[wasm] add atomic opcodes

src/wasm/ast-decoder.cc

Index: src/wasm/ast-decoder.cc
diff --git a/src/wasm/ast-decoder.cc b/src/wasm/ast-decoder.cc
index ff5211d8fb80dbc2729193db331fd873fb7180fb..ea7ddcf52813b5f2b6dcdfd0c2a56403b3ab7c13 100644
--- a/src/wasm/ast-decoder.cc
+++ b/src/wasm/ast-decoder.cc
@@ -1158,6 +1158,24 @@ class WasmFullDecoder : public WasmDecoder {
             len += DecodeSimdOpcode(opcode);
             break;
           }
+          case kAtomicPrefix: {
+            if (!module_ || module_->origin != kAsmJsOrigin) {
+              error("Atomics are allowed only in AsmJs modules");
+              break;
+            }
+            if (!FLAG_wasm_atomics_prototype) {
+              error("Invalid opcode (enable with --wasm_atomics_prototype)");
+              break;
+            }
+            len = 2;
+            byte atomic_opcode = checked_read_u8(pc_, 1, "atomic index");
+            opcode = static_cast<WasmOpcode>(opcode << 8 | atomic_opcode);
+            sig = WasmOpcodes::AtomicSignature(opcode);
+            if (sig) {
+              BuildAtomicOperator(opcode);
+            }
+            break;
+          }
           default: {
             // Deal with special asmjs opcodes.
             if (module_ && module_->origin == kAsmJsOrigin) {
@@ -1340,6 +1358,8 @@ class WasmFullDecoder : public WasmDecoder {
     return len;
   }
 
+  void BuildAtomicOperator(WasmOpcode opcode) { UNIMPLEMENTED(); }
+
   void DoReturn() {
     int count = static_cast<int>(sig_->return_count());
     TFNode** buffer = nullptr;