wasm2js: Do not convert x >>> 0 | 0 to x >>> 0 (#2581)

isBinary was used where we should only accept
a signed binary, as removing the | 0 from an unsigned
value may be incorrect.

This does regress a few small things (as can be seen
in the diff). If it's important we can add more sophisticated
optimizations here, perhaps like an assumption that the
signedness of a local never matters.

Fixes emscripten-core/emscripten#10173

Author: kripken

src/tools/wasm2js.cpp

@@ -179,6 +179,14 @@ static void optimizeJS(Ref ast) {
     return false;
   };
 
+  auto isSignedBitwise = [](Ref node) {
+    if (node->isArray() && !node->empty() && node[0] == BINARY) {
+      auto op = node[1];
+      return op == OR || op == AND || op == XOR || op == RSHIFT || op == LSHIFT;
+    }
+    return false;
+  };
+
   auto isUnary = [](Ref node, IString op) {
     return node->isArray() && !node->empty() && node[0] == UNARY_PREFIX &&
            node[1] == op;
@@ -275,9 +283,9 @@ static void optimizeJS(Ref ast) {
       // x | 0 going into a bitwise op => skip the | 0
       node[2] = removeOrZero(node[2]);
       node[3] = removeOrZero(node[3]);
-      // x | 0 | 0  =>  x | 0
+      // (x | 0 or similar) | 0  =>  (x | 0 or similar)
       if (isOrZero(node)) {
-        if (isBitwise(node[2])) {
+        if (isSignedBitwise(node[2])) {
           replaceInPlace(node, node[2]);
         }
       }

test/wasm2js/conversions-modified.2asm.js.opt

@@ -60,7 +60,7 @@ function asmFunc(global, env, buffer) {
 
  function $4($0) {
   $0 = Math_fround($0);
-  return ~~$0 >>> 0;
+  return ~~$0 >>> 0 | 0;
  }
 
  function $5($0) {
@@ -70,19 +70,19 @@ function asmFunc(global, env, buffer) {
 
  function $6($0) {
   $0 = +$0;
-  return ~~$0 >>> 0;
+  return ~~$0 >>> 0 | 0;
  }
 
  function $7($0) {
   $0 = Math_fround($0);
   i64toi32_i32$HIGH_BITS = Math_fround(Math_abs($0)) >= Math_fround(1.0) ? ($0 > Math_fround(0.0) ? ~~Math_fround(Math_min(Math_fround(Math_floor(Math_fround($0 / Math_fround(4294967296.0)))), Math_fround(4294967296.0))) >>> 0 : ~~Math_fround(Math_ceil(Math_fround(Math_fround($0 - Math_fround(~~$0 >>> 0 >>> 0)) / Math_fround(4294967296.0)))) >>> 0) : 0;
-  return ~~$0 >>> 0;
+  return ~~$0 >>> 0 | 0;
  }
 
  function $9($0) {
   $0 = +$0;
   i64toi32_i32$HIGH_BITS = Math_abs($0) >= 1.0 ? ($0 > 0.0 ? ~~Math_min(Math_floor($0 / 4294967296.0), 4294967295.0) >>> 0 : ~~Math_ceil(($0 - +(~~$0 >>> 0 >>> 0)) / 4294967296.0) >>> 0) : 0;
-  return ~~$0 >>> 0;
+  return ~~$0 >>> 0 | 0;
  }
 
  function $11($0) {

test/wasm2js/float-ops.2asm.js.opt

@@ -236,12 +236,12 @@ function asmFunc(global, env, buffer) {
 
  function $41($0) {
   $0 = Math_fround($0);
-  return ~~$0 >>> 0;
+  return ~~$0 >>> 0 | 0;
  }
 
  function $42($0) {
   $0 = +$0;
-  return ~~$0 >>> 0;
+  return ~~$0 >>> 0 | 0;
  }
 
  function $47($0) {

test/wasm2js/i64-rotate.2asm.js.opt

@@ -35,9 +35,9 @@ function asmFunc(global, env, buffer) {
   $5 = $6;
   $3 = $5 & 31;
   if (32 <= $5 >>> 0) {
-   $3 = -1 >>> $3
+   $3 = -1 >>> $3 | 0
   } else {
-   $4 = -1 >>> $3;
+   $4 = -1 >>> $3 | 0;
    $3 = (1 << $3) - 1 << 32 - $3 | -1 >>> $3;
   }
   $5 = $3 & $0;
@@ -66,9 +66,9 @@ function asmFunc(global, env, buffer) {
   $1 = $4 & 31;
   if (32 <= $4 >>> 0) {
    $2 = 0;
-   $0 = $3 >>> $1;
+   $0 = $3 >>> $1 | 0;
   } else {
-   $2 = $3 >>> $1;
+   $2 = $3 >>> $1 | 0;
    $0 = ((1 << $1) - 1 & $3) << 32 - $1 | $0 >>> $1;
   }
   $0 = $0 | $6;
@@ -92,19 +92,19 @@ function asmFunc(global, env, buffer) {
   $5 = $6 & 31;
   if (32 <= $6 >>> 0) {
    $4 = 0;
-   $6 = $3 >>> $5;
+   $6 = $3 >>> $5 | 0;
   } else {
-   $4 = $3 >>> $5;
+   $4 = $3 >>> $5 | 0;
    $6 = ((1 << $5) - 1 & $3) << 32 - $5 | $7 >>> $5;
   }
   $7 = $4;
   $3 = 0 - $2 & 63;
   $5 = $3 & 31;
   if (32 <= $3 >>> 0) {
    $4 = 0;
-   $2 = -1 >>> $5;
+   $2 = -1 >>> $5 | 0;
   } else {
-   $4 = -1 >>> $5;
+   $4 = -1 >>> $5 | 0;
    $2 = (1 << $5) - 1 << 32 - $5 | -1 >>> $5;
   }
   $0 = $2 & $0;

test/wasm2js/stack-modified.2asm.js.opt

@@ -52,15 +52,15 @@ function asmFunc(global, env, buffer) {
 
  function _ZN17compiler_builtins3int3mul3Mul3mul17h070e9a1c69faec5bE($0_1, $1, $2, $3) {
   var $4 = 0, $5 = 0, $6 = 0, $7 = 0, $8 = 0, $9 = 0;
-  $4 = $2 >>> 16;
-  $5 = $0_1 >>> 16;
+  $4 = $2 >>> 16 | 0;
+  $5 = $0_1 >>> 16 | 0;
   $9 = Math_imul($4, $5);
   $6 = $2 & 65535;
   $7 = $0_1 & 65535;
   $8 = Math_imul($6, $7);
-  $5 = ($8 >>> 16) + Math_imul($5, $6) | 0;
+  $5 = ($8 >>> 16 | 0) + Math_imul($5, $6) | 0;
   $4 = ($5 & 65535) + Math_imul($4, $7) | 0;
-  $0_1 = (((Math_imul($1, $2) + $9 | 0) + Math_imul($0_1, $3) | 0) + ($5 >>> 16) | 0) + ($4 >>> 16) | 0;
+  $0_1 = (Math_imul($1, $2) + $9 | 0) + Math_imul($0_1, $3) + ($5 >>> 16) + ($4 >>> 16) | 0;
   $1 = $8 & 65535 | $4 << 16;
   i64toi32_i32$HIGH_BITS = $0_1;
   return $1;