It's not necessary to do rounding for alloca operations when the requested

alignment is equal to the stack alignment.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40004 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 579 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/LoopRotation.cpp b/lib/Transforms/Scalar/LoopRotation.cpp
new file mode 100644
index 0000000000..d35a8edd3c
--- /dev/null
+++ b/lib/Transforms/Scalar/LoopRotation.cpp
@@ -0,0 +1,579 @@
+//===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Devang Patel and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements Loop Rotation Pass.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "loop-rotate"
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Function.h"
+#include "llvm/Instructions.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/SmallVector.h"
+
+using namespace llvm;
+
+#define MAX_HEADER_SIZE 16
+
+STATISTIC(NumRotated, "Number of loops rotated");
+namespace {
+
+  class VISIBILITY_HIDDEN RenameData {
+  public:
+    RenameData(Instruction *O, Value *P, Instruction *H) 
+      : Original(O), PreHeader(P), Header(H) { }
+  public:
+    Instruction *Original; // Original instruction
+    Value *PreHeader; // Original pre-header replacement
+    Instruction *Header; // New header replacement
+  };
+  
+  class VISIBILITY_HIDDEN LoopRotate : public LoopPass {
+
+  public:
+    static char ID; // Pass ID, replacement for typeid
+    LoopRotate() : LoopPass((intptr_t)&ID) {}
+
+    // Rotate Loop L as many times as possible. Return true if
+    // loop is rotated at least once.
+    bool runOnLoop(Loop *L, LPPassManager &LPM);
+
+    // LCSSA form makes instruction renaming easier.
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.addRequiredID(LCSSAID);
+      AU.addPreservedID(LCSSAID);
+      AU.addPreserved<ScalarEvolution>();
+      AU.addPreserved<LoopInfo>();
+      AU.addRequiredID(LoopSimplifyID);
+      AU.addPreservedID(LoopSimplifyID);
+    }
+
+    // Helper functions
+
+    /// Do actual work
+    bool rotateLoop(Loop *L, LPPassManager &LPM);
+    
+    /// Initialize local data
+    void initialize();
+
+    /// Make sure all Exit block PHINodes have required incoming values.
+    /// If incoming value is constant or defined outside the loop then
+    /// PHINode may not have an entry for original pre-header. 
+    void  updateExitBlock();
+
+    /// Return true if this instruction is used outside original header.
+    bool usedOutsideOriginalHeader(Instruction *In);
+
+    /// Find Replacement information for instruction. Return NULL if it is
+    /// not available.
+    const RenameData *findReplacementData(Instruction *I);
+
+    /// After loop rotation, loop pre-header has multiple sucessors.
+    /// Insert one forwarding basic block to ensure that loop pre-header
+    /// has only one successor.
+    void preserveCanonicalLoopForm(LPPassManager &LPM);
+
+  private:
+
+    Loop *L;
+    BasicBlock *OrigHeader;
+    BasicBlock *OrigPreHeader;
+    BasicBlock *OrigLatch;
+    BasicBlock *NewHeader;
+    BasicBlock *Exit;
+    LPPassManager *LPM_Ptr;
+    SmallVector<RenameData, MAX_HEADER_SIZE> LoopHeaderInfo;
+  };
+  
+  char LoopRotate::ID = 0;
+  RegisterPass<LoopRotate> X ("loop-rotate", "Rotate Loops");
+}
+
+LoopPass *llvm::createLoopRotatePass() { return new LoopRotate(); }
+
+/// Rotate Loop L as many times as possible. Return true if
+/// loop is rotated at least once.
+bool LoopRotate::runOnLoop(Loop *Lp, LPPassManager &LPM) {
+
+  bool RotatedOneLoop = false;
+  initialize();
+  LPM_Ptr = &LPM;
+
+  // One loop can be rotated multiple times.
+  while (rotateLoop(Lp,LPM)) {
+    RotatedOneLoop = true;
+    initialize();
+  }
+
+  return RotatedOneLoop;
+}
+
+/// Rotate loop LP. Return true if the loop is rotated.
+bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {
+
+  L = Lp;
+
+  OrigHeader =  L->getHeader();
+  OrigPreHeader = L->getLoopPreheader();
+  OrigLatch = L->getLoopLatch();
+
+  // If loop has only one block then there is not much to rotate.
+  if (L->getBlocks().size() == 1)
+    return false;
+
+  assert (OrigHeader && OrigLatch && OrigPreHeader &&
+          "Loop is not in canonical form");
+
+  // If loop header is not one of the loop exit block then
+  // either this loop is already rotated or it is not 
+  // suitable for loop rotation transformations.
+  if (!L->isLoopExit(OrigHeader))
+    return false;
+
+  BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
+  if (!BI)
+    return false;
+  assert (BI->isConditional() && "Branch Instruction is not condiitional");
+
+  // Updating PHInodes in loops with multiple exits adds complexity. 
+  // Keep it simple, and restrict loop rotation to loops with one exit only.
+  // In future, lift this restriction and support for multiple exits if
+  // required.
+  std::vector<BasicBlock *> ExitBlocks;
+  L->getExitBlocks(ExitBlocks);
+  if (ExitBlocks.size() > 1)
+    return false;
+
+  // Check size of original header and reject
+  // loop if it is very big.
+  if (OrigHeader->getInstList().size() > MAX_HEADER_SIZE)
+    return false;
+
+  // Now, this loop is suitable for rotation.
+
+  // Find new Loop header. NewHeader is a Header's one and only successor
+  // that is inside loop.  Header's other successor is out side the
+  // loop. Otherwise loop is not suitable for rotation.
+  Exit = BI->getSuccessor(0);
+  NewHeader = BI->getSuccessor(1);
+  if (L->contains(Exit))
+    std::swap(Exit, NewHeader);
+  assert (NewHeader && "Unable to determine new loop header");
+  assert(L->contains(NewHeader) && !L->contains(Exit) && 
+         "Unable to determine loop header and exit blocks");
+
+  // Copy PHI nodes and other instructions from original header
+  // into original pre-header. Unlike original header, original pre-header is
+  // not a member of loop. 
+  //
+  // New loop header is one and only successor of original header that 
+  // is inside the loop. All other original header successors are outside 
+  // the loop. Copy PHI Nodes from original header into new loop header. 
+  // Add second incoming value, from original loop pre-header into these phi 
+  // nodes. If a value defined in original header is used outside original 
+  // header then new loop header will need new phi nodes with two incoming 
+  // values, one definition from original header and second definition is 
+  // from original loop pre-header.
+
+  // Remove terminator from Original pre-header. Original pre-header will
+  // receive a clone of original header terminator as a new terminator.
+  OrigPreHeader->getInstList().pop_back();
+  BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
+  PHINode *PN = NULL;
+  for (; (PN = dyn_cast<PHINode>(I)); ++I) {
+    Instruction *In = I;
+
+    // PHI nodes are not copied into original pre-header. Instead their values
+    // are directly propagated.
+    Value * NPV = PN->getIncomingValueForBlock(OrigPreHeader);
+
+    // Create new PHI node with two incoming values for NewHeader.
+    // One incoming value is from OrigLatch (through OrigHeader) and 
+    // second incoming value is from original pre-header.
+    PHINode *NH = new PHINode(In->getType(), In->getName());
+    NH->addIncoming(PN->getIncomingValueForBlock(OrigLatch), OrigHeader);
+    NH->addIncoming(NPV, OrigPreHeader);
+    NewHeader->getInstList().push_front(NH);
+    
+    // "In" can be replaced by NH at various places.
+    LoopHeaderInfo.push_back(RenameData(In, NPV, NH));
+  }
+
+  // Now, handle non-phi instructions.
+  for (; I != E; ++I) {
+    Instruction *In = I;
+
+    assert (!isa<PHINode>(In) && "PHINode is not expected here");
+    // This is not a PHI instruction. Insert its clone into original pre-header.
+    // If this instruction is using a value from same basic block then
+    // update it to use value from cloned instruction.
+    Instruction *C = In->clone();
+    C->setName(In->getName());
+    OrigPreHeader->getInstList().push_back(C);
+
+    for (unsigned opi = 0, e = In->getNumOperands(); opi != e; ++opi) {
+      if (Instruction *OpPhi = dyn_cast<PHINode>(In->getOperand(opi))) {
+        if (const RenameData *D = findReplacementData(OpPhi)) {
+          // This is using values from original header PHI node.
+          // Here, directly used incoming value from original pre-header.
+          C->setOperand(opi, D->PreHeader);
+        }
+      }
+      else if (Instruction *OpInsn = 
+               dyn_cast<Instruction>(In->getOperand(opi))) {
+        if (const RenameData *D = findReplacementData(OpInsn))
+          C->setOperand(opi, D->PreHeader);
+      }
+    }
+
+
+    // If this instruction is used outside this basic block then
+    // create new PHINode for this instruction.
+    Instruction *NewHeaderReplacement = NULL;
+    if (usedOutsideOriginalHeader(In)) {
+      PHINode *PN = new PHINode(In->getType(), In->getName());
+      PN->addIncoming(In, OrigHeader);
+      PN->addIncoming(C, OrigPreHeader);
+      NewHeader->getInstList().push_front(PN);
+      NewHeaderReplacement = PN;
+    } 
+    
+    // "In" can be replaced by NPH or NH at various places.
+    LoopHeaderInfo.push_back(RenameData(In, C, NewHeaderReplacement));
+  }
+
+  // Rename uses of original header instructions to reflect their new
+  // definitions (either from original pre-header node or from newly created
+  // new header PHINodes.
+  //
+  // Original header instructions are used in
+  // 1) Original header:
+  //
+  //    If instruction is used in non-phi instructions then it is using
+  //    defintion from original heder iteself. Do not replace this use
+  //    with definition from new header or original pre-header.
+  //
+  //    If instruction is used in phi node then it is an incoming 
+  //    value. Rename its use to reflect new definition from new-preheader
+  //    or new header.
+  //
+  // 2) Inside loop but not in original header
+  //
+  //    Replace this use to reflect definition from new header.
+  for(unsigned LHI = 0, LHI_E = LoopHeaderInfo.size(); LHI != LHI_E; ++LHI) {
+    const RenameData &ILoopHeaderInfo = LoopHeaderInfo[LHI];
+
+    if (!ILoopHeaderInfo.Header)
+      continue;
+
+    Instruction *OldPhi = ILoopHeaderInfo.Original;
+    Instruction *NewPhi = ILoopHeaderInfo.Header;
+
+    // Before replacing uses, collect them first, so that iterator is
+    // not invalidated.
+    SmallVector<Instruction *, 16> AllUses;
+    for (Value::use_iterator UI = OldPhi->use_begin(), UE = OldPhi->use_end();
+         UI != UE; ++UI) {
+      Instruction *U = cast<Instruction>(UI);
+      AllUses.push_back(U);
+    }
+
+    for (SmallVector<Instruction *, 16>::iterator UI = AllUses.begin(), 
+           UE = AllUses.end(); UI != UE; ++UI) {
+      Instruction *U = *UI;
+      BasicBlock *Parent = U->getParent();
+
+      // Used inside original header
+      if (Parent == OrigHeader) {
+        // Do not rename uses inside original header non-phi instructions.
+        PHINode *PU = dyn_cast<PHINode>(U);
+        if (!PU)
+          continue;
+
+        // Do not rename uses inside original header phi nodes, if the
+        // incoming value is for new header.
+        if (PU->getBasicBlockIndex(NewHeader) != -1
+            && PU->getIncomingValueForBlock(NewHeader) == U)
+          continue;
+        
+       U->replaceUsesOfWith(OldPhi, NewPhi);
+       continue;
+      }
+
+      // Used inside loop, but not in original header.
+      if (L->contains(U->getParent())) {
+        if (U != NewPhi)
+          U->replaceUsesOfWith(OldPhi, NewPhi);
+        continue;
+      }
+      
+      // Used inside Exit Block. Since we are in LCSSA form, U must be PHINode.
+      if (U->getParent() == Exit) {
+        assert (isa<PHINode>(U) && "Use in Exit Block that is not PHINode");
+        
+        PHINode *UPhi = cast<PHINode>(U);
+        // UPhi already has one incoming argument from original header. 
+        // Add second incoming argument from new Pre header.
+        UPhi->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
+      } else {
+        // Used outside Exit block. Create a new PHI node from exit block
+        // to receive value from ne new header ane pre header.
+        PHINode *PN = new PHINode(U->getType(), U->getName());
+        PN->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
+        PN->addIncoming(OldPhi, OrigHeader);
+        Exit->getInstList().push_front(PN);
+        U->replaceUsesOfWith(OldPhi, PN);
+      }
+    }
+  }
+  
+  /// Make sure all Exit block PHINodes have required incoming values.
+  updateExitBlock();
+
+  // Update CFG
+
+  // Removing incoming branch from loop preheader to original header.
+  // Now original header is inside the loop.
+  for (BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
+       I != E; ++I) {
+    Instruction *In = I;
+    PHINode *PN = dyn_cast<PHINode>(In);
+    if (!PN)
+      break;
+
+    PN->removeIncomingValue(OrigPreHeader);
+  }
+
+  // Make NewHeader as the new header for the loop.
+  L->moveToHeader(NewHeader);
+
+  preserveCanonicalLoopForm(LPM);
+
+  NumRotated++;
+  return true;
+}
+
+/// Make sure all Exit block PHINodes have required incoming values.
+/// If incoming value is constant or defined outside the loop then
+/// PHINode may not have an entry for original pre-header. 
+void LoopRotate::updateExitBlock() {
+
+  for (BasicBlock::iterator I = Exit->begin(), E = Exit->end();
+       I != E; ++I) {
+
+    PHINode *PN = dyn_cast<PHINode>(I);
+    if (!PN)
+      break;
+
+    // There is already one incoming value from original pre-header block.
+    if (PN->getBasicBlockIndex(OrigPreHeader) != -1)
+      continue;
+
+    const RenameData *ILoopHeaderInfo;
+    Value *V = PN->getIncomingValueForBlock(OrigHeader);
+    if (isa<Instruction>(V) && 
+        (ILoopHeaderInfo = findReplacementData(cast<Instruction>(V)))) {
+      assert(ILoopHeaderInfo->PreHeader && "Missing New Preheader Instruction");
+      PN->addIncoming(ILoopHeaderInfo->PreHeader, OrigPreHeader);
+    } else {
+      PN->addIncoming(V, OrigPreHeader);
+    }
+  }
+}
+
+/// Initialize local data
+void LoopRotate::initialize() {
+  L = NULL;
+  OrigHeader = NULL;
+  OrigPreHeader = NULL;
+  NewHeader = NULL;
+  Exit = NULL;
+
+  LoopHeaderInfo.clear();
+}
+
+/// Return true if this instruction is used by any instructions in the loop that
+/// aren't in original header.
+bool LoopRotate::usedOutsideOriginalHeader(Instruction *In) {
+
+  for (Value::use_iterator UI = In->use_begin(), UE = In->use_end();
+       UI != UE; ++UI) {
+    Instruction *U = cast<Instruction>(UI);
+    if (U->getParent() != OrigHeader) {
+      if (L->contains(U->getParent()))
+        return true;
+    }
+  }
+
+  return false;
+}
+
+/// Find Replacement information for instruction. Return NULL if it is
+/// not available.
+const RenameData *LoopRotate::findReplacementData(Instruction *In) {
+
+  // Since LoopHeaderInfo is small, linear walk is OK.
+  for(unsigned LHI = 0, LHI_E = LoopHeaderInfo.size(); LHI != LHI_E; ++LHI) {
+    const RenameData &ILoopHeaderInfo = LoopHeaderInfo[LHI];
+    if (ILoopHeaderInfo.Original == In)
+      return &ILoopHeaderInfo;
+  }
+  return NULL;
+}
+
+/// After loop rotation, loop pre-header has multiple sucessors.
+/// Insert one forwarding basic block to ensure that loop pre-header
+/// has only one successor.
+void LoopRotate::preserveCanonicalLoopForm(LPPassManager &LPM) {
+
+  // Right now original pre-header has two successors, new header and
+  // exit block. Insert new block between original pre-header and
+  // new header such that loop's new pre-header has only one successor.
+  BasicBlock *NewPreHeader = new BasicBlock("bb.nph", OrigHeader->getParent(), 
+                                NewHeader);
+  LoopInfo &LI = LPM.getAnalysis<LoopInfo>();
+  if (Loop *PL = LI.getLoopFor(OrigPreHeader))
+    PL->addBasicBlockToLoop(NewPreHeader, LI);
+  new BranchInst(NewHeader, NewPreHeader);
+  
+  BranchInst *OrigPH_BI = cast<BranchInst>(OrigPreHeader->getTerminator());
+  if (OrigPH_BI->getSuccessor(0) == NewHeader)
+    OrigPH_BI->setSuccessor(0, NewPreHeader);
+  else {
+    assert (OrigPH_BI->getSuccessor(1) == NewHeader &&
+            "Unexpected original pre-header terminator");
+    OrigPH_BI->setSuccessor(1, NewPreHeader);
+  }
+  
+  for (BasicBlock::iterator I = NewHeader->begin(), E = NewHeader->end();
+       I != E; ++I) {
+    Instruction *In = I;
+    PHINode *PN = dyn_cast<PHINode>(In);
+    if (!PN)
+      break;
+
+    int index = PN->getBasicBlockIndex(OrigPreHeader);
+    assert (index != -1 && "Expected incoming value from Original PreHeader");
+    PN->setIncomingBlock(index, NewPreHeader);
+    assert (PN->getBasicBlockIndex(OrigPreHeader) == -1 && 
+            "Expected only one incoming value from Original PreHeader");
+  }
+
+  if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
+    DT->addNewBlock(NewPreHeader, OrigPreHeader);
+    DT->changeImmediateDominator(L->getHeader(), NewPreHeader);
+    DT->changeImmediateDominator(Exit, OrigPreHeader);
+    for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
+         BI != BE; ++BI) {
+      BasicBlock *B = *BI;
+      if (L->getHeader() != B) {
+        DomTreeNode *Node = DT->getNode(B);
+        if (Node && Node->getBlock() == OrigHeader)
+          DT->changeImmediateDominator(*BI, L->getHeader());
+      }
+    }
+    DT->changeImmediateDominator(OrigHeader, OrigLatch);
+  }
+
+  if(DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
+
+    // New Preheader's dominance frontier is Exit block.
+    DominanceFrontier::DomSetType NewPHSet;
+    NewPHSet.insert(Exit);
+    DF->addBasicBlock(NewPreHeader, NewPHSet);
+
+    // New Header's dominance frontier now includes itself and Exit block
+    DominanceFrontier::iterator HeadI = DF->find(L->getHeader());
+    if (HeadI != DF->end()) {
+      DominanceFrontier::DomSetType & HeaderSet = HeadI->second;
+      HeaderSet.clear();
+      HeaderSet.insert(L->getHeader());
+      HeaderSet.insert(Exit);
+    } else {
+      DominanceFrontier::DomSetType HeaderSet;
+      HeaderSet.insert(L->getHeader());
+      HeaderSet.insert(Exit);
+      DF->addBasicBlock(L->getHeader(), HeaderSet);
+    }
+
+    // Original header (new Loop Latch)'s dominance frontier is Exit.
+    DominanceFrontier::iterator LatchI = DF->find(L->getLoopLatch());
+    if (LatchI != DF->end()) {
+      DominanceFrontier::DomSetType &LatchSet = LatchI->second;
+      LatchSet = LatchI->second;
+      LatchSet.clear();
+      LatchSet.insert(Exit);
+    } else {
+      DominanceFrontier::DomSetType LatchSet;
+      LatchSet.insert(Exit);
+      DF->addBasicBlock(L->getHeader(), LatchSet);
+    }
+
+    // If a loop block dominates new loop latch then its frontier is
+    // new header and Exit.
+    BasicBlock *NewLatch = L->getLoopLatch();
+    DominatorTree *DT = getAnalysisToUpdate<DominatorTree>();
+    for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
+         BI != BE; ++BI) {
+      BasicBlock *B = *BI;
+      if (DT->dominates(B, NewLatch)) {
+        DominanceFrontier::iterator BDFI = DF->find(B);
+        if (BDFI != DF->end()) {
+          DominanceFrontier::DomSetType &BSet = BDFI->second;
+          BSet = BDFI->second;
+          BSet.clear();
+          BSet.insert(L->getHeader());
+          BSet.insert(Exit);
+        } else {
+          DominanceFrontier::DomSetType BSet;
+          BSet.insert(L->getHeader());
+          BSet.insert(Exit);
+          DF->addBasicBlock(B, BSet);
+        }
+      }
+    }
+  }
+
+  // Preserve canonical loop form, which means Exit block should
+  // have only one predecessor.
+  BasicBlock *NExit = SplitEdge(L->getLoopLatch(), Exit, this);
+
+  // Preserve LCSSA.
+  BasicBlock::iterator I = Exit->begin(), E = Exit->end();
+  PHINode *PN = NULL;
+  for (; (PN = dyn_cast<PHINode>(I)); ++I) {
+    PHINode *NewPN = new PHINode(PN->getType(), PN->getName());
+    unsigned N = PN->getNumIncomingValues();
+    for (unsigned index = 0; index < N; ++index)
+      if (PN->getIncomingBlock(index) == NExit) {
+        NewPN->addIncoming(PN->getIncomingValue(index), L->getLoopLatch());
+        PN->setIncomingValue(index, NewPN);
+        PN->setIncomingBlock(index, NExit);
+        NExit->getInstList().push_front(NewPN);
+      }
+  }
+
+  assert (NewHeader && L->getHeader() == NewHeader 
+          && "Invalid loop header after loop rotation");
+  assert (NewPreHeader && L->getLoopPreheader() == NewPreHeader
+          && "Invalid loop preheader after loop rotation");
+  assert (L->getLoopLatch() 
+          && "Invalid loop latch after loop rotation");
+
+}