Fixed codegen for single-branch if

#KT-2597 Fixed
 #KT-2598 Fixed

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

@@ -687,14 +687,26 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> {
     }
 
     private StackValue generateSingleBranchIf(StackValue condition, JetExpression expression, boolean inverse) {
+        Type expressionType = expressionType(expression);
+        Type targetType = expressionType;
+        if (!expressionType.equals(TUPLE0_TYPE)) {
+            targetType = TYPE_OBJECT;
+        }
+
+        Label elseLabel = new Label();
+        condition.condJump(elseLabel, inverse, v);
+
+        gen(expression, expressionType);
+        StackValue.coerce(expressionType, targetType, v);
+
         Label end = new Label();
+        v.goTo(end);
 
-        condition.condJump(end, inverse, v);
-
-        gen(expression, Type.VOID_TYPE);
+        v.mark(elseLabel);
+        StackValue.putTuple0Instance(v);
 
         v.mark(end);
-        return StackValue.none();
+        return StackValue.onStack(targetType);
     }
 
     @Override

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

@@ -242,6 +242,10 @@ public abstract class StackValue {
             else
                 v.iconst(0);
         }
+        else if (toType.equals(JetTypeMapper.TUPLE0_TYPE) && !fromType.equals(JetTypeMapper.TUPLE0_TYPE)) {
+            pop(fromType, v);
+            putTuple0Instance(v);
+        }
         else if (toType.getSort() == Type.OBJECT && fromType.equals(JetTypeMapper.TYPE_OBJECT) || toType.getSort() == Type.ARRAY) {
                 v.checkcast(toType);
         }

compiler/testData/codegen/regressions/kt2597.kt

@@ -0,0 +1,10 @@
+fun box(): String {
+    var i = 0
+    {
+        if (1 == 1) {
+            i++
+        } else {
+        }
+    }()
+    return "OK"
+}

compiler/testData/codegen/regressions/kt2598.kt

@@ -0,0 +1,9 @@
+fun foo(condition: Boolean): String {
+    val u = if (condition) {
+        "OK"
+    } else {
+    }
+    return u.toString()
+}
+
+fun box() = foo(true)

compiler/tests/org/jetbrains/jet/codegen/ControlStructuresTest.java

@@ -391,4 +391,14 @@ public class ControlStructuresTest extends CodegenTestCase {
         createEnvironmentWithMockJdkAndIdeaAnnotations(ConfigurationKind.JDK_ONLY);
         blackBoxFile("controlStructures/tryCatchFinallyChain.kt");
     }
+
+    public void testKt2597() {
+        createEnvironmentWithMockJdkAndIdeaAnnotations(ConfigurationKind.JDK_ONLY);
+        blackBoxFile("regressions/kt2597.kt");
+    }
+
+    public void testKt2598() {
+        createEnvironmentWithMockJdkAndIdeaAnnotations(ConfigurationKind.JDK_ONLY);
+        blackBoxFile("regressions/kt2598.kt");
+    }
 }