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llvm-project/llvm/lib/Target/AMDGPU/GCNNSAReassign.cpp

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//===-- GCNNSAReassign.cpp - Reassign registers in NSA unstructions -------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
/// \file
/// \brief Try to reassign registers on GFX10+ from non-sequential to sequential
/// in NSA image instructions. Later SIShrinkInstructions pass will relace NSA
/// with sequential versions where possible.
///
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "AMDGPUSubtarget.h"
#include "SIInstrInfo.h"
#include "SIMachineFunctionInfo.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/LiveRegMatrix.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/Support/MathExtras.h"
#include <algorithm>
using namespace llvm;
#define DEBUG_TYPE "amdgpu-nsa-reassign"
STATISTIC(NumNSAInstructions,
"Number of NSA instructions with non-sequential address found");
STATISTIC(NumNSAConverted,
"Number of NSA instructions changed to sequential");
namespace {
class GCNNSAReassign : public MachineFunctionPass {
public:
static char ID;
GCNNSAReassign() : MachineFunctionPass(ID) {
initializeGCNNSAReassignPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
StringRef getPassName() const override { return "GCN NSA Reassign"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LiveIntervals>();
AU.addRequired<VirtRegMap>();
AU.addRequired<LiveRegMatrix>();
AU.setPreservesAll();
MachineFunctionPass::getAnalysisUsage(AU);
}
private:
typedef enum {
NOT_NSA, // Not an NSA instruction
FIXED, // NSA which we cannot modify
NON_CONTIGUOUS, // NSA with non-sequential address which we can try
// to optimize.
CONTIGUOUS // NSA with all sequential address registers
} NSA_Status;
const GCNSubtarget *ST;
const MachineRegisterInfo *MRI;
const SIRegisterInfo *TRI;
VirtRegMap *VRM;
LiveRegMatrix *LRM;
LiveIntervals *LIS;
unsigned MaxNumVGPRs;
const MCPhysReg *CSRegs;
NSA_Status CheckNSA(const MachineInstr &MI, bool Fast = false) const;
bool tryAssignRegisters(SmallVectorImpl<LiveInterval *> &Intervals,
unsigned StartReg) const;
bool canAssign(unsigned StartReg, unsigned NumRegs) const;
bool scavengeRegs(SmallVectorImpl<LiveInterval *> &Intervals) const;
};
} // End anonymous namespace.
INITIALIZE_PASS_BEGIN(GCNNSAReassign, DEBUG_TYPE, "GCN NSA Reassign",
false, false)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_DEPENDENCY(VirtRegMap)
INITIALIZE_PASS_DEPENDENCY(LiveRegMatrix)
INITIALIZE_PASS_END(GCNNSAReassign, DEBUG_TYPE, "GCN NSA Reassign",
false, false)
char GCNNSAReassign::ID = 0;
char &llvm::GCNNSAReassignID = GCNNSAReassign::ID;
bool
GCNNSAReassign::tryAssignRegisters(SmallVectorImpl<LiveInterval *> &Intervals,
unsigned StartReg) const {
unsigned NumRegs = Intervals.size();
for (unsigned N = 0; N < NumRegs; ++N)
if (VRM->hasPhys(Intervals[N]->reg))
LRM->unassign(*Intervals[N]);
for (unsigned N = 0; N < NumRegs; ++N)
if (LRM->checkInterference(*Intervals[N], StartReg + N))
return false;
for (unsigned N = 0; N < NumRegs; ++N)
LRM->assign(*Intervals[N], StartReg + N);
return true;
}
bool GCNNSAReassign::canAssign(unsigned StartReg, unsigned NumRegs) const {
for (unsigned N = 0; N < NumRegs; ++N) {
unsigned Reg = StartReg + N;
if (!MRI->isAllocatable(Reg))
return false;
for (unsigned I = 0; CSRegs[I]; ++I)
if (TRI->isSubRegisterEq(Reg, CSRegs[I]) &&
!LRM->isPhysRegUsed(CSRegs[I]))
return false;
}
return true;
}
bool
GCNNSAReassign::scavengeRegs(SmallVectorImpl<LiveInterval *> &Intervals) const {
unsigned NumRegs = Intervals.size();
if (NumRegs > MaxNumVGPRs)
return false;
unsigned MaxReg = MaxNumVGPRs - NumRegs + AMDGPU::VGPR0;
for (unsigned Reg = AMDGPU::VGPR0; Reg <= MaxReg; ++Reg) {
if (!canAssign(Reg, NumRegs))
continue;
if (tryAssignRegisters(Intervals, Reg))
return true;
}
return false;
}
GCNNSAReassign::NSA_Status
GCNNSAReassign::CheckNSA(const MachineInstr &MI, bool Fast) const {
const AMDGPU::MIMGInfo *Info = AMDGPU::getMIMGInfo(MI.getOpcode());
if (!Info || Info->MIMGEncoding != AMDGPU::MIMGEncGfx10NSA)
return NSA_Status::NOT_NSA;
int VAddr0Idx =
AMDGPU::getNamedOperandIdx(MI.getOpcode(), AMDGPU::OpName::vaddr0);
unsigned VgprBase = 0;
bool NSA = false;
for (unsigned I = 0; I < Info->VAddrDwords; ++I) {
const MachineOperand &Op = MI.getOperand(VAddr0Idx + I);
unsigned Reg = Op.getReg();
if (Register::isPhysicalRegister(Reg) || !VRM->isAssignedReg(Reg))
return NSA_Status::FIXED;
unsigned PhysReg = VRM->getPhys(Reg);
if (!Fast) {
if (!PhysReg)
return NSA_Status::FIXED;
// Bail if address is not a VGPR32. That should be possible to extend the
// optimization to work with subregs of a wider register tuples, but the
// logic to find free registers will be much more complicated with much
// less chances for success. That seems reasonable to assume that in most
// cases a tuple is used because a vector variable contains different
// parts of an address and it is either already consequitive or cannot
// be reassigned if not. If needed it is better to rely on register
// coalescer to process such address tuples.
if (MRI->getRegClass(Reg) != &AMDGPU::VGPR_32RegClass || Op.getSubReg())
return NSA_Status::FIXED;
const MachineInstr *Def = MRI->getUniqueVRegDef(Reg);
if (Def && Def->isCopy() && Def->getOperand(1).getReg() == PhysReg)
return NSA_Status::FIXED;
for (auto U : MRI->use_nodbg_operands(Reg)) {
if (U.isImplicit())
return NSA_Status::FIXED;
const MachineInstr *UseInst = U.getParent();
if (UseInst->isCopy() && UseInst->getOperand(0).getReg() == PhysReg)
return NSA_Status::FIXED;
}
if (!LIS->hasInterval(Reg))
return NSA_Status::FIXED;
}
if (I == 0)
VgprBase = PhysReg;
else if (VgprBase + I != PhysReg)
NSA = true;
}
return NSA ? NSA_Status::NON_CONTIGUOUS : NSA_Status::CONTIGUOUS;
}
bool GCNNSAReassign::runOnMachineFunction(MachineFunction &MF) {
ST = &MF.getSubtarget<GCNSubtarget>();
if (ST->getGeneration() < GCNSubtarget::GFX10)
return false;
MRI = &MF.getRegInfo();
TRI = ST->getRegisterInfo();
VRM = &getAnalysis<VirtRegMap>();
LRM = &getAnalysis<LiveRegMatrix>();
LIS = &getAnalysis<LiveIntervals>();
const SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
MaxNumVGPRs = ST->getMaxNumVGPRs(MF);
MaxNumVGPRs = std::min(ST->getMaxNumVGPRs(MFI->getOccupancy()), MaxNumVGPRs);
CSRegs = MRI->getCalleeSavedRegs();
using Candidate = std::pair<const MachineInstr*, bool>;
SmallVector<Candidate, 32> Candidates;
for (const MachineBasicBlock &MBB : MF) {
for (const MachineInstr &MI : MBB) {
switch (CheckNSA(MI)) {
default:
continue;
case NSA_Status::CONTIGUOUS:
Candidates.push_back(std::make_pair(&MI, true));
break;
case NSA_Status::NON_CONTIGUOUS:
Candidates.push_back(std::make_pair(&MI, false));
++NumNSAInstructions;
break;
}
}
}
bool Changed = false;
for (auto &C : Candidates) {
if (C.second)
continue;
const MachineInstr *MI = C.first;
if (CheckNSA(*MI, true) == NSA_Status::CONTIGUOUS) {
// Already happen to be fixed.
C.second = true;
++NumNSAConverted;
continue;
}
const AMDGPU::MIMGInfo *Info = AMDGPU::getMIMGInfo(MI->getOpcode());
int VAddr0Idx =
AMDGPU::getNamedOperandIdx(MI->getOpcode(), AMDGPU::OpName::vaddr0);
SmallVector<LiveInterval *, 16> Intervals;
SmallVector<unsigned, 16> OrigRegs;
SlotIndex MinInd, MaxInd;
for (unsigned I = 0; I < Info->VAddrDwords; ++I) {
const MachineOperand &Op = MI->getOperand(VAddr0Idx + I);
unsigned Reg = Op.getReg();
LiveInterval *LI = &LIS->getInterval(Reg);
if (llvm::find(Intervals, LI) != Intervals.end()) {
// Same register used, unable to make sequential
Intervals.clear();
break;
}
Intervals.push_back(LI);
OrigRegs.push_back(VRM->getPhys(Reg));
MinInd = I ? std::min(MinInd, LI->beginIndex()) : LI->beginIndex();
MaxInd = I ? std::max(MaxInd, LI->endIndex()) : LI->endIndex();
}
if (Intervals.empty())
continue;
LLVM_DEBUG(dbgs() << "Attempting to reassign NSA: " << *MI
<< "\tOriginal allocation:\t";
for(auto *LI : Intervals)
dbgs() << " " << llvm::printReg((VRM->getPhys(LI->reg)), TRI);
dbgs() << '\n');
bool Success = scavengeRegs(Intervals);
if (!Success) {
LLVM_DEBUG(dbgs() << "\tCannot reallocate.\n");
if (VRM->hasPhys(Intervals.back()->reg)) // Did not change allocation.
continue;
} else {
// Check we did not make it worse for other instructions.
auto I = std::lower_bound(Candidates.begin(), &C, MinInd,
[this](const Candidate &C, SlotIndex I) {
return LIS->getInstructionIndex(*C.first) < I;
});
for (auto E = Candidates.end(); Success && I != E &&
LIS->getInstructionIndex(*I->first) < MaxInd; ++I) {
if (I->second && CheckNSA(*I->first, true) < NSA_Status::CONTIGUOUS) {
Success = false;
LLVM_DEBUG(dbgs() << "\tNSA conversion conflict with " << *I->first);
}
}
}
if (!Success) {
for (unsigned I = 0; I < Info->VAddrDwords; ++I)
if (VRM->hasPhys(Intervals[I]->reg))
LRM->unassign(*Intervals[I]);
for (unsigned I = 0; I < Info->VAddrDwords; ++I)
LRM->assign(*Intervals[I], OrigRegs[I]);
continue;
}
C.second = true;
++NumNSAConverted;
LLVM_DEBUG(dbgs() << "\tNew allocation:\t\t ["
<< llvm::printReg((VRM->getPhys(Intervals.front()->reg)), TRI)
<< " : "
<< llvm::printReg((VRM->getPhys(Intervals.back()->reg)), TRI)
<< "]\n");
Changed = true;
}
return Changed;
}
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