First implementation of store elimination.

test/mjsunit/compiler/store-elimination.js

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-// Flags: --allow-natives-syntax --load-elimination
+// Flags: --allow-natives-syntax --store-elimination
 
-// Test local load elimination of redundant loads and stores.
+// Test local elimination of unobservable stores.
 
 function B(x, y) {
   this.x = x;
   this.y = y;
   return this;
 }
 
-function test_load() {
+function test_store_store() {
   var a = new B(1, 2);
-  return a.x + a.x + a.x + a.x;
+  a.x = 3;  // eliminatable.
+  a.x = 4;
+  return a.x;
 }
 
-function test_store_load() {
-  var a = new B(1, 2);
+function test_store_load_store1() {
+  var a = new B(6, 7);
+  a.x = 3;  // eliminatable.
+  var r = a.y;
   a.x = 4;
-  var f = a.x;
-  a.x = 5;
-  var g = a.x;
-  a.x = 6;
-  var h = a.x;
-  a.x = 7;
-  return f + g + h + a.x;
+  return r;
 }
 
-function test_nonaliasing_store1() {
-  var a = new B(2, 3), b = new B(3, 4);
-  b.x = 4;
-  var f = a.x;
-  b.x = 5;
-  var g = a.x;
-  b.x = 6;
-  var h = a.x;
-  b.x = 7;
-  return f + g + h + a.x;
+function test_store_load_store2() {
+  var a = new B(6, 8);
+  a.x = 3;  // not eliminatable, unless next load is eliminated.
+  var r = a.x;
+  a.x = 4;
+  return r;
+}
+
+function test_store_call_store() {
+  var a = new B(2, 9);
+  a.x = 3;  // not eliminatable.
+  killall();
+  a.x = 4;
+  return a.y;
+}
+
+function test_store_deopt_store() {
+  var a = new B(2, 1);
+  a.x = 3;  // not eliminatable (implicit ValueOf following)
+  var c = a + 2;
+  a.x = 4;
+  return a.y;
 }
 
 function killall() {
   try { } catch(e) { }
 }
 
 %NeverOptimizeFunction(killall);
 
-function test_store_load_kill() {
-  var a = new B(1, 2);
-  a.x = 4;
-  var f = a.x;
-  a.x = 5;
-  var g = a.x;
-  killall();
-  a.x = 6;
-  var h = a.x;
-  a.x = 7;
-  return f + g + h + a.x;
-}
-
-function test_store_store() {
-  var a = new B(6, 7);
-  a.x = 7;
-  a.x = 7;
-  a.x = 7;
-  a.x = 7;
-  return a.x;
-}
-
 function test(x, f) {
   assertEquals(x, f());
   assertEquals(x, f());
   %OptimizeFunctionOnNextCall(f);
   assertEquals(x, f());
 }
 
-test(4, test_load);
-test(22, test_store_load);
-test(8, test_nonaliasing_store1);
-test(22, test_store_load_kill);
-test(7, test_store_store);
+test(4, test_store_store);
+test(7, test_store_load_store1);
+test(3, test_store_load_store2);
+test(9, test_store_call_store);
+test(1, test_store_deopt_store);