[LPM] Conclude my immediate work by making the LoopVectorizer

a FunctionPass. With this change the loop vectorizer no longer is a loop
pass and can readily depend on function analyses. In particular, with
this change we no longer have to form a loop pass manager to run the
loop vectorizer which simplifies the entire pass management of LLVM.

The next step here is to teach the loop vectorizer to leverage profile
information through the profile information providing analysis passes.

llvm-svn: 200074

lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -930,13 +930,21 @@ private:
   }
 };
 
+static void addInnerLoop(Loop *L, SmallVectorImpl<Loop *> &V) {
+  if (L->empty())
+    return V.push_back(L);
+
+  for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
+    addInnerLoop(*I, V);
+}
+
 /// The LoopVectorize Pass.
-struct LoopVectorize : public LoopPass {
+struct LoopVectorize : public FunctionPass {
   /// Pass identification, replacement for typeid
   static char ID;
 
   explicit LoopVectorize(bool NoUnrolling = false, bool AlwaysVectorize = true)
-    : LoopPass(ID),
+    : FunctionPass(ID),
       DisableUnrolling(NoUnrolling),
       AlwaysVectorize(AlwaysVectorize) {
     initializeLoopVectorizePass(*PassRegistry::getPassRegistry());
@@ -951,11 +959,7 @@ struct LoopVectorize : public LoopPass {
   bool DisableUnrolling;
   bool AlwaysVectorize;
 
-  virtual bool runOnLoop(Loop *L, LPPassManager &LPM) {
-    // We only vectorize innermost loops.
-    if (!L->empty())
-      return false;
-
+  virtual bool runOnFunction(Function &F) {
     SE = &getAnalysis<ScalarEvolution>();
     DL = getAnalysisIfAvailable<DataLayout>();
     LI = &getAnalysis<LoopInfo>();
@@ -973,6 +977,32 @@ struct LoopVectorize : public LoopPass {
       return false;
     }
 
+    // Build up a worklist of inner-loops to vectorize. This is necessary as
+    // the act of vectorizing or partially unrolling a loop creates new loops
+    // and can invalidate iterators across the loops.
+    SmallVector<Loop *, 8> Worklist;
+
+    for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
+      addInnerLoop(*I, Worklist);
+
+    // Now walk the identified inner loops.
+    bool Changed = false;
+    while (!Worklist.empty())
+      Changed |= processLoop(Worklist.pop_back_val());
+
+    // Process each loop nest in the function.
+    return Changed;
+  }
+
+  bool processLoop(Loop *L) {
+    // We only handle inner loops, so if there are children just recurse.
+    if (!L->empty()) {
+      bool Changed = false;
+      for (Loop::iterator I = L->begin(), E = L->begin(); I != E; ++I)
+        Changed |= processLoop(*I);
+      return Changed;
+    }
+
     DEBUG(dbgs() << "LV: Checking a loop in \"" <<
           L->getHeader()->getParent()->getName() << "\"\n");
 
@@ -1052,7 +1082,6 @@ struct LoopVectorize : public LoopPass {
   }
 
   virtual void getAnalysisUsage(AnalysisUsage &AU) const {
-    LoopPass::getAnalysisUsage(AU);
     AU.addRequiredID(LoopSimplifyID);
     AU.addRequiredID(LCSSAID);
     AU.addRequired<DominatorTreeWrapperPass>();