emit a global const for Math_fround(0) to avoid function call overheads in the fround polyfill

3 files changed, 44 insertions, 27 deletions

diff --git a/tools/js-optimizer.js b/tools/js-optimizer.js
index db85965d..2914b6e8 100644
--- a/tools/js-optimizer.js
+++ b/tools/js-optimizer.js
@@ -1342,13 +1342,21 @@ var ASM_DOUBLE = 1;
 var ASM_FLOAT = 2;
 var ASM_NONE = 3;
 
-function detectAsmCoercion(node, asmInfo) {
+var ASM_FLOAT_ZERO = null; // TODO: share the entire node?
+
+function detectAsmCoercion(node, asmInfo, inVarDef) {
   // for params, +x vs x|0, for vars, 0.0 vs 0
   if (node[0] === 'num' && node[1].toString().indexOf('.') >= 0) return ASM_DOUBLE;
   if (node[0] === 'unary-prefix') return ASM_DOUBLE;
   if (node[0] === 'call' && node[1][0] === 'name' && node[1][1] === 'Math_fround') return ASM_FLOAT;
   if (asmInfo && node[0] == 'name') return getAsmType(node[1], asmInfo);
-  if (node[0] === 'name') return ASM_NONE;
+  if (node[0] === 'name') {
+    if (!inVarDef) return ASM_NONE;
+    // We are in a variable definition, where Math_fround(0) optimized into a global constant becomes f0 = Math_fround(0)
+    if (!ASM_FLOAT_ZERO) ASM_FLOAT_ZERO = node[1];
+    else assert(ASM_FLOAT_ZERO === node[1]);
+    return ASM_FLOAT;
+  }
   return ASM_INT;
 }
 
@@ -1366,7 +1374,13 @@ function makeAsmVarDef(v, type) {
   switch (type) {
     case ASM_INT: return [v, ['num', 0]];
     case ASM_DOUBLE: return [v, ['unary-prefix', '+', ['num', 0]]];
-    case ASM_FLOAT: return [v, ['call', ['name', 'Math_fround'], [['num', 0]]]];
+    case ASM_FLOAT: {
+      if (ASM_FLOAT_ZERO) {
+        return [v, ['name', ASM_FLOAT_ZERO]];
+      } else {
+        return [v, ['call', ['name', 'Math_fround'], [['num', 0]]]];
+      }
+    }
     default: throw 'wha? ' + JSON.stringify([node, type]) + new Error().stack;
   }
 }
@@ -1409,9 +1423,7 @@ function normalizeAsm(func) {
       var name = v[0];
       var value = v[1];
       if (!(name in data.vars)) {
-        assert(value[0] === 'num' || (value[0] === 'unary-prefix' && value[2][0] === 'num') // must be valid coercion no-op
-                                  || (value[0] === 'call' && value[1][0] === 'name' && value[1][1] === 'Math_fround'));
-        data.vars[name] = detectAsmCoercion(value);
+        data.vars[name] = detectAsmCoercion(value, null, true);
         v.length = 1; // make an un-assigning var
       } else {
         assert(j === 0, 'cannot break in the middle');
@@ -1425,22 +1437,6 @@ function normalizeAsm(func) {
     traverse(stats[i], function(node, type) {
       if (type === 'var') {
         assert(0, 'should be no vars to fix! ' + func[1] + ' : ' + JSON.stringify(node));
-        /*
-        for (var j = 0; j < node[1].length; j++) {
-          var v = node[1][j];
-          var name = v[0];
-          var value = v[1];
-          if (!(name in data.vars)) {
-            if (value[0] != 'name') {
-              data.vars[name] = detectAsmCoercion(value); // detect by coercion
-            } else {
-              var origin = value[1];
-              data.vars[name] = data.vars[origin] || ASM_INT; // detect by origin variable, or assume int for non-locals
-            }
-          }
-        }
-        unVarify(node[1], node);
-        */
       } else if (type === 'call' && node[1][0] === 'function') {
         assert(!node[1][1]); // anonymous functions only
         data.inlines.push(node[1]);
@@ -3721,7 +3717,7 @@ function minifyGlobals(ast) {
   var first = true; // do not minify initial 'var asm ='
   // find the globals
   traverse(ast, function(node, type) {
-    if (type === 'var') {
+    if (type === 'var' || type === 'const') {
       if (first) {
         first = false;
         return;
@@ -4971,10 +4967,19 @@ function safeHeap(ast) {
 
 function optimizeFrounds(ast) {
   // collapse fround(fround(..)), which can happen due to elimination
+  // also emit f0 instead of fround(0) (except in returns)
+  var inReturn = false;
   function fix(node) {
+    if (node[0] === 'return') inReturn = true;
     traverseChildren(node, fix);
-    if (node[0] === 'call' && node[1][0] === 'name' && node[1][1] === 'Math_fround' && node[2][0][0] === 'call' && node[2][0][1][0] === 'name' && node[2][0][1][1] === 'Math_fround') {
-      return node[2][0];
+    if (node[0] === 'return') inReturn = false;
+    if (node[0] === 'call' && node[1][0] === 'name' && node[1][1] === 'Math_fround') {
+      var arg = node[2][0];
+      if (arg[0] === 'num') {
+        if (!inReturn && arg[1] === 0) return ['name', 'f0'];
+      } else if (arg[0] === 'call' && arg[1][0] === 'name' && arg[1][1] === 'Math_fround') {
+        return arg;
+      }
     }
   }
   traverseChildren(ast, fix);
diff --git a/tools/test-js-optimizer-asm-pre-f32.js b/tools/test-js-optimizer-asm-pre-f32.js
index 5471deeb..be515b36 100644
--- a/tools/test-js-optimizer-asm-pre-f32.js
+++ b/tools/test-js-optimizer-asm-pre-f32.js
@@ -14,4 +14,10 @@ function dupe() {
  x = Math_fround(Math_fround(Math_fround(x)));
  x = Math_fround(Math_fround(Math_fround(Math_fround(x))));
 }
-// EMSCRIPTEN_GENERATED_FUNCTIONS: ["badf", "badf2", "dupe"]
+function zeros(x) {
+  x = Math_fround(x);
+  var y = Math_fround(0);
+  print(Math_fround(y) + Math_fround(0));
+  return Math_fround(0); // return needs to stay as is
+}
+// EMSCRIPTEN_GENERATED_FUNCTIONS: ["badf", "badf2", "dupe", "zeros"]
diff --git a/tools/test-js-optimizer-asm-pre-output-f32.js b/tools/test-js-optimizer-asm-pre-output-f32.js
index 19059619..f0f2d0da 100644
--- a/tools/test-js-optimizer-asm-pre-output-f32.js
+++ b/tools/test-js-optimizer-asm-pre-output-f32.js
@@ -4,7 +4,7 @@ function badf() {
  HEAP32[$gep23_asptr >> 2] = $9;
 }
 function badf2() {
- var $9 = Math_fround(0);
+ var $9 = f0;
  $9 = Math_fround($8);
  HEAPF32[$gep23_asptr >> 2] = $9;
 }
@@ -14,4 +14,10 @@ function dupe() {
  x = Math_fround(x);
  x = Math_fround(x);
 }
+function zeros(x) {
+ x = Math_fround(x);
+ var y = f0;
+ print(Math_fround(y) + f0);
+ return Math_fround(0);
+}