Remove the folding of "if (x === null)" to "if (!x)"'

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=142057565

src/com/google/javascript/jscomp/CommandLineRunner.java

@@ -409,12 +409,6 @@ private static class Flags {
         + "may result in incorrect results.")
     private boolean useTypesForOptimization = true;
 
-    @Option(name = "--assume_accurate_null_undefined_types",
-        handler = BooleanOptionHandler.class,
-        usage = "Enables optimizations which rely on accurate distinction between null and "
-        + "undefined types.")
-    private boolean assumeAccurateNullUndefinedTypes = false;
-
     @Option(name = "--assume_function_wrapper",
         handler = BooleanOptionHandler.class,
         usage = "Enable additional optimizations based on the assumption that the output will be "
@@ -1567,8 +1561,6 @@ protected CompilerOptions createOptions() {
       level.setTypeBasedOptimizationOptions(options);
     }
 
-    options.setAssumeAccurateNullUndefinedTypes(flags.assumeAccurateNullUndefinedTypes);
-
     if (flags.assumeFunctionWrapper) {
       level.setWrappedOutputOptimizations(options);
     }

src/com/google/javascript/jscomp/Compiler.java

@@ -337,7 +337,6 @@ public void initOptions(CompilerOptions options) {
       options.setInlineProperties(false);
       options.setUseTypesForLocalOptimization(false);
       options.setUseTypesForOptimization(false);
-      options.setAssumeAccurateNullUndefinedTypes(false);
     }
 
     if (options.legacyCodeCompile) {

src/com/google/javascript/jscomp/CompilerOptions.java

@@ -525,12 +525,6 @@ public enum ExtractPrototypeMemberDeclarationsMode {
   /** Use type information to enable additional optimization opportunities. */
   boolean useTypesForLocalOptimization;
 
-  /**
-   * Assume accurate distinction between null and undefined to enable additional optimization
-   * opportunities.
-   */
-  boolean assumeAccurateNullUndefinedTypes;
-
   //--------------------------------
   // Renaming
   //--------------------------------
@@ -2194,10 +2188,6 @@ public void setUseTypesForLocalOptimization(boolean useTypesForLocalOptimization
     this.useTypesForLocalOptimization = useTypesForLocalOptimization;
   }
 
-  public void setAssumeAccurateNullUndefinedTypes(boolean assumeAccurateNullUndefinedTypes) {
-    this.assumeAccurateNullUndefinedTypes = assumeAccurateNullUndefinedTypes;
-  }
-
   @Deprecated
   public void setUseTypesForOptimization(boolean useTypesForOptimization) {
     if (useTypesForOptimization) {

src/com/google/javascript/jscomp/DefaultPassConfig.java

@@ -1543,12 +1543,10 @@ protected CompilerPass create(AbstractCompiler compiler) {
   /** Various peephole optimizations. */
   private static CompilerPass createPeepholeOptimizationsPass(AbstractCompiler compiler) {
     final boolean late = false;
-    CompilerOptions options = compiler.getOptions();
-    final boolean useTypesForOptimization = options.useTypesForLocalOptimization;
+    final boolean useTypesForOptimization = compiler.getOptions().useTypesForLocalOptimization;
     return new PeepholeOptimizationsPass(compiler,
           new MinimizeExitPoints(compiler),
-          new PeepholeMinimizeConditions(
-              late, useTypesForOptimization, options.assumeAccurateNullUndefinedTypes),
+          new PeepholeMinimizeConditions(late, useTypesForOptimization),
           new PeepholeSubstituteAlternateSyntax(late),
           new PeepholeReplaceKnownMethods(late, useTypesForOptimization),
           new PeepholeRemoveDeadCode(),
@@ -1584,8 +1582,7 @@ protected CompilerPass create(AbstractCompiler compiler) {
       return new PeepholeOptimizationsPass(compiler,
             new StatementFusion(options.aggressiveFusion),
             new PeepholeRemoveDeadCode(),
-            new PeepholeMinimizeConditions(
-                late, useTypesForOptimization, options.assumeAccurateNullUndefinedTypes),
+            new PeepholeMinimizeConditions(late, useTypesForOptimization),
             new PeepholeSubstituteAlternateSyntax(late),
             new PeepholeReplaceKnownMethods(late, useTypesForOptimization),
             new PeepholeFoldConstants(late, useTypesForOptimization),

src/com/google/javascript/jscomp/ExpandJqueryAliases.java

@@ -83,11 +83,9 @@ class ExpandJqueryAliases extends AbstractPostOrderCallback
     // These passes should make the code easier to analyze.
     // Passes, such as StatementFusion, are omitted for this reason.
     final boolean late = false;
-    CompilerOptions options = compiler.getOptions();
-    boolean useTypesForOptimization = options.useTypesForLocalOptimization;
+    boolean useTypesForOptimization = compiler.getOptions().useTypesForLocalOptimization;
     this.peepholePasses = new PeepholeOptimizationsPass(compiler,
-        new PeepholeMinimizeConditions(
-            late, useTypesForOptimization, options.assumeAccurateNullUndefinedTypes),
+        new PeepholeMinimizeConditions(late, useTypesForOptimization),
         new PeepholeSubstituteAlternateSyntax(late),
         new PeepholeReplaceKnownMethods(late, useTypesForOptimization),
         new PeepholeRemoveDeadCode(),

src/com/google/javascript/jscomp/PeepholeMinimizeConditions.java

@@ -40,7 +40,6 @@ class PeepholeMinimizeConditions
 
   private final boolean late;
   private final boolean useTypes;
-  private final boolean assumeAccurateNullUndefinedTypes;
 
   /**
    * @param late When late is false, this mean we are currently running before
@@ -49,11 +48,9 @@ class PeepholeMinimizeConditions
    * merging statements with commas, etc). When this is true, we would
    * do anything to minimize for size.
    */
-  PeepholeMinimizeConditions(boolean late, boolean useTypes,
-      boolean assumeAccurateNullUndefinedTypes) {
+  PeepholeMinimizeConditions(boolean late, boolean useTypes) {
     this.late = late;
     this.useTypes = useTypes;
-    this.assumeAccurateNullUndefinedTypes = assumeAccurateNullUndefinedTypes;
   }
 
   /**
@@ -1074,7 +1071,7 @@ private enum BooleanCoercability {
     RIGHT
   }
 
-  private BooleanCoercability canConvertComparisonToBooleanCoercion(
+  private static BooleanCoercability canConvertComparisonToBooleanCoercion(
       Node left, Node right, Token op) {
     // Convert null or undefined check of an object to coercion.
     boolean leftIsNull = left.isNull();
@@ -1088,10 +1085,7 @@ private BooleanCoercability canConvertComparisonToBooleanCoercion(
     boolean rightIsObjectType = isObjectType(right);
     if (op == Token.SHEQ || op == Token.SHNE) {
       if ((leftIsObjectType && !left.getJSType().isNullable() && rightIsUndefined)
-          || (rightIsObjectType && !right.getJSType().isNullable() && leftIsUndefined)
-          || (assumeAccurateNullUndefinedTypes
-                 && ((leftIsObjectType && !left.getJSType().isVoidable() && rightIsNull)
-                     || (rightIsObjectType && !right.getJSType().isVoidable() && leftIsNull)))) {
+          || (rightIsObjectType && !right.getJSType().isNullable() && leftIsUndefined)) {
         return leftIsNullOrUndefined ? BooleanCoercability.RIGHT : BooleanCoercability.LEFT;
       }
     } else {

test/com/google/javascript/jscomp/CreateSyntheticBlocksTest.java

@@ -46,8 +46,7 @@ public void process(Node externs, Node js) {
         new MinimizeExitPoints(compiler).asCompilerPass().process(externs, js);
         new PeepholeOptimizationsPass(compiler,
             new PeepholeRemoveDeadCode(),
-            new PeepholeMinimizeConditions(true /* late */, false /* useTypes */,
-                false /* assumeAccurateNullUndefinedTypes */),
+            new PeepholeMinimizeConditions(true /* late */, false /* useTypes */),
             new PeepholeFoldConstants(true, false))
             .process(externs, js);
         new MinimizeExitPoints(compiler).asCompilerPass().process(externs, js);

test/com/google/javascript/jscomp/MultiPassTest.java

@@ -188,8 +188,7 @@ private void addPeephole() {
           protected CompilerPass create(AbstractCompiler compiler) {
             final boolean late = false;
             return new PeepholeOptimizationsPass(compiler,
-                new PeepholeMinimizeConditions(
-                    late, false /* useTypes */, false /* assumeAccurateNullUndefinedTypes */),
+                new PeepholeMinimizeConditions(late, false /* useTypes */),
                 new PeepholeSubstituteAlternateSyntax(late),
                 new PeepholeReplaceKnownMethods(late, false),
                 new PeepholeRemoveDeadCode(),

test/com/google/javascript/jscomp/PeepholeIntegrationTest.java

@@ -33,8 +33,7 @@ public void setUp() throws Exception {
   public CompilerPass getProcessor(final Compiler compiler) {
     PeepholeOptimizationsPass peepholePass =
       new PeepholeOptimizationsPass(compiler,
-        new PeepholeMinimizeConditions(
-            late, false /* useTypes */, false /* assumeAccurateNullUndefinedTypes */),
+        new PeepholeMinimizeConditions(late, false /* useTypes */),
         new PeepholeSubstituteAlternateSyntax(late),
         new PeepholeRemoveDeadCode(),
         new PeepholeFoldConstants(late, false)

test/com/google/javascript/jscomp/PeepholeMinimizeConditionsTest.java

@@ -25,20 +25,18 @@ public final class PeepholeMinimizeConditionsTest extends CompilerTestCase {
 
   private boolean late = true;
   private boolean useTypes = true;
-  private boolean assumeAccurateNullUndefinedTypes = true;
 
   @Override
   public void setUp() throws Exception {
     super.setUp();
     late = true;
     useTypes = true;
-    assumeAccurateNullUndefinedTypes = true;
   }
 
   @Override
   public CompilerPass getProcessor(final Compiler compiler) {
     PeepholeOptimizationsPass peepholePass = new PeepholeOptimizationsPass(
-        compiler, new PeepholeMinimizeConditions(late, useTypes, assumeAccurateNullUndefinedTypes));
+        compiler, new PeepholeMinimizeConditions(late, useTypes));
     peepholePass.setRetraverseOnChange(false);
     return peepholePass;
   }
@@ -755,9 +753,9 @@ public void testCoercionSubstitution_booleanResult() {
     enableTypeCheck();
     test("var x = {}; var y = x != null;", "var x = {}; var y = !!x;");
     test("var x = {}; var y = x == null;", "var x = {}; var y = !x;");
-    test("var x = {}; var y = x !== null;", "var x = {}; var y = !!x;");
+    testSame("var x = {}; var y = x !== null;");
     testSame("var x = undefined; var y = x !== null;");
-    test("var x = {}; var y = x === null;", "var x = {}; var y = !x;");
+    testSame("var x = {}; var y = x === null;");
     testSame("var x = undefined; var y = x === null;");
 
     test("var x = 1; var y = x != 0;", "var x = 1; var y = !!x;");
@@ -770,12 +768,12 @@ public void testCoercionSubstitution_if() {
     enableTypeCheck();
     test("var x = {};\nif (x != null) throw 'a';\n", "var x = {};\nif (x) throw 'a';\n");
     test("var x = {};\nif (x == null) throw 'a';\n", "var x = {};\nif (!x) throw 'a';\n");
-    test("var x = {};\nif (x !== null) throw 'a';\n", "var x = {};\nif (x) throw 'a';\n");
-    test("var x = {};\nif (x === null) throw 'a';\n", "var x = {};\nif (!x) throw 'a';\n");
+    testSame("var x = {};\nif (x !== null) throw 'a';\n");
+    testSame("var x = {};\nif (x === null) throw 'a';\n");
     test("var x = {};\nif (null != x) throw 'a';\n", "var x = {};\nif (x) throw 'a';\n");
     test("var x = {};\nif (null == x) throw 'a';\n", "var x = {};\nif (!x) throw 'a';\n");
-    test("var x = {};\nif (null !== x) throw 'a';\n", "var x = {};\nif (x) throw 'a';\n");
-    test("var x = {};\nif (null === x) throw 'a';\n", "var x = {};\nif (!x) throw 'a';\n");
+    testSame("var x = {};\nif (null !== x) throw 'a';\n");
+    testSame("var x = {};\nif (null === x) throw 'a';\n");
 
     test("var x = 1;\nif (x != 0) throw 'a';\n", "var x = 1;\nif (x) throw 'a';\n");
     test("var x = 1;\nif (x == 0) throw 'a';\n", "var x = 1;\nif (!x) throw 'a';\n");
@@ -820,9 +818,8 @@ public void testCoercionSubstitution_nullableType() {
     test(
         "var x = /** @type {?Object} */ ({}); if (x != null) throw 'a';",
         "var x = /** @type {?Object} */ ({}); if (x) throw 'a';");
-    test(
-        "var x = /** @type {?Object} */ ({}); if (x !== null) throw 'a';",
-        "var x = /** @type {?Object} */ ({}); if (x) throw 'a';");
+    // We back off on strict comparison against null.
+    testSame("var x = /** @type {?Object} */ ({}); if (x !== null) throw 'a';");
     test(
         "var x = /** @type {?Object} */ ({}); if (x != undefined) throw 'a';",
         "var x = /** @type {?Object} */ ({}); if (x) throw 'a';");
@@ -868,9 +865,6 @@ public void testCoercionSubstitution_nullableType() {
         "if (/** @type {Array|undefined} */ (window['c']) == null) {}",
         "if (!/** @type {Array|undefined} */ (window['c'])) {}");
     testSame("if (/** @type {Array|undefined} */ (window['c']) === null) {}");
-
-    assumeAccurateNullUndefinedTypes = false;
-    testSame("var x = /** @type {?Object} */ ({}); if (x !== null) throw 'a';");
   }
 
   public void testCoercionSubstitution_unknownType() {