[wasm] Allow atomic operations on non-shared WebAssembly.memory

Currently atomic operations are only allowed on shared WebAssembly.memory.
An attempt to use atomic operations otherwise is a validation failure, there
is an ongoing attempt to allow Wasm atomic operations on any memory object.

https://github.com/WebAssembly/threads/issues/144

This CL adds experimental support for allowing atomic operations on all
memory objects behind the --wasm-atomics-on-non-shared-memory flag. Note
that Wait/Notify may not work as expected as they have additional checks
to ensure that the memory is a SAB.

Bug: v8:9921
Change-Id: Ia65b1a4a96ec026430fcce028465423f600adacd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1895703
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64716}

src/flags/flag-definitions.h

@@ -750,6 +750,8 @@ DEFINE_DEBUG_BOOL(trace_wasm_lazy_compilation, false,
                   "trace lazy compilation of wasm functions")
 DEFINE_BOOL(wasm_grow_shared_memory, true,
             "allow growing shared WebAssembly memory objects")
+DEFINE_BOOL(wasm_atomics_on_non_shared_memory, false,
+            "allow atomic operations on non-shared WebAssembly memory")
 DEFINE_BOOL(wasm_lazy_validation, false,
             "enable lazy validation for lazily compiled wasm functions")
 // wasm-interpret-all resets {asm-,}wasm-lazy-compilation.

src/wasm/function-body-decoder-impl.h

@@ -1695,7 +1695,8 @@ class WasmFullDecoder : public WasmDecoder<validate> {
     return true;
   }
 
-  bool CheckHasSharedMemory() {
+  bool CheckHasMemoryForAtomics() {
+    if (FLAG_wasm_atomics_on_non_shared_memory && CheckHasMemory()) return true;
     if (!VALIDATE(this->module_->has_shared_memory)) {
       this->error(this->pc_ - 1, "Atomic opcodes used without shared memory");
       return false;
@@ -2791,7 +2792,7 @@ class WasmFullDecoder : public WasmDecoder<validate> {
         this->error("invalid atomic opcode");
         return 0;
     }
-    if (!CheckHasSharedMemory()) return 0;
+    if (!CheckHasMemoryForAtomics()) return 0;
     MemoryAccessImmediate<validate> imm(
         this, this->pc_ + 1, ElementSizeLog2Of(memtype.representation()));
     len += imm.length;

test/mjsunit/wasm/atomics-non-shared.js

+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --experimental-wasm-threads --wasm-atomics-on-non-shared-memory
+
+load("test/mjsunit/wasm/wasm-module-builder.js");
+
+// TODO(gdeepti): If non-shared atomics are moving forward, ensure that
+// the tests here are more comprehensive -i.e. reuse atomics.js/atomics64.js
+// and cctests to run on both shared/non-shared memory.
+
+(function TestCompileGenericAtomicOp() {
+  print(arguments.callee.name);
+  let memory = new WebAssembly.Memory({initial: 0, maximum: 10});
+  let builder = new WasmModuleBuilder();
+  builder.addFunction("main", kSig_i_ii)
+    .addBody([
+      kExprLocalGet, 0,
+      kExprLocalGet, 1,
+      kAtomicPrefix,
+      kExprI32AtomicAdd, 2, 0]);
+  builder.addImportedMemory("m", "imported_mem");
+  let module = new WebAssembly.Module(builder.toBuffer());
+})();
+
+(function TestCompileWasmAtomicNotify() {
+  print(arguments.callee.name);
+  let memory = new WebAssembly.Memory({initial: 0, maximum: 10});
+  let builder = new WasmModuleBuilder();
+  builder.addImportedMemory("m", "memory", 0, 20);
+  builder.addFunction("main", kSig_i_ii)
+    .addBody([
+      kExprLocalGet, 0,
+      kExprLocalGet, 1,
+      kAtomicPrefix,
+      kExprAtomicNotify, 0, 0])
+    .exportAs("main");
+  let module = new WebAssembly.Module(builder.toBuffer());
+  let instance = new WebAssembly.Instance(module, {m: {memory}});
+})();
+
+(function TestCompileWasmI32AtomicWait() {
+  print(arguments.callee.name);
+  let memory = new WebAssembly.Memory({initial: 0, maximum: 10});
+  let builder = new WasmModuleBuilder();
+  builder.addImportedMemory("m", "memory", 0, 20);
+  builder.addFunction("main",
+    makeSig([kWasmI32, kWasmI32, kWasmF64], [kWasmI32]))
+    .addBody([
+      kExprLocalGet, 0,
+      kExprLocalGet, 1,
+      kExprLocalGet, 2,
+      kExprI64SConvertF64,
+      kAtomicPrefix,
+      kExprI32AtomicWait, 0, 0])
+      .exportAs("main");
+  let module = new WebAssembly.Module(builder.toBuffer());
+  let instance = new WebAssembly.Instance(module, {m: {memory}});
+})();