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

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//===- SIFixSGPRCopies.cpp - Remove potential VGPR => SGPR copies ---------===//
//
// 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
/// Copies from VGPR to SGPR registers are illegal and the register coalescer
/// will sometimes generate these illegal copies in situations like this:
///
/// Register Class <vsrc> is the union of <vgpr> and <sgpr>
///
/// BB0:
/// %0 <sgpr> = SCALAR_INST
/// %1 <vsrc> = COPY %0 <sgpr>
/// ...
/// BRANCH %cond BB1, BB2
/// BB1:
/// %2 <vgpr> = VECTOR_INST
/// %3 <vsrc> = COPY %2 <vgpr>
/// BB2:
/// %4 <vsrc> = PHI %1 <vsrc>, <%bb.0>, %3 <vrsc>, <%bb.1>
/// %5 <vgpr> = VECTOR_INST %4 <vsrc>
///
///
/// The coalescer will begin at BB0 and eliminate its copy, then the resulting
/// code will look like this:
///
/// BB0:
/// %0 <sgpr> = SCALAR_INST
/// ...
/// BRANCH %cond BB1, BB2
/// BB1:
/// %2 <vgpr> = VECTOR_INST
/// %3 <vsrc> = COPY %2 <vgpr>
/// BB2:
/// %4 <sgpr> = PHI %0 <sgpr>, <%bb.0>, %3 <vsrc>, <%bb.1>
/// %5 <vgpr> = VECTOR_INST %4 <sgpr>
///
/// Now that the result of the PHI instruction is an SGPR, the register
/// allocator is now forced to constrain the register class of %3 to
/// <sgpr> so we end up with final code like this:
///
/// BB0:
/// %0 <sgpr> = SCALAR_INST
/// ...
/// BRANCH %cond BB1, BB2
/// BB1:
/// %2 <vgpr> = VECTOR_INST
/// %3 <sgpr> = COPY %2 <vgpr>
/// BB2:
/// %4 <sgpr> = PHI %0 <sgpr>, <%bb.0>, %3 <sgpr>, <%bb.1>
/// %5 <vgpr> = VECTOR_INST %4 <sgpr>
///
/// Now this code contains an illegal copy from a VGPR to an SGPR.
///
/// In order to avoid this problem, this pass searches for PHI instructions
/// which define a <vsrc> register and constrains its definition class to
/// <vgpr> if the user of the PHI's definition register is a vector instruction.
/// If the PHI's definition class is constrained to <vgpr> then the coalescer
/// will be unable to perform the COPY removal from the above example which
/// ultimately led to the creation of an illegal COPY.
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "GCNSubtarget.h"
#include "MCTargetDesc/AMDGPUMCTargetDesc.h"
#include "llvm/ADT/SetOperations.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/InitializePasses.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
#define DEBUG_TYPE "si-fix-sgpr-copies"
static cl::opt<bool> EnableM0Merge(
"amdgpu-enable-merge-m0",
cl::desc("Merge and hoist M0 initializations"),
cl::init(true));
namespace {
class SIFixSGPRCopies : public MachineFunctionPass {
MachineDominatorTree *MDT;
unsigned NextVGPRToSGPRCopyID;
public:
static char ID;
MachineRegisterInfo *MRI;
const SIRegisterInfo *TRI;
const SIInstrInfo *TII;
SIFixSGPRCopies() : MachineFunctionPass(ID), NextVGPRToSGPRCopyID(0) {}
bool runOnMachineFunction(MachineFunction &MF) override;
unsigned getNextVGPRToSGPRCopyId() { return ++NextVGPRToSGPRCopyID; }
void lowerVGPR2SGPRCopies(MachineFunction &MF);
// Handles copies which source register is:
// 1. Physical register
// 2. AGPR
// 3. Defined by the instruction the merely moves the immediate
bool lowerSpecialCase(MachineInstr &MI);
MachineBasicBlock *processPHINode(MachineInstr &MI);
StringRef getPassName() const override { return "SI Fix SGPR copies"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineDominatorTree>();
AU.addPreserved<MachineDominatorTree>();
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // end anonymous namespace
INITIALIZE_PASS_BEGIN(SIFixSGPRCopies, DEBUG_TYPE,
"SI Fix SGPR copies", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_END(SIFixSGPRCopies, DEBUG_TYPE,
"SI Fix SGPR copies", false, false)
char SIFixSGPRCopies::ID = 0;
char &llvm::SIFixSGPRCopiesID = SIFixSGPRCopies::ID;
FunctionPass *llvm::createSIFixSGPRCopiesPass() {
return new SIFixSGPRCopies();
}
static bool hasVectorOperands(const MachineInstr &MI,
const SIRegisterInfo *TRI) {
const MachineRegisterInfo &MRI = MI.getParent()->getParent()->getRegInfo();
for (const MachineOperand &MO : MI.operands()) {
if (!MO.isReg() || !MO.getReg().isVirtual())
continue;
if (TRI->hasVectorRegisters(MRI.getRegClass(MO.getReg())))
return true;
}
return false;
}
static std::pair<const TargetRegisterClass *, const TargetRegisterClass *>
getCopyRegClasses(const MachineInstr &Copy,
const SIRegisterInfo &TRI,
const MachineRegisterInfo &MRI) {
Register DstReg = Copy.getOperand(0).getReg();
Register SrcReg = Copy.getOperand(1).getReg();
const TargetRegisterClass *SrcRC = SrcReg.isVirtual()
? MRI.getRegClass(SrcReg)
: TRI.getPhysRegClass(SrcReg);
// We don't really care about the subregister here.
// SrcRC = TRI.getSubRegClass(SrcRC, Copy.getOperand(1).getSubReg());
const TargetRegisterClass *DstRC = DstReg.isVirtual()
? MRI.getRegClass(DstReg)
: TRI.getPhysRegClass(DstReg);
return std::make_pair(SrcRC, DstRC);
}
static bool isVGPRToSGPRCopy(const TargetRegisterClass *SrcRC,
const TargetRegisterClass *DstRC,
const SIRegisterInfo &TRI) {
return SrcRC != &AMDGPU::VReg_1RegClass && TRI.isSGPRClass(DstRC) &&
TRI.hasVectorRegisters(SrcRC);
}
static bool isSGPRToVGPRCopy(const TargetRegisterClass *SrcRC,
const TargetRegisterClass *DstRC,
const SIRegisterInfo &TRI) {
return DstRC != &AMDGPU::VReg_1RegClass && TRI.isSGPRClass(SrcRC) &&
TRI.hasVectorRegisters(DstRC);
}
static bool tryChangeVGPRtoSGPRinCopy(MachineInstr &MI,
const SIRegisterInfo *TRI,
const SIInstrInfo *TII) {
MachineRegisterInfo &MRI = MI.getParent()->getParent()->getRegInfo();
auto &Src = MI.getOperand(1);
Register DstReg = MI.getOperand(0).getReg();
Register SrcReg = Src.getReg();
if (!SrcReg.isVirtual() || !DstReg.isVirtual())
return false;
for (const auto &MO : MRI.reg_nodbg_operands(DstReg)) {
const auto *UseMI = MO.getParent();
if (UseMI == &MI)
continue;
if (MO.isDef() || UseMI->getParent() != MI.getParent() ||
UseMI->getOpcode() <= TargetOpcode::GENERIC_OP_END)
return false;
unsigned OpIdx = UseMI->getOperandNo(&MO);
if (OpIdx >= UseMI->getDesc().getNumOperands() ||
!TII->isOperandLegal(*UseMI, OpIdx, &Src))
return false;
}
// Change VGPR to SGPR destination.
MRI.setRegClass(DstReg, TRI->getEquivalentSGPRClass(MRI.getRegClass(DstReg)));
return true;
}
// Distribute an SGPR->VGPR copy of a REG_SEQUENCE into a VGPR REG_SEQUENCE.
//
// SGPRx = ...
// SGPRy = REG_SEQUENCE SGPRx, sub0 ...
// VGPRz = COPY SGPRy
//
// ==>
//
// VGPRx = COPY SGPRx
// VGPRz = REG_SEQUENCE VGPRx, sub0
//
// This exposes immediate folding opportunities when materializing 64-bit
// immediates.
static bool foldVGPRCopyIntoRegSequence(MachineInstr &MI,
const SIRegisterInfo *TRI,
const SIInstrInfo *TII,
MachineRegisterInfo &MRI) {
assert(MI.isRegSequence());
Register DstReg = MI.getOperand(0).getReg();
if (!TRI->isSGPRClass(MRI.getRegClass(DstReg)))
return false;
if (!MRI.hasOneUse(DstReg))
return false;
MachineInstr &CopyUse = *MRI.use_instr_begin(DstReg);
if (!CopyUse.isCopy())
return false;
// It is illegal to have vreg inputs to a physreg defining reg_sequence.
if (CopyUse.getOperand(0).getReg().isPhysical())
return false;
const TargetRegisterClass *SrcRC, *DstRC;
std::tie(SrcRC, DstRC) = getCopyRegClasses(CopyUse, *TRI, MRI);
if (!isSGPRToVGPRCopy(SrcRC, DstRC, *TRI))
return false;
if (tryChangeVGPRtoSGPRinCopy(CopyUse, TRI, TII))
return true;
// TODO: Could have multiple extracts?
unsigned SubReg = CopyUse.getOperand(1).getSubReg();
if (SubReg != AMDGPU::NoSubRegister)
return false;
MRI.setRegClass(DstReg, DstRC);
// SGPRx = ...
// SGPRy = REG_SEQUENCE SGPRx, sub0 ...
// VGPRz = COPY SGPRy
// =>
// VGPRx = COPY SGPRx
// VGPRz = REG_SEQUENCE VGPRx, sub0
MI.getOperand(0).setReg(CopyUse.getOperand(0).getReg());
bool IsAGPR = TRI->isAGPRClass(DstRC);
for (unsigned I = 1, N = MI.getNumOperands(); I != N; I += 2) {
Register SrcReg = MI.getOperand(I).getReg();
unsigned SrcSubReg = MI.getOperand(I).getSubReg();
const TargetRegisterClass *SrcRC = MRI.getRegClass(SrcReg);
assert(TRI->isSGPRClass(SrcRC) &&
"Expected SGPR REG_SEQUENCE to only have SGPR inputs");
SrcRC = TRI->getSubRegClass(SrcRC, SrcSubReg);
const TargetRegisterClass *NewSrcRC = TRI->getEquivalentVGPRClass(SrcRC);
Register TmpReg = MRI.createVirtualRegister(NewSrcRC);
BuildMI(*MI.getParent(), &MI, MI.getDebugLoc(), TII->get(AMDGPU::COPY),
TmpReg)
.add(MI.getOperand(I));
if (IsAGPR) {
const TargetRegisterClass *NewSrcRC = TRI->getEquivalentAGPRClass(SrcRC);
Register TmpAReg = MRI.createVirtualRegister(NewSrcRC);
unsigned Opc = NewSrcRC == &AMDGPU::AGPR_32RegClass ?
AMDGPU::V_ACCVGPR_WRITE_B32_e64 : AMDGPU::COPY;
BuildMI(*MI.getParent(), &MI, MI.getDebugLoc(), TII->get(Opc),
TmpAReg)
.addReg(TmpReg, RegState::Kill);
TmpReg = TmpAReg;
}
MI.getOperand(I).setReg(TmpReg);
}
CopyUse.eraseFromParent();
return true;
}
static bool isSafeToFoldImmIntoCopy(const MachineInstr *Copy,
const MachineInstr *MoveImm,
const SIInstrInfo *TII,
unsigned &SMovOp,
int64_t &Imm) {
if (Copy->getOpcode() != AMDGPU::COPY)
return false;
if (!MoveImm->isMoveImmediate())
return false;
const MachineOperand *ImmOp =
TII->getNamedOperand(*MoveImm, AMDGPU::OpName::src0);
if (!ImmOp->isImm())
return false;
// FIXME: Handle copies with sub-regs.
if (Copy->getOperand(0).getSubReg())
return false;
switch (MoveImm->getOpcode()) {
default:
return false;
case AMDGPU::V_MOV_B32_e32:
SMovOp = AMDGPU::S_MOV_B32;
break;
case AMDGPU::V_MOV_B64_PSEUDO:
SMovOp = AMDGPU::S_MOV_B64;
break;
}
Imm = ImmOp->getImm();
return true;
}
template <class UnaryPredicate>
bool searchPredecessors(const MachineBasicBlock *MBB,
const MachineBasicBlock *CutOff,
UnaryPredicate Predicate) {
if (MBB == CutOff)
return false;
DenseSet<const MachineBasicBlock *> Visited;
SmallVector<MachineBasicBlock *, 4> Worklist(MBB->predecessors());
while (!Worklist.empty()) {
MachineBasicBlock *MBB = Worklist.pop_back_val();
if (!Visited.insert(MBB).second)
continue;
if (MBB == CutOff)
continue;
if (Predicate(MBB))
return true;
Worklist.append(MBB->pred_begin(), MBB->pred_end());
}
return false;
}
// Checks if there is potential path From instruction To instruction.
// If CutOff is specified and it sits in between of that path we ignore
// a higher portion of the path and report it is not reachable.
static bool isReachable(const MachineInstr *From,
const MachineInstr *To,
const MachineBasicBlock *CutOff,
MachineDominatorTree &MDT) {
if (MDT.dominates(From, To))
return true;
const MachineBasicBlock *MBBFrom = From->getParent();
const MachineBasicBlock *MBBTo = To->getParent();
// Do predecessor search.
// We should almost never get here since we do not usually produce M0 stores
// other than -1.
return searchPredecessors(MBBTo, CutOff, [MBBFrom]
(const MachineBasicBlock *MBB) { return MBB == MBBFrom; });
}
// Return the first non-prologue instruction in the block.
static MachineBasicBlock::iterator
getFirstNonPrologue(MachineBasicBlock *MBB, const TargetInstrInfo *TII) {
MachineBasicBlock::iterator I = MBB->getFirstNonPHI();
while (I != MBB->end() && TII->isBasicBlockPrologue(*I))
++I;
return I;
}
// Hoist and merge identical SGPR initializations into a common predecessor.
// This is intended to combine M0 initializations, but can work with any
// SGPR. A VGPR cannot be processed since we cannot guarantee vector
// executioon.
static bool hoistAndMergeSGPRInits(unsigned Reg,
const MachineRegisterInfo &MRI,
const TargetRegisterInfo *TRI,
MachineDominatorTree &MDT,
const TargetInstrInfo *TII) {
// List of inits by immediate value.
using InitListMap = std::map<unsigned, std::list<MachineInstr *>>;
InitListMap Inits;
// List of clobbering instructions.
SmallVector<MachineInstr*, 8> Clobbers;
// List of instructions marked for deletion.
SmallSet<MachineInstr*, 8> MergedInstrs;
bool Changed = false;
for (auto &MI : MRI.def_instructions(Reg)) {
MachineOperand *Imm = nullptr;
for (auto &MO : MI.operands()) {
if ((MO.isReg() && ((MO.isDef() && MO.getReg() != Reg) || !MO.isDef())) ||
(!MO.isImm() && !MO.isReg()) || (MO.isImm() && Imm)) {
Imm = nullptr;
break;
} else if (MO.isImm())
Imm = &MO;
}
if (Imm)
Inits[Imm->getImm()].push_front(&MI);
else
Clobbers.push_back(&MI);
}
for (auto &Init : Inits) {
auto &Defs = Init.second;
for (auto I1 = Defs.begin(), E = Defs.end(); I1 != E; ) {
MachineInstr *MI1 = *I1;
for (auto I2 = std::next(I1); I2 != E; ) {
MachineInstr *MI2 = *I2;
// Check any possible interference
auto interferes = [&](MachineBasicBlock::iterator From,
MachineBasicBlock::iterator To) -> bool {
assert(MDT.dominates(&*To, &*From));
auto interferes = [&MDT, From, To](MachineInstr* &Clobber) -> bool {
const MachineBasicBlock *MBBFrom = From->getParent();
const MachineBasicBlock *MBBTo = To->getParent();
bool MayClobberFrom = isReachable(Clobber, &*From, MBBTo, MDT);
bool MayClobberTo = isReachable(Clobber, &*To, MBBTo, MDT);
if (!MayClobberFrom && !MayClobberTo)
return false;
if ((MayClobberFrom && !MayClobberTo) ||
(!MayClobberFrom && MayClobberTo))
return true;
// Both can clobber, this is not an interference only if both are
// dominated by Clobber and belong to the same block or if Clobber
// properly dominates To, given that To >> From, so it dominates
// both and located in a common dominator.
return !((MBBFrom == MBBTo &&
MDT.dominates(Clobber, &*From) &&
MDT.dominates(Clobber, &*To)) ||
MDT.properlyDominates(Clobber->getParent(), MBBTo));
};
return (llvm::any_of(Clobbers, interferes)) ||
(llvm::any_of(Inits, [&](InitListMap::value_type &C) {
return C.first != Init.first &&
llvm::any_of(C.second, interferes);
}));
};
if (MDT.dominates(MI1, MI2)) {
if (!interferes(MI2, MI1)) {
LLVM_DEBUG(dbgs()
<< "Erasing from "
<< printMBBReference(*MI2->getParent()) << " " << *MI2);
MergedInstrs.insert(MI2);
Changed = true;
++I2;
continue;
}
} else if (MDT.dominates(MI2, MI1)) {
if (!interferes(MI1, MI2)) {
LLVM_DEBUG(dbgs()
<< "Erasing from "
<< printMBBReference(*MI1->getParent()) << " " << *MI1);
MergedInstrs.insert(MI1);
Changed = true;
++I1;
break;
}
} else {
auto *MBB = MDT.findNearestCommonDominator(MI1->getParent(),
MI2->getParent());
if (!MBB) {
++I2;
continue;
}
MachineBasicBlock::iterator I = getFirstNonPrologue(MBB, TII);
if (!interferes(MI1, I) && !interferes(MI2, I)) {
LLVM_DEBUG(dbgs()
<< "Erasing from "
<< printMBBReference(*MI1->getParent()) << " " << *MI1
<< "and moving from "
<< printMBBReference(*MI2->getParent()) << " to "
<< printMBBReference(*I->getParent()) << " " << *MI2);
I->getParent()->splice(I, MI2->getParent(), MI2);
MergedInstrs.insert(MI1);
Changed = true;
++I1;
break;
}
}
++I2;
}
++I1;
}
}
// Remove initializations that were merged into another.
for (auto &Init : Inits) {
auto &Defs = Init.second;
auto I = Defs.begin();
while (I != Defs.end()) {
if (MergedInstrs.count(*I)) {
(*I)->eraseFromParent();
I = Defs.erase(I);
} else
++I;
}
}
// Try to schedule SGPR initializations as early as possible in the MBB.
for (auto &Init : Inits) {
auto &Defs = Init.second;
for (auto MI : Defs) {
auto MBB = MI->getParent();
MachineInstr &BoundaryMI = *getFirstNonPrologue(MBB, TII);
MachineBasicBlock::reverse_iterator B(BoundaryMI);
// Check if B should actually be a boundary. If not set the previous
// instruction as the boundary instead.
if (!TII->isBasicBlockPrologue(*B))
B++;
auto R = std::next(MI->getReverseIterator());
const unsigned Threshold = 50;
// Search until B or Threshold for a place to insert the initialization.
for (unsigned I = 0; R != B && I < Threshold; ++R, ++I)
if (R->readsRegister(Reg, TRI) || R->definesRegister(Reg, TRI) ||
TII->isSchedulingBoundary(*R, MBB, *MBB->getParent()))
break;
// Move to directly after R.
if (&*--R != MI)
MBB->splice(*R, MBB, MI);
}
}
if (Changed)
MRI.clearKillFlags(Reg);
return Changed;
}
bool SIFixSGPRCopies::runOnMachineFunction(MachineFunction &MF) {
// Only need to run this in SelectionDAG path.
if (MF.getProperties().hasProperty(
MachineFunctionProperties::Property::Selected))
return false;
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
MRI = &MF.getRegInfo();
TRI = ST.getRegisterInfo();
TII = ST.getInstrInfo();
MDT = &getAnalysis<MachineDominatorTree>();
// We have to lower VGPR to SGPR copies before the main loop
// because the REG_SEQUENCE and PHI lowering in main loop
// convert the def-use chains to VALU and close the opportunities
// for keeping them scalar.
// TODO: REG_SEQENCE and PHIs are semantically copies. The next patch
// addresses their lowering and unify the processing in one main loop.
lowerVGPR2SGPRCopies(MF);
for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
BI != BE; ++BI) {
MachineBasicBlock *MBB = &*BI;
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
++I) {
MachineInstr &MI = *I;
switch (MI.getOpcode()) {
default:
continue;
case AMDGPU::COPY:
case AMDGPU::WQM:
case AMDGPU::STRICT_WQM:
case AMDGPU::SOFT_WQM:
case AMDGPU::STRICT_WWM: {
Register DstReg = MI.getOperand(0).getReg();
const TargetRegisterClass *SrcRC, *DstRC;
std::tie(SrcRC, DstRC) = getCopyRegClasses(MI, *TRI, *MRI);
if (MI.isCopy()) {
Register SrcReg = MI.getOperand(1).getReg();
if (SrcReg == AMDGPU::SCC) {
Register SCCCopy = MRI->createVirtualRegister(
TRI->getRegClass(AMDGPU::SReg_1_XEXECRegClassID));
I = BuildMI(*MI.getParent(),
std::next(MachineBasicBlock::iterator(MI)),
MI.getDebugLoc(),
TII->get(ST.isWave32() ? AMDGPU::S_CSELECT_B32
: AMDGPU::S_CSELECT_B64),
SCCCopy)
.addImm(-1)
.addImm(0);
I = BuildMI(*MI.getParent(), std::next(I), I->getDebugLoc(),
TII->get(AMDGPU::COPY), DstReg)
.addReg(SCCCopy);
MI.eraseFromParent();
continue;
} else if (DstReg == AMDGPU::SCC) {
unsigned Opcode =
ST.isWave64() ? AMDGPU::S_AND_B64 : AMDGPU::S_AND_B32;
Register Exec = ST.isWave64() ? AMDGPU::EXEC : AMDGPU::EXEC_LO;
Register Tmp = MRI->createVirtualRegister(TRI->getBoolRC());
I = BuildMI(*MI.getParent(),
std::next(MachineBasicBlock::iterator(MI)),
MI.getDebugLoc(), TII->get(Opcode))
.addReg(Tmp, getDefRegState(true))
.addReg(SrcReg)
.addReg(Exec);
MI.eraseFromParent();
continue;
}
}
if (!DstReg.isVirtual()) {
// If the destination register is a physical register there isn't
// really much we can do to fix this.
// Some special instructions use M0 as an input. Some even only use
// the first lane. Insert a readfirstlane and hope for the best.
if (DstReg == AMDGPU::M0 && TRI->hasVectorRegisters(SrcRC)) {
Register TmpReg
= MRI->createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass);
BuildMI(*MBB, MI, MI.getDebugLoc(),
TII->get(AMDGPU::V_READFIRSTLANE_B32), TmpReg)
.add(MI.getOperand(1));
MI.getOperand(1).setReg(TmpReg);
}
continue;
}
if (isSGPRToVGPRCopy(SrcRC, DstRC, *TRI)) {
tryChangeVGPRtoSGPRinCopy(MI, TRI, TII);
}
break;
}
case AMDGPU::PHI: {
MachineBasicBlock *NewBB = processPHINode(MI);
if (NewBB && NewBB != MBB) {
MBB = NewBB;
E = MBB->end();
BI = MachineFunction::iterator(MBB);
BE = MF.end();
}
assert((!NewBB || NewBB == I->getParent()) &&
"moveToVALU did not return the right basic block");
break;
}
case AMDGPU::REG_SEQUENCE: {
if (TRI->hasVectorRegisters(TII->getOpRegClass(MI, 0)) ||
!hasVectorOperands(MI, TRI)) {
foldVGPRCopyIntoRegSequence(MI, TRI, TII, *MRI);
continue;
}
LLVM_DEBUG(dbgs() << "Fixing REG_SEQUENCE: " << MI);
MachineBasicBlock *NewBB = TII->moveToVALU(MI, MDT);
if (NewBB && NewBB != MBB) {
MBB = NewBB;
E = MBB->end();
BI = MachineFunction::iterator(MBB);
BE = MF.end();
}
assert((!NewBB || NewBB == I->getParent()) &&
"moveToVALU did not return the right basic block");
break;
}
case AMDGPU::INSERT_SUBREG: {
const TargetRegisterClass *DstRC, *Src0RC, *Src1RC;
DstRC = MRI->getRegClass(MI.getOperand(0).getReg());
Src0RC = MRI->getRegClass(MI.getOperand(1).getReg());
Src1RC = MRI->getRegClass(MI.getOperand(2).getReg());
if (TRI->isSGPRClass(DstRC) &&
(TRI->hasVectorRegisters(Src0RC) ||
TRI->hasVectorRegisters(Src1RC))) {
LLVM_DEBUG(dbgs() << " Fixing INSERT_SUBREG: " << MI);
MachineBasicBlock *NewBB = TII->moveToVALU(MI, MDT);
if (NewBB && NewBB != MBB) {
MBB = NewBB;
E = MBB->end();
BI = MachineFunction::iterator(MBB);
BE = MF.end();
}
assert((!NewBB || NewBB == I->getParent()) &&
"moveToVALU did not return the right basic block");
}
break;
}
case AMDGPU::V_WRITELANE_B32: {
// Some architectures allow more than one constant bus access without
// SGPR restriction
if (ST.getConstantBusLimit(MI.getOpcode()) != 1)
break;
// Writelane is special in that it can use SGPR and M0 (which would
// normally count as using the constant bus twice - but in this case it
// is allowed since the lane selector doesn't count as a use of the
// constant bus). However, it is still required to abide by the 1 SGPR
// rule. Apply a fix here as we might have multiple SGPRs after
// legalizing VGPRs to SGPRs
int Src0Idx =
AMDGPU::getNamedOperandIdx(MI.getOpcode(), AMDGPU::OpName::src0);
int Src1Idx =
AMDGPU::getNamedOperandIdx(MI.getOpcode(), AMDGPU::OpName::src1);
MachineOperand &Src0 = MI.getOperand(Src0Idx);
MachineOperand &Src1 = MI.getOperand(Src1Idx);
// Check to see if the instruction violates the 1 SGPR rule
if ((Src0.isReg() && TRI->isSGPRReg(*MRI, Src0.getReg()) &&
Src0.getReg() != AMDGPU::M0) &&
(Src1.isReg() && TRI->isSGPRReg(*MRI, Src1.getReg()) &&
Src1.getReg() != AMDGPU::M0)) {
// Check for trivially easy constant prop into one of the operands
// If this is the case then perform the operation now to resolve SGPR
// issue. If we don't do that here we will always insert a mov to m0
// that can't be resolved in later operand folding pass
bool Resolved = false;
for (MachineOperand *MO : {&Src0, &Src1}) {
if (MO->getReg().isVirtual()) {
MachineInstr *DefMI = MRI->getVRegDef(MO->getReg());
if (DefMI && TII->isFoldableCopy(*DefMI)) {
const MachineOperand &Def = DefMI->getOperand(0);
if (Def.isReg() &&
MO->getReg() == Def.getReg() &&
MO->getSubReg() == Def.getSubReg()) {
const MachineOperand &Copied = DefMI->getOperand(1);
if (Copied.isImm() &&
TII->isInlineConstant(APInt(64, Copied.getImm(), true))) {
MO->ChangeToImmediate(Copied.getImm());
Resolved = true;
break;
}
}
}
}
}
if (!Resolved) {
// Haven't managed to resolve by replacing an SGPR with an immediate
// Move src1 to be in M0
BuildMI(*MI.getParent(), MI, MI.getDebugLoc(),
TII->get(AMDGPU::COPY), AMDGPU::M0)
.add(Src1);
Src1.ChangeToRegister(AMDGPU::M0, false);
}
}
break;
}
}
}
}
if (MF.getTarget().getOptLevel() > CodeGenOpt::None && EnableM0Merge)
hoistAndMergeSGPRInits(AMDGPU::M0, *MRI, TRI, *MDT, TII);
return true;
}
MachineBasicBlock *SIFixSGPRCopies::processPHINode(MachineInstr &MI) {
unsigned numVGPRUses = 0;
bool AllAGPRUses = true;
SetVector<const MachineInstr *> worklist;
SmallSet<const MachineInstr *, 4> Visited;
SetVector<MachineInstr *> PHIOperands;
MachineBasicBlock *CreatedBB = nullptr;
worklist.insert(&MI);
Visited.insert(&MI);
while (!worklist.empty()) {
const MachineInstr *Instr = worklist.pop_back_val();
Register Reg = Instr->getOperand(0).getReg();
for (const auto &Use : MRI->use_operands(Reg)) {
const MachineInstr *UseMI = Use.getParent();
AllAGPRUses &= (UseMI->isCopy() &&
TRI->isAGPR(*MRI, UseMI->getOperand(0).getReg())) ||
TRI->isAGPR(*MRI, Use.getReg());
if (UseMI->isCopy() || UseMI->isRegSequence()) {
if (UseMI->isCopy() &&
UseMI->getOperand(0).getReg().isPhysical() &&
!TRI->isSGPRReg(*MRI, UseMI->getOperand(0).getReg())) {
numVGPRUses++;
}
if (Visited.insert(UseMI).second)
worklist.insert(UseMI);
continue;
}
if (UseMI->isPHI()) {
const TargetRegisterClass *UseRC = MRI->getRegClass(Use.getReg());
if (!TRI->isSGPRReg(*MRI, Use.getReg()) &&
UseRC != &AMDGPU::VReg_1RegClass)
numVGPRUses++;
continue;
}
const TargetRegisterClass *OpRC =
TII->getOpRegClass(*UseMI, UseMI->getOperandNo(&Use));
if (!TRI->isSGPRClass(OpRC) && OpRC != &AMDGPU::VS_32RegClass &&
OpRC != &AMDGPU::VS_64RegClass) {
numVGPRUses++;
}
}
}
Register PHIRes = MI.getOperand(0).getReg();
const TargetRegisterClass *RC0 = MRI->getRegClass(PHIRes);
if (AllAGPRUses && numVGPRUses && !TRI->isAGPRClass(RC0)) {
LLVM_DEBUG(dbgs() << "Moving PHI to AGPR: " << MI);
MRI->setRegClass(PHIRes, TRI->getEquivalentAGPRClass(RC0));
for (unsigned I = 1, N = MI.getNumOperands(); I != N; I += 2) {
MachineInstr *DefMI = MRI->getVRegDef(MI.getOperand(I).getReg());
if (DefMI && DefMI->isPHI())
PHIOperands.insert(DefMI);
}
}
bool hasVGPRInput = false;
for (unsigned i = 1; i < MI.getNumOperands(); i += 2) {
Register InputReg = MI.getOperand(i).getReg();
MachineInstr *Def = MRI->getVRegDef(InputReg);
if (TRI->isVectorRegister(*MRI, InputReg)) {
if (Def->isCopy()) {
Register SrcReg = Def->getOperand(1).getReg();
const TargetRegisterClass *RC =
TRI->getRegClassForReg(*MRI, SrcReg);
if (TRI->isSGPRClass(RC))
continue;
}
hasVGPRInput = true;
break;
}
else if (Def->isCopy() &&
TRI->isVectorRegister(*MRI, Def->getOperand(1).getReg())) {
Register SrcReg = Def->getOperand(1).getReg();
MachineInstr *SrcDef = MRI->getVRegDef(SrcReg);
unsigned SMovOp;
int64_t Imm;
if (!isSafeToFoldImmIntoCopy(Def, SrcDef, TII, SMovOp, Imm)) {
hasVGPRInput = true;
break;
} else {
// Formally, if we did not do this right away
// it would be done on the next iteration of the
// runOnMachineFunction main loop. But why not if we can?
MachineFunction *MF = MI.getParent()->getParent();
Def->getOperand(1).ChangeToImmediate(Imm);
Def->addImplicitDefUseOperands(*MF);
Def->setDesc(TII->get(SMovOp));
}
}
}
if ((!TRI->isVectorRegister(*MRI, PHIRes) &&
RC0 != &AMDGPU::VReg_1RegClass) &&
(hasVGPRInput || numVGPRUses > 1)) {
LLVM_DEBUG(dbgs() << "Fixing PHI: " << MI);
CreatedBB = TII->moveToVALU(MI);
}
else {
LLVM_DEBUG(dbgs() << "Legalizing PHI: " << MI);
TII->legalizeOperands(MI, MDT);
}
// Propagate register class back to PHI operands which are PHI themselves.
while (!PHIOperands.empty()) {
processPHINode(*PHIOperands.pop_back_val());
}
return CreatedBB;
}
bool SIFixSGPRCopies::lowerSpecialCase(MachineInstr &MI) {
MachineBasicBlock *MBB = MI.getParent();
const TargetRegisterClass *SrcRC, *DstRC;
std::tie(SrcRC, DstRC) = getCopyRegClasses(MI, *TRI, *MRI);
// We return true to indicate that no further processing needed
if (!isVGPRToSGPRCopy(SrcRC, DstRC, *TRI))
return true;
Register SrcReg = MI.getOperand(1).getReg();
if (!SrcReg.isVirtual() || TRI->isAGPR(*MRI, SrcReg)) {
TII->moveToVALU(MI, MDT);
return true;
}
unsigned SMovOp;
int64_t Imm;
// If we are just copying an immediate, we can replace the copy with
// s_mov_b32.
if (isSafeToFoldImmIntoCopy(&MI, MRI->getVRegDef(SrcReg), TII, SMovOp, Imm)) {
MI.getOperand(1).ChangeToImmediate(Imm);
MI.addImplicitDefUseOperands(*MBB->getParent());
MI.setDesc(TII->get(SMovOp));
return true;
}
return false;
}
class V2SCopyInfo {
public:
// VGPR to SGPR copy being processed
MachineInstr *Copy;
// All SALU instructions reachable from this copy in SSA graph
DenseSet<MachineInstr *> SChain;
// Number of SGPR to VGPR copies that are used to put the SALU computation
// results back to VALU.
unsigned NumSVCopies;
unsigned Score;
// Actual count of v_readfirstlane_b32
// which need to be inserted to keep SChain SALU
unsigned NumReadfirstlanes;
// Current score state. To speedup selection V2SCopyInfos for processing
bool NeedToBeConvertedToVALU = false;
// Unique ID. Used as a key for mapping to keep permanent order.
unsigned ID;
// Count of another VGPR to SGPR copies that contribute to the
// current copy SChain
unsigned SiblingPenalty = 0;
SetVector<unsigned> Siblings;
V2SCopyInfo() : Copy(nullptr), ID(0){};
V2SCopyInfo(unsigned Id, MachineInstr *C, unsigned Width)
: Copy(C), NumSVCopies(0), NumReadfirstlanes(Width / 32), ID(Id){};
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void dump() {
dbgs() << ID << " : " << *Copy << "\n\tS:" << SChain.size()
<< "\n\tSV:" << NumSVCopies << "\n\tSP: " << SiblingPenalty
<< "\nScore: " << Score << "\n";
}
#endif
};
void SIFixSGPRCopies::lowerVGPR2SGPRCopies(MachineFunction &MF) {
DenseMap<unsigned, V2SCopyInfo> Copies;
DenseMap<MachineInstr *, SetVector<unsigned>> SiblingPenalty;
// The main function that computes the VGPR to SGPR copy score
// and determines copy further lowering way: v_readfirstlane_b32 or moveToVALU
auto needToBeConvertedToVALU = [&](V2SCopyInfo *I) -> bool {
if (I->SChain.empty())
return true;
I->Siblings = SiblingPenalty[*std::max_element(
I->SChain.begin(), I->SChain.end(),
[&](MachineInstr *A, MachineInstr *B) -> bool {
return SiblingPenalty[A].size() < SiblingPenalty[B].size();
})];
I->Siblings.remove_if([&](unsigned ID) { return ID == I->ID; });
// The loop below computes the number of another VGPR to SGPR copies
// which contribute to the current copy SALU chain. We assume that all the
// copies with the same source virtual register will be squashed to one by
// regalloc. Also we take careof the copies of the differnt subregs of the
// same register.
SmallSet<std::pair<Register, unsigned>, 4> SrcRegs;
for (auto J : I->Siblings) {
auto InfoIt = Copies.find(J);
if (InfoIt != Copies.end()) {
MachineInstr *SiblingCopy = InfoIt->getSecond().Copy;
if (SiblingCopy->isImplicitDef())
// the COPY has already been MoveToVALUed
continue;
SrcRegs.insert(std::make_pair(SiblingCopy->getOperand(1).getReg(),
SiblingCopy->getOperand(1).getSubReg()));
}
}
I->SiblingPenalty = SrcRegs.size();
unsigned Penalty =
I->NumSVCopies + I->SiblingPenalty + I->NumReadfirstlanes;
unsigned Profit = I->SChain.size();
I->Score = Penalty > Profit ? 0 : Profit - Penalty;
I->NeedToBeConvertedToVALU = I->Score < 3;
return I->NeedToBeConvertedToVALU;
};
auto needProcessing = [](MachineInstr &MI) -> bool {
switch (MI.getOpcode()) {
case AMDGPU::COPY:
case AMDGPU::WQM:
case AMDGPU::STRICT_WQM:
case AMDGPU::SOFT_WQM:
case AMDGPU::STRICT_WWM:
return true;
default:
return false;
}
};
for (MachineFunction::iterator BI = MF.begin(), BE = MF.end(); BI != BE;
++BI) {
MachineBasicBlock *MBB = &*BI;
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
++I) {
MachineInstr &MI = *I;
if (!needProcessing(MI))
continue;
if (lowerSpecialCase(MI))
continue;
// Compute the COPY width to pass it to V2SCopyInfo Ctor
Register DstReg = MI.getOperand(0).getReg();
const TargetRegisterClass *DstRC = TRI->getRegClassForReg(*MRI, DstReg);
V2SCopyInfo In(getNextVGPRToSGPRCopyId(), &MI,
TRI->getRegSizeInBits(*DstRC));
SmallVector<MachineInstr *, 8> AnalysisWorklist;
// Needed because the SSA is not a tree but a graph and may have
// forks and joins. We should not then go same way twice.
DenseSet<MachineInstr *> Visited;
AnalysisWorklist.push_back(&MI);
while (!AnalysisWorklist.empty()) {
MachineInstr *Inst = AnalysisWorklist.pop_back_val();
if (!Visited.insert(Inst).second)
continue;
// Copies and REG_SEQUENCE do not contribute to the final assembly
// So, skip them but take care of the SGPR to VGPR copies bookkeeping.
if (Inst->isCopy() || Inst->isRegSequence()) {
if (TRI->isVGPR(*MRI, Inst->getOperand(0).getReg())) {
if (!Inst->isCopy() ||
!tryChangeVGPRtoSGPRinCopy(*Inst, TRI, TII)) {
In.NumSVCopies++;
continue;
}
}
}
SiblingPenalty[Inst].insert(In.ID);
SmallVector<MachineInstr *, 4> Users;
if ((TII->isSALU(*Inst) && Inst->isCompare()) ||
(Inst->isCopy() && Inst->getOperand(0).getReg() == AMDGPU::SCC)) {
auto I = Inst->getIterator();
auto E = Inst->getParent()->end();
while (++I != E && !I->findRegisterDefOperand(AMDGPU::SCC)) {
if (I->readsRegister(AMDGPU::SCC))
Users.push_back(&*I);
}
} else if (Inst->getNumExplicitDefs() != 0) {
Register Reg = Inst->getOperand(0).getReg();
if (TRI->isSGPRReg(*MRI, Reg))
for (auto &U : MRI->use_instructions(Reg))
Users.push_back(&U);
}
for (auto U : Users) {
if (TII->isSALU(*U))
In.SChain.insert(U);
AnalysisWorklist.push_back(U);
}
}
Copies[In.ID] = In;
}
}
SmallVector<unsigned, 8> LoweringWorklist;
for (auto &C : Copies) {
if (needToBeConvertedToVALU(&C.second))
LoweringWorklist.push_back(C.second.ID);
}
while (!LoweringWorklist.empty()) {
unsigned CurID = LoweringWorklist.pop_back_val();
auto CurInfoIt = Copies.find(CurID);
if (CurInfoIt != Copies.end()) {
V2SCopyInfo C = CurInfoIt->getSecond();
LLVM_DEBUG(dbgs() << "Processing ...\n"; C.dump());
for (auto S : C.Siblings) {
auto SibInfoIt = Copies.find(S);
if (SibInfoIt != Copies.end()) {
V2SCopyInfo &SI = SibInfoIt->getSecond();
LLVM_DEBUG(dbgs() << "Sibling:\n"; SI.dump());
if (!SI.NeedToBeConvertedToVALU) {
set_subtract(SI.SChain, C.SChain);
if (needToBeConvertedToVALU(&SI))
LoweringWorklist.push_back(SI.ID);
}
SI.Siblings.remove_if([&](unsigned ID) { return ID == C.ID; });
}
}
LLVM_DEBUG(dbgs() << "V2S copy " << *C.Copy
<< " is being turned to VALU\n");
Copies.erase(C.ID);
TII->moveToVALU(*C.Copy, MDT);
}
}
// Now do actual lowering
for (auto C : Copies) {
MachineInstr *MI = C.second.Copy;
MachineBasicBlock *MBB = MI->getParent();
// We decide to turn V2S copy to v_readfirstlane_b32
// remove it from the V2SCopies and remove it from all its siblings
LLVM_DEBUG(dbgs() << "V2S copy " << *MI
<< " is being turned to v_readfirstlane_b32"
<< " Score: " << C.second.Score << "\n");
Register DstReg = MI->getOperand(0).getReg();
Register SrcReg = MI->getOperand(1).getReg();
unsigned SubReg = MI->getOperand(1).getSubReg();
const TargetRegisterClass *SrcRC = TRI->getRegClassForReg(*MRI, SrcReg);
SrcRC = TRI->getSubRegClass(SrcRC, SubReg);
size_t SrcSize = TRI->getRegSizeInBits(*SrcRC);
if (SrcSize == 16) {
// HACK to handle possible 16bit VGPR source
auto MIB = BuildMI(*MBB, MI, MI->getDebugLoc(),
TII->get(AMDGPU::V_READFIRSTLANE_B32), DstReg);
MIB.addReg(SrcReg, 0, AMDGPU::NoSubRegister);
} else if (SrcSize == 32) {
auto MIB = BuildMI(*MBB, MI, MI->getDebugLoc(),
TII->get(AMDGPU::V_READFIRSTLANE_B32), DstReg);
MIB.addReg(SrcReg, 0, SubReg);
} else {
auto Result = BuildMI(*MBB, MI, MI->getDebugLoc(),
TII->get(AMDGPU::REG_SEQUENCE), DstReg);
int N = TRI->getRegSizeInBits(*SrcRC) / 32;
for (int i = 0; i < N; i++) {
Register PartialSrc = TII->buildExtractSubReg(
Result, *MRI, MI->getOperand(1), SrcRC,
TRI->getSubRegFromChannel(i), &AMDGPU::VGPR_32RegClass);
Register PartialDst =
MRI->createVirtualRegister(&AMDGPU::SReg_32RegClass);
BuildMI(*MBB, *Result, Result->getDebugLoc(),
TII->get(AMDGPU::V_READFIRSTLANE_B32), PartialDst)
.addReg(PartialSrc);
Result.addReg(PartialDst).addImm(TRI->getSubRegFromChannel(i));
}
}
MI->eraseFromParent();
}
}
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