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Add loop rotation pass. 

llvm-svn: 35714
This commit is contained in:
Devang Patel 2007-04-07 01:25:15 +00:00
parent 0f1509511e
commit f42389ffe5
2 changed files with 438 additions and 0 deletions
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7
llvm/include/llvm/Transforms/Scalar.h
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@ -135,6 +135,13 @@ LoopPass *createLoopUnswitchPass();
//
LoopPass *createLoopUnrollPass();
//===----------------------------------------------------------------------===//
//
// LoopRotate - This pass is a simple loop rotating pass.
//
LoopPass *createLoopRotatePass();
//===----------------------------------------------------------------------===//
//
// PromoteMemoryToRegister - This pass is used to promote memory references to

431
llvm/lib/Transforms/Scalar/LoopRotation.cpp Normal file
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@ -0,0 +1,431 @@
//===- 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-rotation"
#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/Transforms/Utils/Local.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/SmallVector.h"
#include <map>
using namespace llvm;
#define MAX_HEADER_SIZE 16
STATISTIC(NumRotated, "Number of loops rotated");
namespace {
cl::opt<unsigned>
RotateThreshold("rotate-threshold", cl::init(200), cl::Hidden,
cl::desc("The cut-off point for loop rotating"));
class VISIBILITY_HIDDEN InsnReplacementData {
public:
InsnReplacementData(Instruction *O, Instruction *P, Instruction *H)
: Original(O), PreHeader(P), Header(H) {}
public:
Instruction *Original; // Original instruction
Instruction *PreHeader; // New pre-header replacement
Instruction *Header; // New header replacement
};
class VISIBILITY_HIDDEN LoopRotate : public LoopPass {
public:
bool runOnLoop(Loop *L, LPPassManager &LPM);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(LCSSAID);
AU.addPreservedID(LCSSAID);
//AU.addRequired<LoopInfo>();
//AU.addPreserved<LoopInfo>();
}
// 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 new 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.
InsnReplacementData *findReplacementData(Instruction *I);
private:
Loop *L;
BasicBlock *OrigHeader;
BasicBlock *OrigPreHeader;
BasicBlock *OrigLatch;
BasicBlock *NewHeader;
BasicBlock *NewPreHeader;
BasicBlock *Exit;
SmallVector<InsnReplacementData, MAX_HEADER_SIZE> RD;
};
RegisterPass<LoopRotate> X ("loop-rotate", "Rotate Loops");
}
LoopPass *llvm::createLoopRotatePass() { return new LoopRotate(); }
bool LoopRotate::runOnLoop(Loop *Lp, LPPassManager &LPM) {
bool RotatedOneLoop = false;
initialize();
// One loop can be rotated multiple times.
while (rotateLoop(Lp,LPM)) {
RotatedOneLoop = true;
initialize();
}
return RotatedOneLoop;
}
bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {
L = Lp;
if ( NumRotated >= RotateThreshold)
return false;
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;
if (!OrigHeader || !OrigLatch || !OrigPreHeader)
return false;
// 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;
std::vector<BasicBlock *> ExitBlocks;
L->getExitBlocks(ExitBlocks);
if (ExitBlocks.size() > 1)
return false;
// Find new Loop header. NewHeader is a Header's one and only successor
// that is inside loop. Header's all other successors are out side the
// loop. Otherwise loop is not suitable for rotation.
for (unsigned index = 0; index < BI->getNumSuccessors(); ++index) {
BasicBlock *S = BI->getSuccessor(index);
if (L->contains(S)) {
if (!NewHeader)
NewHeader = S;
else
// Loop Header has two successors inside loop. This loop is
// not suitable for rotation.
return false;
} else {
if (!Exit)
Exit = S;
else
// Loop has multiple exits.
return false;
}
}
assert (NewHeader && "Unable to determine new loop header");
// 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.
// Copy Prepare PHI nodes and other instructions from original header
// into new pre-header. Unlike original header, new pre-header is
// not a member of loop. New pre-header has only one predecessor,
// that is original loop pre-header.
//
// 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 new 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 new loop pre-header (which is a clone of original header definition).
NewPreHeader = new BasicBlock("bb.nph", OrigHeader->getParent(), OrigHeader);
for (BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
I != E; ++I) {
Instruction *In = I;
if (PHINode *PN = dyn_cast<PHINode>(I)) {
// Create new PHI node with one value incoming from OrigPreHeader.
// NewPreHeader has only one predecessor, OrigPreHeader.
PHINode *NPH = new PHINode(In->getType(), In->getName());
NPH->addIncoming(PN->getIncomingValueForBlock(OrigPreHeader),
OrigPreHeader);
NewPreHeader->getInstList().push_back(NPH);
// Create new PHI node with two incoming values for NewHeader.
// One incoming value is from OrigLatch (through OrigHeader) and
// second incoming value is from NewPreHeader.
PHINode *NH = new PHINode(In->getType(), In->getName());
NH->addIncoming(PN->getIncomingValueForBlock(OrigLatch), OrigHeader);
NH->addIncoming(NPH, NewPreHeader);
NewHeader->getInstList().push_front(NH);
RD.push_back(InsnReplacementData(In, NPH, NH));
} else {
// This is not a PHI instruction. Insert its clone into NewPreHeader.
// 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());
NewPreHeader->getInstList().push_back(C);
// 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, NewPreHeader);
NewHeader->getInstList().push_front(PN);
NewHeaderReplacement = PN;
}
RD.push_back(InsnReplacementData(In, C, NewHeaderReplacement));
}
}
// Update new pre-header.
// Rename values that are defined in original header to reflects values
// defined in new pre-header.
for (SmallVector<InsnReplacementData, MAX_HEADER_SIZE>::iterator
I = RD.begin(), E = RD.end(); I != E; ++I) {
InsnReplacementData IRD = (*I);
Instruction *In = IRD.Original;
Instruction *C = IRD.PreHeader;
if (C->getParent() != NewPreHeader)
continue;
// PHINodes uses value from pre-header predecessors.
if (isa<PHINode>(In))
continue;
for (unsigned opi = 0; opi < In->getNumOperands(); ++opi) {
if (Instruction *OpPhi = dyn_cast<PHINode>(In->getOperand(opi))) {
if (InsnReplacementData *D = findReplacementData(OpPhi))
C->setOperand(opi, D->PreHeader);
}
else if (Instruction *OpInsn =
dyn_cast<Instruction>(In->getOperand(opi))) {
if (InsnReplacementData *D = findReplacementData(OpInsn))
C->setOperand(opi, D->PreHeader);
}
}
}
// Rename uses of original header instructions to reflect their new
// definitions (either from new 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 new 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 (SmallVector<InsnReplacementData, MAX_HEADER_SIZE>::iterator
I = RD.begin(), E = RD.end(); I != E; ++I) {
InsnReplacementData IRD = (*I);
if (!IRD.Header)
continue;
Instruction *OldPhi = IRD.Original;
Instruction *NewPhi = IRD.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.
if (!isa<PHINode>(U))
continue;
PHINode *PU = dyn_cast<PHINode>(U);
// 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.
assert ( U->getParent() == Exit && "Need to propagate new PHI into Exit blocks");
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(IRD.PreHeader, NewPreHeader);
}
}
/// 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.
OrigHeader->removePredecessor(OrigPreHeader);
// Establish NewPreHeader as loop preheader. Add unconditional branch
// from original loop pre-header to new loop pre-header. Add NewPreHEader
// in loop nest.
BranchInst *PH_BI = cast<BranchInst>(OrigPreHeader->getTerminator());
PH_BI->setSuccessor(0, NewPreHeader);
LoopInfo &LI = LPM.getAnalysis<LoopInfo>();
if (Loop *PL = LI.getLoopFor(OrigPreHeader))
PL->addBasicBlockToLoop(NewPreHeader, LI);
// Make NewHeader as the new header for the loop.
L->moveToHeader(NewHeader);
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 new pre-header.
void LoopRotate::updateExitBlock() {
for (BasicBlock::iterator I = Exit->begin(), E = Exit->end();
I != E; ++I) {
if (!isa<PHINode>(I))
break;
PHINode *PN = dyn_cast<PHINode>(I);
if (PN->getBasicBlockIndex(NewPreHeader) == -1) {
Value *V = PN->getIncomingValueForBlock(OrigHeader);
if (isa<Constant>(V))
PN->addIncoming(V, NewPreHeader);
else {
InsnReplacementData *IRD = findReplacementData(cast<Instruction>(V));
assert (IRD && IRD->PreHeader && "Missing New Preheader Instruction");
PN->addIncoming(IRD->PreHeader, NewPreHeader);
}
}
}
}
/// Initialize local data
void LoopRotate::initialize() {
L = NULL;
OrigHeader = NULL;
OrigPreHeader = NULL;
NewHeader = NULL;
NewPreHeader = NULL;
Exit = NULL;
RD.clear();
}
/// Return true if this instruction is used outside 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.
InsnReplacementData *LoopRotate::findReplacementData(Instruction *In) {
// Since RD is small, linear walk is OK.
for (SmallVector<InsnReplacementData, MAX_HEADER_SIZE>::iterator
I = RD.begin(), E = RD.end(); I != E; ++I)
if ((*I).Original == In)
return &(*I);
return NULL;
}