Introduce DataFlow::Node.getBasicBlock() and use it.

ql/src/InconsistentCode/ConstantLengthComparison.ql

@@ -27,7 +27,7 @@ where
     cond.ensuresNeq(lenA, const) or
     cond.ensuresLeq(const, lenA, _)
   ) and
-  cond.dominates(idx.asInstruction().getBasicBlock()) and
+  cond.dominates(idx.getBasicBlock()) and
   // and that check happens inside the loop body
   cond.getCondition().getParent+() = fs.getBody()
 select cond.getCondition(),

ql/src/InconsistentCode/LengthComparisonOffByOne.ql

@@ -66,7 +66,7 @@ predicate elementRead(
 ) {
   ea.reads(array.getAUse(), getAUse(index)) and
   not array.getType().getUnderlyingType() instanceof MapType and
-  bb = ea.asInstruction().getBasicBlock()
+  bb = ea.getBasicBlock()
 }
 
 predicate isRegexpMethodCall(DataFlow::MethodCallNode c) {

ql/src/semmle/go/dataflow/internal/DataFlowUtil.qll

@@ -40,6 +40,9 @@ class Node extends TNode {
   /** Gets a textual representation of the kind of this data-flow node. */
   string getNodeKind() { none() } // overridden in subclasses
 
+  /** Gets the basic block to which this data-flow node belongs, if any. */
+  BasicBlock getBasicBlock() { result = asInstruction().getBasicBlock() }
+
   /** Gets a textual representation of this element. */
   string toString() { result = "data-flow node" } // overridden in subclasses
 
@@ -752,7 +755,7 @@ abstract class BarrierGuard extends Node {
       result = var.getAUse()
     |
       guards(guard, nd, var) and
-      guard.dominates(result.asInstruction().getBasicBlock())
+      guard.dominates(result.getBasicBlock())
     )
   }
 
@@ -807,7 +810,7 @@ abstract class BarrierGuard extends Node {
       guards(guard, arg) and
       localFlow(inp.getExitNode(fd), arg) and
       ret = outp.getEntryNode(fd) and
-      guard.dominates(ret.asInstruction().getBasicBlock())
+      guard.dominates(ret.getBasicBlock())
     |
       exists(boolean b |
         onlyPossibleReturnOfBool(fd, outp, ret, b) and