[vm, gc] Add flag to disable write barrier elimination.

TEST=ci
Change-Id: Ibf1c8afc21c695c1e959ee7463110dd2c37ed846
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/311822
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

runtime/tests/vm/dart/gc/chunked_binary_trees_array_test.dart

@@ -0,0 +1,121 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+// VMOptions=
+// VMOptions=--verify_store_buffer
+// VMOptions=--verify_after_marking
+// VMOptions=--stress_write_barrier_elimination
+// VMOptions=--no_eliminate_write_barriers
+// VMOptions=--no_inline_alloc
+
+buildTopDown(List n, int depth) {
+  if (depth == 0) return;
+
+  List l = new List<dynamic>.filled(3, null);
+  l[2] = depth; // no-barrier
+  List ll = new List<dynamic>.filled(3, null);
+  ll[2] = depth; // no-barrier
+  List lr = new List<dynamic>.filled(3, null);
+  lr[2] = depth; // no-barrier
+  List r = new List<dynamic>.filled(3, null);
+  r[2] = depth; // no-barrier
+  List rl = new List<dynamic>.filled(3, null);
+  rl[2] = depth; // no-barrier
+  List rr = new List<dynamic>.filled(3, null);
+  rr[2] = depth; // no-barrier
+
+  n[0] = l; // barrier
+  n[1] = r; // barrier
+  l[0] = ll; // no-barrier
+  l[1] = lr; // no-barrier
+  r[0] = rl; // no-barrier
+  r[1] = rr; // no-barrier
+
+  buildTopDown(ll, depth - 1);
+  buildTopDown(lr, depth - 1);
+  buildTopDown(rl, depth - 1);
+  buildTopDown(rr, depth - 1);
+}
+
+checkTopDown(List n, int depth) {
+  if (depth == 0) {
+    if (n[0] != null) throw "Bad";
+    if (n[1] != null) throw "Bad";
+    return;
+  }
+
+  if (n[0][2] != depth) throw "Bad";
+  if (n[0][0][2] != depth) throw "Bad";
+  if (n[0][1][2] != depth) throw "Bad";
+  if (n[1][2] != depth) throw "Bad";
+  if (n[1][1][2] != depth) throw "Bad";
+  checkTopDown(n[0][0]!, depth - 1);
+  checkTopDown(n[0][1]!, depth - 1);
+  checkTopDown(n[1][0]!, depth - 1);
+  checkTopDown(n[1][1]!, depth - 1);
+}
+
+runTopDown() {
+  List n = new List<dynamic>.filled(3, null);
+  n[2] = 10;
+  buildTopDown(n, 10);
+  checkTopDown(n, 10);
+}
+
+List buildBottomUp(int depth) {
+  if (depth == 0) {
+    var n = new List<dynamic>.filled(3, null);
+    n[2] = depth;
+    return n;
+  }
+
+  List ll = buildBottomUp(depth - 1);
+  List lr = buildBottomUp(depth - 1);
+  List rl = buildBottomUp(depth - 1);
+  List rr = buildBottomUp(depth - 1);
+
+  List l = new List<dynamic>.filled(3, null);
+  l[2] = depth; // no-barrier
+  List r = new List<dynamic>.filled(3, null);
+  r[2] = depth; // no-barrier
+  List n = new List<dynamic>.filled(3, null);
+  n[2] = depth; // no-barrier
+
+  n[0] = l; // no-barrier
+  n[1] = r; // no-barrier
+  l[0] = ll; // no-barrier
+  l[1] = lr; // no-barrier
+  r[0] = rl; // no-barrier
+  r[1] = rr; // no-barrier
+
+  return n;
+}
+
+checkButtomUp(List n, int depth) {
+  if (depth == 0) {
+    if (n[0] != null) throw "Bad";
+    if (n[1] != null) throw "Bad";
+    return;
+  }
+
+  if (n[2] != depth) throw "Bad";
+  if (n[0][2] != depth) throw "Bad";
+  if (n[1][2] != depth) throw "Bad";
+  checkButtomUp(n[0][0]!, depth - 1);
+  checkButtomUp(n[0][1]!, depth - 1);
+  checkButtomUp(n[1][0]!, depth - 1);
+  checkButtomUp(n[1][1]!, depth - 1);
+}
+
+runBottomUp() {
+  List n = buildBottomUp(10);
+  checkButtomUp(n, 10);
+}
+
+main() {
+  for (var i = 0; i < 10; i++) {
+    runTopDown();
+    runBottomUp();
+  }
+}

runtime/tests/vm/dart/gc/chunked_binary_trees_test.dart

@@ -0,0 +1,114 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+// VMOptions=
+// VMOptions=--verify_store_buffer
+// VMOptions=--verify_after_marking
+// VMOptions=--stress_write_barrier_elimination
+// VMOptions=--no_eliminate_write_barriers
+// VMOptions=--no_inline_alloc
+
+class Node {
+  Node? left, right;
+  int depth;
+  Node(this.depth);
+}
+
+buildTopDown(Node n, int depth) {
+  if (depth == 0) return;
+
+  Node l = new Node(depth);
+  Node ll = new Node(depth);
+  Node lr = new Node(depth);
+  Node r = new Node(depth);
+  Node rl = new Node(depth);
+  Node rr = new Node(depth);
+  n.left = l; // barrier
+  n.right = r; // barrier
+  l.left = ll; // no-barrier
+  l.right = lr; // no-barrier
+  r.left = rl; // no-barrier
+  r.right = rr; // no-barrier
+
+  buildTopDown(ll, depth - 1);
+  buildTopDown(lr, depth - 1);
+  buildTopDown(rl, depth - 1);
+  buildTopDown(rr, depth - 1);
+}
+
+checkTopDown(Node n, int depth) {
+  if (depth == 0) {
+    if (n.left != null) throw "Bad";
+    if (n.right != null) throw "Bad";
+    return;
+  }
+
+  if (n.left!.depth != depth) throw "Bad";
+  if (n.left!.left!.depth != depth) throw "Bad";
+  if (n.left!.right!.depth != depth) throw "Bad";
+  if (n.right!.depth != depth) throw "Bad";
+  if (n.right!.right!.depth != depth) throw "Bad";
+  checkTopDown(n.left!.left!, depth - 1);
+  checkTopDown(n.left!.right!, depth - 1);
+  checkTopDown(n.right!.left!, depth - 1);
+  checkTopDown(n.right!.right!, depth - 1);
+}
+
+runTopDown() {
+  Node n = new Node(10);
+  buildTopDown(n, 10);
+  checkTopDown(n, 10);
+}
+
+Node buildBottomUp(int depth) {
+  if (depth == 0) {
+    return new Node(depth);
+  }
+
+  Node ll = buildBottomUp(depth - 1);
+  Node lr = buildBottomUp(depth - 1);
+  Node rl = buildBottomUp(depth - 1);
+  Node rr = buildBottomUp(depth - 1);
+
+  Node l = new Node(depth);
+  Node r = new Node(depth);
+  Node n = new Node(depth);
+
+  n.left = l; // no-barrier
+  n.right = r; // no-barrier
+  l.left = ll; // no-barrier
+  l.right = lr; // no-barrier
+  r.left = rl; // no-barrier
+  r.right = rr; // no-barrier
+
+  return n;
+}
+
+checkButtomUp(Node n, int depth) {
+  if (depth == 0) {
+    if (n.left != null) throw "Bad";
+    if (n.right != null) throw "Bad";
+    return;
+  }
+
+  if (n.depth != depth) throw "Bad";
+  if (n.left!.depth != depth) throw "Bad";
+  if (n.right!.depth != depth) throw "Bad";
+  checkButtomUp(n.left!.left!, depth - 1);
+  checkButtomUp(n.left!.right!, depth - 1);
+  checkButtomUp(n.right!.left!, depth - 1);
+  checkButtomUp(n.right!.right!, depth - 1);
+}
+
+runBottomUp() {
+  Node n = buildBottomUp(10);
+  checkButtomUp(n, 10);
+}
+
+main() {
+  for (var i = 0; i < 10; i++) {
+    runTopDown();
+    runBottomUp();
+  }
+}

runtime/tests/vm/dart/gc/splay_c_finalizer_test.dart

@@ -27,6 +27,7 @@
 // VMOptions=--verify_store_buffer
 // VMOptions=--verify_after_marking
 // VMOptions=--stress_write_barrier_elimination
+// VMOptions=--no_eliminate_write_barriers
 // VMOptions=--no_inline_alloc
 // VMOptions=--old_gen_heap_size=150
 

runtime/tests/vm/dart/gc/splay_dart_finalizer_test.dart

@@ -27,6 +27,7 @@
 // VMOptions=--verify_store_buffer
 // VMOptions=--verify_after_marking
 // VMOptions=--stress_write_barrier_elimination
+// VMOptions=--no_eliminate_write_barriers
 // VMOptions=--no_inline_alloc
 // VMOptions=--old_gen_heap_size=150
 

runtime/tests/vm/dart/gc/splay_ephemeron_test.dart

@@ -29,6 +29,7 @@
 // VMOptions=--verify_store_buffer
 // VMOptions=--verify_after_marking
 // VMOptions=--stress_write_barrier_elimination
+// VMOptions=--no_eliminate_write_barriers
 // VMOptions=--no_inline_alloc
 // VMOptions=--old_gen_heap_size=150
 

runtime/tests/vm/dart/gc/splay_test.dart

@@ -27,6 +27,7 @@
 // VMOptions=--profiler --verify_store_buffer
 // VMOptions=--profiler --verify_after_marking
 // VMOptions=--profiler --stress_write_barrier_elimination
+// VMOptions=--profiler --no_eliminate_write_barriers
 // VMOptions=--profiler --no_inline_alloc
 // VMOptions=--profiler --old_gen_heap_size=100
 // VMOptions=--profiler --mark_when_idle

runtime/tests/vm/dart/gc/splay_weak_test.dart

@@ -27,6 +27,7 @@
 // VMOptions=--verify_store_buffer
 // VMOptions=--verify_after_marking
 // VMOptions=--stress_write_barrier_elimination
+// VMOptions=--no_eliminate_write_barriers
 // VMOptions=--no_inline_alloc
 // VMOptions=--old_gen_heap_size=150
 

runtime/tests/vm/dart_2/gc/splay_c_finalizer_test.dart

@@ -31,6 +31,7 @@
 // VMOptions=--verify_store_buffer
 // VMOptions=--verify_after_marking
 // VMOptions=--stress_write_barrier_elimination
+// VMOptions=--no_eliminate_write_barriers
 // VMOptions=--no_inline_alloc
 // VMOptions=--old_gen_heap_size=150
 

runtime/tests/vm/dart_2/gc/splay_dart_finalizer_test.dart

@@ -31,6 +31,7 @@
 // VMOptions=--verify_store_buffer
 // VMOptions=--verify_after_marking
 // VMOptions=--stress_write_barrier_elimination
+// VMOptions=--no_eliminate_write_barriers
 // VMOptions=--no_inline_alloc
 // VMOptions=--old_gen_heap_size=150
 

runtime/tests/vm/dart_2/gc/splay_ephemeron_test.dart

@@ -33,6 +33,7 @@
 // VMOptions=--verify_store_buffer
 // VMOptions=--verify_after_marking
 // VMOptions=--stress_write_barrier_elimination
+// VMOptions=--no_eliminate_write_barriers
 // VMOptions=--no_inline_alloc
 // VMOptions=--old_gen_heap_size=150
 

runtime/tests/vm/dart_2/gc/splay_test.dart

@@ -31,6 +31,7 @@
 // VMOptions=--profiler --verify_store_buffer
 // VMOptions=--profiler --verify_after_marking
 // VMOptions=--profiler --stress_write_barrier_elimination
+// VMOptions=--profiler --no_eliminate_write_barriers
 // VMOptions=--profiler --no_inline_alloc
 // VMOptions=--profiler --old_gen_heap_size=100
 // VMOptions=--profiler --mark_when_idle

runtime/tests/vm/dart_2/gc/splay_weak_test.dart

@@ -31,6 +31,7 @@
 // VMOptions=--verify_store_buffer
 // VMOptions=--verify_after_marking
 // VMOptions=--stress_write_barrier_elimination
+// VMOptions=--no_eliminate_write_barriers
 // VMOptions=--no_inline_alloc
 // VMOptions=--old_gen_heap_size=150
 

runtime/vm/compiler/compiler_pass.cc

@@ -585,7 +585,11 @@ COMPILER_PASS(ReorderBlocks, {
   }
 });
 
-COMPILER_PASS(EliminateWriteBarriers, { EliminateWriteBarriers(flow_graph); });
+COMPILER_PASS(EliminateWriteBarriers, {
+  if (FLAG_eliminate_write_barriers) {
+    EliminateWriteBarriers(flow_graph);
+  }
+});
 
 COMPILER_PASS(FinalizeGraph, {
   // At the end of the pipeline, force recomputing and caching graph

runtime/vm/flag_list.h

@@ -253,6 +253,8 @@ constexpr bool FLAG_support_il_printer = false;
     "Enable magical pragmas for testing purposes. Use at your own risk!")      \
   R(eliminate_type_checks, true, bool, true,                                   \
     "Eliminate type checks when allowed by static type analysis.")             \
+  P(eliminate_write_barriers, bool, true,                                      \
+    "Eliminate write barriers when allowed by allocation invariants.")         \
   D(support_rr, bool, false, "Support running within RR.")                     \
   P(verify_entry_points, bool, false,                                          \
     "Throw API error on invalid member access through native API. See "        \

runtime/vm/thread.cc

@@ -1023,6 +1023,7 @@ class RestoreWriteBarrierInvariantVisitor : public ObjectPointerVisitor {
 void Thread::RestoreWriteBarrierInvariant(RestoreWriteBarrierInvariantOp op) {
   ASSERT(IsAtSafepoint() || OwnsGCSafepoint());
   ASSERT(IsDartMutatorThread());
+  if (!FLAG_eliminate_write_barriers) return;
 
   const StackFrameIterator::CrossThreadPolicy cross_thread_policy =
       StackFrameIterator::kAllowCrossThreadIteration;