Fix over-optimized comparison with null

compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java

@@ -2386,11 +2386,11 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> implem
         Type leftType = expressionType(left);
         Type rightType = expressionType(right);
 
-        if (leftType.equals(JET_NOTHING_TYPE)) {
+        if (JetPsiUtil.isNullConstant(left)) {
             return genCmpWithNull(right, rightType, opToken);
         }
 
-        if (rightType.equals(JET_NOTHING_TYPE)) {
+        if (JetPsiUtil.isNullConstant(right)) {
             return genCmpWithNull(left, leftType, opToken);
         }
 

compiler/testData/codegen/box/primitiveTypes/comparisonWithNullCallsFun.kt

@@ -0,0 +1,13 @@
+var entered = 0
+
+fun foo<T>(t: T): T {
+    entered++
+    return t
+}
+
+fun box(): String {
+    if (foo(null) == null) {}
+    if (null == foo(null)) {}
+    if (foo(null) == foo(null)) {}
+    return if (entered == 4) "OK" else "Fail $entered"
+}

compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxCodegenTestGenerated.java

@@ -2775,6 +2775,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             JetTestUtils.assertAllTestsPresentByMetadata(this.getClass(), "org.jetbrains.jet.generators.tests.GenerateTests", new File("compiler/testData/codegen/box/primitiveTypes"), Pattern.compile("^(.+)\\.kt$"), true);
         }
         
+        @TestMetadata("comparisonWithNullCallsFun.kt")
+        public void testComparisonWithNullCallsFun() throws Exception {
+            blackBoxFileByFullPath("compiler/testData/codegen/box/primitiveTypes/comparisonWithNullCallsFun.kt");
+        }
+        
         @TestMetadata("ea35963.kt")
         public void testEa35963() throws Exception {
             blackBoxFileByFullPath("compiler/testData/codegen/box/primitiveTypes/ea35963.kt");