simplify infinite while loops with a break at the end into a do-while with a condition

3 files changed, 30 insertions, 1 deletions

diff --git a/tools/js-optimizer.js b/tools/js-optimizer.js
index 09791150..57c9cf79 100644
--- a/tools/js-optimizer.js
+++ b/tools/js-optimizer.js
@@ -968,6 +968,7 @@ function simplifyNotComps(ast) {
       }
     }
   });
+  return ast;
 }
 
 function simplifyExpressionsPost(ast) {
@@ -1804,6 +1805,21 @@ function registerize(ast) {
       }
       denormalizeAsm(fun, finalAsmData);
     }
+
+    // Post-registerize optimizations. This is near the end of the pipeline, we can assume all other optimizations except for minification are done
+    traverse(fun, function(node, type) {
+      if (type == 'while' && node[1][0] == 'num' && node[1][1] == 1 && node[2][0] == 'block') {
+        // while (1) { .. if (..) { break } } ==> do { .. } while(..)
+        var stats = node[2][1];
+        var last = stats[stats.length-1];
+        if (last[0] == 'if' && !last[3] && last[2][0] == 'block' && last[2][1][0][0] == 'break' && !last[2][1][0][1]) {
+          var conditionToBreak = last[1];
+          stats.pop();
+          node[0] = 'do';
+          node[1] = simplifyNotComps(['unary-prefix', '!', conditionToBreak]);
+        }
+      }
+    });
   });
 }
 
diff --git a/tools/test-js-optimizer-regs-output.js b/tools/test-js-optimizer-regs-output.js
index fe7de5fb..c1c9ec87 100644
--- a/tools/test-js-optimizer-regs-output.js
+++ b/tools/test-js-optimizer-regs-output.js
@@ -229,4 +229,9 @@ function __ZN14NetworkAddressC1EPKcti(r1) {
   __ZN14NetworkAddressC2EPKcti(r1);
   return;
 }
+function looop() {
+  do {
+    do_it();
+  } while (!condition());
+}
 
diff --git a/tools/test-js-optimizer-regs.js b/tools/test-js-optimizer-regs.js
index 3013e518..b38760cc 100644
--- a/tools/test-js-optimizer-regs.js
+++ b/tools/test-js-optimizer-regs.js
@@ -234,4 +234,12 @@ function __ZN14NetworkAddressC1EPKcti($this) {
   __ZN14NetworkAddressC2EPKcti($this);
   return;
 }
-// EMSCRIPTEN_GENERATED_FUNCTIONS: ["test", "primes", "atomic", "fcntl_open", "ex", "switchey", "__ZN14NetworkAddressC1EPKcti"]
+function looop() {
+  while (1) {
+    do_it();
+    if (condition()) {
+      break;
+    }
+  }
+}
+// EMSCRIPTEN_GENERATED_FUNCTIONS: ["test", "primes", "atomic", "fcntl_open", "ex", "switchey", "__ZN14NetworkAddressC1EPKcti", "looop"]