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

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//===-- BranchFolding.cpp - Fold machine code branch instructions ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass forwards branches to unconditional branches to make them branch
// directly to the target block. This pass often results in dead MBB's, which
// it then removes.
//
// Note that this pass must be run after register allocation, it cannot handle
// SSA form.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineDebugInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineJumpTableInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
static Statistic<> NumDeadBlocks("branchfold", "Number of dead blocks removed");
static Statistic<> NumBranchOpts("branchfold", "Number of branches optimized");
static Statistic<> NumTailMerge ("branchfold", "Number of block tails merged");
namespace {
struct BranchFolder : public MachineFunctionPass {
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const { return "Control Flow Optimizer"; }
const TargetInstrInfo *TII;
MachineDebugInfo *MDI;
bool MadeChange;
private:
// Tail Merging.
bool TailMergeBlocks(MachineFunction &MF);
void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
MachineBasicBlock *NewDest);
// Branch optzn.
bool OptimizeBranches(MachineFunction &MF);
void OptimizeBlock(MachineBasicBlock *MBB);
void RemoveDeadBlock(MachineBasicBlock *MBB);
};
}
FunctionPass *llvm::createBranchFoldingPass() { return new BranchFolder(); }
/// RemoveDeadBlock - Remove the specified dead machine basic block from the
/// function, updating the CFG.
void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
assert(MBB->pred_empty() && "MBB must be dead!");
MachineFunction *MF = MBB->getParent();
// drop all successors.
while (!MBB->succ_empty())
MBB->removeSuccessor(MBB->succ_end()-1);
// If there is DWARF info to active, check to see if there are any DWARF_LABEL
// records in the basic block. If so, unregister them from MachineDebugInfo.
if (MDI && !MBB->empty()) {
unsigned DWARF_LABELOpc = TII->getDWARF_LABELOpcode();
assert(DWARF_LABELOpc &&
"Target supports dwarf but didn't implement getDWARF_LABELOpcode!");
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
I != E; ++I) {
if ((unsigned)I->getOpcode() == DWARF_LABELOpc) {
// The label ID # is always operand #0, an immediate.
MDI->InvalidateLabel(I->getOperand(0).getImm());
}
}
}
// Remove the block.
MF->getBasicBlockList().erase(MBB);
}
bool BranchFolder::runOnMachineFunction(MachineFunction &MF) {
TII = MF.getTarget().getInstrInfo();
if (!TII) return false;
MDI = getAnalysisToUpdate<MachineDebugInfo>();
bool EverMadeChange = false;
bool MadeChangeThisIteration = true;
while (MadeChangeThisIteration) {
MadeChangeThisIteration = false;
MadeChangeThisIteration |= TailMergeBlocks(MF);
MadeChangeThisIteration |= OptimizeBranches(MF);
EverMadeChange |= MadeChangeThisIteration;
}
// See if any jump tables have become mergable or dead as the code generator
// did its thing.
MachineJumpTableInfo *JTI = MF.getJumpTableInfo();
const std::vector<MachineJumpTableEntry> &JTs = JTI->getJumpTables();
if (!JTs.empty()) {
// Figure out how these jump tables should be merged.
std::vector<unsigned> JTMapping;
JTMapping.reserve(JTs.size());
// We always keep the 0th jump table.
JTMapping.push_back(0);
// Scan the jump tables, seeing if there are any duplicates. Note that this
// is N^2, which should be fixed someday.
for (unsigned i = 1, e = JTs.size(); i != e; ++i)
JTMapping.push_back(JTI->getJumpTableIndex(JTs[i].MBBs));
// If a jump table was merge with another one, walk the function rewriting
// references to jump tables to reference the new JT ID's. Keep track of
// whether we see a jump table idx, if not, we can delete the JT.
std::vector<bool> JTIsLive;
JTIsLive.resize(JTs.size());
for (MachineFunction::iterator BB = MF.begin(), E = MF.end();
BB != E; ++BB) {
for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
I != E; ++I)
for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) {
MachineOperand &Op = I->getOperand(op);
if (!Op.isJumpTableIndex()) continue;
unsigned NewIdx = JTMapping[Op.getJumpTableIndex()];
Op.setJumpTableIndex(NewIdx);
// Remember that this JT is live.
JTIsLive[NewIdx] = true;
}
}
// Finally, remove dead jump tables. This happens either because the
// indirect jump was unreachable (and thus deleted) or because the jump
// table was merged with some other one.
for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i)
if (!JTIsLive[i]) {
JTI->RemoveJumpTable(i);
EverMadeChange = true;
}
}
return EverMadeChange;
}
//===----------------------------------------------------------------------===//
// Tail Merging of Blocks
//===----------------------------------------------------------------------===//
/// HashMachineInstr - Compute a hash value for MI and its operands.
static unsigned HashMachineInstr(const MachineInstr *MI) {
unsigned Hash = MI->getOpcode();
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &Op = MI->getOperand(i);
// Merge in bits from the operand if easy.
unsigned OperandHash = 0;
switch (Op.getType()) {
case MachineOperand::MO_Register: OperandHash = Op.getReg(); break;
case MachineOperand::MO_Immediate: OperandHash = Op.getImm(); break;
case MachineOperand::MO_MachineBasicBlock:
OperandHash = Op.getMachineBasicBlock()->getNumber();
break;
case MachineOperand::MO_FrameIndex: OperandHash = Op.getFrameIndex(); break;
case MachineOperand::MO_ConstantPoolIndex:
OperandHash = Op.getConstantPoolIndex();
break;
case MachineOperand::MO_JumpTableIndex:
OperandHash = Op.getJumpTableIndex();
break;
case MachineOperand::MO_GlobalAddress:
case MachineOperand::MO_ExternalSymbol:
// Global address / external symbol are too hard, don't bother, but do
// pull in the offset.
OperandHash = Op.getOffset();
break;
default: break;
}
Hash += ((OperandHash << 3) | Op.getType()) << (i&31);
}
return Hash;
}
/// HashEndOfMBB - Hash the last two instructions in the MBB. We hash two
/// instructions, because cross-jumping only saves code when at least two
/// instructions are removed (since a branch must be inserted).
static unsigned HashEndOfMBB(const MachineBasicBlock *MBB) {
MachineBasicBlock::const_iterator I = MBB->end();
if (I == MBB->begin())
return 0; // Empty MBB.
--I;
unsigned Hash = HashMachineInstr(I);
if (I == MBB->begin())
return Hash; // Single instr MBB.
--I;
// Hash in the second-to-last instruction.
Hash ^= HashMachineInstr(I) << 2;
return Hash;
}
/// ComputeCommonTailLength - Given two machine basic blocks, compute the number
/// of instructions they actually have in common together at their end. Return
/// iterators for the first shared instruction in each block.
static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
MachineBasicBlock *MBB2,
MachineBasicBlock::iterator &I1,
MachineBasicBlock::iterator &I2) {
I1 = MBB1->end();
I2 = MBB2->end();
unsigned TailLen = 0;
while (I1 != MBB1->begin() && I2 != MBB2->begin()) {
--I1; --I2;
if (!I1->isIdenticalTo(I2)) {
++I1; ++I2;
break;
}
++TailLen;
}
return TailLen;
}
/// ReplaceTailWithBranchTo - Delete the instruction OldInst and everything
/// after it, replacing it with an unconditional branch to NewDest. This
/// returns true if OldInst's block is modified, false if NewDest is modified.
void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
MachineBasicBlock *NewDest) {
MachineBasicBlock *OldBB = OldInst->getParent();
// Remove all the old successors of OldBB from the CFG.
while (!OldBB->succ_empty())
OldBB->removeSuccessor(OldBB->succ_begin());
// Remove all the dead instructions from the end of OldBB.
OldBB->erase(OldInst, OldBB->end());
// If OldBB isn't immediately before OldBB, insert a branch to it.
if (++MachineFunction::iterator(OldBB) != MachineFunction::iterator(NewDest))
TII->InsertBranch(*OldBB, NewDest, 0, std::vector<MachineOperand>());
OldBB->addSuccessor(NewDest);
++NumTailMerge;
}
bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
MadeChange = false;
return false;
// Find blocks with no successors.
std::vector<std::pair<unsigned,MachineBasicBlock*> > MergePotentials;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
if (I->succ_empty())
MergePotentials.push_back(std::make_pair(HashEndOfMBB(I), I));
}
// Sort by hash value so that blocks with identical end sequences sort
// together.
std::stable_sort(MergePotentials.begin(), MergePotentials.end());
// Walk through equivalence sets looking for actual exact matches.
while (MergePotentials.size() > 1) {
unsigned CurHash = (MergePotentials.end()-1)->first;
unsigned PrevHash = (MergePotentials.end()-2)->first;
MachineBasicBlock *CurMBB = (MergePotentials.end()-1)->second;
// If there is nothing that matches the hash of the current basic block,
// give up.
if (CurHash != PrevHash) {
MergePotentials.pop_back();
continue;
}
// Determine the actual length of the shared tail between these two basic
// blocks. Because the hash can have collisions, it's possible that this is
// less than 2.
MachineBasicBlock::iterator BBI1, BBI2;
unsigned CommonTailLen =
ComputeCommonTailLength(CurMBB, (MergePotentials.end()-2)->second,
BBI1, BBI2);
// If the tails don't have at least two instructions in common, see if there
// is anything else in the equivalence class that does match.
if (CommonTailLen < 2) {
unsigned FoundMatch = ~0U;
for (int i = MergePotentials.size()-2;
i != -1 && MergePotentials[i].first == CurHash; --i) {
CommonTailLen = ComputeCommonTailLength(CurMBB,
MergePotentials[i].second,
BBI1, BBI2);
if (CommonTailLen >= 2) {
FoundMatch = i;
break;
}
}
// If we didn't find anything that has at least two instructions matching
// this one, bail out.
if (FoundMatch == ~0U) {
MergePotentials.pop_back();
continue;
}
// Otherwise, move the matching block to the right position.
std::swap(MergePotentials[FoundMatch], *(MergePotentials.end()-2));
}
// If either block is the entire common tail, make the longer one branch to
// the shorter one.
MachineBasicBlock *MBB2 = (MergePotentials.end()-2)->second;
if (CurMBB->begin() == BBI1) {
// Hack the end off MBB2, making it jump to CurMBB instead.
ReplaceTailWithBranchTo(BBI2, CurMBB);
// This modifies MBB2, so remove it from the worklist.
MergePotentials.erase(MergePotentials.end()-2);
MadeChange = true;
continue;
} else if (MBB2->begin() == BBI2) {
// Hack the end off CurMBB, making it jump to MBBI@ instead.
ReplaceTailWithBranchTo(BBI1, MBB2);
// This modifies CurMBB, so remove it from the worklist.
MergePotentials.pop_back();
MadeChange = true;
continue;
}
MergePotentials.pop_back();
}
return MadeChange;
}
//===----------------------------------------------------------------------===//
// Branch Optimization
//===----------------------------------------------------------------------===//
bool BranchFolder::OptimizeBranches(MachineFunction &MF) {
MadeChange = false;
for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
MachineBasicBlock *MBB = I++;
OptimizeBlock(MBB);
// If it is dead, remove it.
if (MBB->pred_empty()) {
RemoveDeadBlock(MBB);
MadeChange = true;
++NumDeadBlocks;
}
}
return MadeChange;
}
/// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
/// CFG to be inserted. If we have proven that MBB can only branch to DestA and
/// DestB, remove any other MBB successors from the CFG. DestA and DestB can
/// be null.
static bool CorrectExtraCFGEdges(MachineBasicBlock &MBB,
MachineBasicBlock *DestA,
MachineBasicBlock *DestB,
bool isCond,
MachineFunction::iterator FallThru) {
bool MadeChange = false;
bool AddedFallThrough = false;
// If this block ends with a conditional branch that falls through to its
// successor, set DestB as the successor.
if (isCond) {
if (DestB == 0 && FallThru != MBB.getParent()->end()) {
DestB = FallThru;
AddedFallThrough = true;
}
} else {
// If this is an unconditional branch with no explicit dest, it must just be
// a fallthrough into DestB.
if (DestA == 0 && FallThru != MBB.getParent()->end()) {
DestA = FallThru;
AddedFallThrough = true;
}
}
MachineBasicBlock::pred_iterator SI = MBB.succ_begin();
while (SI != MBB.succ_end()) {
if (*SI == DestA) {
DestA = 0;
++SI;
} else if (*SI == DestB) {
DestB = 0;
++SI;
} else {
// Otherwise, this is a superfluous edge, remove it.
MBB.removeSuccessor(SI);
MadeChange = true;
}
}
if (!AddedFallThrough) {
assert(DestA == 0 && DestB == 0 &&
"MachineCFG is missing edges!");
} else if (isCond) {
assert(DestA == 0 && "MachineCFG is missing edges!");
}
return MadeChange;
}
/// ReplaceUsesOfBlockWith - Given a machine basic block 'BB' that branched to
/// 'Old', change the code and CFG so that it branches to 'New' instead.
static void ReplaceUsesOfBlockWith(MachineBasicBlock *BB,
MachineBasicBlock *Old,
MachineBasicBlock *New,
const TargetInstrInfo *TII) {
assert(Old != New && "Cannot replace self with self!");
MachineBasicBlock::iterator I = BB->end();
while (I != BB->begin()) {
--I;
if (!TII->isTerminatorInstr(I->getOpcode())) break;
// Scan the operands of this machine instruction, replacing any uses of Old
// with New.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
if (I->getOperand(i).isMachineBasicBlock() &&
I->getOperand(i).getMachineBasicBlock() == Old)
I->getOperand(i).setMachineBasicBlock(New);
}
// Update the successor information.
std::vector<MachineBasicBlock*> Succs(BB->succ_begin(), BB->succ_end());
for (int i = Succs.size()-1; i >= 0; --i)
if (Succs[i] == Old) {
BB->removeSuccessor(Old);
BB->addSuccessor(New);
}
}
/// CanFallThrough - Return true of the specified branch condition can transfer
/// control to FallthroughBlock, the block immediately after the branch.
static bool CanFallThrough(MachineBasicBlock *TBB,
MachineBasicBlock *FBB,
const std::vector<MachineOperand> &Cond,
MachineFunction::iterator FallthroughBlock) {
// If there is no branch, control always falls through.
if (TBB == 0) return true;
// If there is some explicit branch to the fallthrough block, it can obviously
// reach, even though the branch should get folded to fall through implicitly.
if (MachineFunction::iterator(TBB) == FallthroughBlock ||
MachineFunction::iterator(FBB) == FallthroughBlock)
return true;
// If it's an unconditional branch to some block not the fall through, it
// doesn't fall through.
if (Cond.empty()) return false;
// Otherwise, if it is conditional and has no explicit false block, it falls
// through.
return FBB == 0;
}
/// OptimizeBlock - Analyze and optimize control flow related to the specified
/// block. This is never called on the entry block.
void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
MachineFunction::iterator FallThrough = MBB;
++FallThrough;
// If this block is empty, make everyone use its fall-through, not the block
// explicitly.
if (MBB->empty()) {
// Dead block? Leave for cleanup later.
if (MBB->pred_empty()) return;
if (FallThrough == MBB->getParent()->end()) {
// TODO: Simplify preds to not branch here if possible!
} else {
// Rewrite all predecessors of the old block to go to the fallthrough
// instead.
while (!MBB->pred_empty()) {
MachineBasicBlock *Pred = *(MBB->pred_end()-1);
ReplaceUsesOfBlockWith(Pred, MBB, FallThrough, TII);
}
// If MBB was the target of a jump table, update jump tables to go to the
// fallthrough instead.
MBB->getParent()->getJumpTableInfo()->
ReplaceMBBInJumpTables(MBB, FallThrough);
MadeChange = true;
}
return;
}
// Check to see if we can simplify the terminator of the block before this
// one.
MachineBasicBlock &PrevBB = *prior(MachineFunction::iterator(MBB));
MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
std::vector<MachineOperand> PriorCond;
bool PriorUnAnalyzable = false;
PriorUnAnalyzable = TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond);
if (!PriorUnAnalyzable) {
// If the CFG for the prior block has extra edges, remove them.
MadeChange |= CorrectExtraCFGEdges(PrevBB, PriorTBB, PriorFBB,
!PriorCond.empty(), MBB);
// If the previous branch is conditional and both conditions go to the same
// destination, remove the branch, replacing it with an unconditional one or
// a fall-through.
if (PriorTBB && PriorTBB == PriorFBB) {
TII->RemoveBranch(PrevBB);
PriorCond.clear();
if (PriorTBB != MBB)
TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond);
MadeChange = true;
++NumBranchOpts;
return OptimizeBlock(MBB);
}
// If the previous branch *only* branches to *this* block (conditional or
// not) remove the branch.
if (PriorTBB == MBB && PriorFBB == 0) {
TII->RemoveBranch(PrevBB);
MadeChange = true;
++NumBranchOpts;
return OptimizeBlock(MBB);
}
// If the prior block branches somewhere else on the condition and here if
// the condition is false, remove the uncond second branch.
if (PriorFBB == MBB) {
TII->RemoveBranch(PrevBB);
TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond);
MadeChange = true;
++NumBranchOpts;
return OptimizeBlock(MBB);
}
// If the prior block branches here on true and somewhere else on false, and
// if the branch condition is reversible, reverse the branch to create a
// fall-through.
if (PriorTBB == MBB) {
std::vector<MachineOperand> NewPriorCond(PriorCond);
if (!TII->ReverseBranchCondition(NewPriorCond)) {
TII->RemoveBranch(PrevBB);
TII->InsertBranch(PrevBB, PriorFBB, 0, NewPriorCond);
MadeChange = true;
++NumBranchOpts;
return OptimizeBlock(MBB);
}
}
}
// Analyze the branch in the current block.
MachineBasicBlock *CurTBB = 0, *CurFBB = 0;
std::vector<MachineOperand> CurCond;
if (!TII->AnalyzeBranch(*MBB, CurTBB, CurFBB, CurCond)) {
// If the CFG for the prior block has extra edges, remove them.
MadeChange |= CorrectExtraCFGEdges(*MBB, CurTBB, CurFBB,
!CurCond.empty(),
++MachineFunction::iterator(MBB));
// If this branch is the only thing in its block, see if we can forward
// other blocks across it.
if (CurTBB && CurCond.empty() && CurFBB == 0 &&
TII->isBranch(MBB->begin()->getOpcode()) && CurTBB != MBB) {
// This block may contain just an unconditional branch. Because there can
// be 'non-branch terminators' in the block, try removing the branch and
// then seeing if the block is empty.
TII->RemoveBranch(*MBB);
// If this block is just an unconditional branch to CurTBB, we can
// usually completely eliminate the block. The only case we cannot
// completely eliminate the block is when the block before this one
// falls through into MBB and we can't understand the prior block's branch
// condition.
if (MBB->empty()) {
bool PredHasNoFallThrough = TII->BlockHasNoFallThrough(PrevBB);
if (PredHasNoFallThrough || !PriorUnAnalyzable ||
!PrevBB.isSuccessor(MBB)) {
// If the prior block falls through into us, turn it into an
// explicit branch to us to make updates simpler.
if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) &&
PriorTBB != MBB && PriorFBB != MBB) {
if (PriorTBB == 0) {
assert(PriorCond.empty() && PriorFBB == 0 &&
"Bad branch analysis");
PriorTBB = MBB;
} else {
assert(PriorFBB == 0 && "Machine CFG out of date!");
PriorFBB = MBB;
}
TII->RemoveBranch(PrevBB);
TII->InsertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond);
}
// Iterate through all the predecessors, revectoring each in-turn.
MachineBasicBlock::pred_iterator PI = MBB->pred_begin();
bool DidChange = false;
bool HasBranchToSelf = false;
while (PI != MBB->pred_end()) {
if (*PI == MBB) {
// If this block has an uncond branch to itself, leave it.
++PI;
HasBranchToSelf = true;
} else {
DidChange = true;
ReplaceUsesOfBlockWith(*PI, MBB, CurTBB, TII);
}
}
// Change any jumptables to go to the new MBB.
MBB->getParent()->getJumpTableInfo()->
ReplaceMBBInJumpTables(MBB, CurTBB);
if (DidChange) {
++NumBranchOpts;
MadeChange = true;
if (!HasBranchToSelf) return;
}
}
}
// Add the branch back if the block is more than just an uncond branch.
TII->InsertBranch(*MBB, CurTBB, 0, CurCond);
}
// If the prior block doesn't fall through into this block, and if this
// block doesn't fall through into some other block, see if we can find a
// place to move this block where a fall-through will happen.
if (!PriorUnAnalyzable && !CanFallThrough(PriorTBB, PriorFBB,
PriorCond, MBB)) {
// Now we know that there was no fall-through into this block, check to
// see if it has fall-throughs.
if (!CanFallThrough(CurTBB, CurFBB, CurCond, FallThrough)) {
// Check all the predecessors of this block. If one of them has no fall
// throughs, move this block right after it.
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
E = MBB->pred_end(); PI != E; ++PI) {
// Analyze the branch at the end of the pred.
MachineBasicBlock *PredBB = *PI;
MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough;
MachineBasicBlock *PredTBB = 0, *PredFBB = 0;
std::vector<MachineOperand> PredCond;
if (PredBB != MBB &&
!TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond) &&
!CanFallThrough(PredTBB, PredFBB, PredCond, PredFallthrough)) {
MBB->moveAfter(PredBB);
MadeChange = true;
return OptimizeBlock(MBB);
}
}
// Check all successors to see if we can move this block before it.
for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
E = MBB->succ_end(); SI != E; ++SI) {
// Analyze the branch at the end of the block before the succ.
MachineBasicBlock *SuccBB = *SI;
MachineFunction::iterator SuccPrev = SuccBB; --SuccPrev;
MachineBasicBlock *SuccPrevTBB = 0, *SuccPrevFBB = 0;
std::vector<MachineOperand> SuccPrevCond;
if (SuccBB != MBB &&
!TII->AnalyzeBranch(*SuccPrev, SuccPrevTBB, SuccPrevFBB,
SuccPrevCond) &&
!CanFallThrough(SuccPrevTBB, SuccPrevFBB, SuccPrevCond, SuccBB)) {
MBB->moveBefore(SuccBB);
MadeChange = true;
return OptimizeBlock(MBB);
}
}
// Okay, there is no really great place to put this block. If, however,
// the block before this one would be a fall-through if this block were
// removed, move this block to the end of the function.
if (FallThrough != MBB->getParent()->end() &&
CanFallThrough(PriorTBB, PriorFBB, PriorCond, FallThrough)) {
MBB->moveAfter(--MBB->getParent()->end());
MadeChange = true;
return;
}
}
}
}
}
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