From d32e2ece05a7139d8fc8eee75e3859e3a53d2254 Mon Sep 17 00:00:00 2001
From: Martin Kustermann <kustermann@google.com>
Date: Mon, 10 Jun 2024 07:11:05 +0000
Subject: [PATCH] [dart2wasm] Move `StackTrace.current` for `as` checks into
 shared runtime code
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When an implicit or explicit `as` check fails we throw a [TypeError]
exception with a stack trace. Though that stack trace doesn't really
have to have the top-frame being where the check failed, it's fine if
there's an additional frame from the runtime code that actually throws
the exception.

Doing so removes `StackTrace.current` from every `as` check and
therefore reduces size.

Change-Id: Ia34b59ebaa54b8cdcd2dc7b153a1e4e2fe1dd0e9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/370340
Reviewed-by: Ömer Ağacan <omersa@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
---
 pkg/dart2wasm/lib/kernel_nodes.dart          |  2 ++
 pkg/dart2wasm/lib/types.dart                 | 16 +++++-----------
 sdk/lib/_internal/wasm/lib/errors_patch.dart |  4 ++--
 sdk/lib/_internal/wasm/lib/type.dart         |  8 ++++++++
 4 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/pkg/dart2wasm/lib/kernel_nodes.dart b/pkg/dart2wasm/lib/kernel_nodes.dart
index 2e50bf292114..b31229f4b890 100644
--- a/pkg/dart2wasm/lib/kernel_nodes.dart
+++ b/pkg/dart2wasm/lib/kernel_nodes.dart
@@ -294,6 +294,8 @@ mixin KernelNodes {
       index.getTopLevelProcedure("dart:core", "_getMasqueradedRuntimeType");
   late final Procedure isSubtype =
       index.getTopLevelProcedure("dart:core", "_isSubtype");
+  late final Procedure asSubtype =
+      index.getTopLevelProcedure("dart:core", "_asSubtype");
   late final Procedure isTypeSubtype =
       index.getTopLevelProcedure("dart:core", "_isTypeSubtype");
   late final Procedure verifyOptimizedTypeCheck =
diff --git a/pkg/dart2wasm/lib/types.dart b/pkg/dart2wasm/lib/types.dart
index 630377ea48a7..f82979ef12f3 100644
--- a/pkg/dart2wasm/lib/types.dart
+++ b/pkg/dart2wasm/lib/types.dart
@@ -426,16 +426,12 @@ class Types {
 
     w.Local operand = b.addLocal(boxedOperandType, isParameter: false);
     b.local_tee(operand);
-    w.Label asCheckBlock = b.block();
-    b.local_get(operand);
-    emitIsTest(codeGen, testedAgainstType, operandType, location);
-    b.br_if(asCheckBlock);
-    b.local_get(operand);
     makeType(codeGen, testedAgainstType);
-    codeGen.call(translator.stackTraceCurrent.reference);
-    codeGen.call(translator.throwAsCheckError.reference);
-    b.unreachable();
-    b.end();
+    final outputs = codeGen.call(translator.asSubtype.reference);
+    for (final _ in outputs) {
+      b.drop();
+    }
+    b.local_get(operand);
     return operand.type;
   }
 
@@ -594,8 +590,6 @@ class Types {
       b.local_get(b.locals[0]);
       translator.constants.instantiateConstant(function, b,
           TypeLiteralConstant(testedAgainstType), nonNullableTypeType);
-      b.call(translator.functions
-          .getFunction(translator.stackTraceCurrent.reference));
       b.call(translator.functions
           .getFunction(translator.throwAsCheckError.reference));
       b.unreachable();
diff --git a/sdk/lib/_internal/wasm/lib/errors_patch.dart b/sdk/lib/_internal/wasm/lib/errors_patch.dart
index 7d34fdcee3b3..551047daa5ea 100644
--- a/sdk/lib/_internal/wasm/lib/errors_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/errors_patch.dart
@@ -65,8 +65,8 @@ class _TypeError extends _Error implements TypeError {
   }
 
   @pragma("wasm:entry-point")
-  static Never _throwAsCheckError(
-      Object? operand, Type? type, StackTrace stackTrace) {
+  static Never _throwAsCheckError(Object? operand, Type? type) {
+    final stackTrace = StackTrace.current;
     final typeError = _TypeError.fromMessageAndStackTrace(
         "Type '${operand.runtimeType}' is not a subtype of type '$type'"
         " in type cast",
diff --git a/sdk/lib/_internal/wasm/lib/type.dart b/sdk/lib/_internal/wasm/lib/type.dart
index ed055830355e..c47a31428417 100644
--- a/sdk/lib/_internal/wasm/lib/type.dart
+++ b/sdk/lib/_internal/wasm/lib/type.dart
@@ -1186,6 +1186,14 @@ bool _isTypeSubtype(_Type s, _Type t) {
   return _TypeUniverse.isSubtype(s, null, t, null);
 }
 
+@pragma("wasm:entry-point")
+@pragma("wasm:prefer-inline")
+void _asSubtype(Object? o, _Type t) {
+  if (!_isSubtype(o, t)) {
+    _TypeError._throwAsCheckError(o, t);
+  }
+}
+
 @pragma("wasm:entry-point")
 bool _verifyOptimizedTypeCheck(
     bool result, Object? o, _Type t, String? location) {