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

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//=======- GCNDPPCombine.cpp - optimization for DPP instructions ---==========//
//
// 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
//
//===----------------------------------------------------------------------===//
// The pass combines V_MOV_B32_dpp instruction with its VALU uses as a DPP src0
// operand. If any of the use instruction cannot be combined with the mov the
// whole sequence is reverted.
//
// $old = ...
// $dpp_value = V_MOV_B32_dpp $old, $vgpr_to_be_read_from_other_lane,
// dpp_controls..., $row_mask, $bank_mask, $bound_ctrl
// $res = VALU $dpp_value [, src1]
//
// to
//
// $res = VALU_DPP $combined_old, $vgpr_to_be_read_from_other_lane, [src1,]
// dpp_controls..., $row_mask, $bank_mask, $combined_bound_ctrl
//
// Combining rules :
//
// if $row_mask and $bank_mask are fully enabled (0xF) and
// $bound_ctrl==DPP_BOUND_ZERO or $old==0
// -> $combined_old = undef,
// $combined_bound_ctrl = DPP_BOUND_ZERO
//
// if the VALU op is binary and
// $bound_ctrl==DPP_BOUND_OFF and
// $old==identity value (immediate) for the VALU op
// -> $combined_old = src1,
// $combined_bound_ctrl = DPP_BOUND_OFF
//
// Otherwise cancel.
//
// The mov_dpp instruction should reside in the same BB as all its uses
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "AMDGPUSubtarget.h"
#include "SIInstrInfo.h"
#include "MCTargetDesc/AMDGPUMCTargetDesc.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.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/CodeGen/TargetRegisterInfo.h"
#include "llvm/Pass.h"
#include <cassert>
using namespace llvm;
#define DEBUG_TYPE "gcn-dpp-combine"
STATISTIC(NumDPPMovsCombined, "Number of DPP moves combined.");
namespace {
class GCNDPPCombine : public MachineFunctionPass {
MachineRegisterInfo *MRI;
const SIInstrInfo *TII;
using RegSubRegPair = TargetInstrInfo::RegSubRegPair;
MachineOperand *getOldOpndValue(MachineOperand &OldOpnd) const;
MachineInstr *createDPPInst(MachineInstr &OrigMI,
MachineInstr &MovMI,
RegSubRegPair CombOldVGPR,
MachineOperand *OldOpnd,
bool CombBCZ) const;
MachineInstr *createDPPInst(MachineInstr &OrigMI,
MachineInstr &MovMI,
RegSubRegPair CombOldVGPR,
bool CombBCZ) const;
bool hasNoImmOrEqual(MachineInstr &MI,
unsigned OpndName,
int64_t Value,
int64_t Mask = -1) const;
bool combineDPPMov(MachineInstr &MI) const;
public:
static char ID;
GCNDPPCombine() : MachineFunctionPass(ID) {
initializeGCNDPPCombinePass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
StringRef getPassName() const override { return "GCN DPP Combine"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // end anonymous namespace
INITIALIZE_PASS(GCNDPPCombine, DEBUG_TYPE, "GCN DPP Combine", false, false)
char GCNDPPCombine::ID = 0;
char &llvm::GCNDPPCombineID = GCNDPPCombine::ID;
FunctionPass *llvm::createGCNDPPCombinePass() {
return new GCNDPPCombine();
}
static int getDPPOp(unsigned Op) {
auto DPP32 = AMDGPU::getDPPOp32(Op);
if (DPP32 != -1)
return DPP32;
auto E32 = AMDGPU::getVOPe32(Op);
return E32 != -1 ? AMDGPU::getDPPOp32(E32) : -1;
}
// tracks the register operand definition and returns:
// 1. immediate operand used to initialize the register if found
// 2. nullptr if the register operand is undef
// 3. the operand itself otherwise
MachineOperand *GCNDPPCombine::getOldOpndValue(MachineOperand &OldOpnd) const {
auto *Def = getVRegSubRegDef(getRegSubRegPair(OldOpnd), *MRI);
if (!Def)
return nullptr;
switch(Def->getOpcode()) {
default: break;
case AMDGPU::IMPLICIT_DEF:
return nullptr;
case AMDGPU::COPY:
case AMDGPU::V_MOV_B32_e32: {
auto &Op1 = Def->getOperand(1);
if (Op1.isImm())
return &Op1;
break;
}
}
return &OldOpnd;
}
MachineInstr *GCNDPPCombine::createDPPInst(MachineInstr &OrigMI,
MachineInstr &MovMI,
RegSubRegPair CombOldVGPR,
bool CombBCZ) const {
assert(MovMI.getOpcode() == AMDGPU::V_MOV_B32_dpp);
auto OrigOp = OrigMI.getOpcode();
auto DPPOp = getDPPOp(OrigOp);
if (DPPOp == -1) {
LLVM_DEBUG(dbgs() << " failed: no DPP opcode\n");
return nullptr;
}
auto DPPInst = BuildMI(*OrigMI.getParent(), OrigMI,
OrigMI.getDebugLoc(), TII->get(DPPOp));
bool Fail = false;
do {
auto *Dst = TII->getNamedOperand(OrigMI, AMDGPU::OpName::vdst);
assert(Dst);
DPPInst.add(*Dst);
int NumOperands = 1;
const int OldIdx = AMDGPU::getNamedOperandIdx(DPPOp, AMDGPU::OpName::old);
if (OldIdx != -1) {
assert(OldIdx == NumOperands);
assert(isOfRegClass(CombOldVGPR, AMDGPU::VGPR_32RegClass, *MRI));
auto *Def = getVRegSubRegDef(CombOldVGPR, *MRI);
DPPInst.addReg(CombOldVGPR.Reg, Def ? 0 : RegState::Undef,
CombOldVGPR.SubReg);
++NumOperands;
} else {
// TODO: this discards MAC/FMA instructions for now, let's add it later
LLVM_DEBUG(dbgs() << " failed: no old operand in DPP instruction,"
" TBD\n");
Fail = true;
break;
}
if (auto *Mod0 = TII->getNamedOperand(OrigMI,
AMDGPU::OpName::src0_modifiers)) {
assert(NumOperands == AMDGPU::getNamedOperandIdx(DPPOp,
AMDGPU::OpName::src0_modifiers));
assert(0LL == (Mod0->getImm() & ~(SISrcMods::ABS | SISrcMods::NEG)));
DPPInst.addImm(Mod0->getImm());
++NumOperands;
} else if (AMDGPU::getNamedOperandIdx(DPPOp,
AMDGPU::OpName::src0_modifiers) != -1) {
DPPInst.addImm(0);
++NumOperands;
}
auto *Src0 = TII->getNamedOperand(MovMI, AMDGPU::OpName::src0);
assert(Src0);
if (!TII->isOperandLegal(*DPPInst.getInstr(), NumOperands, Src0)) {
LLVM_DEBUG(dbgs() << " failed: src0 is illegal\n");
Fail = true;
break;
}
DPPInst.add(*Src0);
DPPInst->getOperand(NumOperands).setIsKill(false);
++NumOperands;
if (auto *Mod1 = TII->getNamedOperand(OrigMI,
AMDGPU::OpName::src1_modifiers)) {
assert(NumOperands == AMDGPU::getNamedOperandIdx(DPPOp,
AMDGPU::OpName::src1_modifiers));
assert(0LL == (Mod1->getImm() & ~(SISrcMods::ABS | SISrcMods::NEG)));
DPPInst.addImm(Mod1->getImm());
++NumOperands;
} else if (AMDGPU::getNamedOperandIdx(DPPOp,
AMDGPU::OpName::src1_modifiers) != -1) {
DPPInst.addImm(0);
++NumOperands;
}
if (auto *Src1 = TII->getNamedOperand(OrigMI, AMDGPU::OpName::src1)) {
if (!TII->isOperandLegal(*DPPInst.getInstr(), NumOperands, Src1)) {
LLVM_DEBUG(dbgs() << " failed: src1 is illegal\n");
Fail = true;
break;
}
DPPInst.add(*Src1);
++NumOperands;
}
if (auto *Src2 = TII->getNamedOperand(OrigMI, AMDGPU::OpName::src2)) {
if (!TII->isOperandLegal(*DPPInst.getInstr(), NumOperands, Src2)) {
LLVM_DEBUG(dbgs() << " failed: src2 is illegal\n");
Fail = true;
break;
}
DPPInst.add(*Src2);
}
DPPInst.add(*TII->getNamedOperand(MovMI, AMDGPU::OpName::dpp_ctrl));
DPPInst.add(*TII->getNamedOperand(MovMI, AMDGPU::OpName::row_mask));
DPPInst.add(*TII->getNamedOperand(MovMI, AMDGPU::OpName::bank_mask));
DPPInst.addImm(CombBCZ ? 1 : 0);
} while (false);
if (Fail) {
DPPInst.getInstr()->eraseFromParent();
return nullptr;
}
LLVM_DEBUG(dbgs() << " combined: " << *DPPInst.getInstr());
return DPPInst.getInstr();
}
static bool isIdentityValue(unsigned OrigMIOp, MachineOperand *OldOpnd) {
assert(OldOpnd->isImm());
switch (OrigMIOp) {
default: break;
case AMDGPU::V_ADD_U32_e32:
case AMDGPU::V_ADD_U32_e64:
case AMDGPU::V_ADD_I32_e32:
case AMDGPU::V_ADD_I32_e64:
case AMDGPU::V_OR_B32_e32:
case AMDGPU::V_OR_B32_e64:
case AMDGPU::V_SUBREV_U32_e32:
case AMDGPU::V_SUBREV_U32_e64:
case AMDGPU::V_SUBREV_I32_e32:
case AMDGPU::V_SUBREV_I32_e64:
case AMDGPU::V_MAX_U32_e32:
case AMDGPU::V_MAX_U32_e64:
case AMDGPU::V_XOR_B32_e32:
case AMDGPU::V_XOR_B32_e64:
if (OldOpnd->getImm() == 0)
return true;
break;
case AMDGPU::V_AND_B32_e32:
case AMDGPU::V_AND_B32_e64:
case AMDGPU::V_MIN_U32_e32:
case AMDGPU::V_MIN_U32_e64:
if (static_cast<uint32_t>(OldOpnd->getImm()) ==
std::numeric_limits<uint32_t>::max())
return true;
break;
case AMDGPU::V_MIN_I32_e32:
case AMDGPU::V_MIN_I32_e64:
if (static_cast<int32_t>(OldOpnd->getImm()) ==
std::numeric_limits<int32_t>::max())
return true;
break;
case AMDGPU::V_MAX_I32_e32:
case AMDGPU::V_MAX_I32_e64:
if (static_cast<int32_t>(OldOpnd->getImm()) ==
std::numeric_limits<int32_t>::min())
return true;
break;
case AMDGPU::V_MUL_I32_I24_e32:
case AMDGPU::V_MUL_I32_I24_e64:
case AMDGPU::V_MUL_U32_U24_e32:
case AMDGPU::V_MUL_U32_U24_e64:
if (OldOpnd->getImm() == 1)
return true;
break;
}
return false;
}
MachineInstr *GCNDPPCombine::createDPPInst(MachineInstr &OrigMI,
MachineInstr &MovMI,
RegSubRegPair CombOldVGPR,
MachineOperand *OldOpndValue,
bool CombBCZ) const {
assert(CombOldVGPR.Reg);
if (!CombBCZ && OldOpndValue && OldOpndValue->isImm()) {
auto *Src1 = TII->getNamedOperand(OrigMI, AMDGPU::OpName::src1);
if (!Src1 || !Src1->isReg()) {
LLVM_DEBUG(dbgs() << " failed: no src1 or it isn't a register\n");
return nullptr;
}
if (!isIdentityValue(OrigMI.getOpcode(), OldOpndValue)) {
LLVM_DEBUG(dbgs() << " failed: old immediate isn't an identity\n");
return nullptr;
}
CombOldVGPR = getRegSubRegPair(*Src1);
if (!isOfRegClass(CombOldVGPR, AMDGPU::VGPR_32RegClass, *MRI)) {
LLVM_DEBUG(dbgs() << " failed: src1 isn't a VGPR32 register\n");
return nullptr;
}
}
return createDPPInst(OrigMI, MovMI, CombOldVGPR, CombBCZ);
}
// returns true if MI doesn't have OpndName immediate operand or the
// operand has Value
bool GCNDPPCombine::hasNoImmOrEqual(MachineInstr &MI, unsigned OpndName,
int64_t Value, int64_t Mask) const {
auto *Imm = TII->getNamedOperand(MI, OpndName);
if (!Imm)
return true;
assert(Imm->isImm());
return (Imm->getImm() & Mask) == Value;
}
bool GCNDPPCombine::combineDPPMov(MachineInstr &MovMI) const {
assert(MovMI.getOpcode() == AMDGPU::V_MOV_B32_dpp);
LLVM_DEBUG(dbgs() << "\nDPP combine: " << MovMI);
auto *DstOpnd = TII->getNamedOperand(MovMI, AMDGPU::OpName::vdst);
assert(DstOpnd && DstOpnd->isReg());
auto DPPMovReg = DstOpnd->getReg();
if (DPPMovReg.isPhysical()) {
LLVM_DEBUG(dbgs() << " failed: dpp move writes physreg\n");
return false;
}
if (execMayBeModifiedBeforeAnyUse(*MRI, DPPMovReg, MovMI)) {
LLVM_DEBUG(dbgs() << " failed: EXEC mask should remain the same"
" for all uses\n");
return false;
}
auto *RowMaskOpnd = TII->getNamedOperand(MovMI, AMDGPU::OpName::row_mask);
assert(RowMaskOpnd && RowMaskOpnd->isImm());
auto *BankMaskOpnd = TII->getNamedOperand(MovMI, AMDGPU::OpName::bank_mask);
assert(BankMaskOpnd && BankMaskOpnd->isImm());
const bool MaskAllLanes = RowMaskOpnd->getImm() == 0xF &&
BankMaskOpnd->getImm() == 0xF;
auto *BCZOpnd = TII->getNamedOperand(MovMI, AMDGPU::OpName::bound_ctrl);
assert(BCZOpnd && BCZOpnd->isImm());
bool BoundCtrlZero = BCZOpnd->getImm();
auto *OldOpnd = TII->getNamedOperand(MovMI, AMDGPU::OpName::old);
auto *SrcOpnd = TII->getNamedOperand(MovMI, AMDGPU::OpName::src0);
assert(OldOpnd && OldOpnd->isReg());
assert(SrcOpnd && SrcOpnd->isReg());
if (OldOpnd->getReg().isPhysical() || SrcOpnd->getReg().isPhysical()) {
LLVM_DEBUG(dbgs() << " failed: dpp move reads physreg\n");
return false;
}
auto * const OldOpndValue = getOldOpndValue(*OldOpnd);
// OldOpndValue is either undef (IMPLICIT_DEF) or immediate or something else
// We could use: assert(!OldOpndValue || OldOpndValue->isImm())
// but the third option is used to distinguish undef from non-immediate
// to reuse IMPLICIT_DEF instruction later
assert(!OldOpndValue || OldOpndValue->isImm() || OldOpndValue == OldOpnd);
bool CombBCZ = false;
if (MaskAllLanes && BoundCtrlZero) { // [1]
CombBCZ = true;
} else {
if (!OldOpndValue || !OldOpndValue->isImm()) {
LLVM_DEBUG(dbgs() << " failed: the DPP mov isn't combinable\n");
return false;
}
if (OldOpndValue->getParent()->getParent() != MovMI.getParent()) {
LLVM_DEBUG(dbgs() <<
" failed: old reg def and mov should be in the same BB\n");
return false;
}
if (OldOpndValue->getImm() == 0) {
if (MaskAllLanes) {
assert(!BoundCtrlZero); // by check [1]
CombBCZ = true;
}
} else if (BoundCtrlZero) {
assert(!MaskAllLanes); // by check [1]
LLVM_DEBUG(dbgs() <<
" failed: old!=0 and bctrl:0 and not all lanes isn't combinable\n");
return false;
}
}
LLVM_DEBUG(dbgs() << " old=";
if (!OldOpndValue)
dbgs() << "undef";
else
dbgs() << *OldOpndValue;
dbgs() << ", bound_ctrl=" << CombBCZ << '\n');
SmallVector<MachineInstr*, 4> OrigMIs, DPPMIs;
DenseMap<MachineInstr*, SmallVector<unsigned, 4>> RegSeqWithOpNos;
auto CombOldVGPR = getRegSubRegPair(*OldOpnd);
// try to reuse previous old reg if its undefined (IMPLICIT_DEF)
if (CombBCZ && OldOpndValue) { // CombOldVGPR should be undef
CombOldVGPR = RegSubRegPair(
MRI->createVirtualRegister(&AMDGPU::VGPR_32RegClass));
auto UndefInst = BuildMI(*MovMI.getParent(), MovMI, MovMI.getDebugLoc(),
TII->get(AMDGPU::IMPLICIT_DEF), CombOldVGPR.Reg);
DPPMIs.push_back(UndefInst.getInstr());
}
OrigMIs.push_back(&MovMI);
bool Rollback = true;
SmallVector<MachineOperand*, 16> Uses;
for (auto &Use : MRI->use_nodbg_operands(DPPMovReg)) {
Uses.push_back(&Use);
}
while (!Uses.empty()) {
MachineOperand *Use = Uses.pop_back_val();
Rollback = true;
auto &OrigMI = *Use->getParent();
LLVM_DEBUG(dbgs() << " try: " << OrigMI);
auto OrigOp = OrigMI.getOpcode();
if (OrigOp == AMDGPU::REG_SEQUENCE) {
Register FwdReg = OrigMI.getOperand(0).getReg();
unsigned FwdSubReg = 0;
if (execMayBeModifiedBeforeAnyUse(*MRI, FwdReg, OrigMI)) {
LLVM_DEBUG(dbgs() << " failed: EXEC mask should remain the same"
" for all uses\n");
break;
}
unsigned OpNo, E = OrigMI.getNumOperands();
for (OpNo = 1; OpNo < E; OpNo += 2) {
if (OrigMI.getOperand(OpNo).getReg() == DPPMovReg) {
FwdSubReg = OrigMI.getOperand(OpNo + 1).getImm();
break;
}
}
if (!FwdSubReg)
break;
for (auto &Op : MRI->use_nodbg_operands(FwdReg)) {
if (Op.getSubReg() == FwdSubReg)
Uses.push_back(&Op);
}
RegSeqWithOpNos[&OrigMI].push_back(OpNo);
continue;
}
if (TII->isVOP3(OrigOp)) {
if (!TII->hasVALU32BitEncoding(OrigOp)) {
LLVM_DEBUG(dbgs() << " failed: VOP3 hasn't e32 equivalent\n");
break;
}
// check if other than abs|neg modifiers are set (opsel for example)
const int64_t Mask = ~(SISrcMods::ABS | SISrcMods::NEG);
if (!hasNoImmOrEqual(OrigMI, AMDGPU::OpName::src0_modifiers, 0, Mask) ||
!hasNoImmOrEqual(OrigMI, AMDGPU::OpName::src1_modifiers, 0, Mask) ||
!hasNoImmOrEqual(OrigMI, AMDGPU::OpName::clamp, 0) ||
!hasNoImmOrEqual(OrigMI, AMDGPU::OpName::omod, 0)) {
LLVM_DEBUG(dbgs() << " failed: VOP3 has non-default modifiers\n");
break;
}
} else if (!TII->isVOP1(OrigOp) && !TII->isVOP2(OrigOp)) {
LLVM_DEBUG(dbgs() << " failed: not VOP1/2/3\n");
break;
}
LLVM_DEBUG(dbgs() << " combining: " << OrigMI);
if (Use == TII->getNamedOperand(OrigMI, AMDGPU::OpName::src0)) {
if (auto *DPPInst = createDPPInst(OrigMI, MovMI, CombOldVGPR,
OldOpndValue, CombBCZ)) {
DPPMIs.push_back(DPPInst);
Rollback = false;
}
} else if (OrigMI.isCommutable() &&
Use == TII->getNamedOperand(OrigMI, AMDGPU::OpName::src1)) {
auto *BB = OrigMI.getParent();
auto *NewMI = BB->getParent()->CloneMachineInstr(&OrigMI);
BB->insert(OrigMI, NewMI);
if (TII->commuteInstruction(*NewMI)) {
LLVM_DEBUG(dbgs() << " commuted: " << *NewMI);
if (auto *DPPInst = createDPPInst(*NewMI, MovMI, CombOldVGPR,
OldOpndValue, CombBCZ)) {
DPPMIs.push_back(DPPInst);
Rollback = false;
}
} else
LLVM_DEBUG(dbgs() << " failed: cannot be commuted\n");
NewMI->eraseFromParent();
} else
LLVM_DEBUG(dbgs() << " failed: no suitable operands\n");
if (Rollback)
break;
OrigMIs.push_back(&OrigMI);
}
Rollback |= !Uses.empty();
for (auto *MI : *(Rollback? &DPPMIs : &OrigMIs))
MI->eraseFromParent();
if (!Rollback) {
for (auto &S : RegSeqWithOpNos) {
if (MRI->use_nodbg_empty(S.first->getOperand(0).getReg())) {
S.first->eraseFromParent();
continue;
}
while (!S.second.empty())
S.first->getOperand(S.second.pop_back_val()).setIsUndef(true);
}
}
return !Rollback;
}
bool GCNDPPCombine::runOnMachineFunction(MachineFunction &MF) {
auto &ST = MF.getSubtarget<GCNSubtarget>();
if (!ST.hasDPP() || skipFunction(MF.getFunction()))
return false;
MRI = &MF.getRegInfo();
TII = ST.getInstrInfo();
assert(MRI->isSSA() && "Must be run on SSA");
bool Changed = false;
for (auto &MBB : MF) {
for (auto I = MBB.rbegin(), E = MBB.rend(); I != E;) {
auto &MI = *I++;
if (MI.getOpcode() == AMDGPU::V_MOV_B32_dpp && combineDPPMov(MI)) {
Changed = true;
++NumDPPMovsCombined;
} else if (MI.getOpcode() == AMDGPU::V_MOV_B64_DPP_PSEUDO) {
auto Split = TII->expandMovDPP64(MI);
for (auto M : { Split.first, Split.second }) {
if (combineDPPMov(*M))
++NumDPPMovsCombined;
}
Changed = true;
}
}
}
return Changed;
}
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