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diff --git a/src/passes/LocalCSE.cpp b/src/passes/LocalCSE.cpp
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+/*
+ * Copyright 2017 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.
+ */
+
+//
+// Local CSE
+//
+// In each linear area of execution,
+//  * track each relevant (big enough) expression
+//  * if already seen, write to a local if not already, and reuse
+//  * invalidate the list as we see effects
+//
+// TODO: global, inter-block gvn etc.
+//
+
+#include <wasm.h>
+#include <wasm-builder.h>
+#include <wasm-traversal.h>
+#include <pass.h>
+#include <ast_utils.h>
+#include <ast/hashed.h>
+
+namespace wasm {
+
+const Index UNUSED = -1;
+
+struct LocalCSE : public WalkerPass<LinearExecutionWalker<LocalCSE>> {
+  bool isFunctionParallel() override { return true; }
+
+  Pass* create() override { return new LocalCSE(); }
+
+  // information for an expression we can reuse
+  struct UsableInfo {
+    Expression** item;
+    Index index; // if not UNUSED, then the local we are assigned to, use that to reuse us
+    EffectAnalyzer effects;
+
+    UsableInfo(Expression** item, PassOptions& passOptions) : item(item), index(UNUSED), effects(passOptions, *item) {}
+  };
+
+  // a list of usables in a linear execution trace
+  typedef HashedExpressionMap<UsableInfo> Usables;
+
+  // locals in current linear execution trace, which we try to sink
+  Usables usables;
+
+  static void doNoteNonLinear(LocalCSE* self, Expression** currp) {
+    self->usables.clear();
+  }
+
+  void checkInvalidations(EffectAnalyzer& effects) {
+    // TODO: this is O(bad)
+    std::vector<HashedExpression> invalidated;
+    for (auto& sinkable : usables) {
+      if (effects.invalidates(sinkable.second.effects)) {
+        invalidated.push_back(sinkable.first);
+      }
+    }
+    for (auto index : invalidated) {
+      usables.erase(index);
+    }
+  }
+
+  std::vector<Expression*> expressionStack;
+
+  static void visitPre(LocalCSE* self, Expression** currp) {
+    // pre operations
+    Expression* curr = *currp;
+
+    EffectAnalyzer effects(self->getPassOptions());
+    if (effects.checkPre(curr)) {
+      self->checkInvalidations(effects);
+    }
+
+    self->expressionStack.push_back(curr);
+  }
+
+  static void visitPost(LocalCSE* self, Expression** currp) {
+    auto* curr = *currp;
+
+    // main operations
+    if (self->isRelevant(curr)) {
+      self->handle(currp, curr);
+    }
+
+    // post operations
+
+    EffectAnalyzer effects(self->getPassOptions());
+    if (effects.checkPost(curr)) {
+      self->checkInvalidations(effects);
+    }
+
+    self->expressionStack.pop_back();
+  }
+
+  // override scan to add a pre and a post check task to all nodes
+  static void scan(LocalCSE* self, Expression** currp) {
+    self->pushTask(visitPost, currp);
+
+    WalkerPass<LinearExecutionWalker<LocalCSE>>::scan(self, currp);
+
+    self->pushTask(visitPre, currp);
+  }
+
+  bool isRelevant(Expression* curr) {
+    if (curr->is<GetLocal>()) {
+      return false; // trivial, this is what we optimize to!
+    }
+    if (!isConcreteWasmType(curr->type)) {
+      return false; // don't bother with unreachable etc.
+    }
+    if (EffectAnalyzer(getPassOptions(), curr).hasSideEffects()) {
+      return false; // we can't combine things with side effects
+    }
+    // check what we care about TODO: use optimize/shrink levels?
+    return Measurer::measure(curr) > 1;
+  }
+
+  void handle(Expression** currp, Expression* curr) {
+    HashedExpression hashed(curr);
+    auto iter = usables.find(hashed);
+    if (iter != usables.end()) {
+      // already exists in the table, this is good to reuse
+      auto& info = iter->second;
+      if (info.index == UNUSED) {
+        // we need to assign to a local. create a new one
+        auto index = info.index = Builder::addVar(getFunction(), curr->type);
+        (*info.item) = Builder(*getModule()).makeTeeLocal(index, *info.item);
+      }
+      replaceCurrent(
+        Builder(*getModule()).makeGetLocal(info.index, curr->type)
+      );
+    } else {
+      // not in table, add this, maybe we can help others later
+      usables.emplace(std::make_pair(hashed, UsableInfo(currp, getPassOptions())));
+    }
+  }
+};
+
+Pass *createLocalCSEPass() {
+  return new LocalCSE();
+}
+
+} // namespace wasm