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IfConversion.cpp
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//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the machine instruction level if-conversion pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Passes.h"
#include "BranchFolding.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LivePhysRegs.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetSchedule.h"
#include "llvm/MC/MCInstrItineraries.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
#define DEBUG_TYPE "ifcvt"
// Hidden options for help debugging.
static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
cl::init(false), cl::Hidden);
static cl::opt<bool> IfCvtBranchFold("ifcvt-branch-fold",
cl::init(true), cl::Hidden);
STATISTIC(NumSimple, "Number of simple if-conversions performed");
STATISTIC(NumSimpleFalse, "Number of simple (F) if-conversions performed");
STATISTIC(NumTriangle, "Number of triangle if-conversions performed");
STATISTIC(NumTriangleRev, "Number of triangle (R) if-conversions performed");
STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
STATISTIC(NumDiamonds, "Number of diamond if-conversions performed");
STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
STATISTIC(NumDupBBs, "Number of duplicated blocks");
STATISTIC(NumUnpred, "Number of true blocks of diamonds unpredicated");
namespace {
class IfConverter : public MachineFunctionPass {
enum IfcvtKind {
ICNotClassfied, // BB data valid, but not classified.
ICSimpleFalse, // Same as ICSimple, but on the false path.
ICSimple, // BB is entry of an one split, no rejoin sub-CFG.
ICTriangleFRev, // Same as ICTriangleFalse, but false path rev condition.
ICTriangleRev, // Same as ICTriangle, but true path rev condition.
ICTriangleFalse, // Same as ICTriangle, but on the false path.
ICTriangle, // BB is entry of a triangle sub-CFG.
ICDiamond // BB is entry of a diamond sub-CFG.
};
/// BBInfo - One per MachineBasicBlock, this is used to cache the result
/// if-conversion feasibility analysis. This includes results from
/// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
/// classification, and common tail block of its successors (if it's a
/// diamond shape), its size, whether it's predicable, and whether any
/// instruction can clobber the 'would-be' predicate.
///
/// IsDone - True if BB is not to be considered for ifcvt.
/// IsBeingAnalyzed - True if BB is currently being analyzed.
/// IsAnalyzed - True if BB has been analyzed (info is still valid).
/// IsEnqueued - True if BB has been enqueued to be ifcvt'ed.
/// IsBrAnalyzable - True if AnalyzeBranch() returns false.
/// HasFallThrough - True if BB may fallthrough to the following BB.
/// IsUnpredicable - True if BB is known to be unpredicable.
/// ClobbersPred - True if BB could modify predicates (e.g. has
/// cmp, call, etc.)
/// NonPredSize - Number of non-predicated instructions.
/// ExtraCost - Extra cost for multi-cycle instructions.
/// ExtraCost2 - Some instructions are slower when predicated
/// BB - Corresponding MachineBasicBlock.
/// TrueBB / FalseBB- See AnalyzeBranch().
/// BrCond - Conditions for end of block conditional branches.
/// Predicate - Predicate used in the BB.
struct BBInfo {
bool IsDone : 1;
bool IsBeingAnalyzed : 1;
bool IsAnalyzed : 1;
bool IsEnqueued : 1;
bool IsBrAnalyzable : 1;
bool HasFallThrough : 1;
bool IsUnpredicable : 1;
bool CannotBeCopied : 1;
bool ClobbersPred : 1;
unsigned NonPredSize;
unsigned ExtraCost;
unsigned ExtraCost2;
MachineBasicBlock *BB;
MachineBasicBlock *TrueBB;
MachineBasicBlock *FalseBB;
SmallVector<MachineOperand, 4> BrCond;
SmallVector<MachineOperand, 4> Predicate;
BBInfo() : IsDone(false), IsBeingAnalyzed(false),
IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
HasFallThrough(false), IsUnpredicable(false),
CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
ExtraCost(0), ExtraCost2(0), BB(nullptr), TrueBB(nullptr),
FalseBB(nullptr) {}
};
/// IfcvtToken - Record information about pending if-conversions to attempt:
/// BBI - Corresponding BBInfo.
/// Kind - Type of block. See IfcvtKind.
/// NeedSubsumption - True if the to-be-predicated BB has already been
/// predicated.
/// NumDups - Number of instructions that would be duplicated due
/// to this if-conversion. (For diamonds, the number of
/// identical instructions at the beginnings of both
/// paths).
/// NumDups2 - For diamonds, the number of identical instructions
/// at the ends of both paths.
struct IfcvtToken {
BBInfo &BBI;
IfcvtKind Kind;
bool NeedSubsumption;
unsigned NumDups;
unsigned NumDups2;
IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
: BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
};
/// BBAnalysis - Results of if-conversion feasibility analysis indexed by
/// basic block number.
std::vector<BBInfo> BBAnalysis;
TargetSchedModel SchedModel;
const TargetLoweringBase *TLI;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
const MachineBlockFrequencyInfo *MBFI;
const MachineBranchProbabilityInfo *MBPI;
MachineRegisterInfo *MRI;
LivePhysRegs Redefs;
LivePhysRegs DontKill;
bool PreRegAlloc;
bool MadeChange;
int FnNum;
public:
static char ID;
IfConverter() : MachineFunctionPass(ID), FnNum(-1) {
initializeIfConverterPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineBlockFrequencyInfo>();
AU.addRequired<MachineBranchProbabilityInfo>();
MachineFunctionPass::getAnalysisUsage(AU);
}
bool runOnMachineFunction(MachineFunction &MF) override;
private:
bool ReverseBranchCondition(BBInfo &BBI);
bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
const BranchProbability &Prediction) const;
bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
bool FalseBranch, unsigned &Dups,
const BranchProbability &Prediction) const;
bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
unsigned &Dups1, unsigned &Dups2) const;
void ScanInstructions(BBInfo &BBI);
BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
std::vector<IfcvtToken*> &Tokens);
bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
bool isTriangle = false, bool RevBranch = false);
void AnalyzeBlocks(MachineFunction &MF, std::vector<IfcvtToken*> &Tokens);
void InvalidatePreds(MachineBasicBlock *BB);
void RemoveExtraEdges(BBInfo &BBI);
bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
unsigned NumDups1, unsigned NumDups2);
void PredicateBlock(BBInfo &BBI,
MachineBasicBlock::iterator E,
SmallVectorImpl<MachineOperand> &Cond,
SmallSet<unsigned, 4> *LaterRedefs = nullptr);
void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
SmallVectorImpl<MachineOperand> &Cond,
bool IgnoreBr = false);
void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges = true);
bool MeetIfcvtSizeLimit(MachineBasicBlock &BB,
unsigned Cycle, unsigned Extra,
const BranchProbability &Prediction) const {
return Cycle > 0 && TII->isProfitableToIfCvt(BB, Cycle, Extra,
Prediction);
}
bool MeetIfcvtSizeLimit(MachineBasicBlock &TBB,
unsigned TCycle, unsigned TExtra,
MachineBasicBlock &FBB,
unsigned FCycle, unsigned FExtra,
const BranchProbability &Prediction) const {
return TCycle > 0 && FCycle > 0 &&
TII->isProfitableToIfCvt(TBB, TCycle, TExtra, FBB, FCycle, FExtra,
Prediction);
}
// blockAlwaysFallThrough - Block ends without a terminator.
bool blockAlwaysFallThrough(BBInfo &BBI) const {
return BBI.IsBrAnalyzable && BBI.TrueBB == nullptr;
}
// IfcvtTokenCmp - Used to sort if-conversion candidates.
static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
int Incr1 = (C1->Kind == ICDiamond)
? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
int Incr2 = (C2->Kind == ICDiamond)
? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
if (Incr1 > Incr2)
return true;
else if (Incr1 == Incr2) {
// Favors subsumption.
if (!C1->NeedSubsumption && C2->NeedSubsumption)
return true;
else if (C1->NeedSubsumption == C2->NeedSubsumption) {
// Favors diamond over triangle, etc.
if ((unsigned)C1->Kind < (unsigned)C2->Kind)
return true;
else if (C1->Kind == C2->Kind)
return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
}
}
return false;
}
};
char IfConverter::ID = 0;
}
char &llvm::IfConverterID = IfConverter::ID;
INITIALIZE_PASS_BEGIN(IfConverter, "if-converter", "If Converter", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
INITIALIZE_PASS_END(IfConverter, "if-converter", "If Converter", false, false)
bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
const TargetSubtargetInfo &ST = MF.getSubtarget();
TLI = ST.getTargetLowering();
TII = ST.getInstrInfo();
TRI = ST.getRegisterInfo();
MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
MRI = &MF.getRegInfo();
SchedModel.init(ST.getSchedModel(), &ST, TII);
if (!TII) return false;
PreRegAlloc = MRI->isSSA();
bool BFChange = false;
if (!PreRegAlloc) {
// Tail merge tend to expose more if-conversion opportunities.
BranchFolder BF(true, false, *MBFI, *MBPI);
BFChange = BF.OptimizeFunction(MF, TII, ST.getRegisterInfo(),
getAnalysisIfAvailable<MachineModuleInfo>());
}
DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum << ") \'"
<< MF.getName() << "\'");
if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
DEBUG(dbgs() << " skipped\n");
return false;
}
DEBUG(dbgs() << "\n");
MF.RenumberBlocks();
BBAnalysis.resize(MF.getNumBlockIDs());
std::vector<IfcvtToken*> Tokens;
MadeChange = false;
unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
// Do an initial analysis for each basic block and find all the potential
// candidates to perform if-conversion.
bool Change = false;
AnalyzeBlocks(MF, Tokens);
while (!Tokens.empty()) {
IfcvtToken *Token = Tokens.back();
Tokens.pop_back();
BBInfo &BBI = Token->BBI;
IfcvtKind Kind = Token->Kind;
unsigned NumDups = Token->NumDups;
unsigned NumDups2 = Token->NumDups2;
delete Token;
// If the block has been evicted out of the queue or it has already been
// marked dead (due to it being predicated), then skip it.
if (BBI.IsDone)
BBI.IsEnqueued = false;
if (!BBI.IsEnqueued)
continue;
BBI.IsEnqueued = false;
bool RetVal = false;
switch (Kind) {
default: llvm_unreachable("Unexpected!");
case ICSimple:
case ICSimpleFalse: {
bool isFalse = Kind == ICSimpleFalse;
if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
DEBUG(dbgs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ?
" false" : "")
<< "): BB#" << BBI.BB->getNumber() << " ("
<< ((Kind == ICSimpleFalse)
? BBI.FalseBB->getNumber()
: BBI.TrueBB->getNumber()) << ") ");
RetVal = IfConvertSimple(BBI, Kind);
DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
if (RetVal) {
if (isFalse) ++NumSimpleFalse;
else ++NumSimple;
}
break;
}
case ICTriangle:
case ICTriangleRev:
case ICTriangleFalse:
case ICTriangleFRev: {
bool isFalse = Kind == ICTriangleFalse;
bool isRev = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
if (DisableTriangle && !isFalse && !isRev) break;
if (DisableTriangleR && !isFalse && isRev) break;
if (DisableTriangleF && isFalse && !isRev) break;
if (DisableTriangleFR && isFalse && isRev) break;
DEBUG(dbgs() << "Ifcvt (Triangle");
if (isFalse)
DEBUG(dbgs() << " false");
if (isRev)
DEBUG(dbgs() << " rev");
DEBUG(dbgs() << "): BB#" << BBI.BB->getNumber() << " (T:"
<< BBI.TrueBB->getNumber() << ",F:"
<< BBI.FalseBB->getNumber() << ") ");
RetVal = IfConvertTriangle(BBI, Kind);
DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
if (RetVal) {
if (isFalse) {
if (isRev) ++NumTriangleFRev;
else ++NumTriangleFalse;
} else {
if (isRev) ++NumTriangleRev;
else ++NumTriangle;
}
}
break;
}
case ICDiamond: {
if (DisableDiamond) break;
DEBUG(dbgs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
<< BBI.TrueBB->getNumber() << ",F:"
<< BBI.FalseBB->getNumber() << ") ");
RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
if (RetVal) ++NumDiamonds;
break;
}
}
Change |= RetVal;
NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
NumTriangleFalse + NumTriangleFRev + NumDiamonds;
if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
break;
}
if (!Change)
break;
MadeChange |= Change;
}
// Delete tokens in case of early exit.
while (!Tokens.empty()) {
IfcvtToken *Token = Tokens.back();
Tokens.pop_back();
delete Token;
}
Tokens.clear();
BBAnalysis.clear();
if (MadeChange && IfCvtBranchFold) {
BranchFolder BF(false, false, *MBFI, *MBPI);
BF.OptimizeFunction(MF, TII, MF.getSubtarget().getRegisterInfo(),
getAnalysisIfAvailable<MachineModuleInfo>());
}
MadeChange |= BFChange;
return MadeChange;
}
/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
/// its 'true' successor.
static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
MachineBasicBlock *TrueBB) {
for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
E = BB->succ_end(); SI != E; ++SI) {
MachineBasicBlock *SuccBB = *SI;
if (SuccBB != TrueBB)
return SuccBB;
}
return nullptr;
}
/// ReverseBranchCondition - Reverse the condition of the end of the block
/// branch. Swap block's 'true' and 'false' successors.
bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
DebugLoc dl; // FIXME: this is nowhere
if (!TII->ReverseBranchCondition(BBI.BrCond)) {
TII->RemoveBranch(*BBI.BB);
TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond, dl);
std::swap(BBI.TrueBB, BBI.FalseBB);
return true;
}
return false;
}
/// getNextBlock - Returns the next block in the function blocks ordering. If
/// it is the end, returns NULL.
static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
MachineFunction::iterator I = BB;
MachineFunction::iterator E = BB->getParent()->end();
if (++I == E)
return nullptr;
return I;
}
/// ValidSimple - Returns true if the 'true' block (along with its
/// predecessor) forms a valid simple shape for ifcvt. It also returns the
/// number of instructions that the ifcvt would need to duplicate if performed
/// in Dups.
bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
const BranchProbability &Prediction) const {
Dups = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
return false;
if (TrueBBI.IsBrAnalyzable)
return false;
if (TrueBBI.BB->pred_size() > 1) {
if (TrueBBI.CannotBeCopied ||
!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize,
Prediction))
return false;
Dups = TrueBBI.NonPredSize;
}
return true;
}
/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid triangle shape for ifcvt.
/// If 'FalseBranch' is true, it checks if 'true' block's false branch
/// branches to the 'false' block rather than the other way around. It also
/// returns the number of instructions that the ifcvt would need to duplicate
/// if performed in 'Dups'.
bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
bool FalseBranch, unsigned &Dups,
const BranchProbability &Prediction) const {
Dups = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
return false;
if (TrueBBI.BB->pred_size() > 1) {
if (TrueBBI.CannotBeCopied)
return false;
unsigned Size = TrueBBI.NonPredSize;
if (TrueBBI.IsBrAnalyzable) {
if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
// Ends with an unconditional branch. It will be removed.
--Size;
else {
MachineBasicBlock *FExit = FalseBranch
? TrueBBI.TrueBB : TrueBBI.FalseBB;
if (FExit)
// Require a conditional branch
++Size;
}
}
if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size, Prediction))
return false;
Dups = Size;
}
MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
MachineFunction::iterator I = TrueBBI.BB;
if (++I == TrueBBI.BB->getParent()->end())
return false;
TExit = I;
}
return TExit && TExit == FalseBBI.BB;
}
/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid diamond shape for ifcvt.
bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
unsigned &Dups1, unsigned &Dups2) const {
Dups1 = Dups2 = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
return false;
MachineBasicBlock *TT = TrueBBI.TrueBB;
MachineBasicBlock *FT = FalseBBI.TrueBB;
if (!TT && blockAlwaysFallThrough(TrueBBI))
TT = getNextBlock(TrueBBI.BB);
if (!FT && blockAlwaysFallThrough(FalseBBI))
FT = getNextBlock(FalseBBI.BB);
if (TT != FT)
return false;
if (!TT && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
return false;
if (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
return false;
// FIXME: Allow true block to have an early exit?
if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
(TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
return false;
// Count duplicate instructions at the beginning of the true and false blocks.
MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
MachineBasicBlock::iterator TIE = TrueBBI.BB->end();
MachineBasicBlock::iterator FIE = FalseBBI.BB->end();
while (TIB != TIE && FIB != FIE) {
// Skip dbg_value instructions. These do not count.
if (TIB->isDebugValue()) {
while (TIB != TIE && TIB->isDebugValue())
++TIB;
if (TIB == TIE)
break;
}
if (FIB->isDebugValue()) {
while (FIB != FIE && FIB->isDebugValue())
++FIB;
if (FIB == FIE)
break;
}
if (!TIB->isIdenticalTo(FIB))
break;
++Dups1;
++TIB;
++FIB;
}
// Now, in preparation for counting duplicate instructions at the ends of the
// blocks, move the end iterators up past any branch instructions.
while (TIE != TIB) {
--TIE;
if (!TIE->isBranch())
break;
}
while (FIE != FIB) {
--FIE;
if (!FIE->isBranch())
break;
}
// If Dups1 includes all of a block, then don't count duplicate
// instructions at the end of the blocks.
if (TIB == TIE || FIB == FIE)
return true;
// Count duplicate instructions at the ends of the blocks.
while (TIE != TIB && FIE != FIB) {
// Skip dbg_value instructions. These do not count.
if (TIE->isDebugValue()) {
while (TIE != TIB && TIE->isDebugValue())
--TIE;
if (TIE == TIB)
break;
}
if (FIE->isDebugValue()) {
while (FIE != FIB && FIE->isDebugValue())
--FIE;
if (FIE == FIB)
break;
}
if (!TIE->isIdenticalTo(FIE))
break;
++Dups2;
--TIE;
--FIE;
}
return true;
}
/// ScanInstructions - Scan all the instructions in the block to determine if
/// the block is predicable. In most cases, that means all the instructions
/// in the block are isPredicable(). Also checks if the block contains any
/// instruction which can clobber a predicate (e.g. condition code register).
/// If so, the block is not predicable unless it's the last instruction.
void IfConverter::ScanInstructions(BBInfo &BBI) {
if (BBI.IsDone)
return;
bool AlreadyPredicated = !BBI.Predicate.empty();
// First analyze the end of BB branches.
BBI.TrueBB = BBI.FalseBB = nullptr;
BBI.BrCond.clear();
BBI.IsBrAnalyzable =
!TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == nullptr;
if (BBI.BrCond.size()) {
// No false branch. This BB must end with a conditional branch and a
// fallthrough.
if (!BBI.FalseBB)
BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
if (!BBI.FalseBB) {
// Malformed bcc? True and false blocks are the same?
BBI.IsUnpredicable = true;
return;
}
}
// Then scan all the instructions.
BBI.NonPredSize = 0;
BBI.ExtraCost = 0;
BBI.ExtraCost2 = 0;
BBI.ClobbersPred = false;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
if (I->isDebugValue())
continue;
if (I->isNotDuplicable())
BBI.CannotBeCopied = true;
bool isPredicated = TII->isPredicated(I);
bool isCondBr = BBI.IsBrAnalyzable && I->isConditionalBranch();
// A conditional branch is not predicable, but it may be eliminated.
if (isCondBr)
continue;
if (!isPredicated) {
BBI.NonPredSize++;
unsigned ExtraPredCost = TII->getPredicationCost(&*I);
unsigned NumCycles = SchedModel.computeInstrLatency(&*I, false);
if (NumCycles > 1)
BBI.ExtraCost += NumCycles-1;
BBI.ExtraCost2 += ExtraPredCost;
} else if (!AlreadyPredicated) {
// FIXME: This instruction is already predicated before the
// if-conversion pass. It's probably something like a conditional move.
// Mark this block unpredicable for now.
BBI.IsUnpredicable = true;
return;
}
if (BBI.ClobbersPred && !isPredicated) {
// Predicate modification instruction should end the block (except for
// already predicated instructions and end of block branches).
// Predicate may have been modified, the subsequent (currently)
// unpredicated instructions cannot be correctly predicated.
BBI.IsUnpredicable = true;
return;
}
// FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
// still potentially predicable.
std::vector<MachineOperand> PredDefs;
if (TII->DefinesPredicate(I, PredDefs))
BBI.ClobbersPred = true;
if (!TII->isPredicable(I)) {
BBI.IsUnpredicable = true;
return;
}
}
}
/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
/// predicated by the specified predicate.
bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
SmallVectorImpl<MachineOperand> &Pred,
bool isTriangle, bool RevBranch) {
// If the block is dead or unpredicable, then it cannot be predicated.
if (BBI.IsDone || BBI.IsUnpredicable)
return false;
// If it is already predicated but we couldn't analyze its terminator, the
// latter might fallthrough, but we can't determine where to.
// Conservatively avoid if-converting again.
if (BBI.Predicate.size() && !BBI.IsBrAnalyzable)
return false;
// If it is already predicated, check if the new predicate subsumes
// its predicate.
if (BBI.Predicate.size() && !TII->SubsumesPredicate(Pred, BBI.Predicate))
return false;
if (BBI.BrCond.size()) {
if (!isTriangle)
return false;
// Test predicate subsumption.
SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
if (RevBranch) {
if (TII->ReverseBranchCondition(Cond))
return false;
}
if (TII->ReverseBranchCondition(RevPred) ||
!TII->SubsumesPredicate(Cond, RevPred))
return false;
}
return true;
}
/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
/// the specified block. Record its successors and whether it looks like an
/// if-conversion candidate.
IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
std::vector<IfcvtToken*> &Tokens) {
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
return BBI;
BBI.BB = BB;
BBI.IsBeingAnalyzed = true;
ScanInstructions(BBI);
// Unanalyzable or ends with fallthrough or unconditional branch, or if is not
// considered for ifcvt anymore.
if (!BBI.IsBrAnalyzable || BBI.BrCond.empty() || BBI.IsDone) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
// Do not ifcvt if either path is a back edge to the entry block.
if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
// Do not ifcvt if true and false fallthrough blocks are the same.
if (!BBI.FalseBB) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
BBInfo &TrueBBI = AnalyzeBlock(BBI.TrueBB, Tokens);
BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
if (TrueBBI.IsDone && FalseBBI.IsDone) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
unsigned Dups = 0;
unsigned Dups2 = 0;
bool TNeedSub = !TrueBBI.Predicate.empty();
bool FNeedSub = !FalseBBI.Predicate.empty();
bool Enqueued = false;
BranchProbability Prediction = MBPI->getEdgeProbability(BB, TrueBBI.BB);
if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, (TrueBBI.NonPredSize - (Dups + Dups2) +
TrueBBI.ExtraCost), TrueBBI.ExtraCost2,
*FalseBBI.BB, (FalseBBI.NonPredSize - (Dups + Dups2) +
FalseBBI.ExtraCost),FalseBBI.ExtraCost2,
Prediction) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
// EBB
// / \_
// | |
// TBB FBB
// \ /
// TailBB
// Note TailBB can be empty.
Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
Dups2));
Enqueued = true;
}
if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
TrueBBI.ExtraCost2, Prediction) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
// Triangle:
// EBB
// | \_
// | |
// | TBB
// | /
// FBB
Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
Enqueued = true;
}
if (ValidTriangle(TrueBBI, FalseBBI, true, Dups, Prediction) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
TrueBBI.ExtraCost2, Prediction) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
Enqueued = true;
}
if (ValidSimple(TrueBBI, Dups, Prediction) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
TrueBBI.ExtraCost2, Prediction) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
// Simple (split, no rejoin):
// EBB
// | \_
// | |
// | TBB---> exit
// |
// FBB
Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
Enqueued = true;
}
if (CanRevCond) {
// Try the other path...
if (ValidTriangle(FalseBBI, TrueBBI, false, Dups,
Prediction.getCompl()) &&
MeetIfcvtSizeLimit(*FalseBBI.BB,
FalseBBI.NonPredSize + FalseBBI.ExtraCost,
FalseBBI.ExtraCost2, Prediction.getCompl()) &&
FeasibilityAnalysis(FalseBBI, RevCond, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
Enqueued = true;
}
if (ValidTriangle(FalseBBI, TrueBBI, true, Dups,
Prediction.getCompl()) &&
MeetIfcvtSizeLimit(*FalseBBI.BB,
FalseBBI.NonPredSize + FalseBBI.ExtraCost,
FalseBBI.ExtraCost2, Prediction.getCompl()) &&
FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
Enqueued = true;
}
if (ValidSimple(FalseBBI, Dups, Prediction.getCompl()) &&
MeetIfcvtSizeLimit(*FalseBBI.BB,
FalseBBI.NonPredSize + FalseBBI.ExtraCost,
FalseBBI.ExtraCost2, Prediction.getCompl()) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
Enqueued = true;
}
}
BBI.IsEnqueued = Enqueued;
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
/// candidates.
void IfConverter::AnalyzeBlocks(MachineFunction &MF,
std::vector<IfcvtToken*> &Tokens) {
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *BB = I;
AnalyzeBlock(BB, Tokens);
}
// Sort to favor more complex ifcvt scheme.
std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
}
/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
/// that all the intervening blocks are empty (given BB can fall through to its
/// next block).
static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
MachineFunction::iterator PI = BB;
MachineFunction::iterator I = std::next(PI);
MachineFunction::iterator TI = ToBB;
MachineFunction::iterator E = BB->getParent()->end();
while (I != TI) {
// Check isSuccessor to avoid case where the next block is empty, but
// it's not a successor.
if (I == E || !I->empty() || !PI->isSuccessor(I))
return false;
PI = I++;
}
return true;
}
/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
/// to determine if it can be if-converted. If predecessor is already enqueued,
/// dequeue it!
void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
for (const auto &Predecessor : BB->predecessors()) {
BBInfo &PBBI = BBAnalysis[Predecessor->getNumber()];
if (PBBI.IsDone || PBBI.BB == BB)
continue;
PBBI.IsAnalyzed = false;
PBBI.IsEnqueued = false;
}
}
/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
///
static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
const TargetInstrInfo *TII) {
DebugLoc dl; // FIXME: this is nowhere
SmallVector<MachineOperand, 0> NoCond;
TII->InsertBranch(*BB, ToBB, nullptr, NoCond, dl);
}
/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
/// successors.
void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
SmallVector<MachineOperand, 4> Cond;
if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
}
/// Behaves like LiveRegUnits::StepForward() but also adds implicit uses to all
/// values defined in MI which are not live/used by MI.
static void UpdatePredRedefs(MachineInstr *MI, LivePhysRegs &Redefs) {
for (ConstMIBundleOperands Ops(MI); Ops.isValid(); ++Ops) {
if (!Ops->isReg() || !Ops->isKill())
continue;
unsigned Reg = Ops->getReg();
if (Reg == 0)
continue;
Redefs.removeReg(Reg);
}
for (MIBundleOperands Ops(MI); Ops.isValid(); ++Ops) {
if (!Ops->isReg() || !Ops->isDef())
continue;
unsigned Reg = Ops->getReg();
if (Reg == 0 || Redefs.contains(Reg))
continue;
Redefs.addReg(Reg);
MachineOperand &Op = *Ops;
MachineInstr *MI = Op.getParent();
MachineInstrBuilder MIB(*MI->getParent()->getParent(), MI);
MIB.addReg(Reg, RegState::Implicit | RegState::Undef);
}
}