forked from OSchip/llvm-project
390 lines
12 KiB
C++
390 lines
12 KiB
C++
//===-- SIFoldOperands.cpp - Fold operands --- ----------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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/// \file
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//===----------------------------------------------------------------------===//
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//
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#include "AMDGPU.h"
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#include "AMDGPUSubtarget.h"
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#include "SIInstrInfo.h"
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#include "llvm/CodeGen/LiveIntervalAnalysis.h"
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#include "llvm/CodeGen/MachineDominators.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetMachine.h"
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#define DEBUG_TYPE "si-fold-operands"
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using namespace llvm;
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namespace {
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class SIFoldOperands : public MachineFunctionPass {
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public:
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static char ID;
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public:
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SIFoldOperands() : MachineFunctionPass(ID) {
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initializeSIFoldOperandsPass(*PassRegistry::getPassRegistry());
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}
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bool runOnMachineFunction(MachineFunction &MF) override;
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const char *getPassName() const override {
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return "SI Fold Operands";
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<MachineDominatorTree>();
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AU.addPreserved<MachineDominatorTree>();
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AU.setPreservesCFG();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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};
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struct FoldCandidate {
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MachineInstr *UseMI;
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unsigned UseOpNo;
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MachineOperand *OpToFold;
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uint64_t ImmToFold;
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FoldCandidate(MachineInstr *MI, unsigned OpNo, MachineOperand *FoldOp) :
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UseMI(MI), UseOpNo(OpNo) {
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if (FoldOp->isImm()) {
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OpToFold = nullptr;
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ImmToFold = FoldOp->getImm();
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} else {
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assert(FoldOp->isReg());
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OpToFold = FoldOp;
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}
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}
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bool isImm() const {
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return !OpToFold;
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}
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};
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} // End anonymous namespace.
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INITIALIZE_PASS_BEGIN(SIFoldOperands, DEBUG_TYPE,
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"SI Fold Operands", false, false)
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INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
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INITIALIZE_PASS_END(SIFoldOperands, DEBUG_TYPE,
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"SI Fold Operands", false, false)
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char SIFoldOperands::ID = 0;
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char &llvm::SIFoldOperandsID = SIFoldOperands::ID;
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FunctionPass *llvm::createSIFoldOperandsPass() {
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return new SIFoldOperands();
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}
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static bool isSafeToFold(unsigned Opcode) {
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switch(Opcode) {
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case AMDGPU::V_MOV_B32_e32:
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case AMDGPU::V_MOV_B32_e64:
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case AMDGPU::V_MOV_B64_PSEUDO:
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case AMDGPU::S_MOV_B32:
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case AMDGPU::S_MOV_B64:
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case AMDGPU::COPY:
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return true;
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default:
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return false;
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}
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}
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static bool updateOperand(FoldCandidate &Fold,
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const TargetRegisterInfo &TRI) {
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MachineInstr *MI = Fold.UseMI;
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MachineOperand &Old = MI->getOperand(Fold.UseOpNo);
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assert(Old.isReg());
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if (Fold.isImm()) {
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Old.ChangeToImmediate(Fold.ImmToFold);
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return true;
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}
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MachineOperand *New = Fold.OpToFold;
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if (TargetRegisterInfo::isVirtualRegister(Old.getReg()) &&
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TargetRegisterInfo::isVirtualRegister(New->getReg())) {
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Old.substVirtReg(New->getReg(), New->getSubReg(), TRI);
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return true;
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}
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// FIXME: Handle physical registers.
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return false;
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}
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static bool isUseMIInFoldList(const std::vector<FoldCandidate> &FoldList,
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const MachineInstr *MI) {
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for (auto Candidate : FoldList) {
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if (Candidate.UseMI == MI)
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return true;
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}
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return false;
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}
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static bool tryAddToFoldList(std::vector<FoldCandidate> &FoldList,
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MachineInstr *MI, unsigned OpNo,
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MachineOperand *OpToFold,
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const SIInstrInfo *TII) {
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if (!TII->isOperandLegal(MI, OpNo, OpToFold)) {
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// Special case for v_mac_f32_e64 if we are trying to fold into src2
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unsigned Opc = MI->getOpcode();
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if (Opc == AMDGPU::V_MAC_F32_e64 &&
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(int)OpNo == AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::src2)) {
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// Check if changing this to a v_mad_f32 instruction will allow us to
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// fold the operand.
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MI->setDesc(TII->get(AMDGPU::V_MAD_F32));
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bool FoldAsMAD = tryAddToFoldList(FoldList, MI, OpNo, OpToFold, TII);
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if (FoldAsMAD) {
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MI->untieRegOperand(OpNo);
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return true;
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}
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MI->setDesc(TII->get(Opc));
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}
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// If we are already folding into another operand of MI, then
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// we can't commute the instruction, otherwise we risk making the
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// other fold illegal.
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if (isUseMIInFoldList(FoldList, MI))
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return false;
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// Operand is not legal, so try to commute the instruction to
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// see if this makes it possible to fold.
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unsigned CommuteIdx0 = TargetInstrInfo::CommuteAnyOperandIndex;
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unsigned CommuteIdx1 = TargetInstrInfo::CommuteAnyOperandIndex;
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bool CanCommute = TII->findCommutedOpIndices(MI, CommuteIdx0, CommuteIdx1);
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if (CanCommute) {
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if (CommuteIdx0 == OpNo)
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OpNo = CommuteIdx1;
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else if (CommuteIdx1 == OpNo)
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OpNo = CommuteIdx0;
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}
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// One of operands might be an Imm operand, and OpNo may refer to it after
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// the call of commuteInstruction() below. Such situations are avoided
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// here explicitly as OpNo must be a register operand to be a candidate
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// for memory folding.
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if (CanCommute && (!MI->getOperand(CommuteIdx0).isReg() ||
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!MI->getOperand(CommuteIdx1).isReg()))
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return false;
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if (!CanCommute ||
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!TII->commuteInstruction(MI, false, CommuteIdx0, CommuteIdx1))
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return false;
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if (!TII->isOperandLegal(MI, OpNo, OpToFold))
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return false;
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}
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FoldList.push_back(FoldCandidate(MI, OpNo, OpToFold));
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return true;
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}
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static void foldOperand(MachineOperand &OpToFold, MachineInstr *UseMI,
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unsigned UseOpIdx,
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std::vector<FoldCandidate> &FoldList,
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SmallVectorImpl<MachineInstr *> &CopiesToReplace,
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const SIInstrInfo *TII, const SIRegisterInfo &TRI,
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MachineRegisterInfo &MRI) {
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const MachineOperand &UseOp = UseMI->getOperand(UseOpIdx);
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// FIXME: Fold operands with subregs.
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if (UseOp.isReg() && ((UseOp.getSubReg() && OpToFold.isReg()) ||
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UseOp.isImplicit())) {
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return;
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}
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bool FoldingImm = OpToFold.isImm();
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APInt Imm;
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if (FoldingImm) {
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unsigned UseReg = UseOp.getReg();
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const TargetRegisterClass *UseRC
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= TargetRegisterInfo::isVirtualRegister(UseReg) ?
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MRI.getRegClass(UseReg) :
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TRI.getPhysRegClass(UseReg);
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Imm = APInt(64, OpToFold.getImm());
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const MCInstrDesc &FoldDesc = TII->get(OpToFold.getParent()->getOpcode());
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const TargetRegisterClass *FoldRC =
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TRI.getRegClass(FoldDesc.OpInfo[0].RegClass);
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// Split 64-bit constants into 32-bits for folding.
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if (FoldRC->getSize() == 8 && UseOp.getSubReg()) {
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if (UseRC->getSize() != 8)
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return;
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if (UseOp.getSubReg() == AMDGPU::sub0) {
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Imm = Imm.getLoBits(32);
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} else {
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assert(UseOp.getSubReg() == AMDGPU::sub1);
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Imm = Imm.getHiBits(32);
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}
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}
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// In order to fold immediates into copies, we need to change the
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// copy to a MOV.
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if (UseMI->getOpcode() == AMDGPU::COPY) {
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unsigned DestReg = UseMI->getOperand(0).getReg();
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const TargetRegisterClass *DestRC
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= TargetRegisterInfo::isVirtualRegister(DestReg) ?
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MRI.getRegClass(DestReg) :
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TRI.getPhysRegClass(DestReg);
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unsigned MovOp = TII->getMovOpcode(DestRC);
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if (MovOp == AMDGPU::COPY)
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return;
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UseMI->setDesc(TII->get(MovOp));
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CopiesToReplace.push_back(UseMI);
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}
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}
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// Special case for REG_SEQUENCE: We can't fold literals into
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// REG_SEQUENCE instructions, so we have to fold them into the
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// uses of REG_SEQUENCE.
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if (UseMI->getOpcode() == AMDGPU::REG_SEQUENCE) {
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unsigned RegSeqDstReg = UseMI->getOperand(0).getReg();
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unsigned RegSeqDstSubReg = UseMI->getOperand(UseOpIdx + 1).getImm();
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for (MachineRegisterInfo::use_iterator
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RSUse = MRI.use_begin(RegSeqDstReg),
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RSE = MRI.use_end(); RSUse != RSE; ++RSUse) {
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MachineInstr *RSUseMI = RSUse->getParent();
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if (RSUse->getSubReg() != RegSeqDstSubReg)
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continue;
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foldOperand(OpToFold, RSUseMI, RSUse.getOperandNo(), FoldList,
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CopiesToReplace, TII, TRI, MRI);
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}
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return;
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}
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const MCInstrDesc &UseDesc = UseMI->getDesc();
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// Don't fold into target independent nodes. Target independent opcodes
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// don't have defined register classes.
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if (UseDesc.isVariadic() ||
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UseDesc.OpInfo[UseOpIdx].RegClass == -1)
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return;
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if (FoldingImm) {
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MachineOperand ImmOp = MachineOperand::CreateImm(Imm.getSExtValue());
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tryAddToFoldList(FoldList, UseMI, UseOpIdx, &ImmOp, TII);
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return;
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}
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tryAddToFoldList(FoldList, UseMI, UseOpIdx, &OpToFold, TII);
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// FIXME: We could try to change the instruction from 64-bit to 32-bit
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// to enable more folding opportunites. The shrink operands pass
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// already does this.
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return;
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}
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bool SIFoldOperands::runOnMachineFunction(MachineFunction &MF) {
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MachineRegisterInfo &MRI = MF.getRegInfo();
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const SIInstrInfo *TII =
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static_cast<const SIInstrInfo *>(MF.getSubtarget().getInstrInfo());
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const SIRegisterInfo &TRI = TII->getRegisterInfo();
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for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
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BI != BE; ++BI) {
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MachineBasicBlock &MBB = *BI;
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MachineBasicBlock::iterator I, Next;
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for (I = MBB.begin(); I != MBB.end(); I = Next) {
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Next = std::next(I);
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MachineInstr &MI = *I;
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if (!isSafeToFold(MI.getOpcode()))
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continue;
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unsigned OpSize = TII->getOpSize(MI, 1);
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MachineOperand &OpToFold = MI.getOperand(1);
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bool FoldingImm = OpToFold.isImm();
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// FIXME: We could also be folding things like FrameIndexes and
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// TargetIndexes.
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if (!FoldingImm && !OpToFold.isReg())
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continue;
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// Folding immediates with more than one use will increase program size.
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// FIXME: This will also reduce register usage, which may be better
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// in some cases. A better heuristic is needed.
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if (FoldingImm && !TII->isInlineConstant(OpToFold, OpSize) &&
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!MRI.hasOneUse(MI.getOperand(0).getReg()))
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continue;
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if (OpToFold.isReg() &&
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!TargetRegisterInfo::isVirtualRegister(OpToFold.getReg()))
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continue;
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// Prevent folding operands backwards in the function. For example,
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// the COPY opcode must not be replaced by 1 in this example:
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//
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// %vreg3<def> = COPY %VGPR0; VGPR_32:%vreg3
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// ...
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// %VGPR0<def> = V_MOV_B32_e32 1, %EXEC<imp-use>
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MachineOperand &Dst = MI.getOperand(0);
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if (Dst.isReg() &&
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!TargetRegisterInfo::isVirtualRegister(Dst.getReg()))
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continue;
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// We need mutate the operands of new mov instructions to add implicit
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// uses of EXEC, but adding them invalidates the use_iterator, so defer
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// this.
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SmallVector<MachineInstr *, 4> CopiesToReplace;
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std::vector<FoldCandidate> FoldList;
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for (MachineRegisterInfo::use_iterator
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Use = MRI.use_begin(MI.getOperand(0).getReg()), E = MRI.use_end();
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Use != E; ++Use) {
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MachineInstr *UseMI = Use->getParent();
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foldOperand(OpToFold, UseMI, Use.getOperandNo(), FoldList,
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CopiesToReplace, TII, TRI, MRI);
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}
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// Make sure we add EXEC uses to any new v_mov instructions created.
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for (MachineInstr *Copy : CopiesToReplace)
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Copy->addImplicitDefUseOperands(MF);
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for (FoldCandidate &Fold : FoldList) {
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if (updateOperand(Fold, TRI)) {
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// Clear kill flags.
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if (!Fold.isImm()) {
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assert(Fold.OpToFold && Fold.OpToFold->isReg());
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// FIXME: Probably shouldn't bother trying to fold if not an
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// SGPR. PeepholeOptimizer can eliminate redundant VGPR->VGPR
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// copies.
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MRI.clearKillFlags(Fold.OpToFold->getReg());
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}
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DEBUG(dbgs() << "Folded source from " << MI << " into OpNo " <<
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Fold.UseOpNo << " of " << *Fold.UseMI << '\n');
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}
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}
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}
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}
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return false;
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}
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