move the endsInUnreachable utility function into DeadEndBlocks

Author: eeckstein

include/swift/SIL/BasicBlockUtils.h

@@ -88,6 +88,13 @@ class DeadEndBlocks {
   bool isComputed() const { return didComputeValue; }
 
   const SILFunction *getFunction() const { return f; }
+  
+  /// Performs a simple check if \p block (or its single successor) ends in an
+  /// "unreachable".
+  ///
+  /// This handles the common case of failure-handling blocks, which e.g.
+  /// contain a call to fatalError().
+  static bool triviallyEndsInUnreachable(SILBasicBlock *block);
 };
 
 /// Compute joint-postdominating set for \p dominatingBlock and \p

lib/SIL/Utils/BasicBlockUtils.cpp

@@ -386,18 +386,18 @@ void DeadEndBlocks::compute() {
   }
 }
 
-//===----------------------------------------------------------------------===//
-//                  Post Dominance Set Completion Utilities
-//===----------------------------------------------------------------------===//
-
-static bool endsInUnreachable(SILBasicBlock *block) {
+bool DeadEndBlocks::triviallyEndsInUnreachable(SILBasicBlock *block) {
   // Handle the case where a single "unreachable" block (e.g. containing a call
   // to fatalError()), is jumped to from multiple source blocks.
   if (SILBasicBlock *singleSucc = block->getSingleSuccessorBlock())
     block = singleSucc;
   return isa<UnreachableInst>(block->getTerminator());
 }
 
+//===----------------------------------------------------------------------===//
+//                  Post Dominance Set Completion Utilities
+//===----------------------------------------------------------------------===//
+
 void swift::findJointPostDominatingSet(
     SILBasicBlock *dominatingBlock, ArrayRef<SILBasicBlock *> dominatedBlockSet,
     function_ref<void(SILBasicBlock *)> inputBlocksFoundDuringWalk,
@@ -482,7 +482,7 @@ void swift::findJointPostDominatingSet(
               // Ignore blocks which end in an unreachable. This is a very
               // simple check, but covers most of the cases, e.g. block which
               // calls fatalError().
-              !endsInUnreachable(succBlock)) {
+              !DeadEndBlocks::triviallyEndsInUnreachable(succBlock)) {
             assert(succBlock->getSinglePredecessorBlock() == predBlock &&
                    "CFG must not contain critical edge");
             // Note that since there are no critical edges in the CFG, we are