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109 lines
3.5 KiB
C++
109 lines
3.5 KiB
C++
//===--------- BreakCriticalMachineEdge.h - Break critical edges ---------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===---------------------------------------------------------------------===//
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//
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// Helper function to break a critical machine edge.
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//
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//===---------------------------------------------------------------------===//
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#ifndef LLVM_CODEGEN_BREAKCRITICALMACHINEEDGE_H
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#define LLVM_CODEGEN_BREAKCRITICALMACHINEEDGE_H
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#include "llvm/CodeGen/MachineJumpTableInfo.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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namespace llvm {
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MachineBasicBlock* SplitCriticalMachineEdge(MachineBasicBlock* src,
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MachineBasicBlock* dst) {
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MachineFunction &MF = *src->getParent();
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const BasicBlock* srcBB = src->getBasicBlock();
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MachineBasicBlock* crit_mbb = MF.CreateMachineBasicBlock(srcBB);
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// modify the llvm control flow graph
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src->removeSuccessor(dst);
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src->addSuccessor(crit_mbb);
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crit_mbb->addSuccessor(dst);
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// insert the new block into the machine function.
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MF.push_back(crit_mbb);
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// insert a unconditional branch linking the new block to dst
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const TargetMachine& TM = MF.getTarget();
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const TargetInstrInfo* TII = TM.getInstrInfo();
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std::vector<MachineOperand> emptyConditions;
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TII->InsertBranch(*crit_mbb, dst, (MachineBasicBlock*)0,
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emptyConditions);
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// modify every branch in src that points to dst to point to the new
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// machine basic block instead:
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MachineBasicBlock::iterator mii = src->end();
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bool found_branch = false;
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while (mii != src->begin()) {
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mii--;
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// if there are no more branches, finish the loop
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if (!mii->getDesc().isTerminator()) {
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break;
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}
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// Scan the operands of this branch, replacing any uses of dst with
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// crit_mbb.
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for (unsigned i = 0, e = mii->getNumOperands(); i != e; ++i) {
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MachineOperand & mo = mii->getOperand(i);
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if (mo.isMBB() && mo.getMBB() == dst) {
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found_branch = true;
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mo.setMBB(crit_mbb);
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}
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}
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}
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// TODO: This is tentative. It may be necessary to fix this code. Maybe
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// I am inserting too many gotos, but I am trusting that the asm printer
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// will optimize the unnecessary gotos.
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if(!found_branch) {
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TII->InsertBranch(*src, crit_mbb, (MachineBasicBlock*)0,
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emptyConditions);
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}
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/// Change all the phi functions in dst, so that the incoming block be
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/// crit_mbb, instead of src
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for(mii = dst->begin(); mii != dst->end(); mii++) {
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/// the first instructions are always phi functions.
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if(mii->getOpcode() != TargetInstrInfo::PHI)
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break;
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// Find the operands corresponding to the source block
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std::vector<unsigned> toRemove;
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unsigned reg = 0;
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for (unsigned u = 0; u != mii->getNumOperands(); ++u)
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if (mii->getOperand(u).isMBB() &&
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mii->getOperand(u).getMBB() == src) {
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reg = mii->getOperand(u-1).getReg();
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toRemove.push_back(u-1);
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}
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// Remove all uses of this MBB
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for (std::vector<unsigned>::reverse_iterator I = toRemove.rbegin(),
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E = toRemove.rend(); I != E; ++I) {
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mii->RemoveOperand(*I+1);
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mii->RemoveOperand(*I);
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}
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// Add a single use corresponding to the new MBB
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mii->addOperand(MachineOperand::CreateReg(reg, false));
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mii->addOperand(MachineOperand::CreateMBB(crit_mbb));
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}
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return crit_mbb;
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}
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}
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#endif
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