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llvm-mirror/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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "branchfolding"
#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/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
2006-11-05 20:31:28 +01:00
#include <algorithm>
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");
static cl::opt<bool> EnableTailMerge("enable-tail-merge", cl::Hidden);
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);
MachineBasicBlock *SplitMBBAt(MachineBasicBlock &CurMBB,
MachineBasicBlock::iterator BBI1);
// Branch optzn.
bool OptimizeBranches(MachineFunction &MF);
void OptimizeBlock(MachineBasicBlock *MBB);
void RemoveDeadBlock(MachineBasicBlock *MBB);
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
2006-10-29 22:05:41 +01:00
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;
}
/// SplitMBBAt - Given a machine basic block and an iterator into it, split the
/// MBB so that the part before the iterator falls into the part starting at the
/// iterator. This returns the new MBB.
MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
MachineBasicBlock::iterator BBI1) {
// Create the fall-through block.
MachineFunction::iterator MBBI = &CurMBB;
MachineBasicBlock *NewMBB = new MachineBasicBlock(CurMBB.getBasicBlock());
CurMBB.getParent()->getBasicBlockList().insert(++MBBI, NewMBB);
// Move all the successors of this block to the specified block.
while (!CurMBB.succ_empty()) {
MachineBasicBlock *S = *(CurMBB.succ_end()-1);
NewMBB->addSuccessor(S);
CurMBB.removeSuccessor(S);
}
// Add an edge from CurMBB to NewMBB for the fall-through.
CurMBB.addSuccessor(NewMBB);
// Splice the code over.
NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end());
return NewMBB;
}
/// EstimateRuntime - Make a rough estimate for how long it will take to run
/// the specified code.
static unsigned EstimateRuntime(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator E,
const TargetInstrInfo *TII) {
unsigned Time = 0;
for (; I != E; ++I) {
const TargetInstrDescriptor &TID = TII->get(I->getOpcode());
if (TID.Flags & M_CALL_FLAG)
Time += 10;
else if (TID.Flags & (M_LOAD_FLAG|M_STORE_FLAG))
Time += 2;
else
++Time;
}
return Time;
}
/// ShouldSplitFirstBlock - We need to either split MBB1 at MBB1I or MBB2 at
/// MBB2I and then insert an unconditional branch in the other block. Determine
/// which is the best to split
static bool ShouldSplitFirstBlock(MachineBasicBlock *MBB1,
MachineBasicBlock::iterator MBB1I,
MachineBasicBlock *MBB2,
MachineBasicBlock::iterator MBB2I,
const TargetInstrInfo *TII) {
// TODO: if we had some notion of which block was hotter, we could split
// the hot block, so it is the fall-through. Since we don't have profile info
// make a decision based on which will hurt most to split.
unsigned MBB1Time = EstimateRuntime(MBB1->begin(), MBB1I, TII);
unsigned MBB2Time = EstimateRuntime(MBB2->begin(), MBB2I, TII);
// If the MBB1 prefix takes "less time" to run than the MBB2 prefix, split the
// MBB1 block so it falls through. This will penalize the MBB2 path, but will
// have a lower overall impact on the program execution.
return MBB1Time < MBB2Time;
}
bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
MadeChange = false;
if (!EnableTailMerge) 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));
}
MachineBasicBlock *MBB2 = (MergePotentials.end()-2)->second;
// If neither block is the entire common tail, split the tail of one block
// to make it redundant with the other tail.
if (CurMBB->begin() != BBI1 && MBB2->begin() != BBI2) {
if (0) { // Enable this to disable partial tail merges.
MergePotentials.pop_back();
continue;
}
// Decide whether we want to split CurMBB or MBB2.
if (ShouldSplitFirstBlock(CurMBB, BBI1, MBB2, BBI2, TII)) {
CurMBB = SplitMBBAt(*CurMBB, BBI1);
BBI1 = CurMBB->begin();
MergePotentials.back().second = CurMBB;
} else {
MBB2 = SplitMBBAt(*MBB2, BBI2);
BBI2 = MBB2->begin();
(MergePotentials.end()-2)->second = MBB2;
}
}
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();
} else {
assert(CurMBB->begin() == BBI1 && "Didn't split block correctly?");
// 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;
}
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);
}
}
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
2006-10-29 22:05:41 +01:00
/// 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.
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
2006-10-29 22:05:41 +01:00
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.
2006-10-26 00:21:37 +02:00
return FBB == 0;
}
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
2006-10-29 22:05:41 +01:00
/// 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);
}
/// IsBetterFallthrough - Return true if it would be clearly better to
/// fall-through to MBB1 than to fall through into MBB2. This has to return
/// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will
/// result in infinite loops.
static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
MachineBasicBlock *MBB2,
const TargetInstrInfo &TII) {
// Right now, we use a simple heuristic. If MBB2 ends with a call, and
// MBB1 doesn't, we prefer to fall through into MBB1. This allows us to
// optimize branches that branch to either a return block or an assert block
// into a fallthrough to the return.
if (MBB1->empty() || MBB2->empty()) return false;
MachineInstr *MBB1I = --MBB1->end();
MachineInstr *MBB2I = --MBB2->end();
return TII.isCall(MBB2I->getOpcode()) && !TII.isCall(MBB1I->getOpcode());
}
/// 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;
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
2006-10-29 22:05:41 +01:00
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);
}
}
// If this block doesn't fall through (e.g. it ends with an uncond branch or
// has no successors) and if the pred falls through into this block, and if
// it would otherwise fall through into the block after this, move this
// block to the end of the function.
//
// We consider it more likely that execution will stay in the function (e.g.
// due to loops) than it is to exit it. This asserts in loops etc, moving
// the assert condition out of the loop body.
if (!PriorCond.empty() && PriorFBB == 0 &&
MachineFunction::iterator(PriorTBB) == FallThrough &&
!CanFallThrough(MBB)) {
bool DoTransform = true;
// We have to be careful that the succs of PredBB aren't both no-successor
// blocks. If neither have successors and if PredBB is the second from
// last block in the function, we'd just keep swapping the two blocks for
// last. Only do the swap if one is clearly better to fall through than
// the other.
if (FallThrough == --MBB->getParent()->end() &&
!IsBetterFallthrough(PriorTBB, MBB, *TII))
DoTransform = false;
// We don't want to do this transformation if we have control flow like:
// br cond BB2
// BB1:
// ..
// jmp BBX
// BB2:
// ..
// ret
//
// In this case, we could actually be moving the return block *into* a
// loop!
if (DoTransform && !MBB->succ_empty() &&
(!CanFallThrough(PriorTBB) || PriorTBB->empty()))
DoTransform = false;
if (DoTransform) {
// Reverse the branch so we will fall through on the previous true cond.
std::vector<MachineOperand> NewPriorCond(PriorCond);
if (!TII->ReverseBranchCondition(NewPriorCond)) {
DOUT << "\nMoving MBB: " << *MBB;
DOUT << "To make fallthrough to: " << *PriorTBB << "\n";
TII->RemoveBranch(PrevBB);
TII->InsertBranch(PrevBB, MBB, 0, NewPriorCond);
// Move this block to the end of the function.
MBB->moveAfter(--MBB->getParent()->end());
MadeChange = true;
++NumBranchOpts;
return;
}
}
}
}
// Analyze the branch in the current block.
MachineBasicBlock *CurTBB = 0, *CurFBB = 0;
std::vector<MachineOperand> CurCond;
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
2006-10-29 22:05:41 +01:00
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 is a two-way branch, and the FBB branches to this block, reverse
// the condition so the single-basic-block loop is faster. Instead of:
// Loop: xxx; jcc Out; jmp Loop
// we want:
// Loop: xxx; jncc Loop; jmp Out
if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) {
std::vector<MachineOperand> NewCond(CurCond);
if (!TII->ReverseBranchCondition(NewCond)) {
TII->RemoveBranch(*MBB);
TII->InsertBranch(*MBB, CurFBB, CurTBB, NewCond);
MadeChange = true;
++NumBranchOpts;
return OptimizeBlock(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);
}
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
2006-10-29 22:05:41 +01:00
}
// 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;
std::vector<MachineOperand> PredCond;
if (PredBB != MBB && !CanFallThrough(PredBB)) {
MBB->moveAfter(PredBB);
MadeChange = true;
return OptimizeBlock(MBB);
}
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
2006-10-29 22:05:41 +01:00
}
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
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// 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;
std::vector<MachineOperand> SuccPrevCond;
if (SuccBB != MBB && !CanFallThrough(SuccPrev)) {
MBB->moveBefore(SuccBB);
MadeChange = true;
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
2006-10-29 22:05:41 +01:00
return OptimizeBlock(MBB);
}
}
Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no 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 :) llvm-svn: 31282
2006-10-29 22:05:41 +01:00
// 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;
}
}
}
}