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[GuardWidening] Introduce range check merging
Sequences of range checks expressed using guards, like guard((I - 2) u< L) guard((I - 1) u< L) guard((I + 0) u< L) guard((I + 1) u< L) guard((I + 2) u< L) can sometimes be combined into a smaller sequence: guard((I - 2) u< L AND (I + 2) u< L) if we can prove that (I - 2) u< L AND (I + 2) u< L implies all of checks expressed in the previous sequence. This change teaches GuardWidening to do this kind of merging when feasible. llvm-svn: 270151
This commit is contained in:
Sanjoy Das
parent
970400db38
commit
14b186a828
@ -130,6 +130,55 @@ class GuardWideningImpl {
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bool widenCondCommon(Value *Cond0, Value *Cond1, Instruction *InsertPt,
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Value *&Result);
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/// Represents a range check of the form \c Base + \c Offset u< \c Length,
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/// with the constraint that \c Length is not negative. \c CheckInst is the
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/// pre-existing instruction in the IR that computes the result of this range
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/// check.
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struct RangeCheck {
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Value *Base;
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ConstantInt *Offset;
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Value *Length;
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ICmpInst *CheckInst;
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RangeCheck() {}
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explicit RangeCheck(Value *Base, ConstantInt *Offset, Value *Length,
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ICmpInst *CheckInst)
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: Base(Base), Offset(Offset), Length(Length), CheckInst(CheckInst) {}
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void print(raw_ostream &OS, bool PrintTypes = false) {
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OS << "Base: ";
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Base->printAsOperand(OS, PrintTypes);
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OS << " Offset: ";
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Offset->printAsOperand(OS, PrintTypes);
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OS << " Length: ";
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Length->printAsOperand(OS, PrintTypes);
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}
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LLVM_DUMP_METHOD void dump() {
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print(dbgs());
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dbgs() << "\n";
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}
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};
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/// Parse \p CheckCond into a conjunction (logical-and) of range checks; and
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/// append them to \p Checks. Returns true on success, may clobber \c Checks
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/// on failure.
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bool parseRangeChecks(Value *CheckCond, SmallVectorImpl<RangeCheck> &Checks) {
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SmallPtrSet<Value *, 8> Visited;
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return parseRangeChecks(CheckCond, Checks, Visited);
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}
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bool parseRangeChecks(Value *CheckCond, SmallVectorImpl<RangeCheck> &Checks,
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SmallPtrSetImpl<Value *> &Visited);
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/// Combine the checks in \p Checks into a smaller set of checks and append
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/// them into \p CombinedChecks. Return true on success (i.e. all of checks
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/// in \p Checks were combined into \p CombinedChecks). Clobbers \p Checks
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/// and \p CombinedChecks on success and on failure.
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bool combineRangeChecks(SmallVectorImpl<RangeCheck> &Checks,
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SmallVectorImpl<RangeCheck> &CombinedChecks);
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/// Can we compute the logical AND of \p Cond0 and \p Cond1 for the price of
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/// computing only one of the two expressions?
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bool isWideningCondProfitable(Value *Cond0, Value *Cond1) {
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@ -386,6 +435,27 @@ bool GuardWideningImpl::widenCondCommon(Value *Cond0, Value *Cond1,
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}
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}
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{
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SmallVector<GuardWideningImpl::RangeCheck, 4> Checks, CombinedChecks;
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if (parseRangeChecks(Cond0, Checks) && parseRangeChecks(Cond1, Checks) &&
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combineRangeChecks(Checks, CombinedChecks)) {
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if (InsertPt) {
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Result = nullptr;
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for (auto &RC : CombinedChecks) {
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makeAvailableAt(RC.CheckInst, InsertPt);
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if (Result)
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Result =
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BinaryOperator::CreateAnd(RC.CheckInst, Result, "", InsertPt);
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else
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Result = RC.CheckInst;
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}
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Result->setName("wide.chk");
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}
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return true;
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}
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}
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// Base case -- just logical-and the two conditions together.
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if (InsertPt) {
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@ -399,6 +469,180 @@ bool GuardWideningImpl::widenCondCommon(Value *Cond0, Value *Cond1,
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return false;
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}
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bool GuardWideningImpl::parseRangeChecks(
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Value *CheckCond, SmallVectorImpl<GuardWideningImpl::RangeCheck> &Checks,
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SmallPtrSetImpl<Value *> &Visited) {
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if (!Visited.insert(CheckCond).second)
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return true;
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using namespace llvm::PatternMatch;
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{
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Value *AndLHS, *AndRHS;
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if (match(CheckCond, m_And(m_Value(AndLHS), m_Value(AndRHS))))
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return parseRangeChecks(AndLHS, Checks) &&
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parseRangeChecks(AndRHS, Checks);
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}
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auto *IC = dyn_cast<ICmpInst>(CheckCond);
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if (!IC || !IC->getOperand(0)->getType()->isIntegerTy() ||
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(IC->getPredicate() != ICmpInst::ICMP_ULT &&
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IC->getPredicate() != ICmpInst::ICMP_UGT))
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return false;
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Value *CmpLHS = IC->getOperand(0), *CmpRHS = IC->getOperand(1);
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if (IC->getPredicate() == ICmpInst::ICMP_UGT)
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std::swap(CmpLHS, CmpRHS);
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auto &DL = IC->getModule()->getDataLayout();
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GuardWideningImpl::RangeCheck Check;
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Check.Base = CmpLHS;
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Check.Offset =
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cast<ConstantInt>(ConstantInt::getNullValue(CmpRHS->getType()));
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Check.Length = CmpRHS;
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Check.CheckInst = IC;
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if (!isKnownNonNegative(Check.Length, DL))
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return false;
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// What we have in \c Check now is a correct interpretation of \p CheckCond.
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// Try to see if we can move some constant offsets into the \c Offset field.
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bool Changed;
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do {
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Value *OpLHS;
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ConstantInt *OpRHS;
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Changed = false;
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#ifndef NDEBUG
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auto *BaseInst = dyn_cast<Instruction>(Check.Base);
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assert((!BaseInst || DT.isReachableFromEntry(BaseInst->getParent())) &&
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"Unreachable instruction?");
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#endif
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if (match(Check.Base, m_Add(m_Value(OpLHS), m_ConstantInt(OpRHS)))) {
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Check.Base = OpLHS;
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Check.Offset =
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ConstantInt::get(Check.Offset->getContext(),
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Check.Offset->getValue() + OpRHS->getValue());
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Changed = true;
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} else if (match(Check.Base, m_Or(m_Value(OpLHS), m_ConstantInt(OpRHS)))) {
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unsigned BitWidth = OpLHS->getType()->getScalarSizeInBits();
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APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
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computeKnownBits(OpLHS, KnownZero, KnownOne, DL);
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if ((OpRHS->getValue() & KnownZero) == OpRHS->getValue()) {
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Check.Base = OpLHS;
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Check.Offset =
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ConstantInt::get(Check.Offset->getContext(),
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Check.Offset->getValue() + OpRHS->getValue());
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Changed = true;
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}
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}
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} while (Changed);
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Checks.push_back(Check);
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return true;
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}
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bool GuardWideningImpl::combineRangeChecks(
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SmallVectorImpl<GuardWideningImpl::RangeCheck> &Checks,
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SmallVectorImpl<GuardWideningImpl::RangeCheck> &RangeChecksOut) {
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unsigned OldCount = Checks.size();
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while (!Checks.empty()) {
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Value *Base = Checks[0].Base;
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Value *Length = Checks[0].Length;
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auto ChecksStart =
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remove_if(Checks, [&](GuardWideningImpl::RangeCheck &RC) {
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return RC.Base == Base && RC.Length == Length;
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});
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unsigned CheckCount = std::distance(ChecksStart, Checks.end());
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assert(CheckCount != 0 && "We know we have at least one!");
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if (CheckCount < 3) {
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RangeChecksOut.insert(RangeChecksOut.end(), ChecksStart, Checks.end());
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Checks.erase(ChecksStart, Checks.end());
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continue;
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}
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// CheckCount will typically be 3 here, but so far there has been no need to
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// hard-code that fact.
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std::sort(ChecksStart, Checks.end(),
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[&](GuardWideningImpl::RangeCheck &LHS,
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GuardWideningImpl::RangeCheck &RHS) {
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return LHS.Offset->getValue().slt(RHS.Offset->getValue());
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});
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// Note: std::sort should not invalidate the ChecksStart iterator.
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ConstantInt *MinOffset = ChecksStart->Offset,
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*MaxOffset = Checks.back().Offset;
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unsigned BitWidth = MaxOffset->getValue().getBitWidth();
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if ((MaxOffset->getValue() - MinOffset->getValue())
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.ugt(APInt::getSignedMinValue(BitWidth)))
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return false;
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APInt MaxDiff = MaxOffset->getValue() - MinOffset->getValue();
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APInt HighOffset = MaxOffset->getValue();
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auto OffsetOK = [&](GuardWideningImpl::RangeCheck &RC) {
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return (HighOffset - RC.Offset->getValue()).ult(MaxDiff);
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};
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if (MaxDiff.isMinValue() ||
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!std::all_of(std::next(ChecksStart), Checks.end(), OffsetOK))
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return false;
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// We have a series of f+1 checks as:
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//
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// I+k_0 u< L ... Chk_0
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// I_k_1 u< L ... Chk_1
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// ...
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// I_k_f u< L ... Chk_(f+1)
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//
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// with forall i in [0,f): k_f-k_i u< k_f-k_0 ... Precond_0
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// k_f-k_0 u< INT_MIN+k_f ... Precond_1
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// k_f != k_0 ... Precond_2
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//
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// Claim:
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// Chk_0 AND Chk_(f+1) implies all the other checks
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//
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// Informal proof sketch:
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//
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// We will show that the integer range [I+k_0,I+k_f] does not unsigned-wrap
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// (i.e. going from I+k_0 to I+k_f does not cross the -1,0 boundary) and
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// thus I+k_f is the greatest unsigned value in that range.
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//
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// This combined with Ckh_(f+1) shows that everything in that range is u< L.
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// Via Precond_0 we know that all of the indices in Chk_0 through Chk_(f+1)
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// lie in [I+k_0,I+k_f], this proving our claim.
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//
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// To see that [I+k_0,I+k_f] is not a wrapping range, note that there are
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// two possibilities: I+k_0 u< I+k_f or I+k_0 >u I+k_f (they can't be equal
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// since k_0 != k_f). In the former case, [I+k_0,I+k_f] is not a wrapping
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// range by definition, and the latter case is impossible:
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//
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// 0-----I+k_f---I+k_0----L---INT_MAX,INT_MIN------------------(-1)
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// xxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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//
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// For Chk_0 to succeed, we'd have to have k_f-k_0 (the range highlighted
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// with 'x' above) to be at least >u INT_MIN.
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RangeChecksOut.emplace_back(Base, MinOffset, Length,
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ChecksStart->CheckInst);
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RangeChecksOut.emplace_back(Base, MaxOffset, Length,
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Checks.back().CheckInst);
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Checks.erase(ChecksStart, Checks.end());
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}
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assert(RangeChecksOut.size() <= OldCount && "We pessimized!");
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return RangeChecksOut.size() != OldCount;
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}
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PreservedAnalyses GuardWideningPass::run(Function &F,
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AnalysisManager<Function> &AM) {
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auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
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197
test/Transforms/GuardWidening/range-check-merging.ll
Normal file
197
test/Transforms/GuardWidening/range-check-merging.ll
Normal file
@ -0,0 +1,197 @@
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; RUN: opt -S -guard-widening < %s | FileCheck %s
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declare void @llvm.experimental.guard(i1,...)
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define void @f_0(i32 %x, i32* %length_buf) {
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; CHECK-LABEL: @f_0(
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; CHECK-NOT: @llvm.experimental.guard
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; CHECK: %wide.chk2 = and i1 %chk3, %chk0
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; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %wide.chk2) [ "deopt"() ]
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; CHECK: ret void
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entry:
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%length = load i32, i32* %length_buf, !range !0
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%chk0 = icmp ult i32 %x, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk0) [ "deopt"() ]
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%x.inc1 = add i32 %x, 1
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%chk1 = icmp ult i32 %x.inc1, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk1) [ "deopt"() ]
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%x.inc2 = add i32 %x, 2
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%chk2 = icmp ult i32 %x.inc2, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk2) [ "deopt"() ]
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%x.inc3 = add i32 %x, 3
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%chk3 = icmp ult i32 %x.inc3, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk3) [ "deopt"() ]
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ret void
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}
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define void @f_1(i32 %x, i32* %length_buf) {
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; CHECK-LABEL: @f_1(
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; CHECK-NOT: llvm.experimental.guard
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; CHECK: %wide.chk2 = and i1 %chk3, %chk0
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; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %wide.chk2) [ "deopt"() ]
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; CHECK: ret void
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entry:
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%length = load i32, i32* %length_buf, !range !0
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%chk0 = icmp ult i32 %x, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk0) [ "deopt"() ]
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%x.inc1 = add i32 %x, 1
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%chk1 = icmp ult i32 %x.inc1, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk1) [ "deopt"() ]
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%x.inc2 = add i32 %x.inc1, 2
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%chk2 = icmp ult i32 %x.inc2, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk2) [ "deopt"() ]
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%x.inc3 = add i32 %x.inc2, 3
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%chk3 = icmp ult i32 %x.inc3, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk3) [ "deopt"() ]
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ret void
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}
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define void @f_2(i32 %a, i32* %length_buf) {
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; CHECK-LABEL: @f_2(
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; CHECK-NOT: llvm.experimental.guard
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; CHECK: %wide.chk2 = and i1 %chk3, %chk0
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; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %wide.chk2) [ "deopt"() ]
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; CHECK: ret void
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entry:
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%x = and i32 %a, 4294967040 ;; 4294967040 == 0xffffff00
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%length = load i32, i32* %length_buf, !range !0
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%chk0 = icmp ult i32 %x, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk0) [ "deopt"() ]
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%x.inc1 = or i32 %x, 1
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%chk1 = icmp ult i32 %x.inc1, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk1) [ "deopt"() ]
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%x.inc2 = or i32 %x, 2
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%chk2 = icmp ult i32 %x.inc2, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk2) [ "deopt"() ]
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%x.inc3 = or i32 %x, 3
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%chk3 = icmp ult i32 %x.inc3, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk3) [ "deopt"() ]
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ret void
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}
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define void @f_3(i32 %a, i32* %length_buf) {
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; CHECK-LABEL: @f_3(
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; CHECK-NOT: llvm.experimental.guard
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; CHECK: %wide.chk2 = and i1 %chk3, %chk0
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; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %wide.chk2) [ "deopt"() ]
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; CHECK: ret void
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entry:
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%x = and i32 %a, 4294967040 ;; 4294967040 == 0xffffff00
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%length = load i32, i32* %length_buf, !range !0
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%chk0 = icmp ult i32 %x, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk0) [ "deopt"() ]
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%x.inc1 = add i32 %x, 1
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%chk1 = icmp ult i32 %x.inc1, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk1) [ "deopt"() ]
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%x.inc2 = or i32 %x.inc1, 2
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%chk2 = icmp ult i32 %x.inc2, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk2) [ "deopt"() ]
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%x.inc3 = add i32 %x.inc2, 3
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%chk3 = icmp ult i32 %x.inc3, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk3) [ "deopt"() ]
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ret void
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}
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define void @f_4(i32 %x, i32* %length_buf) {
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; CHECK-LABEL: @f_4(
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; CHECK-NOT: llvm.experimental.guard
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; Note: we NOT guarding on "and i1 %chk3, %chk0", that would be incorrect.
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; CHECK: %wide.chk2 = and i1 %chk3, %chk1
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; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %wide.chk2) [ "deopt"() ]
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; CHECK: ret void
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entry:
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%length = load i32, i32* %length_buf, !range !0
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%chk0 = icmp ult i32 %x, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk0) [ "deopt"() ]
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%x.inc1 = add i32 %x, -1024
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%chk1 = icmp ult i32 %x.inc1, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk1) [ "deopt"() ]
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%x.inc2 = add i32 %x, 2
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%chk2 = icmp ult i32 %x.inc2, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk2) [ "deopt"() ]
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%x.inc3 = add i32 %x, 3
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%chk3 = icmp ult i32 %x.inc3, %length
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call void(i1, ...) @llvm.experimental.guard(i1 %chk3) [ "deopt"() ]
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ret void
|
||||
}
|
||||
|
||||
define void @f_5(i32 %x, i32* %length_buf) {
|
||||
; CHECK-LABEL: @f_5(
|
||||
; CHECK-NOT: llvm.experimental.guard
|
||||
; CHECK: %wide.chk2 = and i1 %chk1, %chk2
|
||||
; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %wide.chk2) [ "deopt"() ]
|
||||
; CHECK: ret void
|
||||
entry:
|
||||
%length = load i32, i32* %length_buf, !range !0
|
||||
%chk0 = icmp ult i32 %x, %length
|
||||
call void(i1, ...) @llvm.experimental.guard(i1 %chk0) [ "deopt"() ]
|
||||
|
||||
%x.inc1 = add i32 %x, 1
|
||||
%chk1 = icmp ult i32 %x.inc1, %length
|
||||
call void(i1, ...) @llvm.experimental.guard(i1 %chk1) [ "deopt"() ]
|
||||
|
||||
%x.inc2 = add i32 %x.inc1, -200
|
||||
%chk2 = icmp ult i32 %x.inc2, %length
|
||||
call void(i1, ...) @llvm.experimental.guard(i1 %chk2) [ "deopt"() ]
|
||||
|
||||
%x.inc3 = add i32 %x.inc2, 3
|
||||
%chk3 = icmp ult i32 %x.inc3, %length
|
||||
call void(i1, ...) @llvm.experimental.guard(i1 %chk3) [ "deopt"() ]
|
||||
ret void
|
||||
}
|
||||
|
||||
|
||||
; Negative test: we can't merge these checks into
|
||||
;
|
||||
; (%x + -2147483647) u< L && (%x + 3) u< L
|
||||
;
|
||||
; because if %length == INT_MAX and %x == -3 then
|
||||
;
|
||||
; (%x + -2147483647) == i32 2147483646 u< L (L is 2147483647)
|
||||
; (%x + 3) == 0 u< L
|
||||
;
|
||||
; But (%x + 2) == -1 is not u< L
|
||||
;
|
||||
define void @f_6(i32 %x, i32* %length_buf) {
|
||||
; CHECK-LABEL: @f_6(
|
||||
; CHECK-NOT: llvm.experimental.guard
|
||||
; CHECK: %wide.chk = and i1 %chk0, %chk1
|
||||
; CHECK: %wide.chk1 = and i1 %wide.chk, %chk2
|
||||
; CHECK: %wide.chk2 = and i1 %wide.chk1, %chk3
|
||||
; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %wide.chk2) [ "deopt"() ]
|
||||
entry:
|
||||
%length = load i32, i32* %length_buf, !range !0
|
||||
%chk0 = icmp ult i32 %x, %length
|
||||
call void(i1, ...) @llvm.experimental.guard(i1 %chk0) [ "deopt"() ]
|
||||
|
||||
%x.inc1 = add i32 %x, -2147483647 ;; -2147483647 == (i32 INT_MIN)+1 == -(i32 INT_MAX)
|
||||
%chk1 = icmp ult i32 %x.inc1, %length
|
||||
call void(i1, ...) @llvm.experimental.guard(i1 %chk1) [ "deopt"() ]
|
||||
|
||||
%x.inc2 = add i32 %x, 2
|
||||
%chk2 = icmp ult i32 %x.inc2, %length
|
||||
call void(i1, ...) @llvm.experimental.guard(i1 %chk2) [ "deopt"() ]
|
||||
|
||||
%x.inc3 = add i32 %x, 3
|
||||
%chk3 = icmp ult i32 %x.inc3, %length
|
||||
call void(i1, ...) @llvm.experimental.guard(i1 %chk3) [ "deopt"() ]
|
||||
ret void
|
||||
}
|
||||
|
||||
!0 = !{i32 0, i32 2147483648}
|
||||
Loading…
Reference in New Issue
Block a user