llvm-project/llvm/lib/CodeGen/IfConversion.cpp

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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/Debug.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
namespace {
class IfConverter : public MachineFunctionPass {
enum BBICKind {
ICNotAnalyzed, // BB has not been analyzed.
ICReAnalyze, // BB must be re-analyzed.
ICNotClassfied, // BB data valid, but not classified.
ICEarlyExit, // BB is entry of an early-exit sub-CFG.
ICEarlyExitFalse,// Same as ICEarlyExit, but on the false path.
ICTriangle, // BB is entry of a triangle sub-CFG.
ICDiamond, // BB is entry of a diamond sub-CFG.
ICChild, // BB is part of the sub-CFG that'll be predicated.
ICDead // BB has been converted and merged, it's now dead.
};
/// 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.
/// NonPredSize - Number of non-predicated instructions.
/// isPredicable - Is it predicable. (FIXME: Remove.)
/// hasEarlyExit - Ends with a return, indirect jump or br to jumptable.
/// ModifyPredicate - FIXME: Not used right now. True if BB would modify
/// the predicate (e.g. has cmp, call, etc.)
/// 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;
unsigned NonPredSize;
bool isPredicable;
bool hasEarlyExit;
bool ModifyPredicate;
MachineBasicBlock *BB;
MachineBasicBlock *TrueBB;
MachineBasicBlock *FalseBB;
MachineBasicBlock *TailBB;
std::vector<MachineOperand> BrCond;
std::vector<MachineOperand> Predicate;
BBInfo() : Kind(ICNotAnalyzed), NonPredSize(0), isPredicable(false),
hasEarlyExit(false), ModifyPredicate(false),
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:
void StructuralAnalysis(MachineBasicBlock *BB);
void FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond);
bool AttemptRestructuring(BBInfo &BBI);
bool AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates);
void ReTryPreds(MachineBasicBlock *BB);
bool IfConvertEarlyExit(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);
// 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;
DOUT << "\nIfcvt: function \'" << MF.getFunction()->getName() << "\'\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);
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std::vector<BBInfo*> Candidates;
MadeChange = false;
while (true) {
bool Change = false;
// Do an intial analysis for each basic block and finding all the potential
// candidates to perform if-convesion.
Change |= AnalyzeBlocks(MF, Candidates);
while (!Candidates.empty()) {
BBInfo &BBI = *Candidates.back();
Candidates.pop_back();
switch (BBI.Kind) {
default: assert(false && "Unexpected!");
break;
case ICReAnalyze:
// One or more of 'childrean' have been modified, abort!
break;
case ICEarlyExit:
case ICEarlyExitFalse:
DOUT << "Ifcvt (Early exit): BB#" << BBI.BB->getNumber() << "\n";
Change |= IfConvertEarlyExit(BBI);
break;
case ICTriangle:
DOUT << "Ifcvt (Triangle): BB#" << BBI.BB->getNumber() << "\n";
Change |= IfConvertTriangle(BBI);
break;
case ICDiamond:
DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << "\n";
Change |= IfConvertDiamond(BBI);
break;
}
}
MadeChange |= Change;
if (!Change)
break;
}
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;
}
/// StructuralAnalysis - Analyze the structure of the sub-CFG starting from
/// the specified block. Record its successors and whether it looks like an
/// if-conversion candidate.
void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.Kind != ICReAnalyze) {
if (BBI.Kind != ICNotAnalyzed)
return; // Already analyzed.
BBI.BB = BB;
BBI.NonPredSize = std::distance(BB->begin(), BB->end());
}
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// Look for 'root' of a simple (non-nested) triangle or diamond.
BBI.Kind = ICNotClassfied;
bool CanAnalyze = !TII->AnalyzeBranch(*BB, BBI.TrueBB, BBI.FalseBB,
BBI.BrCond);
// Does it end with a return, indirect jump, or jumptable branch?
BBI.hasEarlyExit = TII->BlockHasNoFallThrough(*BB) && !BBI.TrueBB;
if (!CanAnalyze || !BBI.TrueBB || BBI.BrCond.size() == 0)
return;
// Not a candidate if 'true' block is going to be if-converted.
StructuralAnalysis(BBI.TrueBB);
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
// TODO: Only handle very simple cases for now.
if (TrueBBI.FalseBB || TrueBBI.BrCond.size())
return;
// No false branch. This BB must end with a conditional branch and a
// fallthrough.
if (!BBI.FalseBB)
BBI.FalseBB = findFalseBlock(BB, BBI.TrueBB);
assert(BBI.FalseBB && "Expected to find the fallthrough block!");
// Not a candidate if 'false' block is going to be if-converted.
StructuralAnalysis(BBI.FalseBB);
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
// TODO: Only handle very simple cases for now.
if (FalseBBI.FalseBB || FalseBBI.BrCond.size())
return;
unsigned TrueNumPreds = BBI.TrueBB->pred_size();
unsigned FalseNumPreds = BBI.FalseBB->pred_size();
if ((TrueBBI.hasEarlyExit && TrueNumPreds <= 1) &&
!(FalseBBI.hasEarlyExit && FalseNumPreds <=1)) {
BBI.Kind = ICEarlyExit;
TrueBBI.Kind = ICChild;
} else if (!(TrueBBI.hasEarlyExit && TrueNumPreds <= 1) &&
(FalseBBI.hasEarlyExit && FalseNumPreds <=1)) {
BBI.Kind = ICEarlyExitFalse;
FalseBBI.Kind = ICChild;
} else if (TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB) {
// Triangle:
// EBB
// | \_
// | |
// | TBB
// | /
// FBB
BBI.Kind = ICTriangle;
TrueBBI.Kind = FalseBBI.Kind = ICChild;
} else if (TrueBBI.TrueBB == FalseBBI.TrueBB &&
TrueNumPreds <= 1 && FalseNumPreds <= 1) {
// Diamond:
// EBB
// / \_
// | |
// TBB FBB
// \ /
// TailBB
// Note MBB can be empty in case both TBB and FBB are return blocks.
BBI.Kind = ICDiamond;
TrueBBI.Kind = FalseBBI.Kind = ICChild;
BBI.TailBB = TrueBBI.TrueBB;
}
return;
}
/// FeasibilityAnalysis - 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. Note, this function assumes
/// all the terminator instructions can be converted or deleted so it ignore
/// them.
void IfConverter::FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond) {
if (BBI.NonPredSize == 0 || BBI.NonPredSize > TLI->getIfCvtBlockSizeLimit())
return;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
// TODO: check if instruction clobbers predicate.
if (!I->isPredicable())
return;
}
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
return;
BBI.isPredicable = true;
}
/// 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;
StructuralAnalysis(BB);
BBInfo &BBI = BBAnalysis[BB->getNumber()];
switch (BBI.Kind) {
case ICEarlyExit:
case ICEarlyExitFalse:
case ICTriangle:
case ICDiamond:
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;
}
/// TransferPreds - Transfer all the predecessors of FromBB to ToBB.
///
static void TransferPreds(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
std::vector<MachineBasicBlock*> Preds(FromBB->pred_begin(),
FromBB->pred_end());
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
MachineBasicBlock *Pred = Preds[i];
Pred->removeSuccessor(FromBB);
if (!Pred->isSuccessor(ToBB))
Pred->addSuccessor(ToBB);
}
}
/// TransferSuccs - Transfer all the successors of FromBB to ToBB.
///
static void TransferSuccs(MachineBasicBlock *ToBB, MachineBasicBlock *FromBB) {
std::vector<MachineBasicBlock*> Succs(FromBB->succ_begin(),
FromBB->succ_end());
for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
MachineBasicBlock *Succ = Succs[i];
FromBB->removeSuccessor(Succ);
if (!ToBB->isSuccessor(Succ))
ToBB->addSuccessor(Succ);
}
}
/// isNextBlock - Returns true if ToBB the next basic block after BB.
///
static bool isNextBlock(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
MachineFunction::iterator Fallthrough = BB;
return MachineFunction::iterator(ToBB) == ++Fallthrough;
}
/// 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()];
PBBI.Kind = ICReAnalyze;
}
}
/// 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);
}
/// IfConvertEarlyExit - If convert a early exit sub-CFG.
///
bool IfConverter::IfConvertEarlyExit(BBInfo &BBI) {
bool ReverseCond = BBI.Kind == ICEarlyExitFalse;
BBI.Kind = ICNotClassfied;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
BBInfo *CvtBBI = &TrueBBI;
BBInfo *NextBBI = &FalseBBI;
std::vector<MachineOperand> NewCond(BBI.BrCond);
if (ReverseCond) {
std::swap(CvtBBI, NextBBI);
TII->ReverseBranchCondition(NewCond);
}
FeasibilityAnalysis(*CvtBBI, NewCond);
if (!CvtBBI->isPredicable)
return false;
PredicateBlock(*CvtBBI, NewCond);
// Merge converted block into entry block. Also convert the end of the
// block conditional branch (to the non-converted block) into an
// unconditional one.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI);
if (!isNextBlock(BBI.BB, NextBBI->BB))
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
std::copy(NewCond.begin(), NewCond.end(), std::back_inserter(BBI.Predicate));
// Update block info. BB can be iteratively if-converted.
BBI.Kind = ICNotAnalyzed;
BBI.TrueBB = BBI.FalseBB = NULL;
BBI.BrCond.clear();
TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
ReTryPreds(BBI.BB);
CvtBBI->Kind = ICDead;
// FIXME: Must maintain LiveIns.
NumIfConvBBs++;
return true;
}
/// IfConvertTriangle - If convert a triangle sub-CFG.
///
bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
BBI.Kind = ICNotClassfied;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
FeasibilityAnalysis(TrueBBI, BBI.BrCond);
if (!TrueBBI.isPredicable)
return false;
// FIXME: Consider duplicating if BB is small.
if (BBI.TrueBB->pred_size() > 1)
return false;
// Predicate the 'true' block after removing its branch.
TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(TrueBBI, BBI.BrCond);
// If 'true' block has a 'false' successor, add a early exit branch to it.
if (TrueBBI.FalseBB) {
std::vector<MachineOperand> RevCond(TrueBBI.BrCond);
if (TII->ReverseBranchCondition(RevCond))
assert(false && "Unable to reverse branch condition!");
TII->InsertBranch(*BBI.TrueBB, TrueBBI.FalseBB, NULL, RevCond);
}
// Join the 'true' and 'false' blocks if the 'false' block has no other
// predecessors. Otherwise, add a unconditional branch from 'true' to 'false'.
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
if (FalseBBI.BB->pred_size() == 2)
MergeBlocks(TrueBBI, FalseBBI);
else
InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
// Now merge the entry of the triangle with the true block.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, TrueBBI);
std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
std::back_inserter(BBI.Predicate));
// Update block info. BB can be iteratively if-converted.
BBI.Kind = ICNotClassfied;
BBI.TrueBB = BBI.FalseBB = NULL;
BBI.BrCond.clear();
TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
ReTryPreds(BBI.BB);
TrueBBI.Kind = ICDead;
// FIXME: Must maintain LiveIns.
NumIfConvBBs++;
return true;
}
/// IfConvertDiamond - If convert a diamond sub-CFG.
///
bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
BBI.Kind = ICNotClassfied;
bool TrueNeedBr;
bool FalseNeedBr;
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
FeasibilityAnalysis(TrueBBI, BBI.BrCond);
std::vector<MachineOperand> RevCond(BBI.BrCond);
TII->ReverseBranchCondition(RevCond);
FeasibilityAnalysis(FalseBBI, RevCond);
SmallVector<MachineInstr*, 2> Dups;
bool Proceed = TrueBBI.isPredicable && FalseBBI.isPredicable;
if (Proceed) {
// 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.
TrueNeedBr = !TrueBBI.TrueBB && BBI.TrueBB->succ_size();
FalseNeedBr = !FalseBBI.TrueBB && BBI.FalseBB->succ_size();
if (TrueNeedBr && TrueBBI.ModifyPredicate) {
TrueBBI.isPredicable = false;
Proceed = false;
}
if (FalseNeedBr && FalseBBI.ModifyPredicate) {
FalseBBI.isPredicable = false;
Proceed = false;
}
if (Proceed) {
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()) {
Proceed = false;
break; // Can't if-convert. Abort!
}
++TT;
++FT;
}
// One of the two pathes have more terminators, make sure they are
// all predicable.
while (Proceed && TT != BBI.TrueBB->end())
if (!TT->isPredicable()) {
Proceed = false;
break; // Can't if-convert. Abort!
}
while (Proceed && FT != BBI.FalseBB->end())
if (!FT->isPredicable()) {
Proceed = false;
break; // Can't if-convert. Abort!
}
}
}
}
if (!Proceed)
return false;
// Remove the duplicated instructions from the 'true' block.
for (unsigned i = 0, e = Dups.size(); i != e; ++i) {
Dups[i]->eraseFromParent();
--TrueBBI.NonPredSize;
}
// Predicate the 'true' block after removing its branch.
TrueBBI.NonPredSize -= TII->RemoveBranch(*BBI.TrueBB);
PredicateBlock(TrueBBI, BBI.BrCond);
// Predicate the 'false' block.
PredicateBlock(FalseBBI, RevCond, true);
// 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 *CvtBBI;
if (!TrueBBI.ModifyPredicate) {
// Add a conditional branch from 'true' to 'true' successor if needed.
if (TrueNeedBr)
TII->InsertBranch(*BBI.TrueBB, *BBI.TrueBB->succ_begin(), NULL,
BBI.BrCond);
// Add an unconditional branch from 'false' to to 'false' successor if it
// will not be the fallthrough block.
if (FalseNeedBr &&
!isNextBlock(BBI.BB, *BBI.FalseBB->succ_begin()))
InsertUncondBranch(BBI.FalseBB, *BBI.FalseBB->succ_begin(), TII);
MergeBlocks(TrueBBI, FalseBBI);
CvtBBI = &TrueBBI;
} else {
// Add a conditional branch from 'false' to 'false' successor if needed.
if (FalseNeedBr)
TII->InsertBranch(*BBI.FalseBB, *BBI.FalseBB->succ_begin(), NULL,
RevCond);
// Add an unconditional branch from 'true' to to 'true' successor if it
// will not be the fallthrough block.
if (TrueNeedBr &&
!isNextBlock(BBI.BB, *BBI.TrueBB->succ_begin()))
InsertUncondBranch(BBI.TrueBB, *BBI.TrueBB->succ_begin(), TII);
MergeBlocks(FalseBBI, TrueBBI);
CvtBBI = &FalseBBI;
}
// Remove the conditional branch from entry to the blocks.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
bool OkToIfcvt = true;
// Merge the combined block into the entry of the diamond if the entry
// block is its only predecessor. Otherwise, insert an unconditional
// branch from entry to the if-converted block.
if (CvtBBI->BB->pred_size() == 1) {
MergeBlocks(BBI, *CvtBBI);
CvtBBI = &BBI;
OkToIfcvt = false;
} else
InsertUncondBranch(BBI.BB, CvtBBI->BB, TII);
// 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.
if (BBI.TailBB &&
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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.Kind = ICDead;
}
// Update block info. BB may be iteratively if-converted.
if (OkToIfcvt) {
BBI.Kind = ICNotClassfied;
BBI.TrueBB = BBI.FalseBB = NULL;
BBI.BrCond.clear();
TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
ReTryPreds(BBI.BB);
}
TrueBBI.Kind = ICDead;
FalseBBI.Kind = ICDead;
// FIXME: Must maintain LiveIns.
NumIfConvBBs += 2;
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) {
MachineInstr *MI = I;
if (IgnoreTerm && TII->isTerminatorInstr(MI->getOpcode()))
continue;
if (TII->isPredicated(MI))
continue;
if (!TII->PredicateInstruction(MI, Cond)) {
cerr << "Unable to predicate " << *I << "!\n";
abort();
}
}
BBI.NonPredSize = 0;
}
/// 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());
// If FromBBI is previously a successor, remove it from ToBBI's successor
// list and update its TrueBB / FalseBB field if needed.
if (ToBBI.BB->isSuccessor(FromBBI.BB))
ToBBI.BB->removeSuccessor(FromBBI.BB);
// Transfer preds / succs and update size.
TransferPreds(ToBBI.BB, FromBBI.BB);
TransferSuccs(ToBBI.BB, FromBBI.BB);
ToBBI.NonPredSize += FromBBI.NonPredSize;
FromBBI.NonPredSize = 0;
}