From 3aebcb99f7b6aa4b1fe69e7f9e468bfe08daa877 Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Sat, 25 Jan 2014 10:01:55 +0000
Subject: [PATCH] [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
---
 .../Transforms/Vectorize/LoopVectorize.cpp    | 45 +++++++++++++++----
 1 file changed, 37 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 892c42755b4c..9db66e7e6933 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/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>();