diff --git a/src/module.ts b/src/module.ts
index d8396671d9..9dad851750 100644
--- a/src/module.ts
+++ b/src/module.ts
@@ -1106,10 +1106,16 @@ export class Module {
     var func = this.addTemporaryFunction(type, null, expr);
     var names = this.cachedPrecomputeNames;
     if (!names) {
-      this.cachedPrecomputeNames = names = allocI32Array([ this.allocStringCached("precompute") ]);
+      this.cachedPrecomputeNames = names = allocI32Array([
+        this.allocStringCached("vacuum"),
+        this.allocStringCached("precompute")
+      ]);
     }
-    _BinaryenFunctionRunPasses(func, this.ref, names, 1);
+    _BinaryenFunctionRunPasses(func, this.ref, names, 2);
     expr = _BinaryenFunctionGetBody(func);
+    if (_BinaryenExpressionGetId(expr) == ExpressionId.Return) {
+      expr = _BinaryenReturnGetValue(expr);
+    }
     this.removeTemporaryFunction();
 
     // reset optimize levels to previous
@@ -1194,7 +1200,7 @@ export class Module {
     var nested1: ExpressionRef,
         nested2: ExpressionRef;
 
-        switch (_BinaryenExpressionGetId(expr)) {
+    switch (_BinaryenExpressionGetId(expr)) {
       case ExpressionId.Const: {
         switch (_BinaryenExpressionGetType(expr)) {
           case NativeType.I32: {
@@ -1562,12 +1568,12 @@ export class Relooper {
 }
 
 // export function hasSideEffects(expr: ExpressionRef): bool {
-//   switch (_BinaryenExpressionGetId(expr = getPtr(expr))) {
-//     case ExpressionId.GetLocal:
-//     case ExpressionId.GetGlobal:
+//   // TODO: there's more
+//   switch (_BinaryenExpressionGetId(expr)) {
+//     case ExpressionId.LocalGet:
+//     case ExpressionId.GlobalGet:
 //     case ExpressionId.Const:
-//     case ExpressionId.Nop:
-//     case ExpressionId.Unreachable: {
+//     case ExpressionId.Nop: {
 //       return false;
 //     }
 //     case ExpressionId.Block: {
diff --git a/tests/compiler/instanceof.untouched.wat b/tests/compiler/instanceof.untouched.wat
index 7136f6e13a..31257b0dd9 100644
--- a/tests/compiler/instanceof.untouched.wat
+++ b/tests/compiler/instanceof.untouched.wat
@@ -19,56 +19,20 @@
  (export "memory" (memory $0))
  (start $start)
  (func $instanceof/isI32<i32> (; 1 ;) (type $FUNCSIG$ii) (param $0 i32) (result i32)
-  local.get $0
-  drop
   i32.const 1
-  if
-   i32.const 1
-   return
-  else   
-   i32.const 0
-   return
-  end
-  unreachable
+  return
  )
  (func $instanceof/isI32<f64> (; 2 ;) (type $FUNCSIG$id) (param $0 f64) (result i32)
-  local.get $0
-  drop
   i32.const 0
-  if
-   i32.const 1
-   return
-  else   
-   i32.const 0
-   return
-  end
-  unreachable
+  return
  )
  (func $instanceof/isI32<u32> (; 3 ;) (type $FUNCSIG$ii) (param $0 i32) (result i32)
-  local.get $0
-  drop
   i32.const 0
-  if
-   i32.const 1
-   return
-  else   
-   i32.const 0
-   return
-  end
-  unreachable
+  return
  )
  (func $instanceof/isI32<u16> (; 4 ;) (type $FUNCSIG$ii) (param $0 i32) (result i32)
-  local.get $0
-  drop
   i32.const 0
-  if
-   i32.const 1
-   return
-  else   
-   i32.const 0
-   return
-  end
-  unreachable
+  return
  )
  (func $~lib/rt/stub/__retain (; 5 ;) (type $FUNCSIG$ii) (param $0 i32) (result i32)
   local.get $0
diff --git a/tests/compiler/std/arraybuffer.untouched.wat b/tests/compiler/std/arraybuffer.untouched.wat
index efd6512728..17c7ea52f2 100644
--- a/tests/compiler/std/arraybuffer.untouched.wat
+++ b/tests/compiler/std/arraybuffer.untouched.wat
@@ -3320,138 +3320,7 @@
   drop
   local.get $0
   if
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
+   nop
   end
   i32.const 0
   local.set $1
@@ -3462,90 +3331,7 @@
  (func $~lib/arraybuffer/ArrayBuffer.isView<usize> (; 31 ;) (type $FUNCSIG$ii) (param $0 i32) (result i32)
   local.get $0
   if
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    return
-   end
+   nop
   end
   i32.const 0
  )
@@ -3556,138 +3342,12 @@
   drop
   local.get $0
   if
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
    i32.const 1
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
+   local.set $1
    local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
+   call $~lib/rt/pure/__release
+   local.get $1
+   return
   end
   i32.const 0
   local.set $1
@@ -3702,138 +3362,12 @@
   drop
   local.get $0
   if
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
    i32.const 1
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
+   local.set $1
    local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
+   call $~lib/rt/pure/__release
+   local.get $1
+   return
   end
   i32.const 0
   local.set $1
@@ -3848,138 +3382,12 @@
   drop
   local.get $0
   if
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
-   i32.const 0
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
-   local.get $0
-   drop
    i32.const 1
-   if
-    i32.const 1
-    local.set $1
-    local.get $0
-    call $~lib/rt/pure/__release
-    local.get $1
-    return
-   end
+   local.set $1
+   local.get $0
+   call $~lib/rt/pure/__release
+   local.get $1
+   return
   end
   i32.const 0
   local.set $1