Check in LLVM r95781.

1 files changed, 411 insertions, 0 deletions

diff --git a/lib/Analysis/IVUsers.cpp b/lib/Analysis/IVUsers.cpp
new file mode 100644
index 0000000..9c472ae
--- /dev/null
+++ b/lib/Analysis/IVUsers.cpp
@@ -0,0 +1,411 @@
+//===- IVUsers.cpp - Induction Variable Users -------------------*- 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 bookkeeping for "interesting" users of expressions
+// computed from induction variables.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "iv-users"
+#include "llvm/Analysis/IVUsers.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+#include "llvm/Type.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+using namespace llvm;
+
+char IVUsers::ID = 0;
+static RegisterPass<IVUsers>
+X("iv-users", "Induction Variable Users", false, true);
+
+Pass *llvm::createIVUsersPass() {
+  return new IVUsers();
+}
+
+/// containsAddRecFromDifferentLoop - Determine whether expression S involves a
+/// subexpression that is an AddRec from a loop other than L.  An outer loop
+/// of L is OK, but not an inner loop nor a disjoint loop.
+static bool containsAddRecFromDifferentLoop(const SCEV *S, Loop *L) {
+  // This is very common, put it first.
+  if (isa<SCEVConstant>(S))
+    return false;
+  if (const SCEVCommutativeExpr *AE = dyn_cast<SCEVCommutativeExpr>(S)) {
+    for (unsigned int i=0; i< AE->getNumOperands(); i++)
+      if (containsAddRecFromDifferentLoop(AE->getOperand(i), L))
+        return true;
+    return false;
+  }
+  if (const SCEVAddRecExpr *AE = dyn_cast<SCEVAddRecExpr>(S)) {
+    if (const Loop *newLoop = AE->getLoop()) {
+      if (newLoop == L)
+        return false;
+      // if newLoop is an outer loop of L, this is OK.
+      if (newLoop->contains(L))
+        return false;
+    }
+    return true;
+  }
+  if (const SCEVUDivExpr *DE = dyn_cast<SCEVUDivExpr>(S))
+    return containsAddRecFromDifferentLoop(DE->getLHS(), L) ||
+           containsAddRecFromDifferentLoop(DE->getRHS(), L);
+#if 0
+  // SCEVSDivExpr has been backed out temporarily, but will be back; we'll
+  // need this when it is.
+  if (const SCEVSDivExpr *DE = dyn_cast<SCEVSDivExpr>(S))
+    return containsAddRecFromDifferentLoop(DE->getLHS(), L) ||
+           containsAddRecFromDifferentLoop(DE->getRHS(), L);
+#endif
+  if (const SCEVCastExpr *CE = dyn_cast<SCEVCastExpr>(S))
+    return containsAddRecFromDifferentLoop(CE->getOperand(), L);
+  return false;
+}
+
+/// getSCEVStartAndStride - Compute the start and stride of this expression,
+/// returning false if the expression is not a start/stride pair, or true if it
+/// is.  The stride must be a loop invariant expression, but the start may be
+/// a mix of loop invariant and loop variant expressions.  The start cannot,
+/// however, contain an AddRec from a different loop, unless that loop is an
+/// outer loop of the current loop.
+static bool getSCEVStartAndStride(const SCEV *&SH, Loop *L, Loop *UseLoop,
+                                  const SCEV *&Start, const SCEV *&Stride,
+                                  ScalarEvolution *SE, DominatorTree *DT) {
+  const SCEV *TheAddRec = Start;   // Initialize to zero.
+
+  // If the outer level is an AddExpr, the operands are all start values except
+  // for a nested AddRecExpr.
+  if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(SH)) {
+    for (unsigned i = 0, e = AE->getNumOperands(); i != e; ++i)
+      if (const SCEVAddRecExpr *AddRec =
+             dyn_cast<SCEVAddRecExpr>(AE->getOperand(i))) {
+        if (AddRec->getLoop() == L)
+          TheAddRec = SE->getAddExpr(AddRec, TheAddRec);
+        else
+          return false;  // Nested IV of some sort?
+      } else {
+        Start = SE->getAddExpr(Start, AE->getOperand(i));
+      }
+  } else if (isa<SCEVAddRecExpr>(SH)) {
+    TheAddRec = SH;
+  } else {
+    return false;  // not analyzable.
+  }
+
+  const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(TheAddRec);
+  if (!AddRec || AddRec->getLoop() != L) return false;
+
+  // Use getSCEVAtScope to attempt to simplify other loops out of
+  // the picture.
+  const SCEV *AddRecStart = AddRec->getStart();
+  AddRecStart = SE->getSCEVAtScope(AddRecStart, UseLoop);
+  const SCEV *AddRecStride = AddRec->getStepRecurrence(*SE);
+
+  // FIXME: If Start contains an SCEVAddRecExpr from a different loop, other
+  // than an outer loop of the current loop, reject it.  LSR has no concept of
+  // operating on more than one loop at a time so don't confuse it with such
+  // expressions.
+  if (containsAddRecFromDifferentLoop(AddRecStart, L))
+    return false;
+
+  Start = SE->getAddExpr(Start, AddRecStart);
+
+  // If stride is an instruction, make sure it properly dominates the header.
+  // Otherwise we could end up with a use before def situation.
+  if (!isa<SCEVConstant>(AddRecStride)) {
+    BasicBlock *Header = L->getHeader();
+    if (!AddRecStride->properlyDominates(Header, DT))
+      return false;
+
+    DEBUG(dbgs() << "[";
+          WriteAsOperand(dbgs(), L->getHeader(), /*PrintType=*/false);
+          dbgs() << "] Variable stride: " << *AddRec << "\n");
+  }
+
+  Stride = AddRecStride;
+  return true;
+}
+
+/// 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, Instruction *IV,
+                                       Loop *L, LoopInfo *LI, DominatorTree *DT,
+                                       Pass *P) {
+  // 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) return false;  // not a phi, not dominated by latch block.
+
+  // Look at all of the uses of IV 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.
+  unsigned NumUses = 0;
+  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+    if (PN->getIncomingValue(i) == IV) {
+      ++NumUses;
+      if (!DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
+        return false;
+    }
+
+  // Okay, all uses of IV by PN are in predecessor blocks that really are
+  // dominated by the latch block.  Use the post-incremented value.
+  return true;
+}
+
+/// AddUsersIfInteresting - Inspect the specified instruction.  If it is a
+/// reducible SCEV, recursively add its users to the IVUsesByStride set and
+/// return true.  Otherwise, return false.
+bool IVUsers::AddUsersIfInteresting(Instruction *I) {
+  if (!SE->isSCEVable(I->getType()))
+    return false;   // Void and FP expressions cannot be reduced.
+
+  // LSR is not APInt clean, do not touch integers bigger than 64-bits.
+  if (SE->getTypeSizeInBits(I->getType()) > 64)
+    return false;
+
+  if (!Processed.insert(I))
+    return true;    // Instruction already handled.
+
+  // Get the symbolic expression for this instruction.
+  const SCEV *ISE = SE->getSCEV(I);
+  if (isa<SCEVCouldNotCompute>(ISE)) return false;
+
+  // Get the start and stride for this expression.
+  Loop *UseLoop = LI->getLoopFor(I->getParent());
+  const SCEV *Start = SE->getIntegerSCEV(0, ISE->getType());
+  const SCEV *Stride = Start;
+
+  if (!getSCEVStartAndStride(ISE, L, UseLoop, Start, Stride, SE, DT))
+    return false;  // Non-reducible symbolic expression, bail out.
+
+  // Keep things simple. Don't touch loop-variant strides.
+  if (!Stride->isLoopInvariant(L) && L->contains(I))
+    return false;
+
+  SmallPtrSet<Instruction *, 4> UniqueUsers;
+  for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
+       UI != E; ++UI) {
+    Instruction *User = cast<Instruction>(*UI);
+    if (!UniqueUsers.insert(User))
+      continue;
+
+    // Do not infinitely recurse on PHI nodes.
+    if (isa<PHINode>(User) && Processed.count(User))
+      continue;
+
+    // Descend recursively, but not into PHI nodes outside the current loop.
+    // It's important to see the entire expression outside the loop to get
+    // choices that depend on addressing mode use right, although we won't
+    // consider references ouside the loop in all cases.
+    // If User is already in Processed, we don't want to recurse into it again,
+    // but do want to record a second reference in the same instruction.
+    bool AddUserToIVUsers = false;
+    if (LI->getLoopFor(User->getParent()) != L) {
+      if (isa<PHINode>(User) || Processed.count(User) ||
+          !AddUsersIfInteresting(User)) {
+        DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
+                     << "   OF SCEV: " << *ISE << '\n');
+        AddUserToIVUsers = true;
+      }
+    } else if (Processed.count(User) ||
+               !AddUsersIfInteresting(User)) {
+      DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
+                   << "   OF SCEV: " << *ISE << '\n');
+      AddUserToIVUsers = true;
+    }
+
+    if (AddUserToIVUsers) {
+      IVUsersOfOneStride *StrideUses = IVUsesByStride[Stride];
+      if (!StrideUses) {    // First occurrence of this stride?
+        StrideOrder.push_back(Stride);
+        StrideUses = new IVUsersOfOneStride(Stride);
+        IVUses.push_back(StrideUses);
+        IVUsesByStride[Stride] = StrideUses;
+      }
+
+      // Okay, we found a user that we cannot reduce.  Analyze the instruction
+      // and decide what to do with it.  If we are a use inside of the loop, use
+      // the value before incrementation, otherwise use it after incrementation.
+      if (IVUseShouldUsePostIncValue(User, I, L, LI, DT, this)) {
+        // The value used will be incremented by the stride more than we are
+        // expecting, so subtract this off.
+        const SCEV *NewStart = SE->getMinusSCEV(Start, Stride);
+        StrideUses->addUser(NewStart, User, I);
+        StrideUses->Users.back().setIsUseOfPostIncrementedValue(true);
+        DEBUG(dbgs() << "   USING POSTINC SCEV, START=" << *NewStart<< "\n");
+      } else {
+        StrideUses->addUser(Start, User, I);
+      }
+    }
+  }
+  return true;
+}
+
+void IVUsers::AddUser(const SCEV *Stride, const SCEV *Offset,
+                      Instruction *User, Value *Operand) {
+  IVUsersOfOneStride *StrideUses = IVUsesByStride[Stride];
+  if (!StrideUses) {    // First occurrence of this stride?
+    StrideOrder.push_back(Stride);
+    StrideUses = new IVUsersOfOneStride(Stride);
+    IVUses.push_back(StrideUses);
+    IVUsesByStride[Stride] = StrideUses;
+  }
+  IVUsesByStride[Stride]->addUser(Offset, User, Operand);
+}
+
+IVUsers::IVUsers()
+ : LoopPass(&ID) {
+}
+
+void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequired<LoopInfo>();
+  AU.addRequired<DominatorTree>();
+  AU.addRequired<ScalarEvolution>();
+  AU.setPreservesAll();
+}
+
+bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
+
+  L = l;
+  LI = &getAnalysis<LoopInfo>();
+  DT = &getAnalysis<DominatorTree>();
+  SE = &getAnalysis<ScalarEvolution>();
+
+  // Find all uses of induction variables in this loop, and categorize
+  // them by stride.  Start by finding all of the PHI nodes in the header for
+  // this loop.  If they are induction variables, inspect their uses.
+  for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
+    AddUsersIfInteresting(I);
+
+  return false;
+}
+
+/// getReplacementExpr - Return a SCEV expression which computes the
+/// value of the OperandValToReplace of the given IVStrideUse.
+const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &U) const {
+  // Start with zero.
+  const SCEV *RetVal = SE->getIntegerSCEV(0, U.getParent()->Stride->getType());
+  // Create the basic add recurrence.
+  RetVal = SE->getAddRecExpr(RetVal, U.getParent()->Stride, L);
+  // Add the offset in a separate step, because it may be loop-variant.
+  RetVal = SE->getAddExpr(RetVal, U.getOffset());
+  // For uses of post-incremented values, add an extra stride to compute
+  // the actual replacement value.
+  if (U.isUseOfPostIncrementedValue())
+    RetVal = SE->getAddExpr(RetVal, U.getParent()->Stride);
+  return RetVal;
+}
+
+/// getCanonicalExpr - Return a SCEV expression which computes the
+/// value of the SCEV of the given IVStrideUse, ignoring the 
+/// isUseOfPostIncrementedValue flag.
+const SCEV *IVUsers::getCanonicalExpr(const IVStrideUse &U) const {
+  // Start with zero.
+  const SCEV *RetVal = SE->getIntegerSCEV(0, U.getParent()->Stride->getType());
+  // Create the basic add recurrence.
+  RetVal = SE->getAddRecExpr(RetVal, U.getParent()->Stride, L);
+  // Add the offset in a separate step, because it may be loop-variant.
+  RetVal = SE->getAddExpr(RetVal, U.getOffset());
+  return RetVal;
+}
+
+void IVUsers::print(raw_ostream &OS, const Module *M) const {
+  OS << "IV Users for loop ";
+  WriteAsOperand(OS, L->getHeader(), false);
+  if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
+    OS << " with backedge-taken count "
+       << *SE->getBackedgeTakenCount(L);
+  }
+  OS << ":\n";
+
+  for (unsigned Stride = 0, e = StrideOrder.size(); Stride != e; ++Stride) {
+    std::map<const SCEV *, IVUsersOfOneStride*>::const_iterator SI =
+      IVUsesByStride.find(StrideOrder[Stride]);
+    assert(SI != IVUsesByStride.end() && "Stride doesn't exist!");
+    OS << "  Stride " << *SI->first->getType() << " " << *SI->first << ":\n";
+
+    for (ilist<IVStrideUse>::const_iterator UI = SI->second->Users.begin(),
+         E = SI->second->Users.end(); UI != E; ++UI) {
+      OS << "    ";
+      WriteAsOperand(OS, UI->getOperandValToReplace(), false);
+      OS << " = ";
+      OS << *getReplacementExpr(*UI);
+      if (UI->isUseOfPostIncrementedValue())
+        OS << " (post-inc)";
+      OS << " in ";
+      UI->getUser()->print(OS);
+      OS << '\n';
+    }
+  }
+}
+
+void IVUsers::dump() const {
+  print(dbgs());
+}
+
+void IVUsers::releaseMemory() {
+  IVUsesByStride.clear();
+  StrideOrder.clear();
+  Processed.clear();
+  IVUses.clear();
+}
+
+void IVStrideUse::deleted() {
+  // Remove this user from the list.
+  Parent->Users.erase(this);
+  // this now dangles!
+}
+
+void IVUsersOfOneStride::print(raw_ostream &OS) const {
+  OS << "IV Users of one stride:\n";
+
+  if (Stride)
+    OS << "    Stride: " << *Stride << '\n';
+
+  OS << "    Users:\n";
+
+  unsigned Count = 1;
+
+  for (ilist<IVStrideUse>::const_iterator
+         I = Users.begin(), E = Users.end(); I != E; ++I) {
+    const IVStrideUse &SU = *I;
+    OS << "      " << Count++ << '\n';
+    OS << "        Offset: " << *SU.getOffset() << '\n';
+    OS << "         Instr: " << *SU << '\n';
+  }
+}
+
+void IVUsersOfOneStride::dump() const {
+  print(dbgs());
+}