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llvm-project/llvm/lib/Target/AMDGPU/SILowerI1Copies.cpp

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//===-- SILowerI1Copies.cpp - Lower I1 Copies -----------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass lowers all occurrences of i1 values (with a vreg_1 register class)
// to lane masks (64-bit scalar registers). The pass assumes machine SSA form
// and a wave-level control flow graph.
//
// Before this pass, values that are semantically i1 and are defined and used
// within the same basic block are already represented as lane masks in scalar
// registers. However, values that cross basic blocks are always transferred
// between basic blocks in vreg_1 virtual registers and are lowered by this
// pass.
//
// The only instructions that use or define vreg_1 virtual registers are COPY,
// PHI, and IMPLICIT_DEF.
//
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "AMDGPUSubtarget.h"
#include "MCTargetDesc/AMDGPUMCTargetDesc.h"
#include "SIInstrInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachinePostDominators.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/MachineSSAUpdater.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetMachine.h"
#define DEBUG_TYPE "si-i1-copies"
using namespace llvm;
static unsigned createLaneMaskReg(MachineFunction &MF);
static unsigned insertUndefLaneMask(MachineBasicBlock &MBB);
namespace {
class SILowerI1Copies : public MachineFunctionPass {
public:
static char ID;
private:
MachineFunction *MF = nullptr;
MachineDominatorTree *DT = nullptr;
MachinePostDominatorTree *PDT = nullptr;
MachineRegisterInfo *MRI = nullptr;
const GCNSubtarget *ST = nullptr;
const SIInstrInfo *TII = nullptr;
DenseSet<unsigned> ConstrainRegs;
public:
SILowerI1Copies() : MachineFunctionPass(ID) {
initializeSILowerI1CopiesPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
StringRef getPassName() const override { return "SI Lower i1 Copies"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<MachineDominatorTree>();
AU.addRequired<MachinePostDominatorTree>();
MachineFunctionPass::getAnalysisUsage(AU);
}
private:
void lowerCopiesFromI1();
void lowerPhis();
void lowerCopiesToI1();
bool isConstantLaneMask(unsigned Reg, bool &Val) const;
void buildMergeLaneMasks(MachineBasicBlock &MBB,
MachineBasicBlock::iterator I, const DebugLoc &DL,
unsigned DstReg, unsigned PrevReg, unsigned CurReg);
MachineBasicBlock::iterator
getSaluInsertionAtEnd(MachineBasicBlock &MBB) const;
bool isLaneMaskReg(unsigned Reg) const {
return TII->getRegisterInfo().isSGPRReg(*MRI, Reg) &&
TII->getRegisterInfo().getRegSizeInBits(Reg, *MRI) ==
ST->getWavefrontSize();
}
};
/// Helper class that determines the relationship between incoming values of a
/// phi in the control flow graph to determine where an incoming value can
/// simply be taken as a scalar lane mask as-is, and where it needs to be
/// merged with another, previously defined lane mask.
///
/// The approach is as follows:
/// - Determine all basic blocks which, starting from the incoming blocks,
/// a wave may reach before entering the def block (the block containing the
/// phi).
/// - If an incoming block has no predecessors in this set, we can take the
/// incoming value as a scalar lane mask as-is.
/// -- A special case of this is when the def block has a self-loop.
/// - Otherwise, the incoming value needs to be merged with a previously
/// defined lane mask.
/// - If there is a path into the set of reachable blocks that does _not_ go
/// through an incoming block where we can take the scalar lane mask as-is,
/// we need to invent an available value for the SSAUpdater. Choices are
/// 0 and undef, with differing consequences for how to merge values etc.
///
/// TODO: We could use region analysis to quickly skip over SESE regions during
/// the traversal.
///
class PhiIncomingAnalysis {
MachinePostDominatorTree &PDT;
// For each reachable basic block, whether it is a source in the induced
// subgraph of the CFG.
DenseMap<MachineBasicBlock *, bool> ReachableMap;
SmallVector<MachineBasicBlock *, 4> ReachableOrdered;
SmallVector<MachineBasicBlock *, 4> Stack;
SmallVector<MachineBasicBlock *, 4> Predecessors;
public:
PhiIncomingAnalysis(MachinePostDominatorTree &PDT) : PDT(PDT) {}
/// Returns whether \p MBB is a source in the induced subgraph of reachable
/// blocks.
bool isSource(MachineBasicBlock &MBB) const {
return ReachableMap.find(&MBB)->second;
}
ArrayRef<MachineBasicBlock *> predecessors() const { return Predecessors; }
void analyze(MachineBasicBlock &DefBlock,
ArrayRef<MachineBasicBlock *> IncomingBlocks) {
assert(Stack.empty());
ReachableMap.clear();
ReachableOrdered.clear();
Predecessors.clear();
// Insert the def block first, so that it acts as an end point for the
// traversal.
ReachableMap.try_emplace(&DefBlock, false);
ReachableOrdered.push_back(&DefBlock);
for (MachineBasicBlock *MBB : IncomingBlocks) {
if (MBB == &DefBlock) {
ReachableMap[&DefBlock] = true; // self-loop on DefBlock
continue;
}
ReachableMap.try_emplace(MBB, false);
ReachableOrdered.push_back(MBB);
// If this block has a divergent terminator and the def block is its
// post-dominator, the wave may first visit the other successors.
bool Divergent = false;
for (MachineInstr &MI : MBB->terminators()) {
if (MI.getOpcode() == AMDGPU::SI_NON_UNIFORM_BRCOND_PSEUDO ||
MI.getOpcode() == AMDGPU::SI_IF ||
MI.getOpcode() == AMDGPU::SI_ELSE ||
MI.getOpcode() == AMDGPU::SI_LOOP) {
Divergent = true;
break;
}
}
if (Divergent && PDT.dominates(&DefBlock, MBB)) {
for (MachineBasicBlock *Succ : MBB->successors())
Stack.push_back(Succ);
}
}
while (!Stack.empty()) {
MachineBasicBlock *MBB = Stack.pop_back_val();
if (!ReachableMap.try_emplace(MBB, false).second)
continue;
ReachableOrdered.push_back(MBB);
for (MachineBasicBlock *Succ : MBB->successors())
Stack.push_back(Succ);
}
for (MachineBasicBlock *MBB : ReachableOrdered) {
bool HaveReachablePred = false;
for (MachineBasicBlock *Pred : MBB->predecessors()) {
if (ReachableMap.count(Pred)) {
HaveReachablePred = true;
} else {
Stack.push_back(Pred);
}
}
if (!HaveReachablePred)
ReachableMap[MBB] = true;
if (HaveReachablePred) {
for (MachineBasicBlock *UnreachablePred : Stack) {
if (llvm::find(Predecessors, UnreachablePred) == Predecessors.end())
Predecessors.push_back(UnreachablePred);
}
}
Stack.clear();
}
}
};
/// Helper class that detects loops which require us to lower an i1 COPY into
/// bitwise manipulation.
///
/// Unfortunately, we cannot use LoopInfo because LoopInfo does not distinguish
/// between loops with the same header. Consider this example:
///
/// A-+-+
/// | | |
/// B-+ |
/// | |
/// C---+
///
/// A is the header of a loop containing A, B, and C as far as LoopInfo is
/// concerned. However, an i1 COPY in B that is used in C must be lowered to
/// bitwise operations to combine results from different loop iterations when
/// B has a divergent branch (since by default we will compile this code such
/// that threads in a wave are merged at the entry of C).
///
/// The following rule is implemented to determine whether bitwise operations
/// are required: use the bitwise lowering for a def in block B if a backward
/// edge to B is reachable without going through the nearest common
/// post-dominator of B and all uses of the def.
///
/// TODO: This rule is conservative because it does not check whether the
/// relevant branches are actually divergent.
///
/// The class is designed to cache the CFG traversal so that it can be re-used
/// for multiple defs within the same basic block.
///
/// TODO: We could use region analysis to quickly skip over SESE regions during
/// the traversal.
///
class LoopFinder {
MachineDominatorTree &DT;
MachinePostDominatorTree &PDT;
// All visited / reachable block, tagged by level (level 0 is the def block,
// level 1 are all blocks reachable including but not going through the def
// block's IPDOM, etc.).
DenseMap<MachineBasicBlock *, unsigned> Visited;
// Nearest common dominator of all visited blocks by level (level 0 is the
// def block). Used for seeding the SSAUpdater.
SmallVector<MachineBasicBlock *, 4> CommonDominators;
// Post-dominator of all visited blocks.
MachineBasicBlock *VisitedPostDom = nullptr;
// Level at which a loop was found: 0 is not possible; 1 = a backward edge is
// reachable without going through the IPDOM of the def block (if the IPDOM
// itself has an edge to the def block, the loop level is 2), etc.
unsigned FoundLoopLevel = ~0u;
MachineBasicBlock *DefBlock = nullptr;
SmallVector<MachineBasicBlock *, 4> Stack;
SmallVector<MachineBasicBlock *, 4> NextLevel;
public:
LoopFinder(MachineDominatorTree &DT, MachinePostDominatorTree &PDT)
: DT(DT), PDT(PDT) {}
void initialize(MachineBasicBlock &MBB) {
Visited.clear();
CommonDominators.clear();
Stack.clear();
NextLevel.clear();
VisitedPostDom = nullptr;
FoundLoopLevel = ~0u;
DefBlock = &MBB;
}
/// Check whether a backward edge can be reached without going through the
/// given \p PostDom of the def block.
///
/// Return the level of \p PostDom if a loop was found, or 0 otherwise.
unsigned findLoop(MachineBasicBlock *PostDom) {
MachineDomTreeNode *PDNode = PDT.getNode(DefBlock);
if (!VisitedPostDom)
advanceLevel();
unsigned Level = 0;
while (PDNode->getBlock() != PostDom) {
if (PDNode->getBlock() == VisitedPostDom)
advanceLevel();
PDNode = PDNode->getIDom();
Level++;
if (FoundLoopLevel == Level)
return Level;
}
return 0;
}
/// Add undef values dominating the loop and the optionally given additional
/// blocks, so that the SSA updater doesn't have to search all the way to the
/// function entry.
void addLoopEntries(unsigned LoopLevel, MachineSSAUpdater &SSAUpdater,
ArrayRef<MachineBasicBlock *> Blocks = {}) {
assert(LoopLevel < CommonDominators.size());
MachineBasicBlock *Dom = CommonDominators[LoopLevel];
for (MachineBasicBlock *MBB : Blocks)
Dom = DT.findNearestCommonDominator(Dom, MBB);
if (!inLoopLevel(*Dom, LoopLevel, Blocks)) {
SSAUpdater.AddAvailableValue(Dom, insertUndefLaneMask(*Dom));
} else {
// The dominator is part of the loop or the given blocks, so add the
// undef value to unreachable predecessors instead.
for (MachineBasicBlock *Pred : Dom->predecessors()) {
if (!inLoopLevel(*Pred, LoopLevel, Blocks))
SSAUpdater.AddAvailableValue(Pred, insertUndefLaneMask(*Pred));
}
}
}
private:
bool inLoopLevel(MachineBasicBlock &MBB, unsigned LoopLevel,
ArrayRef<MachineBasicBlock *> Blocks) const {
auto DomIt = Visited.find(&MBB);
if (DomIt != Visited.end() && DomIt->second <= LoopLevel)
return true;
if (llvm::find(Blocks, &MBB) != Blocks.end())
return true;
return false;
}
void advanceLevel() {
MachineBasicBlock *VisitedDom;
if (!VisitedPostDom) {
VisitedPostDom = DefBlock;
VisitedDom = DefBlock;
Stack.push_back(DefBlock);
} else {
VisitedPostDom = PDT.getNode(VisitedPostDom)->getIDom()->getBlock();
VisitedDom = CommonDominators.back();
for (unsigned i = 0; i < NextLevel.size();) {
if (PDT.dominates(VisitedPostDom, NextLevel[i])) {
Stack.push_back(NextLevel[i]);
NextLevel[i] = NextLevel.back();
NextLevel.pop_back();
} else {
i++;
}
}
}
unsigned Level = CommonDominators.size();
while (!Stack.empty()) {
MachineBasicBlock *MBB = Stack.pop_back_val();
if (!PDT.dominates(VisitedPostDom, MBB))
NextLevel.push_back(MBB);
Visited[MBB] = Level;
VisitedDom = DT.findNearestCommonDominator(VisitedDom, MBB);
for (MachineBasicBlock *Succ : MBB->successors()) {
if (Succ == DefBlock) {
if (MBB == VisitedPostDom)
FoundLoopLevel = std::min(FoundLoopLevel, Level + 1);
else
FoundLoopLevel = std::min(FoundLoopLevel, Level);
continue;
}
if (Visited.try_emplace(Succ, ~0u).second) {
if (MBB == VisitedPostDom)
NextLevel.push_back(Succ);
else
Stack.push_back(Succ);
}
}
}
CommonDominators.push_back(VisitedDom);
}
};
} // End anonymous namespace.
INITIALIZE_PASS_BEGIN(SILowerI1Copies, DEBUG_TYPE, "SI Lower i1 Copies", false,
false)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_DEPENDENCY(MachinePostDominatorTree)
INITIALIZE_PASS_END(SILowerI1Copies, DEBUG_TYPE, "SI Lower i1 Copies", false,
false)
char SILowerI1Copies::ID = 0;
char &llvm::SILowerI1CopiesID = SILowerI1Copies::ID;
FunctionPass *llvm::createSILowerI1CopiesPass() {
return new SILowerI1Copies();
}
static unsigned createLaneMaskReg(MachineFunction &MF) {
MachineRegisterInfo &MRI = MF.getRegInfo();
return MRI.createVirtualRegister(&AMDGPU::SReg_64RegClass);
}
static unsigned insertUndefLaneMask(MachineBasicBlock &MBB) {
MachineFunction &MF = *MBB.getParent();
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
const SIInstrInfo *TII = ST.getInstrInfo();
unsigned UndefReg = createLaneMaskReg(MF);
BuildMI(MBB, MBB.getFirstTerminator(), {}, TII->get(AMDGPU::IMPLICIT_DEF),
UndefReg);
return UndefReg;
}
/// Lower all instructions that def or use vreg_1 registers.
///
/// In a first pass, we lower COPYs from vreg_1 to vector registers, as can
/// occur around inline assembly. We do this first, before vreg_1 registers
/// are changed to scalar mask registers.
///
/// Then we lower all defs of vreg_1 registers. Phi nodes are lowered before
/// all others, because phi lowering looks through copies and can therefore
/// often make copy lowering unnecessary.
bool SILowerI1Copies::runOnMachineFunction(MachineFunction &TheMF) {
MF = &TheMF;
MRI = &MF->getRegInfo();
DT = &getAnalysis<MachineDominatorTree>();
PDT = &getAnalysis<MachinePostDominatorTree>();
ST = &MF->getSubtarget<GCNSubtarget>();
TII = ST->getInstrInfo();
lowerCopiesFromI1();
lowerPhis();
lowerCopiesToI1();
for (unsigned Reg : ConstrainRegs)
MRI->constrainRegClass(Reg, &AMDGPU::SReg_64_XEXECRegClass);
ConstrainRegs.clear();
return true;
}
void SILowerI1Copies::lowerCopiesFromI1() {
SmallVector<MachineInstr *, 4> DeadCopies;
for (MachineBasicBlock &MBB : *MF) {
for (MachineInstr &MI : MBB) {
if (MI.getOpcode() != AMDGPU::COPY)
continue;
unsigned DstReg = MI.getOperand(0).getReg();
unsigned SrcReg = MI.getOperand(1).getReg();
if (!TargetRegisterInfo::isVirtualRegister(SrcReg) ||
MRI->getRegClass(SrcReg) != &AMDGPU::VReg_1RegClass)
continue;
if (isLaneMaskReg(DstReg) ||
(TargetRegisterInfo::isVirtualRegister(DstReg) &&
MRI->getRegClass(DstReg) == &AMDGPU::VReg_1RegClass))
continue;
// Copy into a 32-bit vector register.
LLVM_DEBUG(dbgs() << "Lower copy from i1: " << MI);
DebugLoc DL = MI.getDebugLoc();
assert(TII->getRegisterInfo().getRegSizeInBits(DstReg, *MRI) == 32);
assert(!MI.getOperand(0).getSubReg());
ConstrainRegs.insert(SrcReg);
BuildMI(MBB, MI, DL, TII->get(AMDGPU::V_CNDMASK_B32_e64), DstReg)
.addImm(0)
.addImm(-1)
.addReg(SrcReg);
DeadCopies.push_back(&MI);
}
for (MachineInstr *MI : DeadCopies)
MI->eraseFromParent();
DeadCopies.clear();
}
}
void SILowerI1Copies::lowerPhis() {
MachineSSAUpdater SSAUpdater(*MF);
LoopFinder LF(*DT, *PDT);
PhiIncomingAnalysis PIA(*PDT);
SmallVector<MachineInstr *, 4> DeadPhis;
SmallVector<MachineBasicBlock *, 4> IncomingBlocks;
SmallVector<unsigned, 4> IncomingRegs;
SmallVector<unsigned, 4> IncomingUpdated;
for (MachineBasicBlock &MBB : *MF) {
LF.initialize(MBB);
for (MachineInstr &MI : MBB.phis()) {
unsigned DstReg = MI.getOperand(0).getReg();
if (MRI->getRegClass(DstReg) != &AMDGPU::VReg_1RegClass)
continue;
LLVM_DEBUG(dbgs() << "Lower PHI: " << MI);
MRI->setRegClass(DstReg, &AMDGPU::SReg_64RegClass);
// Collect incoming values.
for (unsigned i = 1; i < MI.getNumOperands(); i += 2) {
assert(i + 1 < MI.getNumOperands());
unsigned IncomingReg = MI.getOperand(i).getReg();
MachineBasicBlock *IncomingMBB = MI.getOperand(i + 1).getMBB();
MachineInstr *IncomingDef = MRI->getUniqueVRegDef(IncomingReg);
if (IncomingDef->getOpcode() == AMDGPU::COPY) {
IncomingReg = IncomingDef->getOperand(1).getReg();
assert(isLaneMaskReg(IncomingReg));
assert(!IncomingDef->getOperand(1).getSubReg());
} else if (IncomingDef->getOpcode() == AMDGPU::IMPLICIT_DEF) {
continue;
} else {
assert(IncomingDef->isPHI());
}
IncomingBlocks.push_back(IncomingMBB);
IncomingRegs.push_back(IncomingReg);
}
// Phis in a loop that are observed outside the loop receive a simple but
// conservatively correct treatment.
MachineBasicBlock *PostDomBound = &MBB;
for (MachineInstr &Use : MRI->use_instructions(DstReg)) {
PostDomBound =
PDT->findNearestCommonDominator(PostDomBound, Use.getParent());
}
unsigned FoundLoopLevel = LF.findLoop(PostDomBound);
SSAUpdater.Initialize(DstReg);
if (FoundLoopLevel) {
LF.addLoopEntries(FoundLoopLevel, SSAUpdater, IncomingBlocks);
for (unsigned i = 0; i < IncomingRegs.size(); ++i) {
IncomingUpdated.push_back(createLaneMaskReg(*MF));
SSAUpdater.AddAvailableValue(IncomingBlocks[i],
IncomingUpdated.back());
}
for (unsigned i = 0; i < IncomingRegs.size(); ++i) {
MachineBasicBlock &IMBB = *IncomingBlocks[i];
buildMergeLaneMasks(
IMBB, getSaluInsertionAtEnd(IMBB), {}, IncomingUpdated[i],
SSAUpdater.GetValueInMiddleOfBlock(&IMBB), IncomingRegs[i]);
}
} else {
// The phi is not observed from outside a loop. Use a more accurate
// lowering.
PIA.analyze(MBB, IncomingBlocks);
for (MachineBasicBlock *MBB : PIA.predecessors())
SSAUpdater.AddAvailableValue(MBB, insertUndefLaneMask(*MBB));
for (unsigned i = 0; i < IncomingRegs.size(); ++i) {
MachineBasicBlock &IMBB = *IncomingBlocks[i];
if (PIA.isSource(IMBB)) {
IncomingUpdated.push_back(0);
SSAUpdater.AddAvailableValue(&IMBB, IncomingRegs[i]);
} else {
IncomingUpdated.push_back(createLaneMaskReg(*MF));
SSAUpdater.AddAvailableValue(&IMBB, IncomingUpdated.back());
}
}
for (unsigned i = 0; i < IncomingRegs.size(); ++i) {
if (!IncomingUpdated[i])
continue;
MachineBasicBlock &IMBB = *IncomingBlocks[i];
buildMergeLaneMasks(
IMBB, getSaluInsertionAtEnd(IMBB), {}, IncomingUpdated[i],
SSAUpdater.GetValueInMiddleOfBlock(&IMBB), IncomingRegs[i]);
}
}
unsigned NewReg = SSAUpdater.GetValueInMiddleOfBlock(&MBB);
if (NewReg != DstReg) {
MRI->replaceRegWith(NewReg, DstReg);
// Ensure that DstReg has a single def and mark the old PHI node for
// deletion.
MI.getOperand(0).setReg(NewReg);
DeadPhis.push_back(&MI);
}
IncomingBlocks.clear();
IncomingRegs.clear();
IncomingUpdated.clear();
}
for (MachineInstr *MI : DeadPhis)
MI->eraseFromParent();
DeadPhis.clear();
}
}
void SILowerI1Copies::lowerCopiesToI1() {
MachineSSAUpdater SSAUpdater(*MF);
LoopFinder LF(*DT, *PDT);
SmallVector<MachineInstr *, 4> DeadCopies;
for (MachineBasicBlock &MBB : *MF) {
LF.initialize(MBB);
for (MachineInstr &MI : MBB) {
if (MI.getOpcode() != AMDGPU::IMPLICIT_DEF &&
MI.getOpcode() != AMDGPU::COPY)
continue;
unsigned DstReg = MI.getOperand(0).getReg();
if (!TargetRegisterInfo::isVirtualRegister(DstReg) ||
MRI->getRegClass(DstReg) != &AMDGPU::VReg_1RegClass)
continue;
if (MRI->use_empty(DstReg)) {
DeadCopies.push_back(&MI);
continue;
}
LLVM_DEBUG(dbgs() << "Lower Other: " << MI);
MRI->setRegClass(DstReg, &AMDGPU::SReg_64RegClass);
if (MI.getOpcode() == AMDGPU::IMPLICIT_DEF)
continue;
DebugLoc DL = MI.getDebugLoc();
unsigned SrcReg = MI.getOperand(1).getReg();
assert(!MI.getOperand(1).getSubReg());
if (!TargetRegisterInfo::isVirtualRegister(SrcReg) ||
!isLaneMaskReg(SrcReg)) {
assert(TII->getRegisterInfo().getRegSizeInBits(SrcReg, *MRI) == 32);
unsigned TmpReg = createLaneMaskReg(*MF);
BuildMI(MBB, MI, DL, TII->get(AMDGPU::V_CMP_NE_U32_e64), TmpReg)
.addReg(SrcReg)
.addImm(0);
MI.getOperand(1).setReg(TmpReg);
SrcReg = TmpReg;
}
// Defs in a loop that are observed outside the loop must be transformed
// into appropriate bit manipulation.
MachineBasicBlock *PostDomBound = &MBB;
for (MachineInstr &Use : MRI->use_instructions(DstReg)) {
PostDomBound =
PDT->findNearestCommonDominator(PostDomBound, Use.getParent());
}
unsigned FoundLoopLevel = LF.findLoop(PostDomBound);
if (FoundLoopLevel) {
SSAUpdater.Initialize(DstReg);
SSAUpdater.AddAvailableValue(&MBB, DstReg);
LF.addLoopEntries(FoundLoopLevel, SSAUpdater);
buildMergeLaneMasks(MBB, MI, DL, DstReg,
SSAUpdater.GetValueInMiddleOfBlock(&MBB), SrcReg);
DeadCopies.push_back(&MI);
}
}
for (MachineInstr *MI : DeadCopies)
MI->eraseFromParent();
DeadCopies.clear();
}
}
bool SILowerI1Copies::isConstantLaneMask(unsigned Reg, bool &Val) const {
const MachineInstr *MI;
for (;;) {
MI = MRI->getUniqueVRegDef(Reg);
if (MI->getOpcode() != AMDGPU::COPY)
break;
Reg = MI->getOperand(1).getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg))
return false;
if (!isLaneMaskReg(Reg))
return false;
}
if (MI->getOpcode() != AMDGPU::S_MOV_B64)
return false;
if (!MI->getOperand(1).isImm())
return false;
int64_t Imm = MI->getOperand(1).getImm();
if (Imm == 0) {
Val = false;
return true;
}
if (Imm == -1) {
Val = true;
return true;
}
return false;
}
static void instrDefsUsesSCC(const MachineInstr &MI, bool &Def, bool &Use) {
Def = false;
Use = false;
for (const MachineOperand &MO : MI.operands()) {
if (MO.isReg() && MO.getReg() == AMDGPU::SCC) {
if (MO.isUse())
Use = true;
else
Def = true;
}
}
}
/// Return a point at the end of the given \p MBB to insert SALU instructions
/// for lane mask calculation. Take terminators and SCC into account.
MachineBasicBlock::iterator
SILowerI1Copies::getSaluInsertionAtEnd(MachineBasicBlock &MBB) const {
auto InsertionPt = MBB.getFirstTerminator();
bool TerminatorsUseSCC = false;
for (auto I = InsertionPt, E = MBB.end(); I != E; ++I) {
bool DefsSCC;
instrDefsUsesSCC(*I, DefsSCC, TerminatorsUseSCC);
if (TerminatorsUseSCC || DefsSCC)
break;
}
if (!TerminatorsUseSCC)
return InsertionPt;
while (InsertionPt != MBB.begin()) {
InsertionPt--;
bool DefSCC, UseSCC;
instrDefsUsesSCC(*InsertionPt, DefSCC, UseSCC);
if (DefSCC)
return InsertionPt;
}
// We should have at least seen an IMPLICIT_DEF or COPY
llvm_unreachable("SCC used by terminator but no def in block");
}
void SILowerI1Copies::buildMergeLaneMasks(MachineBasicBlock &MBB,
MachineBasicBlock::iterator I,
const DebugLoc &DL, unsigned DstReg,
unsigned PrevReg, unsigned CurReg) {
bool PrevVal;
bool PrevConstant = isConstantLaneMask(PrevReg, PrevVal);
bool CurVal;
bool CurConstant = isConstantLaneMask(CurReg, CurVal);
if (PrevConstant && CurConstant) {
if (PrevVal == CurVal) {
BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), DstReg).addReg(CurReg);
} else if (CurVal) {
BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), DstReg).addReg(AMDGPU::EXEC);
} else {
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_XOR_B64), DstReg)
.addReg(AMDGPU::EXEC)
.addImm(-1);
}
return;
}
unsigned PrevMaskedReg = 0;
unsigned CurMaskedReg = 0;
if (!PrevConstant) {
if (CurConstant && CurVal) {
PrevMaskedReg = PrevReg;
} else {
PrevMaskedReg = createLaneMaskReg(*MF);
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_ANDN2_B64), PrevMaskedReg)
.addReg(PrevReg)
.addReg(AMDGPU::EXEC);
}
}
if (!CurConstant) {
// TODO: check whether CurReg is already masked by EXEC
if (PrevConstant && PrevVal) {
CurMaskedReg = CurReg;
} else {
CurMaskedReg = createLaneMaskReg(*MF);
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_AND_B64), CurMaskedReg)
.addReg(CurReg)
.addReg(AMDGPU::EXEC);
}
}
if (PrevConstant && !PrevVal) {
BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), DstReg)
.addReg(CurMaskedReg);
} else if (CurConstant && !CurVal) {
BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), DstReg)
.addReg(PrevMaskedReg);
} else if (PrevConstant && PrevVal) {
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_ORN2_B64), DstReg)
.addReg(CurMaskedReg)
.addReg(AMDGPU::EXEC);
} else {
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_OR_B64), DstReg)
.addReg(PrevMaskedReg)
.addReg(CurMaskedReg ? CurMaskedReg : (unsigned)AMDGPU::EXEC);
}
}
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