2004-07-31 18:01:27 +08:00
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//===-- BranchFolding.cpp - Fold machine code branch instructions ---------===//
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2005-04-22 06:36:52 +08:00
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//
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2004-07-31 18:01:27 +08:00
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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2005-04-22 06:36:52 +08:00
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//
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2004-07-31 18:01:27 +08:00
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//===----------------------------------------------------------------------===//
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//
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// This pass forwards branches to unconditional branches to make them branch
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// directly to the target block. This pass often results in dead MBB's, which
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// it then removes.
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//
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// Note that this pass must be run after register allocation, it cannot handle
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// SSA form.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/Passes.h"
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2006-10-18 07:17:27 +08:00
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#include "llvm/CodeGen/MachineDebugInfo.h"
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2004-07-31 18:01:27 +08:00
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#include "llvm/CodeGen/MachineFunctionPass.h"
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2006-10-18 01:13:52 +08:00
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#include "llvm/CodeGen/MachineJumpTableInfo.h"
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2004-07-31 18:01:27 +08:00
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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2006-10-21 08:47:49 +08:00
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#include "llvm/Support/CommandLine.h"
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#include "llvm/ADT/Statistic.h"
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2004-09-02 06:55:40 +08:00
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#include "llvm/ADT/STLExtras.h"
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2004-07-31 18:01:27 +08:00
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using namespace llvm;
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2006-10-21 08:47:49 +08:00
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static Statistic<> NumDeadBlocks("branchfold", "Number of dead blocks removed");
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static Statistic<> NumBranchOpts("branchfold", "Number of branches optimized");
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static Statistic<> NumTailMerge ("branchfold", "Number of block tails merged");
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static cl::opt<bool> EnableTailMerge("enable-tail-merge");
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2004-07-31 18:01:27 +08:00
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namespace {
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struct BranchFolder : public MachineFunctionPass {
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virtual bool runOnMachineFunction(MachineFunction &MF);
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2006-10-14 08:21:48 +08:00
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virtual const char *getPassName() const { return "Control Flow Optimizer"; }
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const TargetInstrInfo *TII;
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MachineDebugInfo *MDI;
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2006-10-14 08:21:48 +08:00
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bool MadeChange;
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2004-07-31 18:01:27 +08:00
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private:
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2006-10-21 08:47:49 +08:00
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// Tail Merging.
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bool TailMergeBlocks(MachineFunction &MF);
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void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
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MachineBasicBlock *NewDest);
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// Branch optzn.
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bool OptimizeBranches(MachineFunction &MF);
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2006-10-14 08:21:48 +08:00
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void OptimizeBlock(MachineFunction::iterator MBB);
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2006-10-18 07:17:27 +08:00
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void RemoveDeadBlock(MachineBasicBlock *MBB);
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2004-07-31 18:01:27 +08:00
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};
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}
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FunctionPass *llvm::createBranchFoldingPass() { return new BranchFolder(); }
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2006-10-18 01:13:52 +08:00
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/// RemoveDeadBlock - Remove the specified dead machine basic block from the
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/// function, updating the CFG.
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2006-10-18 07:17:27 +08:00
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void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
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2006-10-18 01:13:52 +08:00
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assert(MBB->pred_empty() && "MBB must be dead!");
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2006-10-18 07:17:27 +08:00
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2006-10-18 01:13:52 +08:00
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MachineFunction *MF = MBB->getParent();
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// drop all successors.
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while (!MBB->succ_empty())
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MBB->removeSuccessor(MBB->succ_end()-1);
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2006-10-18 07:17:27 +08:00
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// If there is DWARF info to active, check to see if there are any DWARF_LABEL
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// records in the basic block. If so, unregister them from MachineDebugInfo.
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if (MDI && !MBB->empty()) {
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unsigned DWARF_LABELOpc = TII->getDWARF_LABELOpcode();
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assert(DWARF_LABELOpc &&
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"Target supports dwarf but didn't implement getDWARF_LABELOpcode!");
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for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
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I != E; ++I) {
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if ((unsigned)I->getOpcode() == DWARF_LABELOpc) {
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// The label ID # is always operand #0, an immediate.
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MDI->RemoveLabelInfo(I->getOperand(0).getImm());
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}
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}
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}
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2006-10-18 01:13:52 +08:00
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// Remove the block.
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MF->getBasicBlockList().erase(MBB);
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}
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2004-07-31 18:01:27 +08:00
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bool BranchFolder::runOnMachineFunction(MachineFunction &MF) {
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TII = MF.getTarget().getInstrInfo();
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if (!TII) return false;
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2006-10-18 07:17:27 +08:00
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MDI = getAnalysisToUpdate<MachineDebugInfo>();
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2006-10-14 08:21:48 +08:00
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2004-07-31 18:01:27 +08:00
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bool EverMadeChange = false;
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2006-10-21 08:47:49 +08:00
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bool MadeChangeThisIteration = true;
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while (MadeChangeThisIteration) {
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MadeChangeThisIteration = false;
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MadeChangeThisIteration |= TailMergeBlocks(MF);
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MadeChangeThisIteration |= OptimizeBranches(MF);
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EverMadeChange |= MadeChangeThisIteration;
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}
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return EverMadeChange;
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}
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//===----------------------------------------------------------------------===//
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// Tail Merging of Blocks
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//===----------------------------------------------------------------------===//
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/// HashMachineInstr - Compute a hash value for MI and its operands.
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static unsigned HashMachineInstr(const MachineInstr *MI) {
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unsigned Hash = MI->getOpcode();
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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const MachineOperand &Op = MI->getOperand(i);
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// Merge in bits from the operand if easy.
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unsigned OperandHash = 0;
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switch (Op.getType()) {
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case MachineOperand::MO_Register: OperandHash = Op.getReg(); break;
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case MachineOperand::MO_Immediate: OperandHash = Op.getImm(); break;
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case MachineOperand::MO_MachineBasicBlock:
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OperandHash = Op.getMachineBasicBlock()->getNumber();
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break;
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case MachineOperand::MO_FrameIndex: OperandHash = Op.getFrameIndex(); break;
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case MachineOperand::MO_ConstantPoolIndex:
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OperandHash = Op.getConstantPoolIndex();
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break;
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case MachineOperand::MO_JumpTableIndex:
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OperandHash = Op.getJumpTableIndex();
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break;
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case MachineOperand::MO_GlobalAddress:
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case MachineOperand::MO_ExternalSymbol:
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// Global address / external symbol are too hard, don't bother, but do
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// pull in the offset.
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OperandHash = Op.getOffset();
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break;
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default: break;
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}
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Hash += ((OperandHash << 3) | Op.getType()) << (i&31);
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}
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return Hash;
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}
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/// HashEndOfMBB - Hash the last two instructions in the MBB. We hash two
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/// instructions, because cross-jumping only saves code when at least two
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/// instructions are removed (since a branch must be inserted).
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static unsigned HashEndOfMBB(const MachineBasicBlock *MBB) {
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MachineBasicBlock::const_iterator I = MBB->end();
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if (I == MBB->begin())
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return 0; // Empty MBB.
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--I;
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unsigned Hash = HashMachineInstr(I);
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if (I == MBB->begin())
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return Hash; // Single instr MBB.
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--I;
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// Hash in the second-to-last instruction.
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Hash ^= HashMachineInstr(I) << 2;
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return Hash;
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}
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/// ComputeCommonTailLength - Given two machine basic blocks, compute the number
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/// of instructions they actually have in common together at their end. Return
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/// iterators for the first shared instruction in each block.
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static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
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MachineBasicBlock *MBB2,
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MachineBasicBlock::iterator &I1,
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MachineBasicBlock::iterator &I2) {
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I1 = MBB1->end();
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I2 = MBB2->end();
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unsigned TailLen = 0;
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while (I1 != MBB1->begin() && I2 != MBB2->begin()) {
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--I1; --I2;
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if (!I1->isIdenticalTo(I2)) {
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++I1; ++I2;
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break;
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}
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++TailLen;
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}
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return TailLen;
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}
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/// ReplaceTailWithBranchTo - Delete the instruction OldInst and everything
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/// after it, replacing it with an unconditional branch to NewDest.
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void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
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MachineBasicBlock *NewDest) {
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MachineBasicBlock *OldBB = OldInst->getParent();
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// Remove all the old successors of OldBB from the CFG.
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while (!OldBB->succ_empty())
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OldBB->removeSuccessor(OldBB->succ_begin());
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// Remove all the dead instructions from the end of OldBB.
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OldBB->erase(OldInst, OldBB->end());
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TII->InsertBranch(*OldBB, NewDest, 0, std::vector<MachineOperand>());
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OldBB->addSuccessor(NewDest);
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++NumTailMerge;
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}
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bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
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MadeChange = false;
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if (!EnableTailMerge)
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return false;
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// Find blocks with no successors.
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std::vector<std::pair<unsigned,MachineBasicBlock*> > MergePotentials;
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for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
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if (I->succ_empty())
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MergePotentials.push_back(std::make_pair(HashEndOfMBB(I), I));
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}
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// Sort by hash value so that blocks with identical end sequences sort
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// together.
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std::stable_sort(MergePotentials.begin(), MergePotentials.end());
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// Walk through equivalence sets looking for actual exact matches.
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while (MergePotentials.size() > 1) {
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unsigned CurHash = (MergePotentials.end()-1)->first;
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unsigned PrevHash = (MergePotentials.end()-2)->first;
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MachineBasicBlock *CurMBB = (MergePotentials.end()-1)->second;
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// If there is nothing that matches the hash of the current basic block,
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// give up.
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if (CurHash != PrevHash) {
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MergePotentials.pop_back();
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continue;
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}
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2006-10-14 08:21:48 +08:00
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2006-10-21 08:47:49 +08:00
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// Determine the actual length of the shared tail between these two basic
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// blocks. Because the hash can have collisions, it's possible that this is
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// less than 2.
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MachineBasicBlock::iterator BBI1, BBI2;
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unsigned CommonTailLen =
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ComputeCommonTailLength(CurMBB, (MergePotentials.end()-2)->second,
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BBI1, BBI2);
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// If the tails don't have at least two instructions in common, see if there
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// is anything else in the equivalence class that does match.
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if (CommonTailLen < 2) {
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unsigned FoundMatch = ~0U;
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for (int i = MergePotentials.size()-2;
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i != -1 && MergePotentials[i].first == CurHash; --i) {
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CommonTailLen = ComputeCommonTailLength(CurMBB,
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MergePotentials[i].second,
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BBI1, BBI2);
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if (CommonTailLen >= 2) {
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FoundMatch = i;
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break;
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}
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}
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2006-10-18 01:13:52 +08:00
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2006-10-21 08:47:49 +08:00
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// If we didn't find anything that has at least two instructions matching
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// this one, bail out.
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if (FoundMatch == ~0U) {
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MergePotentials.pop_back();
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continue;
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2004-07-31 18:01:27 +08:00
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}
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2006-10-21 08:47:49 +08:00
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// Otherwise, move the matching block to the right position.
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std::swap(MergePotentials[FoundMatch], *(MergePotentials.end()-2));
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}
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// If either block is the entire common tail, make the longer one branch to
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// the shorter one.
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MachineBasicBlock *MBB2 = (MergePotentials.end()-2)->second;
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if (CurMBB->begin() == BBI1) {
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// Hack the end off MBB2, making it jump to CurMBB instead.
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ReplaceTailWithBranchTo(BBI2, CurMBB);
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// This modifies MBB2, so remove it from the worklist.
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MergePotentials.erase(MergePotentials.end()-2);
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MadeChange = true;
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continue;
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} else if (MBB2->begin() == BBI2) {
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// Hack the end off CurMBB, making it jump to MBBI@ instead.
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ReplaceTailWithBranchTo(BBI1, MBB2);
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// This modifies CurMBB, so remove it from the worklist.
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MergePotentials.pop_back();
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MadeChange = true;
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continue;
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}
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MergePotentials.pop_back();
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2004-07-31 18:01:27 +08:00
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}
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2006-10-21 08:47:49 +08:00
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return MadeChange;
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}
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2004-07-31 18:01:27 +08:00
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2006-10-21 08:47:49 +08:00
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//===----------------------------------------------------------------------===//
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// Branch Optimization
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//===----------------------------------------------------------------------===//
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bool BranchFolder::OptimizeBranches(MachineFunction &MF) {
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MadeChange = false;
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for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) {
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MachineBasicBlock *MBB = I++;
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OptimizeBlock(MBB);
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// If it is dead, remove it.
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if (MBB->pred_empty()) {
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RemoveDeadBlock(MBB);
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MadeChange = true;
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++NumDeadBlocks;
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}
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}
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return MadeChange;
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2004-07-31 18:01:27 +08:00
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}
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2006-10-21 08:47:49 +08:00
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2004-07-31 18:01:27 +08:00
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/// ReplaceUsesOfBlockWith - Given a machine basic block 'BB' that branched to
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/// 'Old', change the code and CFG so that it branches to 'New' instead.
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static void ReplaceUsesOfBlockWith(MachineBasicBlock *BB,
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MachineBasicBlock *Old,
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MachineBasicBlock *New,
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2006-10-14 08:21:48 +08:00
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const TargetInstrInfo *TII) {
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2004-07-31 18:01:27 +08:00
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assert(Old != New && "Cannot replace self with self!");
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MachineBasicBlock::iterator I = BB->end();
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while (I != BB->begin()) {
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--I;
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2006-10-14 08:21:48 +08:00
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if (!TII->isTerminatorInstr(I->getOpcode())) break;
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2004-07-31 18:01:27 +08:00
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// Scan the operands of this machine instruction, replacing any uses of Old
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// with New.
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|
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);
|
|
|
|
}
|
|
|
|
|
2006-10-14 04:43:10 +08:00
|
|
|
// Update the successor information.
|
2004-07-31 18:01:27 +08:00
|
|
|
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);
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
2006-10-14 08:21:48 +08:00
|
|
|
/// OptimizeBlock - Analyze and optimize control flow related to the specified
|
|
|
|
/// block. This is never called on the entry block.
|
|
|
|
void BranchFolder::OptimizeBlock(MachineFunction::iterator MBB) {
|
2006-10-14 04:43:10 +08:00
|
|
|
// If this block is empty, make everyone use its fall-through, not the block
|
2004-07-31 18:01:27 +08:00
|
|
|
// explicitly.
|
|
|
|
if (MBB->empty()) {
|
2006-10-14 08:21:48 +08:00
|
|
|
if (MBB->pred_empty()) return; // dead block? Leave for cleanup later.
|
|
|
|
|
|
|
|
MachineFunction::iterator FallThrough = next(MBB);
|
|
|
|
|
2006-10-18 01:13:52 +08:00
|
|
|
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.
|
2006-10-14 08:21:48 +08:00
|
|
|
while (!MBB->pred_empty()) {
|
|
|
|
MachineBasicBlock *Pred = *(MBB->pred_end()-1);
|
|
|
|
ReplaceUsesOfBlockWith(Pred, MBB, FallThrough, TII);
|
|
|
|
}
|
2006-10-18 01:13:52 +08:00
|
|
|
|
|
|
|
// If MBB was the target of a jump table, update jump tables to go to the
|
|
|
|
// fallthrough instead.
|
|
|
|
MBB->getParent()->getJumpTableInfo()->ReplaceMBBInJumpTables(MBB,
|
|
|
|
FallThrough);
|
2006-10-14 08:21:48 +08:00
|
|
|
MadeChange = true;
|
2004-07-31 18:01:27 +08:00
|
|
|
}
|
2006-10-14 08:21:48 +08:00
|
|
|
return;
|
2004-07-31 18:01:27 +08:00
|
|
|
}
|
|
|
|
|
2006-10-14 08:21:48 +08:00
|
|
|
// Check to see if we can simplify the terminator of the block before this
|
|
|
|
// one.
|
Enable deleting branches to successor blocks. With the previous patches,
branch folding can now compile stuff like this:
void foo(int W, int X, int Y, int Z) {
if (W & 1) {
for (; X;--X) bar();
} else if (W & 2) {
for (; Y;--Y) bar();
} else if (W & 4) {
for (; Z;--Z) bar();
} else if (W & 8) {
for (; W;--W) bar();
}
if (W) {
bar();
}
}
contrived testcase where loops exits all end up merging together. To have
the loop merges be:
...
cmplw cr0, r30, r27
bne cr0, LBB1_14 ;bb38
LBB1_16: ;cond_next48.loopexit
mr r27, r29
LBB1_20: ;cond_next48
cmplwi cr0, r27, 0
beq cr0, LBB1_22 ;UnifiedReturnBlock
...
instead of:
...
cmplw cr0, r30, r27
bne cr0, LBB1_14 ;bb38
LBB1_16: ;cond_next48.loopexit
mr r27, r29
b LBB1_20 ;cond_next48
LBB1_17: ;cond_next48.loopexit1
b LBB1_20 ;cond_next48
LBB1_18: ;cond_next48.loopexit2
b LBB1_20 ;cond_next48
LBB1_19: ;cond_next48.loopexit3
LBB1_20: ;cond_next48
cmplwi cr0, r27, 0
beq cr0, LBB1_22 ;UnifiedReturnBlock
...
This is CodeGen/PowerPC/branch-opt.ll
llvm-svn: 31006
2006-10-18 02:16:40 +08:00
|
|
|
MachineBasicBlock &PrevBB = *prior(MBB);
|
|
|
|
|
2006-10-14 08:21:48 +08:00
|
|
|
MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
|
|
|
|
std::vector<MachineOperand> PriorCond;
|
Enable deleting branches to successor blocks. With the previous patches,
branch folding can now compile stuff like this:
void foo(int W, int X, int Y, int Z) {
if (W & 1) {
for (; X;--X) bar();
} else if (W & 2) {
for (; Y;--Y) bar();
} else if (W & 4) {
for (; Z;--Z) bar();
} else if (W & 8) {
for (; W;--W) bar();
}
if (W) {
bar();
}
}
contrived testcase where loops exits all end up merging together. To have
the loop merges be:
...
cmplw cr0, r30, r27
bne cr0, LBB1_14 ;bb38
LBB1_16: ;cond_next48.loopexit
mr r27, r29
LBB1_20: ;cond_next48
cmplwi cr0, r27, 0
beq cr0, LBB1_22 ;UnifiedReturnBlock
...
instead of:
...
cmplw cr0, r30, r27
bne cr0, LBB1_14 ;bb38
LBB1_16: ;cond_next48.loopexit
mr r27, r29
b LBB1_20 ;cond_next48
LBB1_17: ;cond_next48.loopexit1
b LBB1_20 ;cond_next48
LBB1_18: ;cond_next48.loopexit2
b LBB1_20 ;cond_next48
LBB1_19: ;cond_next48.loopexit3
LBB1_20: ;cond_next48
cmplwi cr0, r27, 0
beq cr0, LBB1_22 ;UnifiedReturnBlock
...
This is CodeGen/PowerPC/branch-opt.ll
llvm-svn: 31006
2006-10-18 02:16:40 +08:00
|
|
|
if (!TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond)) {
|
2006-10-14 08:21:48 +08:00
|
|
|
// If the previous branch is conditional and both conditions go to the same
|
|
|
|
// destination, remove the branch, replacing it with an unconditional one.
|
|
|
|
if (PriorTBB && PriorTBB == PriorFBB) {
|
|
|
|
TII->RemoveBranch(*prior(MBB));
|
|
|
|
PriorCond.clear();
|
|
|
|
if (PriorTBB != &*MBB)
|
|
|
|
TII->InsertBranch(*prior(MBB), PriorTBB, 0, PriorCond);
|
|
|
|
MadeChange = true;
|
2006-10-21 08:47:49 +08:00
|
|
|
++NumBranchOpts;
|
2006-10-14 08:21:48 +08:00
|
|
|
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(*prior(MBB));
|
|
|
|
MadeChange = true;
|
2006-10-21 08:47:49 +08:00
|
|
|
++NumBranchOpts;
|
2006-10-14 08:21:48 +08:00
|
|
|
return OptimizeBlock(MBB);
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
2006-10-14 04:43:10 +08:00
|
|
|
#if 0
|
|
|
|
|
|
|
|
if (MBB->pred_size() == 1) {
|
|
|
|
// If this block has a single predecessor, and if that block has a single
|
|
|
|
// successor, merge this block into that block.
|
|
|
|
MachineBasicBlock *Pred = *MBB->pred_begin();
|
|
|
|
if (Pred->succ_size() == 1) {
|
|
|
|
// Delete all of the terminators from end of the pred block. NOTE, this
|
|
|
|
// assumes that terminators do not have side effects!
|
|
|
|
// FIXME: This doesn't work for FP_REG_KILL.
|
|
|
|
|
|
|
|
while (!Pred->empty() && TII.isTerminatorInstr(Pred->back().getOpcode()))
|
|
|
|
Pred->pop_back();
|
|
|
|
|
|
|
|
// Splice the instructions over.
|
|
|
|
Pred->splice(Pred->end(), MBB, MBB->begin(), MBB->end());
|
|
|
|
|
|
|
|
// If MBB does not end with a barrier, add a goto instruction to the end.
|
|
|
|
if (Pred->empty() || !TII.isBarrier(Pred->back().getOpcode()))
|
|
|
|
TII.insertGoto(*Pred, *next(MBB));
|
|
|
|
|
|
|
|
// Update the CFG now.
|
|
|
|
Pred->removeSuccessor(Pred->succ_begin());
|
|
|
|
while (!MBB->succ_empty()) {
|
|
|
|
Pred->addSuccessor(*(MBB->succ_end()-1));
|
|
|
|
MBB->removeSuccessor(MBB->succ_end()-1);
|
|
|
|
}
|
|
|
|
return true;
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
// If BB falls through into Old, insert an unconditional branch to New.
|
|
|
|
MachineFunction::iterator BBSucc = BB; ++BBSucc;
|
|
|
|
if (BBSucc != BB->getParent()->end() && &*BBSucc == Old)
|
|
|
|
TII.insertGoto(*BB, *New);
|
|
|
|
|
|
|
|
|
2004-07-31 18:01:27 +08:00
|
|
|
if (MBB->pred_size() == 1) {
|
|
|
|
// If this block has a single predecessor, and if that block has a single
|
|
|
|
// successor, merge this block into that block.
|
|
|
|
MachineBasicBlock *Pred = *MBB->pred_begin();
|
|
|
|
if (Pred->succ_size() == 1) {
|
|
|
|
// Delete all of the terminators from end of the pred block. NOTE, this
|
|
|
|
// assumes that terminators do not have side effects!
|
2006-10-14 04:43:10 +08:00
|
|
|
// FIXME: This doesn't work for FP_REG_KILL.
|
|
|
|
|
2004-07-31 18:01:27 +08:00
|
|
|
while (!Pred->empty() && TII.isTerminatorInstr(Pred->back().getOpcode()))
|
|
|
|
Pred->pop_back();
|
|
|
|
|
|
|
|
// Splice the instructions over.
|
|
|
|
Pred->splice(Pred->end(), MBB, MBB->begin(), MBB->end());
|
|
|
|
|
|
|
|
// If MBB does not end with a barrier, add a goto instruction to the end.
|
|
|
|
if (Pred->empty() || !TII.isBarrier(Pred->back().getOpcode()))
|
2004-07-31 23:14:29 +08:00
|
|
|
TII.insertGoto(*Pred, *next(MBB));
|
2004-07-31 18:01:27 +08:00
|
|
|
|
|
|
|
// Update the CFG now.
|
|
|
|
Pred->removeSuccessor(Pred->succ_begin());
|
|
|
|
while (!MBB->succ_empty()) {
|
|
|
|
Pred->addSuccessor(*(MBB->succ_end()-1));
|
|
|
|
MBB->removeSuccessor(MBB->succ_end()-1);
|
|
|
|
}
|
|
|
|
return true;
|
|
|
|
}
|
|
|
|
}
|
|
|
|
|
|
|
|
// If the first instruction in this block is an unconditional branch, and if
|
|
|
|
// there are predecessors, fold the branch into the predecessors.
|
|
|
|
if (!MBB->pred_empty() && isUncondBranch(MBB->begin(), TII)) {
|
|
|
|
MachineInstr *Br = MBB->begin();
|
|
|
|
assert(Br->getNumOperands() == 1 && Br->getOperand(0).isMachineBasicBlock()
|
|
|
|
&& "Uncond branch should take one MBB argument!");
|
|
|
|
MachineBasicBlock *Dest = Br->getOperand(0).getMachineBasicBlock();
|
2005-04-22 06:36:52 +08:00
|
|
|
|
2004-07-31 18:01:27 +08:00
|
|
|
while (!MBB->pred_empty()) {
|
|
|
|
MachineBasicBlock *Pred = *(MBB->pred_end()-1);
|
|
|
|
ReplaceUsesOfBlockWith(Pred, MBB, Dest, TII);
|
|
|
|
}
|
|
|
|
return true;
|
|
|
|
}
|
|
|
|
|
|
|
|
// If the last instruction is an unconditional branch and the fall through
|
|
|
|
// block is the destination, just delete the branch.
|
|
|
|
if (isUncondBranch(--MBB->end(), TII)) {
|
|
|
|
MachineBasicBlock::iterator MI = --MBB->end();
|
|
|
|
MachineInstr *UncondBr = MI;
|
2004-07-31 23:14:29 +08:00
|
|
|
MachineFunction::iterator FallThrough = next(MBB);
|
2004-07-31 18:01:27 +08:00
|
|
|
|
2004-07-31 23:03:52 +08:00
|
|
|
MachineFunction::iterator UncondDest =
|
|
|
|
MI->getOperand(0).getMachineBasicBlock();
|
|
|
|
if (UncondDest == FallThrough) {
|
2004-07-31 18:01:27 +08:00
|
|
|
// Just delete the branch. This does not effect the CFG.
|
|
|
|
MBB->erase(UncondBr);
|
|
|
|
return true;
|
|
|
|
}
|
|
|
|
|
|
|
|
// Okay, so we don't have a fall-through. Check to see if we have an
|
|
|
|
// conditional branch that would be a fall through if we reversed it. If
|
|
|
|
// so, invert the condition and delete the uncond branch.
|
|
|
|
if (MI != MBB->begin() && isCondBranch(--MI, TII)) {
|
|
|
|
// We assume that conditional branches always have the branch dest as the
|
|
|
|
// last operand. This could be generalized in the future if needed.
|
|
|
|
unsigned LastOpnd = MI->getNumOperands()-1;
|
2004-07-31 23:14:29 +08:00
|
|
|
if (MachineFunction::iterator(
|
|
|
|
MI->getOperand(LastOpnd).getMachineBasicBlock()) == FallThrough) {
|
2004-07-31 18:01:27 +08:00
|
|
|
// Change the cond branch to go to the uncond dest, nuke the uncond,
|
|
|
|
// then reverse the condition.
|
|
|
|
MI->getOperand(LastOpnd).setMachineBasicBlock(UncondDest);
|
|
|
|
MBB->erase(UncondBr);
|
|
|
|
TII.reverseBranchCondition(MI);
|
|
|
|
return true;
|
|
|
|
}
|
|
|
|
}
|
|
|
|
}
|
2006-10-14 04:43:10 +08:00
|
|
|
#endif
|
2004-07-31 18:01:27 +08:00
|
|
|
}
|