wasm2js: optimize loads (#2085)

When loading a boolean, prefer the signed heap (which is more commonly used, and may be faster).
We never use HEAPU32 (HEAP32 is always enough), just remove it.

Author: kripken

src/tools/wasm2js.cpp

@@ -189,6 +189,10 @@ static void optimizeJS(Ref ast) {
 
   auto getHeapFromAccess = [](Ref node) { return node[1]->getIString(); };
 
+  auto setHeapOnAccess = [](Ref node, IString heap) {
+    node[1] = ValueBuilder::makeName(heap);
+  };
+
   auto isIntegerHeap = [](IString heap) {
     return heap == HEAP8 || heap == HEAPU8 || heap == HEAP16 ||
            heap == HEAPU16 || heap == HEAP32 || heap == HEAPU32;
@@ -236,6 +240,21 @@ static void optimizeJS(Ref ast) {
     else if (isBitwise(node)) {
       node[2] = removeOrZero(node[2]);
       node[3] = removeOrZero(node[3]);
+      // A load into an & may allow using a simpler heap, e.g. HEAPU8[..] & 1
+      // (a load of a boolean) may be HEAP8[..] & 1. The signed heaps are more
+      // commonly used, so it compresses better, and also they seem to have
+      // better performance (perhaps since HEAPU32 is at risk of not being a
+      // smallint).
+      if (node[1] == AND && isHeapAccess(node[2])) {
+        auto heap = getHeapFromAccess(node[2]);
+        if (isConstantAnd(node, 1)) {
+          if (heap == HEAPU8) {
+            setHeapOnAccess(node[2], HEAP8);
+          } else if (heap == HEAPU16) {
+            setHeapOnAccess(node[2], HEAP16);
+          }
+        }
+      }
     }
     // +(+x) => +x
     else if (isPlus(node)) {
@@ -280,7 +299,6 @@ static void optimizeJS(Ref ast) {
 
   // Remove unnecessary break/continue labels, when referring to the top level.
 
-  // XXX IString invalid("__wasm2js$INVALID_LABEL__");
   std::vector<Ref> breakCapturers;
   std::vector<Ref> continueCapturers;
   std::unordered_map<IString, Ref>

src/wasm2js.h

@@ -420,7 +420,6 @@ void Wasm2JSBuilder::addBasics(Ref ast) {
   addHeap(HEAP32, INT32ARRAY);
   addHeap(HEAPU8, UINT8ARRAY);
   addHeap(HEAPU16, UINT16ARRAY);
-  addHeap(HEAPU32, UINT32ARRAY);
   addHeap(HEAPF32, FLOAT32ARRAY);
   addHeap(HEAPF64, FLOAT64ARRAY);
   // core asm.js imports
@@ -1687,7 +1686,6 @@ void Wasm2JSBuilder::addMemoryGrowthFuncs(Ref ast, Module* wasm) {
   setHeap(HEAP32, INT32ARRAY);
   setHeap(HEAPU8, UINT8ARRAY);
   setHeap(HEAPU16, UINT16ARRAY);
-  setHeap(HEAPU32, UINT32ARRAY);
   setHeap(HEAPF32, FLOAT32ARRAY);
   setHeap(HEAPF64, FLOAT64ARRAY);
 

test/binaryen.js/emit_asmjs.js.txt

@@ -6,7 +6,6 @@ function asmFunc(global, env, buffer) {
  var HEAP32 = new global.Int32Array(buffer);
  var HEAPU8 = new global.Uint8Array(buffer);
  var HEAPU16 = new global.Uint16Array(buffer);
- var HEAPU32 = new global.Uint32Array(buffer);
  var HEAPF32 = new global.Float32Array(buffer);
  var HEAPF64 = new global.Float64Array(buffer);
  var Math_imul = global.Math.imul;

test/wasm2js.asserts.js

@@ -37,7 +37,6 @@ function asmFunc0(global, env, buffer) {
  var HEAP32 = new global.Int32Array(buffer);
  var HEAPU8 = new global.Uint8Array(buffer);
  var HEAPU16 = new global.Uint16Array(buffer);
- var HEAPU32 = new global.Uint32Array(buffer);
  var HEAPF32 = new global.Float32Array(buffer);
  var HEAPF64 = new global.Float64Array(buffer);
  var Math_imul = global.Math.imul;

test/wasm2js.traps.js

@@ -37,7 +37,6 @@ function asmFunc0(global, env, buffer) {
  var HEAP32 = new global.Int32Array(buffer);
  var HEAPU8 = new global.Uint8Array(buffer);
  var HEAPU16 = new global.Uint16Array(buffer);
- var HEAPU32 = new global.Uint32Array(buffer);
  var HEAPF32 = new global.Float32Array(buffer);
  var HEAPF64 = new global.Float64Array(buffer);
  var Math_imul = global.Math.imul;

test/wasm2js/address.2asm.js

@@ -7,7 +7,6 @@ function asmFunc(global, env, buffer) {
  var HEAP32 = new global.Int32Array(buffer);
  var HEAPU8 = new global.Uint8Array(buffer);
  var HEAPU16 = new global.Uint16Array(buffer);
- var HEAPU32 = new global.Uint32Array(buffer);
  var HEAPF32 = new global.Float32Array(buffer);
  var HEAPF64 = new global.Float64Array(buffer);
  var Math_imul = global.Math.imul;
@@ -59,7 +58,6 @@ function asmFunc(global, env, buffer) {
    HEAP32 = new global.Int32Array(newBuffer);
    HEAPU8 = new global.Uint8Array(newBuffer);
    HEAPU16 = new global.Uint16Array(newBuffer);
-   HEAPU32 = new global.Uint32Array(newBuffer);
    HEAPF32 = new global.Float32Array(newBuffer);
    HEAPF64 = new global.Float64Array(newBuffer);
    buffer = newBuffer;

test/wasm2js/base64.2asm.js

@@ -6,7 +6,6 @@ function asmFunc(global, env, buffer) {
  var HEAP32 = new global.Int32Array(buffer);
  var HEAPU8 = new global.Uint8Array(buffer);
  var HEAPU16 = new global.Uint16Array(buffer);
- var HEAPU32 = new global.Uint32Array(buffer);
  var HEAPF32 = new global.Float32Array(buffer);
  var HEAPF64 = new global.Float64Array(buffer);
  var Math_imul = global.Math.imul;

test/wasm2js/base64.2asm.js.opt

@@ -6,7 +6,6 @@ function asmFunc(global, env, buffer) {
  var HEAP32 = new global.Int32Array(buffer);
  var HEAPU8 = new global.Uint8Array(buffer);
  var HEAPU16 = new global.Uint16Array(buffer);
- var HEAPU32 = new global.Uint32Array(buffer);
  var HEAPF32 = new global.Float32Array(buffer);
  var HEAPF64 = new global.Float64Array(buffer);
  var Math_imul = global.Math.imul;

test/wasm2js/block.2asm.js

@@ -6,7 +6,6 @@ function asmFunc(global, env, buffer) {
  var HEAP32 = new global.Int32Array(buffer);
  var HEAPU8 = new global.Uint8Array(buffer);
  var HEAPU16 = new global.Uint16Array(buffer);
- var HEAPU32 = new global.Uint32Array(buffer);
  var HEAPF32 = new global.Float32Array(buffer);
  var HEAPF64 = new global.Float64Array(buffer);
  var Math_imul = global.Math.imul;

test/wasm2js/br.2asm.js

@@ -7,7 +7,6 @@ function asmFunc(global, env, buffer) {
  var HEAP32 = new global.Int32Array(buffer);
  var HEAPU8 = new global.Uint8Array(buffer);
  var HEAPU16 = new global.Uint16Array(buffer);
- var HEAPU32 = new global.Uint32Array(buffer);
  var HEAPF32 = new global.Float32Array(buffer);
  var HEAPF64 = new global.Float64Array(buffer);
  var Math_imul = global.Math.imul;
@@ -772,7 +771,6 @@ function asmFunc(global, env, buffer) {
  var HEAP32 = new global.Int32Array(buffer);
  var HEAPU8 = new global.Uint8Array(buffer);
  var HEAPU16 = new global.Uint16Array(buffer);
- var HEAPU32 = new global.Uint32Array(buffer);
  var HEAPF32 = new global.Float32Array(buffer);
  var HEAPF64 = new global.Float64Array(buffer);
  var Math_imul = global.Math.imul;