llvm-project/llvm/lib/Target/R600/SILoadStoreOptimizer.cpp

435 lines
14 KiB
C++

//===-- SILoadStoreOptimizer.cpp ------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass tries to fuse DS instructions with close by immediate offsets.
// This will fuse operations such as
// ds_read_b32 v0, v2 offset:16
// ds_read_b32 v1, v2 offset:32
// ==>
// ds_read2_b32 v[0:1], v2, offset0:4 offset1:8
//
//
// Future improvements:
//
// - This currently relies on the scheduler to place loads and stores next to
// each other, and then only merges adjacent pairs of instructions. It would
// be good to be more flexible with interleaved instructions, and possibly run
// before scheduling. It currently missing stores of constants because loading
// the constant into the data register is placed between the stores, although
// this is arguably a scheduling problem.
//
// - Live interval recomputing seems inefficient. This currently only matches
// one pair, and recomputes live intervals and moves on to the next pair. It
// would be better to compute a list of all merges that need to occur
//
// - With a list of instructions to process, we can also merge more. If a
// cluster of loads have offsets that are too large to fit in the 8-bit
// offsets, but are close enough to fit in the 8 bits, we can add to the base
// pointer and use the new reduced offsets.
//
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "SIInstrInfo.h"
#include "SIRegisterInfo.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
#define DEBUG_TYPE "si-load-store-opt"
namespace {
class SILoadStoreOptimizer : public MachineFunctionPass {
private:
const TargetMachine *TM;
const SIInstrInfo *TII;
const SIRegisterInfo *TRI;
MachineRegisterInfo *MRI;
LiveIntervals *LIS;
static bool offsetsCanBeCombined(unsigned Offset0,
unsigned Offset1,
unsigned EltSize);
MachineBasicBlock::iterator findMatchingDSInst(MachineBasicBlock::iterator I,
unsigned EltSize);
void updateRegDefsUses(unsigned SrcReg,
unsigned DstReg,
unsigned SubIdx);
MachineBasicBlock::iterator mergeRead2Pair(
MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Paired,
unsigned EltSize);
MachineBasicBlock::iterator mergeWrite2Pair(
MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Paired,
unsigned EltSize);
public:
static char ID;
SILoadStoreOptimizer() :
MachineFunctionPass(ID),
TM(nullptr),
TII(nullptr),
TRI(nullptr),
MRI(nullptr),
LIS(nullptr) {
}
SILoadStoreOptimizer(const TargetMachine &TM_) :
MachineFunctionPass(ID),
TM(&TM_),
TII(static_cast<const SIInstrInfo*>(TM->getSubtargetImpl()->getInstrInfo())) {
initializeSILoadStoreOptimizerPass(*PassRegistry::getPassRegistry());
}
bool optimizeBlock(MachineBasicBlock &MBB);
bool runOnMachineFunction(MachineFunction &MF) override;
const char *getPassName() const override {
return "SI Load / Store Optimizer";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addPreserved<SlotIndexes>();
AU.addPreserved<LiveIntervals>();
AU.addPreserved<LiveVariables>();
AU.addRequired<LiveIntervals>();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // End anonymous namespace.
INITIALIZE_PASS_BEGIN(SILoadStoreOptimizer, DEBUG_TYPE,
"SI Load / Store Optimizer", false, false)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_DEPENDENCY(LiveVariables)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_PASS_END(SILoadStoreOptimizer, DEBUG_TYPE,
"SI Load / Store Optimizer", false, false)
char SILoadStoreOptimizer::ID = 0;
char &llvm::SILoadStoreOptimizerID = SILoadStoreOptimizer::ID;
FunctionPass *llvm::createSILoadStoreOptimizerPass(TargetMachine &TM) {
return new SILoadStoreOptimizer(TM);
}
bool SILoadStoreOptimizer::offsetsCanBeCombined(unsigned Offset0,
unsigned Offset1,
unsigned Size) {
// XXX - Would the same offset be OK? Is there any reason this would happen or
// be useful?
if (Offset0 == Offset1)
return false;
// This won't be valid if the offset isn't aligned.
if ((Offset0 % Size != 0) || (Offset1 % Size != 0))
return false;
unsigned EltOffset0 = Offset0 / Size;
unsigned EltOffset1 = Offset1 / Size;
// Check if the new offsets fit in the reduced 8-bit range.
if (isUInt<8>(EltOffset0) && isUInt<8>(EltOffset1))
return true;
// If the offset in elements doesn't fit in 8-bits, we might be able to use
// the stride 64 versions.
if ((EltOffset0 % 64 != 0) || (EltOffset1 % 64) != 0)
return false;
return isUInt<8>(EltOffset0 / 64) && isUInt<8>(EltOffset1 / 64);
}
MachineBasicBlock::iterator
SILoadStoreOptimizer::findMatchingDSInst(MachineBasicBlock::iterator I,
unsigned EltSize){
MachineBasicBlock::iterator E = I->getParent()->end();
MachineBasicBlock::iterator MBBI = I;
++MBBI;
if (MBBI->getOpcode() != I->getOpcode())
return E;
// Don't merge volatiles.
if (MBBI->hasOrderedMemoryRef())
return E;
int AddrIdx = AMDGPU::getNamedOperandIdx(I->getOpcode(), AMDGPU::OpName::addr);
const MachineOperand &AddrReg0 = I->getOperand(AddrIdx);
const MachineOperand &AddrReg1 = MBBI->getOperand(AddrIdx);
// Check same base pointer. Be careful of subregisters, which can occur with
// vectors of pointers.
if (AddrReg0.getReg() == AddrReg1.getReg() &&
AddrReg0.getSubReg() == AddrReg1.getSubReg()) {
int OffsetIdx = AMDGPU::getNamedOperandIdx(I->getOpcode(),
AMDGPU::OpName::offset);
unsigned Offset0 = I->getOperand(OffsetIdx).getImm() & 0xffff;
unsigned Offset1 = MBBI->getOperand(OffsetIdx).getImm() & 0xffff;
// Check both offsets fit in the reduced range.
if (offsetsCanBeCombined(Offset0, Offset1, EltSize))
return MBBI;
}
return E;
}
void SILoadStoreOptimizer::updateRegDefsUses(unsigned SrcReg,
unsigned DstReg,
unsigned SubIdx) {
for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(SrcReg),
E = MRI->reg_end(); I != E; ) {
MachineOperand &O = *I;
++I;
O.substVirtReg(DstReg, SubIdx, *TRI);
}
}
MachineBasicBlock::iterator SILoadStoreOptimizer::mergeRead2Pair(
MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Paired,
unsigned EltSize) {
MachineBasicBlock *MBB = I->getParent();
// Be careful, since the addresses could be subregisters themselves in weird
// cases, like vectors of pointers.
const MachineOperand *AddrReg = TII->getNamedOperand(*I, AMDGPU::OpName::addr);
const MachineOperand *M0Reg = TII->getNamedOperand(*I, AMDGPU::OpName::m0);
unsigned DestReg0 = TII->getNamedOperand(*I, AMDGPU::OpName::vdst)->getReg();
unsigned DestReg1
= TII->getNamedOperand(*Paired, AMDGPU::OpName::vdst)->getReg();
unsigned Offset0
= TII->getNamedOperand(*I, AMDGPU::OpName::offset)->getImm() & 0xffff;
unsigned Offset1
= TII->getNamedOperand(*Paired, AMDGPU::OpName::offset)->getImm() & 0xffff;
unsigned NewOffset0 = Offset0 / EltSize;
unsigned NewOffset1 = Offset1 / EltSize;
unsigned Opc = (EltSize == 4) ? AMDGPU::DS_READ2_B32 : AMDGPU::DS_READ2_B64;
// Prefer the st64 form if we can use it, even if we can fit the offset in the
// non st64 version. I'm not sure if there's any real reason to do this.
bool UseST64 = (NewOffset0 % 64 == 0) && (NewOffset1 % 64 == 0);
if (UseST64) {
NewOffset0 /= 64;
NewOffset1 /= 64;
Opc = (EltSize == 4) ? AMDGPU::DS_READ2ST64_B32 : AMDGPU::DS_READ2ST64_B64;
}
assert((isUInt<8>(NewOffset0) && isUInt<8>(NewOffset1)) &&
(NewOffset0 != NewOffset1) &&
"Computed offset doesn't fit");
const MCInstrDesc &Read2Desc = TII->get(Opc);
const TargetRegisterClass *SuperRC
= (EltSize == 4) ? &AMDGPU::VReg_64RegClass : &AMDGPU::VReg_128RegClass;
unsigned DestReg = MRI->createVirtualRegister(SuperRC);
DebugLoc DL = I->getDebugLoc();
MachineInstrBuilder Read2
= BuildMI(*MBB, I, DL, Read2Desc, DestReg)
.addImm(0) // gds
.addOperand(*AddrReg) // addr
.addImm(NewOffset0) // offset0
.addImm(NewOffset1) // offset1
.addOperand(*M0Reg) // M0
.addMemOperand(*I->memoperands_begin())
.addMemOperand(*Paired->memoperands_begin());
LIS->InsertMachineInstrInMaps(Read2);
unsigned SubRegIdx0 = (EltSize == 4) ? AMDGPU::sub0 : AMDGPU::sub0_sub1;
unsigned SubRegIdx1 = (EltSize == 4) ? AMDGPU::sub1 : AMDGPU::sub2_sub3;
updateRegDefsUses(DestReg0, DestReg, SubRegIdx0);
updateRegDefsUses(DestReg1, DestReg, SubRegIdx1);
LIS->RemoveMachineInstrFromMaps(I);
LIS->RemoveMachineInstrFromMaps(Paired);
I->eraseFromParent();
Paired->eraseFromParent();
LiveInterval &AddrRegLI = LIS->getInterval(AddrReg->getReg());
LIS->shrinkToUses(&AddrRegLI);
LiveInterval &M0RegLI = LIS->getInterval(M0Reg->getReg());
LIS->shrinkToUses(&M0RegLI);
// Currently m0 is treated as a register class with one member instead of an
// implicit physical register. We are using the virtual register for the first
// one, but we still need to update the live range of the now unused second m0
// virtual register to avoid verifier errors.
const MachineOperand *PairedM0Reg
= TII->getNamedOperand(*Paired, AMDGPU::OpName::m0);
LiveInterval &PairedM0RegLI = LIS->getInterval(PairedM0Reg->getReg());
LIS->shrinkToUses(&PairedM0RegLI);
LIS->getInterval(DestReg); // Create new LI
DEBUG(dbgs() << "Inserted read2: " << *Read2 << '\n');
return Read2.getInstr();
}
MachineBasicBlock::iterator SILoadStoreOptimizer::mergeWrite2Pair(
MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Paired,
unsigned EltSize) {
MachineBasicBlock *MBB = I->getParent();
// Be sure to use .addOperand(), and not .addReg() with these. We want to be
// sure we preserve the subregister index and any register flags set on them.
const MachineOperand *Addr = TII->getNamedOperand(*I, AMDGPU::OpName::addr);
const MachineOperand *M0Reg = TII->getNamedOperand(*I, AMDGPU::OpName::m0);
const MachineOperand *Data0 = TII->getNamedOperand(*I, AMDGPU::OpName::data0);
const MachineOperand *Data1
= TII->getNamedOperand(*Paired, AMDGPU::OpName::data0);
unsigned Offset0
= TII->getNamedOperand(*I, AMDGPU::OpName::offset)->getImm() & 0xffff;
unsigned Offset1
= TII->getNamedOperand(*Paired, AMDGPU::OpName::offset)->getImm() & 0xffff;
unsigned NewOffset0 = Offset0 / EltSize;
unsigned NewOffset1 = Offset1 / EltSize;
unsigned Opc = (EltSize == 4) ? AMDGPU::DS_WRITE2_B32 : AMDGPU::DS_WRITE2_B64;
// Prefer the st64 form if we can use it, even if we can fit the offset in the
// non st64 version. I'm not sure if there's any real reason to do this.
bool UseST64 = (NewOffset0 % 64 == 0) && (NewOffset1 % 64 == 0);
if (UseST64) {
NewOffset0 /= 64;
NewOffset1 /= 64;
Opc = (EltSize == 4) ? AMDGPU::DS_WRITE2ST64_B32 : AMDGPU::DS_WRITE2ST64_B64;
}
assert((isUInt<8>(NewOffset0) && isUInt<8>(NewOffset1)) &&
(NewOffset0 != NewOffset1) &&
"Computed offset doesn't fit");
const MCInstrDesc &Write2Desc = TII->get(Opc);
DebugLoc DL = I->getDebugLoc();
MachineInstrBuilder Write2
= BuildMI(*MBB, I, DL, Write2Desc)
.addImm(0) // gds
.addOperand(*Addr) // addr
.addOperand(*Data0) // data0
.addOperand(*Data1) // data1
.addImm(NewOffset0) // offset0
.addImm(NewOffset1) // offset1
.addOperand(*M0Reg) // m0
.addMemOperand(*I->memoperands_begin())
.addMemOperand(*Paired->memoperands_begin());
// XXX - How do we express subregisters here?
unsigned OrigRegs[] = { Data0->getReg(), Data1->getReg(), Addr->getReg(),
M0Reg->getReg()};
LIS->RemoveMachineInstrFromMaps(I);
LIS->RemoveMachineInstrFromMaps(Paired);
I->eraseFromParent();
Paired->eraseFromParent();
LIS->repairIntervalsInRange(MBB, Write2, Write2, OrigRegs);
DEBUG(dbgs() << "Inserted write2 inst: " << *Write2 << '\n');
return Write2.getInstr();
}
// Scan through looking for adjacent LDS operations with constant offsets from
// the same base register. We rely on the scheduler to do the hard work of
// clustering nearby loads, and assume these are all adjacent.
bool SILoadStoreOptimizer::optimizeBlock(MachineBasicBlock &MBB) {
bool Modified = false;
for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E;) {
MachineInstr &MI = *I;
// Don't combine if volatile.
if (MI.hasOrderedMemoryRef()) {
++I;
continue;
}
unsigned Opc = MI.getOpcode();
if (Opc == AMDGPU::DS_READ_B32 || Opc == AMDGPU::DS_READ_B64) {
unsigned Size = (Opc == AMDGPU::DS_READ_B64) ? 8 : 4;
MachineBasicBlock::iterator Match = findMatchingDSInst(I, Size);
if (Match != E) {
Modified = true;
I = mergeRead2Pair(I, Match, Size);
} else {
++I;
}
continue;
} else if (Opc == AMDGPU::DS_WRITE_B32 || Opc == AMDGPU::DS_WRITE_B64) {
unsigned Size = (Opc == AMDGPU::DS_WRITE_B64) ? 8 : 4;
MachineBasicBlock::iterator Match = findMatchingDSInst(I, Size);
if (Match != E) {
Modified = true;
I = mergeWrite2Pair(I, Match, Size);
} else {
++I;
}
continue;
}
++I;
}
return Modified;
}
bool SILoadStoreOptimizer::runOnMachineFunction(MachineFunction &MF) {
const TargetSubtargetInfo *STM = MF.getTarget().getSubtargetImpl();
TRI = static_cast<const SIRegisterInfo*>(STM->getRegisterInfo());
TII = static_cast<const SIInstrInfo*>(STM->getInstrInfo());
MRI = &MF.getRegInfo();
LIS = &getAnalysis<LiveIntervals>();
DEBUG(dbgs() << "Running SILoadStoreOptimizer\n");
assert(!MRI->isSSA());
bool Modified = false;
for (MachineBasicBlock &MBB : MF)
Modified |= optimizeBlock(MBB);
return Modified;
}