llvm-6502/lib/Transforms/Scalar/LoopRotation.cpp
Dan Gohman 844731a7f1 Clean up the use of static and anonymous namespaces. This turned up
several things that were neither in an anonymous namespace nor static
but not intended to be global.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51017 91177308-0d34-0410-b5e6-96231b3b80d8
2008-05-13 00:00:25 +00:00

606 lines
21 KiB
C++

//===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file 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(LoopSimplifyID);
AU.addPreservedID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addPreservedID(LCSSAID);
AU.addPreserved<ScalarEvolution>();
AU.addPreserved<LoopInfo>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<DominanceFrontier>();
}
// 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;
static 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 conditional");
// 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.
SmallVector<BasicBlock*, 8> 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 = PHINode::Create(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)) {
// FIXME: remove this when we have first-class aggregates.
if (isa<StructType>(In->getType())) {
// Can't create PHI nodes for this type. If there are any getResults
// not defined in this block, move them back to this block. PHI
// nodes will be created for all getResults later.
BasicBlock::iterator InsertPoint;
if (InvokeInst *II = dyn_cast<InvokeInst>(In)) {
InsertPoint = II->getNormalDest()->begin();
while (isa<PHINode>(InsertPoint))
++InsertPoint;
} else {
InsertPoint = I; // call
++InsertPoint;
}
for (Value::use_iterator UI = In->use_begin(), UE = In->use_end();
UI != UE; ++UI) {
GetResultInst *InGR = cast<GetResultInst>(UI);
if (InGR->getParent() != OrigHeader) {
// Move InGR to immediately after the call or in the normal dest of
// the invoke. It will be picked up, cloned and PHI'd on the next
// iteration.
InGR->moveBefore(InsertPoint);
}
}
} else {
PHINode *PN = PHINode::Create(In->getType(), In->getName());
PN->addIncoming(In, OrigHeader);
PN->addIncoming(C, OrigPreHeader);
NewHeader->getInstList().push_front(PN);
NewHeaderReplacement = PN;
}
}
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 = PHINode::Create(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 = BasicBlock::Create("bb.nph", OrigHeader->getParent(),
NewHeader);
LoopInfo &LI = LPM.getAnalysis<LoopInfo>();
if (Loop *PL = LI.getLoopFor(OrigPreHeader))
PL->addBasicBlockToLoop(NewPreHeader, LI.getBase());
BranchInst::Create(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 = PHINode::Create(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");
}