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//===-- TwoAddressInstructionPass.cpp - Two-Address instruction pass ------===//
//
// 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 file implements the TwoAddress instruction pass which is used
// by most register allocators. Two-Address instructions are rewritten
// from:
//
// A = B op C
//
// to:
//
// A = B
// A op= C
//
// Note that if a register allocator chooses to use this pass, that it
// has to be capable of handling the non-SSA nature of these rewritten
// virtual registers.
//
// It is also worth noting that the duplicate operand of the two
// address instruction is removed.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "twoaddrinstr"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Function.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <iostream>
using namespace llvm;
namespace {
Statistic<> NumTwoAddressInstrs("twoaddressinstruction",
"Number of two-address instructions");
Statistic<> NumCommuted("twoaddressinstruction",
"Number of instructions commuted to coalesce");
Statistic<> NumConvertedTo3Addr("twoaddressinstruction",
"Number of instructions promoted to 3-address");
struct TwoAddressInstructionPass : public MachineFunctionPass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
/// runOnMachineFunction - pass entry point
bool runOnMachineFunction(MachineFunction&);
};
RegisterPass<TwoAddressInstructionPass>
X("twoaddressinstruction", "Two-Address instruction pass");
}
const PassInfo *llvm::TwoAddressInstructionPassID = X.getPassInfo();
void TwoAddressInstructionPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LiveVariables>();
AU.addPreserved<LiveVariables>();
AU.addPreservedID(PHIEliminationID);
MachineFunctionPass::getAnalysisUsage(AU);
}
/// runOnMachineFunction - Reduce two-address instructions to two
/// operands.
///
bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
DEBUG(std::cerr << "Machine Function\n");
const TargetMachine &TM = MF.getTarget();
const MRegisterInfo &MRI = *TM.getRegisterInfo();
const TargetInstrInfo &TII = *TM.getInstrInfo();
LiveVariables &LV = getAnalysis<LiveVariables>();
bool MadeChange = false;
DEBUG(std::cerr << "********** REWRITING TWO-ADDR INSTRS **********\n");
DEBUG(std::cerr << "********** Function: "
<< MF.getFunction()->getName() << '\n');
for (MachineFunction::iterator mbbi = MF.begin(), mbbe = MF.end();
mbbi != mbbe; ++mbbi) {
for (MachineBasicBlock::iterator mi = mbbi->begin(), me = mbbi->end();
mi != me; ++mi) {
unsigned opcode = mi->getOpcode();
// ignore if it is not a two-address instruction
if (!TII.isTwoAddrInstr(opcode))
continue;
++NumTwoAddressInstrs;
DEBUG(std::cerr << '\t'; mi->print(std::cerr, &TM));
assert(mi->getOperand(1).isRegister() && mi->getOperand(1).getReg() &&
mi->getOperand(1).isUse() && "two address instruction invalid");
// if the two operands are the same we just remove the use
// and mark the def as def&use, otherwise we have to insert a copy.
if (mi->getOperand(0).getReg() != mi->getOperand(1).getReg()) {
// rewrite:
// a = b op c
// to:
// a = b
// a = a op c
unsigned regA = mi->getOperand(0).getReg();
unsigned regB = mi->getOperand(1).getReg();
assert(MRegisterInfo::isVirtualRegister(regA) &&
MRegisterInfo::isVirtualRegister(regB) &&
"cannot update physical register live information");
#ifndef NDEBUG
// First, verify that we do not have a use of a in the instruction (a =
// b + a for example) because our transformation will not work. This
// should never occur because we are in SSA form.
for (unsigned i = 1; i != mi->getNumOperands(); ++i)
assert(!mi->getOperand(i).isRegister() ||
mi->getOperand(i).getReg() != regA);
#endif
// If this instruction is not the killing user of B, see if we can
// rearrange the code to make it so. Making it the killing user will
// allow us to coalesce A and B together, eliminating the copy we are
// about to insert.
if (!LV.KillsRegister(mi, regB)) {
const TargetInstrDescriptor &TID = TII.get(opcode);
// If this instruction is commutative, check to see if C dies. If so,
// swap the B and C operands. This makes the live ranges of A and C
// joinable.
if (TID.Flags & M_COMMUTABLE) {
assert(mi->getOperand(2).isRegister() &&
"Not a proper commutative instruction!");
unsigned regC = mi->getOperand(2).getReg();
if (LV.KillsRegister(mi, regC)) {
DEBUG(std::cerr << "2addr: COMMUTING : " << *mi);
MachineInstr *NewMI = TII.commuteInstruction(mi);
if (NewMI == 0) {
DEBUG(std::cerr << "2addr: COMMUTING FAILED!\n");
} else {
DEBUG(std::cerr << "2addr: COMMUTED TO: " << *NewMI);
// If the instruction changed to commute it, update livevar.
if (NewMI != mi) {
LV.instructionChanged(mi, NewMI); // Update live variables
mbbi->insert(mi, NewMI); // Insert the new inst
mbbi->erase(mi); // Nuke the old inst.
mi = NewMI;
}
++NumCommuted;
regB = regC;
goto InstructionRearranged;
}
}
}
// If this instruction is potentially convertible to a true
// three-address instruction,
if (TID.Flags & M_CONVERTIBLE_TO_3_ADDR)
if (MachineInstr *New = TII.convertToThreeAddress(mi)) {
DEBUG(std::cerr << "2addr: CONVERTING 2-ADDR: " << *mi);
DEBUG(std::cerr << "2addr: TO 3-ADDR: " << *New);
LV.instructionChanged(mi, New); // Update live variables
mbbi->insert(mi, New); // Insert the new inst
mbbi->erase(mi); // Nuke the old inst.
mi = New;
++NumConvertedTo3Addr;
assert(!TII.isTwoAddrInstr(New->getOpcode()) &&
"convertToThreeAddress returned a 2-addr instruction??");
// Done with this instruction.
continue;
}
}
InstructionRearranged:
const TargetRegisterClass* rc = MF.getSSARegMap()->getRegClass(regA);
MRI.copyRegToReg(*mbbi, mi, regA, regB, rc);
MachineBasicBlock::iterator prevMi = prior(mi);
DEBUG(std::cerr << "\t\tprepend:\t"; prevMi->print(std::cerr, &TM));
// Update live variables for regA
LiveVariables::VarInfo& varInfo = LV.getVarInfo(regA);
varInfo.DefInst = prevMi;
// update live variables for regB
if (LV.removeVirtualRegisterKilled(regB, mbbi, mi))
LV.addVirtualRegisterKilled(regB, prevMi);
if (LV.removeVirtualRegisterDead(regB, mbbi, mi))
LV.addVirtualRegisterDead(regB, prevMi);
// replace all occurences of regB with regA
for (unsigned i = 1, e = mi->getNumOperands(); i != e; ++i) {
if (mi->getOperand(i).isRegister() &&
mi->getOperand(i).getReg() == regB)
mi->getOperand(i).setReg(regA);
}
}
assert(mi->getOperand(0).isDef());
mi->getOperand(0).setUse();
mi->RemoveOperand(1);
MadeChange = true;
DEBUG(std::cerr << "\t\trewrite to:\t"; mi->print(std::cerr, &TM));
}
}
return MadeChange;
}
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