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

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//===-- SIShrinkInstructions.cpp - Shrink Instructions --------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
/// The pass tries to use the 32-bit encoding for instructions when possible.
//===----------------------------------------------------------------------===//
//
#include "AMDGPU.h"
#include "AMDGPUSubtarget.h"
#include "SIInstrInfo.h"
#include "MCTargetDesc/AMDGPUMCTargetDesc.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#define DEBUG_TYPE "si-shrink-instructions"
STATISTIC(NumInstructionsShrunk,
"Number of 64-bit instruction reduced to 32-bit.");
STATISTIC(NumLiteralConstantsFolded,
"Number of literal constants folded into 32-bit instructions.");
using namespace llvm;
namespace {
class SIShrinkInstructions : public MachineFunctionPass {
public:
static char ID;
public:
SIShrinkInstructions() : MachineFunctionPass(ID) {
}
bool runOnMachineFunction(MachineFunction &MF) override;
StringRef getPassName() const override { return "SI Shrink Instructions"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // End anonymous namespace.
INITIALIZE_PASS(SIShrinkInstructions, DEBUG_TYPE,
"SI Shrink Instructions", false, false)
char SIShrinkInstructions::ID = 0;
FunctionPass *llvm::createSIShrinkInstructionsPass() {
return new SIShrinkInstructions();
}
/// This function checks \p MI for operands defined by a move immediate
/// instruction and then folds the literal constant into the instruction if it
/// can. This function assumes that \p MI is a VOP1, VOP2, or VOPC instructions.
static bool foldImmediates(MachineInstr &MI, const SIInstrInfo *TII,
MachineRegisterInfo &MRI, bool TryToCommute = true) {
assert(TII->isVOP1(MI) || TII->isVOP2(MI) || TII->isVOPC(MI));
int Src0Idx = AMDGPU::getNamedOperandIdx(MI.getOpcode(), AMDGPU::OpName::src0);
// Try to fold Src0
MachineOperand &Src0 = MI.getOperand(Src0Idx);
if (Src0.isReg()) {
unsigned Reg = Src0.getReg();
if (TargetRegisterInfo::isVirtualRegister(Reg) && MRI.hasOneUse(Reg)) {
MachineInstr *Def = MRI.getUniqueVRegDef(Reg);
if (Def && Def->isMoveImmediate()) {
MachineOperand &MovSrc = Def->getOperand(1);
bool ConstantFolded = false;
if (MovSrc.isImm() && (isInt<32>(MovSrc.getImm()) ||
isUInt<32>(MovSrc.getImm()))) {
// It's possible to have only one component of a super-reg defined by
// a single mov, so we need to clear any subregister flag.
Src0.setSubReg(0);
Src0.ChangeToImmediate(MovSrc.getImm());
ConstantFolded = true;
} else if (MovSrc.isFI()) {
Src0.setSubReg(0);
Src0.ChangeToFrameIndex(MovSrc.getIndex());
ConstantFolded = true;
}
if (ConstantFolded) {
assert(MRI.use_empty(Reg));
Def->eraseFromParent();
++NumLiteralConstantsFolded;
return true;
}
}
}
}
// We have failed to fold src0, so commute the instruction and try again.
if (TryToCommute && MI.isCommutable()) {
if (TII->commuteInstruction(MI)) {
if (foldImmediates(MI, TII, MRI, false))
return true;
// Commute back.
TII->commuteInstruction(MI);
}
}
return false;
}
static bool isKImmOperand(const SIInstrInfo *TII, const MachineOperand &Src) {
return isInt<16>(Src.getImm()) &&
!TII->isInlineConstant(*Src.getParent(),
Src.getParent()->getOperandNo(&Src));
}
static bool isKUImmOperand(const SIInstrInfo *TII, const MachineOperand &Src) {
return isUInt<16>(Src.getImm()) &&
!TII->isInlineConstant(*Src.getParent(),
Src.getParent()->getOperandNo(&Src));
}
static bool isKImmOrKUImmOperand(const SIInstrInfo *TII,
const MachineOperand &Src,
bool &IsUnsigned) {
if (isInt<16>(Src.getImm())) {
IsUnsigned = false;
return !TII->isInlineConstant(Src);
}
if (isUInt<16>(Src.getImm())) {
IsUnsigned = true;
return !TII->isInlineConstant(Src);
}
return false;
}
/// \returns true if the constant in \p Src should be replaced with a bitreverse
/// of an inline immediate.
static bool isReverseInlineImm(const SIInstrInfo *TII,
const MachineOperand &Src,
int32_t &ReverseImm) {
if (!isInt<32>(Src.getImm()) || TII->isInlineConstant(Src))
return false;
ReverseImm = reverseBits<int32_t>(static_cast<int32_t>(Src.getImm()));
return ReverseImm >= -16 && ReverseImm <= 64;
}
/// Copy implicit register operands from specified instruction to this
/// instruction that are not part of the instruction definition.
static void copyExtraImplicitOps(MachineInstr &NewMI, MachineFunction &MF,
const MachineInstr &MI) {
for (unsigned i = MI.getDesc().getNumOperands() +
MI.getDesc().getNumImplicitUses() +
MI.getDesc().getNumImplicitDefs(), e = MI.getNumOperands();
i != e; ++i) {
const MachineOperand &MO = MI.getOperand(i);
if ((MO.isReg() && MO.isImplicit()) || MO.isRegMask())
NewMI.addOperand(MF, MO);
}
}
static void shrinkScalarCompare(const SIInstrInfo *TII, MachineInstr &MI) {
// cmpk instructions do scc = dst <cc op> imm16, so commute the instruction to
// get constants on the RHS.
if (!MI.getOperand(0).isReg())
TII->commuteInstruction(MI, false, 0, 1);
const MachineOperand &Src1 = MI.getOperand(1);
if (!Src1.isImm())
return;
int SOPKOpc = AMDGPU::getSOPKOp(MI.getOpcode());
if (SOPKOpc == -1)
return;
// eq/ne is special because the imm16 can be treated as signed or unsigned,
// and initially selectd to the unsigned versions.
if (SOPKOpc == AMDGPU::S_CMPK_EQ_U32 || SOPKOpc == AMDGPU::S_CMPK_LG_U32) {
bool HasUImm;
if (isKImmOrKUImmOperand(TII, Src1, HasUImm)) {
if (!HasUImm) {
SOPKOpc = (SOPKOpc == AMDGPU::S_CMPK_EQ_U32) ?
AMDGPU::S_CMPK_EQ_I32 : AMDGPU::S_CMPK_LG_I32;
}
MI.setDesc(TII->get(SOPKOpc));
}
return;
}
const MCInstrDesc &NewDesc = TII->get(SOPKOpc);
if ((TII->sopkIsZext(SOPKOpc) && isKUImmOperand(TII, Src1)) ||
(!TII->sopkIsZext(SOPKOpc) && isKImmOperand(TII, Src1))) {
MI.setDesc(NewDesc);
}
}
bool SIShrinkInstructions::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
return false;
MachineRegisterInfo &MRI = MF.getRegInfo();
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
const SIInstrInfo *TII = ST.getInstrInfo();
std::vector<unsigned> I1Defs;
for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
BI != BE; ++BI) {
MachineBasicBlock &MBB = *BI;
MachineBasicBlock::iterator I, Next;
for (I = MBB.begin(); I != MBB.end(); I = Next) {
Next = std::next(I);
MachineInstr &MI = *I;
if (MI.getOpcode() == AMDGPU::V_MOV_B32_e32) {
// If this has a literal constant source that is the same as the
// reversed bits of an inline immediate, replace with a bitreverse of
// that constant. This saves 4 bytes in the common case of materializing
// sign bits.
// Test if we are after regalloc. We only want to do this after any
// optimizations happen because this will confuse them.
// XXX - not exactly a check for post-regalloc run.
MachineOperand &Src = MI.getOperand(1);
if (Src.isImm() &&
TargetRegisterInfo::isPhysicalRegister(MI.getOperand(0).getReg())) {
int32_t ReverseImm;
if (isReverseInlineImm(TII, Src, ReverseImm)) {
MI.setDesc(TII->get(AMDGPU::V_BFREV_B32_e32));
Src.setImm(ReverseImm);
continue;
}
}
}
// Combine adjacent s_nops to use the immediate operand encoding how long
// to wait.
//
// s_nop N
// s_nop M
// =>
// s_nop (N + M)
if (MI.getOpcode() == AMDGPU::S_NOP &&
Next != MBB.end() &&
(*Next).getOpcode() == AMDGPU::S_NOP) {
MachineInstr &NextMI = *Next;
// The instruction encodes the amount to wait with an offset of 1,
// i.e. 0 is wait 1 cycle. Convert both to cycles and then convert back
// after adding.
uint8_t Nop0 = MI.getOperand(0).getImm() + 1;
uint8_t Nop1 = NextMI.getOperand(0).getImm() + 1;
// Make sure we don't overflow the bounds.
if (Nop0 + Nop1 <= 8) {
NextMI.getOperand(0).setImm(Nop0 + Nop1 - 1);
MI.eraseFromParent();
}
continue;
}
// FIXME: We also need to consider movs of constant operands since
// immediate operands are not folded if they have more than one use, and
// the operand folding pass is unaware if the immediate will be free since
// it won't know if the src == dest constraint will end up being
// satisfied.
if (MI.getOpcode() == AMDGPU::S_ADD_I32 ||
MI.getOpcode() == AMDGPU::S_MUL_I32) {
const MachineOperand *Dest = &MI.getOperand(0);
MachineOperand *Src0 = &MI.getOperand(1);
MachineOperand *Src1 = &MI.getOperand(2);
if (!Src0->isReg() && Src1->isReg()) {
if (TII->commuteInstruction(MI, false, 1, 2))
std::swap(Src0, Src1);
}
// FIXME: This could work better if hints worked with subregisters. If
// we have a vector add of a constant, we usually don't get the correct
// allocation due to the subregister usage.
if (TargetRegisterInfo::isVirtualRegister(Dest->getReg()) &&
Src0->isReg()) {
MRI.setRegAllocationHint(Dest->getReg(), 0, Src0->getReg());
MRI.setRegAllocationHint(Src0->getReg(), 0, Dest->getReg());
continue;
}
if (Src0->isReg() && Src0->getReg() == Dest->getReg()) {
if (Src1->isImm() && isKImmOperand(TII, *Src1)) {
unsigned Opc = (MI.getOpcode() == AMDGPU::S_ADD_I32) ?
AMDGPU::S_ADDK_I32 : AMDGPU::S_MULK_I32;
MI.setDesc(TII->get(Opc));
MI.tieOperands(0, 1);
}
}
}
// Try to use s_cmpk_*
if (MI.isCompare() && TII->isSOPC(MI)) {
shrinkScalarCompare(TII, MI);
continue;
}
// Try to use S_MOVK_I32, which will save 4 bytes for small immediates.
if (MI.getOpcode() == AMDGPU::S_MOV_B32) {
const MachineOperand &Dst = MI.getOperand(0);
MachineOperand &Src = MI.getOperand(1);
if (Src.isImm() &&
TargetRegisterInfo::isPhysicalRegister(Dst.getReg())) {
int32_t ReverseImm;
if (isKImmOperand(TII, Src))
MI.setDesc(TII->get(AMDGPU::S_MOVK_I32));
else if (isReverseInlineImm(TII, Src, ReverseImm)) {
MI.setDesc(TII->get(AMDGPU::S_BREV_B32));
Src.setImm(ReverseImm);
}
}
continue;
}
if (!TII->hasVALU32BitEncoding(MI.getOpcode()))
continue;
if (!TII->canShrink(MI, MRI)) {
// Try commuting the instruction and see if that enables us to shrink
// it.
if (!MI.isCommutable() || !TII->commuteInstruction(MI) ||
!TII->canShrink(MI, MRI))
continue;
}
// getVOPe32 could be -1 here if we started with an instruction that had
// a 32-bit encoding and then commuted it to an instruction that did not.
if (!TII->hasVALU32BitEncoding(MI.getOpcode()))
continue;
int Op32 = AMDGPU::getVOPe32(MI.getOpcode());
if (TII->isVOPC(Op32)) {
unsigned DstReg = MI.getOperand(0).getReg();
if (TargetRegisterInfo::isVirtualRegister(DstReg)) {
// VOPC instructions can only write to the VCC register. We can't
// force them to use VCC here, because this is only one register and
// cannot deal with sequences which would require multiple copies of
// VCC, e.g. S_AND_B64 (vcc = V_CMP_...), (vcc = V_CMP_...)
//
// So, instead of forcing the instruction to write to VCC, we provide
// a hint to the register allocator to use VCC and then we will run
// this pass again after RA and shrink it if it outputs to VCC.
MRI.setRegAllocationHint(MI.getOperand(0).getReg(), 0, AMDGPU::VCC);
continue;
}
if (DstReg != AMDGPU::VCC)
continue;
}
if (Op32 == AMDGPU::V_CNDMASK_B32_e32) {
// We shrink V_CNDMASK_B32_e64 using regalloc hints like we do for VOPC
// instructions.
const MachineOperand *Src2 =
TII->getNamedOperand(MI, AMDGPU::OpName::src2);
if (!Src2->isReg())
continue;
unsigned SReg = Src2->getReg();
if (TargetRegisterInfo::isVirtualRegister(SReg)) {
MRI.setRegAllocationHint(SReg, 0, AMDGPU::VCC);
continue;
}
if (SReg != AMDGPU::VCC)
continue;
}
// Check for the bool flag output for instructions like V_ADD_I32_e64.
const MachineOperand *SDst = TII->getNamedOperand(MI,
AMDGPU::OpName::sdst);
// Check the carry-in operand for v_addc_u32_e64.
const MachineOperand *Src2 = TII->getNamedOperand(MI,
AMDGPU::OpName::src2);
if (SDst) {
if (SDst->getReg() != AMDGPU::VCC) {
if (TargetRegisterInfo::isVirtualRegister(SDst->getReg()))
MRI.setRegAllocationHint(SDst->getReg(), 0, AMDGPU::VCC);
continue;
}
// All of the instructions with carry outs also have an SGPR input in
// src2.
if (Src2 && Src2->getReg() != AMDGPU::VCC) {
if (TargetRegisterInfo::isVirtualRegister(Src2->getReg()))
MRI.setRegAllocationHint(Src2->getReg(), 0, AMDGPU::VCC);
continue;
}
}
// We can shrink this instruction
LLVM_DEBUG(dbgs() << "Shrinking " << MI);
MachineInstr *Inst32 = TII->buildShrunkInst(MI, Op32);
++NumInstructionsShrunk;
// Copy extra operands not present in the instruction definition.
copyExtraImplicitOps(*Inst32, MF, MI);
MI.eraseFromParent();
foldImmediates(*Inst32, TII, MRI);
LLVM_DEBUG(dbgs() << "e32 MI = " << *Inst32 << '\n');
}
}
return false;
}
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