Move getUniqueExitBlocks from LoopBase to Loop, since they depend on

LoopSimplify form, which is currently only available on Loops (and
not MachineLoops). Also, move the code out of the header file.

llvm-svn: 80923

1 files changed, 68 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/LoopInfo.cpp b/llvm/lib/Analysis/LoopInfo.cpp
index 25264801193..4245702ea10 100644
--- a/llvm/lib/Analysis/LoopInfo.cpp
+++ b/llvm/lib/Analysis/LoopInfo.cpp
@@ -294,6 +294,74 @@ bool Loop::isLoopSimplifyForm() const {
   return true;
 }
 
+/// getUniqueExitBlocks - Return all unique successor blocks of this loop.
+/// These are the blocks _outside of the current loop_ which are branched to.
+/// This assumes that loop is in canonical form.
+///
+void
+Loop::getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const {
+  // Sort the blocks vector so that we can use binary search to do quick
+  // lookups.
+  SmallVector<BasicBlock *, 128> LoopBBs(block_begin(), block_end());
+  std::sort(LoopBBs.begin(), LoopBBs.end());
+
+  std::vector<BasicBlock *> switchExitBlocks;
+
+  for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) {
+
+    BasicBlock *current = *BI;
+    switchExitBlocks.clear();
+
+    typedef GraphTraits<BasicBlock *> BlockTraits;
+    typedef GraphTraits<Inverse<BasicBlock *> > InvBlockTraits;
+    for (BlockTraits::ChildIteratorType I =
+         BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI);
+         I != E; ++I) {
+      // If block is inside the loop then it is not a exit block.
+      if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I))
+        continue;
+
+      InvBlockTraits::ChildIteratorType PI = InvBlockTraits::child_begin(*I);
+      BasicBlock *firstPred = *PI;
+
+      // If current basic block is this exit block's first predecessor
+      // then only insert exit block in to the output ExitBlocks vector.
+      // This ensures that same exit block is not inserted twice into
+      // ExitBlocks vector.
+      if (current != firstPred)
+        continue;
+
+      // If a terminator has more then two successors, for example SwitchInst,
+      // then it is possible that there are multiple edges from current block
+      // to one exit block.
+      if (std::distance(BlockTraits::child_begin(current),
+                        BlockTraits::child_end(current)) <= 2) {
+        ExitBlocks.push_back(*I);
+        continue;
+      }
+
+      // In case of multiple edges from current block to exit block, collect
+      // only one edge in ExitBlocks. Use switchExitBlocks to keep track of
+      // duplicate edges.
+      if (std::find(switchExitBlocks.begin(), switchExitBlocks.end(), *I)
+          == switchExitBlocks.end()) {
+        switchExitBlocks.push_back(*I);
+        ExitBlocks.push_back(*I);
+      }
+    }
+  }
+}
+
+/// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one
+/// block, return that block. Otherwise return null.
+BasicBlock *Loop::getUniqueExitBlock() const {
+  SmallVector<BasicBlock *, 8> UniqueExitBlocks;
+  getUniqueExitBlocks(UniqueExitBlocks);
+  if (UniqueExitBlocks.size() == 1)
+    return UniqueExitBlocks[0];
+  return 0;
+}
+
 //===----------------------------------------------------------------------===//
 // LoopInfo implementation
 //