#define DEBUG_TYPE "loop-rotate"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Function.h"
#include "llvm/IntrinsicInst.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/Transforms/Utils/SSAUpdater.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 LoopRotate : public LoopPass {
public:
static char ID; LoopRotate() : LoopPass(&ID) {}
bool runOnLoop(Loop *L, LPPassManager &LPM);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(LoopSimplifyID);
AU.addPreservedID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addPreservedID(LCSSAID);
AU.addPreserved<ScalarEvolution>();
AU.addRequired<LoopInfo>();
AU.addPreserved<LoopInfo>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<DominanceFrontier>();
}
bool rotateLoop(Loop *L, LPPassManager &LPM);
void initialize();
void preserveCanonicalLoopForm(LPPassManager &LPM);
private:
Loop *L;
BasicBlock *OrigHeader;
BasicBlock *OrigPreHeader;
BasicBlock *OrigLatch;
BasicBlock *NewHeader;
BasicBlock *Exit;
LPPassManager *LPM_Ptr;
};
}
char LoopRotate::ID = 0;
static RegisterPass<LoopRotate> X("loop-rotate", "Rotate Loops");
Pass *llvm::createLoopRotatePass() { return new LoopRotate(); }
bool LoopRotate::runOnLoop(Loop *Lp, LPPassManager &LPM) {
bool RotatedOneLoop = false;
initialize();
LPM_Ptr = &LPM;
while (rotateLoop(Lp,LPM)) {
RotatedOneLoop = true;
initialize();
}
return RotatedOneLoop;
}
bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {
L = Lp;
OrigPreHeader = L->getLoopPreheader();
if (!OrigPreHeader) return false;
OrigLatch = L->getLoopLatch();
if (!OrigLatch) return false;
OrigHeader = L->getHeader();
if (L->getBlocks().size() == 1)
return false;
if (!L->isLoopExiting(OrigHeader))
return false;
BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
if (!BI)
return false;
assert(BI->isConditional() && "Branch Instruction is not conditional");
SmallVector<BasicBlock*, 8> ExitBlocks;
L->getExitBlocks(ExitBlocks);
if (ExitBlocks.size() > 1)
return false;
unsigned Size = 0;
for (BasicBlock::const_iterator OI = OrigHeader->begin(),
OE = OrigHeader->end(); OI != OE; ++OI) {
if (isa<PHINode>(OI))
continue; if (isa<DbgInfoIntrinsic>(OI))
continue; Size++;
}
if (Size > MAX_HEADER_SIZE)
return false;
if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
SE->forgetLoop(L);
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");
assert(NewHeader->getSinglePredecessor() &&
"New header doesn't have one pred!");
FoldSingleEntryPHINodes(NewHeader);
BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
DenseMap<const Value *, Value *> ValueMap;
for (; PHINode *PN = dyn_cast<PHINode>(I); ++I)
ValueMap[PN] = PN->getIncomingValue(PN->getBasicBlockIndex(OrigPreHeader));
TerminatorInst *LoopEntryBranch = OrigPreHeader->getTerminator();
for (; I != E; ++I) {
Instruction *C = I->clone();
C->setName(I->getName());
C->insertBefore(LoopEntryBranch);
ValueMap[I] = C;
}
TerminatorInst *TI = OrigHeader->getTerminator();
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
for (BasicBlock::iterator BI = TI->getSuccessor(i)->begin();
PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreHeader);
LoopEntryBranch->eraseFromParent();
for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreHeader));
SSAUpdater SSA;
for (I = OrigHeader->begin(); I != E; ++I) {
Value *OrigHeaderVal = I;
Value *OrigPreHeaderVal = ValueMap[OrigHeaderVal];
SSA.Initialize(OrigHeaderVal);
SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
SSA.AddAvailableValue(OrigPreHeader, OrigPreHeaderVal);
for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
UE = OrigHeaderVal->use_end(); UI != UE; ) {
Use &U = UI.getUse();
++UI;
Instruction *UserInst = cast<Instruction>(U.getUser());
if (!isa<PHINode>(UserInst)) {
BasicBlock *UserBB = UserInst->getParent();
if (UserBB == OrigHeader)
continue;
if (UserBB == OrigPreHeader) {
U = OrigPreHeaderVal;
continue;
}
}
SSA.RewriteUse(U);
}
}
L->moveToHeader(NewHeader);
preserveCanonicalLoopForm(LPM);
NumRotated++;
return true;
}
void LoopRotate::initialize() {
L = NULL;
OrigHeader = NULL;
OrigPreHeader = NULL;
NewHeader = NULL;
Exit = NULL;
}
void LoopRotate::preserveCanonicalLoopForm(LPPassManager &LPM) {
BasicBlock *NewPreHeader = BasicBlock::Create(OrigHeader->getContext(),
"bb.nph",
OrigHeader->getParent(),
NewHeader);
LoopInfo &LI = 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);
}
PHINode *PN;
for (BasicBlock::iterator I = NewHeader->begin();
(PN = dyn_cast<PHINode>(I)); ++I) {
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 = getAnalysisIfAvailable<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 = getAnalysisIfAvailable<DominanceFrontier>()) {
DominanceFrontier::DomSetType NewPHSet;
NewPHSet.insert(Exit);
DF->addBasicBlock(NewPreHeader, NewPHSet);
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);
}
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);
}
BasicBlock *NewLatch = L->getLoopLatch();
assert(NewLatch == OrigHeader && "NewLatch is inequal to OrigHeader");
if (DominatorTree *DT = getAnalysisIfAvailable<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.erase(NewLatch);
BSet.insert(L->getHeader());
BSet.insert(Exit);
} else {
DominanceFrontier::DomSetType BSet;
BSet.insert(L->getHeader());
BSet.insert(Exit);
DF->addBasicBlock(B, BSet);
}
}
}
}
}
SplitEdge(L->getLoopLatch(), Exit, this);
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");
}