[wasm] Allocate SAB when memory is shared

When shared memory is defined in the module bytes, and not imported/exported
underlying memory should be a SharedArrayBuffer. This was missing in the
allocate flow during instantiation. Fixed to use a SharedArrayBuffer.

BUG=v8:6532

Change-Id: Ic62ed3fd578a0e03124ee40b273e6a4ea474bba4
Reviewed-on: https://chromium-review.googlesource.com/835348Reviewed-by: Eric Holk <eholk@chromium.org>
Reviewed-by: Ben Smith <binji@chromium.org>
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50255}

src/wasm/module-compiler.cc

@@ -3175,8 +3175,11 @@ Handle<JSArrayBuffer> InstanceBuilder::AllocateMemory(uint32_t num_pages) {
     return Handle<JSArrayBuffer>::null();
   }
   const bool enable_guard_regions = use_trap_handler();
+  const bool is_shared_memory =
+      module_->has_shared_memory && i::FLAG_experimental_wasm_threads;
   Handle<JSArrayBuffer> mem_buffer = NewArrayBuffer(
-      isolate_, num_pages * WasmModule::kPageSize, enable_guard_regions);
+      isolate_, num_pages * WasmModule::kPageSize, enable_guard_regions,
+      is_shared_memory ? i::SharedFlag::kShared : i::SharedFlag::kNotShared);
 
   if (mem_buffer.is_null()) {
     thrower_->RangeError("Out of memory: wasm memory");

test/mjsunit/wasm/shared-memory.js

@@ -7,20 +7,23 @@
 load("test/mjsunit/wasm/wasm-constants.js");
 load("test/mjsunit/wasm/wasm-module-builder.js");
 
-function assertMemoryIsValid(memory) {
+function assertMemoryIsValid(memory, shared) {
   assertSame(WebAssembly.Memory.prototype, memory.__proto__);
   assertSame(WebAssembly.Memory, memory.constructor);
   assertTrue(memory instanceof Object);
   assertTrue(memory instanceof WebAssembly.Memory);
+  if (shared) {
+    assertTrue(memory.buffer instanceof SharedArrayBuffer);
+    // Assert that the buffer is frozen when memory is shared.
+    assertTrue(Object.isFrozen(memory.buffer));
+  }
 }
 
 (function TestConstructorWithShared() {
   print("TestConstructorWithShared");
   let memory = new WebAssembly.Memory({
     initial: 0, maximum: 10, shared: true});
-  assertMemoryIsValid(memory);
-  // Assert that the buffer is frozen when memory is shared.
-  assertTrue(Object.isFrozen(memory.buffer));
+  assertMemoryIsValid(memory, true);
 })();
 
 (function TestConstructorWithUndefinedShared() {
@@ -36,7 +39,7 @@ function assertMemoryIsValid(memory) {
   // For numeric values, shared = true.
   let memory = new WebAssembly.Memory({
     initial: 0, maximum: 10, shared: 2098665});
-  assertMemoryIsValid(memory);
+  assertMemoryIsValid(memory, true);
 })();
 
 (function TestConstructorWithEmptyStringShared() {
@@ -101,3 +104,29 @@ function assertMemoryIsValid(memory) {
   assertThrows(() => new WebAssembly.Instance(module,
          {m: {imported_mem: memory}}), WebAssembly.LinkError);
 })();
+
+(function TestInstantiateWithSharedDefined() {
+  print("TestInstantiateWithSharedDefined");
+  let builder = new WasmModuleBuilder();
+  builder.addMemory(2, 10, true, "shared");
+  let module = new WebAssembly.Module(builder.toBuffer());
+  let instance = new WebAssembly.Instance(module);
+  assertMemoryIsValid(instance.exports.memory, true);
+})();
+
+(function TestAtomicOpWithSharedMemoryDefined() {
+  print("TestAtomicOpWithSharedMemoryDefined");
+  let builder = new WasmModuleBuilder();
+  builder.addMemory(2, 10, false, "shared");
+  builder.addFunction("main", kSig_i_ii)
+    .addBody([
+      kExprGetLocal, 0,
+      kExprGetLocal, 1,
+      kAtomicPrefix,
+      kExprI32AtomicAdd, 2, 0])
+    .exportFunc();
+  let module = new WebAssembly.Module(builder.toBuffer());
+  let instance = new WebAssembly.Instance(module);
+  assertEquals(0, instance.exports.main(0, 0x11111111));
+  assertEquals(0x11111111, instance.exports.main(0, 0x11111111));
+})();

test/mjsunit/wasm/wasm-module-builder.js

@@ -409,7 +409,6 @@ class WasmModuleBuilder {
         }
         section.emit_u32v(wasm.memory.min);
         if (has_max) section.emit_u32v(wasm.memory.max);
-        if (wasm.memory.shared) section.emit_u8(1);
       });
     }