mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-19 19:29:31 +00:00
successors), and make island block movement more general. This compiles CodeGen/X86/2006-04-27-ISelFoldingBug.ll to: _loadAndRLEsource_no_exit_2E_1_label_2E_0: subl $8, %esp movl %esi, 4(%esp) movl %ebx, (%esp) movl 16(%esp), %eax movl 12(%esp), %ecx LBB1_3: #label.0 movl _last, %edx movl %edx, %esi incl %esi movl %esi, _last movl %ecx, %ebx # TRUNCATE movb %bl, %bl movl _block, %esi movb %bl, 1(%esi,%edx) cmpl %eax, _last jge LBB1_2 #codeRepl5.exitStub LBB1_4: #label.0 cmpl $257, %ecx je LBB1_2 #codeRepl5.exitStub LBB1_1: #label.0.no_exit.1_crit_edge.exitStub movl $1, %eax movl (%esp), %ebx movl 4(%esp), %esi addl $8, %esp ret LBB1_2: #codeRepl5.exitStub xorl %eax, %eax movl (%esp), %ebx movl 4(%esp), %esi addl $8, %esp ret instead of: _loadAndRLEsource_no_exit_2E_1_label_2E_0: subl $8, %esp movl %esi, 4(%esp) movl %ebx, (%esp) movl 16(%esp), %eax movl 12(%esp), %ecx jmp LBB1_3 #label.0 LBB1_1: #label.0.no_exit.1_crit_edge.exitStub movl $1, %eax movl (%esp), %ebx movl 4(%esp), %esi addl $8, %esp ret LBB1_2: #codeRepl5.exitStub xorl %eax, %eax movl (%esp), %ebx movl 4(%esp), %esi addl $8, %esp ret LBB1_3: #label.0 movl _last, %edx movl %edx, %esi incl %esi movl %esi, _last movl %ecx, %ebx # TRUNCATE movb %bl, %bl movl _block, %esi movb %bl, 1(%esi,%edx) cmpl %eax, _last jge LBB1_2 #codeRepl5.exitStub LBB1_4: #label.0 cmpl $257, %ecx jne LBB1_1 #label.0.no_exit.1_crit_edge.exitStub jmp LBB1_2 #codeRepl5.exitStub ... which is much better layout :) git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31282 91177308-0d34-0410-b5e6-96231b3b80d8
724 lines
27 KiB
C++
724 lines
27 KiB
C++
//===-- 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);
|
|
|
|
bool CanFallThrough(MachineBasicBlock *CurBB);
|
|
bool CanFallThrough(MachineBasicBlock *CurBB, bool BranchUnAnalyzable,
|
|
MachineBasicBlock *TBB, MachineBasicBlock *FBB,
|
|
const std::vector<MachineOperand> &Cond);
|
|
};
|
|
}
|
|
|
|
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 if the specified block (with the specified
|
|
/// branch condition) can implicitly transfer control to the block after it by
|
|
/// falling off the end of it. This should return false if it can reach the
|
|
/// block after it, but it uses an explicit branch to do so (e.g. a table jump).
|
|
///
|
|
/// True is a conservative answer.
|
|
///
|
|
bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB,
|
|
bool BranchUnAnalyzable,
|
|
MachineBasicBlock *TBB, MachineBasicBlock *FBB,
|
|
const std::vector<MachineOperand> &Cond) {
|
|
MachineFunction::iterator Fallthrough = CurBB;
|
|
++Fallthrough;
|
|
// If FallthroughBlock is off the end of the function, it can't fall through.
|
|
if (Fallthrough == CurBB->getParent()->end())
|
|
return false;
|
|
|
|
// If FallthroughBlock isn't a successor of CurBB, no fallthrough is possible.
|
|
if (!CurBB->isSuccessor(Fallthrough))
|
|
return false;
|
|
|
|
// If we couldn't analyze the branch, assume it could fall through.
|
|
if (BranchUnAnalyzable) return true;
|
|
|
|
// 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) == Fallthrough ||
|
|
MachineFunction::iterator(FBB) == Fallthrough)
|
|
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;
|
|
}
|
|
|
|
/// CanFallThrough - Return true if the specified can implicitly transfer
|
|
/// control to the block after it by falling off the end of it. This should
|
|
/// return false if it can reach the block after it, but it uses an explicit
|
|
/// branch to do so (e.g. a table jump).
|
|
///
|
|
/// True is a conservative answer.
|
|
///
|
|
bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB) {
|
|
MachineBasicBlock *TBB = 0, *FBB = 0;
|
|
std::vector<MachineOperand> Cond;
|
|
bool CurUnAnalyzable = TII->AnalyzeBranch(*CurBB, TBB, FBB, Cond);
|
|
return CanFallThrough(CurBB, CurUnAnalyzable, TBB, FBB, Cond);
|
|
}
|
|
|
|
/// 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 =
|
|
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;
|
|
bool CurUnAnalyzable = TII->AnalyzeBranch(*MBB, CurTBB, CurFBB, CurCond);
|
|
if (!CurUnAnalyzable) {
|
|
// 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 (!CanFallThrough(&PrevBB, PriorUnAnalyzable,
|
|
PriorTBB, PriorFBB, PriorCond)) {
|
|
// Now we know that there was no fall-through into this block, check to
|
|
// see if it has a fall-through into its successor.
|
|
if (!CanFallThrough(MBB, CurUnAnalyzable, CurTBB, CurFBB, CurCond)) {
|
|
// 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 && !CanFallThrough(PredBB)) {
|
|
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 && !CanFallThrough(SuccPrev)) {
|
|
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() &&
|
|
PrevBB.isSuccessor(FallThrough)) {
|
|
MBB->moveAfter(--MBB->getParent()->end());
|
|
MadeChange = true;
|
|
return;
|
|
}
|
|
}
|
|
}
|
|
}
|