Expressions should not appear twice in the ast (#1191)

3 files changed, 23 insertions, 1 deletions

diff --git a/src/wasm-emscripten.cpp b/src/wasm-emscripten.cpp
index 7463ec594..9c617a31e 100644
--- a/src/wasm-emscripten.cpp
+++ b/src/wasm-emscripten.cpp
@@ -129,7 +129,8 @@ void generateStackAllocFunction(LinkerObject& linker) {
   Block* block = builder.makeBlock();
   block->list.push_back(setStackLocal);
   block->list.push_back(storeStack);
-  block->list.push_back(getStackLocal);
+  GetLocal* getStackLocal2 = builder.makeGetLocal(1, i32);
+  block->list.push_back(getStackLocal2);
   block->type = i32;
   function->body = block;
 
diff --git a/src/wasm-validator.h b/src/wasm-validator.h
index 0851d33e8..ceaaee890 100644
--- a/src/wasm-validator.h
+++ b/src/wasm-validator.h
@@ -39,6 +39,7 @@
 
 #include <set>
 #include <sstream>
+#include <unordered_set>
 
 #include "wasm.h"
 #include "wasm-printing.h"
@@ -83,6 +84,8 @@ struct WasmValidator : public PostWalker<WasmValidator> {
 
   std::set<Name> labelNames; // Binaryen IR requires that label names must be unique - IR generators must ensure that
 
+  std::unordered_set<Expression*> seenExpressions; // expressions must not appear twice
+
   void noteLabelName(Name name);
 
 public:
diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index 5534eb7b9..85e2193fa 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -559,6 +559,24 @@ void WasmValidator::visitFunction(Function *curr) {
   shouldBeTrue(breakTargets.empty(), curr->body, "all named break targets must exist");
   returnType = unreachable;
   labelNames.clear();
+  // expressions must not be seen more than once
+  struct Walker : public PostWalker<Walker, UnifiedExpressionVisitor<Walker>> {
+    std::unordered_set<Expression*>& seen;
+    std::vector<Expression*> dupes;
+
+    Walker(std::unordered_set<Expression*>& seen) : seen(seen) {}
+
+    void visitExpression(Expression* curr) {
+      bool inserted;
+      std::tie(std::ignore, inserted) = seen.insert(curr);
+      if (!inserted) dupes.push_back(curr);
+    }
+  };
+  Walker walker(seenExpressions);
+  walker.walk(curr->body);
+  for (auto* bad : walker.dupes) {
+    fail("expression seen more than once in the tree", bad);
+  }
 }
 
 static bool checkOffset(Expression* curr, Address add, Address max) {