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//===- RegAllocBase.cpp - Register Allocator Base Class -------------------===//
//
// 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 defines the RegAllocBase class which provides common functionality
// for LiveIntervalUnion-based register allocators.
//
//===----------------------------------------------------------------------===//
#include "RegAllocBase.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/LiveRegMatrix.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Spiller.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Timer.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
using namespace llvm;
#define DEBUG_TYPE "regalloc"
STATISTIC(NumNewQueued, "Number of new live ranges queued");
// Temporary verification option until we can put verification inside
// MachineVerifier.
static cl::opt<bool, true>
VerifyRegAlloc("verify-regalloc", cl::location(RegAllocBase::VerifyEnabled),
cl::Hidden, cl::desc("Verify during register allocation"));
const char RegAllocBase::TimerGroupName[] = "regalloc";
const char RegAllocBase::TimerGroupDescription[] = "Register Allocation";
bool RegAllocBase::VerifyEnabled = false;
//===----------------------------------------------------------------------===//
// RegAllocBase Implementation
//===----------------------------------------------------------------------===//
// Pin the vtable to this file.
void RegAllocBase::anchor() {}
void RegAllocBase::init(VirtRegMap &vrm, LiveIntervals &lis,
LiveRegMatrix &mat) {
TRI = &vrm.getTargetRegInfo();
MRI = &vrm.getRegInfo();
VRM = &vrm;
LIS = &lis;
Matrix = &mat;
MRI->freezeReservedRegs(vrm.getMachineFunction());
RegClassInfo.runOnMachineFunction(vrm.getMachineFunction());
}
// Visit all the live registers. If they are already assigned to a physical
// register, unify them with the corresponding LiveIntervalUnion, otherwise push
// them on the priority queue for later assignment.
void RegAllocBase::seedLiveRegs() {
NamedRegionTimer T("seed", "Seed Live Regs", TimerGroupName,
TimerGroupDescription, TimePassesIsEnabled);
for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
Register Reg = Register::index2VirtReg(i);
if (MRI->reg_nodbg_empty(Reg))
continue;
enqueue(&LIS->getInterval(Reg));
}
}
// Top-level driver to manage the queue of unassigned VirtRegs and call the
// selectOrSplit implementation.
void RegAllocBase::allocatePhysRegs() {
seedLiveRegs();
// Continue assigning vregs one at a time to available physical registers.
while (const LiveInterval *VirtReg = dequeue()) {
assert(!VRM->hasPhys(VirtReg->reg()) && "Register already assigned");
// Unused registers can appear when the spiller coalesces snippets.
if (MRI->reg_nodbg_empty(VirtReg->reg())) {
LLVM_DEBUG(dbgs() << "Dropping unused " << *VirtReg << '\n');
aboutToRemoveInterval(*VirtReg);
LIS->removeInterval(VirtReg->reg());
continue;
}
// Invalidate all interference queries, live ranges could have changed.
Matrix->invalidateVirtRegs();
// selectOrSplit requests the allocator to return an available physical
// register if possible and populate a list of new live intervals that
// result from splitting.
LLVM_DEBUG(dbgs() << "\nselectOrSplit "
<< TRI->getRegClassName(MRI->getRegClass(VirtReg->reg()))
<< ':' << *VirtReg << " w=" << VirtReg->weight() << '\n');
using VirtRegVec = SmallVector<Register, 4>;
VirtRegVec SplitVRegs;
MCRegister AvailablePhysReg = selectOrSplit(*VirtReg, SplitVRegs);
if (AvailablePhysReg == ~0u) {
// selectOrSplit failed to find a register!
// Probably caused by an inline asm.
MachineInstr *MI = nullptr;
for (MachineRegisterInfo::reg_instr_iterator
I = MRI->reg_instr_begin(VirtReg->reg()),
E = MRI->reg_instr_end();
I != E;) {
MI = &*(I++);
if (MI->isInlineAsm())
break;
}
const TargetRegisterClass *RC = MRI->getRegClass(VirtReg->reg());
ArrayRef<MCPhysReg> AllocOrder = RegClassInfo.getOrder(RC);
if (AllocOrder.empty())
report_fatal_error("no registers from class available to allocate");
else if (MI && MI->isInlineAsm()) {
MI->emitError("inline assembly requires more registers than available");
} else if (MI) {
LLVMContext &Context =
MI->getParent()->getParent()->getMMI().getModule()->getContext();
Context.emitError("ran out of registers during register allocation");
} else {
report_fatal_error("ran out of registers during register allocation");
}
// Keep going after reporting the error.
VRM->assignVirt2Phys(VirtReg->reg(), AllocOrder.front());
} else if (AvailablePhysReg)
Matrix->assign(*VirtReg, AvailablePhysReg);
for (Register Reg : SplitVRegs) {
assert(LIS->hasInterval(Reg));
LiveInterval *SplitVirtReg = &LIS->getInterval(Reg);
assert(!VRM->hasPhys(SplitVirtReg->reg()) && "Register already assigned");
if (MRI->reg_nodbg_empty(SplitVirtReg->reg())) {
assert(SplitVirtReg->empty() && "Non-empty but used interval");
LLVM_DEBUG(dbgs() << "not queueing unused " << *SplitVirtReg << '\n');
aboutToRemoveInterval(*SplitVirtReg);
LIS->removeInterval(SplitVirtReg->reg());
continue;
}
LLVM_DEBUG(dbgs() << "queuing new interval: " << *SplitVirtReg << "\n");
assert(SplitVirtReg->reg().isVirtual() &&
"expect split value in virtual register");
enqueue(SplitVirtReg);
++NumNewQueued;
}
}
}
void RegAllocBase::postOptimization() {
spiller().postOptimization();
for (auto *DeadInst : DeadRemats) {
LIS->RemoveMachineInstrFromMaps(*DeadInst);
DeadInst->eraseFromParent();
}
DeadRemats.clear();
}
void RegAllocBase::enqueue(const LiveInterval *LI) {
const Register Reg = LI->reg();
assert(Reg.isVirtual() && "Can only enqueue virtual registers");
if (VRM->hasPhys(Reg))
return;
const TargetRegisterClass &RC = *MRI->getRegClass(Reg);
if (ShouldAllocateClass(*TRI, RC)) {
LLVM_DEBUG(dbgs() << "Enqueuing " << printReg(Reg, TRI) << '\n');
enqueueImpl(LI);
} else {
LLVM_DEBUG(dbgs() << "Not enqueueing " << printReg(Reg, TRI)
<< " in skipped register class\n");
}
}
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