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26d68261ae
llvm-mirror/lib/CodeGen/IfConversion.cpp
Evan Cheng 26d68261ae Fix typo. 
llvm-svn: 37577
2007-06-14 21:26:08 +00:00

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//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the Evan Cheng and 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ifcvt"
#include "llvm/Function.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
namespace {
// Hidden options for help debugging.
cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
cl::opt<bool> DisableSimple("disable-ifcvt-simple",
cl::init(false), cl::Hidden);
cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
cl::init(false), cl::Hidden);
cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
cl::init(false), cl::Hidden);
cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
cl::init(false), cl::Hidden);
cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
cl::init(false), cl::Hidden);
cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
cl::init(false), cl::Hidden);
cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
cl::init(false), 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");
namespace {
class IfConverter : public MachineFunctionPass {
enum BBICKind {
ICNotClassfied, // BB data valid, but not classified.
ICSimple, // BB is entry of an one split, no rejoin sub-CFG.
ICSimpleFalse, // Same as ICSimple, but on the false path.
ICTriangle, // BB is entry of a triangle sub-CFG.
ICTriangleRev, // Same as ICTriangle, but true path rev condition.
ICTriangleFalse, // Same as ICTriangle, but on the false path.
ICTriangleFRev, // Same as ICTriangleFalse, but false path rev condition.
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.
///
/// Kind - Type of block. See BBICKind.
/// 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.
/// ClobbersPredicate- True if BB would modify the predicate (e.g. has
/// cmp, call, etc.)
/// NonPredSize - Number of non-predicated instructions.
/// BB - Corresponding MachineBasicBlock.
/// TrueBB / FalseBB- See AnalyzeBranch().
/// BrCond - Conditions for end of block conditional branches.
/// Predicate - Predicate used in the BB.
struct BBInfo {
BBICKind Kind;
bool IsDone : 1;
bool IsBeingAnalyzed : 1;
bool IsAnalyzed : 1;
bool IsEnqueued : 1;
bool IsBrAnalyzable : 1;
bool HasFallThrough : 1;
bool IsUnpredicable : 1;
bool ClobbersPred : 1;
unsigned NonPredSize;
MachineBasicBlock *BB;
MachineBasicBlock *TrueBB;
MachineBasicBlock *FalseBB;
MachineBasicBlock *TailBB;
std::vector<MachineOperand> BrCond;
std::vector<MachineOperand> Predicate;
BBInfo() : Kind(ICNotClassfied), IsDone(false), IsBeingAnalyzed(false),
IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
HasFallThrough(false), IsUnpredicable(false),
ClobbersPred(false), NonPredSize(0),
BB(0), TrueBB(0), FalseBB(0), TailBB(0) {}
};
/// Roots - Basic blocks that do not have successors. These are the starting
/// points of Graph traversal.
std::vector<MachineBasicBlock*> Roots;
/// BBAnalysis - Results of if-conversion feasibility analysis indexed by
/// basic block number.
std::vector<BBInfo> BBAnalysis;
const TargetLowering *TLI;
const TargetInstrInfo *TII;
bool MadeChange;
public:
static char ID;
IfConverter() : MachineFunctionPass((intptr_t)&ID) {}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const { return "If converter"; }
private:
bool ReverseBranchCondition(BBInfo &BBI);
bool ValidSimple(BBInfo &TrueBBI) const;
bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
bool FalseBranch = false) const;
bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const;
void ScanInstructions(BBInfo &BBI);
BBInfo &AnalyzeBlock(MachineBasicBlock *BB);
bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond,
bool isTriangle = false, bool RevBranch = false);
bool AttemptRestructuring(BBInfo &BBI);
bool AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates);
void ReTryPreds(MachineBasicBlock *BB);
void RemoveExtraEdges(BBInfo &BBI);
bool IfConvertSimple(BBInfo &BBI);
bool IfConvertTriangle(BBInfo &BBI);
bool IfConvertDiamond(BBInfo &BBI);
void PredicateBlock(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm = false);
void MergeBlocks(BBInfo &TrueBBI, BBInfo &FalseBBI);
// blockAlwaysFallThrough - Block ends without a terminator.
bool blockAlwaysFallThrough(BBInfo &BBI) const {
return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
}
// IfcvtCandidateCmp - Used to sort if-conversion candidates.
static bool IfcvtCandidateCmp(BBInfo* C1, BBInfo* C2){
// Favor diamond over triangle, etc.
return (unsigned)C1->Kind < (unsigned)C2->Kind;
}
};
char IfConverter::ID = 0;
}
FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
TLI = MF.getTarget().getTargetLowering();
TII = MF.getTarget().getInstrInfo();
if (!TII) return false;
static int FnNum = -1;
DOUT << "\nIfcvt: function (" << ++FnNum << ") \'"
<< MF.getFunction()->getName() << "\'";
if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
DOUT << " skipped\n";
return false;
}
DOUT << "\n";
MF.RenumberBlocks();
BBAnalysis.resize(MF.getNumBlockIDs());
// Look for root nodes, i.e. blocks without successors.
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
if (I->succ_size() == 0)
Roots.push_back(I);
std::vector<BBInfo*> Candidates;
MadeChange = false;
while (IfCvtLimit == -1 || (int)NumIfConvBBs < IfCvtLimit) {
// Do an intial analysis for each basic block and finding all the potential
// candidates to perform if-convesion.
bool Change = AnalyzeBlocks(MF, Candidates);
while (!Candidates.empty()) {
BBInfo &BBI = *Candidates.back();
Candidates.pop_back();
// 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.IsEnqueued || BBI.IsDone)
continue;
BBI.IsEnqueued = false;
bool RetVal = false;
switch (BBI.Kind) {
default: assert(false && "Unexpected!");
break;
case ICSimple:
case ICSimpleFalse: {
bool isFalse = BBI.Kind == ICSimpleFalse;
if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
DOUT << "Ifcvt (Simple" << (BBI.Kind == ICSimpleFalse ? " false" : "")
<< "): BB#" << BBI.BB->getNumber() << " ("
<< ((BBI.Kind == ICSimpleFalse)
? BBI.FalseBB->getNumber() : BBI.TrueBB->getNumber()) << ") ";
RetVal = IfConvertSimple(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal)
if (isFalse) NumSimpleFalse++;
else NumSimple++;
break;
}
case ICTriangle:
case ICTriangleRev:
case ICTriangleFalse:
case ICTriangleFRev: {
bool isFalse = BBI.Kind == ICTriangleFalse;
bool isRev = (BBI.Kind == ICTriangleRev || BBI.Kind == ICTriangleFRev);
if (DisableTriangle && !isFalse && !isRev) break;
if (DisableTriangleR && !isFalse && isRev) break;
if (DisableTriangleF && isFalse && !isRev) break;
if (DisableTriangleFR && isFalse && isRev) break;
DOUT << "Ifcvt (Triangle";
if (isFalse)
DOUT << " false";
if (isRev)
DOUT << " rev";
DOUT << "): BB#" << BBI.BB->getNumber() << " (T:"
<< BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber()
<< ") ";
RetVal = IfConvertTriangle(BBI);
DOUT << (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;
DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
<< BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber();
if (BBI.TailBB)
DOUT << "," << BBI.TailBB->getNumber() ;
DOUT << ") ";
RetVal = IfConvertDiamond(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal) NumDiamonds++;
break;
}
Change |= RetVal;
if (IfCvtLimit != -1 && (int)NumIfConvBBs >= IfCvtLimit)
break;
}
if (!Change)
break;
MadeChange |= Change;
}
Roots.clear();
BBAnalysis.clear();
return MadeChange;
}
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 NULL;
}
bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
if (!TII->ReverseBranchCondition(BBI.BrCond)) {
TII->RemoveBranch(*BBI.BB);
TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond);
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 NULL;
return I;
}
/// ValidSimple - Returns true if the 'true' block (along with its
/// predecessor) forms a valid simple shape for ifcvt.
bool IfConverter::ValidSimple(BBInfo &TrueBBI) const {
if (TrueBBI.IsBeingAnalyzed)
return false;
return !blockAlwaysFallThrough(TrueBBI) &&
TrueBBI.BrCond.size() == 0 && TrueBBI.BB->pred_size() == 1;
}
/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid triangle shape for ifcvt.
bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
bool FalseBranch) const {
if (TrueBBI.IsBeingAnalyzed)
return false;
if (TrueBBI.BB->pred_size() != 1)
return false;
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) const {
if (TrueBBI.IsBeingAnalyzed || FalseBBI.IsBeingAnalyzed)
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 == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
return false;
// FIXME: Allow false block to have an early exit?
return (TrueBBI.BB->pred_size() == 1 &&
FalseBBI.BB->pred_size() == 1 &&
!TrueBBI.FalseBB && !FalseBBI.FalseBB);
}
/// 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 has M_PREDICABLE flag. 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;
// First analyze the end of BB branches.
BBI.TrueBB = BBI.FalseBB = NULL;
BBI.BrCond.clear();
BBI.IsBrAnalyzable =
!TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
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);
assert(BBI.FalseBB && "Expected to find the fallthrough block!");
}
// Then scan all the instructions.
BBI.NonPredSize = 0;
BBI.ClobbersPred = false;
bool SeenCondBr = false;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
const TargetInstrDescriptor *TID = I->getInstrDescriptor();
bool isPredicated = TII->isPredicated(I);
bool isCondBr = BBI.IsBrAnalyzable &&
(TID->Flags & M_BRANCH_FLAG) != 0 && (TID->Flags & M_BARRIER_FLAG) == 0;
if (!isPredicated && !isCondBr)
BBI.NonPredSize++;
if (BBI.ClobbersPred && !isPredicated) {
// Predicate modification instruction should end the block (except for
// already predicated instructions and end of block branches).
if (isCondBr) {
SeenCondBr = true;
// Conditional branches is not predicable. But it may be eliminated.
continue;
}
// Predicate may have been modified, the subsequent (currently)
// unpredocated instructions cannot be correctly predicated.
BBI.IsUnpredicable = true;
return;
}
if (TID->Flags & M_CLOBBERS_PRED)
BBI.ClobbersPred = true;
if (!I->isPredicable()) {
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,
std::vector<MachineOperand> &Pred,
bool isTriangle, bool RevBranch) {
// Forget about it if it's unpredicable.
if (BBI.IsUnpredicable)
return false;
// If the block is dead, or it is going to be the entry block of a sub-CFG
// that will be if-converted, then it cannot be predicated.
if (BBI.IsDone || BBI.IsEnqueued)
return false;
// Check predication threshold.
if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
return false;
// If it is already predicated, check if its predicate subsumes the new
// predicate.
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
return false;
if (BBI.BrCond.size()) {
if (!isTriangle)
return false;
// Test predicate subsumsion.
std::vector<MachineOperand> RevPred(Pred);
std::vector<MachineOperand> Cond(BBI.BrCond);
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) {
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
return BBI;
BBI.BB = BB;
BBI.IsBeingAnalyzed = true;
BBI.Kind = ICNotClassfied;
ScanInstructions(BBI);
// Unanalyable or ends with fallthrough or unconditional branch.
if (!BBI.IsBrAnalyzable || BBI.BrCond.size() == 0) {
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;
}
BBInfo &TrueBBI = AnalyzeBlock(BBI.TrueBB);
BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB);
if (TrueBBI.IsDone && FalseBBI.IsDone) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
std::vector<MachineOperand> RevCond(BBI.BrCond);
bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI) &&
!(TrueBBI.ClobbersPred && FalseBBI.ClobbersPred) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
// EBB
// / \_
// | |
// TBB FBB
// \ /
// TailBB
// Note TailBB can be empty.
BBI.Kind = ICDiamond;
BBI.TailBB = TrueBBI.TrueBB;
} else {
// FIXME: Consider duplicating if BB is small.
if (ValidTriangle(TrueBBI, FalseBBI) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
// Triangle:
// EBB
// | \_
// | |
// | TBB
// | /
// FBB
BBI.Kind = ICTriangle;
} else if (ValidTriangle(TrueBBI, FalseBBI, true) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
BBI.Kind = ICTriangleRev;
} else if (ValidSimple(TrueBBI) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
// Simple (split, no rejoin):
// EBB
// | \_
// | |
// | TBB---> exit
// |
// FBB
BBI.Kind = ICSimple;
} else if (CanRevCond) {
// Try the other path...
if (ValidTriangle(FalseBBI, TrueBBI) &&
FeasibilityAnalysis(FalseBBI, RevCond, true)) {
BBI.Kind = ICTriangleFalse;
} else if (ValidTriangle(FalseBBI, TrueBBI, true) &&
FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
BBI.Kind = ICTriangleFRev;
} else if (ValidSimple(FalseBBI) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
BBI.Kind = ICSimpleFalse;
}
}
}
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
/// AttemptRestructuring - Restructure the sub-CFG rooted in the given block to
/// expose more if-conversion opportunities. e.g.
///
/// cmp
/// b le BB1
/// / \____
/// / |
/// cmp |
/// b eq BB1 |
/// / \____ |
/// / \ |
/// BB1
/// ==>
///
/// cmp
/// b eq BB1
/// / \____
/// / |
/// cmp |
/// b le BB1 |
/// / \____ |
/// / \ |
/// BB1
bool IfConverter::AttemptRestructuring(BBInfo &BBI) {
return false;
}
/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
/// candidates. It returns true if any CFG restructuring is done to expose more
/// if-conversion opportunities.
bool IfConverter::AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates) {
bool Change = false;
std::set<MachineBasicBlock*> Visited;
for (unsigned i = 0, e = Roots.size(); i != e; ++i) {
for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
MachineBasicBlock *BB = *I;
BBInfo &BBI = AnalyzeBlock(BB);
switch (BBI.Kind) {
case ICSimple:
case ICSimpleFalse:
case ICTriangle:
case ICTriangleRev:
case ICTriangleFalse:
case ICTriangleFRev:
case ICDiamond:
BBI.IsEnqueued = true;
Candidates.push_back(&BBI);
break;
default:
Change |= AttemptRestructuring(BBI);
break;
}
}
}
// Sort to favor more complex ifcvt scheme.
std::stable_sort(Candidates.begin(), Candidates.end(), IfcvtCandidateCmp);
return Change;
}
/// 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 I = BB;
MachineFunction::iterator TI = ToBB;
MachineFunction::iterator E = BB->getParent()->end();
while (++I != TI)
if (I == E || !I->empty())
return false;
return true;
}
/// ReTryPreds - Invalidate predecessor BB info so it would be re-analyzed
/// to determine if it can be if-converted.
void IfConverter::ReTryPreds(MachineBasicBlock *BB) {
for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
E = BB->pred_end(); PI != E; ++PI) {
BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
if (!PBBI.IsDone && PBBI.Kind == ICNotClassfied) {
assert(!PBBI.IsEnqueued && "Unexpected");
PBBI.IsAnalyzed = false;
}
}
}
/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
///
static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
const TargetInstrInfo *TII) {
std::vector<MachineOperand> NoCond;
TII->InsertBranch(*BB, ToBB, NULL, NoCond);
}
/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
/// successors.
void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
MachineBasicBlock *TBB = NULL, *FBB = NULL;
std::vector<MachineOperand> Cond;
bool isAnalyzable = !TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond);
bool CanFallthrough = isAnalyzable && (TBB == NULL || FBB == NULL);
if (BBI.TrueBB && BBI.BB->isSuccessor(BBI.TrueBB))
if (!(BBI.TrueBB == TBB || BBI.TrueBB == FBB ||
(CanFallthrough && getNextBlock(BBI.BB) == BBI.TrueBB)))
BBI.BB->removeSuccessor(BBI.TrueBB);
if (BBI.FalseBB && BBI.BB->isSuccessor(BBI.FalseBB))
if (!(BBI.FalseBB == TBB || BBI.FalseBB == FBB ||
(CanFallthrough && getNextBlock(BBI.BB) == BBI.FalseBB)))
BBI.BB->removeSuccessor(BBI.FalseBB);
}
/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
///
bool IfConverter::IfConvertSimple(BBInfo &BBI) {
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
BBInfo *CvtBBI = &TrueBBI;
BBInfo *NextBBI = &FalseBBI;
std::vector<MachineOperand> Cond(BBI.BrCond);
if (BBI.Kind == ICSimpleFalse) {
std::swap(CvtBBI, NextBBI);
TII->ReverseBranchCondition(Cond);
}
PredicateBlock(*CvtBBI, Cond);
// Merge converted block into entry block.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI);
bool IterIfcvt = true;
if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
BBI.HasFallThrough = false;
// Now ifcvt'd block will look like this:
// BB:
// ...
// t, f = cmp
// if t op
// b BBf
//
// We cannot further ifcvt this block because the unconditional branch
// will have to be predicated on the new condition, that will not be
// available if cmp executes.
IterIfcvt = false;
}
RemoveExtraEdges(BBI);
// Update block info. BB can be iteratively if-converted.
if (!IterIfcvt)
BBI.IsDone = true;
ReTryPreds(BBI.BB);
CvtBBI->IsDone = true;
// FIXME: Must maintain LiveIns.
return true;
}
/// IfConvertTriangle - If convert a triangle sub-CFG.
///
bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
BBInfo *CvtBBI = &TrueBBI;
BBInfo *NextBBI = &FalseBBI;
std::vector<MachineOperand> Cond(BBI.BrCond);
if (BBI.Kind == ICTriangleFalse || BBI.Kind == ICTriangleFRev) {
std::swap(CvtBBI, NextBBI);
TII->ReverseBranchCondition(Cond);
}
if (BBI.Kind == ICTriangleRev || BBI.Kind == ICTriangleFRev) {
ReverseBranchCondition(*CvtBBI);
// BB has been changed, modify its predecessors (except for this
// one) so they don't get ifcvt'ed based on bad intel.
for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
MachineBasicBlock *PBB = *PI;
if (PBB == BBI.BB)
continue;
BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
if (PBBI.IsEnqueued)
PBBI.IsEnqueued = false;
}
}
// Predicate the 'true' block after removing its branch.
CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
PredicateBlock(*CvtBBI, Cond);
// If 'true' block has a 'false' successor, add an exit branch to it.
bool HasEarlyExit = CvtBBI->FalseBB != NULL;
if (HasEarlyExit) {
std::vector<MachineOperand> RevCond(CvtBBI->BrCond);
if (TII->ReverseBranchCondition(RevCond))
assert(false && "Unable to reverse branch condition!");
TII->InsertBranch(*CvtBBI->BB, CvtBBI->FalseBB, NULL, RevCond);
}
// Now merge the entry of the triangle with the true block.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI);
// Merge in the 'false' block if the 'false' block has no other
// predecessors. Otherwise, add a unconditional branch from to 'false'.
bool FalseBBDead = false;
bool IterIfcvt = true;
bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
if (!isFallThrough) {
// Only merge them if the true block does not fallthrough to the false
// block. By not merging them, we make it possible to iteratively
// ifcvt the blocks.
if (!HasEarlyExit && NextBBI->BB->pred_size() == 1) {
MergeBlocks(BBI, *NextBBI);
FalseBBDead = true;
} else {
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
BBI.HasFallThrough = false;
}
// Mixed predicated and unpredicated code. This cannot be iteratively
// predicated.
IterIfcvt = false;
}
RemoveExtraEdges(BBI);
// Update block info. BB can be iteratively if-converted.
if (!IterIfcvt)
BBI.IsDone = true;
ReTryPreds(BBI.BB);
CvtBBI->IsDone = true;
if (FalseBBDead)
NextBBI->IsDone = true;
// FIXME: Must maintain LiveIns.
return true;
}
/// IfConvertDiamond - If convert a diamond sub-CFG.
///
bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
SmallVector<MachineInstr*, 2> Dups;
if (!BBI.TailBB) {
// No common merge block. Check if the terminators (e.g. return) are
// the same or predicable.
MachineBasicBlock::iterator TT = BBI.TrueBB->getFirstTerminator();
MachineBasicBlock::iterator FT = BBI.FalseBB->getFirstTerminator();
while (TT != BBI.TrueBB->end() && FT != BBI.FalseBB->end()) {
if (TT->isIdenticalTo(FT))
Dups.push_back(TT); // Will erase these later.
else if (!TT->isPredicable() && !FT->isPredicable())
return false; // Can't if-convert. Abort!
++TT;
++FT;
}
// One of the two pathes have more terminators, make sure they are
// all predicable.
while (TT != BBI.TrueBB->end()) {
if (!TT->isPredicable()) {
return false; // Can't if-convert. Abort!
}
++TT;
}
while (FT != BBI.FalseBB->end()) {
if (!FT->isPredicable()) {
return false; // Can't if-convert. Abort!
}
++FT;
}
}
// Remove the duplicated instructions from the 'true' block.
for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
Dups[i]->eraseFromParent();
--TrueBBI.NonPredSize;
}
// Merge the 'true' and 'false' blocks by copying the instructions
// from the 'false' block to the 'true' block. That is, unless the true
// block would clobber the predicate, in that case, do the opposite.
BBInfo *BBI1 = &TrueBBI;
BBInfo *BBI2 = &FalseBBI;
std::vector<MachineOperand> RevCond(BBI.BrCond);
TII->ReverseBranchCondition(RevCond);
std::vector<MachineOperand> *Cond1 = &BBI.BrCond;
std::vector<MachineOperand> *Cond2 = &RevCond;
// Check the 'true' and 'false' blocks if either isn't ended with a branch.
// Either the block fallthrough to another block or it ends with a
// return. If it's the former, add a branch to its successor.
bool NeedBr1 = !BBI1->TrueBB && BBI1->BB->succ_size();
bool NeedBr2 = !BBI2->TrueBB && BBI2->BB->succ_size();
if ((TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred) ||
(!TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred &&
NeedBr1 && !NeedBr2)) {
std::swap(BBI1, BBI2);
std::swap(Cond1, Cond2);
std::swap(NeedBr1, NeedBr2);
}
// Predicate the 'true' block after removing its branch.
BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
PredicateBlock(*BBI1, *Cond1);
// Add an early exit branch if needed.
if (NeedBr1)
TII->InsertBranch(*BBI1->BB, *BBI1->BB->succ_begin(), NULL, *Cond1);
// Predicate the 'false' block.
PredicateBlock(*BBI2, *Cond2, true);
// Add an unconditional branch from 'false' to to 'false' successor if it
// will not be the fallthrough block.
if (NeedBr2 && !NeedBr1) {
// If BBI2 isn't going to be merged in, then the existing fallthrough
// or branch is fine.
if (!canFallThroughTo(BBI.BB, *BBI2->BB->succ_begin())) {
InsertUncondBranch(BBI2->BB, *BBI2->BB->succ_begin(), TII);
BBI2->HasFallThrough = false;
}
}
// Keep them as two separate blocks if there is an early exit.
if (!NeedBr1)
MergeBlocks(*BBI1, *BBI2);
// Remove the conditional branch from entry to the blocks.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
// Merge the combined block into the entry of the diamond.
MergeBlocks(BBI, *BBI1);
// 'True' and 'false' aren't combined, see if we need to add a unconditional
// branch to the 'false' block.
if (NeedBr1 && !canFallThroughTo(BBI.BB, BBI2->BB)) {
InsertUncondBranch(BBI.BB, BBI2->BB, TII);
BBI1->HasFallThrough = false;
}
// If the if-converted block fallthrough or unconditionally branch into the
// tail block, and the tail block does not have other predecessors, then
// fold the tail block in as well.
BBInfo *CvtBBI = NeedBr1 ? BBI2 : &BBI;
if (BBI.TailBB &&
BBI.TailBB->pred_size() == 1 && CvtBBI->BB->succ_size() == 1) {
CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
BBInfo TailBBI = BBAnalysis[BBI.TailBB->getNumber()];
MergeBlocks(*CvtBBI, TailBBI);
TailBBI.IsDone = true;
}
RemoveExtraEdges(BBI);
// Update block info.
BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
// FIXME: Must maintain LiveIns.
return true;
}
/// PredicateBlock - Predicate every instruction in the block with the specified
/// condition. If IgnoreTerm is true, skip over all terminator instructions.
void IfConverter::PredicateBlock(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
bool IgnoreTerm) {
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
continue;
if (TII->isPredicated(I))
continue;
if (!TII->PredicateInstruction(I, Cond)) {
cerr << "Unable to predicate " << *I << "!\n";
abort();
}
}
BBI.IsAnalyzed = false;
BBI.NonPredSize = 0;
std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
NumIfConvBBs++;
}
/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
///
void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
ToBBI.BB->splice(ToBBI.BB->end(),
FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
// Redirect all branches to FromBB to ToBB.
std::vector<MachineBasicBlock *> Preds(FromBBI.BB->pred_begin(),
FromBBI.BB->pred_end());
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
MachineBasicBlock *Pred = Preds[i];
if (Pred == ToBBI.BB)
continue;
Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB);
}
std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
FromBBI.BB->succ_end());
MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
MachineBasicBlock *Succ = Succs[i];
// Fallthrough edge can't be transferred.
if (Succ == FallThrough)
continue;
FromBBI.BB->removeSuccessor(Succ);
if (!ToBBI.BB->isSuccessor(Succ))
ToBBI.BB->addSuccessor(Succ);
}
// Now FromBBI always fall through to the next block!
if (NBB)
FromBBI.BB->addSuccessor(NBB);
ToBBI.NonPredSize += FromBBI.NonPredSize;
FromBBI.NonPredSize = 0;
ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
ToBBI.HasFallThrough = FromBBI.HasFallThrough;
std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
std::back_inserter(ToBBI.Predicate));
FromBBI.Predicate.clear();
ToBBI.IsAnalyzed = false;
FromBBI.IsAnalyzed = false;
}
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