Do not treat `atomic.fence` as using a memory (#5603)

* Do not treat `atomic.fence` as using a memory

Update RemoveUnusedModuleElements so that it no longer keeps the memory alive
due to an `atomic.fence` instruction and update validation to allow modules to
use `atomic.fence` without a memory.

* update wasm2js tests

2 files changed, 0 insertions, 3 deletions

diff --git a/src/passes/RemoveUnusedModuleElements.cpp b/src/passes/RemoveUnusedModuleElements.cpp
index 6ad804e0b..103be5e4a 100644
--- a/src/passes/RemoveUnusedModuleElements.cpp
+++ b/src/passes/RemoveUnusedModuleElements.cpp
@@ -138,7 +138,6 @@ struct ReferenceFinder : public PostWalker<ReferenceFinder> {
   void visitAtomicRMW(AtomicRMW* curr) { usesMemory = true; }
   void visitAtomicWait(AtomicWait* curr) { usesMemory = true; }
   void visitAtomicNotify(AtomicNotify* curr) { usesMemory = true; }
-  void visitAtomicFence(AtomicFence* curr) { usesMemory = true; }
   void visitMemoryInit(MemoryInit* curr) { usesMemory = true; }
   void visitDataDrop(DataDrop* curr) {
     // TODO: Replace this with a use of a data segment (#5224).
diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index 123a15c1e..8abcd92fe 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -1172,8 +1172,6 @@ void FunctionValidator::visitAtomicNotify(AtomicNotify* curr) {
 }
 
 void FunctionValidator::visitAtomicFence(AtomicFence* curr) {
-  shouldBeFalse(
-    getModule()->memories.empty(), curr, "Memory operations require a memory");
   shouldBeTrue(getModule()->features.hasAtomics(),
                curr,
                "Atomic operations require threads [--enable-threads]");