426 lines
16 KiB
C++
426 lines
16 KiB
C++
//===- CodeMoverUtils.cpp - CodeMover Utilities ----------------------------==//
|
|
//
|
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
|
|
// See https://llvm.org/LICENSE.txt for license information.
|
|
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This family of functions perform movements on basic blocks, and instructions
|
|
// contained within a function.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Transforms/Utils/CodeMoverUtils.h"
|
|
#include "llvm/ADT/Optional.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/Analysis/DependenceAnalysis.h"
|
|
#include "llvm/Analysis/PostDominators.h"
|
|
#include "llvm/Analysis/ValueTracking.h"
|
|
#include "llvm/IR/Dominators.h"
|
|
|
|
using namespace llvm;
|
|
|
|
#define DEBUG_TYPE "codemover-utils"
|
|
|
|
STATISTIC(HasDependences,
|
|
"Cannot move across instructions that has memory dependences");
|
|
STATISTIC(MayThrowException, "Cannot move across instructions that may throw");
|
|
STATISTIC(NotControlFlowEquivalent,
|
|
"Instructions are not control flow equivalent");
|
|
STATISTIC(NotMovedPHINode, "Movement of PHINodes are not supported");
|
|
STATISTIC(NotMovedTerminator, "Movement of Terminator are not supported");
|
|
|
|
namespace {
|
|
/// Represent a control condition. A control condition is a condition of a
|
|
/// terminator to decide which successors to execute. The pointer field
|
|
/// represents the address of the condition of the terminator. The integer field
|
|
/// is a bool, it is true when the basic block is executed when V is true. For
|
|
/// example, `br %cond, bb0, bb1` %cond is a control condition of bb0 with the
|
|
/// integer field equals to true, while %cond is a control condition of bb1 with
|
|
/// the integer field equals to false.
|
|
using ControlCondition = PointerIntPair<Value *, 1, bool>;
|
|
#ifndef NDEBUG
|
|
raw_ostream &operator<<(raw_ostream &OS, const ControlCondition &C) {
|
|
OS << "[" << *C.getPointer() << ", " << (C.getInt() ? "true" : "false")
|
|
<< "]";
|
|
return OS;
|
|
}
|
|
#endif
|
|
|
|
/// Represent a set of control conditions required to execute ToBB from FromBB.
|
|
class ControlConditions {
|
|
using ConditionVectorTy = SmallVector<ControlCondition, 6>;
|
|
|
|
/// A SmallVector of control conditions.
|
|
ConditionVectorTy Conditions;
|
|
|
|
public:
|
|
/// Return a ControlConditions which stores all conditions required to execute
|
|
/// \p BB from \p Dominator. If \p MaxLookup is non-zero, it limits the
|
|
/// number of conditions to collect. Return None if not all conditions are
|
|
/// collected successfully, or we hit the limit.
|
|
static const Optional<ControlConditions>
|
|
collectControlConditions(const BasicBlock &BB, const BasicBlock &Dominator,
|
|
const DominatorTree &DT,
|
|
const PostDominatorTree &PDT,
|
|
unsigned MaxLookup = 6);
|
|
|
|
/// Return true if there exists no control conditions required to execute ToBB
|
|
/// from FromBB.
|
|
bool isUnconditional() const { return Conditions.empty(); }
|
|
|
|
/// Return a constant reference of Conditions.
|
|
const ConditionVectorTy &getControlConditions() const { return Conditions; }
|
|
|
|
/// Add \p V as one of the ControlCondition in Condition with IsTrueCondition
|
|
/// equals to \p True. Return true if inserted successfully.
|
|
bool addControlCondition(ControlCondition C);
|
|
|
|
/// Return true if for all control conditions in Conditions, there exists an
|
|
/// equivalent control condition in \p Other.Conditions.
|
|
bool isEquivalent(const ControlConditions &Other) const;
|
|
|
|
/// Return true if \p C1 and \p C2 are equivalent.
|
|
static bool isEquivalent(const ControlCondition &C1,
|
|
const ControlCondition &C2);
|
|
|
|
private:
|
|
ControlConditions() = default;
|
|
|
|
static bool isEquivalent(const Value &V1, const Value &V2);
|
|
static bool isInverse(const Value &V1, const Value &V2);
|
|
};
|
|
} // namespace
|
|
|
|
static bool domTreeLevelBefore(DominatorTree *DT, const Instruction *InstA,
|
|
const Instruction *InstB) {
|
|
// Use ordered basic block in case the 2 instructions are in the same
|
|
// block.
|
|
if (InstA->getParent() == InstB->getParent())
|
|
return InstA->comesBefore(InstB);
|
|
|
|
DomTreeNode *DA = DT->getNode(InstA->getParent());
|
|
DomTreeNode *DB = DT->getNode(InstB->getParent());
|
|
return DA->getLevel() < DB->getLevel();
|
|
}
|
|
|
|
const Optional<ControlConditions> ControlConditions::collectControlConditions(
|
|
const BasicBlock &BB, const BasicBlock &Dominator, const DominatorTree &DT,
|
|
const PostDominatorTree &PDT, unsigned MaxLookup) {
|
|
assert(DT.dominates(&Dominator, &BB) && "Expecting Dominator to dominate BB");
|
|
|
|
ControlConditions Conditions;
|
|
unsigned NumConditions = 0;
|
|
|
|
// BB is executed unconditional from itself.
|
|
if (&Dominator == &BB)
|
|
return Conditions;
|
|
|
|
const BasicBlock *CurBlock = &BB;
|
|
// Walk up the dominator tree from the associated DT node for BB to the
|
|
// associated DT node for Dominator.
|
|
do {
|
|
assert(DT.getNode(CurBlock) && "Expecting a valid DT node for CurBlock");
|
|
BasicBlock *IDom = DT.getNode(CurBlock)->getIDom()->getBlock();
|
|
assert(DT.dominates(&Dominator, IDom) &&
|
|
"Expecting Dominator to dominate IDom");
|
|
|
|
// Limitation: can only handle branch instruction currently.
|
|
const BranchInst *BI = dyn_cast<BranchInst>(IDom->getTerminator());
|
|
if (!BI)
|
|
return None;
|
|
|
|
bool Inserted = false;
|
|
if (PDT.dominates(CurBlock, IDom)) {
|
|
LLVM_DEBUG(dbgs() << CurBlock->getName()
|
|
<< " is executed unconditionally from "
|
|
<< IDom->getName() << "\n");
|
|
} else if (PDT.dominates(CurBlock, BI->getSuccessor(0))) {
|
|
LLVM_DEBUG(dbgs() << CurBlock->getName() << " is executed when \""
|
|
<< *BI->getCondition() << "\" is true from "
|
|
<< IDom->getName() << "\n");
|
|
Inserted = Conditions.addControlCondition(
|
|
ControlCondition(BI->getCondition(), true));
|
|
} else if (PDT.dominates(CurBlock, BI->getSuccessor(1))) {
|
|
LLVM_DEBUG(dbgs() << CurBlock->getName() << " is executed when \""
|
|
<< *BI->getCondition() << "\" is false from "
|
|
<< IDom->getName() << "\n");
|
|
Inserted = Conditions.addControlCondition(
|
|
ControlCondition(BI->getCondition(), false));
|
|
} else
|
|
return None;
|
|
|
|
if (Inserted)
|
|
++NumConditions;
|
|
|
|
if (MaxLookup != 0 && NumConditions > MaxLookup)
|
|
return None;
|
|
|
|
CurBlock = IDom;
|
|
} while (CurBlock != &Dominator);
|
|
|
|
return Conditions;
|
|
}
|
|
|
|
bool ControlConditions::addControlCondition(ControlCondition C) {
|
|
bool Inserted = false;
|
|
if (none_of(Conditions, [&](ControlCondition &Exists) {
|
|
return ControlConditions::isEquivalent(C, Exists);
|
|
})) {
|
|
Conditions.push_back(C);
|
|
Inserted = true;
|
|
}
|
|
|
|
LLVM_DEBUG(dbgs() << (Inserted ? "Inserted " : "Not inserted ") << C << "\n");
|
|
return Inserted;
|
|
}
|
|
|
|
bool ControlConditions::isEquivalent(const ControlConditions &Other) const {
|
|
if (Conditions.empty() && Other.Conditions.empty())
|
|
return true;
|
|
|
|
if (Conditions.size() != Other.Conditions.size())
|
|
return false;
|
|
|
|
return all_of(Conditions, [&](const ControlCondition &C) {
|
|
return any_of(Other.Conditions, [&](const ControlCondition &OtherC) {
|
|
return ControlConditions::isEquivalent(C, OtherC);
|
|
});
|
|
});
|
|
}
|
|
|
|
bool ControlConditions::isEquivalent(const ControlCondition &C1,
|
|
const ControlCondition &C2) {
|
|
if (C1.getInt() == C2.getInt()) {
|
|
if (isEquivalent(*C1.getPointer(), *C2.getPointer()))
|
|
return true;
|
|
} else if (isInverse(*C1.getPointer(), *C2.getPointer()))
|
|
return true;
|
|
|
|
return false;
|
|
}
|
|
|
|
// FIXME: Use SCEV and reuse GVN/CSE logic to check for equivalence between
|
|
// Values.
|
|
// Currently, isEquivalent rely on other passes to ensure equivalent conditions
|
|
// have the same value, e.g. GVN.
|
|
bool ControlConditions::isEquivalent(const Value &V1, const Value &V2) {
|
|
return &V1 == &V2;
|
|
}
|
|
|
|
bool ControlConditions::isInverse(const Value &V1, const Value &V2) {
|
|
if (const CmpInst *Cmp1 = dyn_cast<CmpInst>(&V1))
|
|
if (const CmpInst *Cmp2 = dyn_cast<CmpInst>(&V2)) {
|
|
if (Cmp1->getPredicate() == Cmp2->getInversePredicate() &&
|
|
Cmp1->getOperand(0) == Cmp2->getOperand(0) &&
|
|
Cmp1->getOperand(1) == Cmp2->getOperand(1))
|
|
return true;
|
|
|
|
if (Cmp1->getPredicate() ==
|
|
CmpInst::getSwappedPredicate(Cmp2->getInversePredicate()) &&
|
|
Cmp1->getOperand(0) == Cmp2->getOperand(1) &&
|
|
Cmp1->getOperand(1) == Cmp2->getOperand(0))
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
bool llvm::isControlFlowEquivalent(const Instruction &I0, const Instruction &I1,
|
|
const DominatorTree &DT,
|
|
const PostDominatorTree &PDT) {
|
|
return isControlFlowEquivalent(*I0.getParent(), *I1.getParent(), DT, PDT);
|
|
}
|
|
|
|
bool llvm::isControlFlowEquivalent(const BasicBlock &BB0, const BasicBlock &BB1,
|
|
const DominatorTree &DT,
|
|
const PostDominatorTree &PDT) {
|
|
if (&BB0 == &BB1)
|
|
return true;
|
|
|
|
if ((DT.dominates(&BB0, &BB1) && PDT.dominates(&BB1, &BB0)) ||
|
|
(PDT.dominates(&BB0, &BB1) && DT.dominates(&BB1, &BB0)))
|
|
return true;
|
|
|
|
// If the set of conditions required to execute BB0 and BB1 from their common
|
|
// dominator are the same, then BB0 and BB1 are control flow equivalent.
|
|
const BasicBlock *CommonDominator = DT.findNearestCommonDominator(&BB0, &BB1);
|
|
LLVM_DEBUG(dbgs() << "The nearest common dominator of " << BB0.getName()
|
|
<< " and " << BB1.getName() << " is "
|
|
<< CommonDominator->getName() << "\n");
|
|
|
|
const Optional<ControlConditions> BB0Conditions =
|
|
ControlConditions::collectControlConditions(BB0, *CommonDominator, DT,
|
|
PDT);
|
|
if (BB0Conditions == None)
|
|
return false;
|
|
|
|
const Optional<ControlConditions> BB1Conditions =
|
|
ControlConditions::collectControlConditions(BB1, *CommonDominator, DT,
|
|
PDT);
|
|
if (BB1Conditions == None)
|
|
return false;
|
|
|
|
return BB0Conditions->isEquivalent(*BB1Conditions);
|
|
}
|
|
|
|
static bool reportInvalidCandidate(const Instruction &I,
|
|
llvm::Statistic &Stat) {
|
|
++Stat;
|
|
LLVM_DEBUG(dbgs() << "Unable to move instruction: " << I << ". "
|
|
<< Stat.getDesc());
|
|
return false;
|
|
}
|
|
|
|
/// Collect all instructions in between \p StartInst and \p EndInst, and store
|
|
/// them in \p InBetweenInsts.
|
|
static void
|
|
collectInstructionsInBetween(Instruction &StartInst, const Instruction &EndInst,
|
|
SmallPtrSetImpl<Instruction *> &InBetweenInsts) {
|
|
assert(InBetweenInsts.empty() && "Expecting InBetweenInsts to be empty");
|
|
|
|
/// Get the next instructions of \p I, and push them to \p WorkList.
|
|
auto getNextInsts = [](Instruction &I,
|
|
SmallPtrSetImpl<Instruction *> &WorkList) {
|
|
if (Instruction *NextInst = I.getNextNode())
|
|
WorkList.insert(NextInst);
|
|
else {
|
|
assert(I.isTerminator() && "Expecting a terminator instruction");
|
|
for (BasicBlock *Succ : successors(&I))
|
|
WorkList.insert(&Succ->front());
|
|
}
|
|
};
|
|
|
|
SmallPtrSet<Instruction *, 10> WorkList;
|
|
getNextInsts(StartInst, WorkList);
|
|
while (!WorkList.empty()) {
|
|
Instruction *CurInst = *WorkList.begin();
|
|
WorkList.erase(CurInst);
|
|
|
|
if (CurInst == &EndInst)
|
|
continue;
|
|
|
|
if (!InBetweenInsts.insert(CurInst).second)
|
|
continue;
|
|
|
|
getNextInsts(*CurInst, WorkList);
|
|
}
|
|
}
|
|
|
|
bool llvm::isSafeToMoveBefore(Instruction &I, Instruction &InsertPoint,
|
|
DominatorTree &DT, const PostDominatorTree *PDT,
|
|
DependenceInfo *DI) {
|
|
// Skip tests when we don't have PDT or DI
|
|
if (!PDT || !DI)
|
|
return false;
|
|
|
|
// Cannot move itself before itself.
|
|
if (&I == &InsertPoint)
|
|
return false;
|
|
|
|
// Not moved.
|
|
if (I.getNextNode() == &InsertPoint)
|
|
return true;
|
|
|
|
if (isa<PHINode>(I) || isa<PHINode>(InsertPoint))
|
|
return reportInvalidCandidate(I, NotMovedPHINode);
|
|
|
|
if (I.isTerminator())
|
|
return reportInvalidCandidate(I, NotMovedTerminator);
|
|
|
|
// TODO remove this limitation.
|
|
if (!isControlFlowEquivalent(I, InsertPoint, DT, *PDT))
|
|
return reportInvalidCandidate(I, NotControlFlowEquivalent);
|
|
|
|
if (!DT.dominates(&InsertPoint, &I))
|
|
for (const Use &U : I.uses())
|
|
if (auto *UserInst = dyn_cast<Instruction>(U.getUser()))
|
|
if (UserInst != &InsertPoint && !DT.dominates(&InsertPoint, U))
|
|
return false;
|
|
if (!DT.dominates(&I, &InsertPoint))
|
|
for (const Value *Op : I.operands())
|
|
if (auto *OpInst = dyn_cast<Instruction>(Op))
|
|
if (&InsertPoint == OpInst || !DT.dominates(OpInst, &InsertPoint))
|
|
return false;
|
|
|
|
DT.updateDFSNumbers();
|
|
const bool MoveForward = domTreeLevelBefore(&DT, &I, &InsertPoint);
|
|
Instruction &StartInst = (MoveForward ? I : InsertPoint);
|
|
Instruction &EndInst = (MoveForward ? InsertPoint : I);
|
|
SmallPtrSet<Instruction *, 10> InstsToCheck;
|
|
collectInstructionsInBetween(StartInst, EndInst, InstsToCheck);
|
|
if (!MoveForward)
|
|
InstsToCheck.insert(&InsertPoint);
|
|
|
|
// Check if there exists instructions which may throw, may synchonize, or may
|
|
// never return, from I to InsertPoint.
|
|
if (!isSafeToSpeculativelyExecute(&I))
|
|
if (llvm::any_of(InstsToCheck, [](Instruction *I) {
|
|
if (I->mayThrow())
|
|
return true;
|
|
|
|
const CallBase *CB = dyn_cast<CallBase>(I);
|
|
if (!CB)
|
|
return false;
|
|
if (!CB->hasFnAttr(Attribute::WillReturn))
|
|
return true;
|
|
if (!CB->hasFnAttr(Attribute::NoSync))
|
|
return true;
|
|
|
|
return false;
|
|
})) {
|
|
return reportInvalidCandidate(I, MayThrowException);
|
|
}
|
|
|
|
// Check if I has any output/flow/anti dependences with instructions from \p
|
|
// StartInst to \p EndInst.
|
|
if (llvm::any_of(InstsToCheck, [&DI, &I](Instruction *CurInst) {
|
|
auto DepResult = DI->depends(&I, CurInst, true);
|
|
if (DepResult && (DepResult->isOutput() || DepResult->isFlow() ||
|
|
DepResult->isAnti()))
|
|
return true;
|
|
return false;
|
|
}))
|
|
return reportInvalidCandidate(I, HasDependences);
|
|
|
|
return true;
|
|
}
|
|
|
|
bool llvm::isSafeToMoveBefore(BasicBlock &BB, Instruction &InsertPoint,
|
|
DominatorTree &DT, const PostDominatorTree *PDT,
|
|
DependenceInfo *DI) {
|
|
return llvm::all_of(BB, [&](Instruction &I) {
|
|
if (BB.getTerminator() == &I)
|
|
return true;
|
|
|
|
return isSafeToMoveBefore(I, InsertPoint, DT, PDT, DI);
|
|
});
|
|
}
|
|
|
|
void llvm::moveInstructionsToTheBeginning(BasicBlock &FromBB, BasicBlock &ToBB,
|
|
DominatorTree &DT,
|
|
const PostDominatorTree &PDT,
|
|
DependenceInfo &DI) {
|
|
for (auto It = ++FromBB.rbegin(); It != FromBB.rend();) {
|
|
Instruction *MovePos = ToBB.getFirstNonPHIOrDbg();
|
|
Instruction &I = *It;
|
|
// Increment the iterator before modifying FromBB.
|
|
++It;
|
|
|
|
if (isSafeToMoveBefore(I, *MovePos, DT, &PDT, &DI))
|
|
I.moveBefore(MovePos);
|
|
}
|
|
}
|
|
|
|
void llvm::moveInstructionsToTheEnd(BasicBlock &FromBB, BasicBlock &ToBB,
|
|
DominatorTree &DT,
|
|
const PostDominatorTree &PDT,
|
|
DependenceInfo &DI) {
|
|
Instruction *MovePos = ToBB.getTerminator();
|
|
while (FromBB.size() > 1) {
|
|
Instruction &I = FromBB.front();
|
|
if (isSafeToMoveBefore(I, *MovePos, DT, &PDT, &DI))
|
|
I.moveBefore(MovePos);
|
|
}
|
|
}
|