diff --git a/std/assembly/string.ts b/std/assembly/string.ts
index bd7dc91323..7e158e25e8 100644
--- a/std/assembly/string.ts
+++ b/std/assembly/string.ts
@@ -641,19 +641,21 @@ export namespace String {
       while (strOff < strEnd) {
         let c1 = <u32>load<u16>(strOff);
         if (c1 < 128) {
-          if (nullTerminated && !c1) break;
-          bufLen += 1; strOff += 2;
+          // @ts-ignore: cast
+          if (nullTerminated & !c1) break;
+          bufLen += 1;
         } else if (c1 < 2048) {
-          bufLen += 2; strOff += 2;
+          bufLen += 2;
         } else {
           if ((c1 & 0xFC00) == 0xD800 && strOff + 2 < strEnd) {
             if ((<u32>load<u16>(strOff, 2) & 0xFC00) == 0xDC00) {
-              strOff += 4; bufLen += 4;
+              bufLen += 4; strOff += 4;
               continue;
             }
           }
-          strOff += 2; bufLen += 3;
+          bufLen += 3;
         }
+        strOff += 2;
       }
       return bufLen;
     }
@@ -669,29 +671,34 @@ export namespace String {
         let c1 = <u32>load<u16>(strOff);
         if (c1 < 128) {
           store<u8>(bufOff, c1);
-          bufOff += 1; strOff += 2;
+          bufOff++;
         } else if (c1 < 2048) {
-          store<u8>(bufOff, c1 >> 6      | 192);
-          store<u8>(bufOff, c1      & 63 | 128, 1);
-          bufOff += 2; strOff += 2;
+          let b0 = c1 >> 6 | 192;
+          let b1 = c1 & 63 | 128;
+          store<u16>(bufOff, b1 << 8 | b0);
+          bufOff += 2;
         } else {
           if ((c1 & 0xFC00) == 0xD800 && strOff + 2 < strEnd) {
             let c2 = <u32>load<u16>(strOff, 2);
             if ((c2 & 0xFC00) == 0xDC00) {
               c1 = 0x10000 + ((c1 & 0x03FF) << 10) | (c2 & 0x03FF);
-              store<u8>(bufOff, c1 >> 18      | 240);
-              store<u8>(bufOff, c1 >> 12 & 63 | 128, 1);
-              store<u8>(bufOff, c1 >> 6  & 63 | 128, 2);
-              store<u8>(bufOff, c1       & 63 | 128, 3);
-              strOff += 4; bufOff += 4;
+              let b0 = c1 >> 18 | 240;
+              let b1 = c1 >> 12 & 63 | 128;
+              let b2 = c1 >> 6  & 63 | 128;
+              let b3 = c1       & 63 | 128;
+              store<u32>(bufOff, b3 << 24 | b2 << 16 | b1 << 8 | b0);
+              bufOff += 4; strOff += 4;
               continue;
             }
           }
-          store<u8>(bufOff, c1 >> 12      | 224);
-          store<u8>(bufOff, c1 >> 6  & 63 | 128, 1);
-          store<u8>(bufOff, c1       & 63 | 128, 2);
-          strOff += 2; bufOff += 3;
+          let b0 = c1 >> 12 | 224;
+          let b1 = c1 >> 6  & 63 | 128;
+          let b2 = c1       & 63 | 128;
+          store<u16>(bufOff, b1 << 8 | b0);
+          store<u8>(bufOff, b2, 2);
+          bufOff += 3;
         }
+        strOff += 2;
       }
       assert(strOff <= strEnd);
       if (nullTerminated) {
@@ -713,36 +720,38 @@ export namespace String {
       var str = __alloc(len << 1, idof<String>()); // max is one u16 char per u8 byte
       var strOff = str;
       while (bufOff < bufEnd) {
-        let cp = <u32>load<u8>(bufOff++);
-        if (cp < 128) {
-          if (nullTerminated && !cp) break;
-          store<u16>(strOff, cp);
-          strOff += 2;
-        } else if (cp > 191 && cp < 224) {
-          if (bufEnd - bufOff < 1) break;
-          store<u16>(strOff, (cp & 31) << 6 | load<u8>(bufOff++) & 63);
-          strOff += 2;
-        } else if (cp > 239 && cp < 365) {
-          if (bufEnd - bufOff < 3) break;
-          cp = (
-            (cp                  &  7) << 18 |
-            (load<u8>(bufOff)    & 63) << 12 |
-            (load<u8>(bufOff, 1) & 63) << 6  |
-             load<u8>(bufOff, 2) & 63
-          ) - 0x10000;
-          bufOff += 3;
-          store<u16>(strOff, 0xD800 | (cp >> 10));
-          store<u16>(strOff, 0xDC00 | (cp & 1023), 2);
-          strOff += 4;
+        let u0 = <u32>load<u8>(bufOff); ++bufOff;
+        if (!(u0 & 128)) {
+          // @ts-ignore: cast
+          if (nullTerminated & !u0) break;
+          store<u16>(strOff, u0);
         } else {
-          if (bufEnd - bufOff < 2) break;
-          store<u16>(strOff,
-            (cp                  & 15) << 12 |
-            (load<u8>(bufOff)    & 63) << 6  |
-             load<u8>(bufOff, 1) & 63
-          );
-          bufOff += 2; strOff += 2;
+          if (bufEnd == bufOff) break;
+          let u1 = <u32>load<u8>(bufOff) & 63; ++bufOff;
+          if ((u0 & 224) == 192) {
+            store<u16>(strOff, (u0 & 31) << 6 | u1);
+          } else {
+            if (bufEnd == bufOff) break;
+            let u2 = <u32>load<u8>(bufOff) & 63; ++bufOff;
+            if ((u0 & 240) == 224) {
+              u0 = (u0 & 15) << 12 | u1 << 6 | u2;
+            } else {
+              if (bufEnd == bufOff) break;
+              u0 = (u0 & 7) << 18 | u1 << 12 | u2 << 6 | <u32>load<u8>(bufOff) & 63;
+              ++bufOff;
+            }
+            if (u0 < 0x10000) {
+              store<u16>(strOff, u0);
+            } else {
+              u0 -= 0x10000;
+              let lo = u0 >> 10 | 0xD800;
+              let hi = (u0 & 0x03FF) | 0xDC00;
+              store<u32>(strOff, lo | (hi << 16));
+              strOff += 2;
+            }
+          }
         }
+        strOff += 2;
       }
       return changetype<String>(__realloc(str, strOff - str)); // retains
     }
@@ -755,7 +764,7 @@ export namespace String {
     }
 
     export function encode(str: string): ArrayBuffer {
-      var size = changetype<BLOCK>(changetype<usize>(str) - BLOCK_OVERHEAD).rtSize;
+      var size = UTF16.byteLength(str);
       var buf = __alloc(size, idof<ArrayBuffer>());
       memory.copy(buf, changetype<usize>(str), <usize>size);
       return changetype<ArrayBuffer>(buf); // retains
diff --git a/tests/compiler/std/string-encoding.optimized.wat b/tests/compiler/std/string-encoding.optimized.wat
index fcdd0df991..cb8ad9bd81 100644
--- a/tests/compiler/std/string-encoding.optimized.wat
+++ b/tests/compiler/std/string-encoding.optimized.wat
@@ -99,7 +99,13 @@
    call $~lib/rt/pure/decrement
   end
  )
- (func $~lib/rt/tlsf/removeBlock (; 9 ;) (param $0 i32) (param $1 i32)
+ (func $~lib/string/String.UTF16.byteLength (; 9 ;) (param $0 i32) (result i32)
+  local.get $0
+  i32.const 16
+  i32.sub
+  i32.load offset=12
+ )
+ (func $~lib/rt/tlsf/removeBlock (; 10 ;) (param $0 i32) (param $1 i32)
   (local $2 i32)
   (local $3 i32)
   (local $4 i32)
@@ -265,7 +271,7 @@
    end
   end
  )
- (func $~lib/rt/tlsf/insertBlock (; 10 ;) (param $0 i32) (param $1 i32)
+ (func $~lib/rt/tlsf/insertBlock (; 11 ;) (param $0 i32) (param $1 i32)
   (local $2 i32)
   (local $3 i32)
   (local $4 i32)
@@ -548,7 +554,7 @@
   i32.or
   i32.store offset=4
  )
- (func $~lib/rt/tlsf/addMemory (; 11 ;) (param $0 i32) (param $1 i32) (param $2 i32)
+ (func $~lib/rt/tlsf/addMemory (; 12 ;) (param $0 i32) (param $1 i32) (param $2 i32)
   (local $3 i32)
   (local $4 i32)
   local.get $2
@@ -662,7 +668,7 @@
   local.get $1
   call $~lib/rt/tlsf/insertBlock
  )
- (func $~lib/rt/tlsf/maybeInitialize (; 12 ;) (result i32)
+ (func $~lib/rt/tlsf/maybeInitialize (; 13 ;) (result i32)
   (local $0 i32)
   (local $1 i32)
   (local $2 i32)
@@ -749,7 +755,7 @@
   end
   local.get $0
  )
- (func $~lib/rt/tlsf/prepareSize (; 13 ;) (param $0 i32) (result i32)
+ (func $~lib/rt/tlsf/prepareSize (; 14 ;) (param $0 i32) (result i32)
   local.get $0
   i32.const 1073741808
   i32.ge_u
@@ -773,7 +779,7 @@
   i32.gt_u
   select
  )
- (func $~lib/rt/tlsf/searchBlock (; 14 ;) (param $0 i32) (param $1 i32) (result i32)
+ (func $~lib/rt/tlsf/searchBlock (; 15 ;) (param $0 i32) (param $1 i32) (result i32)
   (local $2 i32)
   local.get $1
   i32.const 256
@@ -904,7 +910,7 @@
    end
   end
  )
- (func $~lib/rt/tlsf/growMemory (; 15 ;) (param $0 i32) (param $1 i32)
+ (func $~lib/rt/tlsf/growMemory (; 16 ;) (param $0 i32) (param $1 i32)
   (local $2 i32)
   memory.size
   local.tee $2
@@ -966,7 +972,7 @@
   i32.shl
   call $~lib/rt/tlsf/addMemory
  )
- (func $~lib/rt/tlsf/prepareBlock (; 16 ;) (param $0 i32) (param $1 i32) (param $2 i32)
+ (func $~lib/rt/tlsf/prepareBlock (; 17 ;) (param $0 i32) (param $1 i32) (param $2 i32)
   (local $3 i32)
   (local $4 i32)
   local.get $1
@@ -1042,7 +1048,7 @@
    i32.store
   end
  )
- (func $~lib/rt/tlsf/allocateBlock (; 17 ;) (param $0 i32) (param $1 i32) (param $2 i32) (result i32)
+ (func $~lib/rt/tlsf/allocateBlock (; 18 ;) (param $0 i32) (param $1 i32) (param $2 i32) (result i32)
   (local $3 i32)
   (local $4 i32)
   global.get $~lib/rt/tlsf/collectLock
@@ -1124,7 +1130,7 @@
   call $~lib/rt/rtrace/onalloc
   local.get $3
  )
- (func $~lib/rt/tlsf/__alloc (; 18 ;) (param $0 i32) (param $1 i32) (result i32)
+ (func $~lib/rt/tlsf/__alloc (; 19 ;) (param $0 i32) (param $1 i32) (result i32)
   call $~lib/rt/tlsf/maybeInitialize
   local.get $0
   local.get $1
@@ -1132,7 +1138,7 @@
   i32.const 16
   i32.add
  )
- (func $~lib/memory/memory.copy (; 19 ;) (param $0 i32) (param $1 i32) (param $2 i32)
+ (func $~lib/memory/memory.copy (; 20 ;) (param $0 i32) (param $1 i32) (param $2 i32)
   (local $3 i32)
   (local $4 i32)
   block $~lib/util/memory/memmove|inlined.0
@@ -1305,13 +1311,11 @@
    end
   end
  )
- (func $~lib/string/String.UTF16.encode (; 20 ;) (param $0 i32) (result i32)
+ (func $~lib/string/String.UTF16.encode (; 21 ;) (param $0 i32) (result i32)
   (local $1 i32)
   (local $2 i32)
   local.get $0
-  i32.const 16
-  i32.sub
-  i32.load offset=12
+  call $~lib/string/String.UTF16.byteLength
   local.tee $1
   i32.const 0
   call $~lib/rt/tlsf/__alloc
@@ -1322,12 +1326,6 @@
   local.get $2
   call $~lib/rt/pure/__retain
  )
- (func $~lib/arraybuffer/ArrayBuffer#get:byteLength (; 21 ;) (param $0 i32) (result i32)
-  local.get $0
-  i32.const 16
-  i32.sub
-  i32.load offset=12
- )
  (func $std/string-encoding/testUTF16Encode (; 22 ;)
   (local $0 i32)
   (local $1 i32)
@@ -1335,7 +1333,7 @@
   call $~lib/string/String.UTF16.encode
   local.tee $1
   local.tee $0
-  call $~lib/arraybuffer/ArrayBuffer#get:byteLength
+  call $~lib/string/String.UTF16.byteLength
   i32.const 12
   i32.ne
   if
@@ -1507,7 +1505,7 @@
  (func $~lib/string/String.UTF16.decode (; 24 ;) (param $0 i32) (result i32)
   local.get $0
   local.get $0
-  call $~lib/arraybuffer/ArrayBuffer#get:byteLength
+  call $~lib/string/String.UTF16.byteLength
   call $~lib/string/String.UTF16.decodeUnsafe
  )
  (func $~lib/string/String#get:length (; 25 ;) (param $0 i32) (result i32)
@@ -1663,14 +1661,15 @@
   (local $7 i32)
   i32.const 32
   call $~lib/string/String.UTF16.encode
-  local.set $0
-  i32.const 28
-  i32.load
+  local.set $2
+  i32.const 32
+  call $~lib/string/String.UTF16.byteLength
   local.set $1
-  local.get $0
+  local.get $2
+  local.tee $0
   i32.const 0
   call $~lib/string/String.UTF16.decodeUnsafe
-  local.tee $2
+  local.tee $3
   i32.const 288
   call $~lib/string/String.__eq
   i32.eqz
@@ -1685,7 +1684,7 @@
   local.get $0
   local.get $1
   call $~lib/string/String.UTF16.decodeUnsafe
-  local.tee $3
+  local.tee $4
   i32.const 32
   call $~lib/string/String.__eq
   i32.eqz
@@ -1700,7 +1699,7 @@
   local.get $0
   i32.const 4
   call $~lib/string/String.UTF16.decodeUnsafe
-  local.tee $4
+  local.tee $5
   i32.const 304
   call $~lib/string/String.__eq
   i32.eqz
@@ -1717,7 +1716,7 @@
   i32.add
   i32.const 2
   call $~lib/string/String.UTF16.decodeUnsafe
-  local.tee $5
+  local.tee $6
   i32.const 336
   call $~lib/string/String.__eq
   i32.eqz
@@ -1734,7 +1733,7 @@
   i32.add
   i32.const 4
   call $~lib/string/String.UTF16.decodeUnsafe
-  local.tee $6
+  local.tee $7
   i32.const 368
   call $~lib/string/String.__eq
   i32.eqz
@@ -1751,7 +1750,7 @@
   i32.add
   i32.const 4
   call $~lib/string/String.UTF16.decodeUnsafe
-  local.tee $7
+  local.tee $1
   i32.const 400
   call $~lib/string/String.__eq
   i32.eqz
@@ -1768,7 +1767,7 @@
   i32.add
   i32.const 0
   call $~lib/string/String.UTF16.decodeUnsafe
-  local.tee $1
+  local.tee $0
   i32.const 288
   call $~lib/string/String.__eq
   i32.eqz
@@ -1780,8 +1779,6 @@
    call $~lib/builtins/abort
    unreachable
   end
-  local.get $2
-  call $~lib/rt/pure/__release
   local.get $3
   call $~lib/rt/pure/__release
   local.get $4
@@ -1796,6 +1793,8 @@
   call $~lib/rt/pure/__release
   local.get $0
   call $~lib/rt/pure/__release
+  local.get $2
+  call $~lib/rt/pure/__release
  )
  (func $~lib/string/String.UTF8.byteLength (; 30 ;) (param $0 i32) (param $1 i32) (result i32)
   (local $2 i32)
@@ -1823,26 +1822,23 @@
      local.tee $3
      i32.const 128
      i32.lt_u
-     if
+     if (result i32)
+      local.get $1
       local.get $3
       i32.eqz
-      i32.const 0
-      local.get $1
-      select
+      i32.and
       br_if $while-break|0
       local.get $2
       i32.const 1
       i32.add
-      local.set $2
      else
       local.get $3
       i32.const 2048
       i32.lt_u
-      if
+      if (result i32)
        local.get $2
        i32.const 2
        i32.add
-       local.set $2
       else
        local.get $0
        i32.const 2
@@ -1864,23 +1860,23 @@
         i32.const 56320
         i32.eq
         if
-         local.get $0
-         i32.const 4
-         i32.add
-         local.set $0
          local.get $2
          i32.const 4
          i32.add
          local.set $2
+         local.get $0
+         i32.const 4
+         i32.add
+         local.set $0
          br $while-continue|0
         end
        end
        local.get $2
        i32.const 3
        i32.add
-       local.set $2
       end
      end
+     local.set $2
      local.get $0
      i32.const 2
      i32.add
@@ -1933,7 +1929,7 @@
   i32.sub
   i32.load offset=12
   i32.add
-  local.set $5
+  local.set $6
   local.get $0
   local.get $1
   call $~lib/string/String.UTF8.byteLength
@@ -1948,12 +1944,12 @@
   i32.const 0
   i32.ne
   i32.sub
-  local.set $6
+  local.set $7
   local.get $4
   local.set $0
   loop $while-continue|0
    local.get $0
-   local.get $6
+   local.get $7
    i32.lt_u
    if
     local.get $3
@@ -1965,10 +1961,6 @@
      local.get $0
      local.get $2
      i32.store8
-     local.get $3
-     i32.const 2
-     i32.add
-     local.set $3
      local.get $0
      i32.const 1
      i32.add
@@ -1983,18 +1975,15 @@
       i32.shr_u
       i32.const 192
       i32.or
-      i32.store8
-      local.get $0
       local.get $2
       i32.const 63
       i32.and
       i32.const 128
       i32.or
-      i32.store8 offset=1
-      local.get $3
-      i32.const 2
-      i32.add
-      local.set $3
+      i32.const 8
+      i32.shl
+      i32.or
+      i32.store16
       local.get $0
       i32.const 2
       i32.add
@@ -2002,7 +1991,7 @@
       local.get $3
       i32.const 2
       i32.add
-      local.get $5
+      local.get $6
       i32.lt_u
       i32.const 0
       local.get $2
@@ -2014,13 +2003,12 @@
       if
        local.get $3
        i32.load16_u offset=2
-       local.tee $7
+       local.tee $5
        i32.const 64512
        i32.and
        i32.const 56320
        i32.eq
        if
-        local.get $0
         local.get $2
         i32.const 1023
         i32.and
@@ -2028,49 +2016,55 @@
         i32.shl
         i32.const 65536
         i32.add
-        local.get $7
+        local.get $5
         i32.const 1023
         i32.and
         i32.or
         local.tee $2
-        i32.const 18
-        i32.shr_u
-        i32.const 240
-        i32.or
-        i32.store8
-        local.get $0
-        local.get $2
-        i32.const 12
-        i32.shr_u
         i32.const 63
         i32.and
         i32.const 128
         i32.or
-        i32.store8 offset=1
+        local.set $5
         local.get $0
         local.get $2
+        i32.const 18
+        i32.shr_u
+        i32.const 240
+        i32.or
+        local.get $5
+        i32.const 24
+        i32.shl
+        local.get $2
         i32.const 6
         i32.shr_u
         i32.const 63
         i32.and
         i32.const 128
         i32.or
-        i32.store8 offset=2
-        local.get $0
+        i32.const 16
+        i32.shl
+        i32.or
         local.get $2
+        i32.const 12
+        i32.shr_u
         i32.const 63
         i32.and
         i32.const 128
         i32.or
-        i32.store8 offset=3
-        local.get $3
-        i32.const 4
-        i32.add
-        local.set $3
+        i32.const 8
+        i32.shl
+        i32.or
+        i32.or
+        i32.store
         local.get $0
         i32.const 4
         i32.add
         local.set $0
+        local.get $3
+        i32.const 4
+        i32.add
+        local.set $3
         br $while-continue|0
        end
       end
@@ -2080,8 +2074,6 @@
       i32.shr_u
       i32.const 224
       i32.or
-      i32.store8
-      local.get $0
       local.get $2
       i32.const 6
       i32.shr_u
@@ -2089,7 +2081,10 @@
       i32.and
       i32.const 128
       i32.or
-      i32.store8 offset=1
+      i32.const 8
+      i32.shl
+      i32.or
+      i32.store16
       local.get $0
       local.get $2
       i32.const 63
@@ -2097,26 +2092,26 @@
       i32.const 128
       i32.or
       i32.store8 offset=2
-      local.get $3
-      i32.const 2
-      i32.add
-      local.set $3
       local.get $0
       i32.const 3
       i32.add
      end
     end
     local.set $0
+    local.get $3
+    i32.const 2
+    i32.add
+    local.set $3
     br $while-continue|0
    end
   end
   local.get $3
-  local.get $5
+  local.get $6
   i32.gt_u
   if
    i32.const 0
    i32.const 432
-   i32.const 696
+   i32.const 703
    i32.const 6
    call $~lib/builtins/abort
    unreachable
@@ -2138,7 +2133,7 @@
   call $~lib/string/String.UTF8.encode
   local.tee $1
   local.tee $0
-  call $~lib/arraybuffer/ArrayBuffer#get:byteLength
+  call $~lib/string/String.UTF16.byteLength
   i32.const 10
   i32.ne
   if
@@ -2280,7 +2275,7 @@
   call $~lib/string/String.UTF8.encode
   local.tee $1
   local.tee $0
-  call $~lib/arraybuffer/ArrayBuffer#get:byteLength
+  call $~lib/string/String.UTF16.byteLength
   i32.const 11
   i32.ne
   if
@@ -2587,16 +2582,17 @@
   (local $4 i32)
   (local $5 i32)
   (local $6 i32)
+  (local $7 i32)
   local.get $0
   local.get $1
   i32.add
-  local.tee $5
+  local.tee $4
   local.get $0
   i32.lt_u
   if
    i32.const 0
    i32.const 432
-   i32.const 712
+   i32.const 719
    i32.const 6
    call $~lib/builtins/abort
    unreachable
@@ -2607,174 +2603,159 @@
   i32.const 1
   call $~lib/rt/tlsf/__alloc
   local.tee $6
-  local.set $3
+  local.set $1
   loop $while-continue|0
    local.get $0
-   local.get $5
+   local.get $4
    i32.lt_u
    if
     block $while-break|0
      local.get $0
-     local.tee $1
+     i32.load8_u
+     local.set $3
+     local.get $0
      i32.const 1
      i32.add
      local.set $0
-     local.get $1
-     i32.load8_u
-     local.tee $4
+     local.get $3
      i32.const 128
-     i32.lt_u
+     i32.and
      if
+      local.get $0
       local.get $4
-      i32.eqz
-      i32.const 0
-      local.get $2
-      select
+      i32.eq
       br_if $while-break|0
-      local.get $3
-      local.get $4
-      i32.store16
-      local.get $3
-      i32.const 2
+      local.get $0
+      i32.load8_u
+      i32.const 63
+      i32.and
+      local.set $5
+      local.get $0
+      i32.const 1
       i32.add
-      local.set $3
-     else
-      local.get $4
+      local.set $0
+      local.get $3
       i32.const 224
-      i32.lt_u
-      i32.const 0
-      local.get $4
-      i32.const 191
-      i32.gt_u
-      select
+      i32.and
+      i32.const 192
+      i32.eq
       if
+       local.get $1
        local.get $5
-       local.get $0
-       i32.sub
-       i32.const 1
-       i32.lt_u
-       br_if $while-break|0
-       local.get $0
-       local.tee $1
-       i32.const 1
-       i32.add
-       local.set $0
        local.get $3
-       local.get $1
-       i32.load8_u
-       i32.const 63
-       i32.and
-       local.get $4
        i32.const 31
        i32.and
        i32.const 6
        i32.shl
        i32.or
        i32.store16
-       local.get $3
-       i32.const 2
-       i32.add
-       local.set $3
       else
+       local.get $0
        local.get $4
-       i32.const 365
-       i32.lt_u
-       i32.const 0
-       local.get $4
-       i32.const 239
-       i32.gt_u
-       select
-       if (result i32)
+       i32.eq
+       br_if $while-break|0
+       local.get $0
+       i32.load8_u
+       i32.const 63
+       i32.and
+       local.set $7
+       local.get $0
+       i32.const 1
+       i32.add
+       local.set $0
+       local.get $3
+       i32.const 240
+       i32.and
+       i32.const 224
+       i32.eq
+       if
+        local.get $7
+        local.get $3
+        i32.const 15
+        i32.and
+        i32.const 12
+        i32.shl
         local.get $5
+        i32.const 6
+        i32.shl
+        i32.or
+        i32.or
+        local.set $3
+       else
         local.get $0
-        i32.sub
-        i32.const 3
-        i32.lt_u
+        local.get $4
+        i32.eq
         br_if $while-break|0
-        local.get $3
         local.get $0
-        i32.load8_u offset=2
+        i32.load8_u
         i32.const 63
         i32.and
-        local.get $4
+        local.get $3
         i32.const 7
         i32.and
         i32.const 18
         i32.shl
-        local.get $0
-        i32.load8_u
-        i32.const 63
-        i32.and
+        local.get $5
         i32.const 12
         i32.shl
         i32.or
-        local.get $0
-        i32.load8_u offset=1
-        i32.const 63
-        i32.and
+        local.get $7
         i32.const 6
         i32.shl
         i32.or
         i32.or
+        local.set $3
+        local.get $0
+        i32.const 1
+        i32.add
+        local.set $0
+       end
+       local.get $3
+       i32.const 65536
+       i32.lt_u
+       if
+        local.get $1
+        local.get $3
+        i32.store16
+       else
+        local.get $1
+        local.get $3
         i32.const 65536
         i32.sub
-        local.tee $1
+        local.tee $3
         i32.const 10
         i32.shr_u
         i32.const 55296
         i32.or
-        i32.store16
         local.get $3
-        local.get $1
         i32.const 1023
         i32.and
         i32.const 56320
         i32.or
-        i32.store16 offset=2
-        local.get $3
-        i32.const 4
-        i32.add
-        local.set $3
-        local.get $0
-        i32.const 3
-        i32.add
-       else
-        local.get $5
-        local.get $0
-        i32.sub
-        i32.const 2
-        i32.lt_u
-        br_if $while-break|0
-        local.get $3
-        local.get $0
-        i32.load8_u offset=1
-        i32.const 63
-        i32.and
-        local.get $4
-        i32.const 15
-        i32.and
-        i32.const 12
-        i32.shl
-        local.get $0
-        i32.load8_u
-        i32.const 63
-        i32.and
-        i32.const 6
+        i32.const 16
         i32.shl
         i32.or
-        i32.or
-        i32.store16
-        local.get $3
-        i32.const 2
-        i32.add
-        local.set $3
-        local.get $0
+        i32.store
+        local.get $1
         i32.const 2
         i32.add
+        local.set $1
        end
-       local.set $0
       end
+     else
+      local.get $2
+      local.get $3
+      i32.eqz
+      i32.and
+      br_if $while-break|0
+      local.get $1
+      local.get $3
+      i32.store16
      end
+     local.get $1
+     i32.const 2
+     i32.add
+     local.set $1
      br $while-continue|0
     end
    end
@@ -2782,7 +2763,7 @@
   call $~lib/rt/tlsf/maybeInitialize
   local.get $6
   call $~lib/rt/tlsf/checkUsedBlock
-  local.get $3
+  local.get $1
   local.get $6
   i32.sub
   call $~lib/rt/tlsf/reallocateBlock
@@ -2793,7 +2774,7 @@
  (func $~lib/string/String.UTF8.decode (; 39 ;) (param $0 i32) (param $1 i32) (result i32)
   local.get $0
   local.get $0
-  call $~lib/arraybuffer/ArrayBuffer#get:byteLength
+  call $~lib/string/String.UTF16.byteLength
   local.get $1
   call $~lib/string/String.UTF8.decodeUnsafe
  )
@@ -2865,7 +2846,7 @@
   i32.const 1
   call $~lib/string/String.UTF8.encode
   local.tee $0
-  call $~lib/arraybuffer/ArrayBuffer#get:byteLength
+  call $~lib/string/String.UTF16.byteLength
   i32.const 4
   i32.ne
   if
@@ -3180,9 +3161,9 @@
   local.get $3
   call $~lib/rt/pure/__release
  )
- (func $~start (; 44 ;)
-  i32.const 28
-  i32.load
+ (func $start:std/string-encoding (; 44 ;)
+  i32.const 32
+  call $~lib/string/String.UTF16.byteLength
   i32.const 12
   i32.ne
   if
@@ -3207,7 +3188,10 @@
   i32.const 13696
   call $std/string-encoding/testLarge
  )
- (func $~lib/rt/pure/decrement (; 45 ;) (param $0 i32)
+ (func $~start (; 45 ;)
+  call $start:std/string-encoding
+ )
+ (func $~lib/rt/pure/decrement (; 46 ;) (param $0 i32)
   (local $1 i32)
   (local $2 i32)
   local.get $0
@@ -3275,7 +3259,7 @@
    i32.store offset=4
   end
  )
- (func $~lib/rt/__visit_members (; 46 ;) (param $0 i32)
+ (func $~lib/rt/__visit_members (; 47 ;) (param $0 i32)
   block $switch$1$default
    block $switch$1$case$4
     block $switch$1$case$2
diff --git a/tests/compiler/std/string-encoding.untouched.wat b/tests/compiler/std/string-encoding.untouched.wat
index 142628dfd5..f01ce1e805 100644
--- a/tests/compiler/std/string-encoding.untouched.wat
+++ b/tests/compiler/std/string-encoding.untouched.wat
@@ -2758,9 +2758,7 @@
   call $~lib/rt/pure/__retain
   local.set $0
   local.get $0
-  i32.const 16
-  i32.sub
-  i32.load offset=12
+  call $~lib/string/String.UTF16.byteLength
   local.set $1
   local.get $1
   i32.const 0
@@ -3410,12 +3408,9 @@
      i32.lt_u
      if
       local.get $1
-      if (result i32)
-       local.get $6
-       i32.eqz
-      else
-       i32.const 0
-      end
+      local.get $6
+      i32.eqz
+      i32.and
       if
        br $while-break|0
       end
@@ -3423,10 +3418,6 @@
       i32.const 1
       i32.add
       local.set $4
-      local.get $2
-      i32.const 2
-      i32.add
-      local.set $2
      else
       local.get $6
       i32.const 2048
@@ -3436,10 +3427,6 @@
        i32.const 2
        i32.add
        local.set $4
-       local.get $2
-       i32.const 2
-       i32.add
-       local.set $2
       else
        local.get $6
        i32.const 64512
@@ -3463,27 +3450,27 @@
         i32.const 56320
         i32.eq
         if
-         local.get $2
-         i32.const 4
-         i32.add
-         local.set $2
          local.get $4
          i32.const 4
          i32.add
          local.set $4
+         local.get $2
+         i32.const 4
+         i32.add
+         local.set $2
          br $while-continue|0
         end
        end
-       local.get $2
-       i32.const 2
-       i32.add
-       local.set $2
        local.get $4
        i32.const 3
        i32.add
        local.set $4
       end
      end
+     local.get $2
+     i32.const 2
+     i32.add
+     local.set $2
      br $while-continue|0
     end
    end
@@ -3534,6 +3521,10 @@
   (local $8 i32)
   (local $9 i32)
   (local $10 i32)
+  (local $11 i32)
+  (local $12 i32)
+  (local $13 i32)
+  (local $14 i32)
   local.get $0
   call $~lib/rt/pure/__retain
   local.set $0
@@ -3585,37 +3576,34 @@
      i32.const 1
      i32.add
      local.set $7
-     local.get $2
-     i32.const 2
-     i32.add
-     local.set $2
     else
      local.get $9
      i32.const 2048
      i32.lt_u
      if
-      local.get $7
       local.get $9
       i32.const 6
       i32.shr_u
       i32.const 192
       i32.or
-      i32.store8
-      local.get $7
+      local.set $10
       local.get $9
       i32.const 63
       i32.and
       i32.const 128
       i32.or
-      i32.store8 offset=1
+      local.set $11
+      local.get $7
+      local.get $11
+      i32.const 8
+      i32.shl
+      local.get $10
+      i32.or
+      i32.store16
       local.get $7
       i32.const 2
       i32.add
       local.set $7
-      local.get $2
-      i32.const 2
-      i32.add
-      local.set $2
      else
       local.get $9
       i32.const 64512
@@ -3634,8 +3622,8 @@
       if
        local.get $2
        i32.load16_u offset=2
-       local.set $10
-       local.get $10
+       local.set $11
+       local.get $11
        i32.const 64512
        i32.and
        i32.const 56320
@@ -3648,19 +3636,17 @@
         i32.const 10
         i32.shl
         i32.add
-        local.get $10
+        local.get $11
         i32.const 1023
         i32.and
         i32.or
         local.set $9
-        local.get $7
         local.get $9
         i32.const 18
         i32.shr_u
         i32.const 240
         i32.or
-        i32.store8
-        local.get $7
+        local.set $10
         local.get $9
         i32.const 12
         i32.shr_u
@@ -3668,8 +3654,7 @@
         i32.and
         i32.const 128
         i32.or
-        i32.store8 offset=1
-        local.get $7
+        local.set $12
         local.get $9
         i32.const 6
         i32.shr_u
@@ -3677,33 +3662,45 @@
         i32.and
         i32.const 128
         i32.or
-        i32.store8 offset=2
-        local.get $7
+        local.set $13
         local.get $9
         i32.const 63
         i32.and
         i32.const 128
         i32.or
-        i32.store8 offset=3
-        local.get $2
-        i32.const 4
-        i32.add
-        local.set $2
+        local.set $14
+        local.get $7
+        local.get $14
+        i32.const 24
+        i32.shl
+        local.get $13
+        i32.const 16
+        i32.shl
+        i32.or
+        local.get $12
+        i32.const 8
+        i32.shl
+        i32.or
+        local.get $10
+        i32.or
+        i32.store
         local.get $7
         i32.const 4
         i32.add
         local.set $7
+        local.get $2
+        i32.const 4
+        i32.add
+        local.set $2
         br $while-continue|0
        end
       end
-      local.get $7
       local.get $9
       i32.const 12
       i32.shr_u
       i32.const 224
       i32.or
-      i32.store8
-      local.get $7
+      local.set $11
       local.get $9
       i32.const 6
       i32.shr_u
@@ -3711,24 +3708,33 @@
       i32.and
       i32.const 128
       i32.or
-      i32.store8 offset=1
-      local.get $7
+      local.set $14
       local.get $9
       i32.const 63
       i32.and
       i32.const 128
       i32.or
+      local.set $13
+      local.get $7
+      local.get $14
+      i32.const 8
+      i32.shl
+      local.get $11
+      i32.or
+      i32.store16
+      local.get $7
+      local.get $13
       i32.store8 offset=2
-      local.get $2
-      i32.const 2
-      i32.add
-      local.set $2
       local.get $7
       i32.const 3
       i32.add
       local.set $7
      end
     end
+    local.get $2
+    i32.const 2
+    i32.add
+    local.set $2
     br $while-continue|0
    end
   end
@@ -3739,7 +3745,7 @@
   if
    i32.const 0
    i32.const 432
-   i32.const 696
+   i32.const 703
    i32.const 6
    call $~lib/builtins/abort
    unreachable
@@ -4278,6 +4284,9 @@
   (local $7 i32)
   (local $8 i32)
   (local $9 i32)
+  (local $10 i32)
+  (local $11 i32)
+  (local $12 i32)
   local.get $0
   local.set $3
   local.get $0
@@ -4291,7 +4300,7 @@
   if
    i32.const 0
    i32.const 432
-   i32.const 712
+   i32.const 719
    i32.const 6
    call $~lib/builtins/abort
    unreachable
@@ -4313,92 +4322,96 @@
     local.get $7
     if
      local.get $3
-     local.tee $8
+     i32.load8_u
+     local.set $8
+     local.get $3
      i32.const 1
      i32.add
      local.set $3
      local.get $8
-     i32.load8_u
-     local.set $8
-     local.get $8
      i32.const 128
-     i32.lt_u
+     i32.and
+     i32.eqz
      if
       local.get $2
-      if (result i32)
-       local.get $8
-       i32.eqz
-      else
-       i32.const 0
-      end
+      local.get $8
+      i32.eqz
+      i32.and
       if
        br $while-break|0
       end
       local.get $6
       local.get $8
       i32.store16
-      local.get $6
-      i32.const 2
-      i32.add
-      local.set $6
      else
-      local.get $8
-      i32.const 191
-      i32.gt_u
-      if (result i32)
-       local.get $8
-       i32.const 224
-       i32.lt_u
-      else
-       i32.const 0
+      local.get $4
+      local.get $3
+      i32.eq
+      if
+       br $while-break|0
       end
+      local.get $3
+      i32.load8_u
+      i32.const 63
+      i32.and
+      local.set $9
+      local.get $3
+      i32.const 1
+      i32.add
+      local.set $3
+      local.get $8
+      i32.const 224
+      i32.and
+      i32.const 192
+      i32.eq
       if
-       local.get $4
-       local.get $3
-       i32.sub
-       i32.const 1
-       i32.lt_u
-       if
-        br $while-break|0
-       end
        local.get $6
        local.get $8
        i32.const 31
        i32.and
        i32.const 6
        i32.shl
-       local.get $3
-       local.tee $9
-       i32.const 1
-       i32.add
-       local.set $3
        local.get $9
+       i32.or
+       i32.store16
+      else
+       local.get $4
+       local.get $3
+       i32.eq
+       if
+        br $while-break|0
+       end
+       local.get $3
        i32.load8_u
        i32.const 63
        i32.and
-       i32.or
-       i32.store16
-       local.get $6
-       i32.const 2
+       local.set $10
+       local.get $3
+       i32.const 1
        i32.add
-       local.set $6
-      else
+       local.set $3
        local.get $8
-       i32.const 239
-       i32.gt_u
-       if (result i32)
+       i32.const 240
+       i32.and
+       i32.const 224
+       i32.eq
+       if
         local.get $8
-        i32.const 365
-        i32.lt_u
+        i32.const 15
+        i32.and
+        i32.const 12
+        i32.shl
+        local.get $9
+        i32.const 6
+        i32.shl
+        i32.or
+        local.get $10
+        i32.or
+        local.set $8
        else
-        i32.const 0
-       end
-       if
         local.get $4
         local.get $3
-        i32.sub
-        i32.const 3
-        i32.lt_u
+        i32.eq
         if
          br $while-break|0
         end
@@ -4407,82 +4420,56 @@
         i32.and
         i32.const 18
         i32.shl
-        local.get $3
-        i32.load8_u
-        i32.const 63
-        i32.and
+        local.get $9
         i32.const 12
         i32.shl
         i32.or
-        local.get $3
-        i32.load8_u offset=1
-        i32.const 63
-        i32.and
+        local.get $10
         i32.const 6
         i32.shl
         i32.or
         local.get $3
-        i32.load8_u offset=2
+        i32.load8_u
         i32.const 63
         i32.and
         i32.or
-        i32.const 65536
-        i32.sub
         local.set $8
         local.get $3
-        i32.const 3
+        i32.const 1
         i32.add
         local.set $3
+       end
+       local.get $8
+       i32.const 65536
+       i32.lt_u
+       if
         local.get $6
-        i32.const 55296
+        local.get $8
+        i32.store16
+       else
+        local.get $8
+        i32.const 65536
+        i32.sub
+        local.set $8
         local.get $8
         i32.const 10
         i32.shr_u
+        i32.const 55296
         i32.or
-        i32.store16
-        local.get $6
-        i32.const 56320
+        local.set $11
         local.get $8
         i32.const 1023
         i32.and
+        i32.const 56320
         i32.or
-        i32.store16 offset=2
-        local.get $6
-        i32.const 4
-        i32.add
-        local.set $6
-       else
-        local.get $4
-        local.get $3
-        i32.sub
-        i32.const 2
-        i32.lt_u
-        if
-         br $while-break|0
-        end
+        local.set $12
         local.get $6
-        local.get $8
-        i32.const 15
-        i32.and
-        i32.const 12
-        i32.shl
-        local.get $3
-        i32.load8_u
-        i32.const 63
-        i32.and
-        i32.const 6
+        local.get $11
+        local.get $12
+        i32.const 16
         i32.shl
         i32.or
-        local.get $3
-        i32.load8_u offset=1
-        i32.const 63
-        i32.and
-        i32.or
-        i32.store16
-        local.get $3
-        i32.const 2
-        i32.add
-        local.set $3
+        i32.store
         local.get $6
         i32.const 2
         i32.add
@@ -4490,6 +4477,10 @@
        end
       end
      end
+     local.get $6
+     i32.const 2
+     i32.add
+     local.set $6
      br $while-continue|0
     end
    end