngineSet = false;
   let wasmEngine = join(__dirname, "../starling.wasm");
+  let aotCache = join(__dirname, "../starling-ics.wevalcache");
   let customInputSet = false;
   let input = join(process.cwd(), "bin/index.js");
   let customOutputSet = false;
@@ -36,6 +38,10 @@ export async function parseInputs(cliInputs) {
         enablePBL = true;
         break;
       }
+      case "--enable-experimental-aot": {
+        enableAOT = true;
+        break;
+      }
       case "-V":
       case "--version": {
         return { version: true };
@@ -66,6 +72,14 @@ export async function parseInputs(cliInputs) {
         }
         break;
       }
+      case "--aot-cache": {
+        if (isAbsolute(value)) {
+          aotCache = value;
+        } else {
+          aotCache = join(process.cwd(), value);
+        }
+        break;
+      }
       default: {
         // The reason this is not another `case` and is an `if` using `startsWith`
         // is because previous versions of the CLI allowed an arbitrary amount of
@@ -108,10 +122,22 @@ export async function parseInputs(cliInputs) {
       }
     }
   }
+
+  if (!starlingMonkey && enableAOT) {
+    // enableAOT requires StarlingMonkey.
+    console.log("AOT option is not compatible with pre-StarlingMonkey engine; please use StarlingMonkey.");
+    process.exit(1);
+  }
+  if (!customEngineSet && enableAOT) {
+      wasmEngine = join(__dirname, "../starling-weval.wasm");
+  }
+
   return {
     enableExperimentalHighResolutionTimeMethods,
     enableExperimentalTopLevelAwait,
     enablePBL,
+    enableAOT,
+    aotCache,
     input,
     output,
     starlingMonkey,

src/printHelp.js

@@ -16,6 +16,7 @@ OPTIONS:
     --engine-wasm <engine-wasm>                             The JS engine Wasm file path
     --enable-experimental-high-resolution-time-methods      Enable experimental high-resolution fastly.now() method
     --enable-experimental-top-level-await                   Enable experimental top level await
+    --enable-experimental-aot                               Enable ahead-of-time compilation of JavaScript for faster execution
 
 ARGS:
     <input>     The input JS script's file path [default: bin/index.js]