[dart2wasm] Basic FFI support

Implements memory access through the `Pointer`, `Struct` and `Union` FFI
types. `Pointer` supports `fromAddress`, `address`, `elementAt`, `cast`,
`value`, `ref` (only getter), `[]`, `[]=` (not for structs and unions),
`==` and `hashCode`. Structs and unions support getters and setters for
their members.

`Pointer`, `Struct` and `Union` are all represented as `i32`, both
internally and in imports and exports. They currently don't have any
boxed representation, which means they can't be nullable (a `Pointer`
can still contain `nullptr` - the C null) and can't be assigned to
supertypes (i.e. `Object`, `dynamic`, type variables), stored in
containers nor passed as arguments or return values of local functions
or function expressions. To pass an FFI value in these situations, box
it manually by storing it in a field.

For the FFI integer types, only the explicitly sized versions (e.g.
`Int8`, `Uint32`) are supported.

Whenever the feature is used, the module will import a memory by the
name "ffi.memory", which will be accessed by the operations.

This also adds an optional commandline argument to `run_wasm.js` to
specify the module containing the FFI code. When such a module is
specified, it will be instantiated first, and its exports will appear as
imports to the Dart module under the "ffi" module name.

Change-Id: Ie55b072056f972b42db6b75e0c676944bbe88c1a
Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-debug-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/237686
Reviewed-by: Joshua Litt <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Aske Simon Christensen <[email protected]>

Author: askeksa

pkg/dart2wasm/bin/run_wasm.js

@@ -2,16 +2,21 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
-// Runner V8 script for testing dart2wasm, takes ".wasm" file as argument.
+// Runner V8 script for testing dart2wasm, takes ".wasm" files as arguments.
+//
 // Run as follows:
 //
-// $> d8 --experimental-wasm-gc --wasm-gc-js-interop run_wasm.js -- <file_name>.wasm
+// $> d8 --experimental-wasm-gc --wasm-gc-js-interop run_wasm.js -- <dart_module>.wasm [<ffi_module>.wasm]
+//
+// If an FFI module is specified, it will be instantiated first, and its
+// exports will be supplied as imports to the Dart module under the 'ffi'
+// module name.
 
 function stringFromDartString(string) {
-    var length = inst.exports.$stringLength(string);
+    var length = dartInstance.exports.$stringLength(string);
     var array = new Array(length);
     for (var i = 0; i < length; i++) {
-        array[i] = inst.exports.$stringRead(string, i);
+        array[i] = dartInstance.exports.$stringRead(string, i);
     }
     return String.fromCharCode(...array);
 }
@@ -23,15 +28,15 @@ function stringToDartString(string) {
         range |= string.codePointAt(i);
     }
     if (range < 256) {
-        var dartString = inst.exports.$stringAllocate1(length);
+        var dartString = dartInstance.exports.$stringAllocate1(length);
         for (var i = 0; i < length; i++) {
-            inst.exports.$stringWrite1(dartString, i, string.codePointAt(i));
+            dartInstance.exports.$stringWrite1(dartString, i, string.codePointAt(i));
         }
         return dartString;
     } else {
-        var dartString = inst.exports.$stringAllocate2(length);
+        var dartString = dartInstance.exports.$stringAllocate2(length);
         for (var i = 0; i < length; i++) {
-            inst.exports.$stringWrite2(dartString, i, string.codePointAt(i));
+            dartInstance.exports.$stringWrite2(dartString, i, string.codePointAt(i));
         }
         return dartString;
     }
@@ -44,7 +49,7 @@ var dart2wasm = {
     },
     scheduleCallback: function(milliseconds, closure) {
         setTimeout(function() {
-            inst.exports.$call0(closure);
+            dartInstance.exports.$call0(closure);
         }, milliseconds);
     },
     getCurrentStackTrace: function() {
@@ -62,15 +67,28 @@ var dart2wasm = {
     }
 };
 
-// Create a Wasm module from the binary wasm file.
-var bytes = readbuffer(arguments[0]);
-var module = new WebAssembly.Module(bytes);
+function instantiate(filename, imports) {
+    // Create a Wasm module from the binary wasm file.
+    var bytes = readbuffer(filename);
+    var module = new WebAssembly.Module(bytes);
+    return new WebAssembly.Instance(module, imports);
+}
 
-// Instantiate the Wasm module, importing from the global scope.
+// Import from the global scope.
 var importObject = (typeof window !== 'undefined')
     ? window
     : Realm.global(Realm.current());
-var inst = new WebAssembly.Instance(module, importObject);
 
-var result = inst.exports.main();
+// Is an FFI module specified?
+if (arguments.length > 1) {
+    // instantiate FFI module
+    var ffiInstance = instantiate(arguments[1], {});
+    // Make its exports available as imports under the 'ffi' module name
+    importObject.ffi = ffiInstance.exports;
+}
+
+// Instantiate the Dart module, importing from the global scope.
+var dartInstance = instantiate(arguments[0], importObject);
+
+var result = dartInstance.exports.main();
 if (result) console.log(result);

pkg/dart2wasm/lib/code_generator.dart

@@ -236,7 +236,9 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
       ClassInfo info = translator.classInfo[cls]!;
       thisLocal = paramLocals[0];
       w.RefType thisType = info.nonNullableType;
-      if (translator.needsConversion(paramLocals[0].type, thisType)) {
+      if (translator.needsConversion(paramLocals[0].type, thisType) &&
+          !(cls == translator.ffiPointerClass ||
+              translator.isFfiCompound(cls))) {
         preciseThisLocal = addLocal(thisType);
         b.local_get(paramLocals[0]);
         translator.ref_cast(b, info);
@@ -988,6 +990,10 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
   @override
   w.ValueType visitConstructorInvocation(
       ConstructorInvocation node, w.ValueType expectedType) {
+    w.ValueType? intrinsicResult =
+        intrinsifier.generateConstructorIntrinsic(node);
+    if (intrinsicResult != null) return intrinsicResult;
+
     ClassInfo info = translator.classInfo[node.target.enclosingClass]!;
     translator.functions.allocateClass(info.classId);
     w.Local temp = addLocal(info.nonNullableType);
@@ -1014,6 +1020,7 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
       StaticInvocation node, w.ValueType expectedType) {
     w.ValueType? intrinsicResult = intrinsifier.generateStaticIntrinsic(node);
     if (intrinsicResult != null) return intrinsicResult;
+
     _visitArguments(node.arguments, node.targetReference, 0);
     return _call(node.targetReference);
   }
@@ -1042,6 +1049,7 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
       InstanceInvocation node, w.ValueType expectedType) {
     w.ValueType? intrinsicResult = intrinsifier.generateInstanceIntrinsic(node);
     if (intrinsicResult != null) return intrinsicResult;
+
     Procedure target = node.interfaceTarget;
     if (node.kind == InstanceAccessKind.Object) {
       switch (target.name.text) {
@@ -1096,6 +1104,7 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
   w.ValueType visitEqualsCall(EqualsCall node, w.ValueType expectedType) {
     w.ValueType? intrinsicResult = intrinsifier.generateEqualsIntrinsic(node);
     if (intrinsicResult != null) return intrinsicResult;
+
     Member? singleTarget = translator.singleTarget(node);
     if (singleTarget == translator.coreTypes.objectEquals) {
       // Plain reference comparison
@@ -1352,6 +1361,7 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
     w.ValueType? intrinsicResult =
         intrinsifier.generateStaticGetterIntrinsic(node);
     if (intrinsicResult != null) return intrinsicResult;
+
     Member target = node.target;
     if (target is Field) {
       return translator.globals.readGlobal(b, target);
@@ -1493,6 +1503,9 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
 
   w.ValueType _directGet(
       Member target, Expression receiver, w.ValueType? Function() intrinsify) {
+    w.ValueType? intrinsicResult = intrinsify();
+    if (intrinsicResult != null) return intrinsicResult;
+
     if (target is Field) {
       ClassInfo info = translator.classInfo[target.enclosingClass]!;
       int fieldIndex = translator.fieldIndex[target]!;
@@ -1504,8 +1517,6 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
     } else {
       // Instance call of getter
       assert(target is Procedure && target.isGetter);
-      w.ValueType? intrinsicResult = intrinsify();
-      if (intrinsicResult != null) return intrinsicResult;
       w.BaseFunction targetFunction =
           translator.functions.getFunction(target.reference);
       wrap(receiver, targetFunction.type.inputs.single);

pkg/dart2wasm/lib/dispatch_table.dart

@@ -125,8 +125,8 @@ class SelectorInfo {
     List<w.ValueType> inputs = List.generate(
         inputSets.length,
         (i) => translator.typeForInfo(
-            upperBound(inputSets[i]), inputNullable[i]) as w.ValueType);
-    inputs[0] = translator.ensureBoxed(inputs[0]);
+                upperBound(inputSets[i]), inputNullable[i], ensureBoxed: i == 0)
+            as w.ValueType);
     if (name == '==') {
       // == can't be called with null
       inputs[1] = inputs[1].withNullability(false);