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llvm-project/llvm/lib/CodeGen/ProcessImplicitDefs.cpp

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//===---------------------- ProcessImplicitDefs.cpp -----------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "processimplicitdefs"
#include "llvm/CodeGen/ProcessImplicitDefs.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
using namespace llvm;
char ProcessImplicitDefs::ID = 0;
static RegisterPass<ProcessImplicitDefs> X("processimpdefs",
"Process Implicit Definitions.");
void ProcessImplicitDefs::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addPreserved<AliasAnalysis>();
AU.addPreserved<LiveVariables>();
AU.addRequired<LiveVariables>();
AU.addPreservedID(MachineLoopInfoID);
AU.addPreservedID(MachineDominatorsID);
AU.addPreservedID(TwoAddressInstructionPassID);
AU.addPreservedID(PHIEliminationID);
MachineFunctionPass::getAnalysisUsage(AU);
}
bool ProcessImplicitDefs::CanTurnIntoImplicitDef(MachineInstr *MI,
unsigned Reg, unsigned OpIdx,
const TargetInstrInfo *tii_) {
unsigned SrcReg, DstReg, SrcSubReg, DstSubReg;
if (tii_->isMoveInstr(*MI, SrcReg, DstReg, SrcSubReg, DstSubReg) &&
Reg == SrcReg && SrcSubReg == 0 && DstSubReg == 0)
return true;
if (OpIdx == 2 && MI->isSubregToReg())
return true;
if (OpIdx == 1 && MI->isExtractSubreg())
return true;
return false;
}
/// processImplicitDefs - Process IMPLICIT_DEF instructions and make sure
/// there is one implicit_def for each use. Add isUndef marker to
/// implicit_def defs and their uses.
bool ProcessImplicitDefs::runOnMachineFunction(MachineFunction &fn) {
DEBUG(dbgs() << "********** PROCESS IMPLICIT DEFS **********\n"
<< "********** Function: "
<< ((Value*)fn.getFunction())->getName() << '\n');
bool Changed = false;
const TargetInstrInfo *tii_ = fn.getTarget().getInstrInfo();
const TargetRegisterInfo *tri_ = fn.getTarget().getRegisterInfo();
MachineRegisterInfo *mri_ = &fn.getRegInfo();
LiveVariables *lv_ = &getAnalysis<LiveVariables>();
SmallSet<unsigned, 8> ImpDefRegs;
SmallVector<MachineInstr*, 8> ImpDefMIs;
SmallVector<MachineInstr*, 4> RUses;
SmallPtrSet<MachineBasicBlock*,16> Visited;
SmallPtrSet<MachineInstr*, 8> ModInsts;
MachineBasicBlock *Entry = fn.begin();
for (df_ext_iterator<MachineBasicBlock*, SmallPtrSet<MachineBasicBlock*,16> >
DFI = df_ext_begin(Entry, Visited), E = df_ext_end(Entry, Visited);
DFI != E; ++DFI) {
MachineBasicBlock *MBB = *DFI;
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
I != E; ) {
MachineInstr *MI = &*I;
++I;
if (MI->isImplicitDef()) {
if (MI->getOperand(0).getSubReg())
continue;
unsigned Reg = MI->getOperand(0).getReg();
ImpDefRegs.insert(Reg);
if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
for (const unsigned *SS = tri_->getSubRegisters(Reg); *SS; ++SS)
ImpDefRegs.insert(*SS);
}
ImpDefMIs.push_back(MI);
continue;
}
if (MI->isInsertSubreg()) {
MachineOperand &MO = MI->getOperand(2);
if (ImpDefRegs.count(MO.getReg())) {
// %reg1032<def> = INSERT_SUBREG %reg1032, undef, 2
// This is an identity copy, eliminate it now.
if (MO.isKill()) {
LiveVariables::VarInfo& vi = lv_->getVarInfo(MO.getReg());
vi.removeKill(MI);
}
MI->eraseFromParent();
Changed = true;
continue;
}
}
bool ChangedToImpDef = false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand& MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isUse() || MO.isUndef())
continue;
unsigned Reg = MO.getReg();
if (!Reg)
continue;
if (!ImpDefRegs.count(Reg))
continue;
// Use is a copy, just turn it into an implicit_def.
if (CanTurnIntoImplicitDef(MI, Reg, i, tii_)) {
bool isKill = MO.isKill();
MI->setDesc(tii_->get(TargetOpcode::IMPLICIT_DEF));
for (int j = MI->getNumOperands() - 1, ee = 0; j > ee; --j)
MI->RemoveOperand(j);
if (isKill) {
ImpDefRegs.erase(Reg);
LiveVariables::VarInfo& vi = lv_->getVarInfo(Reg);
vi.removeKill(MI);
}
ChangedToImpDef = true;
Changed = true;
break;
}
Changed = true;
MO.setIsUndef();
if (MO.isKill() || MI->isRegTiedToDefOperand(i)) {
// Make sure other uses of
for (unsigned j = i+1; j != e; ++j) {
MachineOperand &MOJ = MI->getOperand(j);
if (MOJ.isReg() && MOJ.isUse() && MOJ.getReg() == Reg)
MOJ.setIsUndef();
}
ImpDefRegs.erase(Reg);
}
}
if (ChangedToImpDef) {
// Backtrack to process this new implicit_def.
--I;
} else {
for (unsigned i = 0; i != MI->getNumOperands(); ++i) {
MachineOperand& MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
ImpDefRegs.erase(MO.getReg());
}
}
}
// Any outstanding liveout implicit_def's?
for (unsigned i = 0, e = ImpDefMIs.size(); i != e; ++i) {
MachineInstr *MI = ImpDefMIs[i];
unsigned Reg = MI->getOperand(0).getReg();
if (TargetRegisterInfo::isPhysicalRegister(Reg) ||
!ImpDefRegs.count(Reg)) {
// Delete all "local" implicit_def's. That include those which define
// physical registers since they cannot be liveout.
MI->eraseFromParent();
Changed = true;
continue;
}
// If there are multiple defs of the same register and at least one
// is not an implicit_def, do not insert implicit_def's before the
// uses.
bool Skip = false;
SmallVector<MachineInstr*, 4> DeadImpDefs;
for (MachineRegisterInfo::def_iterator DI = mri_->def_begin(Reg),
DE = mri_->def_end(); DI != DE; ++DI) {
MachineInstr *DeadImpDef = &*DI;
if (!DeadImpDef->isImplicitDef()) {
Skip = true;
break;
}
DeadImpDefs.push_back(DeadImpDef);
}
if (Skip)
continue;
// The only implicit_def which we want to keep are those that are live
// out of its block.
for (unsigned j = 0, ee = DeadImpDefs.size(); j != ee; ++j)
DeadImpDefs[j]->eraseFromParent();
Changed = true;
// Process each use instruction once.
for (MachineRegisterInfo::use_iterator UI = mri_->use_begin(Reg),
UE = mri_->use_end(); UI != UE; ++UI) {
if (UI.getOperand().isUndef())
continue;
MachineInstr *RMI = &*UI;
if (ModInsts.insert(RMI))
RUses.push_back(RMI);
}
for (unsigned i = 0, e = RUses.size(); i != e; ++i) {
MachineInstr *RMI = RUses[i];
// Turn a copy use into an implicit_def.
unsigned SrcReg, DstReg, SrcSubReg, DstSubReg;
if (tii_->isMoveInstr(*RMI, SrcReg, DstReg, SrcSubReg, DstSubReg) &&
Reg == SrcReg && SrcSubReg == 0 && DstSubReg == 0) {
RMI->setDesc(tii_->get(TargetOpcode::IMPLICIT_DEF));
bool isKill = false;
SmallVector<unsigned, 4> Ops;
for (unsigned j = 0, ee = RMI->getNumOperands(); j != ee; ++j) {
MachineOperand &RRMO = RMI->getOperand(j);
if (RRMO.isReg() && RRMO.getReg() == Reg) {
Ops.push_back(j);
if (RRMO.isKill())
isKill = true;
}
}
// Leave the other operands along.
for (unsigned j = 0, ee = Ops.size(); j != ee; ++j) {
unsigned OpIdx = Ops[j];
RMI->RemoveOperand(OpIdx-j);
}
// Update LiveVariables varinfo if the instruction is a kill.
if (isKill) {
LiveVariables::VarInfo& vi = lv_->getVarInfo(Reg);
vi.removeKill(RMI);
}
continue;
}
// Replace Reg with a new vreg that's marked implicit.
const TargetRegisterClass* RC = mri_->getRegClass(Reg);
unsigned NewVReg = mri_->createVirtualRegister(RC);
bool isKill = true;
for (unsigned j = 0, ee = RMI->getNumOperands(); j != ee; ++j) {
MachineOperand &RRMO = RMI->getOperand(j);
if (RRMO.isReg() && RRMO.getReg() == Reg) {
RRMO.setReg(NewVReg);
RRMO.setIsUndef();
if (isKill) {
// Only the first operand of NewVReg is marked kill.
RRMO.setIsKill();
isKill = false;
}
}
}
}
RUses.clear();
ModInsts.clear();
}
ImpDefRegs.clear();
ImpDefMIs.clear();
}
return Changed;
}
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