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//===- RegisterClassInfo.cpp - Dynamic Register Class Info ----------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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/ADT/ArrayRef.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetFrameLowering.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
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() = default;
void RegisterClassInfo::runOnMachineFunction(const MachineFunction &mf) {
bool Update = false;
MF = &mf;
// Allocate new array the first time we see a new target.
if (MF->getSubtarget().getRegisterInfo() != TRI) {
TRI = MF->getSubtarget().getRegisterInfo();
RegClass.reset(new RCInfo[TRI->getNumRegClasses()]);
Update = true;
}
// Does this MF have different CSRs?
assert(TRI && "no register info set");
// Get the callee saved registers.
const MCPhysReg *CSR = MF->getRegInfo().getCalleeSavedRegs();
if (Update || CSR != CalleeSavedRegs) {
// Build a CSRAlias map. Every CSR alias saves the last
// overlapping CSR.
CalleeSavedAliases.assign(TRI->getNumRegs(), 0);
for (const MCPhysReg *I = CSR; *I; ++I)
for (MCRegAliasIterator AI(*I, TRI, true); AI.isValid(); ++AI)
CalleeSavedAliases[*AI] = *I;
Update = true;
}
CalleeSavedRegs = 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) {
unsigned NumPSets = TRI->getNumRegPressureSets();
PSetLimits.reset(new unsigned[NumPSets]);
std::fill(&PSetLimits[0], &PSetLimits[NumPSets], 0);
++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 {
assert(RC && "no register class given");
RCInfo &RCI = RegClass[RC->getID()];
auto &STI = MF->getSubtarget();
// 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 (CalleeSavedAliases[PhysReg] &&
!STI.ignoreCSRForAllocationOrder(*MF, 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, *MF))
if (Super != RC && getNumAllocatableRegs(Super) > RCI.NumRegs)
RCI.ProperSubClass = true;
RCI.MinCost = uint8_t(MinCost);
RCI.LastCostChange = LastCostChange;
LLVM_DEBUG({
dbgs() << "AllocationOrder(" << TRI->getRegClassName(RC) << ") = [";
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 (const TargetRegisterClass *C : TRI->regclasses()) {
const int *PSetID = TRI->getRegClassPressureSets(C);
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(C).WeightLimit;
if (!RC || NUnits > NumRCUnits) {
RC = C;
NumRCUnits = NUnits;
}
}
assert(RC && "Failed to find register class");
compute(RC);
unsigned NAllocatableRegs = getNumAllocatableRegs(RC);
unsigned RegPressureSetLimit = TRI->getRegPressureSetLimit(*MF, Idx);
// If all the regs are reserved, return raw RegPressureSetLimit.
// One example is VRSAVERC in PowerPC.
// Avoid returning zero, getRegPressureSetLimit(Idx) assumes computePSetLimit
// return non-zero value.
if (NAllocatableRegs == 0)
return RegPressureSetLimit;
unsigned NReserved = RC->getNumRegs() - NAllocatableRegs;
return RegPressureSetLimit - TRI->getRegClassWeight(RC).RegWeight * NReserved;
}
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