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

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//===-- SIOptimizeExecMasking.cpp -----------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "AMDGPUSubtarget.h"
#include "MCTargetDesc/AMDGPUMCTargetDesc.h"
#include "SIInstrInfo.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
#define DEBUG_TYPE "si-optimize-exec-masking"
namespace {
class SIOptimizeExecMasking : public MachineFunctionPass {
public:
static char ID;
public:
SIOptimizeExecMasking() : MachineFunctionPass(ID) {
initializeSIOptimizeExecMaskingPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
StringRef getPassName() const override {
return "SI optimize exec mask operations";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // End anonymous namespace.
INITIALIZE_PASS_BEGIN(SIOptimizeExecMasking, DEBUG_TYPE,
"SI optimize exec mask operations", false, false)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_END(SIOptimizeExecMasking, DEBUG_TYPE,
"SI optimize exec mask operations", false, false)
char SIOptimizeExecMasking::ID = 0;
char &llvm::SIOptimizeExecMaskingID = SIOptimizeExecMasking::ID;
/// If \p MI is a copy from exec, return the register copied to.
static Register isCopyFromExec(const MachineInstr &MI, const GCNSubtarget &ST) {
switch (MI.getOpcode()) {
case AMDGPU::COPY:
case AMDGPU::S_MOV_B64:
case AMDGPU::S_MOV_B64_term:
case AMDGPU::S_MOV_B32:
case AMDGPU::S_MOV_B32_term: {
const MachineOperand &Src = MI.getOperand(1);
if (Src.isReg() &&
Src.getReg() == (ST.isWave32() ? AMDGPU::EXEC_LO : AMDGPU::EXEC))
return MI.getOperand(0).getReg();
}
}
return AMDGPU::NoRegister;
}
/// If \p MI is a copy to exec, return the register copied from.
static Register isCopyToExec(const MachineInstr &MI, const GCNSubtarget &ST) {
switch (MI.getOpcode()) {
case AMDGPU::COPY:
case AMDGPU::S_MOV_B64:
case AMDGPU::S_MOV_B32: {
const MachineOperand &Dst = MI.getOperand(0);
if (Dst.isReg() &&
Dst.getReg() == (ST.isWave32() ? AMDGPU::EXEC_LO : AMDGPU::EXEC) &&
MI.getOperand(1).isReg())
return MI.getOperand(1).getReg();
break;
}
case AMDGPU::S_MOV_B64_term:
case AMDGPU::S_MOV_B32_term:
llvm_unreachable("should have been replaced");
}
return Register();
}
/// If \p MI is a logical operation on an exec value,
/// return the register copied to.
static Register isLogicalOpOnExec(const MachineInstr &MI) {
switch (MI.getOpcode()) {
case AMDGPU::S_AND_B64:
case AMDGPU::S_OR_B64:
case AMDGPU::S_XOR_B64:
case AMDGPU::S_ANDN2_B64:
case AMDGPU::S_ORN2_B64:
case AMDGPU::S_NAND_B64:
case AMDGPU::S_NOR_B64:
case AMDGPU::S_XNOR_B64: {
const MachineOperand &Src1 = MI.getOperand(1);
if (Src1.isReg() && Src1.getReg() == AMDGPU::EXEC)
return MI.getOperand(0).getReg();
const MachineOperand &Src2 = MI.getOperand(2);
if (Src2.isReg() && Src2.getReg() == AMDGPU::EXEC)
return MI.getOperand(0).getReg();
break;
}
case AMDGPU::S_AND_B32:
case AMDGPU::S_OR_B32:
case AMDGPU::S_XOR_B32:
case AMDGPU::S_ANDN2_B32:
case AMDGPU::S_ORN2_B32:
case AMDGPU::S_NAND_B32:
case AMDGPU::S_NOR_B32:
case AMDGPU::S_XNOR_B32: {
const MachineOperand &Src1 = MI.getOperand(1);
if (Src1.isReg() && Src1.getReg() == AMDGPU::EXEC_LO)
return MI.getOperand(0).getReg();
const MachineOperand &Src2 = MI.getOperand(2);
if (Src2.isReg() && Src2.getReg() == AMDGPU::EXEC_LO)
return MI.getOperand(0).getReg();
break;
}
}
return AMDGPU::NoRegister;
}
static unsigned getSaveExecOp(unsigned Opc) {
switch (Opc) {
case AMDGPU::S_AND_B64:
return AMDGPU::S_AND_SAVEEXEC_B64;
case AMDGPU::S_OR_B64:
return AMDGPU::S_OR_SAVEEXEC_B64;
case AMDGPU::S_XOR_B64:
return AMDGPU::S_XOR_SAVEEXEC_B64;
case AMDGPU::S_ANDN2_B64:
return AMDGPU::S_ANDN2_SAVEEXEC_B64;
case AMDGPU::S_ORN2_B64:
return AMDGPU::S_ORN2_SAVEEXEC_B64;
case AMDGPU::S_NAND_B64:
return AMDGPU::S_NAND_SAVEEXEC_B64;
case AMDGPU::S_NOR_B64:
return AMDGPU::S_NOR_SAVEEXEC_B64;
case AMDGPU::S_XNOR_B64:
return AMDGPU::S_XNOR_SAVEEXEC_B64;
case AMDGPU::S_AND_B32:
return AMDGPU::S_AND_SAVEEXEC_B32;
case AMDGPU::S_OR_B32:
return AMDGPU::S_OR_SAVEEXEC_B32;
case AMDGPU::S_XOR_B32:
return AMDGPU::S_XOR_SAVEEXEC_B32;
case AMDGPU::S_ANDN2_B32:
return AMDGPU::S_ANDN2_SAVEEXEC_B32;
case AMDGPU::S_ORN2_B32:
return AMDGPU::S_ORN2_SAVEEXEC_B32;
case AMDGPU::S_NAND_B32:
return AMDGPU::S_NAND_SAVEEXEC_B32;
case AMDGPU::S_NOR_B32:
return AMDGPU::S_NOR_SAVEEXEC_B32;
case AMDGPU::S_XNOR_B32:
return AMDGPU::S_XNOR_SAVEEXEC_B32;
default:
return AMDGPU::INSTRUCTION_LIST_END;
}
}
// These are only terminators to get correct spill code placement during
// register allocation, so turn them back into normal instructions.
static bool removeTerminatorBit(const SIInstrInfo &TII, MachineInstr &MI) {
switch (MI.getOpcode()) {
case AMDGPU::S_MOV_B32_term: {
bool RegSrc = MI.getOperand(1).isReg();
MI.setDesc(TII.get(RegSrc ? AMDGPU::COPY : AMDGPU::S_MOV_B32));
return true;
}
case AMDGPU::S_MOV_B64_term: {
bool RegSrc = MI.getOperand(1).isReg();
MI.setDesc(TII.get(RegSrc ? AMDGPU::COPY : AMDGPU::S_MOV_B64));
return true;
}
case AMDGPU::S_XOR_B64_term: {
// This is only a terminator to get the correct spill code placement during
// register allocation.
MI.setDesc(TII.get(AMDGPU::S_XOR_B64));
return true;
}
case AMDGPU::S_XOR_B32_term: {
// This is only a terminator to get the correct spill code placement during
// register allocation.
MI.setDesc(TII.get(AMDGPU::S_XOR_B32));
return true;
}
case AMDGPU::S_OR_B64_term: {
// This is only a terminator to get the correct spill code placement during
// register allocation.
MI.setDesc(TII.get(AMDGPU::S_OR_B64));
return true;
}
case AMDGPU::S_OR_B32_term: {
// This is only a terminator to get the correct spill code placement during
// register allocation.
MI.setDesc(TII.get(AMDGPU::S_OR_B32));
return true;
}
case AMDGPU::S_ANDN2_B64_term: {
// This is only a terminator to get the correct spill code placement during
// register allocation.
MI.setDesc(TII.get(AMDGPU::S_ANDN2_B64));
return true;
}
case AMDGPU::S_ANDN2_B32_term: {
// This is only a terminator to get the correct spill code placement during
// register allocation.
MI.setDesc(TII.get(AMDGPU::S_ANDN2_B32));
return true;
}
default:
return false;
}
}
// Turn all pseudoterminators in the block into their equivalent non-terminator
// instructions. Returns the reverse iterator to the first non-terminator
// instruction in the block.
static MachineBasicBlock::reverse_iterator fixTerminators(
const SIInstrInfo &TII,
MachineBasicBlock &MBB) {
MachineBasicBlock::reverse_iterator I = MBB.rbegin(), E = MBB.rend();
bool Seen = false;
MachineBasicBlock::reverse_iterator FirstNonTerm = I;
for (; I != E; ++I) {
if (!I->isTerminator())
return Seen ? FirstNonTerm : I;
if (removeTerminatorBit(TII, *I)) {
if (!Seen) {
FirstNonTerm = I;
Seen = true;
}
}
}
return FirstNonTerm;
}
static MachineBasicBlock::reverse_iterator findExecCopy(
const SIInstrInfo &TII,
const GCNSubtarget &ST,
MachineBasicBlock &MBB,
MachineBasicBlock::reverse_iterator I,
unsigned CopyToExec) {
const unsigned InstLimit = 25;
auto E = MBB.rend();
for (unsigned N = 0; N <= InstLimit && I != E; ++I, ++N) {
Register CopyFromExec = isCopyFromExec(*I, ST);
if (CopyFromExec.isValid())
return I;
}
return E;
}
// XXX - Seems LivePhysRegs doesn't work correctly since it will incorrectly
// report the register as unavailable because a super-register with a lane mask
// is unavailable.
static bool isLiveOut(const MachineBasicBlock &MBB, unsigned Reg) {
for (MachineBasicBlock *Succ : MBB.successors()) {
if (Succ->isLiveIn(Reg))
return true;
}
return false;
}
bool SIOptimizeExecMasking::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
return false;
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
const SIRegisterInfo *TRI = ST.getRegisterInfo();
const SIInstrInfo *TII = ST.getInstrInfo();
MCRegister Exec = ST.isWave32() ? AMDGPU::EXEC_LO : AMDGPU::EXEC;
// Optimize sequences emitted for control flow lowering. They are originally
// emitted as the separate operations because spill code may need to be
// inserted for the saved copy of exec.
//
// x = copy exec
// z = s_<op>_b64 x, y
// exec = copy z
// =>
// x = s_<op>_saveexec_b64 y
//
for (MachineBasicBlock &MBB : MF) {
MachineBasicBlock::reverse_iterator I = fixTerminators(*TII, MBB);
MachineBasicBlock::reverse_iterator E = MBB.rend();
if (I == E)
continue;
// It's possible to see other terminator copies after the exec copy. This
// can happen if control flow pseudos had their outputs used by phis.
Register CopyToExec;
unsigned SearchCount = 0;
const unsigned SearchLimit = 5;
while (I != E && SearchCount++ < SearchLimit) {
CopyToExec = isCopyToExec(*I, ST);
if (CopyToExec)
break;
++I;
}
if (!CopyToExec)
continue;
// Scan backwards to find the def.
auto CopyToExecInst = &*I;
auto CopyFromExecInst = findExecCopy(*TII, ST, MBB, I, CopyToExec);
if (CopyFromExecInst == E) {
auto PrepareExecInst = std::next(I);
if (PrepareExecInst == E)
continue;
// Fold exec = COPY (S_AND_B64 reg, exec) -> exec = S_AND_B64 reg, exec
if (CopyToExecInst->getOperand(1).isKill() &&
isLogicalOpOnExec(*PrepareExecInst) == CopyToExec) {
LLVM_DEBUG(dbgs() << "Fold exec copy: " << *PrepareExecInst);
PrepareExecInst->getOperand(0).setReg(Exec);
LLVM_DEBUG(dbgs() << "into: " << *PrepareExecInst << '\n');
CopyToExecInst->eraseFromParent();
}
continue;
}
if (isLiveOut(MBB, CopyToExec)) {
// The copied register is live out and has a second use in another block.
LLVM_DEBUG(dbgs() << "Exec copy source register is live out\n");
continue;
}
Register CopyFromExec = CopyFromExecInst->getOperand(0).getReg();
MachineInstr *SaveExecInst = nullptr;
SmallVector<MachineInstr *, 4> OtherUseInsts;
for (MachineBasicBlock::iterator J
= std::next(CopyFromExecInst->getIterator()), JE = I->getIterator();
J != JE; ++J) {
if (SaveExecInst && J->readsRegister(Exec, TRI)) {
LLVM_DEBUG(dbgs() << "exec read prevents saveexec: " << *J << '\n');
// Make sure this is inserted after any VALU ops that may have been
// scheduled in between.
SaveExecInst = nullptr;
break;
}
bool ReadsCopyFromExec = J->readsRegister(CopyFromExec, TRI);
if (J->modifiesRegister(CopyToExec, TRI)) {
if (SaveExecInst) {
LLVM_DEBUG(dbgs() << "Multiple instructions modify "
<< printReg(CopyToExec, TRI) << '\n');
SaveExecInst = nullptr;
break;
}
unsigned SaveExecOp = getSaveExecOp(J->getOpcode());
if (SaveExecOp == AMDGPU::INSTRUCTION_LIST_END)
break;
if (ReadsCopyFromExec) {
SaveExecInst = &*J;
LLVM_DEBUG(dbgs() << "Found save exec op: " << *SaveExecInst << '\n');
continue;
} else {
LLVM_DEBUG(dbgs()
<< "Instruction does not read exec copy: " << *J << '\n');
break;
}
} else if (ReadsCopyFromExec && !SaveExecInst) {
// Make sure no other instruction is trying to use this copy, before it
// will be rewritten by the saveexec, i.e. hasOneUse. There may have
// been another use, such as an inserted spill. For example:
//
// %sgpr0_sgpr1 = COPY %exec
// spill %sgpr0_sgpr1
// %sgpr2_sgpr3 = S_AND_B64 %sgpr0_sgpr1
//
LLVM_DEBUG(dbgs() << "Found second use of save inst candidate: " << *J
<< '\n');
break;
}
if (SaveExecInst && J->readsRegister(CopyToExec, TRI)) {
assert(SaveExecInst != &*J);
OtherUseInsts.push_back(&*J);
}
}
if (!SaveExecInst)
continue;
LLVM_DEBUG(dbgs() << "Insert save exec op: " << *SaveExecInst << '\n');
MachineOperand &Src0 = SaveExecInst->getOperand(1);
MachineOperand &Src1 = SaveExecInst->getOperand(2);
MachineOperand *OtherOp = nullptr;
if (Src0.isReg() && Src0.getReg() == CopyFromExec) {
OtherOp = &Src1;
} else if (Src1.isReg() && Src1.getReg() == CopyFromExec) {
if (!SaveExecInst->isCommutable())
break;
OtherOp = &Src0;
} else
llvm_unreachable("unexpected");
CopyFromExecInst->eraseFromParent();
auto InsPt = SaveExecInst->getIterator();
const DebugLoc &DL = SaveExecInst->getDebugLoc();
BuildMI(MBB, InsPt, DL, TII->get(getSaveExecOp(SaveExecInst->getOpcode())),
CopyFromExec)
.addReg(OtherOp->getReg());
SaveExecInst->eraseFromParent();
CopyToExecInst->eraseFromParent();
for (MachineInstr *OtherInst : OtherUseInsts) {
OtherInst->substituteRegister(CopyToExec, Exec,
AMDGPU::NoSubRegister, *TRI);
}
}
return true;
}
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