Subzero: Recognize single-block loops during loop depth analysis.

src/IceLoopAnalyzer.cpp

 //===- subzero/src/IceLoopAnalyzer.cpp - Loop Analysis --------------------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 16 matching lines @@
 }
 
 NodeList::const_iterator LoopAnalyzer::LoopNode::successorsEnd() const {
   return BB->getOutEdges().end();
 }
 
 void LoopAnalyzer::LoopNode::incrementLoopNestDepth() {
   BB->incrementLoopNestDepth();
 }
 
+bool LoopAnalyzer::LoopNode::hasSelfEdge() const {
+  for (CfgNode *Succ : BB->getOutEdges()) {
+    if (Succ == BB)
+      return true;
+  }
+  return false;
+}
+
 LoopAnalyzer::LoopAnalyzer(Cfg *Fn) : Func(Fn) {
   const NodeList &Nodes = Func->getNodes();
 
   // Allocate memory ahead of time. This is why a vector is used instead of a
   // stack which doesn't support reserving (or bulk erasure used below).
   AllNodes.reserve(Nodes.size());
   WorkStack.reserve(Nodes.size());
   LoopStack.reserve(Nodes.size());
 
   // Create the LoopNodes from the function's CFG
@@ skipping 61 matching lines @@
     else if (Succ.isOnStack())
       Node.tryLink(Succ.getIndex());
   }
 
   if (Node.getLowLink() != Node.getIndex())
     return nullptr;
 
   // Single node means no loop in the CFG
   if (LoopStack.back() == &Node) {
     LoopStack.back()->setOnStack(false);
+    if (Node.hasSelfEdge())
+      LoopStack.back()->incrementLoopNestDepth();
     LoopStack.back()->setDeleted();
     ++NumDeletedNodes;
     LoopStack.pop_back();
     return nullptr;
   }
 
   // Reaching here means a loop has been found! It consists of the nodes on the
   // top of the stack, down until the current node being processed, Node, is
   // found.
   for (auto It = LoopStack.rbegin(); It != LoopStack.rend(); ++It) {
     (*It)->setOnStack(false);
     (*It)->incrementLoopNestDepth();
     // Remove the loop from the stack and delete the head node
     if (*It == &Node) {
       (*It)->setDeleted();
       ++NumDeletedNodes;
       LoopStack.erase(It.base() - 1, LoopStack.end());
       break;
     }
   }
 
   return nullptr;
 }
 
 } // end of namespace Ice