From e6bb649ec63059d795a31198c3c569c137e7ad59 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sun, 26 Dec 2010 19:39:38 +0000
Subject: [PATCH] actually add the file...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122563 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LoopIdiomRecognize.cpp | 103 +++++++++++++++++++
 1 file changed, 103 insertions(+)
 create mode 100644 lib/Transforms/Scalar/LoopIdiomRecognize.cpp

diff --git a/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
new file mode 100644
index 00000000000..270c4afcc1d
--- /dev/null
+++ b/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -0,0 +1,103 @@
+//===-- LoopIdiomRecognize.cpp - Loop idiom recognition -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass implements an idiom recognizer that transforms simple loops into a
+// non-loop form.  In cases that this kicks in, it can be a significant
+// performance win.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "loop-idiom"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+// TODO: Recognize "N" size array multiplies: replace with call to blas or
+// something.
+
+namespace {
+  class LoopIdiomRecognize : public LoopPass {
+  public:
+    static char ID;
+    explicit LoopIdiomRecognize() : LoopPass(ID) {
+      initializeLoopIdiomRecognizePass(*PassRegistry::getPassRegistry());
+    }
+
+    bool runOnLoop(Loop *L, LPPassManager &LPM);
+
+    bool scanBlock(BasicBlock *BB, Loop *L);
+    
+    /// This transformation requires natural loop information & requires that
+    /// loop preheaders be inserted into the CFG.
+    ///
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.addRequired<LoopInfo>();
+      AU.addPreserved<LoopInfo>();
+      AU.addRequiredID(LoopSimplifyID);
+      AU.addPreservedID(LoopSimplifyID);
+      AU.addRequiredID(LCSSAID);
+      AU.addPreservedID(LCSSAID);
+      AU.addRequired<ScalarEvolution>();
+      AU.addPreserved<ScalarEvolution>();
+      AU.addPreserved<DominatorTree>();
+    }
+  };
+}
+
+char LoopIdiomRecognize::ID = 0;
+INITIALIZE_PASS_BEGIN(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
+                      false, false)
+INITIALIZE_PASS_DEPENDENCY(LoopInfo)
+INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
+INITIALIZE_PASS_DEPENDENCY(LCSSA)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
+INITIALIZE_PASS_END(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
+                    false, false)
+
+Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognize(); }
+
+bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
+  // We only look at trivial single basic block loops.
+  // TODO: eventually support more complex loops, scanning the header.
+  if (L->getBlocks().size() != 1)
+    return false;
+  
+  BasicBlock *BB = L->getHeader();
+  DEBUG(dbgs() << "Loop Idiom Recognize: F[" << BB->getParent()->getName()
+               << "] Loop %" << BB->getName() << "\n");
+
+  return scanBlock(BB, L);
+}
+
+/// scanBlock - Look over a block to see if we can promote anything out of it.
+bool LoopIdiomRecognize::scanBlock(BasicBlock *BB, Loop *L) {
+  ScalarEvolution &SE = getAnalysis<ScalarEvolution>();
+  
+  for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
+    // Look for store instructions, which may be memsets.
+    StoreInst *SI = dyn_cast<StoreInst>(I++);
+    if (SI == 0) continue;
+    
+    // See if the pointer expression is an AddRec like {base,+,1} on the current
+    // loop, which indicates a strided store.  If we have something else, it's a
+    // random store we can't handle.
+    const SCEVAddRecExpr *Ev =
+      dyn_cast<SCEVAddRecExpr>(SE.getSCEV(SI->getPointerOperand()));
+    if (Ev == 0 || Ev->getLoop() != L)
+      continue;
+    
+    errs() << "Found strided store: " << *Ev << "\n";
+  }
+  
+  return false;
+}
+