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

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//===-- SIWholeQuadMode.cpp - enter and suspend whole quad mode -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \file
/// \brief This pass adds instructions to enable whole quad mode for pixel
/// shaders, and whole wavefront mode for all programs.
///
/// Whole quad mode is required for derivative computations, but it interferes
/// with shader side effects (stores and atomics). This pass is run on the
/// scheduled machine IR but before register coalescing, so that machine SSA is
/// available for analysis. It ensures that WQM is enabled when necessary, but
/// disabled around stores and atomics.
///
/// When necessary, this pass creates a function prolog
///
/// S_MOV_B64 LiveMask, EXEC
/// S_WQM_B64 EXEC, EXEC
///
/// to enter WQM at the top of the function and surrounds blocks of Exact
/// instructions by
///
/// S_AND_SAVEEXEC_B64 Tmp, LiveMask
/// ...
/// S_MOV_B64 EXEC, Tmp
///
/// We also compute when a sequence of instructions requires Whole Wavefront
/// Mode (WWM) and insert instructions to save and restore it:
///
/// S_OR_SAVEEXEC_B64 Tmp, -1
/// ...
/// S_MOV_B64 EXEC, Tmp
///
/// In order to avoid excessive switching during sequences of Exact
/// instructions, the pass first analyzes which instructions must be run in WQM
/// (aka which instructions produce values that lead to derivative
/// computations).
///
/// Basic blocks are always exited in WQM as long as some successor needs WQM.
///
/// There is room for improvement given better control flow analysis:
///
/// (1) at the top level (outside of control flow statements, and as long as
/// kill hasn't been used), one SGPR can be saved by recovering WQM from
/// the LiveMask (this is implemented for the entry block).
///
/// (2) when entire regions (e.g. if-else blocks or entire loops) only
/// consist of exact and don't-care instructions, the switch only has to
/// be done at the entry and exit points rather than potentially in each
/// block of the region.
///
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "AMDGPUSubtarget.h"
#include "SIInstrInfo.h"
#include "SIMachineFunctionInfo.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervals.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/SlotIndexes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "si-wqm"
namespace {
enum {
StateWQM = 0x1,
StateWWM = 0x2,
StateExact = 0x4,
};
struct PrintState {
public:
int State;
explicit PrintState(int State) : State(State) {}
};
#ifndef NDEBUG
static raw_ostream &operator<<(raw_ostream &OS, const PrintState &PS) {
if (PS.State & StateWQM)
OS << "WQM";
if (PS.State & StateWWM) {
if (PS.State & StateWQM)
OS << '|';
OS << "WWM";
}
if (PS.State & StateExact) {
if (PS.State & (StateWQM | StateWWM))
OS << '|';
OS << "Exact";
}
return OS;
}
#endif
struct InstrInfo {
char Needs = 0;
char Disabled = 0;
char OutNeeds = 0;
};
struct BlockInfo {
char Needs = 0;
char InNeeds = 0;
char OutNeeds = 0;
};
struct WorkItem {
MachineBasicBlock *MBB = nullptr;
MachineInstr *MI = nullptr;
WorkItem() = default;
WorkItem(MachineBasicBlock *MBB) : MBB(MBB) {}
WorkItem(MachineInstr *MI) : MI(MI) {}
};
class SIWholeQuadMode : public MachineFunctionPass {
private:
CallingConv::ID CallingConv;
const SIInstrInfo *TII;
const SIRegisterInfo *TRI;
MachineRegisterInfo *MRI;
LiveIntervals *LIS;
DenseMap<const MachineInstr *, InstrInfo> Instructions;
DenseMap<MachineBasicBlock *, BlockInfo> Blocks;
SmallVector<MachineInstr *, 1> LiveMaskQueries;
SmallVector<MachineInstr *, 4> LowerToCopyInstrs;
void printInfo();
void markInstruction(MachineInstr &MI, char Flag,
std::vector<WorkItem> &Worklist);
void markInstructionUses(const MachineInstr &MI, char Flag,
std::vector<WorkItem> &Worklist);
char scanInstructions(MachineFunction &MF, std::vector<WorkItem> &Worklist);
void propagateInstruction(MachineInstr &MI, std::vector<WorkItem> &Worklist);
void propagateBlock(MachineBasicBlock &MBB, std::vector<WorkItem> &Worklist);
char analyzeFunction(MachineFunction &MF);
bool requiresCorrectState(const MachineInstr &MI) const;
MachineBasicBlock::iterator saveSCC(MachineBasicBlock &MBB,
MachineBasicBlock::iterator Before);
MachineBasicBlock::iterator
prepareInsertion(MachineBasicBlock &MBB, MachineBasicBlock::iterator First,
MachineBasicBlock::iterator Last, bool PreferLast,
bool SaveSCC);
void toExact(MachineBasicBlock &MBB, MachineBasicBlock::iterator Before,
unsigned SaveWQM, unsigned LiveMaskReg);
void toWQM(MachineBasicBlock &MBB, MachineBasicBlock::iterator Before,
unsigned SavedWQM);
void toWWM(MachineBasicBlock &MBB, MachineBasicBlock::iterator Before,
unsigned SaveOrig);
void fromWWM(MachineBasicBlock &MBB, MachineBasicBlock::iterator Before,
unsigned SavedOrig);
void processBlock(MachineBasicBlock &MBB, unsigned LiveMaskReg, bool isEntry);
void lowerLiveMaskQueries(unsigned LiveMaskReg);
void lowerCopyInstrs();
public:
static char ID;
SIWholeQuadMode() :
MachineFunctionPass(ID) { }
bool runOnMachineFunction(MachineFunction &MF) override;
StringRef getPassName() const override { return "SI Whole Quad Mode"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LiveIntervals>();
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // end anonymous namespace
char SIWholeQuadMode::ID = 0;
INITIALIZE_PASS_BEGIN(SIWholeQuadMode, DEBUG_TYPE, "SI Whole Quad Mode", false,
false)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_END(SIWholeQuadMode, DEBUG_TYPE, "SI Whole Quad Mode", false,
false)
char &llvm::SIWholeQuadModeID = SIWholeQuadMode::ID;
FunctionPass *llvm::createSIWholeQuadModePass() {
return new SIWholeQuadMode;
}
#ifndef NDEBUG
LLVM_DUMP_METHOD void SIWholeQuadMode::printInfo() {
for (const auto &BII : Blocks) {
dbgs() << "\n"
<< printMBBReference(*BII.first) << ":\n"
<< " InNeeds = " << PrintState(BII.second.InNeeds)
<< ", Needs = " << PrintState(BII.second.Needs)
<< ", OutNeeds = " << PrintState(BII.second.OutNeeds) << "\n\n";
for (const MachineInstr &MI : *BII.first) {
auto III = Instructions.find(&MI);
if (III == Instructions.end())
continue;
dbgs() << " " << MI << " Needs = " << PrintState(III->second.Needs)
<< ", OutNeeds = " << PrintState(III->second.OutNeeds) << '\n';
}
}
}
#endif
void SIWholeQuadMode::markInstruction(MachineInstr &MI, char Flag,
std::vector<WorkItem> &Worklist) {
InstrInfo &II = Instructions[&MI];
assert(!(Flag & StateExact) && Flag != 0);
// Remove any disabled states from the flag. The user that required it gets
// an undefined value in the helper lanes. For example, this can happen if
// the result of an atomic is used by instruction that requires WQM, where
// ignoring the request for WQM is correct as per the relevant specs.
Flag &= ~II.Disabled;
// Ignore if the flag is already encompassed by the existing needs, or we
// just disabled everything.
if ((II.Needs & Flag) == Flag)
return;
II.Needs |= Flag;
Worklist.push_back(&MI);
}
/// Mark all instructions defining the uses in \p MI with \p Flag.
void SIWholeQuadMode::markInstructionUses(const MachineInstr &MI, char Flag,
std::vector<WorkItem> &Worklist) {
for (const MachineOperand &Use : MI.uses()) {
if (!Use.isReg() || !Use.isUse())
continue;
unsigned Reg = Use.getReg();
// Handle physical registers that we need to track; this is mostly relevant
// for VCC, which can appear as the (implicit) input of a uniform branch,
// e.g. when a loop counter is stored in a VGPR.
if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
if (Reg == AMDGPU::EXEC)
continue;
for (MCRegUnitIterator RegUnit(Reg, TRI); RegUnit.isValid(); ++RegUnit) {
LiveRange &LR = LIS->getRegUnit(*RegUnit);
const VNInfo *Value = LR.Query(LIS->getInstructionIndex(MI)).valueIn();
if (!Value)
continue;
// Since we're in machine SSA, we do not need to track physical
// registers across basic blocks.
if (Value->isPHIDef())
continue;
markInstruction(*LIS->getInstructionFromIndex(Value->def), Flag,
Worklist);
}
continue;
}
for (MachineInstr &DefMI : MRI->def_instructions(Use.getReg()))
markInstruction(DefMI, Flag, Worklist);
}
}
// Scan instructions to determine which ones require an Exact execmask and
// which ones seed WQM requirements.
char SIWholeQuadMode::scanInstructions(MachineFunction &MF,
std::vector<WorkItem> &Worklist) {
char GlobalFlags = 0;
bool WQMOutputs = MF.getFunction().hasFnAttribute("amdgpu-ps-wqm-outputs");
SmallVector<MachineInstr *, 4> SetInactiveInstrs;
// We need to visit the basic blocks in reverse post-order so that we visit
// defs before uses, in particular so that we don't accidentally mark an
// instruction as needing e.g. WQM before visiting it and realizing it needs
// WQM disabled.
ReversePostOrderTraversal<MachineFunction *> RPOT(&MF);
for (auto BI = RPOT.begin(), BE = RPOT.end(); BI != BE; ++BI) {
MachineBasicBlock &MBB = **BI;
BlockInfo &BBI = Blocks[&MBB];
for (auto II = MBB.begin(), IE = MBB.end(); II != IE; ++II) {
MachineInstr &MI = *II;
InstrInfo &III = Instructions[&MI];
unsigned Opcode = MI.getOpcode();
char Flags = 0;
if (TII->isDS(Opcode) && CallingConv == CallingConv::AMDGPU_PS) {
Flags = StateWQM;
} else if (TII->isWQM(Opcode)) {
// Sampling instructions don't need to produce results for all pixels
// in a quad, they just require all inputs of a quad to have been
// computed for derivatives.
markInstructionUses(MI, StateWQM, Worklist);
GlobalFlags |= StateWQM;
continue;
} else if (Opcode == AMDGPU::WQM) {
// The WQM intrinsic requires its output to have all the helper lanes
// correct, so we need it to be in WQM.
Flags = StateWQM;
LowerToCopyInstrs.push_back(&MI);
} else if (Opcode == AMDGPU::WWM) {
// The WWM intrinsic doesn't make the same guarantee, and plus it needs
// to be executed in WQM or Exact so that its copy doesn't clobber
// inactive lanes.
markInstructionUses(MI, StateWWM, Worklist);
GlobalFlags |= StateWWM;
LowerToCopyInstrs.push_back(&MI);
continue;
} else if (Opcode == AMDGPU::V_SET_INACTIVE_B32 ||
Opcode == AMDGPU::V_SET_INACTIVE_B64) {
III.Disabled = StateWWM;
MachineOperand &Inactive = MI.getOperand(2);
if (Inactive.isReg()) {
if (Inactive.isUndef()) {
LowerToCopyInstrs.push_back(&MI);
} else {
unsigned Reg = Inactive.getReg();
if (TargetRegisterInfo::isVirtualRegister(Reg)) {
for (MachineInstr &DefMI : MRI->def_instructions(Reg))
markInstruction(DefMI, StateWWM, Worklist);
}
}
}
SetInactiveInstrs.push_back(&MI);
continue;
} else if (TII->isDisableWQM(MI)) {
BBI.Needs |= StateExact;
if (!(BBI.InNeeds & StateExact)) {
BBI.InNeeds |= StateExact;
Worklist.push_back(&MBB);
}
GlobalFlags |= StateExact;
III.Disabled = StateWQM | StateWWM;
continue;
} else {
if (Opcode == AMDGPU::SI_PS_LIVE) {
LiveMaskQueries.push_back(&MI);
} else if (WQMOutputs) {
// The function is in machine SSA form, which means that physical
// VGPRs correspond to shader inputs and outputs. Inputs are
// only used, outputs are only defined.
for (const MachineOperand &MO : MI.defs()) {
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (!TRI->isVirtualRegister(Reg) &&
TRI->hasVGPRs(TRI->getPhysRegClass(Reg))) {
Flags = StateWQM;
break;
}
}
}
if (!Flags)
continue;
}
markInstruction(MI, Flags, Worklist);
GlobalFlags |= Flags;
}
}
// Mark sure that any SET_INACTIVE instructions are computed in WQM if WQM is
// ever used anywhere in the function. This implements the corresponding
// semantics of @llvm.amdgcn.set.inactive.
if (GlobalFlags & StateWQM) {
for (MachineInstr *MI : SetInactiveInstrs)
markInstruction(*MI, StateWQM, Worklist);
}
return GlobalFlags;
}
void SIWholeQuadMode::propagateInstruction(MachineInstr &MI,
std::vector<WorkItem>& Worklist) {
MachineBasicBlock *MBB = MI.getParent();
InstrInfo II = Instructions[&MI]; // take a copy to prevent dangling references
BlockInfo &BI = Blocks[MBB];
// Control flow-type instructions and stores to temporary memory that are
// followed by WQM computations must themselves be in WQM.
if ((II.OutNeeds & StateWQM) && !(II.Disabled & StateWQM) &&
(MI.isTerminator() || (TII->usesVM_CNT(MI) && MI.mayStore()))) {
Instructions[&MI].Needs = StateWQM;
II.Needs = StateWQM;
}
// Propagate to block level
if (II.Needs & StateWQM) {
BI.Needs |= StateWQM;
if (!(BI.InNeeds & StateWQM)) {
BI.InNeeds |= StateWQM;
Worklist.push_back(MBB);
}
}
// Propagate backwards within block
if (MachineInstr *PrevMI = MI.getPrevNode()) {
char InNeeds = (II.Needs & ~StateWWM) | II.OutNeeds;
if (!PrevMI->isPHI()) {
InstrInfo &PrevII = Instructions[PrevMI];
if ((PrevII.OutNeeds | InNeeds) != PrevII.OutNeeds) {
PrevII.OutNeeds |= InNeeds;
Worklist.push_back(PrevMI);
}
}
}
// Propagate WQM flag to instruction inputs
assert(!(II.Needs & StateExact));
if (II.Needs != 0)
markInstructionUses(MI, II.Needs, Worklist);
}
void SIWholeQuadMode::propagateBlock(MachineBasicBlock &MBB,
std::vector<WorkItem>& Worklist) {
BlockInfo BI = Blocks[&MBB]; // Make a copy to prevent dangling references.
// Propagate through instructions
if (!MBB.empty()) {
MachineInstr *LastMI = &*MBB.rbegin();
InstrInfo &LastII = Instructions[LastMI];
if ((LastII.OutNeeds | BI.OutNeeds) != LastII.OutNeeds) {
LastII.OutNeeds |= BI.OutNeeds;
Worklist.push_back(LastMI);
}
}
// Predecessor blocks must provide for our WQM/Exact needs.
for (MachineBasicBlock *Pred : MBB.predecessors()) {
BlockInfo &PredBI = Blocks[Pred];
if ((PredBI.OutNeeds | BI.InNeeds) == PredBI.OutNeeds)
continue;
PredBI.OutNeeds |= BI.InNeeds;
PredBI.InNeeds |= BI.InNeeds;
Worklist.push_back(Pred);
}
// All successors must be prepared to accept the same set of WQM/Exact data.
for (MachineBasicBlock *Succ : MBB.successors()) {
BlockInfo &SuccBI = Blocks[Succ];
if ((SuccBI.InNeeds | BI.OutNeeds) == SuccBI.InNeeds)
continue;
SuccBI.InNeeds |= BI.OutNeeds;
Worklist.push_back(Succ);
}
}
char SIWholeQuadMode::analyzeFunction(MachineFunction &MF) {
std::vector<WorkItem> Worklist;
char GlobalFlags = scanInstructions(MF, Worklist);
while (!Worklist.empty()) {
WorkItem WI = Worklist.back();
Worklist.pop_back();
if (WI.MI)
propagateInstruction(*WI.MI, Worklist);
else
propagateBlock(*WI.MBB, Worklist);
}
return GlobalFlags;
}
/// Whether \p MI really requires the exec state computed during analysis.
///
/// Scalar instructions must occasionally be marked WQM for correct propagation
/// (e.g. thread masks leading up to branches), but when it comes to actual
/// execution, they don't care about EXEC.
bool SIWholeQuadMode::requiresCorrectState(const MachineInstr &MI) const {
if (MI.isTerminator())
return true;
// Skip instructions that are not affected by EXEC
if (TII->isScalarUnit(MI))
return false;
// Generic instructions such as COPY will either disappear by register
// coalescing or be lowered to SALU or VALU instructions.
if (MI.isTransient()) {
if (MI.getNumExplicitOperands() >= 1) {
const MachineOperand &Op = MI.getOperand(0);
if (Op.isReg()) {
if (TRI->isSGPRReg(*MRI, Op.getReg())) {
// SGPR instructions are not affected by EXEC
return false;
}
}
}
}
return true;
}
MachineBasicBlock::iterator
SIWholeQuadMode::saveSCC(MachineBasicBlock &MBB,
MachineBasicBlock::iterator Before) {
unsigned SaveReg = MRI->createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass);
MachineInstr *Save =
BuildMI(MBB, Before, DebugLoc(), TII->get(AMDGPU::COPY), SaveReg)
.addReg(AMDGPU::SCC);
MachineInstr *Restore =
BuildMI(MBB, Before, DebugLoc(), TII->get(AMDGPU::COPY), AMDGPU::SCC)
.addReg(SaveReg);
LIS->InsertMachineInstrInMaps(*Save);
LIS->InsertMachineInstrInMaps(*Restore);
LIS->createAndComputeVirtRegInterval(SaveReg);
return Restore;
}
// Return an iterator in the (inclusive) range [First, Last] at which
// instructions can be safely inserted, keeping in mind that some of the
// instructions we want to add necessarily clobber SCC.
MachineBasicBlock::iterator SIWholeQuadMode::prepareInsertion(
MachineBasicBlock &MBB, MachineBasicBlock::iterator First,
MachineBasicBlock::iterator Last, bool PreferLast, bool SaveSCC) {
if (!SaveSCC)
return PreferLast ? Last : First;
LiveRange &LR = LIS->getRegUnit(*MCRegUnitIterator(AMDGPU::SCC, TRI));
auto MBBE = MBB.end();
SlotIndex FirstIdx = First != MBBE ? LIS->getInstructionIndex(*First)
: LIS->getMBBEndIdx(&MBB);
SlotIndex LastIdx =
Last != MBBE ? LIS->getInstructionIndex(*Last) : LIS->getMBBEndIdx(&MBB);
SlotIndex Idx = PreferLast ? LastIdx : FirstIdx;
const LiveRange::Segment *S;
for (;;) {
S = LR.getSegmentContaining(Idx);
if (!S)
break;
if (PreferLast) {
SlotIndex Next = S->start.getBaseIndex();
if (Next < FirstIdx)
break;
Idx = Next;
} else {
SlotIndex Next = S->end.getNextIndex().getBaseIndex();
if (Next > LastIdx)
break;
Idx = Next;
}
}
MachineBasicBlock::iterator MBBI;
if (MachineInstr *MI = LIS->getInstructionFromIndex(Idx))
MBBI = MI;
else {
assert(Idx == LIS->getMBBEndIdx(&MBB));
MBBI = MBB.end();
}
if (S)
MBBI = saveSCC(MBB, MBBI);
return MBBI;
}
void SIWholeQuadMode::toExact(MachineBasicBlock &MBB,
MachineBasicBlock::iterator Before,
unsigned SaveWQM, unsigned LiveMaskReg) {
MachineInstr *MI;
if (SaveWQM) {
MI = BuildMI(MBB, Before, DebugLoc(), TII->get(AMDGPU::S_AND_SAVEEXEC_B64),
SaveWQM)
.addReg(LiveMaskReg);
} else {
MI = BuildMI(MBB, Before, DebugLoc(), TII->get(AMDGPU::S_AND_B64),
AMDGPU::EXEC)
.addReg(AMDGPU::EXEC)
.addReg(LiveMaskReg);
}
LIS->InsertMachineInstrInMaps(*MI);
}
void SIWholeQuadMode::toWQM(MachineBasicBlock &MBB,
MachineBasicBlock::iterator Before,
unsigned SavedWQM) {
MachineInstr *MI;
if (SavedWQM) {
MI = BuildMI(MBB, Before, DebugLoc(), TII->get(AMDGPU::COPY), AMDGPU::EXEC)
.addReg(SavedWQM);
} else {
MI = BuildMI(MBB, Before, DebugLoc(), TII->get(AMDGPU::S_WQM_B64),
AMDGPU::EXEC)
.addReg(AMDGPU::EXEC);
}
LIS->InsertMachineInstrInMaps(*MI);
}
void SIWholeQuadMode::toWWM(MachineBasicBlock &MBB,
MachineBasicBlock::iterator Before,
unsigned SaveOrig) {
MachineInstr *MI;
assert(SaveOrig);
MI = BuildMI(MBB, Before, DebugLoc(), TII->get(AMDGPU::S_OR_SAVEEXEC_B64),
SaveOrig)
.addImm(-1);
LIS->InsertMachineInstrInMaps(*MI);
}
void SIWholeQuadMode::fromWWM(MachineBasicBlock &MBB,
MachineBasicBlock::iterator Before,
unsigned SavedOrig) {
MachineInstr *MI;
assert(SavedOrig);
MI = BuildMI(MBB, Before, DebugLoc(), TII->get(AMDGPU::EXIT_WWM), AMDGPU::EXEC)
.addReg(SavedOrig);
LIS->InsertMachineInstrInMaps(*MI);
}
void SIWholeQuadMode::processBlock(MachineBasicBlock &MBB, unsigned LiveMaskReg,
bool isEntry) {
auto BII = Blocks.find(&MBB);
if (BII == Blocks.end())
return;
const BlockInfo &BI = BII->second;
// This is a non-entry block that is WQM throughout, so no need to do
// anything.
if (!isEntry && BI.Needs == StateWQM && BI.OutNeeds != StateExact)
return;
DEBUG(dbgs() << "\nProcessing block " << printMBBReference(MBB) << ":\n");
unsigned SavedWQMReg = 0;
unsigned SavedNonWWMReg = 0;
bool WQMFromExec = isEntry;
char State = (isEntry || !(BI.InNeeds & StateWQM)) ? StateExact : StateWQM;
char NonWWMState = 0;
auto II = MBB.getFirstNonPHI(), IE = MBB.end();
if (isEntry)
++II; // Skip the instruction that saves LiveMask
// This stores the first instruction where it's safe to switch from WQM to
// Exact or vice versa.
MachineBasicBlock::iterator FirstWQM = IE;
// This stores the first instruction where it's safe to switch from WWM to
// Exact/WQM or to switch to WWM. It must always be the same as, or after,
// FirstWQM since if it's safe to switch to/from WWM, it must be safe to
// switch to/from WQM as well.
MachineBasicBlock::iterator FirstWWM = IE;
for (;;) {
MachineBasicBlock::iterator Next = II;
char Needs = StateExact | StateWQM; // WWM is disabled by default
char OutNeeds = 0;
if (FirstWQM == IE)
FirstWQM = II;
if (FirstWWM == IE)
FirstWWM = II;
// First, figure out the allowed states (Needs) based on the propagated
// flags.
if (II != IE) {
MachineInstr &MI = *II;
if (requiresCorrectState(MI)) {
auto III = Instructions.find(&MI);
if (III != Instructions.end()) {
if (III->second.Needs & StateWWM)
Needs = StateWWM;
else if (III->second.Needs & StateWQM)
Needs = StateWQM;
else
Needs &= ~III->second.Disabled;
OutNeeds = III->second.OutNeeds;
}
} else {
// If the instruction doesn't actually need a correct EXEC, then we can
// safely leave WWM enabled.
Needs = StateExact | StateWQM | StateWWM;
}
if (MI.isTerminator() && OutNeeds == StateExact)
Needs = StateExact;
if (MI.getOpcode() == AMDGPU::SI_ELSE && BI.OutNeeds == StateExact)
MI.getOperand(3).setImm(1);
++Next;
} else {
// End of basic block
if (BI.OutNeeds & StateWQM)
Needs = StateWQM;
else if (BI.OutNeeds == StateExact)
Needs = StateExact;
else
Needs = StateWQM | StateExact;
}
// Now, transition if necessary.
if (!(Needs & State)) {
MachineBasicBlock::iterator First;
if (State == StateWWM || Needs == StateWWM) {
// We must switch to or from WWM
First = FirstWWM;
} else {
// We only need to switch to/from WQM, so we can use FirstWQM
First = FirstWQM;
}
MachineBasicBlock::iterator Before =
prepareInsertion(MBB, First, II, Needs == StateWQM,
Needs == StateExact || WQMFromExec);
if (State == StateWWM) {
assert(SavedNonWWMReg);
fromWWM(MBB, Before, SavedNonWWMReg);
State = NonWWMState;
}
if (Needs == StateWWM) {
NonWWMState = State;
SavedNonWWMReg = MRI->createVirtualRegister(&AMDGPU::SReg_64RegClass);
toWWM(MBB, Before, SavedNonWWMReg);
State = StateWWM;
} else {
if (State == StateWQM && (Needs & StateExact) && !(Needs & StateWQM)) {
if (!WQMFromExec && (OutNeeds & StateWQM))
SavedWQMReg = MRI->createVirtualRegister(&AMDGPU::SReg_64RegClass);
toExact(MBB, Before, SavedWQMReg, LiveMaskReg);
State = StateExact;
} else if (State == StateExact && (Needs & StateWQM) &&
!(Needs & StateExact)) {
assert(WQMFromExec == (SavedWQMReg == 0));
toWQM(MBB, Before, SavedWQMReg);
if (SavedWQMReg) {
LIS->createAndComputeVirtRegInterval(SavedWQMReg);
SavedWQMReg = 0;
}
State = StateWQM;
} else {
// We can get here if we transitioned from WWM to a non-WWM state that
// already matches our needs, but we shouldn't need to do anything.
assert(Needs & State);
}
}
}
if (Needs != (StateExact | StateWQM | StateWWM)) {
if (Needs != (StateExact | StateWQM))
FirstWQM = IE;
FirstWWM = IE;
}
if (II == IE)
break;
II = Next;
}
}
void SIWholeQuadMode::lowerLiveMaskQueries(unsigned LiveMaskReg) {
for (MachineInstr *MI : LiveMaskQueries) {
const DebugLoc &DL = MI->getDebugLoc();
unsigned Dest = MI->getOperand(0).getReg();
MachineInstr *Copy =
BuildMI(*MI->getParent(), MI, DL, TII->get(AMDGPU::COPY), Dest)
.addReg(LiveMaskReg);
LIS->ReplaceMachineInstrInMaps(*MI, *Copy);
MI->eraseFromParent();
}
}
void SIWholeQuadMode::lowerCopyInstrs() {
for (MachineInstr *MI : LowerToCopyInstrs) {
for (unsigned i = MI->getNumExplicitOperands() - 1; i > 1; i--)
MI->RemoveOperand(i);
MI->setDesc(TII->get(AMDGPU::COPY));
}
}
bool SIWholeQuadMode::runOnMachineFunction(MachineFunction &MF) {
Instructions.clear();
Blocks.clear();
LiveMaskQueries.clear();
LowerToCopyInstrs.clear();
CallingConv = MF.getFunction().getCallingConv();
const SISubtarget &ST = MF.getSubtarget<SISubtarget>();
TII = ST.getInstrInfo();
TRI = &TII->getRegisterInfo();
MRI = &MF.getRegInfo();
LIS = &getAnalysis<LiveIntervals>();
char GlobalFlags = analyzeFunction(MF);
unsigned LiveMaskReg = 0;
if (!(GlobalFlags & StateWQM)) {
lowerLiveMaskQueries(AMDGPU::EXEC);
if (!(GlobalFlags & StateWWM))
return !LiveMaskQueries.empty();
} else {
// Store a copy of the original live mask when required
MachineBasicBlock &Entry = MF.front();
MachineBasicBlock::iterator EntryMI = Entry.getFirstNonPHI();
if (GlobalFlags & StateExact || !LiveMaskQueries.empty()) {
LiveMaskReg = MRI->createVirtualRegister(&AMDGPU::SReg_64RegClass);
MachineInstr *MI = BuildMI(Entry, EntryMI, DebugLoc(),
TII->get(AMDGPU::COPY), LiveMaskReg)
.addReg(AMDGPU::EXEC);
LIS->InsertMachineInstrInMaps(*MI);
}
lowerLiveMaskQueries(LiveMaskReg);
if (GlobalFlags == StateWQM) {
// For a shader that needs only WQM, we can just set it once.
BuildMI(Entry, EntryMI, DebugLoc(), TII->get(AMDGPU::S_WQM_B64),
AMDGPU::EXEC)
.addReg(AMDGPU::EXEC);
lowerCopyInstrs();
// EntryMI may become invalid here
return true;
}
}
DEBUG(printInfo());
lowerCopyInstrs();
// Handle the general case
for (auto BII : Blocks)
processBlock(*BII.first, LiveMaskReg, BII.first == &*MF.begin());
// Physical registers like SCC aren't tracked by default anyway, so just
// removing the ranges we computed is the simplest option for maintaining
// the analysis results.
LIS->removeRegUnit(*MCRegUnitIterator(AMDGPU::SCC, TRI));
return true;
}
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