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//===-- RegisterClassInfo.cpp - Dynamic Register Class Info ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the RegisterClassInfo class which provides dynamic
// information about target register classes. Callee-saved vs. caller-saved and
// reserved registers depend on calling conventions and other dynamic
// information, so some things cannot be determined statically.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
#define DEBUG_TYPE "regalloc"
static cl::opt<unsigned>
StressRA("stress-regalloc", cl::Hidden, cl::init(0), cl::value_desc("N"),
cl::desc("Limit all regclasses to N registers"));
RegisterClassInfo::RegisterClassInfo()
: Tag(0), MF(nullptr), TRI(nullptr), CalleeSaved(nullptr) {}
void RegisterClassInfo::runOnMachineFunction(const MachineFunction &mf) {
bool Update = false;
MF = &mf;
// Allocate new array the first time we see a new target.
if (MF->getTarget().getRegisterInfo() != TRI) {
TRI = MF->getTarget().getRegisterInfo();
RegClass.reset(new RCInfo[TRI->getNumRegClasses()]);
unsigned NumPSets = TRI->getNumRegPressureSets();
PSetLimits.reset(new unsigned[NumPSets]);
std::fill(&PSetLimits[0], &PSetLimits[NumPSets], 0);
Update = true;
}
// Does this MF have different CSRs?
const MCPhysReg *CSR = TRI->getCalleeSavedRegs(MF);
if (Update || CSR != CalleeSaved) {
// Build a CSRNum map. Every CSR alias gets an entry pointing to the last
// overlapping CSR.
CSRNum.clear();
CSRNum.resize(TRI->getNumRegs(), 0);
for (unsigned N = 0; unsigned Reg = CSR[N]; ++N)
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
CSRNum[*AI] = N + 1; // 0 means no CSR, 1 means CalleeSaved[0], ...
Update = true;
}
CalleeSaved = CSR;
// Different reserved registers?
const BitVector &RR = MF->getRegInfo().getReservedRegs();
if (Reserved.size() != RR.size() || RR != Reserved) {
Update = true;
Reserved = RR;
}
// Invalidate cached information from previous function.
if (Update)
++Tag;
}
/// compute - Compute the preferred allocation order for RC with reserved
/// registers filtered out. Volatile registers come first followed by CSR
/// aliases ordered according to the CSR order specified by the target.
void RegisterClassInfo::compute(const TargetRegisterClass *RC) const {
RCInfo &RCI = RegClass[RC->getID()];
// Raw register count, including all reserved regs.
unsigned NumRegs = RC->getNumRegs();
if (!RCI.Order)
RCI.Order.reset(new MCPhysReg[NumRegs]);
unsigned N = 0;
SmallVector<MCPhysReg, 16> CSRAlias;
unsigned MinCost = 0xff;
unsigned LastCost = ~0u;
unsigned LastCostChange = 0;
// FIXME: Once targets reserve registers instead of removing them from the
// allocation order, we can simply use begin/end here.
ArrayRef<MCPhysReg> RawOrder = RC->getRawAllocationOrder(*MF);
for (unsigned i = 0; i != RawOrder.size(); ++i) {
unsigned PhysReg = RawOrder[i];
// Remove reserved registers from the allocation order.
if (Reserved.test(PhysReg))
continue;
unsigned Cost = TRI->getCostPerUse(PhysReg);
MinCost = std::min(MinCost, Cost);
if (CSRNum[PhysReg])
// PhysReg aliases a CSR, save it for later.
CSRAlias.push_back(PhysReg);
else {
if (Cost != LastCost)
LastCostChange = N;
RCI.Order[N++] = PhysReg;
LastCost = Cost;
}
}
RCI.NumRegs = N + CSRAlias.size();
assert (RCI.NumRegs <= NumRegs && "Allocation order larger than regclass");
// CSR aliases go after the volatile registers, preserve the target's order.
for (unsigned i = 0, e = CSRAlias.size(); i != e; ++i) {
unsigned PhysReg = CSRAlias[i];
unsigned Cost = TRI->getCostPerUse(PhysReg);
if (Cost != LastCost)
LastCostChange = N;
RCI.Order[N++] = PhysReg;
LastCost = Cost;
}
// Register allocator stress test. Clip register class to N registers.
if (StressRA && RCI.NumRegs > StressRA)
RCI.NumRegs = StressRA;
// Check if RC is a proper sub-class.
if (const TargetRegisterClass *Super = TRI->getLargestLegalSuperClass(RC))
if (Super != RC && getNumAllocatableRegs(Super) > RCI.NumRegs)
RCI.ProperSubClass = true;
RCI.MinCost = uint8_t(MinCost);
RCI.LastCostChange = LastCostChange;
DEBUG({
dbgs() << "AllocationOrder(" << RC->getName() << ") = [";
for (unsigned I = 0; I != RCI.NumRegs; ++I)
dbgs() << ' ' << PrintReg(RCI.Order[I], TRI);
dbgs() << (RCI.ProperSubClass ? " ] (sub-class)\n" : " ]\n");
});
// RCI is now up-to-date.
RCI.Tag = Tag;
}
/// This is not accurate because two overlapping register sets may have some
/// nonoverlapping reserved registers. However, computing the allocation order
/// for all register classes would be too expensive.
unsigned RegisterClassInfo::computePSetLimit(unsigned Idx) const {
const TargetRegisterClass *RC = nullptr;
unsigned NumRCUnits = 0;
for (TargetRegisterInfo::regclass_iterator
RI = TRI->regclass_begin(), RE = TRI->regclass_end(); RI != RE; ++RI) {
const int *PSetID = TRI->getRegClassPressureSets(*RI);
for (; *PSetID != -1; ++PSetID) {
if ((unsigned)*PSetID == Idx)
break;
}
if (*PSetID == -1)
continue;
// Found a register class that counts against this pressure set.
// For efficiency, only compute the set order for the largest set.
unsigned NUnits = TRI->getRegClassWeight(*RI).WeightLimit;
if (!RC || NUnits > NumRCUnits) {
RC = *RI;
NumRCUnits = NUnits;
}
}
compute(RC);
unsigned NReserved = RC->getNumRegs() - getNumAllocatableRegs(RC);
return TRI->getRegPressureSetLimit(Idx)
- TRI->getRegClassWeight(RC).RegWeight * NReserved;
}
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