[llvm][NFC] Factor out logic for getting incoming & back Loop edges

Reviewers: davidxl

Reviewed By: davidxl

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59967

llvm-svn: 357284

llvm/include/llvm/Analysis/LoopInfo.h

@@ -521,6 +521,11 @@ public:
   ///
   PHINode *getCanonicalInductionVariable() const;
 
+  /// Obtain the unique incoming and back edge. Return false if they are
+  /// non-unique or the loop is dead; otherwise, return true.
+  bool getIncomingAndBackEdge(BasicBlock *&Incoming,
+                              BasicBlock *&Backedge) const;
+
   /// Return true if the Loop is in LCSSA form.
   bool isLCSSAForm(DominatorTree &DT) const;
 

llvm/lib/Analysis/LoopInfo.cpp

@@ -109,24 +109,37 @@ bool Loop::makeLoopInvariant(Instruction *I, bool &Changed,
   return true;
 }
 
-PHINode *Loop::getCanonicalInductionVariable() const {
+bool Loop::getIncomingAndBackEdge(BasicBlock *&Incoming,
+                                  BasicBlock *&Backedge) const {
   BasicBlock *H = getHeader();
 
-  BasicBlock *Incoming = nullptr, *Backedge = nullptr;
+  Incoming = nullptr;
+  Backedge = nullptr;
   pred_iterator PI = pred_begin(H);
   assert(PI != pred_end(H) && "Loop must have at least one backedge!");
   Backedge = *PI++;
   if (PI == pred_end(H))
-    return nullptr; // dead loop
+    return false; // dead loop
   Incoming = *PI++;
   if (PI != pred_end(H))
-    return nullptr; // multiple backedges?
+    return false; // multiple backedges?
 
   if (contains(Incoming)) {
     if (contains(Backedge))
-      return nullptr;
+      return false;
     std::swap(Incoming, Backedge);
   } else if (!contains(Backedge))
+    return false;
+
+  assert(Incoming && Backedge && "expected non-null incoming and backedges");
+  return true;
+}
+
+PHINode *Loop::getCanonicalInductionVariable() const {
+  BasicBlock *H = getHeader();
+
+  BasicBlock *Incoming = nullptr, *Backedge = nullptr;
+  if (!getIncomingAndBackEdge(Incoming, Backedge))
     return nullptr;
 
   // Loop over all of the PHI nodes, looking for a canonical indvar.