add memory-growth safe eliminator mode

1 files changed, 10 insertions, 2 deletions

diff --git a/tools/js-optimizer.js b/tools/js-optimizer.js
index 222bd0f4..e62402a9 100644
--- a/tools/js-optimizer.js
+++ b/tools/js-optimizer.js
@@ -1396,13 +1396,16 @@ function registerize(ast) {
 //  FUNCTION_TABLE[x]();
 //
 // to be optimized (f could replace FUNCTION_TABLE, so in general JS eliminating x is not valid).
+//
+// In memSafe mode, we are more careful and assume functions can replace HEAP and FUNCTION_TABLE, which
+// can happen in ALLOW_MEMORY_GROWTH mode
 
 var ELIMINATION_SAFE_NODES = set('var', 'assign', 'call', 'if', 'toplevel', 'do', 'return'); // do is checked carefully, however
 var NODES_WITHOUT_ELIMINATION_SIDE_EFFECTS = set('name', 'num', 'string', 'binary', 'sub', 'unary-prefix');
 var IGNORABLE_ELIMINATOR_SCAN_NODES = set('num', 'toplevel', 'string', 'break', 'continue', 'dot'); // dot can only be STRING_TABLE.*
 var ABORTING_ELIMINATOR_SCAN_NODES = set('new', 'object', 'function', 'defun', 'switch', 'for', 'while', 'array', 'throw'); // we could handle some of these, TODO, but nontrivial (e.g. for while, the condition is hit multiple times after the body)
 
-function eliminate(ast) {
+function eliminate(ast, memSafe) {
   // Find variables that have a single use, and if they can be eliminated, do so
   traverseGeneratedFunctions(ast, function(func, type) {
     //printErr('eliminate in ' + func[1]);
@@ -1613,7 +1616,7 @@ function eliminate(ast) {
             }
           }
         } else if (type == 'sub') {
-          traverseInOrder(node[1], false, true); // evaluate inner
+          traverseInOrder(node[1], false, !memSafe); // evaluate inner
           traverseInOrder(node[2]); // evaluate outer
           if (!ignoreSub) { // ignoreSub means we are a write (happening later), not a read
             // do the memory access
@@ -1834,6 +1837,10 @@ function eliminate(ast) {
   new ExpressionOptimizer(ast).run();
 }
 
+function eliminateMemSafe(ast) {
+  eliminate(ast, true);
+}
+
 // Passes table
 
 var compress = false, printMetadata = true;
@@ -1852,6 +1859,7 @@ var passes = {
   loopOptimizer: loopOptimizer,
   registerize: registerize,
   eliminate: eliminate,
+  eliminateMemSafe: eliminateMemSafe,
   compress: function() { compress = true; },
   noPrintMetadata: function() { printMetadata = false; }
 };