From 4f876565ff4ead7f0527bbcc6b9dce71654d3ed1 Mon Sep 17 00:00:00 2001
From: Alon Zakai <alonzakai@gmail.com>
Date: Thu, 29 Dec 2011 15:27:37 -0800
Subject: clean optimizeShifts

---
 tools/js-optimizer.js                | 34 ++++++++++++++++++----------------
 tools/test-js-optimizer-t2-output.js |  6 ++----
 tools/test-js-optimizer-t2.js        |  6 ++----
 3 files changed, 22 insertions(+), 24 deletions(-)

(limited to 'tools')

diff --git a/tools/js-optimizer.js b/tools/js-optimizer.js
index 738ee7ee..9eaf1916 100644
--- a/tools/js-optimizer.js
+++ b/tools/js-optimizer.js
@@ -354,7 +354,7 @@ function simplifyExpressionsPre(ast) {
 //  HEAP[x >> 2]
 // very often. We can in some cases do the shift on the variable itself when it is set,
 // to greatly reduce the number of shift operations.
-// XXX x << 24 >> 24 - are we breaking that? only optimize small shifts!
+// TODO: when shifting a variable, if there are other uses, keep an unshifted version too, to prevent slowdowns?
 function optimizeShifts(ast) {
   traverseGeneratedFunctions(ast, function(fun) {
     var funMore = true;
@@ -403,23 +403,25 @@ function optimizeShifts(ast) {
       traverse(fun, function(node, type) {
         if (type == 'binary' && node[1] == '>>' && node[3][0] == 'num') {
           var shifts = node[3][1];
-          // Push the >> inside the value elements, doing some simplification while we are there
-          function addShift(subNode) {
-            if (subNode[0] == 'binary' && subNode[1] == '+') {
-              subNode[2] = addShift(subNode[2]);
-              subNode[3] = addShift(subNode[3]);
-              return subNode;
-            }
-            if (subNode[0] == 'name' && !subNode[2]) { // names are returned with a shift, but we also note their being shifted
-              var name = subNode[1];
-              if (vars[name]) {
-                vars[name].timesShifted[shifts]++;
-                subNode[2] = true;
+          if (shifts >= 0 && shifts <= 3) {
+            // Push the >> inside the value elements
+            function addShift(subNode) {
+              if (subNode[0] == 'binary' && subNode[1] == '+') {
+                subNode[2] = addShift(subNode[2]);
+                subNode[3] = addShift(subNode[3]);
+                return subNode;
+              }
+              if (subNode[0] == 'name' && !subNode[2]) { // names are returned with a shift, but we also note their being shifted
+                var name = subNode[1];
+                if (vars[name]) {
+                  vars[name].timesShifted[shifts]++;
+                  subNode[2] = true;
+                }
               }
+              return ['binary', '>>', subNode, ['num', shifts]];
             }
-            return ['binary', '>>', subNode, ['num', shifts]];
+            return addShift(node[2]);
           }
-          return addShift(node[2]);
         }
       });
       traverse(fun, function(node, type) {
@@ -454,7 +456,7 @@ function optimizeShifts(ast) {
           }
         }
       }
-      //printErr(dump(vars));
+      //printErr(JSON.stringify(vars));
       function cleanNotes() { // We need to mark 'name' nodes as 'processed' in some passes here; this cleans the notes up
         traverse(fun, function(node, type) {
           if (node[0] == 'name' && node[2]) {
diff --git a/tools/test-js-optimizer-t2-output.js b/tools/test-js-optimizer-t2-output.js
index dd2069fd..04f1d0f4 100644
--- a/tools/test-js-optimizer-t2-output.js
+++ b/tools/test-js-optimizer-t2-output.js
@@ -52,10 +52,8 @@ function shifty($id) {
   q(HEAP32[$parameters_addr + 1416 + $p]);
   pause(5);
   var $res_spec242 = get($real), $cp = get("b"), $tileno = arguments[2];
-  while (get(1)) {
-    q(HEAP32[$parameters_addr + 1406 + ($res_spec242 - 1)]);
-    q(HEAP32[(HEAP32[($cp >> 2) + 27] >> 2) + $tileno * 1397 + 105]);
-  }
+  q(HEAP32[$parameters_addr + 1406 + ($res_spec242 - 1)]);
+  q(HEAP32[(HEAP32[($cp >> 2) + 27] >> 2) + $tileno * 1397 + 105]);
   pause(6);
   q($idx << 3);
   q(1 << $idx << 1);
diff --git a/tools/test-js-optimizer-t2.js b/tools/test-js-optimizer-t2.js
index 55417ec0..ffda2703 100644
--- a/tools/test-js-optimizer-t2.js
+++ b/tools/test-js-optimizer-t2.js
@@ -60,10 +60,8 @@ function shifty($id) {
   pause(5);
   // loops count as more uses!
   var $res_spec242 = get($real), $cp = get('b'), $tileno = arguments[2];
-  while (get(1)) {
-    q(HEAP32[($parameters_addr + 5624 + (($res_spec242 - 1 | 0) << 2) | 0) >> 2]);
-    q(HEAP32[(HEAP32[($cp + 108 | 0) >> 2] + $tileno * 5588 + 420 | 0) >> 2]);
-  }
+  q(HEAP32[($parameters_addr + 5624 + (($res_spec242 - 1 | 0) << 2) | 0) >> 2]);
+  q(HEAP32[(HEAP32[($cp + 108 | 0) >> 2] + $tileno * 5588 + 420 | 0) >> 2]);
   pause(6);
   q($idx << 1 << 2);
   q(1 << $idx << 1); // Do not turn this into the slower 1 << $idx + 1 (which is identical though)
-- 
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