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swift-mirror/lib/SILPasses/SimplifyCFG.cpp
Erik Eckstein 665c1b8894 SimplifyCFG: fix wrong jump threading in case of block-args with multiple uses. 
This fixes rdar://problem/20565538
(at least part of it).



Swift SVN r27432
2015-04-17 15:26:59 +00:00

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//===--- SimplifyCFG.cpp - Clean up the SIL CFG ---------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "sil-simplify-cfg"
#include "swift/SILPasses/Passes.h"
#include "swift/SIL/Dominance.h"
#include "swift/SIL/SILArgument.h"
#include "swift/SIL/SILModule.h"
#include "swift/SIL/SILUndef.h"
#include "swift/SILAnalysis/DominanceAnalysis.h"
#include "swift/SILAnalysis/SimplifyInstruction.h"
#include "swift/SILPasses/Transforms.h"
#include "swift/SILPasses/Utils/CFG.h"
#include "swift/SILPasses/Utils/Local.h"
#include "swift/SILPasses/Utils/SILInliner.h"
#include "swift/SILPasses/Utils/SILSSAUpdater.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Debug.h"
using namespace swift;
STATISTIC(NumBlocksDeleted, "Number of unreachable blocks removed");
STATISTIC(NumBlocksMerged, "Number of blocks merged together");
STATISTIC(NumJumpThreads, "Number of jumps threaded");
STATISTIC(NumConstantFolded, "Number of terminators constant folded");
STATISTIC(NumDeadArguments, "Number of unused arguments removed");
//===----------------------------------------------------------------------===//
// CFG Simplification
//===----------------------------------------------------------------------===//
/// dominatorBasedSimplify iterates between dominator based simplifation of
/// terminator branch condition values and cfg simplification. This is the
/// maximum number of iterations we run. The number is the maximum number of
/// iterations encountered when compiling the stdlib on April 2 2015.
///
static unsigned MaxIterationsOfDominatorBasedSimplify = 10;
namespace {
class SimplifyCFG {
SILFunction &Fn;
SILPassManager *PM;
// WorklistList is the actual list that we iterate over (for determinism).
// Slots may be null, which should be ignored.
SmallVector<SILBasicBlock*, 32> WorklistList;
// WorklistMap keeps track of which slot a BB is in, allowing efficient
// containment query, and allows efficient removal.
llvm::SmallDenseMap<SILBasicBlock*, unsigned, 32> WorklistMap;
// Keep track of loop headers - we don't want to jump-thread through them.
SmallPtrSet<SILBasicBlock *, 32> LoopHeaders;
// Dominance and post-dominance info for the current function
DominanceInfo *DT;
PostDominanceInfo *PDT;
bool ShouldVerify;
public:
SimplifyCFG(SILFunction &Fn, SILPassManager *PM, bool Verify) :
Fn(Fn), PM(PM), ShouldVerify(Verify) {}
bool run();
bool simplifyBlockArgs() {
auto *DA = PM->getAnalysis<DominanceAnalysis>();
auto *PDA = PM->getAnalysis<PostDominanceAnalysis>();
DT = DA->get(&Fn);
PDT = PDA->get(&Fn);
bool Changed = false;
for (SILBasicBlock &BB : Fn) {
Changed |= simplifyArgs(&BB);
}
DT = nullptr;
PDT = nullptr;
return Changed;
}
private:
void clearWorklist() {
WorklistMap.clear();
WorklistList.clear();
}
/// popWorklist - Return the next basic block to look at, or null if the
/// worklist is empty. This handles skipping over null entries in the
/// worklist.
SILBasicBlock *popWorklist() {
while (!WorklistList.empty())
if (auto *BB = WorklistList.pop_back_val()) {
WorklistMap.erase(BB);
return BB;
}
return nullptr;
}
/// addToWorklist - Add the specified block to the work list if it isn't
/// already present.
void addToWorklist(SILBasicBlock *BB) {
unsigned &Entry = WorklistMap[BB];
if (Entry != 0) return;
WorklistList.push_back(BB);
Entry = WorklistList.size();
}
/// removeFromWorklist - Remove the specified block from the worklist if
/// present.
void removeFromWorklist(SILBasicBlock *BB) {
assert(BB && "Cannot add null pointer to the worklist");
auto It = WorklistMap.find(BB);
if (It == WorklistMap.end()) return;
// If the BB is in the worklist, null out its entry.
if (It->second) {
assert(WorklistList[It->second-1] == BB && "Consistency error");
WorklistList[It->second-1] = nullptr;
}
// Remove it from the map as well.
WorklistMap.erase(It);
if (LoopHeaders.count(BB))
LoopHeaders.erase(BB);
}
bool simplifyBlocks();
bool canonicalizeSwitchEnums();
bool dominatorBasedSimplify(DominanceAnalysis *DA,
PostDominanceAnalysis *PDA);
/// \brief Remove the basic block if it has no predecessors. Returns true
/// If the block was removed.
bool removeIfDead(SILBasicBlock *BB);
bool tryJumpThreading(BranchInst *BI);
bool tailDuplicateObjCMethodCallSuccessorBlocks();
bool simplifyAfterDroppingPredecessor(SILBasicBlock *BB);
bool simplifyBranchOperands(OperandValueArrayRef Operands);
bool simplifyBranchBlock(BranchInst *BI);
bool simplifyCondBrBlock(CondBranchInst *BI);
bool simplifyCheckedCastBranchBlock(CheckedCastBranchInst *CCBI);
bool simplifyCheckedCastAddrBranchBlock(CheckedCastAddrBranchInst *CCABI);
bool simplifyTermWithIdenticalDestBlocks(SILBasicBlock *BB);
bool simplifySwitchEnumUnreachableBlocks(SwitchEnumInst *SEI);
bool simplifySwitchEnumBlock(SwitchEnumInst *SEI);
bool simplifyUnreachableBlock(UnreachableInst *UI);
bool simplifyArgument(SILBasicBlock *BB, unsigned i);
bool simplifyArgs(SILBasicBlock *BB);
bool trySimplifyCheckedCastBr(TermInst *Term, DominanceInfo *DT);
void findLoopHeaders();
};
class RemoveUnreachable {
SILFunction &Fn;
llvm::SmallSet<SILBasicBlock *, 8> Visited;
public:
RemoveUnreachable(SILFunction &Fn) : Fn(Fn) { }
void visit(SILBasicBlock *BB);
bool run();
};
} // end anonymous namespace
/// Return true if there are any users of V outside the specified block.
static bool isUsedOutsideOfBlock(SILValue V, SILBasicBlock *BB) {
for (auto UI : V.getUses())
if (UI->getUser()->getParent() != BB)
return true;
return false;
}
/// Helper function to perform SSA updates in case of jump threading.
void swift::updateSSAAfterCloning(BaseThreadingCloner &Cloner,
SILBasicBlock *SrcBB,
SILBasicBlock *DestBB) {
// We are updating SSA form. This means we need to be able to insert phi
// nodes. To make sure we can do this split all critical edges from
// instructions that don't support block arguments.
splitAllCriticalEdges(*DestBB->getParent(), true, nullptr, nullptr);
SILSSAUpdater SSAUp;
for (auto AvailValPair : Cloner.AvailVals) {
ValueBase *Inst = AvailValPair.first;
if (Inst->use_empty())
continue;
for (unsigned i = 0, e = Inst->getNumTypes(); i != e; ++i) {
// Get the result index for the cloned instruction. This is going to be
// the result index stored in the available value for arguments (we look
// through the phi node) and the same index as the original value
// otherwise.
unsigned ResIdx = i;
if (isa<SILArgument>(Inst))
ResIdx = AvailValPair.second.getResultNumber();
SILValue Res(Inst, i);
SILValue NewRes(AvailValPair.second.getDef(), ResIdx);
SmallVector<UseWrapper, 16> UseList;
// Collect the uses of the value.
for (auto Use : Res.getUses())
UseList.push_back(UseWrapper(Use));
SSAUp.Initialize(Res.getType());
SSAUp.AddAvailableValue(DestBB, Res);
SSAUp.AddAvailableValue(SrcBB, NewRes);
if (UseList.empty())
continue;
// Update all the uses.
for (auto U : UseList) {
Operand *Use = U;
SILInstruction *User = Use->getUser();
assert(User && "Missing user");
// Ignore uses in the same basic block.
if (User->getParent() == DestBB)
continue;
SSAUp.RewriteUse(*Use);
}
}
}
}
template <class SwitchEnumTy, class SwitchEnumCaseTy>
static SILBasicBlock *replaceSwitchDest(SwitchEnumTy *S,
SmallVectorImpl<SwitchEnumCaseTy> &Cases,
unsigned EdgeIdx,
SILBasicBlock *NewDest) {
auto *DefaultBB = S->hasDefault() ? S->getDefaultBB() : nullptr;
for (unsigned i = 0, e = S->getNumCases(); i != e; ++i)
if (EdgeIdx != i)
Cases.push_back(S->getCase(i));
else
Cases.push_back(std::make_pair(S->getCase(i).first, NewDest));
if (EdgeIdx == S->getNumCases())
DefaultBB = NewDest;
return DefaultBB;
}
/// Perform a dominator-based jump-threading for checked_cast_br [exact]
/// instructions if they use the same condition (modulo upcasts and downcasts).
/// This is very beneficial for code that:
/// - references the same object multiple times (e.g. x.f1() + x.f2())
/// - and for method invocation chaining (e.g. x.f3().f4().f5())
bool
SimplifyCFG::trySimplifyCheckedCastBr(TermInst *Term, DominanceInfo *DT) {
// Ignore unreachable blocks.
if (!DT->getNode(Term->getParent()))
return false;
SmallVector<SILBasicBlock *, 16> BBs;
auto Result = tryCheckedCastBrJumpThreading(Term, DT, BBs);
if (Result) {
for (auto BB: BBs)
addToWorklist(BB);
}
return Result;
}
/// Holds information about a use of a terminator condition.
struct CondUseInfo {
CondUseInfo(Operand *Use, size_t SuccessorIdx, bool inverted) :
Use(Use), SuccessorIdx(SuccessorIdx), inverted(inverted) {}
/// The use.
Operand *Use;
/// Specifies the successor of the terminator which dominates the use.
size_t SuccessorIdx;
/// For boolean conditions: true if the use is an inverted condition of the
/// original.
bool inverted;
};
/// Returns the underlying condition of a value.
/// It strips expect-intrinsics and boolean xor-invertions.
static SILValue getUnderlying(SILValue V, bool &inverted) {
if (auto *BI = dyn_cast<BuiltinInst>(V)) {
// Expect-intrinsics have no effect, so we can see through them.
if (BI->getIntrinsicInfo().ID == llvm::Intrinsic::expect)
return BI->getArguments()[0];
if (BI->getBuiltinInfo().ID == BuiltinValueKind::Xor) {
// Check if it's a boolean invertion of the condition.
OperandValueArrayRef Args = BI->getArguments();
if (auto *IL = dyn_cast<IntegerLiteralInst>(Args[1])) {
if (IL->getValue().isAllOnesValue()) {
inverted = !inverted;
return Args[0];
}
}
}
}
return SILValue();
}
/// Collects uses down the dominator tree.
/// We collect only uses which are dominated by a successor of the original
/// terminator instruction.
static void collectUsesDown(SmallVectorImpl<CondUseInfo> &Uses, SILValue Cond,
bool inverted,
const TermInst::SuccessorListTy &Successors,
DominanceInfo *DT) {
for (Operand *UI : Cond.getUses()) {
SILInstruction *User = UI->getUser();
SILBasicBlock *UserBlock = User->getParentBB();
// Check which successor (if any) dominates the use.
for (size_t SuccIdx = 0, Size = Successors.size(); SuccIdx < Size;
++SuccIdx) {
SILBasicBlock *SuccBB = Successors[SuccIdx].getBB();
if (DT->dominates(SuccBB, UserBlock) && SuccBB->getSinglePredecessor()) {
// The successor dominates the use. So we collect the use.
Uses.push_back({ UI, SuccIdx, inverted });
bool newInverted = inverted;
if (getUnderlying(User, newInverted) == Cond) {
// Continue to collect uses of this User.
collectUsesDown(Uses, User, newInverted, Successors, DT);
}
break;
}
}
}
}
/// Collects uses up the dominator tree.
static void collectUsesUp(SmallVectorImpl<CondUseInfo> &Uses, SILValue Cond,
bool inverted,
const TermInst::SuccessorListTy &Successors,
DominanceInfo *DT) {
do {
collectUsesDown(Uses, Cond, inverted, Successors, DT);
Cond = getUnderlying(Cond, inverted);
} while (Cond);
}
/// Replaces uses of a cond_br condition in blocks which are dominated by the
/// cond_br's successors. Such uses can be replaced with literals.
static bool propagateCondBrCondition(CondBranchInst *CBR, DominanceInfo *DT) {
// Ignore unreachable blocks.
if (!DT->getNode(CBR->getParent()))
return false;
IntegerLiteralInst *LiteralInsts[2] = { nullptr, nullptr };
auto Successors = CBR->getSuccessors();
assert(Successors[0].getBB() == CBR->getTrueBB());
assert(Successors[1].getBB() == CBR->getFalseBB());
SmallVector<CondUseInfo, 8> Uses;
SILValue Cond = CBR->getCondition();
// Collect all uses of the cond_br condition which are dominated by either the
// true- or false-block.
collectUsesUp(Uses, Cond, false, Successors, DT);
bool Changed = false;
for (const CondUseInfo &CUI : Uses) {
size_t Idx = CUI.SuccessorIdx;
int Literal = CUI.inverted ? Idx : 1 - Idx;
assert(Literal < 2);
if (!LiteralInsts[Literal]) {
// Create a 0- or 1- literal in the cond_br's block.
SILInstruction *User = CUI.Use->getUser();
LiteralInsts[Literal] = SILBuilderWithScope<1>(CBR).
createIntegerLiteral(User->getLoc(), Cond.getType(), Literal);
}
// Replace the use of the cond_br condition with a literal.
CUI.Use->set(LiteralInsts[Literal]);
Changed = true;
}
return Changed;
}
/// Optimizes uses of a switch_enum condition in blocks which are dominated by
/// the switch_enum's successors.
static bool propagateSwitchEnumCondition(SwitchEnumInst *SWI, DominanceInfo *DT) {
// Ignore unreachable blocks.
if (!DT->getNode(SWI->getParent()))
return false;
auto Successors = SWI->getSuccessors();
SmallVector<CondUseInfo, 8> Uses;
SILValue EnumVal = SWI->getOperand();
collectUsesUp(Uses, EnumVal, false, Successors, DT);
bool Changed = false;
for (const CondUseInfo &CUI : Uses) {
size_t Idx = CUI.SuccessorIdx;
SILBasicBlock *DstBlock = Successors[Idx].getBB();
auto Case = SWI->getUniqueCaseForDestination(DstBlock);
if (!Case)
continue;
EnumElementDecl *EnumElement = Case.get();
SILInstruction *User = CUI.Use->getUser();
if (SwitchEnumInst *DomSWI = dyn_cast<SwitchEnumInst>(User)) {
// The SWI successor dominates another switch_enum which share the same
// condition. We know the case so we can just instantantiate the
// enum_inst and make the dominated switch_enum use it.
SILBuilderWithScope<1> Builder(DomSWI);
SILValue NewEnum;
// Do we have a payload.
auto EnumTy = EnumVal->getType(0);
if (EnumElement->hasArgumentType()) {
auto Ty = EnumTy.getEnumElementType(EnumElement, DomSWI->getModule());
SILValue UED(Builder.createUncheckedEnumData(DomSWI->getLoc(), EnumVal,
EnumElement, Ty),
0);
NewEnum = Builder.createEnum(DomSWI->getLoc(), UED, EnumElement, EnumTy);
} else
NewEnum = Builder.createEnum(DomSWI->getLoc(), SILValue(), EnumElement,
EnumTy);
DomSWI->setOperand(0, NewEnum);
Changed = true;
continue;
}
if (SelectEnumInst *DomSEI = dyn_cast<SelectEnumInst>(User)) {
// No point in replacing an unused select_enum.
if (DomSEI->use_empty())
continue;
// The SWI successor dominates a select_enum which share the same
// condition.
SILValue selected;
for (unsigned i = 0, e = DomSEI->getNumCases(); i < e; ++i) {
auto casePair = DomSEI->getCase(i);
if (casePair.first == EnumElement) {
selected = casePair.second;
break;
}
}
if (!selected)
selected = DomSEI->getDefaultResult();
DomSEI->replaceAllUsesWith(selected.getDef());
Changed = true;
continue;
}
}
return Changed;
}
// Simplifications that walk the dominator tree to prove redundancy in
// conditional branching.
bool SimplifyCFG::dominatorBasedSimplify(DominanceAnalysis *DA,
PostDominanceAnalysis *PDA) {
bool Changed = false;
// Get the dominator tree.
DT = DA->get(&Fn);
unsigned MaxIter = MaxIterationsOfDominatorBasedSimplify;
bool HasChangedInCurrentIter = false;
do {
HasChangedInCurrentIter = false;
// Do dominator based simplification of terminator condition. This does not
// and MUST NOT change the CFG without updating the dominator tree to
// reflect such change.
for (auto &BB : Fn) {
// Any method called from this loop should update
// the DT if it changes anything related to dominators.
TermInst *Term = BB.getTerminator();
switch (Term->getKind()) {
case ValueKind::CondBranchInst:
HasChangedInCurrentIter |=
propagateCondBrCondition(cast<CondBranchInst>(Term), DT);
break;
case ValueKind::SwitchEnumInst:
HasChangedInCurrentIter |=
propagateSwitchEnumCondition(cast<SwitchEnumInst>(Term), DT);
break;
case ValueKind::SwitchValueInst:
// TODO: handle switch_value
break;
case ValueKind::CheckedCastBranchInst:
if (trySimplifyCheckedCastBr(BB.getTerminator(), DT)) {
HasChangedInCurrentIter = true;
// FIXME: trySimplifyCheckedCastBr function should preserve the
// dominator tree but its code to do so is buggy.
DT->recalculate(Fn);
}
break;
default:
break;
}
}
if (ShouldVerify)
DT->verify();
// Simplify terminators. This changes the CFG and therefore invalidates the
// dom tree.
DominanceInfo *InvalidDT = DT;
DT = nullptr;
// Simplify terminators.
bool HaveChangedCFG = false;
for (auto &BB : Fn) {
auto *Term = BB.getTerminator();
if (auto *SEI = dyn_cast<SwitchEnumInst>(Term))
HaveChangedCFG |= simplifySwitchEnumBlock(SEI);
else if (auto *CondBr = dyn_cast<CondBranchInst>(Term))
HaveChangedCFG |= simplifyCondBrBlock(CondBr);
}
HasChangedInCurrentIter |= HaveChangedCFG;
// Remove unreachable blocks.
if (HaveChangedCFG)
HasChangedInCurrentIter |= RemoveUnreachable(Fn).run();
// Recompute the dominator tree if we have changed the CFG so we can used it
// in simplifyArgs and the following iteration.
DT = InvalidDT;
if (HaveChangedCFG)
DT->recalculate(Fn);
// Simplify the block argument list. This is extremely subtle: simplifyArgs
// will not change the CFG iff the PDT is null. Really we should move that
// one optimization out of simplifyArgs ... I am squinting at you
// simplifySwitchEnumToSelectEnum.
// simplifyArgs does use the dominator tree, though.
PDT = nullptr;
for (auto &BB : Fn)
HasChangedInCurrentIter |= simplifyArgs(&BB);
if (ShouldVerify)
DT->verify();
Changed |= HasChangedInCurrentIter;
} while (HasChangedInCurrentIter && --MaxIter);
// Do the simplification that requires both the dom and postdom tree.
PDT = PDA->get(&Fn);
for (auto &BB : Fn)
Changed |= simplifyArgs(&BB);
if (ShouldVerify)
DT->verify();
// The functions we used to simplify the CFG put things in the worklist. Clear
// it here.
clearWorklist();
return Changed;
}
// If BB is trivially unreachable, remove it from the worklist, add its
// successors to the worklist, and then remove the block.
bool SimplifyCFG::removeIfDead(SILBasicBlock *BB) {
if (!BB->pred_empty() || BB == &*Fn.begin())
return false;
removeFromWorklist(BB);
// Add successor blocks to the worklist since their predecessor list is about
// to change.
for (auto &S : BB->getSuccessors())
addToWorklist(S);
removeDeadBlock(BB);
++NumBlocksDeleted;
return true;
}
/// This is called when a predecessor of a block is dropped, to simplify the
/// block and add it to the worklist.
bool SimplifyCFG::simplifyAfterDroppingPredecessor(SILBasicBlock *BB) {
// TODO: If BB has only one predecessor and has bb args, fold them away, then
// use instsimplify on all the users of those values - even ones outside that
// block.
// Make sure that DestBB is in the worklist, as well as its remaining
// predecessors, since they may not be able to be simplified.
addToWorklist(BB);
for (auto *P : BB->getPreds())
addToWorklist(P);
return false;
}
/// couldSimplifyUsers - Check to see if any simplifications are possible if
/// "Val" is substituted for BBArg. If so, return true, if nothing obvious
/// is possible, return false.
static bool couldSimplifyUsers(SILArgument *BBArg, SILValue Val) {
// If the value being substituted is an enum, check to see if there are any
// switches on it.
auto *EI = dyn_cast<EnumInst>(Val);
if (!EI)
return false;
for (auto UI : BBArg->getUses()) {
auto *User = UI->getUser();
// We only know we can simplify if the switch_enum user is in the block we
// are trying to jump thread.
// The value must not be define in the same basic block as the switch enum
// user. If this is the case we have a single block switch_enum loop.
if (isa<SwitchEnumInst>(User) || isa<SelectEnumInst>(User))
if (BBArg->getParent() == User->getParent() &&
EI->getParent() != BBArg->getParent())
return true;
// Also allow enum of enum, which usually can be combined to a single
// instruction. This helps to simplify the creation of an enum from an
// integer raw value.
if (isa<EnumInst>(User))
if (BBArg->getParent() == User->getParent() &&
EI->getParent() != BBArg->getParent())
return true;
}
return false;
}
void SimplifyCFG::findLoopHeaders() {
/// Find back edges in the CFG. This performs a dfs search and identifies
/// back edges as edges going to an ancestor in the dfs search. If a basic
/// block is the target of such a back edge we will identify it as a header.
LoopHeaders.clear();
SmallPtrSet<SILBasicBlock *, 16> Visited;
SmallPtrSet<SILBasicBlock *, 16> InDFSStack;
SmallVector<std::pair<SILBasicBlock *, SILBasicBlock::succ_iterator>, 16>
DFSStack;
auto EntryBB = &Fn.front();
DFSStack.push_back(std::make_pair(EntryBB, EntryBB->succ_begin()));
Visited.insert(EntryBB);
InDFSStack.insert(EntryBB);
while (!DFSStack.empty()) {
auto &D = DFSStack.back();
// No successors.
if (D.second == D.first->succ_end()) {
// Retreat the dfs search.
DFSStack.pop_back();
InDFSStack.erase(D.first);
} else {
// Visit the next successor.
SILBasicBlock *NextSucc = *(D.second);
++D.second;
if (Visited.insert(NextSucc).second) {
InDFSStack.insert(NextSucc);
DFSStack.push_back(std::make_pair(NextSucc, NextSucc->succ_begin()));
} else if (InDFSStack.count(NextSucc)) {
// We have already visited this node and it is in our dfs search. This
// is a back-edge.
LoopHeaders.insert(NextSucc);
}
}
}
}
/// tryJumpThreading - Check to see if it looks profitable to duplicate the
/// destination of an unconditional jump into the bottom of this block.
bool SimplifyCFG::tryJumpThreading(BranchInst *BI) {
auto *DestBB = BI->getDestBB();
auto *SrcBB = BI->getParent();
// If the destination block ends with a return, we don't want to duplicate it.
// We want to maintain the canonical form of a single return where possible.
if (isa<ReturnInst>(DestBB->getTerminator()))
return false;
// We need to update SSA if a value duplicated is used outside of the
// duplicated block.
bool NeedToUpdateSSA = false;
// Are the arguments to this block used outside of the block.
for (auto Arg : DestBB->getBBArgs())
if ((NeedToUpdateSSA |= isUsedOutsideOfBlock(Arg, DestBB))) {
break;
}
// We don't have a great cost model at the SIL level, so we don't want to
// blissly duplicate tons of code with a goal of improved performance (we'll
// leave that to LLVM). However, doing limited code duplication can lead to
// major second order simplifications. Here we only do it if there are
// "constant" arguments to the branch or if we know how to fold something
// given the duplication.
bool WantToThread = false;
if (isa<CondBranchInst>(DestBB->getTerminator()))
for (auto V : BI->getArgs()) {
if (isa<IntegerLiteralInst>(V) || isa<FloatLiteralInst>(V)) {
WantToThread = true;
break;
}
}
if (!WantToThread) {
for (unsigned i = 0, e = BI->getArgs().size(); i != e; ++i)
if (couldSimplifyUsers(DestBB->getBBArg(i), BI->getArg(i))) {
WantToThread = true;
break;
}
}
// If we don't have anything that we can simplify, don't do it.
if (!WantToThread) return false;
// If it looks potentially interesting, decide whether we *can* do the
// operation and whether the block is small enough to be worth duplicating.
unsigned Cost = 0;
for (auto &Inst : DestBB->getInstList()) {
if (!Inst.isTriviallyDuplicatable())
return false;
// Don't jumpthread function calls.
if (isa<ApplyInst>(Inst))
return false;
// This is a really trivial cost model, which is only intended as a starting
// point.
if (instructionInlineCost(Inst) != InlineCost::Free)
if (++Cost == 4) return false;
// We need to update ssa if a value is used outside the duplicated block.
if (!NeedToUpdateSSA)
NeedToUpdateSSA |= isUsedOutsideOfBlock(&Inst, DestBB);
}
// Don't jump thread through a potential header - this can produce irreducible
// control flow.
if (!isa<SwitchEnumInst>(DestBB->getTerminator()) &&
LoopHeaders.count(DestBB))
return false;
// Okay, it looks like we want to do this and we can. Duplicate the
// destination block into this one, rewriting uses of the BBArgs to use the
// branch arguments as we go.
ThreadingCloner Cloner(BI);
for (auto &I : *DestBB)
Cloner.process(&I);
// Once all the instructions are copied, we can nuke BI itself. We also add
// this block back to the worklist now that the terminator (likely) can be
// simplified.
addToWorklist(BI->getParent());
BI->eraseFromParent();
if (NeedToUpdateSSA)
updateSSAAfterCloning(Cloner, SrcBB, DestBB);
// We may be able to simplify DestBB now that it has one fewer predecessor.
simplifyAfterDroppingPredecessor(DestBB);
++NumJumpThreads;
return true;
}
/// simplifyBranchOperands - Simplify operands of branches, since it can
/// result in exposing opportunities for CFG simplification.
bool SimplifyCFG::simplifyBranchOperands(OperandValueArrayRef Operands) {
bool Simplified = false;
for (auto O = Operands.begin(), E = Operands.end(); O != E; ++O)
if (auto *I = dyn_cast<SILInstruction>(*O))
if (SILValue Result = simplifyInstruction(I)) {
SILValue(I, 0).replaceAllUsesWith(Result.getDef());
if (isInstructionTriviallyDead(I)) {
I->eraseFromParent();
Simplified = true;
}
}
return Simplified;
}
/// \return If this basic blocks has a single br instruction passing all of the
/// arguments in the original order, then returns the destination of that br.
static SILBasicBlock *getTrampolineDest(SILBasicBlock *SBB) {
// Ignore blocks with more than one instruction.
if (SBB->getTerminator() != SBB->begin())
return nullptr;
BranchInst *BI = dyn_cast<BranchInst>(SBB->getTerminator());
if (!BI)
return nullptr;
// Disallow infinite loops.
if (BI->getDestBB() == SBB)
return nullptr;
auto BrArgs = BI->getArgs();
if (BrArgs.size() != SBB->getNumBBArg())
return nullptr;
// Check that the arguments are the same and in the right order.
for (int i = 0, e = SBB->getNumBBArg(); i < e; ++i) {
SILArgument *BBArg = SBB->getBBArg(i);
if (BrArgs[i] != BBArg)
return nullptr;
// The arguments may not be used in another block, because when the
// predecessor of SBB directly jumps to the successor, the SBB block does
// not dominate the other use anymore.
if (!BBArg->hasOneUse())
return nullptr;
}
return BI->getDestBB();
}
/// \return If this is a basic block without any arguments and it has
/// a single br instruction, return this br.
static BranchInst *getTrampolineWithoutBBArgsTerminator(SILBasicBlock *SBB) {
if (!SBB->bbarg_empty())
return nullptr;
// Ignore blocks with more than one instruction.
if (SBB->getTerminator() != SBB->begin())
return nullptr;
BranchInst *BI = dyn_cast<BranchInst>(SBB->getTerminator());
if (!BI)
return nullptr;
// Disallow infinite loops.
if (BI->getDestBB() == SBB)
return nullptr;
return BI;
}
/// simplifyBranchBlock - Simplify a basic block that ends with an unconditional
/// branch.
bool SimplifyCFG::simplifyBranchBlock(BranchInst *BI) {
// First simplify instructions generating branch operands since that
// can expose CFG simplifications.
bool Simplified = simplifyBranchOperands(BI->getArgs());
auto *BB = BI->getParent(), *DestBB = BI->getDestBB();
// If this block branches to a block with a single predecessor, then
// merge the DestBB into this BB.
if (BB != DestBB && DestBB->getSinglePredecessor()) {
// If there are any BB arguments in the destination, replace them with the
// branch operands, since they must dominate the dest block.
for (unsigned i = 0, e = BI->getArgs().size(); i != e; ++i)
SILValue(DestBB->getBBArg(i)).replaceAllUsesWith(BI->getArg(i));
// Zap BI and move all of the instructions from DestBB into this one.
BI->eraseFromParent();
BB->getInstList().splice(BB->end(), DestBB->getInstList(),
DestBB->begin(), DestBB->end());
// Revisit this block now that we've changed it and remove the DestBB.
addToWorklist(BB);
// This can also expose opportunities in the successors of
// the merged block.
for (auto &Succ : BB->getSuccessors())
addToWorklist(Succ);
if (LoopHeaders.count(DestBB))
LoopHeaders.insert(BB);
removeFromWorklist(DestBB);
DestBB->eraseFromParent();
++NumBlocksMerged;
return true;
}
// If the destination block is a simple trampoline (jump to another block)
// then jump directly.
if (SILBasicBlock *TrampolineDest = getTrampolineDest(DestBB)) {
SILBuilderWithScope<1>(BI).createBranch(BI->getLoc(), TrampolineDest,
BI->getArgs());
// Eliminating the trampoline can expose opportuntities to improve the
// new block we branch to.
if (LoopHeaders.count(DestBB))
LoopHeaders.insert(BB);
addToWorklist(TrampolineDest);
BI->eraseFromParent();
removeIfDead(DestBB);
addToWorklist(BB);
return true;
}
// If this unconditional branch has BBArgs, check to see if duplicating the
// destination would allow it to be simplified. This is a simple form of jump
// threading.
if (!BI->getArgs().empty() &&
tryJumpThreading(BI))
return true;
return Simplified;
}
/// \brief Check if replacing an existing edge of the terminator by another
/// one which has a DestBB as its destination would create a critical edge.
static bool wouldIntroduceCriticalEdge(TermInst *T, SILBasicBlock *DestBB) {
auto SrcSuccs = T->getSuccessors();
if (SrcSuccs.size() <= 1)
return false;
assert(!DestBB->pred_empty() && "There should be a predecessor");
if (DestBB->getSinglePredecessor())
return false;
return true;
}
/// \brief Returns the first cond_fail if it is the first side-effect
/// instruction in this block.
static CondFailInst *getFistCondFail(SILBasicBlock *BB) {
auto It = BB->begin();
CondFailInst *CondFail = nullptr;
// Skip instructions that don't have side-effects.
while (It != BB->end() && !(CondFail = dyn_cast<CondFailInst>(It))) {
if (It->mayHaveSideEffects())
return nullptr;
++It;
}
return CondFail;
}
/// \brief Is the first side-effect instruction in this block a cond_fail that
/// is guarantueed to fail.
static bool isCondFailBlock(SILBasicBlock *BB,
CondFailInst *&OrigCondFailInst) {
CondFailInst *CondFail = getFistCondFail(BB);
if (!CondFail)
return false;
auto *IL = dyn_cast<IntegerLiteralInst>(CondFail->getOperand());
if (!IL)
return false;
OrigCondFailInst = CondFail;
return IL->getValue() != 0;
}
/// \brief Creates a new cond_fail instruction, optionally with an xor inverted
/// condition.
static void createCondFail(CondFailInst *Orig, SILValue Cond, bool inverted,
SILBuilder &Builder) {
if (inverted) {
auto *True = Builder.createIntegerLiteral(Orig->getLoc(), Cond.getType(), 1);
Cond = Builder.createBuiltinBinaryFunction(Orig->getLoc(), "xor",
Cond.getType(), Cond.getType(),
{Cond, True});
}
Builder.createCondFail(Orig->getLoc(), Cond);
}
/// simplifyCondBrBlock - Simplify a basic block that ends with a conditional
/// branch.
bool SimplifyCFG::simplifyCondBrBlock(CondBranchInst *BI) {
// First simplify instructions generating branch operands since that
// can expose CFG simplifications.
simplifyBranchOperands(OperandValueArrayRef(BI->getAllOperands()));
auto *ThisBB = BI->getParent();
SILBasicBlock *TrueSide = BI->getTrueBB();
SILBasicBlock *FalseSide = BI->getFalseBB();
auto TrueArgs = BI->getTrueArgs();
auto FalseArgs = BI->getFalseArgs();
// If the condition is an integer literal, we can constant fold the branch.
if (auto *IL = dyn_cast<IntegerLiteralInst>(BI->getCondition())) {
bool isFalse = !IL->getValue();
auto LiveArgs = isFalse ? FalseArgs : TrueArgs;
auto *LiveBlock = isFalse ? FalseSide : TrueSide;
auto *DeadBlock = !isFalse ? FalseSide : TrueSide;
auto *ThisBB = BI->getParent();
SILBuilderWithScope<1>(BI).createBranch(BI->getLoc(), LiveBlock, LiveArgs);
BI->eraseFromParent();
if (IL->use_empty()) IL->eraseFromParent();
addToWorklist(ThisBB);
simplifyAfterDroppingPredecessor(DeadBlock);
addToWorklist(LiveBlock);
++NumConstantFolded;
return true;
}
// If the destination block is a simple trampoline (jump to another block)
// then jump directly.
SILBasicBlock *TrueTrampolineDest = getTrampolineDest(TrueSide);
if (TrueTrampolineDest && TrueTrampolineDest != FalseSide) {
SILBuilderWithScope<1>(BI)
.createCondBranch(BI->getLoc(), BI->getCondition(),
TrueTrampolineDest, TrueArgs,
FalseSide, FalseArgs);
BI->eraseFromParent();
if (LoopHeaders.count(TrueSide))
LoopHeaders.insert(ThisBB);
removeIfDead(TrueSide);
addToWorklist(ThisBB);
return true;
}
SILBasicBlock *FalseTrampolineDest = getTrampolineDest(FalseSide);
if (FalseTrampolineDest && FalseTrampolineDest != TrueSide) {
SILBuilderWithScope<1>(BI)
.createCondBranch(BI->getLoc(), BI->getCondition(),
TrueSide, TrueArgs,
FalseTrampolineDest, FalseArgs);
BI->eraseFromParent();
if (LoopHeaders.count(FalseSide))
LoopHeaders.insert(ThisBB);
removeIfDead(FalseSide);
addToWorklist(ThisBB);
return true;
}
// Simplify cond_br where both sides jump to the same blocks with the same
// args.
if (TrueArgs == FalseArgs && (TrueSide == FalseTrampolineDest ||
FalseSide == TrueTrampolineDest)) {
SILBuilderWithScope<1>(BI).createBranch(BI->getLoc(),
TrueTrampolineDest ? FalseSide : TrueSide, TrueArgs);
BI->eraseFromParent();
addToWorklist(ThisBB);
addToWorklist(TrueSide);
++NumConstantFolded;
return true;
}
auto *TrueTrampolineBr = getTrampolineWithoutBBArgsTerminator(TrueSide);
if (TrueTrampolineBr &&
!wouldIntroduceCriticalEdge(BI, TrueTrampolineBr->getDestBB())) {
SILBuilderWithScope<1>(BI).createCondBranch(
BI->getLoc(), BI->getCondition(),
TrueTrampolineBr->getDestBB(), TrueTrampolineBr->getArgs(),
FalseSide, FalseArgs);
BI->eraseFromParent();
if (LoopHeaders.count(TrueSide))
LoopHeaders.insert(ThisBB);
removeIfDead(TrueSide);
addToWorklist(ThisBB);
return true;
}
auto *FalseTrampolineBr = getTrampolineWithoutBBArgsTerminator(FalseSide);
if (FalseTrampolineBr &&
!wouldIntroduceCriticalEdge(BI, FalseTrampolineBr->getDestBB())) {
SILBuilderWithScope<1>(BI).createCondBranch(
BI->getLoc(), BI->getCondition(),
TrueSide, TrueArgs,
FalseTrampolineBr->getDestBB(), FalseTrampolineBr->getArgs());
BI->eraseFromParent();
if (LoopHeaders.count(FalseSide))
LoopHeaders.insert(ThisBB);
removeIfDead(FalseSide);
addToWorklist(ThisBB);
return true;
}
// If we have a (cond (select_enum)) on a two element enum, always have the
// first case as our checked tag. If we have the second, create a new
// select_enum with the first case and swap our operands. This simplifies
// later dominance based processing.
if (auto *SEI = dyn_cast<SelectEnumInst>(BI->getCondition())) {
EnumDecl *E = SEI->getEnumOperand().getType().getEnumOrBoundGenericEnum();
auto AllElts = E->getAllElements();
auto Iter = AllElts.begin();
EnumElementDecl *FirstElt = *Iter;
if (SEI->getNumCases() >= 1
&& SEI->getCase(0).first != FirstElt) {
++Iter;
if (Iter != AllElts.end() &&
std::next(Iter) == AllElts.end() &&
*Iter == SEI->getCase(0).first) {
EnumElementDecl *SecondElt = *Iter;
SILValue FirstValue;
// SelectEnum must be exhaustive, so the second case must be handled
// either by a case or the default.
if (SEI->getNumCases() >= 2) {
assert(FirstElt == SEI->getCase(1).first
&& "select_enum missing a case?!");
FirstValue = SEI->getCase(1).second;
} else {
FirstValue = SEI->getDefaultResult();
}
std::pair<EnumElementDecl*, SILValue> SwappedCases[2] = {
{FirstElt, SEI->getCase(0).second},
{SecondElt, FirstValue},
};
auto *NewSEI = SILBuilderWithScope<1>(SEI)
.createSelectEnum(SEI->getLoc(),
SEI->getEnumOperand(),
SEI->getType(),
SILValue(),
SwappedCases);
// We only change the condition to be NewEITI instead of all uses since
// EITI may have other uses besides this one that need to be updated.
BI->setCondition(NewSEI);
BI->swapSuccessors();
addToWorklist(BI->getParent());
addToWorklist(TrueSide);
addToWorklist(FalseSide);
return true;
}
}
}
// Simplify a condition branch to a block starting with "cond_fail 1".
//
// cond_br %cond, TrueSide, FalseSide
// TrueSide:
// cond_fail 1
//
bool IsTrueSideFailing;
CondFailInst *OrigCFI = nullptr;
if ((IsTrueSideFailing = isCondFailBlock(TrueSide, OrigCFI)) ||
isCondFailBlock(FalseSide, OrigCFI)) {
auto LiveArgs = IsTrueSideFailing ? FalseArgs : TrueArgs;
auto *LiveBlock = IsTrueSideFailing ? FalseSide : TrueSide;
auto *DeadBlock = !IsTrueSideFailing ? FalseSide : TrueSide;
auto *ThisBB = BI->getParent();
auto CFCondition = BI->getCondition();
// If the false side is failing, negate the branch condition.
SILBuilderWithScope<1> Builder(BI);
createCondFail(OrigCFI, CFCondition, !IsTrueSideFailing, Builder);
SILBuilderWithScope<1>(BI).createBranch(BI->getLoc(), LiveBlock, LiveArgs);
BI->eraseFromParent();
addToWorklist(ThisBB);
simplifyAfterDroppingPredecessor(DeadBlock);
addToWorklist(LiveBlock);
return true;
}
return false;
}
// Does this basic block consist of only an "unreachable" instruction?
static bool isOnlyUnreachable(SILBasicBlock *BB) {
auto *Term = BB->getTerminator();
if (!isa<UnreachableInst>(Term))
return false;
return (&*BB->begin() == BB->getTerminator());
}
/// simplifySwitchEnumUnreachableBlocks - Attempt to replace a
/// switch_enum_inst where all but one block consists of just an
/// "unreachable" with an unchecked_enum_data and branch.
bool SimplifyCFG::simplifySwitchEnumUnreachableBlocks(SwitchEnumInst *SEI) {
auto Count = SEI->getNumCases();
SILBasicBlock *Dest = nullptr;
EnumElementDecl *Element = nullptr;
if (SEI->hasDefault())
if (!isOnlyUnreachable(SEI->getDefaultBB()))
Dest = SEI->getDefaultBB();
for (unsigned i = 0; i < Count; ++i) {
auto EnumCase = SEI->getCase(i);
if (isOnlyUnreachable(EnumCase.second))
continue;
if (Dest)
return false;
assert(!Element && "Did not expect to have an element without a block!");
Element = EnumCase.first;
Dest = EnumCase.second;
}
if (!Dest) {
addToWorklist(SEI->getParent());
SILBuilderWithScope<1>(SEI).createUnreachable(SEI->getLoc());
SEI->eraseFromParent();
return true;
}
if (!Element || !Element->hasArgumentType() || Dest->bbarg_empty()) {
assert(Dest->bbarg_empty() && "Unexpected argument at destination!");
SILBuilderWithScope<1>(SEI).createBranch(SEI->getLoc(), Dest);
addToWorklist(SEI->getParent());
addToWorklist(Dest);
SEI->eraseFromParent();
return true;
}
auto &Mod = SEI->getModule();
auto OpndTy = SEI->getOperand()->getType(0);
auto Ty = OpndTy.getEnumElementType(Element, Mod);
auto *UED = SILBuilderWithScope<1>(SEI)
.createUncheckedEnumData(SEI->getLoc(), SEI->getOperand(), Element, Ty);
assert(Dest->bbarg_size() == 1 && "Expected only one argument!");
ArrayRef<SILValue> Args = { UED };
SILBuilderWithScope<1>(SEI).createBranch(SEI->getLoc(), Dest, Args);
addToWorklist(SEI->getParent());
addToWorklist(Dest);
SEI->eraseFromParent();
return true;
}
/// simplifySwitchEnumBlock - Simplify a basic block that ends with a
/// switch_enum instruction that gets its operand from a an enum
/// instruction.
bool SimplifyCFG::simplifySwitchEnumBlock(SwitchEnumInst *SEI) {
auto *EI = dyn_cast<EnumInst>(SEI->getOperand());
// If the operand is not from an enum, see if this is a case where
// only one destination of the branch has code that does not end
// with unreachable.
if (!EI)
return simplifySwitchEnumUnreachableBlocks(SEI);
auto *LiveBlock = SEI->getCaseDestination(EI->getElement());
auto *ThisBB = SEI->getParent();
bool DroppedLiveBlock = false;
// Copy the successors into a vector, dropping one entry for the liveblock.
SmallVector<SILBasicBlock*, 4> Dests;
for (auto &S : SEI->getSuccessors()) {
if (S == LiveBlock && !DroppedLiveBlock) {
DroppedLiveBlock = true;
continue;
}
Dests.push_back(S);
}
if (EI->hasOperand() && !LiveBlock->bbarg_empty())
SILBuilderWithScope<1>(SEI).createBranch(SEI->getLoc(), LiveBlock,
EI->getOperand());
else
SILBuilderWithScope<1>(SEI).createBranch(SEI->getLoc(), LiveBlock);
SEI->eraseFromParent();
if (EI->use_empty()) EI->eraseFromParent();
addToWorklist(ThisBB);
for (auto B : Dests)
simplifyAfterDroppingPredecessor(B);
addToWorklist(LiveBlock);
++NumConstantFolded;
return true;
}
/// simplifyUnreachableBlock - Simplify blocks ending with unreachable by
/// removing instructions that are safe to delete backwards until we
/// hit an instruction we cannot delete.
bool SimplifyCFG::simplifyUnreachableBlock(UnreachableInst *UI) {
bool Changed = false;
auto BB = UI->getParent();
auto I = std::next(BB->rbegin());
auto End = BB->rend();
SmallVector<SILInstruction *, 8> DeadInstrs;
// Walk backwards deleting instructions that should be safe to delete
// in a block that ends with unreachable.
while (I != End) {
auto MaybeDead = I++;
switch (MaybeDead->getKind()) {
// These technically have side effects, but not ones that matter
// in a block that we shouldn't really reach...
case ValueKind::StrongRetainInst:
case ValueKind::StrongReleaseInst:
case ValueKind::RetainValueInst:
case ValueKind::ReleaseValueInst:
break;
default:
if (MaybeDead->mayHaveSideEffects()) {
if (Changed)
for (auto Dead : DeadInstrs)
Dead->eraseFromParent();
return Changed;
}
}
for (unsigned i = 0, e = MaybeDead->getNumTypes(); i != e; ++i)
if (!SILValue(&*MaybeDead, i).use_empty()) {
auto Undef = SILUndef::get(MaybeDead->getType(i), BB->getModule());
SILValue(&*MaybeDead, i).replaceAllUsesWith(Undef);
}
DeadInstrs.push_back(&*MaybeDead);
Changed = true;
}
// If this block was changed and it now consists of only the unreachable,
// make sure we process its predecessors.
if (Changed) {
for (auto Dead : DeadInstrs)
Dead->eraseFromParent();
if (isOnlyUnreachable(BB))
for (auto *P : BB->getPreds())
addToWorklist(P);
}
return Changed;
}
bool SimplifyCFG::simplifyCheckedCastBranchBlock(CheckedCastBranchInst *CCBI) {
auto SuccessBB = CCBI->getSuccessBB();
auto FailureBB = CCBI->getFailureBB();
auto ThisBB = CCBI->getParent();
CastOptimizer CastOpt(
[](SILInstruction *I, ValueBase *V){} /* ReplaceInstUsesAction */,
[](SILInstruction *I) { /* EraseInstAction */
I->eraseFromParent();
},
[&]() { /* WillSucceedAction */
removeIfDead(FailureBB);
addToWorklist(ThisBB);
},
[&]() { /* WillFailAction */
removeIfDead(SuccessBB);
addToWorklist(ThisBB);
});
return CastOpt.simplifyCheckedCastBranchInst(CCBI) != nullptr;
}
bool
SimplifyCFG::
simplifyCheckedCastAddrBranchBlock(CheckedCastAddrBranchInst *CCABI) {
auto SuccessBB = CCABI->getSuccessBB();
auto FailureBB = CCABI->getFailureBB();
auto ThisBB = CCABI->getParent();
CastOptimizer CastOpt(
[](SILInstruction *I, ValueBase *V){} /* ReplaceInstUsesAction */,
[](SILInstruction *I) { /* EraseInstAction */
I->eraseFromParent();
},
[&]() { /* WillSucceedAction */
removeIfDead(FailureBB);
addToWorklist(ThisBB);
},
[&]() { /* WillFailAction */
removeIfDead(SuccessBB);
addToWorklist(ThisBB);
});
return CastOpt.simplifyCheckedCastAddrBranchInst(CCABI) != nullptr;
}
// Replace the terminator of BB with a simple branch if all successors go
// to trampoline jumps to the same destination block. The successor blocks
// and the destination blocks may have no arguments.
bool SimplifyCFG::simplifyTermWithIdenticalDestBlocks(SILBasicBlock *BB) {
SILBasicBlock *commonDest = nullptr;
for (const SILSuccessor &Succ : BB->getSuccessors()) {
SILBasicBlock *SuccBlock = Succ.getBB();
if (SuccBlock->getNumBBArg() != 0)
return false;
SILBasicBlock *DestBlock = getTrampolineDest(SuccBlock);
if (!DestBlock)
return false;
if (!commonDest) {
commonDest = DestBlock;
} else if (DestBlock != commonDest) {
return false;
}
}
if (!commonDest)
return false;
assert(commonDest->getNumBBArg() == 0 &&
"getTrampolineDest should have checked that commonDest has no args");
TermInst *Term = BB->getTerminator();
SILBuilderWithScope<1>(Term).createBranch(Term->getLoc(), commonDest, {});
Term->eraseFromParent();
addToWorklist(BB);
addToWorklist(commonDest);
return true;
}
void RemoveUnreachable::visit(SILBasicBlock *BB) {
if (!Visited.insert(BB).second)
return;
for (auto &Succ : BB->getSuccessors())
visit(Succ);
}
bool RemoveUnreachable::run() {
bool Changed = false;
// Clear each time we run so that we can run multiple times.
Visited.clear();
// Visit all blocks reachable from the entry block of the function.
visit(Fn.begin());
// Remove the blocks we never reached.
for (auto It = Fn.begin(), End = Fn.end(); It != End; ) {
auto *BB = &*It++;
if (!Visited.count(BB)) {
removeDeadBlock(BB);
Changed = true;
}
}
return Changed;
}
/// Checks if the block contains a cond_fail as first side-effect instruction
/// and trys to move it to the predecessors (if benefitial). A sequence
///
/// bb1:
/// br bb3(%c)
/// bb2:
/// %i = integer_literal
/// br bb3(%i) // at least one input argument must be constant
/// bb3(%a) // = BB
/// cond_fail %a // %a must not have other uses
///
/// is replaced with
///
/// bb1:
/// cond_fail %c
/// br bb3(%c)
/// bb2:
/// %i = integer_literal
/// cond_fail %i
/// br bb3(%i)
/// bb3(%a) // %a is dead
///
static bool tryMoveCondFailToPreds(SILBasicBlock *BB) {
CondFailInst *CFI = getFistCondFail(BB);
if (!CFI)
return false;
// Find the underlying condition value of the cond_fail.
SILValue cond = CFI->getOperand();
bool inverted = false;
while (auto *BI = dyn_cast<BuiltinInst>(cond)) {
// This is not a correctness check, but we only want to to the optimization
// if the condition gets dead after moving the cond_fail.
if (!BI->hasOneUse())
return false;
OperandValueArrayRef Args = BI->getArguments();
if (BI->getBuiltinInfo().ID == BuiltinValueKind::Xor) {
// Check if it's a boolean invertion of the condition.
if (auto *IL = dyn_cast<IntegerLiteralInst>(Args[1])) {
if (IL->getValue().isAllOnesValue()) {
cond = Args[0];
inverted = !inverted;
continue;
}
} else if (auto *IL = dyn_cast<IntegerLiteralInst>(Args[0])) {
if (IL->getValue().isAllOnesValue()) {
cond = Args[1];
inverted = !inverted;
continue;
}
}
}
break;
}
// Check if the condition is a single-used argument in the current block.
SILArgument *condArg = dyn_cast<SILArgument>(cond);
if (!condArg || !condArg->hasOneUse())
return false;
if (condArg->getParent() != BB)
return false;
// Check if some of the predecessor blocks provide a constant for the
// cond_fail condition. So that the optimization has a positive effect.
bool somePredsAreConst = false;
for (auto *Pred : BB->getPreds()) {
// The cond_fail must post-dominate the predecessor block. We may not
// execute the cond_fail speculatively.
if (!Pred->getSingleSuccessor())
return false;
SILValue incoming = condArg->getIncomingValue(Pred);
if (isa<IntegerLiteralInst>(incoming)) {
somePredsAreConst = true;
break;
}
}
if (!somePredsAreConst)
return false;
DEBUG(llvm::dbgs() << "### move to predecessors: " << *CFI);
// Move the cond_fail to the predecessor blocks.
for (auto *Pred : BB->getPreds()) {
SILValue incoming = condArg->getIncomingValue(Pred);
SILBuilderWithScope<4> Builder(Pred->getTerminator());
createCondFail(CFI, incoming, inverted, Builder);
}
CFI->eraseFromParent();
return true;
}
bool SimplifyCFG::simplifyBlocks() {
bool Changed = false;
// Add all of the blocks to the function.
for (auto &BB : Fn)
addToWorklist(&BB);
// Iteratively simplify while there is still work to do.
while (SILBasicBlock *BB = popWorklist()) {
// If the block is dead, remove it.
if (removeIfDead(BB)) {
Changed = true;
continue;
}
// Otherwise, try to simplify the terminator.
TermInst *TI = BB->getTerminator();
switch (TI->getKind()) {
case ValueKind::BranchInst:
Changed |= simplifyBranchBlock(cast<BranchInst>(TI));
break;
case ValueKind::CondBranchInst:
Changed |= simplifyCondBrBlock(cast<CondBranchInst>(TI));
break;
case ValueKind::SwitchValueInst:
// FIXME: Optimize for known switch values.
Changed |= simplifyTermWithIdenticalDestBlocks(BB);
break;
case ValueKind::SwitchEnumInst:
Changed |= simplifySwitchEnumBlock(cast<SwitchEnumInst>(TI));
Changed |= simplifyTermWithIdenticalDestBlocks(BB);
break;
case ValueKind::UnreachableInst:
Changed |= simplifyUnreachableBlock(cast<UnreachableInst>(TI));
break;
case ValueKind::CheckedCastBranchInst:
Changed |= simplifyCheckedCastBranchBlock(cast<CheckedCastBranchInst>(TI));
break;
case ValueKind::CheckedCastAddrBranchInst:
Changed |= simplifyCheckedCastAddrBranchBlock(cast<CheckedCastAddrBranchInst>(TI));
break;
case ValueKind::SwitchEnumAddrInst:
Changed |= simplifyTermWithIdenticalDestBlocks(BB);
break;
default:
break;
}
// If the block has a cond_fail, try to move it to the predecessors.
Changed |= tryMoveCondFailToPreds(BB);
// Simplify the block argument list.
Changed |= simplifyArgs(BB);
}
return Changed;
}
/// Canonicalize all switch_enum and switch_enum_addr instructions.
/// If possible, replace the default with the corresponding unique case.
bool SimplifyCFG::canonicalizeSwitchEnums() {
bool Changed = false;
for (auto &BB : Fn) {
TermInst *TI = BB.getTerminator();
SwitchEnumInstBase *SWI = dyn_cast<SwitchEnumInstBase>(TI);
if (!SWI)
continue;
if (!SWI->hasDefault())
continue;
NullablePtr<EnumElementDecl> elementDecl = SWI->getUniqueCaseForDefault();
if (!elementDecl)
continue;
// Construct a new instruction by copying all the case entries.
SmallVector<std::pair<EnumElementDecl*, SILBasicBlock*>, 4> CaseBBs;
for (int idx = 0, numIdcs = SWI->getNumCases(); idx < numIdcs; idx++) {
CaseBBs.push_back(SWI->getCase(idx));
}
// Add the default-entry of the original instruction as case-entry.
CaseBBs.push_back(std::make_pair(elementDecl.get(), SWI->getDefaultBB()));
if (SWI->getKind() == ValueKind::SwitchEnumInst) {
SILBuilderWithScope<1>(SWI).createSwitchEnum(SWI->getLoc(),
SWI->getOperand(), nullptr, CaseBBs);
} else {
assert(SWI->getKind() == ValueKind::SwitchEnumAddrInst &&
"unknown switch_enum instruction");
SILBuilderWithScope<1>(SWI).createSwitchEnumAddr(SWI->getLoc(),
SWI->getOperand(), nullptr, CaseBBs);
}
SWI->eraseFromParent();
Changed = true;
}
return Changed;
}
static SILBasicBlock *isObjCMethodCallBlock(SILBasicBlock &Block) {
auto *Branch = dyn_cast<BranchInst>(Block.getTerminator());
if (!Branch)
return nullptr;
for (auto &Inst : Block) {
// Look for a objc method call.
auto *Apply = dyn_cast<ApplyInst>(&Inst);
if (!Apply)
continue;
auto *Callee = dyn_cast<WitnessMethodInst>(Apply->getCallee());
if (!Callee || !Callee->getMember().isForeign)
continue;
return Branch->getDestBB();
}
return nullptr;
}
/// We want to duplicate small blocks that contain a least on release and have
/// multiple predecessor.
static bool shouldTailDuplicate(SILBasicBlock &Block) {
unsigned Cost = 0;
bool SawRelease = false;
if (isa<ReturnInst>(Block.getTerminator()))
return false;
if (Block.getSinglePredecessor())
return false;
for (auto &Inst : Block) {
if (!Inst.isTriviallyDuplicatable())
return false;
if (isa<ApplyInst>(&Inst))
return false;
if (isa<ReleaseValueInst>(&Inst) ||
isa<StrongReleaseInst>(&Inst))
SawRelease = true;
if (instructionInlineCost(Inst) != InlineCost::Free)
if (++Cost == 12)
return false;
}
return SawRelease;
}
/// Tail duplicate successor blocks of blocks that perform an objc method call
/// and who contain releases. Cloning such blocks can allow ARC to sink retain
/// releases onto the ObjC path.
bool SimplifyCFG::tailDuplicateObjCMethodCallSuccessorBlocks() {
SmallVector<SILBasicBlock *, 16> ObjCBlocks;
// Collect blocks to tail duplicate.
for (auto &BB : Fn) {
SILBasicBlock *DestBB;
if ((DestBB = isObjCMethodCallBlock(BB)) && !LoopHeaders.count(DestBB) &&
shouldTailDuplicate(*DestBB))
ObjCBlocks.push_back(&BB);
}
bool Changed = false;
for (auto *BB : ObjCBlocks) {
auto *Branch = cast<BranchInst>(BB->getTerminator());
auto *DestBB = Branch->getDestBB();
Changed = true;
// Okay, it looks like we want to do this and we can. Duplicate the
// destination block into this one, rewriting uses of the BBArgs to use the
// branch arguments as we go.
ThreadingCloner Cloner(Branch);
for (auto &I : *DestBB)
Cloner.process(&I);
Branch->eraseFromParent();
updateSSAAfterCloning(Cloner, BB, DestBB);
}
return Changed;
}
bool SimplifyCFG::run() {
RemoveUnreachable RU(Fn);
// First remove any block not reachable from the entry.
bool Changed = RU.run();
// Find the set of loop headers. We don't want to jump-thread through headers.
findLoopHeaders();
DT = nullptr;
PDT = nullptr;
if (simplifyBlocks()) {
// Simplifying other blocks might have resulted in unreachable
// loops.
RU.run();
Changed = true;
}
// Do simplifications that require the dominator tree to be accurate.
DominanceAnalysis *DA = PM->getAnalysis<DominanceAnalysis>();
PostDominanceAnalysis *PDA = PM->getAnalysis<PostDominanceAnalysis>();
if (Changed) {
// Force dominator recomputation since we modifed the cfg.
DA->invalidate(&Fn, SILAnalysis::PreserveKind::Nothing);
PDA->invalidate(&Fn, SILAnalysis::PreserveKind::Nothing);
}
Changed |= dominatorBasedSimplify(DA, PDA);
DT = nullptr;
PDT = nullptr;
// Now attempt to simplify the remaining blocks.
if (simplifyBlocks()) {
// Simplifying other blocks might have resulted in unreachable
// loops.
RU.run();
Changed = true;
}
if (tailDuplicateObjCMethodCallSuccessorBlocks()) {
Changed = true;
if (simplifyBlocks())
RU.run();
}
// Split all critical edges from non cond_br terminators.
Changed |= splitAllCriticalEdges(Fn, true, nullptr, nullptr);
// Canonicalize switch_enum instructions.
Changed |= canonicalizeSwitchEnums();
return Changed;
}
static void
removeArgumentFromTerminator(SILBasicBlock *BB, SILBasicBlock *Dest, int idx) {
TermInst *Branch = BB->getTerminator();
SILBuilderWithScope<2> Builder(Branch);
if (CondBranchInst *CBI = dyn_cast<CondBranchInst>(Branch)) {
DEBUG(llvm::dbgs() << "*** Fixing CondBranchInst.\n");
SmallVector<SILValue, 8> TrueArgs;
SmallVector<SILValue, 8> FalseArgs;
for (auto A : CBI->getTrueArgs())
TrueArgs.push_back(A);
for (auto A : CBI->getFalseArgs())
FalseArgs.push_back(A);
if (Dest == CBI->getTrueBB())
TrueArgs.erase(TrueArgs.begin() + idx);
if (Dest == CBI->getFalseBB())
FalseArgs.erase(FalseArgs.begin() + idx);
Builder.createCondBranch(CBI->getLoc(), CBI->getCondition(),
CBI->getTrueBB(), TrueArgs,
CBI->getFalseBB(), FalseArgs);
Branch->eraseFromParent();
return;
}
if (BranchInst *BI = dyn_cast<BranchInst>(Branch)) {
DEBUG(llvm::dbgs() << "*** Fixing BranchInst.\n");
SmallVector<SILValue, 8> Args;
for (auto A : BI->getArgs())
Args.push_back(A);
Args.erase(Args.begin() + idx);
Builder.createBranch(BI->getLoc(), BI->getDestBB(), Args);
Branch->eraseFromParent();
return;
}
llvm_unreachable("unsupported terminator");
}
/// Is an argument from this terminator considered mandatory?
static bool hasMandatoryArgument(TermInst *term) {
// It's more maintainable to just white-list the instructions that
// *do* have mandatory arguments.
return (!isa<BranchInst>(term) && !isa<CondBranchInst>(term));
}
// Get the element of Aggregate corresponding to the one extracted by
// Extract.
static SILValue getInsertedValue(SILInstruction *Aggregate,
SILInstruction *Extract) {
if (auto *Struct = dyn_cast<StructInst>(Aggregate)) {
auto *SEI = cast<StructExtractInst>(Extract);
return Struct->getFieldValue(SEI->getField());
}
auto *Tuple = cast<TupleInst>(Aggregate);
auto *TEI = cast<TupleExtractInst>(Extract);
return Tuple->getElement(TEI->getFieldNo());
}
/// Check a diamond-form property of graphs generated by swith_enum
/// instructions, who only produce integer values by each of BBs handling its
/// case tags.
/// In such graphs, switch_enum dominates any blocks processing cases and all
/// those blocks processing different cases are post-dominated by a single
/// basic block consuming those values, where all the paths join.
static bool isDiamondForm(SILBasicBlock *BB, SILBasicBlock *PredBB,
SILBasicBlock *PostBB, DominanceInfo *DT,
PostDominanceInfo *PDT) {
if (PredBB && !DT->dominates(PredBB, BB))
return false;
if (PostBB && !PDT->dominates(PostBB, BB))
return false;
return true;
}
/// Check if a basic blocks consists of a single branch instruction.
static bool isSingleBranchBlock(SILBasicBlock *BB) {
TermInst *TI = BB->getTerminator();
if (!isa<BranchInst>(TI))
return false;
return TI == BB->begin();
}
/// Find a parent SwitchEnumInst of a basic block. If SEI is set, then
/// only return non-nullptr if the found SwitchEnumInst is the same one as SEI.
/// We consider only those predecessor blocks which are post-dominated by
/// PostBB and dominated by SEI. This ensures that we have a diamond-like CFG
/// starting at SEI and ending at PostBB.
static SwitchEnumInst *
getSwitchEnumPred(SILBasicBlock *BB, SwitchEnumInst *SEI, SILBasicBlock *PostBB,
SmallPtrSet<SILBasicBlock *, 8> &Blocks,
SmallPtrSet<SILBasicBlock *, 8> Visited, DominanceInfo *DT,
PostDominanceInfo *PDT) {
if (BB->pred_empty())
return nullptr;
// Any BB can be visited only once.
if (Visited.count(BB))
return nullptr;
// Remember that this BB was seen already.
Visited.insert(BB);
// Only consider blocks which are post-dominated by PostBB and
// dominated by SEI.
if (!isDiamondForm(BB, (SEI) ? SEI->getParent() : nullptr, PostBB, DT, PDT))
return nullptr;
// Check that this block only produces the value, but does not
// have any side effects.
bool BBHasIntegerLiteral = false;
auto First = BB->begin();
auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
if (!BI)
return nullptr;
if (BI != First) {
// There may be only one instruction before the branch.
if (BI != next(First))
return nullptr;
// There are some instructions besides the branch.
// It should be only an integer literal instruction.
// Handle only integer values for now.
auto *ILI = dyn_cast<IntegerLiteralInst>(First);
if (!ILI)
return nullptr;
// Check that this literal is used by the terminator.
for (auto U : ILI->getUses())
if (U->getUser() != BI)
return nullptr;
// The branch can pass arguments only to the PostBB.
if (BI->getDestBB() != PostBB)
return nullptr;
BBHasIntegerLiteral = true;
}
// Each BB on the path should have only a single branch instruction.
// The only exception is a BB which has a BB ending with switch_enum
// as its single predecessor. Such a block may have an integer_literal
// instruction before the branch.
for (auto PredBB : BB->getPreds()) {
SwitchEnumInst *PredSEI;
if (isSingleBranchBlock(PredBB)) {
PredSEI = getSwitchEnumPred(PredBB, SEI, PostBB, Blocks, Visited,
DT, PDT);
} else {
// Check if a predecessor BB terminates with a switch_enum instruction
PredSEI = dyn_cast<SwitchEnumInst>(PredBB->getTerminator());
if (!PredSEI)
return nullptr;
// Remember that this BB is immediately reachable from a switch_enum.
Blocks.insert(BB);
}
if (!PredSEI)
return nullptr;
if (SEI && PredSEI != SEI)
return nullptr;
if (!SEI)
SEI = PredSEI;
}
return SEI;
}
/// Helper function to produce a SILValue from a result value
/// produced by a basic block responsible for handling a
/// specific enum tag.
static SILValue
getSILValueFromCaseResult(SILBuilder &B, SILLocation Loc,
SILType Type, SILValue Val) {
if (auto *IL = dyn_cast<IntegerLiteralInst>(Val)) {
auto Value = IL->getValue();
if (Value.getBitWidth() != 1)
return B.createIntegerLiteral(Loc, Type, Value);
else
// This is a boolean value
return B.createIntegerLiteral(Loc, Type, Value.getBoolValue());
} else {
llvm::errs() << "Non IntegerLiteralInst switch case result\n";
Val.dump();
return Val;
}
}
/// Given an integer argument, see if it is ultimately matching whether
/// a given enum is of a given tag. If so, create a new select_enum instruction
/// This is used to simplify arbitrary simple switch_enum diamonds into
/// select_enums.
bool simplifySwitchEnumToSelectEnum(SILBasicBlock *BB, unsigned ArgNum,
SILArgument *IntArg, DominanceInfo *DT,
PostDominanceInfo *PDT) {
if (!DT || !PDT)
return false;
auto &Fn = *BB->getParent();
// Don't know which values should be passed if there is more
// than one basic block argument.
if (BB->bbarg_size() > 1)
return false;
// Mapping from case values to the results corresponding to this case value.
SmallVector<std::pair<EnumElementDecl *, SILValue>, 8> CaseToValue;
// Mapping from BB responsible for a specific case value to the result it
// produces.
llvm::DenseMap<SILBasicBlock *, SILValue> BBToValue;
// switch_enum instruction to be replaced.
SwitchEnumInst *SEI = nullptr;
bool HasNonSwitchEnumPreds = false;
// Iterate over all immediate predecessors of the target basic block.
// - Check that each one stems directly or indirectly from the same
// switch_enum instruction.
// - Remember for each case tag of the switch_enum instruction which
// integer value it produces.
// - Check that each block handling a given case tag of a switch_enum
// only produces an integer value and does not have any side-effects.
for (auto P : BB->getPreds()) {
// Only handle branch instructions.
auto *TI = P->getTerminator();
if (!isa<BranchInst>(TI))
return false;
// Find the Nth argument passed to BB.
auto Arg = TI->getOperand(ArgNum);
auto *SI = dyn_cast<SILInstruction>(Arg);
if (!SI) {
return false;
} else {
// Handle integer values
auto *IntLit = dyn_cast<IntegerLiteralInst>(SI);
if (!IntLit) {
// TODO: SI may be any instruction that dominates the switch_enum
// instruction?
//if (!DT->dominates(SI->getParent(), P))
return false;
}
}
// Set of blocks that branch to/reach this basic block P and are immediate
// successors of a switch_enum instruction.
SmallPtrSet<SILBasicBlock *, 8> Blocks;
// Set of blocks visited during a search for a parent switch_enum instruction.
SmallPtrSet<SILBasicBlock *, 8> Visited;
// Try to find a parent SwitchEnumInst for the current predecessor of BB.
auto *PredSEI = getSwitchEnumPred(P, SEI, BB, Blocks, Visited, DT, PDT);
// Predecessor is not produced by a switch_enum instruction, bail.
if (!PredSEI) {
HasNonSwitchEnumPreds = true;
continue;
}
// Check if all predecessors stem from the same switch_enum instruction.
if (SEI) {
if (SEI != PredSEI) {
// It comes from a different switch_enum instruction, bail.
HasNonSwitchEnumPreds = true;
continue;
}
} else {
SEI = PredSEI;
}
// Remember the result value used to branch to this instruction.
for (auto B : Blocks)
BBToValue[B] = Arg;
}
if (!SEI)
return false;
// Insert the new enum_select instruction right after enum_switch
SILBuilder B(SEI);
// Form a set of case_tag:result pairs for select_enum
for (unsigned i = 0, e = SEI->getNumCases(); i != e; ++i) {
std::pair<EnumElementDecl *, SILBasicBlock *> Pair = SEI->getCase(i);
// If one of the branches is not covered, bail
if (!BBToValue.count(Pair.second))
return false;
auto CaseValue = BBToValue[Pair.second];
auto CaseSILValue = getSILValueFromCaseResult(B, SEI->getLoc(),
IntArg->getType(),
CaseValue);
CaseToValue.push_back(std::make_pair(Pair.first, CaseSILValue));
}
// Default value for select_enum.
SILValue DefaultSILValue = SILValue();
if (SEI->hasDefault()) {
// Try to define a default case for enum_select based
// on the default case of enum_switch.
// If default branch is not covered, bail
if (!BBToValue.count(SEI->getDefaultBB()))
return false;
auto DefaultValue = BBToValue[SEI->getDefaultBB()];
DefaultSILValue = getSILValueFromCaseResult(B, SEI->getLoc(),
IntArg->getType(),
DefaultValue);
} else {
// Try to see if enum_switch covers all possible cases.
// If it does, then pick one of those cases as a default.
// Count the number of possible case tags for a given enum type
auto *Enum = SEI->getOperand().getType().getEnumOrBoundGenericEnum();
unsigned ElemCount = 0;
for (auto E : Enum->getAllElements()) {
if (E)
ElemCount++;
}
// Check if all possible cases are covered.
if (ElemCount == SEI->getNumCases()) {
// This enum_switch instruction is exhaustive.
// Make the last case a default.
auto Pair = CaseToValue.pop_back_val();
DefaultSILValue = Pair.second;
}
}
// We don't need to have explicit cases for any case tags which produce the
// same result as the default branch.
if (DefaultSILValue != SILValue()) {
auto DefaultValue = DefaultSILValue;
auto *DefaultSI = dyn_cast<IntegerLiteralInst>(DefaultValue);
for (auto I = CaseToValue.begin(); I != CaseToValue.end();) {
auto CaseValue = I->second;
if (CaseValue == DefaultValue) {
I = CaseToValue.erase(I);
continue;
}
if (DefaultSI) {
if (auto CaseSI = dyn_cast<IntegerLiteralInst>(CaseValue)) {
if (DefaultSI->getValue() == CaseSI->getValue()) {
I = CaseToValue.erase(I);
continue;
}
}
}
++I;
}
}
// Create a new select_enum instruction
auto SelectInst = B.createSelectEnum(SEI->getLoc(), SEI->getOperand(),
IntArg->getType(),
DefaultSILValue, CaseToValue);
if (!HasNonSwitchEnumPreds) {
// Check that all uses of IntArg are dominated by SelectInst
bool SelectDominatesAllArgUses = true;
for(auto U : IntArg->getUses()) {
if (!DT->dominates(SelectInst->getParent(), U->getUser()->getParent())) {
SelectDominatesAllArgUses = false;
break;
}
}
// If all uses of IntArg are dominated by SelectInst, it is safe
// to replace IntArg by the result of SelectInst because
// it is the only incoming value for the IntArg.
if (SelectDominatesAllArgUses) {
IntArg->replaceAllUsesWith(SelectInst);
}
}
// Do not replace the bbarg
SmallVector<SILValue, 4> Args;
Args.push_back(SelectInst);
B.setInsertionPoint(SelectInst->getNextNode());
B.createBranch(SEI->getLoc(), BB, Args);
// Remove switch_enum instruction
SEI->getParent()->getTerminator()->eraseFromParent();
// We have modified the CFG recompute the (post)dominators.
PDT->recalculate(Fn);
DT->recalculate(Fn);
return true;
}
/// Collected information for a select_value case or default case.
struct CaseInfo {
/// The input value or null if it is the default case.
IntegerLiteralInst *Literal = nullptr;
/// The result value.
SILInstruction *Result = nullptr;
/// The block which conains the cond_br of the input value comparison
/// or the block which assigns the default value.
SILBasicBlock *CmpOrDefault = nullptr;
};
/// Get information about a potential select_value case (or default).
/// \p Input is set to the common input value.
/// \p Pred is the predecessor block of the last merge block of the CFG pattern.
/// \p ArgNum is the index of the argument passed to the merge block.
CaseInfo getCaseInfo(SILValue &Input, SILBasicBlock *Pred, unsigned ArgNum) {
CaseInfo CaseInfo;
auto *TI = Pred->getTerminator();
if (!isa<BranchInst>(TI))
return CaseInfo;
// Find the Nth argument passed to BB.
auto Arg = TI->getOperand(ArgNum);
// Currently we only accept enums as result values.
auto *EI2 = dyn_cast<EnumInst>(Arg);
if (!EI2)
return CaseInfo;
if (EI2->hasOperand()) {
// ... or enums with enum data. This is exactly the pattern for an enum
// with integer raw value initialization.
auto *EI1 = dyn_cast<EnumInst>(EI2->getOperand());
if (!EI1)
return CaseInfo;
// But not enums with enums with data.
if (EI1->hasOperand())
return CaseInfo;
}
// Check if we come to the Pred block by comparing the input value to a
// constant.
SILBasicBlock *CmpBlock = Pred->getSinglePredecessor();
if (!CmpBlock)
return CaseInfo;
auto *CmpInst = dyn_cast<CondBranchInst>(CmpBlock->getTerminator());
if (!CmpInst)
return CaseInfo;
auto *CondInst = dyn_cast<BuiltinInst>(CmpInst->getCondition());
if (!CondInst)
return CaseInfo;
if (!CondInst->getName().str().startswith("cmp_eq"))
return CaseInfo;
auto CondArgs = CondInst->getArguments();
assert(CondArgs.size() == 2);
SILValue Arg1 = CondArgs[0];
SILValue Arg2 = CondArgs[1];
if (isa<IntegerLiteralInst>(Arg1))
std::swap(Arg1, Arg2);
auto *CmpVal = dyn_cast<IntegerLiteralInst>(Arg2);
if (!CmpVal)
return CaseInfo;
SILBasicBlock *FalseBB = CmpInst->getFalseBB();
if (!FalseBB)
return CaseInfo;
// Check for a common input value.
if (Input && Input != Arg1)
return CaseInfo;
Input = Arg1;
CaseInfo.Result = EI2;
if (CmpInst->getTrueBB() == Pred) {
// This is a case for the select_value.
CaseInfo.Literal = CmpVal;
CaseInfo.CmpOrDefault = CmpBlock;
} else {
// This is the default for the select_value.
CaseInfo.CmpOrDefault = Pred;
}
return CaseInfo;
}
/// Move an instruction which is an operand to the new SelectValueInst to its
/// correct place.
/// Either the instruction is somewhere inside the CFG pattern, then we move it
/// up, immediately before the SelectValueInst in the pattern's dominating
/// entry block. Or it is somewhere above the entry block, then we can leave the
/// instruction there.
void moveIfNotDominating(SILInstruction *I, SILInstruction *InsertPos,
DominanceInfo *DT) {
SILBasicBlock *InstBlock = I->getParent();
SILBasicBlock *InsertBlock = InsertPos->getParent();
if (!DT->dominates(InstBlock, InsertBlock)) {
assert(DT->dominates(InsertBlock, InstBlock));
I->moveBefore(InsertPos);
}
}
/// Simplify a pattern of integer compares to a select_value.
/// \code
/// if input == 1 {
/// result = Enum.A
/// } else if input == 2 {
/// result = Enum.B
/// ...
/// } else {
/// result = Enum.X
/// }
/// \endcode
/// Currently this only works if the input value is an integer and the result
/// value is an enum.
/// \p MergeBlock The "last" block which contains an argument in which all
/// result values are merged.
/// \p ArgNum The index of the block argument which is the result value.
/// \p DT The dominance info.
/// \return Returns true if a select_value is generated.
bool simplifyToSelectValue(SILBasicBlock *MergeBlock, unsigned ArgNum,
DominanceInfo *DT) {
if (!DT)
return false;
// Collect all case infos from the merge block's predecessors.
SmallPtrSet<SILBasicBlock *, 8> FoundCmpBlocks;
SmallVector<CaseInfo, 8> CaseInfos;
SILValue Input;
for (auto *Pred : MergeBlock->getPreds()) {
CaseInfo CaseInfo = getCaseInfo(Input, Pred, ArgNum);
if (!CaseInfo.Result)
return false;
FoundCmpBlocks.insert(CaseInfo.CmpOrDefault);
CaseInfos.push_back(CaseInfo);
}
SmallVector<std::pair<SILValue, SILValue>, 8> Cases;
SILValue defaultResult;
// The block of the first input value compare. It dominates all other blocks
// in this CFG pattern.
SILBasicBlock *dominatingBlock = nullptr;
// Build the cases for the SelectValueInst and find the first dominatingBlock.
for (auto &CaseInfo : CaseInfos) {
if (CaseInfo.Literal) {
auto *BrInst = cast<CondBranchInst>(CaseInfo.CmpOrDefault->getTerminator());
if (FoundCmpBlocks.count(BrInst->getFalseBB()) != 1)
return false;
Cases.push_back({CaseInfo.Literal, CaseInfo.Result});
SILBasicBlock *Pred = CaseInfo.CmpOrDefault->getSinglePredecessor();
if (!Pred || FoundCmpBlocks.count(Pred) == 0) {
// There may be only a single block whose predecessor we didn't see. And
// this is the entry block to the CFG pattern.
if (dominatingBlock)
return false;
dominatingBlock = CaseInfo.CmpOrDefault;
}
} else {
if (defaultResult)
return false;
defaultResult = CaseInfo.Result;
}
}
if (!defaultResult)
return false;
if (!dominatingBlock)
return false;
// Generate the select_value right before the first cond_br of the pattern.
SILInstruction *insertPos = dominatingBlock->getTerminator();
SILBuilder B(insertPos);
// Move all needed operands to a place where they dominate the select_value.
for (auto &CaseInfo : CaseInfos) {
if (CaseInfo.Literal)
moveIfNotDominating(CaseInfo.Literal, insertPos, DT);
auto *EI2 = dyn_cast<EnumInst>(CaseInfo.Result);
assert(EI2);
if (EI2->hasOperand()) {
auto *EI1 = dyn_cast<EnumInst>(EI2->getOperand());
assert(EI1);
assert(!EI1->hasOperand());
moveIfNotDominating(EI1, insertPos, DT);
}
moveIfNotDominating(EI2, insertPos, DT);
}
SILArgument *bbArg = MergeBlock->getBBArg(ArgNum);
auto SelectInst = B.createSelectValue(dominatingBlock->getTerminator()->getLoc(),
Input, bbArg->getType(),
defaultResult, Cases);
bbArg->replaceAllUsesWith(SelectInst);
return true;
}
// Attempt to simplify the ith argument of BB. We simplify cases
// where there is a single use of the argument that is an extract from
// a struct or tuple and where the predecessors all build the struct
// or tuple and pass it directly.
bool SimplifyCFG::simplifyArgument(SILBasicBlock *BB, unsigned i) {
auto *A = BB->getBBArg(i);
// Try to create a select_value.
if (simplifyToSelectValue(BB, i, DT))
return true;
// If we are reading an i1, then check to see if it comes from
// a switch_enum. If so, we may be able to lower this sequence to
// a select_enum.
if (A->getType().is<BuiltinIntegerType>())
return simplifySwitchEnumToSelectEnum(BB, i, A, DT, PDT);
// For now, just focus on cases where there is a single use.
if (!A->hasOneUse())
return false;
auto *Use = *A->use_begin();
auto *User = cast<SILInstruction>(Use->getUser());
if (!dyn_cast<StructExtractInst>(User) &&
!dyn_cast<TupleExtractInst>(User))
return false;
// For now, just handle the case where all predecessors are
// unconditional branches.
for (auto *Pred : BB->getPreds()) {
if (!isa<BranchInst>(Pred->getTerminator()))
return false;
auto *Branch = cast<BranchInst>(Pred->getTerminator());
if (!isa<StructInst>(Branch->getArg(i)) &&
!isa<TupleInst>(Branch->getArg(i)))
return false;
}
// Okay, we'll replace the BB arg with one with the right type, replace
// the uses in this block, and then rewrite the branch operands.
A->replaceAllUsesWith(SILUndef::get(A->getType(), BB->getModule()));
auto *NewArg = BB->replaceBBArg(i, User->getType(0));
User->replaceAllUsesWith(NewArg);
User->eraseFromParent();
// Rewrite the branch operand for each incoming branch.
for (auto *Pred : BB->getPreds()) {
if (auto *Branch = cast<BranchInst>(Pred->getTerminator())) {
auto V = getInsertedValue(cast<SILInstruction>(Branch->getArg(i)),
User);
Branch->setOperand(i, V);
addToWorklist(Pred);
}
}
return true;
}
static void tryToReplaceArgWithIncomingValue(SILBasicBlock *BB, unsigned i,
DominanceInfo *DT) {
auto *A = BB->getBBArg(i);
SmallVector<SILValue, 4> Incoming;
if (!A->getIncomingValues(Incoming) || Incoming.empty())
return;
SILValue V = Incoming[0];
for (size_t Idx = 1, Size = Incoming.size(); Idx < Size; ++Idx) {
if (Incoming[Idx] != V)
return;
}
// If the incoming values of all predecessors are equal usually this means
// that the common incoming value dominates the BB. But: this might be not
// the case if BB is unreachable. Therefore we still have to check it.
if (!DT->dominates(V.getDef()->getParentBB(), BB))
return;
A->replaceAllUsesWith(V.getDef());
}
bool SimplifyCFG::simplifyArgs(SILBasicBlock *BB) {
// Ignore blocks with no arguments.
if (BB->bbarg_empty())
return false;
// Ignore the entry block.
if (BB->pred_empty())
return false;
// Ignore blocks that are successors of terminators with mandatory args.
for (SILBasicBlock *pred : BB->getPreds()) {
if (hasMandatoryArgument(pred->getTerminator()))
return false;
}
bool Changed = false;
for (int i = BB->getNumBBArg() - 1; i >= 0; --i) {
SILArgument *A = BB->getBBArg(i);
// Replace a block argument if all incoming values are equal. If this
// succeeds, argument A will have no uses afterwards.
if (DT)
tryToReplaceArgWithIncomingValue(BB, i, DT);
// Try to simplify the argument
if (!A->use_empty()) {
if (simplifyArgument(BB, i))
Changed = true;
continue;
}
DEBUG(llvm::dbgs() << "*** Erasing " << i <<"th BB argument.\n");
NumDeadArguments++;
Changed = true;
BB->eraseBBArg(i);
// Determine the set of predecessors in case any predecessor has
// two edges to this block (e.g. a conditional branch where both
// sides reach this block).
llvm::SmallPtrSet<SILBasicBlock *, 4> PredBBs;
for (auto *Pred : BB->getPreds())
PredBBs.insert(Pred);
for (auto *Pred : PredBBs)
removeArgumentFromTerminator(Pred, BB, i);
}
return Changed;
}
namespace {
class SimplifyCFGPass : public SILFunctionTransform {
/// The entry point to the transformation.
void run() override {
if (SimplifyCFG(*getFunction(), PM, getOptions().VerifyAll).run())
invalidateAnalysis(SILAnalysis::PreserveKind::Nothing);
}
StringRef getName() override { return "Simplify CFG"; }
};
} // end anonymous namespace
SILTransform *swift::createSimplifyCFG() {
return new SimplifyCFGPass();
}
//===----------------------------------------------------------------------===//
// Passes only for Testing
//===----------------------------------------------------------------------===//
namespace {
// Used to test critical edge splitting with sil-opt.
class SplitCriticalEdges : public SILFunctionTransform {
bool OnlyNonCondBrEdges;
public:
SplitCriticalEdges(bool SplitOnlyNonCondBrEdges)
: OnlyNonCondBrEdges(SplitOnlyNonCondBrEdges) {}
void run() override {
auto &Fn = *getFunction();
// Split all critical egdes from all or non only cond_br terminators.
bool Changed =
splitAllCriticalEdges(Fn, OnlyNonCondBrEdges, nullptr, nullptr);
if (Changed)
invalidateAnalysis(SILAnalysis::PreserveKind::Calls);
}
StringRef getName() override { return "Split Critical Edges"; }
};
// Used to test SimplifyCFG::simplifyArgs with sil-opt.
class SimplifyBBArgs : public SILFunctionTransform {
public:
SimplifyBBArgs() {}
/// The entry point to the transformation.
void run() override {
if (SimplifyCFG(*getFunction(), PM, getOptions().VerifyAll)
.simplifyBlockArgs())
invalidateAnalysis(SILAnalysis::PreserveKind::Calls);
}
StringRef getName() override { return "Simplify Block Args"; }
};
} // End anonymous namespace.
/// Splits all critical edges in a function.
SILTransform *swift::createSplitAllCriticalEdges() {
return new SplitCriticalEdges(false);
}
/// Splits all critical edges from non cond_br terminators in a function.
SILTransform *swift::createSplitNonCondBrCriticalEdges() {
return new SplitCriticalEdges(true);
}
// Simplifies basic block arguments.
SILTransform *swift::createSimplifyBBArgs() {
return new SimplifyBBArgs();
}
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