use voidExecute in loops

com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/control/ForNode.java

@@ -125,8 +125,8 @@ public final class ForNode extends AbstractLoopNode implements RSyntaxNode, RSyn
             }
             try {
                 if (conditionProfile.profile(index <= length)) {
-                    writeElementNode.execute(frame);
-                    body.execute(frame);
+                    writeElementNode.voidExecute(frame);
+                    body.voidExecute(frame);
                     return true;
                 } else {
                     return false;

com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/control/RepeatNode.java

@@ -73,7 +73,7 @@ public final class RepeatNode extends AbstractLoopNode implements RSyntaxNode, R
         @Override
         public boolean executeRepeating(VirtualFrame frame) {
             try {
-                body.execute(frame);
+                body.voidExecute(frame);
                 normalBlock.enter();
                 return true;
             } catch (BreakException e) {

com.oracle.truffle.r.nodes/src/com/oracle/truffle/r/nodes/control/WhileNode.java

@@ -82,7 +82,7 @@ public final class WhileNode extends AbstractLoopNode implements RSyntaxNode, RS
         public boolean executeRepeating(VirtualFrame frame) {
             try {
                 if (conditionProfile.profile(condition.executeByte(frame) == RRuntime.LOGICAL_TRUE)) {
-                    body.execute(frame);
+                    body.voidExecute(frame);
                     normalBlock.enter();
                     return true;
                 } else {