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

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//===-- 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 "AMDGPUSubtarget.h"
#include "SIInstrInfo.h"
#include "SIRegisterInfo.h"
#include "Utils/AMDGPUBaseInfo.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include <cassert>
#include <iterator>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "si-load-store-opt"
namespace {
class SILoadStoreOptimizer : public MachineFunctionPass {
typedef struct {
MachineBasicBlock::iterator I;
MachineBasicBlock::iterator Paired;
unsigned EltSize;
unsigned Offset0;
unsigned Offset1;
unsigned BaseOff;
bool UseST64;
SmallVector<MachineInstr*, 8> InstsToMove;
} CombineInfo;
private:
const SIInstrInfo *TII = nullptr;
const SIRegisterInfo *TRI = nullptr;
MachineRegisterInfo *MRI = nullptr;
AliasAnalysis *AA = nullptr;
static bool offsetsCanBeCombined(CombineInfo &CI);
bool findMatchingDSInst(CombineInfo &CI);
MachineBasicBlock::iterator mergeRead2Pair(CombineInfo &CI);
MachineBasicBlock::iterator mergeWrite2Pair(CombineInfo &CI);
public:
static char ID;
SILoadStoreOptimizer() : MachineFunctionPass(ID) {
initializeSILoadStoreOptimizerPass(*PassRegistry::getPassRegistry());
}
bool optimizeBlock(MachineBasicBlock &MBB);
bool runOnMachineFunction(MachineFunction &MF) override;
StringRef getPassName() const override { return "SI Load / Store Optimizer"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<AAResultsWrapperPass>();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // end anonymous namespace.
INITIALIZE_PASS_BEGIN(SILoadStoreOptimizer, DEBUG_TYPE,
"SI Load / Store Optimizer", false, false)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_END(SILoadStoreOptimizer, DEBUG_TYPE,
"SI Load / Store Optimizer", false, false)
char SILoadStoreOptimizer::ID = 0;
char &llvm::SILoadStoreOptimizerID = SILoadStoreOptimizer::ID;
FunctionPass *llvm::createSILoadStoreOptimizerPass() {
return new SILoadStoreOptimizer();
}
static void moveInstsAfter(MachineBasicBlock::iterator I,
ArrayRef<MachineInstr*> InstsToMove) {
MachineBasicBlock *MBB = I->getParent();
++I;
for (MachineInstr *MI : InstsToMove) {
MI->removeFromParent();
MBB->insert(I, MI);
}
}
static void addDefsToList(const MachineInstr &MI,
SmallVectorImpl<const MachineOperand *> &Defs) {
for (const MachineOperand &Def : MI.defs()) {
Defs.push_back(&Def);
}
}
static bool memAccessesCanBeReordered(MachineBasicBlock::iterator A,
MachineBasicBlock::iterator B,
const SIInstrInfo *TII,
AliasAnalysis * AA) {
return (TII->areMemAccessesTriviallyDisjoint(*A, *B, AA) ||
// RAW or WAR - cannot reorder
// WAW - cannot reorder
// RAR - safe to reorder
!(A->mayStore() || B->mayStore()));
}
// Add MI and its defs to the lists if MI reads one of the defs that are
// already in the list. Returns true in that case.
static bool
addToListsIfDependent(MachineInstr &MI,
SmallVectorImpl<const MachineOperand *> &Defs,
SmallVectorImpl<MachineInstr*> &Insts) {
for (const MachineOperand *Def : Defs) {
bool ReadDef = MI.readsVirtualRegister(Def->getReg());
// If ReadDef is true, then there is a use of Def between I
// and the instruction that I will potentially be merged with. We
// will need to move this instruction after the merged instructions.
if (ReadDef) {
Insts.push_back(&MI);
addDefsToList(MI, Defs);
return true;
}
}
return false;
}
static bool
canMoveInstsAcrossMemOp(MachineInstr &MemOp,
ArrayRef<MachineInstr*> InstsToMove,
const SIInstrInfo *TII,
AliasAnalysis *AA) {
assert(MemOp.mayLoadOrStore());
for (MachineInstr *InstToMove : InstsToMove) {
if (!InstToMove->mayLoadOrStore())
continue;
if (!memAccessesCanBeReordered(MemOp, *InstToMove, TII, AA))
return false;
}
return true;
}
bool SILoadStoreOptimizer::offsetsCanBeCombined(CombineInfo &CI) {
// XXX - Would the same offset be OK? Is there any reason this would happen or
// be useful?
if (CI.Offset0 == CI.Offset1)
return false;
// This won't be valid if the offset isn't aligned.
if ((CI.Offset0 % CI.EltSize != 0) || (CI.Offset1 % CI.EltSize != 0))
return false;
unsigned EltOffset0 = CI.Offset0 / CI.EltSize;
unsigned EltOffset1 = CI.Offset1 / CI.EltSize;
CI.UseST64 = false;
CI.BaseOff = 0;
// 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 &&
isUInt<8>(EltOffset0 / 64) && isUInt<8>(EltOffset1 / 64)) {
CI.Offset0 = EltOffset0 / 64;
CI.Offset1 = EltOffset1 / 64;
CI.UseST64 = true;
return true;
}
// Check if the new offsets fit in the reduced 8-bit range.
if (isUInt<8>(EltOffset0) && isUInt<8>(EltOffset1)) {
CI.Offset0 = EltOffset0;
CI.Offset1 = EltOffset1;
return true;
}
// Try to shift base address to decrease offsets.
unsigned OffsetDiff = std::abs((int)EltOffset1 - (int)EltOffset0);
CI.BaseOff = std::min(CI.Offset0, CI.Offset1);
if ((OffsetDiff % 64 == 0) && isUInt<8>(OffsetDiff / 64)) {
CI.Offset0 = (EltOffset0 - CI.BaseOff / CI.EltSize) / 64;
CI.Offset1 = (EltOffset1 - CI.BaseOff / CI.EltSize) / 64;
CI.UseST64 = true;
return true;
}
if (isUInt<8>(OffsetDiff)) {
CI.Offset0 = EltOffset0 - CI.BaseOff / CI.EltSize;
CI.Offset1 = EltOffset1 - CI.BaseOff / CI.EltSize;
return true;
}
return false;
}
bool SILoadStoreOptimizer::findMatchingDSInst(CombineInfo &CI) {
MachineBasicBlock::iterator E = CI.I->getParent()->end();
MachineBasicBlock::iterator MBBI = CI.I;
++MBBI;
SmallVector<const MachineOperand *, 8> DefsToMove;
addDefsToList(*CI.I, DefsToMove);
for ( ; MBBI != E; ++MBBI) {
if (MBBI->getOpcode() != CI.I->getOpcode()) {
// This is not a matching DS instruction, but we can keep looking as
// long as one of these conditions are met:
// 1. It is safe to move I down past MBBI.
// 2. It is safe to move MBBI down past the instruction that I will
// be merged into.
if (MBBI->hasUnmodeledSideEffects())
// We can't re-order this instruction with respect to other memory
// opeations, so we fail both conditions mentioned above.
return false;
if (MBBI->mayLoadOrStore() &&
!memAccessesCanBeReordered(*CI.I, *MBBI, TII, AA)) {
// We fail condition #1, but we may still be able to satisfy condition
// #2. Add this instruction to the move list and then we will check
// if condition #2 holds once we have selected the matching instruction.
CI.InstsToMove.push_back(&*MBBI);
addDefsToList(*MBBI, DefsToMove);
continue;
}
// When we match I with another DS instruction we will be moving I down
// to the location of the matched instruction any uses of I will need to
// be moved down as well.
addToListsIfDependent(*MBBI, DefsToMove, CI.InstsToMove);
continue;
}
// Don't merge volatiles.
if (MBBI->hasOrderedMemoryRef())
return false;
// Handle a case like
// DS_WRITE_B32 addr, v, idx0
// w = DS_READ_B32 addr, idx0
// DS_WRITE_B32 addr, f(w), idx1
// where the DS_READ_B32 ends up in InstsToMove and therefore prevents
// merging of the two writes.
if (addToListsIfDependent(*MBBI, DefsToMove, CI.InstsToMove))
continue;
int AddrIdx = AMDGPU::getNamedOperandIdx(CI.I->getOpcode(),
AMDGPU::OpName::addr);
const MachineOperand &AddrReg0 = CI.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(CI.I->getOpcode(),
AMDGPU::OpName::offset);
CI.Offset0 = CI.I->getOperand(OffsetIdx).getImm() & 0xffff;
CI.Offset1 = MBBI->getOperand(OffsetIdx).getImm() & 0xffff;
CI.Paired = MBBI;
// Check both offsets fit in the reduced range.
// We also need to go through the list of instructions that we plan to
// move and make sure they are all safe to move down past the merged
// instruction.
if (offsetsCanBeCombined(CI))
if (canMoveInstsAcrossMemOp(*MBBI, CI.InstsToMove, TII, AA))
return true;
}
// We've found a load/store that we couldn't merge for some reason.
// We could potentially keep looking, but we'd need to make sure that
// it was safe to move I and also all the instruction in InstsToMove
// down past this instruction.
// check if we can move I across MBBI and if we can move all I's users
if (!memAccessesCanBeReordered(*CI.I, *MBBI, TII, AA) ||
!canMoveInstsAcrossMemOp(*MBBI, CI.InstsToMove, TII, AA))
break;
}
return false;
}
MachineBasicBlock::iterator SILoadStoreOptimizer::mergeRead2Pair(
CombineInfo &CI) {
MachineBasicBlock *MBB = CI.I->getParent();
// Be careful, since the addresses could be subregisters themselves in weird
// cases, like vectors of pointers.
const auto *AddrReg = TII->getNamedOperand(*CI.I, AMDGPU::OpName::addr);
const auto *Dest0 = TII->getNamedOperand(*CI.I, AMDGPU::OpName::vdst);
const auto *Dest1 = TII->getNamedOperand(*CI.Paired, AMDGPU::OpName::vdst);
unsigned NewOffset0 = CI.Offset0;
unsigned NewOffset1 = CI.Offset1;
unsigned Opc = (CI.EltSize == 4) ? AMDGPU::DS_READ2_B32
: AMDGPU::DS_READ2_B64;
if (CI.UseST64)
Opc = (CI.EltSize == 4) ? AMDGPU::DS_READ2ST64_B32
: AMDGPU::DS_READ2ST64_B64;
unsigned SubRegIdx0 = (CI.EltSize == 4) ? AMDGPU::sub0 : AMDGPU::sub0_sub1;
unsigned SubRegIdx1 = (CI.EltSize == 4) ? AMDGPU::sub1 : AMDGPU::sub2_sub3;
if (NewOffset0 > NewOffset1) {
// Canonicalize the merged instruction so the smaller offset comes first.
std::swap(NewOffset0, NewOffset1);
std::swap(SubRegIdx0, SubRegIdx1);
}
assert((isUInt<8>(NewOffset0) && isUInt<8>(NewOffset1)) &&
(NewOffset0 != NewOffset1) &&
"Computed offset doesn't fit");
const MCInstrDesc &Read2Desc = TII->get(Opc);
const TargetRegisterClass *SuperRC
= (CI.EltSize == 4) ? &AMDGPU::VReg_64RegClass : &AMDGPU::VReg_128RegClass;
unsigned DestReg = MRI->createVirtualRegister(SuperRC);
DebugLoc DL = CI.I->getDebugLoc();
unsigned BaseReg = AddrReg->getReg();
unsigned BaseRegFlags = 0;
if (CI.BaseOff) {
BaseReg = MRI->createVirtualRegister(&AMDGPU::VGPR_32RegClass);
BaseRegFlags = RegState::Kill;
BuildMI(*MBB, CI.Paired, DL, TII->get(AMDGPU::V_ADD_I32_e32), BaseReg)
.addImm(CI.BaseOff)
.addReg(AddrReg->getReg());
}
MachineInstrBuilder Read2 =
BuildMI(*MBB, CI.Paired, DL, Read2Desc, DestReg)
.addReg(BaseReg, BaseRegFlags) // addr
.addImm(NewOffset0) // offset0
.addImm(NewOffset1) // offset1
.addImm(0) // gds
.setMemRefs(CI.I->mergeMemRefsWith(*CI.Paired));
(void)Read2;
const MCInstrDesc &CopyDesc = TII->get(TargetOpcode::COPY);
// Copy to the old destination registers.
BuildMI(*MBB, CI.Paired, DL, CopyDesc)
.add(*Dest0) // Copy to same destination including flags and sub reg.
.addReg(DestReg, 0, SubRegIdx0);
MachineInstr *Copy1 = BuildMI(*MBB, CI.Paired, DL, CopyDesc)
.add(*Dest1)
.addReg(DestReg, RegState::Kill, SubRegIdx1);
moveInstsAfter(Copy1, CI.InstsToMove);
MachineBasicBlock::iterator Next = std::next(CI.I);
CI.I->eraseFromParent();
CI.Paired->eraseFromParent();
DEBUG(dbgs() << "Inserted read2: " << *Read2 << '\n');
return Next;
}
MachineBasicBlock::iterator SILoadStoreOptimizer::mergeWrite2Pair(
CombineInfo &CI) {
MachineBasicBlock *MBB = CI.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(*CI.I, AMDGPU::OpName::addr);
const MachineOperand *Data0 = TII->getNamedOperand(*CI.I, AMDGPU::OpName::data0);
const MachineOperand *Data1
= TII->getNamedOperand(*CI.Paired, AMDGPU::OpName::data0);
unsigned NewOffset0 = CI.Offset0;
unsigned NewOffset1 = CI.Offset1;
unsigned Opc = (CI.EltSize == 4) ? AMDGPU::DS_WRITE2_B32
: AMDGPU::DS_WRITE2_B64;
if (CI.UseST64)
Opc = (CI.EltSize == 4) ? AMDGPU::DS_WRITE2ST64_B32
: AMDGPU::DS_WRITE2ST64_B64;
if (NewOffset0 > NewOffset1) {
// Canonicalize the merged instruction so the smaller offset comes first.
std::swap(NewOffset0, NewOffset1);
std::swap(Data0, Data1);
}
assert((isUInt<8>(NewOffset0) && isUInt<8>(NewOffset1)) &&
(NewOffset0 != NewOffset1) &&
"Computed offset doesn't fit");
const MCInstrDesc &Write2Desc = TII->get(Opc);
DebugLoc DL = CI.I->getDebugLoc();
unsigned BaseReg = Addr->getReg();
unsigned BaseRegFlags = 0;
if (CI.BaseOff) {
BaseReg = MRI->createVirtualRegister(&AMDGPU::VGPR_32RegClass);
BaseRegFlags = RegState::Kill;
BuildMI(*MBB, CI.Paired, DL, TII->get(AMDGPU::V_ADD_I32_e32), BaseReg)
.addImm(CI.BaseOff)
.addReg(Addr->getReg());
}
MachineInstrBuilder Write2 =
BuildMI(*MBB, CI.Paired, DL, Write2Desc)
.addReg(BaseReg, BaseRegFlags) // addr
.add(*Data0) // data0
.add(*Data1) // data1
.addImm(NewOffset0) // offset0
.addImm(NewOffset1) // offset1
.addImm(0) // gds
.setMemRefs(CI.I->mergeMemRefsWith(*CI.Paired));
moveInstsAfter(Write2, CI.InstsToMove);
MachineBasicBlock::iterator Next = std::next(CI.I);
CI.I->eraseFromParent();
CI.Paired->eraseFromParent();
DEBUG(dbgs() << "Inserted write2 inst: " << *Write2 << '\n');
return Next;
}
// 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;
}
CombineInfo CI;
CI.I = I;
unsigned Opc = MI.getOpcode();
if (Opc == AMDGPU::DS_READ_B32 || Opc == AMDGPU::DS_READ_B64) {
CI.EltSize = (Opc == AMDGPU::DS_READ_B64) ? 8 : 4;
if (findMatchingDSInst(CI)) {
Modified = true;
I = mergeRead2Pair(CI);
} else {
++I;
}
continue;
} else if (Opc == AMDGPU::DS_WRITE_B32 || Opc == AMDGPU::DS_WRITE_B64) {
CI.EltSize = (Opc == AMDGPU::DS_WRITE_B64) ? 8 : 4;
if (findMatchingDSInst(CI)) {
Modified = true;
I = mergeWrite2Pair(CI);
} else {
++I;
}
continue;
}
++I;
}
return Modified;
}
bool SILoadStoreOptimizer::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(*MF.getFunction()))
return false;
const SISubtarget &STM = MF.getSubtarget<SISubtarget>();
if (!STM.loadStoreOptEnabled())
return false;
TII = STM.getInstrInfo();
TRI = &TII->getRegisterInfo();
MRI = &MF.getRegInfo();
AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
DEBUG(dbgs() << "Running SILoadStoreOptimizer\n");
bool Modified = false;
for (MachineBasicBlock &MBB : MF)
Modified |= optimizeBlock(MBB);
return Modified;
}
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