--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/Analysis/ScalarEvolutionNormalization.cpp	Thu Dec 12 13:56:28 2013 +0900
@@ -0,0 +1,231 @@
+//===- ScalarEvolutionNormalization.cpp - See below -------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements utilities for working with "normalized" expressions.
+// See the comments at the top of ScalarEvolutionNormalization.h for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/ScalarEvolutionNormalization.h"
+using namespace llvm;
+
+/// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
+/// and now we need to decide whether the user should use the preinc or post-inc
+/// value.  If this user should use the post-inc version of the IV, return true.
+///
+/// Choosing wrong here can break dominance properties (if we choose to use the
+/// post-inc value when we cannot) or it can end up adding extra live-ranges to
+/// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
+/// should use the post-inc value).
+static bool IVUseShouldUsePostIncValue(Instruction *User, Value *Operand,
+                                       const Loop *L, DominatorTree *DT) {
+  // If the user is in the loop, use the preinc value.
+  if (L->contains(User)) return false;
+
+  BasicBlock *LatchBlock = L->getLoopLatch();
+  if (!LatchBlock)
+    return false;
+
+  // Ok, the user is outside of the loop.  If it is dominated by the latch
+  // block, use the post-inc value.
+  if (DT->dominates(LatchBlock, User->getParent()))
+    return true;
+
+  // There is one case we have to be careful of: PHI nodes.  These little guys
+  // can live in blocks that are not dominated by the latch block, but (since
+  // their uses occur in the predecessor block, not the block the PHI lives in)
+  // should still use the post-inc value.  Check for this case now.
+  PHINode *PN = dyn_cast<PHINode>(User);
+  if (!PN || !Operand) return false; // not a phi, not dominated by latch block.
+
+  // Look at all of the uses of Operand by the PHI node.  If any use corresponds
+  // to a block that is not dominated by the latch block, give up and use the
+  // preincremented value.
+  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+    if (PN->getIncomingValue(i) == Operand &&
+        !DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
+      return false;
+
+  // Okay, all uses of Operand by PN are in predecessor blocks that really are
+  // dominated by the latch block.  Use the post-incremented value.
+  return true;
+}
+
+namespace {
+
+/// Hold the state used during post-inc expression transformation, including a
+/// map of transformed expressions.
+class PostIncTransform {
+  TransformKind Kind;
+  PostIncLoopSet &Loops;
+  ScalarEvolution &SE;
+  DominatorTree &DT;
+
+  DenseMap<const SCEV*, const SCEV*> Transformed;
+
+public:
+  PostIncTransform(TransformKind kind, PostIncLoopSet &loops,
+                   ScalarEvolution &se, DominatorTree &dt):
+    Kind(kind), Loops(loops), SE(se), DT(dt) {}
+
+  const SCEV *TransformSubExpr(const SCEV *S, Instruction *User,
+                               Value *OperandValToReplace);
+
+protected:
+  const SCEV *TransformImpl(const SCEV *S, Instruction *User,
+                            Value *OperandValToReplace);
+};
+
+} // namespace
+
+/// Implement post-inc transformation for all valid expression types.
+const SCEV *PostIncTransform::
+TransformImpl(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
+
+  if (const SCEVCastExpr *X = dyn_cast<SCEVCastExpr>(S)) {
+    const SCEV *O = X->getOperand();
+    const SCEV *N = TransformSubExpr(O, User, OperandValToReplace);
+    if (O != N)
+      switch (S->getSCEVType()) {
+      case scZeroExtend: return SE.getZeroExtendExpr(N, S->getType());
+      case scSignExtend: return SE.getSignExtendExpr(N, S->getType());
+      case scTruncate: return SE.getTruncateExpr(N, S->getType());
+      default: llvm_unreachable("Unexpected SCEVCastExpr kind!");
+      }
+    return S;
+  }
+
+  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
+    // An addrec. This is the interesting part.
+    SmallVector<const SCEV *, 8> Operands;
+    const Loop *L = AR->getLoop();
+    // The addrec conceptually uses its operands at loop entry.
+    Instruction *LUser = L->getHeader()->begin();
+    // Transform each operand.
+    for (SCEVNAryExpr::op_iterator I = AR->op_begin(), E = AR->op_end();
+         I != E; ++I) {
+      Operands.push_back(TransformSubExpr(*I, LUser, 0));
+    }
+    // Conservatively use AnyWrap until/unless we need FlagNW.
+    const SCEV *Result = SE.getAddRecExpr(Operands, L, SCEV::FlagAnyWrap);
+    switch (Kind) {
+    case NormalizeAutodetect:
+      // Normalize this SCEV by subtracting the expression for the final step.
+      // We only allow affine AddRecs to be normalized, otherwise we would not
+      // be able to correctly denormalize.
+      // e.g. {1,+,3,+,2} == {-2,+,1,+,2} + {3,+,2}
+      // Normalized form:   {-2,+,1,+,2}
+      // Denormalized form: {1,+,3,+,2}
+      //
+      // However, denormalization would use the a different step expression than
+      // normalization (see getPostIncExpr), generating the wrong final
+      // expression: {-2,+,1,+,2} + {1,+,2} => {-1,+,3,+,2}
+      if (AR->isAffine() &&
+          IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
+        Result = SE.getMinusSCEV(Result, AR->getStepRecurrence(SE));
+        Loops.insert(L);
+      }
+#if 0
+      // This assert is conceptually correct, but ScalarEvolution currently
+      // sometimes fails to canonicalize two equal SCEVs to exactly the same
+      // form. It's possibly a pessimization when this happens, but it isn't a
+      // correctness problem, so disable this assert for now.
+      assert(S == TransformSubExpr(Result, User, OperandValToReplace) &&
+             "SCEV normalization is not invertible!");
+#endif
+      break;
+    case Normalize:
+      if (Loops.count(L)) {
+        const SCEV *TransformedStep =
+          TransformSubExpr(AR->getStepRecurrence(SE),
+                           User, OperandValToReplace);
+        Result = SE.getMinusSCEV(Result, TransformedStep);
+      }
+#if 0
+      // See the comment on the assert above.
+      assert(S == TransformSubExpr(Result, User, OperandValToReplace) &&
+             "SCEV normalization is not invertible!");
+#endif
+      break;
+    case Denormalize:
+      if (Loops.count(L))
+        Result = cast<SCEVAddRecExpr>(Result)->getPostIncExpr(SE);
+      break;
+    }
+    return Result;
+  }
+
+  if (const SCEVNAryExpr *X = dyn_cast<SCEVNAryExpr>(S)) {
+    SmallVector<const SCEV *, 8> Operands;
+    bool Changed = false;
+    // Transform each operand.
+    for (SCEVNAryExpr::op_iterator I = X->op_begin(), E = X->op_end();
+         I != E; ++I) {
+      const SCEV *O = *I;
+      const SCEV *N = TransformSubExpr(O, User, OperandValToReplace);
+      Changed |= N != O;
+      Operands.push_back(N);
+    }
+    // If any operand actually changed, return a transformed result.
+    if (Changed)
+      switch (S->getSCEVType()) {
+      case scAddExpr: return SE.getAddExpr(Operands);
+      case scMulExpr: return SE.getMulExpr(Operands);
+      case scSMaxExpr: return SE.getSMaxExpr(Operands);
+      case scUMaxExpr: return SE.getUMaxExpr(Operands);
+      default: llvm_unreachable("Unexpected SCEVNAryExpr kind!");
+      }
+    return S;
+  }
+
+  if (const SCEVUDivExpr *X = dyn_cast<SCEVUDivExpr>(S)) {
+    const SCEV *LO = X->getLHS();
+    const SCEV *RO = X->getRHS();
+    const SCEV *LN = TransformSubExpr(LO, User, OperandValToReplace);
+    const SCEV *RN = TransformSubExpr(RO, User, OperandValToReplace);
+    if (LO != LN || RO != RN)
+      return SE.getUDivExpr(LN, RN);
+    return S;
+  }
+
+  llvm_unreachable("Unexpected SCEV kind!");
+}
+
+/// Manage recursive transformation across an expression DAG. Revisiting
+/// expressions would lead to exponential recursion.
+const SCEV *PostIncTransform::
+TransformSubExpr(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
+
+  if (isa<SCEVConstant>(S) || isa<SCEVUnknown>(S))
+    return S;
+
+  const SCEV *Result = Transformed.lookup(S);
+  if (Result)
+    return Result;
+
+  Result = TransformImpl(S, User, OperandValToReplace);
+  Transformed[S] = Result;
+  return Result;
+}
+
+/// Top level driver for transforming an expression DAG into its requested
+/// post-inc form (either "Normalized" or "Denormalized".
+const SCEV *llvm::TransformForPostIncUse(TransformKind Kind,
+                                         const SCEV *S,
+                                         Instruction *User,
+                                         Value *OperandValToReplace,
+                                         PostIncLoopSet &Loops,
+                                         ScalarEvolution &SE,
+                                         DominatorTree &DT) {
+  PostIncTransform Transform(Kind, Loops, SE, DT);
+  return Transform.TransformSubExpr(S, User, OperandValToReplace);
+}