[dart2wasm] Remove dynamic module hacks in dispatch table

The dispatch table was so far getting rows for selectors even though
we don't need to call those via dispatch table:

* if there's only 0 targets in the module then it's unreachable
* if there's only 1 targets in the module then we can call it directly

Only if we have >1 targets in the module do we need a dispatch
table entry for the selector.

So we update the dynamic module updatable function mechanism to handle
the

   * unreachable
   * direct call
   * dispatch table call

cases just like we do in the normal code generator.

Change-Id: I7144771d61fefa09c215e28dd498a4f888c73d22
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/428981
Reviewed-by: Nate Biggs <[email protected]>
Reviewed-by: Ömer Ağacan <[email protected]>
Commit-Queue: Martin Kustermann <[email protected]>

Author: mkustermann

pkg/dart2wasm/lib/dispatch_table.dart

@@ -864,9 +864,11 @@ class DispatchTable {
 }
 
 bool _isUsedViaDispatchTableCall(SelectorInfo selector) {
-  if (selector.isDynamicSubmoduleCallable) return true;
-  if (selector.callCount == 0) return false;
-  if (selector.isDynamicSubmoduleOverridable) return true;
+  // If there's no callers in this module and no callers in dynamic modules then
+  // there's no need for us to create a dispatch table entry.
+  if (selector.callCount == 0 && !selector.isDynamicSubmoduleCallable) {
+    return false;
+  }
 
   final targets = selector.targets(unchecked: false);
 

pkg/dart2wasm/lib/dynamic_modules.dart

@@ -25,6 +25,7 @@ import 'dynamic_module_kernel_metadata.dart';
 import 'intrinsics.dart' show MemberIntrinsic;
 import 'kernel_nodes.dart';
 import 'modules.dart';
+import 'param_info.dart';
 import 'record_class_generator.dart' show dynamicModulesRecordsLibraryUri;
 import 'reference_extensions.dart';
 import 'target.dart';
@@ -719,25 +720,50 @@ class DynamicModuleInfo {
   }
 
   void Function(w.FunctionBuilder) buildSelectorBranch(
-      Reference target, SelectorInfo mainSelector) {
+      Reference interfaceTarget, SelectorInfo mainSelector) {
     return (w.FunctionBuilder function) {
-      final localSelector = translator.dispatchTable.selectorForTarget(target);
-      final localSignature = localSelector.signature;
+      final localSelector =
+          translator.dispatchTable.selectorForTarget(interfaceTarget);
       final ib = function.body;
 
-      final uncheckedOffset = localSelector.targets(unchecked: true).offset;
-      final checkedOffset = localSelector.targets(unchecked: false).offset;
-
-      if (uncheckedOffset == null && checkedOffset == null) {
+      final uncheckedTargets = localSelector.targets(unchecked: true);
+      final checkedTargets = localSelector.targets(unchecked: false);
+
+      // Whether we use checked+unchecked (or normal) we'll have the same
+      // class-id ranges - only the actual target `Reference` may be a unchecked
+      // or checked one.
+      assert(uncheckedTargets.targetRanges.length ==
+          checkedTargets.targetRanges.length);
+
+      // NOTE: Keep this in sync with
+      // `code_generator.dart:AstCodeGenerator._virtualCall`.
+      final bool noTarget = checkedTargets.targetRanges.isEmpty;
+      final bool directCall = checkedTargets.targetRanges.length == 1;
+      final callPolymorphicDispatcher =
+          !directCall && checkedTargets.staticDispatchRanges.isNotEmpty;
+      // disabled for dyn overridable selectors atm
+      assert(!callPolymorphicDispatcher);
+
+      if (noTarget) {
+        ib.comment('No targets in local module for ${localSelector.name}');
         ib.unreachable();
         ib.end();
         return;
       }
 
-      final generalizedMainSignature = _getGeneralizedSignature(mainSelector);
+      final w.FunctionType localSignature;
+      final ParameterInfo localParamInfo;
+      if (directCall) {
+        final target = checkedTargets.targetRanges.single.target;
+        localSignature = translator.signatureForDirectCall(target);
+        localParamInfo = translator.paramInfoForDirectCall(target);
+      } else {
+        localSignature = localSelector.signature;
+        localParamInfo = localSelector.paramInfo;
+      }
 
+      final generalizedMainSignature = _getGeneralizedSignature(mainSelector);
       final mainParamInfo = mainSelector.paramInfo;
-      final localParamInfo = localSelector.paramInfo;
 
       assert(mainParamInfo.takesContextOrReceiver ==
           localParamInfo.takesContextOrReceiver);
@@ -799,36 +825,58 @@ class DynamicModuleInfo {
             ib, constant, localSignature.inputs[localsIndex]);
       }
 
-      ib.local_get(ib.locals[function.type.inputs.length - 2]);
-      if (isSubmodule) {
-        translator.callReference(translator.scopeClassId.reference, ib);
-      }
-      if (checkedOffset == uncheckedOffset) {
-        if (checkedOffset != 0) {
-          ib.i32_const(checkedOffset!);
-          ib.i32_add();
-        }
-      } else if (checkedOffset != 0 || uncheckedOffset != 0) {
-        // Check if the invocation is checked or unchecked and use the
-        // appropriate offset.
-        ib.local_get(ib.locals[function.type.inputs.length - 1]);
-        ib.if_(const [], const [w.NumType.i32]);
-        if (uncheckedOffset != null) {
-          ib.i32_const(uncheckedOffset);
+      if (directCall) {
+        if (!localSelector.useMultipleEntryPoints) {
+          final target = checkedTargets.targetRanges.single.target;
+          ib.invoke(translator.directCallTarget(target));
         } else {
-          ib.unreachable();
+          final uncheckedTarget = uncheckedTargets.targetRanges.single.target;
+          final checkedTarget = checkedTargets.targetRanges.single.target;
+          // Check if the invocation is checked or unchecked and use the
+          // appropriate offset.
+          ib.local_get(ib.locals[function.type.inputs.length - 1]);
+          ib.if_(const [], localSignature.outputs);
+          ib.invoke(translator.directCallTarget(uncheckedTarget));
+          ib.else_();
+          ib.invoke(translator.directCallTarget(checkedTarget));
+          ib.end();
         }
-        ib.else_();
-        if (checkedOffset != null) {
-          ib.i32_const(checkedOffset);
-        } else {
-          ib.unreachable();
+      } else {
+        ib.local_get(ib.locals[function.type.inputs.length - 2]);
+        if (isSubmodule) {
+          translator.callReference(translator.scopeClassId.reference, ib);
         }
-        ib.end();
-        ib.i32_add();
+
+        ib.comment('Local dispatch table call to "${localSelector.name}"');
+        final uncheckedOffset = uncheckedTargets.offset;
+        final checkedOffset = checkedTargets.offset;
+        if (!localSelector.useMultipleEntryPoints) {
+          if (checkedOffset != 0) {
+            ib.i32_const(checkedOffset!);
+            ib.i32_add();
+          }
+        } else if (checkedOffset != 0 || uncheckedOffset != 0) {
+          // Check if the invocation is checked or unchecked and use the
+          // appropriate offset.
+          ib.local_get(ib.locals[function.type.inputs.length - 1]);
+          ib.if_(const [], const [w.NumType.i32]);
+          if (uncheckedOffset != null) {
+            ib.i32_const(uncheckedOffset);
+          } else {
+            ib.unreachable();
+          }
+          ib.else_();
+          if (checkedOffset != null) {
+            ib.i32_const(checkedOffset);
+          } else {
+            ib.unreachable();
+          }
+          ib.end();
+          ib.i32_add();
+        }
+        final table = translator.dispatchTable.getWasmTable(ib.module);
+        ib.call_indirect(localSignature, table);
       }
-      final table = translator.dispatchTable.getWasmTable(ib.module);
-      ib.call_indirect(localSignature, table);
       translator.convertType(ib, localSignature.outputs.single,
           generalizedMainSignature.outputs.single);
       ib.end();