uncommaify between ifs that can potentially be simplified

emcc

@@ -1689,7 +1689,9 @@ try:
 
       js_optimizer_queue += ['simplifyExpressions']
 
-      if debug_level == 0 or profiling: js_optimizer_queue += ['simplifyIfs']
+      # simplify ifs if it is ok to make the code somewhat unreadable, and unless outlining (simplified ifs
+      # with commaified code breaks late aggressive variable elimination)
+      if (debug_level == 0 or profiling) and shared.Settings.OUTLINING_LIMIT == 0: js_optimizer_queue += ['simplifyIfs']
 
       if opt_level >= 3 and shared.Settings.PRECISE_F32: js_optimizer_queue += ['optimizeFrounds']
 

tools/js-optimizer.js

@@ -140,6 +140,8 @@ var ALTER_FLOW = set('break', 'continue', 'return');
 var BREAK_CAPTURERS = set('do', 'while', 'for', 'switch');
 var CONTINUE_CAPTURERS = LOOP;
 
+var COMMABLE = set('assign', 'binary', 'unary-prefix', 'unary-postfix', 'name', 'num', 'call', 'seq', 'conditional', 'sub');
+
 var FUNCTIONS_THAT_ALWAYS_THROW = set('abort', '___resumeException', '___cxa_throw', '___cxa_rethrow');
 
 var NULL_NODE = ['name', 'null'];
@@ -832,8 +834,29 @@ function simplifyIfs(ast) {
       var body = node[2];
       // recurse to handle chains
       while (body[0] === 'block') {
-        if (body[1].length !== 1) break;
-        var singleton = body[1][0];
+        var stats = body[1];
+        if (stats.length > 1) {
+          var last = stats[stats.length-1];
+          if (last[0] === 'if' && !last[3]) {
+            // try to commaify - turn everything between the ifs into a comma operator inside the second if
+            var ok = true;
+            for (var i = 0; i < stats.length-1; i++) {
+              var curr = stats[i];
+              if (curr[0] === 'stat') curr = curr[1];
+              if (!(curr[0] in COMMABLE)) ok = false;
+            }
+            if (ok) {
+              for (var i = stats.length-2; i >= 0; i--) {
+                var curr = stats[i];
+                if (curr[0] === 'stat') curr = curr[1];
+                last[1] = ['seq', curr, last[1]];
+              }
+              stats = body[1] = [last];
+            }
+          }
+        }
+        if (stats.length !== 1) break;
+        var singleton = stats[0];
         if (singleton[0] === 'if' && !singleton[3]) {
           node[1] = ['conditional', node[1], singleton[1], ['num', 0]];
           body = node[2] = singleton[2];

tools/test-js-optimizer-si-output.js

@@ -23,7 +23,7 @@ function a() {
   h();
  }
  if (x) {
-  f();
+  return;
   if (y) {
    g();
   }
@@ -32,13 +32,13 @@ function a() {
   g();
  }
  if (x) {
-  f();
+  return;
   if (y ? z : 0) {
    g();
   }
  }
  if (x ? y : 0) {
-  f();
+  return;
   if (z) {
    g();
   }
@@ -55,5 +55,16 @@ function a() {
   }
   f();
  }
+ if (x ? (f(), x = x + 2 | 0, y) : 0) {
+  g();
+ }
+ if (x) {
+  f();
+  x = x + 2 | 0;
+  return;
+  if (y) {
+   g();
+  }
+ }
 }
 

tools/test-js-optimizer-si.js

@@ -25,7 +25,7 @@ function a() {
     h();
   }
   if (x) {
-    f();
+    return;
     if (y) {
       g();
     }
@@ -38,7 +38,7 @@ function a() {
     }
   }
   if (x) {
-    f();
+    return;
     if (y) {
       if (z) {
         g();
@@ -47,7 +47,7 @@ function a() {
   }
   if (x) {
     if (y) {
-      f();
+      return;
       if (z) {
         g();
       }
@@ -69,5 +69,20 @@ function a() {
     }
     f();
   }
+  if (x) {
+    f();
+    x = x + 2 | 0;
+    if (y) {
+      g();
+    }
+  }
+  if (x) {
+    f();
+    x = x + 2 | 0;
+    return;
+    if (y) {
+      g();
+    }
+  }
 }