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diff --git a/src/passes/OptimizeForJS.cpp b/src/passes/OptimizeForJS.cpp
new file mode 100644
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+++ b/src/passes/OptimizeForJS.cpp
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+/*
+ * Copyright 2021 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <pass.h>
+#include <wasm.h>
+
+#include "wasm-builder.h"
+#include <ir/abstract.h>
+#include <ir/literal-utils.h>
+#include <ir/localize.h>
+#include <ir/match.h>
+
+namespace wasm {
+
+struct OptimizeForJSPass : public WalkerPass<PostWalker<OptimizeForJSPass>> {
+  bool isFunctionParallel() override { return true; }
+
+  Pass* create() override { return new OptimizeForJSPass; }
+
+  void visitBinary(Binary* curr) {
+    using namespace Abstract;
+    using namespace Match;
+    {
+      // Rewrite popcnt(x) == 1   ==>   !!x & !(x & (x - 1))
+      Expression* x;
+      if (matches(curr, binary(Eq, unary(Popcnt, any(&x)), ival(1)))) {
+        rewritePopcntEqualOne(x);
+      }
+    }
+  }
+
+  void rewritePopcntEqualOne(Expression* expr) {
+    // popcnt(x) == 1   ==>   !!x & !(x & (x - 1))
+    BinaryOp andOp, subOp;
+    UnaryOp eqzOp;
+    Literal litOne;
+    Type type = expr->type;
+
+    switch (type.getBasic()) {
+      case Type::i32:
+        eqzOp = EqZInt32;
+        andOp = AndInt32;
+        subOp = SubInt32;
+        litOne = Literal::makeOne(Type::i32);
+        break;
+
+      case Type::i64:
+        eqzOp = EqZInt64;
+        andOp = AndInt64;
+        subOp = SubInt64;
+        litOne = Literal::makeOne(Type::i64);
+        break;
+
+      default:
+        return;
+    }
+
+    Localizer temp(expr, getFunction(), getModule());
+    Builder builder(*getModule());
+
+    replaceCurrent(builder.makeBinary(
+      AndInt32,
+      builder.makeUnary(
+        EqZInt32,
+        builder.makeUnary(eqzOp, builder.makeLocalGet(temp.index, type))),
+      builder.makeUnary(
+        eqzOp,
+        builder.makeBinary(
+          andOp,
+          builder.makeLocalGet(temp.index, type),
+          builder.makeBinary(subOp,
+                             builder.makeLocalGet(temp.index, type),
+                             builder.makeConst(litOne))))));
+  }
+};
+
+Pass* createOptimizeForJSPass() { return new OptimizeForJSPass(); }
+
+} // namespace wasm