JVM_IR: Generate better code for null checks.

Simplify ifs when branches have condition true/false.

Simplify blocks containing only a variable declaration
and a variable get of the same variable. Simplify to
just the condition.

Do not introduce temporary variables for constants for
null checks. Constants have no side-effects and can be
reloaded freely instead of going through a local.

This simplifies code such as "42.toLong()!!" so that the
resulting code has no branches and uses no locals. The
simplifications happen as follows:

```
block
  temp = 42.toLong()
  when
    (temp == null) throw NPE
    (true) load temp

---> null test simplification

block
  temp = 42.toLong()
  when
    (false) throw NPE
    (true) load temp

---> when simplification

block
  temp = 42.toLong()
  load temp

---> block simplification

42.toLong()
```

compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java

@@ -1459,6 +1459,24 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
         }
     }
 
+    @TestMetadata("compiler/testData/codegen/bytecodeText/exclExcl")
+    @TestDataPath("$PROJECT_ROOT")
+    @RunWith(JUnit3RunnerWithInners.class)
+    public static class ExclExcl extends AbstractBytecodeTextTest {
+        private void runTest(String testDataFilePath) throws Exception {
+            KotlinTestUtils.runTest(this::doTest, TargetBackend.ANY, testDataFilePath);
+        }
+
+        public void testAllFilesPresentInExclExcl() throws Exception {
+            KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/bytecodeText/exclExcl"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.ANY, true);
+        }
+
+        @TestMetadata("primitive.kt")
+        public void testPrimitive() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/exclExcl/primitive.kt");
+        }
+    }
+
     @TestMetadata("compiler/testData/codegen/bytecodeText/forLoop")
     @TestDataPath("$PROJECT_ROOT")
     @RunWith(JUnit3RunnerWithInners.class)