[dart2wasm] Add support for dispatch table calls to unchecked entries

Now that we have support for generating checked & unchecked entrypoints,
we can make dispatch tables also target unchecked entry points.

This is beneficial especially in cases where there's dispatches on
`this` that require covariant checks but we don't know the target method (i.e. we cannot devirtualize it because the method we
dispatch to may beoverriden).

We keep the existing selectors that we have, but a selector will now
have

  * one row if none of the implementations of the selector need to
    perform type checks
    => `SelectorInfo` has a `SelectorTargets _normal`

  * two rows if any of the implementations of the selector need t
    perform
    a type check
    => `SelectorInfo` has a `SelectorTargets _checked`
    => `SelectorInfo` has a `SelectorTargets _unchecked`

Once an unchecked entrypoint is also used in the dispatch table (only
if there's any unchecked calls to that selector) then binaryen can no
longer optimize the signature of the function. It means we may have
perform e.g. downcasts / boxing in the unchecked entry where we
wouldn't do before (because we only had static calls to unchecked entry
before this PR).

So we're going to force-inline calls to unchecked entrypoints. This
avoids sometimes down casts and boxing. It also seems to actually
shrink the binary size.

Change-Id: I3ba4980c42886cc883fb610533f5fac9cce39b65
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/407740
Reviewed-by: Ömer Ağacan <[email protected]>
Commit-Queue: Martin Kustermann <[email protected]>

Author: mkustermann

pkg/dart2wasm/lib/code_generator.dart

@@ -670,11 +670,13 @@ abstract class AstCodeGenerator
   List<w.ValueType> call(Reference target) {
     final targetModule = translator.moduleForReference(target);
     final isLocalModuleCall = targetModule == b.module;
+    final name = translator.functions.getFunctionName(target);
 
     if (isLocalModuleCall) {
+      b.comment('Direct call to $name');
       return b.invoke(translator.directCallTarget(target));
     } else {
-      b.comment('Indirect call to $target');
+      b.comment('Direct call to $name (across modules)');
       return translator.callReference(target, b);
     }
   }
@@ -1669,7 +1671,7 @@ abstract class AstCodeGenerator
             translateExpression(node.receiver, signature.inputs.first),
         (w.FunctionType signature, ParameterInfo paramInfo) {
       _visitArguments(node.arguments, signature, paramInfo, 1);
-    });
+    }, useUncheckedEntry: useUncheckedEntry);
   }
 
   @override
@@ -1808,18 +1810,21 @@ abstract class AstCodeGenerator
         }
       }
 
+      final useUncheckedEntry =
+          translator.canUseUncheckedEntry(node.left, node);
       if (singleTarget != null) {
         left();
         right();
         call(translator.getFunctionEntry(singleTarget.reference,
-            uncheckedEntry: translator.canUseUncheckedEntry(node, node.left)));
+            uncheckedEntry: useUncheckedEntry));
       } else {
         _virtualCall(
           node,
           node.interfaceTarget,
           _VirtualCallKind.Call,
           left,
           right,
+          useUncheckedEntry: useUncheckedEntry,
         );
       }
       if (leftNullable || rightNullable) {
@@ -1853,33 +1858,34 @@ abstract class AstCodeGenerator
       _VirtualCallKind kind,
       void Function(w.FunctionType signature) pushReceiver,
       void Function(w.FunctionType signature, ParameterInfo) pushArguments,
-      {bool useUncheckedEntry = false}) {
+      {required bool useUncheckedEntry}) {
     assert(kind != _VirtualCallKind.Get || !useUncheckedEntry);
     SelectorInfo selector = translator.dispatchTable.selectorForTarget(
         interfaceTarget.referenceAs(
             getter: kind.isGetter, setter: kind.isSetter));
+    final name = selector.entryPointName(useUncheckedEntry);
     assert(selector.name == interfaceTarget.name.text);
 
     pushReceiver(selector.signature);
 
-    if (selector.targetRanges.length == 1) {
+    final targets = selector.targets(unchecked: useUncheckedEntry);
+
+    if (targets.targetRanges.length == 1) {
       // TODO(natebiggs): Ensure dynamic modules exclude this.
 
-      assert(selector.staticDispatchRanges.length == 1);
-      final target = translator.getFunctionEntry(
-          selector.targetRanges[0].target,
-          uncheckedEntry: useUncheckedEntry);
+      assert(targets.staticDispatchRanges.length == 1);
+      final target = targets.targetRanges.single.target;
       final signature = translator.signatureForDirectCall(target);
       final paramInfo = translator.paramInfoForDirectCall(target);
       pushArguments(signature, paramInfo);
       return translator.outputOrVoid(call(target));
     }
 
-    if (selector.targetRanges.isEmpty) {
+    if (targets.targetRanges.isEmpty) {
       // TODO(natebiggs): Ensure dynamic modules exclude this.
 
       // Unreachable call
-      b.comment("Virtual call of ${selector.name} with no targets"
+      b.comment("Virtual call of $name with no targets"
           " at ${node.location}");
       pushArguments(selector.signature, selector.paramInfo);
       for (int i = 0; i < selector.signature.inputs.length; ++i) {
@@ -1897,16 +1903,18 @@ abstract class AstCodeGenerator
     b.local_tee(receiverVar);
     pushArguments(selector.signature, selector.paramInfo);
 
-    if (selector.staticDispatchRanges.isNotEmpty) {
+    if (targets.staticDispatchRanges.isNotEmpty) {
       // TODO(natebiggs): Ensure dynamic modules exclude this.
 
       b.invoke(translator
           .getPolymorphicDispatchersForModule(b.module)
-          .getPolymorphicDispatcher(selector));
+          .getPolymorphicDispatcher(selector,
+              useUncheckedEntry: useUncheckedEntry));
     } else {
-      b.comment("Instance $kind of '${selector.name}'");
+      b.comment("Instance $kind of '$name'");
       b.local_get(receiverVar);
-      translator.callDispatchTable(b, selector);
+      translator.callDispatchTable(b, selector,
+          useUncheckedEntry: useUncheckedEntry);
     }
 
     return translator.outputOrVoid(selector.signature.outputs);
@@ -2039,7 +2047,7 @@ abstract class AstCodeGenerator
         w.Label nullLabel = b.block();
         translateExpression(node.receiver, translator.topInfo.nullableType);
         b.br_on_null(nullLabel);
-      }, (_, __) {});
+      }, (_, __) {}, useUncheckedEntry: false);
       b.br(doneLabel);
       b.end(); // nullLabel
       switch (target.name.text) {
@@ -2069,7 +2077,8 @@ abstract class AstCodeGenerator
           _VirtualCallKind.Get,
           (signature) =>
               translateExpression(node.receiver, signature.inputs.first),
-          (_, __) {});
+          (_, __) {},
+          useUncheckedEntry: false);
     }
   }
 
@@ -2181,7 +2190,7 @@ abstract class AstCodeGenerator
         b.br_on_null(nullLabel);
         translator.convertType(
             b, translator.topInfo.nullableType, signature.inputs[0]);
-      }, (_, __) {});
+      }, (_, __) {}, useUncheckedEntry: false);
       b.br(doneLabel);
       b.end(); // nullLabel
       switch (target.name.text) {
@@ -2212,7 +2221,8 @@ abstract class AstCodeGenerator
         _VirtualCallKind.Get,
         (signature) =>
             translateExpression(node.receiver, signature.inputs.first),
-        (_, __) {});
+        (_, __) {},
+        useUncheckedEntry: false);
   }
 
   @override
@@ -3187,13 +3197,13 @@ CodeGenerator? getInlinableMemberCodeGenerator(Translator translator,
 
 class SynchronousProcedureCodeGenerator extends AstCodeGenerator {
   final Procedure member;
-  final SynchronousProcedureKind kind;
+  final EntryPoint kind;
 
   SynchronousProcedureCodeGenerator(Translator translator,
       w.FunctionType functionType, this.member, this.kind)
       : super(translator, functionType, member) {
-    assert(!translator.needToCheckTypesFor(member) ||
-        kind != SynchronousProcedureKind.normal);
+    assert(
+        !translator.needToCheckTypesFor(member) || kind != EntryPoint.normal);
   }
 
   @override
@@ -3216,16 +3226,16 @@ class SynchronousProcedureCodeGenerator extends AstCodeGenerator {
     closures = translator.getClosures(member);
 
     switch (kind) {
-      case SynchronousProcedureKind.normal:
+      case EntryPoint.normal:
         b.comment('Normal Entry');
         _makeNonMultiEntryPointFunction();
-      case SynchronousProcedureKind.checked:
+      case EntryPoint.checked:
         b.comment('Checked Entry');
         _makeMultipleEntryPoint(true);
-      case SynchronousProcedureKind.unchecked:
+      case EntryPoint.unchecked:
         b.comment('Unchecked Entry');
         _makeMultipleEntryPoint(false);
-      case SynchronousProcedureKind.body:
+      case EntryPoint.body:
         b.comment('Body for Checked & Unchecked Entry');
         _makeMultipleEntryPointSharedBody();
         break;