Proper instructions for elvis operator

We should not mark elvis operator unused, for the rhs may have desired side-effects

compiler/frontend/src/org/jetbrains/jet/lang/cfg/JetControlFlowBuilder.java

@@ -101,6 +101,7 @@ public interface JetControlFlowBuilder {
     enum PredefinedOperation {
         AND,
         OR,
+        ELVIS,
         NOT_NULL_ASSERTION
     }
     void predefinedOperation(@NotNull JetExpression expression, @Nullable PredefinedOperation operation);

compiler/frontend/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java

@@ -250,7 +250,7 @@ public class JetControlFlowProcessor {
         public void visitBinaryExpression(@NotNull JetBinaryExpression expression) {
             JetSimpleNameExpression operationReference = expression.getOperationReference();
             IElementType operationType = operationReference.getReferencedNameElementType();
-            if (!ImmutableSet.of(ANDAND, OROR, EQ, ELVIS).contains(operationType)) {
+            if (!ImmutableSet.of(ANDAND, OROR, EQ, JetTokens.ELVIS).contains(operationType)) {
                 mark(expression);
             }
             JetExpression right = expression.getRight();
@@ -296,13 +296,14 @@ public class JetControlFlowProcessor {
                     generateBothArguments(expression);
                 }
             }
-            else if (operationType == ELVIS) {
+            else if (operationType == JetTokens.ELVIS) {
                 generateInstructions(expression.getLeft(), false);
                 Label afterElvis = builder.createUnboundLabel();
                 builder.jumpOnTrue(afterElvis);
                 if (right != null) {
                     generateInstructions(right, false);
                 }
+                builder.predefinedOperation(expression, JetControlFlowBuilder.PredefinedOperation.ELVIS);
                 builder.bindLabel(afterElvis);
             }
             else if (operationType == JetTokens.EQEQ || operationType == JetTokens.EXCLEQ) {

compiler/testData/cfg/deadCode/returnInElvis.instructions

@@ -9,6 +9,7 @@ L0:
     ret L1                      NEXT:[<END>]
 -   jt(L2)                      NEXT:[r(null), <END>]              PREV:[]
 -   r(null)                     PREV:[]
+-   r(return ?: null)           PREV:[]
 L1:
 L2:
     <END>                       NEXT:[<SINK>]                      PREV:[ret L1]

compiler/testData/cfg/lastElvis.instructions

@@ -0,0 +1,23 @@
+== test ==
+fun test(a: Any?) {
+    a ?: ""
+}
+---------------------
+L0:
+    <START>
+    v(a: Any?)
+    w(a)
+    mark({ a ?: "" })
+    r(a)
+    jt(L2)               NEXT:[mark(""), <END>]
+    mark("")
+    r("")
+    r(a ?: "")
+L1:
+L2:
+    <END>                NEXT:[<SINK>]               PREV:[jt(L2), r(a ?: "")]
+error:
+    <ERROR>              PREV:[]
+sink:
+    <SINK>               PREV:[<ERROR>, <END>]
+=====================

compiler/testData/cfg/lastElvis.kt

@@ -0,0 +1,3 @@
+fun test(a: Any?) {
+    a ?: ""
+}

compiler/testData/diagnostics/tests/controlFlowAnalysis/unusedElvis.kt

@@ -0,0 +1,9 @@
+fun foo(a: Any?) {
+    a ?: ""
+}
+
+fun foo1(a: Any?) {
+    a ?: sideEffect()
+}
+
+fun sideEffect() {}

compiler/tests/org/jetbrains/jet/cfg/ControlFlowTestGenerated.java

@@ -142,6 +142,11 @@ public class ControlFlowTestGenerated extends AbstractControlFlowTest {
         doTest("compiler/testData/cfg/invoke.kt");
     }
     
+    @TestMetadata("lastElvis.kt")
+    public void testLastElvis() throws Exception {
+        doTest("compiler/testData/cfg/lastElvis.kt");
+    }
+    
     @TestMetadata("LazyBooleans.kt")
     public void testLazyBooleans() throws Exception {
         doTest("compiler/testData/cfg/LazyBooleans.kt");

compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java

@@ -1572,6 +1572,11 @@ public class JetDiagnosticsTestGenerated extends AbstractDiagnosticsTestWithEage
                 doTest("compiler/testData/diagnostics/tests/controlFlowAnalysis/unreachableCode.kt");
             }
             
+            @TestMetadata("unusedElvis.kt")
+            public void testUnusedElvis() throws Exception {
+                doTest("compiler/testData/diagnostics/tests/controlFlowAnalysis/unusedElvis.kt");
+            }
+            
         }
         
         @TestMetadata("compiler/testData/diagnostics/tests/controlStructures")