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//===-- RegUsageInfoCollector.cpp - Register Usage Information Collector --===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
/// This pass is required to take advantage of the interprocedural register
/// allocation infrastructure.
/// This pass is simple MachineFunction pass which collects register usage
/// details by iterating through each physical registers and checking
/// MRI::isPhysRegUsed() then creates a RegMask based on this details.
/// The pass then stores this RegMask in PhysicalRegisterUsageInfo.cpp
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegisterUsageInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/CodeGen/TargetFrameLowering.h"
using namespace llvm;
#define DEBUG_TYPE "ip-regalloc"
"Number of functions optimized for callee saved registers");
namespace {
class RegUsageInfoCollector : public MachineFunctionPass {
RegUsageInfoCollector() : MachineFunctionPass(ID) {
PassRegistry &Registry = *PassRegistry::getPassRegistry();
StringRef getPassName() const override {
return "Register Usage Information Collector Pass";
void getAnalysisUsage(AnalysisUsage &AU) const override {
bool runOnMachineFunction(MachineFunction &MF) override;
// Call determineCalleeSaves and then also set the bits for subregs and
// fully saved superregs.
static void computeCalleeSavedRegs(BitVector &SavedRegs, MachineFunction &MF);
static char ID;
} // end of anonymous namespace
char RegUsageInfoCollector::ID = 0;
INITIALIZE_PASS_BEGIN(RegUsageInfoCollector, "RegUsageInfoCollector",
"Register Usage Information Collector", false, false)
INITIALIZE_PASS_END(RegUsageInfoCollector, "RegUsageInfoCollector",
"Register Usage Information Collector", false, false)
FunctionPass *llvm::createRegUsageInfoCollector() {
return new RegUsageInfoCollector();
bool RegUsageInfoCollector::runOnMachineFunction(MachineFunction &MF) {
MachineRegisterInfo *MRI = &MF.getRegInfo();
const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
const TargetMachine &TM = MF.getTarget();
LLVM_DEBUG(dbgs() << " -------------------- " << getPassName()
<< " -------------------- \n");
LLVM_DEBUG(dbgs() << "Function Name : " << MF.getName() << "\n");
std::vector<uint32_t> RegMask;
// Compute the size of the bit vector to represent all the registers.
// The bit vector is broken into 32-bit chunks, thus takes the ceil of
// the number of registers divided by 32 for the size.
unsigned RegMaskSize = MachineOperand::getRegMaskSize(TRI->getNumRegs());
RegMask.resize(RegMaskSize, ~((uint32_t)0));
const Function &F = MF.getFunction();
PhysicalRegisterUsageInfo &PRUI = getAnalysis<PhysicalRegisterUsageInfo>();
LLVM_DEBUG(dbgs() << "Clobbered Registers: ");
BitVector SavedRegs;
computeCalleeSavedRegs(SavedRegs, MF);
const BitVector &UsedPhysRegsMask = MRI->getUsedPhysRegsMask();
auto SetRegAsDefined = [&RegMask] (unsigned Reg) {
RegMask[Reg / 32] &= ~(1u << Reg % 32);
// Scan all the physical registers. When a register is defined in the current
// function set it and all the aliasing registers as defined in the regmask.
for (unsigned PReg = 1, PRegE = TRI->getNumRegs(); PReg < PRegE; ++PReg) {
// Don't count registers that are saved and restored.
if (SavedRegs.test(PReg))
// If a register is defined by an instruction mark it as defined together
// with all it's unsaved aliases.
if (!MRI->def_empty(PReg)) {
for (MCRegAliasIterator AI(PReg, TRI, true); AI.isValid(); ++AI)
if (!SavedRegs.test(*AI))
// If a register is in the UsedPhysRegsMask set then mark it as defined.
// All clobbered aliases will also be in the set, so we can skip setting
// as defined all the aliases here.
if (UsedPhysRegsMask.test(PReg))
if (TargetFrameLowering::isSafeForNoCSROpt(F)) {
LLVM_DEBUG(dbgs() << MF.getName()
<< " function optimized for not having CSR.\n");
for (unsigned PReg = 1, PRegE = TRI->getNumRegs(); PReg < PRegE; ++PReg)
if (MachineOperand::clobbersPhysReg(&(RegMask[0]), PReg))
LLVM_DEBUG(dbgs() << printReg(PReg, TRI) << " ");
LLVM_DEBUG(dbgs() << " \n----------------------------------------\n");
PRUI.storeUpdateRegUsageInfo(F, RegMask);
return false;
void RegUsageInfoCollector::
computeCalleeSavedRegs(BitVector &SavedRegs, MachineFunction &MF) {
const TargetFrameLowering &TFI = *MF.getSubtarget().getFrameLowering();
const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
// Target will return the set of registers that it saves/restores as needed.
TFI.determineCalleeSaves(MF, SavedRegs);
// Insert subregs.
const MCPhysReg *CSRegs = TRI.getCalleeSavedRegs(&MF);
for (unsigned i = 0; CSRegs[i]; ++i) {
unsigned Reg = CSRegs[i];
if (SavedRegs.test(Reg))
for (MCSubRegIterator SR(Reg, &TRI, false); SR.isValid(); ++SR)
// Insert any register fully saved via subregisters.
for (unsigned PReg = 1, PRegE = TRI.getNumRegs(); PReg < PRegE; ++PReg) {
if (SavedRegs.test(PReg))
// Check if PReg is fully covered by its subregs.
bool CoveredBySubRegs = false;
for (const TargetRegisterClass *RC : TRI.regclasses())
if (RC->CoveredBySubRegs && RC->contains(PReg)) {
CoveredBySubRegs = true;
if (!CoveredBySubRegs)
// Add PReg to SavedRegs if all subregs are saved.
bool AllSubRegsSaved = true;
for (MCSubRegIterator SR(PReg, &TRI, false); SR.isValid(); ++SR)
if (!SavedRegs.test(*SR)) {
AllSubRegsSaved = false;
if (AllSubRegsSaved)