[loop-arc] Add a simple Loop visitor that visits loops bottom up in the loop tree.

Author: gottesmm

include/swift/SILPasses/Utils/LoopUtils.h

@@ -20,6 +20,7 @@
 
 namespace swift {
 
+class SILFunction;
 class SILBasicBlock;
 class SILLoop;
 class DominanceInfo;
@@ -34,6 +35,24 @@ bool canonicalizeLoop(SILLoop *L, DominanceInfo *DT, SILLoopInfo *LI);
 /// information. We update loop info and dominance info while we do this.
 bool canonicalizeAllLoops(DominanceInfo *DT, SILLoopInfo *LI);
 
+/// A visitor that visits loops in a function in a bottom up order. It only
+/// performs the visit.
+class SILLoopVisitor {
+  SILFunction *F;
+  SILLoopInfo *LI;
+
+public:
+  SILLoopVisitor(SILFunction *Func, SILLoopInfo *LInfo) : F(Func), LI(LInfo) {}
+  virtual ~SILLoopVisitor() {}
+
+  void run();
+
+  SILFunction *getFunction() const { return F; }
+
+  virtual void runOnLoop(SILLoop *L) = 0;
+  virtual void runOnFunction(SILFunction *F) = 0;
+};
+
 } // end swift namespace
 
 #endif

lib/SILPasses/Utils/LoopUtils.cpp

@@ -236,3 +236,34 @@ bool swift::canonicalizeAllLoops(DominanceInfo *DT, SILLoopInfo *LI) {
 
   return MadeChange;
 }
+
+//===----------------------------------------------------------------------===//
+//                                Loop Visitor
+//===----------------------------------------------------------------------===//
+
+void SILLoopVisitor::run() {
+  // We visit the loop nest inside out via a depth first, post order using
+  // this
+  // worklist.
+  llvm::SmallVector<std::pair<SILLoop *, bool>, 32> Worklist;
+  for (auto *L : LI->getTopLevelLoops()) {
+    Worklist.push_back({L, L->empty()});
+  }
+
+  while (Worklist.size()) {
+    SILLoop *L;
+    bool Visited;
+    std::tie(L, Visited) = Worklist.pop_back_val();
+
+    if (!Visited) {
+      Worklist.push_back({L, true});
+      for (auto *SubLoop : L->getSubLoops()) {
+        Worklist.push_back({SubLoop, SubLoop->empty()});
+      }
+      continue;
+    }
+    runOnLoop(L);
+  }
+
+  runOnFunction(F);
+}