wasm2js: remove unnecessary labels (#2108)

Author: kripken

scripts/fuzz_opt.py

@@ -26,7 +26,7 @@
 
 # parameters
 
-NANS = False
+NANS = True
 
 FEATURE_OPTS = []  # '--all-features' etc
 
@@ -44,7 +44,7 @@
   '--experimental-wasm-return-call'
 ]
 
-INPUT_SIZE_LIMIT = 50 * 1024
+INPUT_SIZE_LIMIT = 150 * 1024
 
 LOG_LIMIT = 125
 
@@ -145,10 +145,7 @@ def run_bynterp(wasm):
 
 def run_wasm2js(wasm):
   wrapper = run([in_bin('wasm-opt'), wasm, '--emit-js-wrapper=/dev/stdout'] + FEATURE_OPTS)
-  cmd = [in_bin('wasm2js'), wasm, '--emscripten']
-  if random.random() < 0.5:
-    cmd += ['-O']
-  main = run(cmd + FEATURE_OPTS)
+  main = run([in_bin('wasm2js'), wasm, '--emscripten'] + FEATURE_OPTS)
   with open(os.path.join(options.binaryen_root, 'scripts', 'wasm2js.js')) as f:
     glue = f.read()
   with open('js.js', 'w') as f:
@@ -165,9 +162,9 @@ def run_wasm2js(wasm):
 def run_vms(prefix):
   wasm = prefix + 'wasm'
   results = []
-  # results.append(run_bynterp(wasm))
-  # results.append(fix_output(run_vm([os.path.expanduser('d8'), prefix + 'js'] + V8_OPTS + ['--', wasm])))
-  results.append(run_wasm2js(wasm))
+  results.append(run_bynterp(wasm))
+  results.append(fix_output(run_vm([os.path.expanduser('d8'), prefix + 'js'] + V8_OPTS + ['--', wasm])))
+  # results.append(run_wasm2js(wasm))
 
   # append to add results from VMs
   # results += [fix_output(run_vm([os.path.expanduser('d8'), prefix + 'js'] + V8_OPTS + ['--', prefix + 'wasm']))]

src/tools/wasm2js.cpp

@@ -136,6 +136,12 @@ static void replaceInPlace(Ref target, Ref value) {
   }
 }
 
+static void replaceInPlaceIfPossible(Ref target, Ref value) {
+  if (target->isArray() && value->isArray()) {
+    replaceInPlace(target, value);
+  }
+}
+
 static void optimizeJS(Ref ast) {
   // Helpers
 
@@ -377,7 +383,8 @@ static void optimizeJS(Ref ast) {
     }
   });
 
-  // Remove unnecessary break/continue labels, when referring to the top level.
+  // Remove unnecessary break/continue labels, when the name is that of the
+  // highest target anyhow, which we would reach without the name.
 
   std::vector<Ref> breakCapturers;
   std::vector<Ref> continueCapturers;
@@ -437,6 +444,30 @@ static void optimizeJS(Ref ast) {
         }
       }
     });
+
+  // Remove unnecessary block/loop labels.
+
+  std::set<IString> usedLabelNames;
+
+  traversePost(ast, [&](Ref node) {
+    if (node->isArray() && !node->empty()) {
+      if (node[0] == BREAK || node[0] == CONTINUE) {
+        if (!node[1]->isNull()) {
+          auto label = node[1]->getIString();
+          usedLabelNames.insert(label);
+        }
+      } else if (node[0] == LABEL) {
+        auto label = node[1]->getIString();
+        if (usedLabelNames.count(label)) {
+          // It's used; just erase it from the data structure.
+          usedLabelNames.erase(label);
+        } else {
+          // It's not used - get rid of it.
+          replaceInPlaceIfPossible(node, node[2]);
+        }
+      }
+    }
+  });
 }
 
 static void emitWasm(Module& wasm,

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

@@ -22,7 +22,7 @@ function asmFunc(global, env, buffer) {
  var nan = global.NaN;
  var infinity = global.Infinity;
  function $0() {
-  loop : while (1) continue;
+  while (1) continue;
  }
 
  function $1() {

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

@@ -57,7 +57,7 @@ function asmFunc(global, env, buffer) {
 
  function __wasm_popcnt_i64($0, $1) {
   var $2 = 0, $3 = 0, $4 = 0, $5 = 0;
-  label$2 : while (1) {
+  while (1) {
    $5 = $3;
    $2 = $4;
    if ($0 | $1) {

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

@@ -30,7 +30,7 @@ function asmFunc(global, env, buffer) {
   var $2 = 0, $3 = 0, $4 = 0;
   $2 = $1;
   $3 = 1;
-  label$2 : while (1) {
+  while (1) {
    if ($0_1 | $2) {
     $3 = _ZN17compiler_builtins3int3mul3Mul3mul17h070e9a1c69faec5bE($0_1, $2, $3, $4);
     $4 = i64toi32_i32$HIGH_BITS;

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

@@ -98,7 +98,7 @@ function asmFunc(global, env, buffer) {
 
  function __wasm_popcnt_i32($0) {
   var $1_1 = 0, $2 = 0;
-  label$2 : while (1) {
+  while (1) {
    $2 = $1_1;
    if ($0) {
     $0 = $0 - 1 & $0;
@@ -112,7 +112,7 @@ function asmFunc(global, env, buffer) {
 
  function __wasm_popcnt_i64($0, $1_1) {
   var $2 = 0, $3 = 0, $4 = 0, $5 = 0;
-  label$2 : while (1) {
+  while (1) {
    $5 = $3;
    $2 = $4;
    if ($0 | $1_1) {