diff --git a/src/passes/MergeBlocks.cpp b/src/passes/MergeBlocks.cpp
index d26817e1851..5794e1379ca 100644
--- a/src/passes/MergeBlocks.cpp
+++ b/src/passes/MergeBlocks.cpp
@@ -17,9 +17,53 @@
 //
 // Merges blocks to their parents.
 //
+// We also restructure blocks in order to enable such merging. For
+// example,
+//
+//  (i32.store
+//    (block
+//      (call $foo)
+//      (i32.load (i32.const 100))
+//    )
+//    (i32.const 0)
+//  )
+//
+// can be transformed into
+//
+//  (block
+//    (call $foo)
+//    (i32.store
+//      (block
+//        (i32.load (i32.const 100))
+//      )
+//      (i32.const 0)
+//    )
+//  )
+//
+// after which the internal block can go away, and
+// the new external block might be mergeable. This is always
+// worth it if the internal block ends up with 1 item.
+// For the second operand,
+//
+//  (i32.store
+//    (i32.const 100)
+//    (block
+//      (call $foo)
+//      (i32.load (i32.const 200))
+//    )
+//  )
+//
+// The order of operations requires that the first execute
+// before. We can do the same operation, but only if the
+// first has no side effects, or the code we are moving out
+// has no side effects.
+// If we can do this to both operands, we can generate a
+// single outside block.
+//
 
 #include <wasm.h>
 #include <pass.h>
+#include <ast_utils.h>
 
 namespace wasm {
 
@@ -50,6 +94,86 @@ struct MergeBlocks : public WalkerPass<PostWalker<MergeBlocks, Visitor<MergeBloc
       }
     }
   }
+
+  Block* optimize(Expression* curr, Expression*& child, Block* outer = nullptr, Expression** dependency1 = nullptr, Expression** dependency2 = nullptr) {
+    if (!child) return outer;
+    if (dependency1 && *dependency1 && EffectAnalyzer(*dependency1).hasSideEffects()) return outer;
+    if (dependency2 && *dependency2 && EffectAnalyzer(*dependency2).hasSideEffects()) return outer;
+    if (auto* block = child->dynCast<Block>()) {
+      if (block->list.size() >= 2) {
+        child = block->list.back();
+        if (outer == nullptr) {
+          // reuse the block, move it out
+          block->list.back() = curr;
+          block->finalize(); // last block element was our input, and is now our output, which may differ TODO optimize
+          replaceCurrent(block);
+          return block;
+        } else {
+          // append to an existing outer block
+          assert(outer->list.back() == curr);
+          outer->list.pop_back();
+          for (Index i = 0; i < block->list.size() - 1; i++) {
+            outer->list.push_back(block->list[i]);
+          }
+          outer->list.push_back(curr);
+        }
+      }
+    }
+    return outer;
+  }
+
+  void visitUnary(Unary* curr) {
+    optimize(curr, curr->value);
+  }
+  void visitSetLocal(SetLocal* curr) {
+    optimize(curr, curr->value);
+  }
+  void visitLoad(Load* curr) {
+    optimize(curr, curr->ptr);
+  }
+  void visitReturn(Return* curr) {
+    optimize(curr, curr->value);
+  }
+
+  void visitBinary(Binary* curr) {
+    optimize(curr, curr->right, optimize(curr, curr->left), &curr->left);
+  }
+  void visitStore(Store* curr) {
+    optimize(curr, curr->value, optimize(curr, curr->ptr), &curr->ptr);
+  }
+
+  void visitSelect(Select* curr) {
+    optimize(curr, curr->condition, optimize(curr, curr->ifFalse, optimize(curr, curr->ifTrue), &curr->ifTrue), &curr->ifTrue, &curr->ifFalse);
+  }
+
+  void visitBreak(Break* curr) {
+    optimize(curr, curr->condition, optimize(curr, curr->value), &curr->value);
+  }
+  void visitSwitch(Switch* curr) {
+    optimize(curr, curr->condition, optimize(curr, curr->value), &curr->value);
+  }
+
+  template<typename T>
+  void handleCall(T* curr, Block* outer = nullptr) {
+    for (Index i = 0; i < curr->operands.size(); i++) {
+      outer = optimize(curr, curr->operands[i], outer);
+      if (EffectAnalyzer(curr->operands[i]).hasSideEffects()) return;
+    }
+  }
+
+  void visitCall(Call* curr) {
+    handleCall(curr);
+  }
+
+  void visitCallImport(CallImport* curr) {
+    handleCall(curr);
+  }
+
+  void visitCallIndirect(CallIndirect* curr) {
+    auto* outer = optimize(curr, curr->target);
+    if (EffectAnalyzer(curr->target).hasSideEffects()) return;
+    handleCall(curr, outer);
+  }
 };
 
 static RegisterPass<MergeBlocks> registerPass("merge-blocks", "merges blocks to their parents");
diff --git a/src/tools/binaryen-shell.cpp b/src/tools/binaryen-shell.cpp
index 8f5fbe4e5b4..96f506934bf 100644
--- a/src/tools/binaryen-shell.cpp
+++ b/src/tools/binaryen-shell.cpp
@@ -198,50 +198,51 @@ int main(int argc, const char* argv[]) {
 
   auto input(read_file<std::vector<char>>(options.extra["infile"], Flags::Text, options.debug ? Flags::Debug : Flags::Release));
 
-  if (options.debug) std::cerr << "parsing text to s-expressions...\n";
-  SExpressionParser parser(input.data());
-  Element& root = *parser.root;
-
-  // A .wast may have multiple modules, with some asserts after them
   bool checked = false;
-  size_t i = 0;
-  while (i < root.size()) {
-    Element& curr = *root[i];
-    IString id = curr[0]->str();
-    if (id == MODULE) {
-      if (options.debug) std::cerr << "parsing s-expressions to wasm...\n";
-      Module wasm;
-      std::unique_ptr<SExpressionWasmBuilder> builder;
-      try {
+
+  try {
+    if (options.debug) std::cerr << "parsing text to s-expressions...\n";
+    SExpressionParser parser(input.data());
+    Element& root = *parser.root;
+
+    // A .wast may have multiple modules, with some asserts after them
+    size_t i = 0;
+    while (i < root.size()) {
+      Element& curr = *root[i];
+      IString id = curr[0]->str();
+      if (id == MODULE) {
+        if (options.debug) std::cerr << "parsing s-expressions to wasm...\n";
+        Module wasm;
+        std::unique_ptr<SExpressionWasmBuilder> builder;
         builder = make_unique<SExpressionWasmBuilder>(wasm, *root[i]);
-      } catch (ParseException& p) {
-        p.dump(std::cerr);
-        abort();
-      }
-      i++;
-      assert(WasmValidator().validate(wasm));
-
-      MixedArena moreModuleAllocations;
-
-      if (passes.size() > 0) {
-        if (options.debug) std::cerr << "running passes...\n";
-        PassRunner passRunner(&wasm);
-        if (options.debug) passRunner.setDebug(true);
-        for (auto& passName : passes) {
-          if (passName == "O") {
-            passRunner.addDefaultOptimizationPasses();
-          } else {
-            passRunner.add(passName);
+        i++;
+        assert(WasmValidator().validate(wasm));
+
+        MixedArena moreModuleAllocations;
+
+        if (passes.size() > 0) {
+          if (options.debug) std::cerr << "running passes...\n";
+          PassRunner passRunner(&wasm);
+          if (options.debug) passRunner.setDebug(true);
+          for (auto& passName : passes) {
+            if (passName == "O") {
+              passRunner.addDefaultOptimizationPasses();
+            } else {
+              passRunner.add(passName);
+            }
           }
+          passRunner.run();
+          assert(WasmValidator().validate(wasm));
         }
-        passRunner.run();
-        assert(WasmValidator().validate(wasm));
-      }
 
-      run_asserts(&i, &checked, &wasm, &root, &builder, entry);
-    } else {
-      run_asserts(&i, &checked, nullptr, &root, nullptr, entry);
+        run_asserts(&i, &checked, &wasm, &root, &builder, entry);
+      } else {
+        run_asserts(&i, &checked, nullptr, &root, nullptr, entry);
+      }
     }
+  } catch (ParseException& p) {
+    p.dump(std::cerr);
+    abort();
   }
 
   if (checked) {
diff --git a/src/wasm-s-parser.h b/src/wasm-s-parser.h
index dae32186693..bb6fe3fd459 100644
--- a/src/wasm-s-parser.h
+++ b/src/wasm-s-parser.h
@@ -173,7 +173,7 @@ class SExpressionParser {
         curr->list().push_back(parseString());
       }
     }
-    assert(stack.size() == 0); 
+    if (stack.size() != 0) throw ParseException("stack is not empty", curr->line, curr->col);
     return curr;
   }
 
diff --git a/test/emcc_hello_world.fromasm b/test/emcc_hello_world.fromasm
index 6f6da8ed3e7..d5e961a9221 100644
--- a/test/emcc_hello_world.fromasm
+++ b/test/emcc_hello_world.fromasm
@@ -19091,16 +19091,14 @@
                 )
               )
             )
+            (i32.store
+              (i32.const 168)
+              (i32.const 0)
+            )
             (return
-              (block
-                (i32.store
-                  (i32.const 168)
-                  (i32.const 0)
-                )
-                (i32.div_u
-                  (get_local $7)
-                  (get_local $5)
-                )
+              (i32.div_u
+                (get_local $7)
+                (get_local $5)
               )
             )
           )
@@ -19109,12 +19107,12 @@
               (i32.eqz
                 (get_local $2)
               )
-              (return
-                (block
-                  (i32.store
-                    (i32.const 168)
-                    (i32.const 0)
-                  )
+              (block
+                (i32.store
+                  (i32.const 168)
+                  (i32.const 0)
+                )
+                (return
                   (i32.const 0)
                 )
               )
@@ -19133,14 +19131,12 @@
                 (i32.const 0)
               )
             )
+            (i32.store
+              (i32.const 168)
+              (i32.const 0)
+            )
             (return
-              (block
-                (i32.store
-                  (i32.const 168)
-                  (i32.const 0)
-                )
-                (i32.const 0)
-              )
+              (i32.const 0)
             )
           )
         )
@@ -19181,16 +19177,14 @@
                   )
                 )
               )
+              (i32.store
+                (i32.const 168)
+                (i32.const 0)
+              )
               (return
-                (block
-                  (i32.store
-                    (i32.const 168)
-                    (i32.const 0)
-                  )
-                  (i32.div_u
-                    (get_local $6)
-                    (get_local $5)
-                  )
+                (i32.div_u
+                  (get_local $6)
+                  (get_local $5)
                 )
               )
             )
@@ -19220,16 +19214,14 @@
                   )
                 )
               )
+              (i32.store
+                (i32.const 168)
+                (i32.const 0)
+              )
               (return
-                (block
-                  (i32.store
-                    (i32.const 168)
-                    (i32.const 0)
-                  )
-                  (i32.div_u
-                    (get_local $6)
-                    (get_local $8)
-                  )
+                (i32.div_u
+                  (get_local $6)
+                  (get_local $8)
                 )
               )
             )
@@ -19279,17 +19271,15 @@
                   )
                 )
               )
+              (i32.store
+                (i32.const 168)
+                (i32.const 0)
+              )
               (return
-                (block
-                  (i32.store
-                    (i32.const 168)
-                    (i32.const 0)
-                  )
-                  (i32.shr_u
-                    (get_local $6)
-                    (i32.ctz
-                      (get_local $8)
-                    )
+                (i32.shr_u
+                  (get_local $6)
+                  (i32.ctz
+                    (get_local $8)
                   )
                 )
               )
@@ -19358,12 +19348,12 @@
               (get_local $4)
               (i32.const 0)
             )
-            (return
-              (block
-                (i32.store
-                  (i32.const 168)
-                  (i32.const 0)
-                )
+            (block
+              (i32.store
+                (i32.const 168)
+                (i32.const 0)
+              )
+              (return
                 (i32.const 0)
               )
             )
@@ -19388,14 +19378,12 @@
               )
             )
           )
+          (i32.store
+            (i32.const 168)
+            (i32.const 0)
+          )
           (return
-            (block
-              (i32.store
-                (i32.const 168)
-                (i32.const 0)
-              )
-              (i32.const 0)
-            )
+            (i32.const 0)
           )
         )
         (block
@@ -19481,12 +19469,12 @@
                   (get_local $4)
                   (i32.const 0)
                 )
-                (return
-                  (block
-                    (i32.store
-                      (i32.const 168)
-                      (i32.const 0)
-                    )
+                (block
+                  (i32.store
+                    (i32.const 168)
+                    (i32.const 0)
+                  )
+                  (return
                     (i32.const 0)
                   )
                 )
@@ -19511,14 +19499,12 @@
                   )
                 )
               )
+              (i32.store
+                (i32.const 168)
+                (i32.const 0)
+              )
               (return
-                (block
-                  (i32.store
-                    (i32.const 168)
-                    (i32.const 0)
-                  )
-                  (i32.const 0)
-                )
+                (i32.const 0)
               )
             )
           )
@@ -19684,18 +19670,18 @@
               (get_local $5)
               (i32.const 1)
             )
-            (return
-              (block
-                (i32.store
-                  (i32.const 168)
-                  (i32.or
-                    (get_local $9)
-                    (i32.and
-                      (get_local $1)
-                      (i32.const 0)
-                    )
+            (block
+              (i32.store
+                (i32.const 168)
+                (i32.or
+                  (get_local $9)
+                  (i32.and
+                    (get_local $1)
+                    (i32.const 0)
                   )
                 )
+              )
+              (return
                 (i32.or
                   (i32.const 0)
                   (i32.and
@@ -19705,22 +19691,22 @@
                 )
               )
             )
-            (return
-              (block
-                (i32.store
-                  (i32.const 168)
-                  (i32.or
-                    (i32.const 0)
-                    (i32.shr_u
-                      (get_local $6)
-                      (set_local $0
-                        (i32.ctz
-                          (get_local $5)
-                        )
+            (block
+              (i32.store
+                (i32.const 168)
+                (i32.or
+                  (i32.const 0)
+                  (i32.shr_u
+                    (get_local $6)
+                    (set_local $0
+                      (i32.ctz
+                        (get_local $5)
                       )
                     )
                   )
                 )
+              )
+              (return
                 (i32.or
                   (i32.shl
                     (get_local $6)
diff --git a/test/emcc_hello_world.fromasm.imprecise b/test/emcc_hello_world.fromasm.imprecise
index fac02cca9bf..0b7f2497b14 100644
--- a/test/emcc_hello_world.fromasm.imprecise
+++ b/test/emcc_hello_world.fromasm.imprecise
@@ -19089,16 +19089,14 @@
                 )
               )
             )
+            (i32.store
+              (i32.const 168)
+              (i32.const 0)
+            )
             (return
-              (block
-                (i32.store
-                  (i32.const 168)
-                  (i32.const 0)
-                )
-                (i32.div_u
-                  (get_local $7)
-                  (get_local $5)
-                )
+              (i32.div_u
+                (get_local $7)
+                (get_local $5)
               )
             )
           )
@@ -19107,12 +19105,12 @@
               (i32.eqz
                 (get_local $2)
               )
-              (return
-                (block
-                  (i32.store
-                    (i32.const 168)
-                    (i32.const 0)
-                  )
+              (block
+                (i32.store
+                  (i32.const 168)
+                  (i32.const 0)
+                )
+                (return
                   (i32.const 0)
                 )
               )
@@ -19131,14 +19129,12 @@
                 (i32.const 0)
               )
             )
+            (i32.store
+              (i32.const 168)
+              (i32.const 0)
+            )
             (return
-              (block
-                (i32.store
-                  (i32.const 168)
-                  (i32.const 0)
-                )
-                (i32.const 0)
-              )
+              (i32.const 0)
             )
           )
         )
@@ -19179,16 +19175,14 @@
                   )
                 )
               )
+              (i32.store
+                (i32.const 168)
+                (i32.const 0)
+              )
               (return
-                (block
-                  (i32.store
-                    (i32.const 168)
-                    (i32.const 0)
-                  )
-                  (i32.div_u
-                    (get_local $6)
-                    (get_local $5)
-                  )
+                (i32.div_u
+                  (get_local $6)
+                  (get_local $5)
                 )
               )
             )
@@ -19218,16 +19212,14 @@
                   )
                 )
               )
+              (i32.store
+                (i32.const 168)
+                (i32.const 0)
+              )
               (return
-                (block
-                  (i32.store
-                    (i32.const 168)
-                    (i32.const 0)
-                  )
-                  (i32.div_u
-                    (get_local $6)
-                    (get_local $8)
-                  )
+                (i32.div_u
+                  (get_local $6)
+                  (get_local $8)
                 )
               )
             )
@@ -19277,17 +19269,15 @@
                   )
                 )
               )
+              (i32.store
+                (i32.const 168)
+                (i32.const 0)
+              )
               (return
-                (block
-                  (i32.store
-                    (i32.const 168)
-                    (i32.const 0)
-                  )
-                  (i32.shr_u
-                    (get_local $6)
-                    (i32.ctz
-                      (get_local $8)
-                    )
+                (i32.shr_u
+                  (get_local $6)
+                  (i32.ctz
+                    (get_local $8)
                   )
                 )
               )
@@ -19356,12 +19346,12 @@
               (get_local $4)
               (i32.const 0)
             )
-            (return
-              (block
-                (i32.store
-                  (i32.const 168)
-                  (i32.const 0)
-                )
+            (block
+              (i32.store
+                (i32.const 168)
+                (i32.const 0)
+              )
+              (return
                 (i32.const 0)
               )
             )
@@ -19386,14 +19376,12 @@
               )
             )
           )
+          (i32.store
+            (i32.const 168)
+            (i32.const 0)
+          )
           (return
-            (block
-              (i32.store
-                (i32.const 168)
-                (i32.const 0)
-              )
-              (i32.const 0)
-            )
+            (i32.const 0)
           )
         )
         (block
@@ -19479,12 +19467,12 @@
                   (get_local $4)
                   (i32.const 0)
                 )
-                (return
-                  (block
-                    (i32.store
-                      (i32.const 168)
-                      (i32.const 0)
-                    )
+                (block
+                  (i32.store
+                    (i32.const 168)
+                    (i32.const 0)
+                  )
+                  (return
                     (i32.const 0)
                   )
                 )
@@ -19509,14 +19497,12 @@
                   )
                 )
               )
+              (i32.store
+                (i32.const 168)
+                (i32.const 0)
+              )
               (return
-                (block
-                  (i32.store
-                    (i32.const 168)
-                    (i32.const 0)
-                  )
-                  (i32.const 0)
-                )
+                (i32.const 0)
               )
             )
           )
@@ -19682,18 +19668,18 @@
               (get_local $5)
               (i32.const 1)
             )
-            (return
-              (block
-                (i32.store
-                  (i32.const 168)
-                  (i32.or
-                    (get_local $9)
-                    (i32.and
-                      (get_local $1)
-                      (i32.const 0)
-                    )
+            (block
+              (i32.store
+                (i32.const 168)
+                (i32.or
+                  (get_local $9)
+                  (i32.and
+                    (get_local $1)
+                    (i32.const 0)
                   )
                 )
+              )
+              (return
                 (i32.or
                   (i32.const 0)
                   (i32.and
@@ -19703,22 +19689,22 @@
                 )
               )
             )
-            (return
-              (block
-                (i32.store
-                  (i32.const 168)
-                  (i32.or
-                    (i32.const 0)
-                    (i32.shr_u
-                      (get_local $6)
-                      (set_local $0
-                        (i32.ctz
-                          (get_local $5)
-                        )
+            (block
+              (i32.store
+                (i32.const 168)
+                (i32.or
+                  (i32.const 0)
+                  (i32.shr_u
+                    (get_local $6)
+                    (set_local $0
+                      (i32.ctz
+                        (get_local $5)
                       )
                     )
                   )
                 )
+              )
+              (return
                 (i32.or
                   (i32.shl
                     (get_local $6)
diff --git a/test/min.fromasm b/test/min.fromasm
index 45b2f8c1927..51750dd531a 100644
--- a/test/min.fromasm
+++ b/test/min.fromasm
@@ -10,15 +10,13 @@
     )
   )
   (func $neg (param $0 i32) (param $1 i32) (result f32)
+    (i32.store
+      (get_local $0)
+      (get_local $1)
+    )
     (f32.neg
-      (block
-        (i32.store
-          (get_local $0)
-          (get_local $1)
-        )
-        (f32.load
-          (get_local $0)
-        )
+      (f32.load
+        (get_local $0)
       )
     )
   )
diff --git a/test/min.fromasm.imprecise b/test/min.fromasm.imprecise
index 45b2f8c1927..51750dd531a 100644
--- a/test/min.fromasm.imprecise
+++ b/test/min.fromasm.imprecise
@@ -10,15 +10,13 @@
     )
   )
   (func $neg (param $0 i32) (param $1 i32) (result f32)
+    (i32.store
+      (get_local $0)
+      (get_local $1)
+    )
     (f32.neg
-      (block
-        (i32.store
-          (get_local $0)
-          (get_local $1)
-        )
-        (f32.load
-          (get_local $0)
-        )
+      (f32.load
+        (get_local $0)
       )
     )
   )
diff --git a/test/passes/merge-blocks.txt b/test/passes/merge-blocks.txt
index 2b4278f7c83..f5d772c7495 100644
--- a/test/passes/merge-blocks.txt
+++ b/test/passes/merge-blocks.txt
@@ -1,5 +1,18 @@
 (module
   (memory 256 256)
+  (type $i (func (param i32)))
+  (type $ii (func (param i32 i32)))
+  (type $iii (func (param i32 i32 i32)))
+  (table $call-i)
+  (func $call-i (param $0 i32)
+    (nop)
+  )
+  (func $call-ii (param $0 i32) (param $1 i32)
+    (nop)
+  )
+  (func $call-iii (param $0 i32) (param $1 i32) (param $2 i32)
+    (nop)
+  )
   (func $b0-yes (param $i1 i32)
     (block $topmost
       (block $block0
@@ -82,4 +95,443 @@
       (i32.const 20)
     )
   )
+  (func $unary
+    (local $x i32)
+    (i32.eqz
+      (block $block0
+        (i32.const 10)
+      )
+    )
+    (block $block1
+      (i32.const 10)
+      (i32.eqz
+        (i32.const 20)
+      )
+    )
+    (block $block2
+      (i32.const 10)
+      (i32.const 20)
+      (i32.eqz
+        (i32.const 30)
+      )
+    )
+    (block $block3
+      (i32.const 10)
+      (set_local $x
+        (i32.const 20)
+      )
+    )
+    (block $block4
+      (i32.const 10)
+      (i32.load
+        (i32.const 20)
+      )
+    )
+    (block $block5
+      (i32.const 10)
+      (return
+        (unreachable)
+      )
+    )
+  )
+  (func $binary
+    (i32.add
+      (block $block0
+        (i32.const 10)
+      )
+      (i32.const 20)
+    )
+    (block $block1
+      (i32.const 10)
+      (i32.add
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+    (block $block2
+      (i32.const 10)
+      (i32.const 20)
+      (i32.add
+        (i32.const 30)
+        (i32.const 40)
+      )
+    )
+    (i32.add
+      (i32.const 10)
+      (block $block3
+        (i32.const 20)
+      )
+    )
+    (block $block4
+      (i32.const 20)
+      (i32.add
+        (i32.const 10)
+        (i32.const 30)
+      )
+    )
+    (block $block5
+      (i32.const 20)
+      (i32.const 30)
+      (i32.add
+        (i32.const 10)
+        (i32.const 40)
+      )
+    )
+    (i32.add
+      (block $block6
+        (i32.const 10)
+      )
+      (block $block7
+        (i32.const 20)
+      )
+    )
+    (block $block8
+      (i32.const 10)
+      (i32.const 30)
+      (i32.add
+        (i32.const 20)
+        (i32.const 40)
+      )
+    )
+    (block $block10
+      (i32.const 10)
+      (i32.const 20)
+      (i32.const 40)
+      (i32.const 50)
+      (i32.add
+        (i32.const 30)
+        (i32.const 60)
+      )
+    )
+    (block $block12
+      (i32.const 20)
+      (i32.store
+        (i32.const 10)
+        (i32.const 30)
+      )
+    )
+    (block $block13
+      (i32.const 10)
+      (i32.store
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+    (i32.add
+      (unreachable)
+      (block $block14
+        (i32.const 10)
+        (i32.const 20)
+      )
+    )
+    (block $block15
+      (unreachable)
+      (i32.const 20)
+      (i32.add
+        (i32.const 10)
+        (i32.const 30)
+      )
+    )
+  )
+  (func $trinary
+    (block $block0
+      (i32.const 10)
+      (i32.const 30)
+      (i32.const 50)
+      (select
+        (i32.const 20)
+        (i32.const 40)
+        (i32.const 60)
+      )
+    )
+    (block $block4
+      (i32.const 20)
+      (i32.const 40)
+      (select
+        (block $block3
+          (i32.const 10)
+        )
+        (i32.const 30)
+        (i32.const 50)
+      )
+    )
+    (block $block6
+      (i32.const 10)
+      (i32.const 40)
+      (select
+        (i32.const 20)
+        (block $block7
+          (i32.const 30)
+        )
+        (i32.const 50)
+      )
+    )
+    (block $block9
+      (i32.const 10)
+      (i32.const 30)
+      (select
+        (i32.const 20)
+        (i32.const 40)
+        (block $block11
+          (i32.const 50)
+        )
+      )
+    )
+    (block $block14
+      (i32.const 30)
+      (select
+        (block $block12
+          (i32.const 10)
+        )
+        (block $block13
+          (i32.const 20)
+        )
+        (i32.const 40)
+      )
+    )
+    (block $block16
+      (i32.const 20)
+      (select
+        (block $block15
+          (i32.const 10)
+        )
+        (i32.const 30)
+        (block $block17
+          (i32.const 40)
+        )
+      )
+    )
+    (block $block18
+      (i32.const 10)
+      (select
+        (i32.const 20)
+        (block $block19
+          (i32.const 30)
+        )
+        (block $block20
+          (i32.const 40)
+        )
+      )
+    )
+    (block $block21
+      (unreachable)
+      (i32.const 30)
+      (i32.const 50)
+      (select
+        (i32.const 20)
+        (i32.const 40)
+        (i32.const 60)
+      )
+    )
+    (block $block24
+      (i32.const 10)
+      (select
+        (unreachable)
+        (block $block25
+          (i32.const 30)
+          (i32.const 40)
+        )
+        (block $block26
+          (i32.const 50)
+          (i32.const 60)
+        )
+      )
+    )
+    (block $block27
+      (i32.const 10)
+      (unreachable)
+      (i32.const 50)
+      (select
+        (i32.const 20)
+        (i32.const 40)
+        (i32.const 60)
+      )
+    )
+    (block $block30
+      (i32.const 10)
+      (i32.const 30)
+      (select
+        (i32.const 20)
+        (unreachable)
+        (block $block32
+          (i32.const 50)
+          (i32.const 60)
+        )
+      )
+    )
+    (block $block33
+      (i32.const 10)
+      (i32.const 30)
+      (unreachable)
+      (select
+        (i32.const 20)
+        (i32.const 40)
+        (i32.const 60)
+      )
+    )
+    (block $block36
+      (i32.const 10)
+      (i32.const 30)
+      (i32.const 50)
+      (select
+        (i32.const 20)
+        (i32.const 40)
+        (unreachable)
+      )
+    )
+  )
+  (func $breaks
+    (block $out
+      (block $block0
+        (i32.const 10)
+        (br $out
+          (i32.const 20)
+        )
+      )
+      (block $block1
+        (i32.const 10)
+        (br_if $out
+          (i32.const 20)
+        )
+      )
+      (block $block2
+        (i32.const 10)
+        (i32.const 30)
+        (br_if $out
+          (i32.const 20)
+          (i32.const 40)
+        )
+      )
+      (block $block4
+        (i32.const 10)
+        (br_table $out $out
+          (i32.const 20)
+        )
+      )
+      (block $block5
+        (i32.const 10)
+        (i32.const 30)
+        (br_table $out $out
+          (i32.const 20)
+          (i32.const 40)
+        )
+      )
+    )
+  )
+  (func $calls
+    (call $call-i
+      (block $block0
+        (i32.const 10)
+      )
+    )
+    (block $block1
+      (i32.const 10)
+      (call $call-i
+        (i32.const 20)
+      )
+    )
+    (block $block2
+      (i32.const 10)
+      (i32.const 20)
+      (call $call-i
+        (i32.const 30)
+      )
+    )
+    (block $block3
+      (i32.const 10)
+      (i32.const 30)
+      (call $call-ii
+        (i32.const 20)
+        (i32.const 40)
+      )
+    )
+    (block $block5
+      (unreachable)
+      (i32.const 20)
+      (call $call-ii
+        (i32.const 10)
+        (i32.const 30)
+      )
+    )
+    (block $block7
+      (i32.const 10)
+      (call $call-ii
+        (unreachable)
+        (block $block8
+          (i32.const 20)
+          (i32.const 30)
+        )
+      )
+    )
+    (block $block9
+      (i32.const 10)
+      (unreachable)
+      (call $call-ii
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+    (block $block11
+      (i32.const 10)
+      (i32.const 30)
+      (call $call-ii
+        (i32.const 20)
+        (unreachable)
+      )
+    )
+    (block $block13
+      (i32.const 10)
+      (i32.const 30)
+      (i32.const 50)
+      (call $call-iii
+        (i32.const 20)
+        (i32.const 40)
+        (i32.const 60)
+      )
+    )
+    (block $block16
+      (i32.const 10)
+      (i32.const 40)
+      (call $call-iii
+        (i32.const 20)
+        (i32.const 30)
+        (i32.const 50)
+      )
+    )
+    (block $block18
+      (i32.const 10)
+      (i32.const 30)
+      (i32.const 50)
+      (call_indirect $ii
+        (i32.const 20)
+        (i32.const 40)
+        (i32.const 60)
+      )
+    )
+    (call_indirect $ii
+      (unreachable)
+      (block $block21
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block $block22
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+  )
+  (func $block-type-change
+    (local $0 f64)
+    (local $1 f64)
+    (if
+      (block $block0
+        (nop)
+        (f64.gt
+          (get_local $0)
+          (get_local $1)
+        )
+      )
+      (nop)
+    )
+  )
 )
diff --git a/test/passes/merge-blocks.wast b/test/passes/merge-blocks.wast
index 09eefefdb4e..a4a9873e900 100644
--- a/test/passes/merge-blocks.wast
+++ b/test/passes/merge-blocks.wast
@@ -1,5 +1,15 @@
 (module
   (memory 256 256)
+  (type $i (func (param i32)))
+  (type $ii (func (param i32) (param i32)))
+  (type $iii (func (param i32) (param i32) (param i32)))
+  (table $call-i)
+  (func $call-i (param i32)
+  )
+  (func $call-ii (param i32) (param i32)
+  )
+  (func $call-iii (param i32) (param i32) (param i32)
+  )
   (func $b0-yes (param $i1 i32)
     (block $topmost
       (block
@@ -82,5 +92,501 @@
       (i32.const 20)
     )
   )
+  (func $unary
+    (local $x i32)
+    (i32.eqz
+      (block
+        (i32.const 10)
+      )
+    )
+    (i32.eqz
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+    )
+    (i32.eqz
+      (block
+        (i32.const 10)
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+    (set_local $x
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+    )
+    (i32.load
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+    )
+    (return
+      (block
+        (i32.const 10)
+        (unreachable)
+      )
+    )
+  )
+  (func $binary
+    (i32.add
+      (block
+        (i32.const 10)
+      )
+      (i32.const 20)
+    )
+    (i32.add
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (i32.const 30)
+    )
+    (i32.add
+      (block
+        (i32.const 10)
+        (i32.const 20)
+        (i32.const 30)
+      )
+      (i32.const 40)
+    )
+    (i32.add
+      (i32.const 10)
+      (block
+        (i32.const 20)
+      )
+    )
+    (i32.add
+      (i32.const 10)
+      (block
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+    (i32.add
+      (i32.const 10)
+      (block
+        (i32.const 20)
+        (i32.const 30)
+        (i32.const 40)
+      )
+    )
+    (i32.add
+      (block
+        (i32.const 10)
+      )
+      (block
+        (i32.const 20)
+      )
+    )
+    (i32.add
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+    )
+    (i32.add
+      (block
+        (i32.const 10)
+        (i32.const 20)
+        (i32.const 30)
+      )
+      (block
+        (i32.const 40)
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+    (i32.store
+      (i32.const 10)
+      (block
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+    (i32.store
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (i32.const 30)
+    )
+    (i32.add
+      (unreachable) ;; do not move across this TODO: move non-side-effecting
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+    )
+    (i32.add
+      (block
+        (unreachable) ;; moves out, so does not block the rest
+        (i32.const 10)
+      )
+      (block
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+  )
+  (func $trinary
+    (select
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+      )
+      (block
+        (i32.const 20)
+        (i32.const 30)
+      )
+      (block
+        (i32.const 40)
+        (i32.const 50)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+      )
+      (block
+        (i32.const 40)
+        (i32.const 50)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+      )
+      (block
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+      )
+      (block
+        (i32.const 20)
+        (i32.const 30)
+      )
+      (block
+        (i32.const 40)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+      )
+      (block
+        (i32.const 40)
+      )
+    )
+    ;; now for bad stuff
+    (select
+      (block
+        (unreachable)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+        (unreachable)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (unreachable)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (unreachable)
+      )
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (unreachable)
+        (i32.const 60)
+      )
+    )
+    (select
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+        (unreachable)
+      )
+    )
+  )
+  (func $breaks
+    (block $out
+      (br $out
+        (block
+          (i32.const 10)
+          (i32.const 20)
+        )
+      )
+      (br_if $out
+        (block
+          (i32.const 10)
+          (i32.const 20)
+        )
+      )
+      (br_if $out
+        (block
+          (i32.const 10)
+          (i32.const 20)
+        )
+        (block
+          (i32.const 30)
+          (i32.const 40)
+        )
+      )
+      (br_table $out $out
+        (block
+          (i32.const 10)
+          (i32.const 20)
+        )
+      )
+      (br_table $out $out
+        (block
+          (i32.const 10)
+          (i32.const 20)
+        )
+        (block
+          (i32.const 30)
+          (i32.const 40)
+        )
+      )
+    )
+  )
+  (func $calls
+    (call $call-i
+      (block
+        (i32.const 10)
+      )
+    )
+    (call $call-i
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+    )
+    (call $call-i
+      (block
+        (i32.const 10)
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+    (call $call-ii
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+    )
+    (call $call-ii
+      (block
+        (unreachable)
+        (i32.const 10)
+      )
+      (block
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+    (call $call-ii
+      (block
+        (i32.const 10)
+        (unreachable)
+      )
+      (block
+        (i32.const 20)
+        (i32.const 30)
+      )
+    )
+    (call $call-ii
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (unreachable)
+        (i32.const 30)
+      )
+    )
+    (call $call-ii
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (unreachable)
+      )
+    )
+    (call $call-iii
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+    (call $call-iii
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (i32.const 30)
+      (block
+        (i32.const 40)
+        (i32.const 50)
+      )
+    )
+    (call_indirect $ii
+      (block
+        (i32.const 10)
+        (i32.const 20)
+      )
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+    (call_indirect $ii
+      (unreachable)
+      (block
+        (i32.const 30)
+        (i32.const 40)
+      )
+      (block
+        (i32.const 50)
+        (i32.const 60)
+      )
+    )
+  )
+  (func $block-type-change
+    (local $0 f64)
+    (local $1 f64)
+    (if
+      (f64.gt
+        (get_local $0)
+        (block
+          (nop)
+          (get_local $1)
+        )
+      )
+      (nop)
+    )
+  )
 )
 
diff --git a/test/unit.asm.js b/test/unit.asm.js
index 77fbe408bd1..8fb28b99074 100644
--- a/test/unit.asm.js
+++ b/test/unit.asm.js
@@ -214,11 +214,17 @@ function asm(global, env, buffer) {
     (HEAPF32[tempDoublePtr >> 2] = f, HEAP32[tempDoublePtr >> 2] | 0); // f32->i32
     (HEAPF32[tempDoublePtr >> 2] = d, HEAP32[tempDoublePtr >> 2] | 0); // f64 with implict f32 conversion, ->i32
   }
+  function recursiveBlockMerging(x) {
+    x = x | 0;
+    lb((1, x) + (2, 3) + (((4, 5), 6), 7) + (8, (9, (10, (11, 12))))) | 0;
+    x = (lb(1) | 0, x) + (lb(2) | 0, lb(3) | 0) + (((lb(4) | 0, lb(5) | 0), lb(6) | 0), lb(7) | 0) + (lb(8) | 0, (lb(9) | 0, (lb(10) | 0, (lb(11) | 0, lb(12) | 0)))) | 0;
+    return x | 0;
+  }
 
   function lb(a) {
    a = a | 0;
    HEAP32[a >> 2] = n + 136 + 8;
-   return;
+   return 0;
   }
 
   function z() {
diff --git a/test/unit.fromasm b/test/unit.fromasm
index 23f6c48bada..f828c415a76 100644
--- a/test/unit.fromasm
+++ b/test/unit.fromasm
@@ -363,7 +363,68 @@
   (func $bitcasts (param $0 i32) (param $1 f32)
     (nop)
   )
-  (func $lb (param $0 i32)
+  (func $recursiveBlockMerging (param $0 i32) (result i32)
+    (call $lb
+      (i32.add
+        (i32.add
+          (i32.add
+            (get_local $0)
+            (i32.const 3)
+          )
+          (i32.const 7)
+        )
+        (i32.const 12)
+      )
+    )
+    (call $lb
+      (i32.const 1)
+    )
+    (call $lb
+      (i32.const 2)
+    )
+    (i32.add
+      (i32.add
+        (i32.add
+          (get_local $0)
+          (call $lb
+            (i32.const 3)
+          )
+        )
+        (block
+          (call $lb
+            (i32.const 4)
+          )
+          (call $lb
+            (i32.const 5)
+          )
+          (call $lb
+            (i32.const 6)
+          )
+          (call $lb
+            (i32.const 7)
+          )
+        )
+      )
+      (block
+        (call $lb
+          (i32.const 8)
+        )
+        (call $lb
+          (i32.const 9)
+        )
+        (call $lb
+          (i32.const 10)
+        )
+        (call $lb
+          (i32.const 11)
+        )
+        (call $lb
+          (i32.const 12)
+        )
+      )
+    )
+  )
+  (func $lb (param $0 i32) (result i32)
     (i32.store
       (get_local $0)
       (i32.add
@@ -376,6 +437,7 @@
         (i32.const 8)
       )
     )
+    (i32.const 0)
   )
   (func $z
     (nop)
diff --git a/test/unit.fromasm.imprecise b/test/unit.fromasm.imprecise
index 347ea4e8845..1bb1ae48508 100644
--- a/test/unit.fromasm.imprecise
+++ b/test/unit.fromasm.imprecise
@@ -355,7 +355,68 @@
   (func $bitcasts (param $0 i32) (param $1 f32)
     (nop)
   )
-  (func $lb (param $0 i32)
+  (func $recursiveBlockMerging (param $0 i32) (result i32)
+    (call $lb
+      (i32.add
+        (i32.add
+          (i32.add
+            (get_local $0)
+            (i32.const 3)
+          )
+          (i32.const 7)
+        )
+        (i32.const 12)
+      )
+    )
+    (call $lb
+      (i32.const 1)
+    )
+    (call $lb
+      (i32.const 2)
+    )
+    (i32.add
+      (i32.add
+        (i32.add
+          (get_local $0)
+          (call $lb
+            (i32.const 3)
+          )
+        )
+        (block
+          (call $lb
+            (i32.const 4)
+          )
+          (call $lb
+            (i32.const 5)
+          )
+          (call $lb
+            (i32.const 6)
+          )
+          (call $lb
+            (i32.const 7)
+          )
+        )
+      )
+      (block
+        (call $lb
+          (i32.const 8)
+        )
+        (call $lb
+          (i32.const 9)
+        )
+        (call $lb
+          (i32.const 10)
+        )
+        (call $lb
+          (i32.const 11)
+        )
+        (call $lb
+          (i32.const 12)
+        )
+      )
+    )
+  )
+  (func $lb (param $0 i32) (result i32)
     (i32.store
       (get_local $0)
       (i32.add
@@ -368,6 +429,7 @@
         (i32.const 8)
       )
     )
+    (i32.const 0)
   )
   (func $z
     (nop)
diff --git a/test/unit.fromasm.imprecise.no-opts b/test/unit.fromasm.imprecise.no-opts
index 4b765e4dcaa..70f8d286bc4 100644
--- a/test/unit.fromasm.imprecise.no-opts
+++ b/test/unit.fromasm.imprecise.no-opts
@@ -562,7 +562,114 @@
       )
     )
   )
-  (func $lb (param $a i32)
+  (func $recursiveBlockMerging (param $x i32) (result i32)
+    (call $lb
+      (i32.add
+        (i32.add
+          (i32.add
+            (block
+              (i32.const 1)
+              (get_local $x)
+            )
+            (block
+              (i32.const 2)
+              (i32.const 3)
+            )
+          )
+          (block
+            (block
+              (block
+                (i32.const 4)
+                (i32.const 5)
+              )
+              (i32.const 6)
+            )
+            (i32.const 7)
+          )
+        )
+        (block
+          (i32.const 8)
+          (block
+            (i32.const 9)
+            (block
+              (i32.const 10)
+              (block
+                (i32.const 11)
+                (i32.const 12)
+              )
+            )
+          )
+        )
+      )
+    )
+    (set_local $x
+      (i32.add
+        (i32.add
+          (i32.add
+            (block
+              (call $lb
+                (i32.const 1)
+              )
+              (get_local $x)
+            )
+            (block
+              (call $lb
+                (i32.const 2)
+              )
+              (call $lb
+                (i32.const 3)
+              )
+            )
+          )
+          (block
+            (block
+              (block
+                (call $lb
+                  (i32.const 4)
+                )
+                (call $lb
+                  (i32.const 5)
+                )
+              )
+              (call $lb
+                (i32.const 6)
+              )
+            )
+            (call $lb
+              (i32.const 7)
+            )
+          )
+        )
+        (block
+          (call $lb
+            (i32.const 8)
+          )
+          (block
+            (call $lb
+              (i32.const 9)
+            )
+            (block
+              (call $lb
+                (i32.const 10)
+              )
+              (block
+                (call $lb
+                  (i32.const 11)
+                )
+                (call $lb
+                  (i32.const 12)
+                )
+              )
+            )
+          )
+        )
+      )
+    )
+    (return
+      (get_local $x)
+    )
+  )
+  (func $lb (param $a i32) (result i32)
     (i32.store
       (get_local $a)
       (i32.add
@@ -575,7 +682,9 @@
         (i32.const 8)
       )
     )
-    (return)
+    (return
+      (i32.const 0)
+    )
   )
   (func $z
     (nop)
diff --git a/test/unit.fromasm.no-opts b/test/unit.fromasm.no-opts
index ddfa055779f..07311b00e20 100644
--- a/test/unit.fromasm.no-opts
+++ b/test/unit.fromasm.no-opts
@@ -566,7 +566,114 @@
       )
     )
   )
-  (func $lb (param $a i32)
+  (func $recursiveBlockMerging (param $x i32) (result i32)
+    (call $lb
+      (i32.add
+        (i32.add
+          (i32.add
+            (block
+              (i32.const 1)
+              (get_local $x)
+            )
+            (block
+              (i32.const 2)
+              (i32.const 3)
+            )
+          )
+          (block
+            (block
+              (block
+                (i32.const 4)
+                (i32.const 5)
+              )
+              (i32.const 6)
+            )
+            (i32.const 7)
+          )
+        )
+        (block
+          (i32.const 8)
+          (block
+            (i32.const 9)
+            (block
+              (i32.const 10)
+              (block
+                (i32.const 11)
+                (i32.const 12)
+              )
+            )
+          )
+        )
+      )
+    )
+    (set_local $x
+      (i32.add
+        (i32.add
+          (i32.add
+            (block
+              (call $lb
+                (i32.const 1)
+              )
+              (get_local $x)
+            )
+            (block
+              (call $lb
+                (i32.const 2)
+              )
+              (call $lb
+                (i32.const 3)
+              )
+            )
+          )
+          (block
+            (block
+              (block
+                (call $lb
+                  (i32.const 4)
+                )
+                (call $lb
+                  (i32.const 5)
+                )
+              )
+              (call $lb
+                (i32.const 6)
+              )
+            )
+            (call $lb
+              (i32.const 7)
+            )
+          )
+        )
+        (block
+          (call $lb
+            (i32.const 8)
+          )
+          (block
+            (call $lb
+              (i32.const 9)
+            )
+            (block
+              (call $lb
+                (i32.const 10)
+              )
+              (block
+                (call $lb
+                  (i32.const 11)
+                )
+                (call $lb
+                  (i32.const 12)
+                )
+              )
+            )
+          )
+        )
+      )
+    )
+    (return
+      (get_local $x)
+    )
+  )
+  (func $lb (param $a i32) (result i32)
     (i32.store
       (get_local $a)
       (i32.add
@@ -579,7 +686,9 @@
         (i32.const 8)
       )
     )
-    (return)
+    (return
+      (i32.const 0)
+    )
   )
   (func $z
     (nop)