llvm-6502/lib/Analysis/LoopInfo.cpp
Dan Gohman f17e9511f1 Factor out the predicate code for loopsimplify form exit blocks into
a separate helper function.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86159 91177308-0d34-0410-b5e6-96231b3b80d8
2009-11-05 19:21:41 +00:00

419 lines
15 KiB
C++

//===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the LoopInfo class that is used to identify natural loops
// and determine the loop depth of various nodes of the CFG. Note that the
// loops identified may actually be several natural loops that share the same
// header node... not just a single natural loop.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include <algorithm>
using namespace llvm;
// Always verify loopinfo if expensive checking is enabled.
#ifdef XDEBUG
bool VerifyLoopInfo = true;
#else
bool VerifyLoopInfo = false;
#endif
static cl::opt<bool,true>
VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo),
cl::desc("Verify loop info (time consuming)"));
char LoopInfo::ID = 0;
static RegisterPass<LoopInfo>
X("loops", "Natural Loop Information", true, true);
//===----------------------------------------------------------------------===//
// Loop implementation
//
/// isLoopInvariant - Return true if the specified value is loop invariant
///
bool Loop::isLoopInvariant(Value *V) const {
if (Instruction *I = dyn_cast<Instruction>(V))
return isLoopInvariant(I);
return true; // All non-instructions are loop invariant
}
/// isLoopInvariant - Return true if the specified instruction is
/// loop-invariant.
///
bool Loop::isLoopInvariant(Instruction *I) const {
return !contains(I->getParent());
}
/// makeLoopInvariant - If the given value is an instruciton inside of the
/// loop and it can be hoisted, do so to make it trivially loop-invariant.
/// Return true if the value after any hoisting is loop invariant. This
/// function can be used as a slightly more aggressive replacement for
/// isLoopInvariant.
///
/// If InsertPt is specified, it is the point to hoist instructions to.
/// If null, the terminator of the loop preheader is used.
///
bool Loop::makeLoopInvariant(Value *V, bool &Changed,
Instruction *InsertPt) const {
if (Instruction *I = dyn_cast<Instruction>(V))
return makeLoopInvariant(I, Changed, InsertPt);
return true; // All non-instructions are loop-invariant.
}
/// makeLoopInvariant - If the given instruction is inside of the
/// loop and it can be hoisted, do so to make it trivially loop-invariant.
/// Return true if the instruction after any hoisting is loop invariant. This
/// function can be used as a slightly more aggressive replacement for
/// isLoopInvariant.
///
/// If InsertPt is specified, it is the point to hoist instructions to.
/// If null, the terminator of the loop preheader is used.
///
bool Loop::makeLoopInvariant(Instruction *I, bool &Changed,
Instruction *InsertPt) const {
// Test if the value is already loop-invariant.
if (isLoopInvariant(I))
return true;
if (!I->isSafeToSpeculativelyExecute())
return false;
if (I->mayReadFromMemory())
return false;
// Determine the insertion point, unless one was given.
if (!InsertPt) {
BasicBlock *Preheader = getLoopPreheader();
// Without a preheader, hoisting is not feasible.
if (!Preheader)
return false;
InsertPt = Preheader->getTerminator();
}
// Don't hoist instructions with loop-variant operands.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (!makeLoopInvariant(I->getOperand(i), Changed, InsertPt))
return false;
// Hoist.
I->moveBefore(InsertPt);
Changed = true;
return true;
}
/// getCanonicalInductionVariable - Check to see if the loop has a canonical
/// induction variable: an integer recurrence that starts at 0 and increments
/// by one each time through the loop. If so, return the phi node that
/// corresponds to it.
///
/// The IndVarSimplify pass transforms loops to have a canonical induction
/// variable.
///
PHINode *Loop::getCanonicalInductionVariable() const {
BasicBlock *H = getHeader();
BasicBlock *Incoming = 0, *Backedge = 0;
typedef GraphTraits<Inverse<BasicBlock*> > InvBlockTraits;
InvBlockTraits::ChildIteratorType PI = InvBlockTraits::child_begin(H);
assert(PI != InvBlockTraits::child_end(H) &&
"Loop must have at least one backedge!");
Backedge = *PI++;
if (PI == InvBlockTraits::child_end(H)) return 0; // dead loop
Incoming = *PI++;
if (PI != InvBlockTraits::child_end(H)) return 0; // multiple backedges?
if (contains(Incoming)) {
if (contains(Backedge))
return 0;
std::swap(Incoming, Backedge);
} else if (!contains(Backedge))
return 0;
// Loop over all of the PHI nodes, looking for a canonical indvar.
for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
if (ConstantInt *CI =
dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming)))
if (CI->isNullValue())
if (Instruction *Inc =
dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
if (Inc->getOpcode() == Instruction::Add &&
Inc->getOperand(0) == PN)
if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
if (CI->equalsInt(1))
return PN;
}
return 0;
}
/// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
/// the canonical induction variable value for the "next" iteration of the
/// loop. This always succeeds if getCanonicalInductionVariable succeeds.
///
Instruction *Loop::getCanonicalInductionVariableIncrement() const {
if (PHINode *PN = getCanonicalInductionVariable()) {
bool P1InLoop = contains(PN->getIncomingBlock(1));
return cast<Instruction>(PN->getIncomingValue(P1InLoop));
}
return 0;
}
/// getTripCount - Return a loop-invariant LLVM value indicating the number of
/// times the loop will be executed. Note that this means that the backedge
/// of the loop executes N-1 times. If the trip-count cannot be determined,
/// this returns null.
///
/// The IndVarSimplify pass transforms loops to have a form that this
/// function easily understands.
///
Value *Loop::getTripCount() const {
// Canonical loops will end with a 'cmp ne I, V', where I is the incremented
// canonical induction variable and V is the trip count of the loop.
Instruction *Inc = getCanonicalInductionVariableIncrement();
if (Inc == 0) return 0;
PHINode *IV = cast<PHINode>(Inc->getOperand(0));
BasicBlock *BackedgeBlock =
IV->getIncomingBlock(contains(IV->getIncomingBlock(1)));
if (BranchInst *BI = dyn_cast<BranchInst>(BackedgeBlock->getTerminator()))
if (BI->isConditional()) {
if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
if (ICI->getOperand(0) == Inc) {
if (BI->getSuccessor(0) == getHeader()) {
if (ICI->getPredicate() == ICmpInst::ICMP_NE)
return ICI->getOperand(1);
} else if (ICI->getPredicate() == ICmpInst::ICMP_EQ) {
return ICI->getOperand(1);
}
}
}
}
return 0;
}
/// getSmallConstantTripCount - Returns the trip count of this loop as a
/// normal unsigned value, if possible. Returns 0 if the trip count is unknown
/// of not constant. Will also return 0 if the trip count is very large
/// (>= 2^32)
unsigned Loop::getSmallConstantTripCount() const {
Value* TripCount = this->getTripCount();
if (TripCount) {
if (ConstantInt *TripCountC = dyn_cast<ConstantInt>(TripCount)) {
// Guard against huge trip counts.
if (TripCountC->getValue().getActiveBits() <= 32) {
return (unsigned)TripCountC->getZExtValue();
}
}
}
return 0;
}
/// getSmallConstantTripMultiple - Returns the largest constant divisor of the
/// trip count of this loop as a normal unsigned value, if possible. This
/// means that the actual trip count is always a multiple of the returned
/// value (don't forget the trip count could very well be zero as well!).
///
/// Returns 1 if the trip count is unknown or not guaranteed to be the
/// multiple of a constant (which is also the case if the trip count is simply
/// constant, use getSmallConstantTripCount for that case), Will also return 1
/// if the trip count is very large (>= 2^32).
unsigned Loop::getSmallConstantTripMultiple() const {
Value* TripCount = this->getTripCount();
// This will hold the ConstantInt result, if any
ConstantInt *Result = NULL;
if (TripCount) {
// See if the trip count is constant itself
Result = dyn_cast<ConstantInt>(TripCount);
// if not, see if it is a multiplication
if (!Result)
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TripCount)) {
switch (BO->getOpcode()) {
case BinaryOperator::Mul:
Result = dyn_cast<ConstantInt>(BO->getOperand(1));
break;
default:
break;
}
}
}
// Guard against huge trip counts.
if (Result && Result->getValue().getActiveBits() <= 32) {
return (unsigned)Result->getZExtValue();
} else {
return 1;
}
}
/// isLCSSAForm - Return true if the Loop is in LCSSA form
bool Loop::isLCSSAForm() const {
// Sort the blocks vector so that we can use binary search to do quick
// lookups.
SmallPtrSet<BasicBlock *, 16> LoopBBs(block_begin(), block_end());
for (block_iterator BI = block_begin(), E = block_end(); BI != E; ++BI) {
BasicBlock *BB = *BI;
for (BasicBlock ::iterator I = BB->begin(), E = BB->end(); I != E;++I)
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
++UI) {
BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
if (PHINode *P = dyn_cast<PHINode>(*UI)) {
UserBB = P->getIncomingBlock(UI);
}
// Check the current block, as a fast-path. Most values are used in
// the same block they are defined in.
if (UserBB != BB && !LoopBBs.count(UserBB))
return false;
}
}
return true;
}
/// isLoopSimplifyForm - Return true if the Loop is in the form that
/// the LoopSimplify form transforms loops to, which is sometimes called
/// normal form.
bool Loop::isLoopSimplifyForm() const {
// Normal-form loops have a preheader, a single backedge, and all of their
// exits have all their predecessors inside the loop.
return getLoopPreheader() && getLoopLatch() && hasDedicatedExits();
}
/// hasDedicatedExits - Return true if no exit block for the loop
/// has a predecessor that is outside the loop.
bool Loop::hasDedicatedExits() const {
// Sort the blocks vector so that we can use binary search to do quick
// lookups.
SmallPtrSet<BasicBlock *, 16> LoopBBs(block_begin(), block_end());
// Each predecessor of each exit block of a normal loop is contained
// within the loop.
SmallVector<BasicBlock *, 4> ExitBlocks;
getExitBlocks(ExitBlocks);
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
for (pred_iterator PI = pred_begin(ExitBlocks[i]),
PE = pred_end(ExitBlocks[i]); PI != PE; ++PI)
if (!LoopBBs.count(*PI))
return false;
// All the requirements are met.
return true;
}
/// getUniqueExitBlocks - Return all unique successor blocks of this loop.
/// These are the blocks _outside of the current loop_ which are branched to.
/// This assumes that loop is in canonical form.
///
void
Loop::getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const {
assert(isLoopSimplifyForm() &&
"getUniqueExitBlocks assumes the loop is in canonical form!");
// Sort the blocks vector so that we can use binary search to do quick
// lookups.
SmallVector<BasicBlock *, 128> LoopBBs(block_begin(), block_end());
std::sort(LoopBBs.begin(), LoopBBs.end());
SmallVector<BasicBlock *, 32> switchExitBlocks;
for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) {
BasicBlock *current = *BI;
switchExitBlocks.clear();
typedef GraphTraits<BasicBlock *> BlockTraits;
typedef GraphTraits<Inverse<BasicBlock *> > InvBlockTraits;
for (BlockTraits::ChildIteratorType I =
BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI);
I != E; ++I) {
// If block is inside the loop then it is not a exit block.
if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I))
continue;
InvBlockTraits::ChildIteratorType PI = InvBlockTraits::child_begin(*I);
BasicBlock *firstPred = *PI;
// If current basic block is this exit block's first predecessor
// then only insert exit block in to the output ExitBlocks vector.
// This ensures that same exit block is not inserted twice into
// ExitBlocks vector.
if (current != firstPred)
continue;
// If a terminator has more then two successors, for example SwitchInst,
// then it is possible that there are multiple edges from current block
// to one exit block.
if (std::distance(BlockTraits::child_begin(current),
BlockTraits::child_end(current)) <= 2) {
ExitBlocks.push_back(*I);
continue;
}
// In case of multiple edges from current block to exit block, collect
// only one edge in ExitBlocks. Use switchExitBlocks to keep track of
// duplicate edges.
if (std::find(switchExitBlocks.begin(), switchExitBlocks.end(), *I)
== switchExitBlocks.end()) {
switchExitBlocks.push_back(*I);
ExitBlocks.push_back(*I);
}
}
}
}
/// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one
/// block, return that block. Otherwise return null.
BasicBlock *Loop::getUniqueExitBlock() const {
SmallVector<BasicBlock *, 8> UniqueExitBlocks;
getUniqueExitBlocks(UniqueExitBlocks);
if (UniqueExitBlocks.size() == 1)
return UniqueExitBlocks[0];
return 0;
}
//===----------------------------------------------------------------------===//
// LoopInfo implementation
//
bool LoopInfo::runOnFunction(Function &) {
releaseMemory();
LI.Calculate(getAnalysis<DominatorTree>().getBase()); // Update
return false;
}
void LoopInfo::verifyAnalysis() const {
// LoopInfo is a FunctionPass, but verifying every loop in the function
// each time verifyAnalysis is called is very expensive. The
// -verify-loop-info option can enable this. In order to perform some
// checking by default, LoopPass has been taught to call verifyLoop
// manually during loop pass sequences.
if (!VerifyLoopInfo) return;
for (iterator I = begin(), E = end(); I != E; ++I) {
assert(!(*I)->getParentLoop() && "Top-level loop has a parent!");
(*I)->verifyLoopNest();
}
// TODO: check BBMap consistency.
}
void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<DominatorTree>();
}
void LoopInfo::print(raw_ostream &OS, const Module*) const {
LI.print(OS);
}