llvm-6502/lib/Transforms/Scalar/LoopUnroll.cpp
Chris Lattner decc86db0c Fix a bug where we could corrupt a parent loop's header info if we unrolled
a nested loop.  This fixes Transforms/LoopUnroll/2005-03-06-BadLoopInfoUpdate.ll
and PR532


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20493 91177308-0d34-0410-b5e6-96231b3b80d8
2005-03-06 20:57:32 +00:00

314 lines
11 KiB
C++

//===-- LoopUnroll.cpp - Loop unroller pass -------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass implements a simple loop unroller. It works best when loops have
// been canonicalized by the -indvars pass, allowing it to determine the trip
// counts of loops easily.
//
// This pass is currently extremely limited. It only currently only unrolls
// single basic block loops that execute a constant number of times.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loop-unroll"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Transforms/Utils/Cloning.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/STLExtras.h"
#include "llvm/IntrinsicInst.h"
#include <cstdio>
#include <set>
#include <algorithm>
using namespace llvm;
namespace {
Statistic<> NumUnrolled("loop-unroll", "Number of loops completely unrolled");
cl::opt<unsigned>
UnrollThreshold("unroll-threshold", cl::init(100), cl::Hidden,
cl::desc("The cut-off point for loop unrolling"));
class LoopUnroll : public FunctionPass {
LoopInfo *LI; // The current loop information
public:
virtual bool runOnFunction(Function &F);
bool visitLoop(Loop *L);
/// This transformation requires natural loop information & requires that
/// loop preheaders be inserted into the CFG...
///
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(LoopSimplifyID);
AU.addRequired<LoopInfo>();
AU.addPreserved<LoopInfo>();
}
};
RegisterOpt<LoopUnroll> X("loop-unroll", "Unroll loops");
}
FunctionPass *llvm::createLoopUnrollPass() { return new LoopUnroll(); }
bool LoopUnroll::runOnFunction(Function &F) {
bool Changed = false;
LI = &getAnalysis<LoopInfo>();
// Transform all the top-level loops. Copy the loop list so that the child
// can update the loop tree if it needs to delete the loop.
std::vector<Loop*> SubLoops(LI->begin(), LI->end());
for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
Changed |= visitLoop(SubLoops[i]);
return Changed;
}
/// ApproximateLoopSize - Approximate the size of the loop after it has been
/// unrolled.
static unsigned ApproximateLoopSize(const Loop *L) {
unsigned Size = 0;
for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i) {
BasicBlock *BB = L->getBlocks()[i];
Instruction *Term = BB->getTerminator();
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
if (isa<PHINode>(I) && BB == L->getHeader()) {
// Ignore PHI nodes in the header.
} else if (I->hasOneUse() && I->use_back() == Term) {
// Ignore instructions only used by the loop terminator.
} else if (DbgInfoIntrinsic *DbgI = dyn_cast<DbgInfoIntrinsic>(I)) {
// Ignore debug instructions
} else {
++Size;
}
// TODO: Ignore expressions derived from PHI and constants if inval of phi
// is a constant, or if operation is associative. This will get induction
// variables.
}
}
return Size;
}
// RemapInstruction - Convert the instruction operands from referencing the
// current values into those specified by ValueMap.
//
static inline void RemapInstruction(Instruction *I,
std::map<const Value *, Value*> &ValueMap) {
for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
Value *Op = I->getOperand(op);
std::map<const Value *, Value*>::iterator It = ValueMap.find(Op);
if (It != ValueMap.end()) Op = It->second;
I->setOperand(op, Op);
}
}
bool LoopUnroll::visitLoop(Loop *L) {
bool Changed = false;
// Recurse through all subloops before we process this loop. Copy the loop
// list so that the child can update the loop tree if it needs to delete the
// loop.
std::vector<Loop*> SubLoops(L->begin(), L->end());
for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
Changed |= visitLoop(SubLoops[i]);
// We only handle single basic block loops right now.
if (L->getBlocks().size() != 1)
return Changed;
BasicBlock *BB = L->getHeader();
BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
if (BI == 0) return Changed; // Must end in a conditional branch
ConstantInt *TripCountC = dyn_cast_or_null<ConstantInt>(L->getTripCount());
if (!TripCountC) return Changed; // Must have constant trip count!
uint64_t TripCountFull = TripCountC->getRawValue();
if (TripCountFull != TripCountC->getRawValue() || TripCountFull == 0)
return Changed; // More than 2^32 iterations???
unsigned LoopSize = ApproximateLoopSize(L);
DEBUG(std::cerr << "Loop Unroll: F[" << BB->getParent()->getName()
<< "] Loop %" << BB->getName() << " Loop Size = " << LoopSize
<< " Trip Count = " << TripCountFull << " - ");
uint64_t Size = (uint64_t)LoopSize*TripCountFull;
if (Size > UnrollThreshold) {
DEBUG(std::cerr << "TOO LARGE: " << Size << ">" << UnrollThreshold << "\n");
return Changed;
}
DEBUG(std::cerr << "UNROLLING!\n");
unsigned TripCount = (unsigned)TripCountFull;
BasicBlock *LoopExit = BI->getSuccessor(L->contains(BI->getSuccessor(0)));
// Create a new basic block to temporarily hold all of the cloned code.
BasicBlock *NewBlock = new BasicBlock();
// For the first iteration of the loop, we should use the precloned values for
// PHI nodes. Insert associations now.
std::map<const Value*, Value*> LastValueMap;
std::vector<PHINode*> OrigPHINode;
for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
OrigPHINode.push_back(PN);
if (Instruction *I =dyn_cast<Instruction>(PN->getIncomingValueForBlock(BB)))
if (I->getParent() == BB)
LastValueMap[I] = I;
}
// Remove the exit branch from the loop
BB->getInstList().erase(BI);
assert(TripCount != 0 && "Trip count of 0 is impossible!");
for (unsigned It = 1; It != TripCount; ++It) {
char SuffixBuffer[100];
sprintf(SuffixBuffer, ".%d", It);
std::map<const Value*, Value*> ValueMap;
BasicBlock *New = CloneBasicBlock(BB, ValueMap, SuffixBuffer);
// Loop over all of the PHI nodes in the block, changing them to use the
// incoming values from the previous block.
for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
PHINode *NewPHI = cast<PHINode>(ValueMap[OrigPHINode[i]]);
Value *InVal = NewPHI->getIncomingValueForBlock(BB);
if (Instruction *InValI = dyn_cast<Instruction>(InVal))
if (InValI->getParent() == BB)
InVal = LastValueMap[InValI];
ValueMap[OrigPHINode[i]] = InVal;
New->getInstList().erase(NewPHI);
}
for (BasicBlock::iterator I = New->begin(), E = New->end(); I != E; ++I)
RemapInstruction(I, ValueMap);
// Now that all of the instructions are remapped, splice them into the end
// of the NewBlock.
NewBlock->getInstList().splice(NewBlock->end(), New->getInstList());
delete New;
// LastValue map now contains values from this iteration.
std::swap(LastValueMap, ValueMap);
}
// If there was more than one iteration, replace any uses of values computed
// in the loop with values computed during the last iteration of the loop.
if (TripCount != 1) {
std::set<User*> Users;
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
Users.insert(I->use_begin(), I->use_end());
// We don't want to reprocess entries with PHI nodes in them. For this
// reason, we look at each operand of each user exactly once, performing the
// stubstitution exactly once.
for (std::set<User*>::iterator UI = Users.begin(), E = Users.end(); UI != E;
++UI) {
Instruction *I = cast<Instruction>(*UI);
if (I->getParent() != BB && I->getParent() != NewBlock)
RemapInstruction(I, LastValueMap);
}
}
// Now that we cloned the block as many times as we needed, stitch the new
// code into the original block and delete the temporary block.
BB->getInstList().splice(BB->end(), NewBlock->getInstList());
delete NewBlock;
// Now loop over the PHI nodes in the original block, setting them to their
// incoming values.
BasicBlock *Preheader = L->getLoopPreheader();
for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) {
PHINode *PN = OrigPHINode[i];
PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader));
BB->getInstList().erase(PN);
}
// Finally, add an unconditional branch to the block to continue into the exit
// block.
new BranchInst(LoopExit, BB);
// At this point, the code is well formed. We now do a quick sweep over the
// inserted code, doing constant propagation and dead code elimination as we
// go.
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
Instruction *Inst = I++;
if (isInstructionTriviallyDead(Inst))
BB->getInstList().erase(Inst);
else if (Constant *C = ConstantFoldInstruction(Inst)) {
Inst->replaceAllUsesWith(C);
BB->getInstList().erase(Inst);
}
}
// Update the loop information for this loop.
Loop *Parent = L->getParentLoop();
// Move all of the basic blocks in the loop into the parent loop.
LI->changeLoopFor(BB, Parent);
// Remove the loop from the parent.
if (Parent)
delete Parent->removeChildLoop(std::find(Parent->begin(), Parent->end(),L));
else
delete LI->removeLoop(std::find(LI->begin(), LI->end(), L));
// FIXME: Should update dominator analyses
// Now that everything is up-to-date that will be, we fold the loop block into
// the preheader and exit block, updating our analyses as we go.
LoopExit->getInstList().splice(LoopExit->begin(), BB->getInstList(),
BB->getInstList().begin(),
prior(BB->getInstList().end()));
LoopExit->getInstList().splice(LoopExit->begin(), Preheader->getInstList(),
Preheader->getInstList().begin(),
prior(Preheader->getInstList().end()));
// Make all other blocks in the program branch to LoopExit now instead of
// Preheader.
Preheader->replaceAllUsesWith(LoopExit);
Function *F = LoopExit->getParent();
if (Parent) {
// Otherwise, if this is a sub-loop, and the preheader was the loop header
// of the parent loop, move the exit block to be the new parent loop header.
if (Parent->getHeader() == Preheader) {
assert(Parent->contains(LoopExit) &&
"Exit block isn't contained in parent?");
Parent->moveToHeader(LoopExit);
}
} else {
// If the preheader was the entry block of this function, move the exit
// block to be the new entry of the function.
if (Preheader == &F->front())
F->getBasicBlockList().splice(F->begin(),
F->getBasicBlockList(), LoopExit);
}
// Remove BB and LoopExit from our analyses.
LI->removeBlock(Preheader);
LI->removeBlock(BB);
// Actually delete the blocks now.
F->getBasicBlockList().erase(Preheader);
F->getBasicBlockList().erase(BB);
++NumUnrolled;
return true;
}