if a shared variable is a result of the block, release it only after it has been put

#KT-2151 Fixed

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

@@ -917,8 +917,13 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> {
                 final Type sharedVarType = typeMapper.getSharedVarType(variableDescriptor);
                 final Type type = sharedVarType != null ? sharedVarType : asmType(variableDescriptor.getType());
                 if(sharedVarType != null) {
-                    v.aconst(null);
-                    v.store(index, TYPE_OBJECT);
+                    if (answer instanceof StackValue.Shared && index == ((StackValue.Shared) answer).getIndex()) {
+                        ((StackValue.Shared) answer).releaseOnPut();
+                    }
+                    else {
+                        v.aconst(null);
+                        v.store(index, TYPE_OBJECT);
+                    }
                 }
 
                 v.visitLocalVariable(var.getName(), type.getDescriptor(), null, blockStart, blockEnd, index);

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

@@ -924,20 +924,33 @@ public abstract class StackValue {
 
     public static class Shared extends StackValue {
         private final int index;
+        private boolean isReleaseOnPut = false;
 
         public Shared(int index, Type type) {
             super(type);
             this.index = index;
         }
 
+        public void releaseOnPut() {
+            isReleaseOnPut = true;
+        }
+
+        public int getIndex() {
+            return index;
+        }
+
         @Override
         public void put(Type type, InstructionAdapter v) {
             v.load(index, JetTypeMapper.TYPE_OBJECT);
             Type refType = refType(this.type);
             Type sharedType = sharedTypeForType(this.type);
             v.visitFieldInsn(Opcodes.GETFIELD, sharedType.getInternalName(), "ref", refType.getDescriptor());
-            StackValue.onStack(refType).coerce(this.type, v);
-            StackValue.onStack(this.type).coerce(type, v);
+            coerce(refType, this.type, v);
+            coerce(this.type, type, v);
+            if (isReleaseOnPut) {
+                v.aconst(null);
+                v.store(index, JetTypeMapper.TYPE_OBJECT);
+            }
         }
 
         @Override

compiler/testData/codegen/regressions/kt2151.kt

@@ -0,0 +1,11 @@
+fun foo(): String {
+    return if (true) {
+        var x = "OK"
+        fun foo() { x += "fail" }
+        x
+    } else "fail"
+}
+
+fun box(): String {
+    return foo()
+}

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

@@ -62,4 +62,8 @@ public class ClosuresGenTest extends CodegenTestCase {
     public void testEnclosingThis() throws Exception {
         blackBoxFile("classes/enclosingThis.jet");
     }
+
+    public void testKt2151() {
+        blackBoxFile("regressions/kt2151.kt");
+    }
 }