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

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//===----------------------- SIFrameLowering.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 "SIFrameLowering.h"
#include "AMDGPUSubtarget.h"
#include "SIInstrInfo.h"
#include "SIMachineFunctionInfo.h"
#include "SIRegisterInfo.h"
#include "MCTargetDesc/AMDGPUMCTargetDesc.h"
#include "llvm/CodeGen/LivePhysRegs.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/RegisterScavenging.h"
using namespace llvm;
static ArrayRef<MCPhysReg> getAllSGPR128(const GCNSubtarget &ST,
const MachineFunction &MF) {
return makeArrayRef(AMDGPU::SGPR_128RegClass.begin(),
ST.getMaxNumSGPRs(MF) / 4);
}
static ArrayRef<MCPhysReg> getAllSGPRs(const GCNSubtarget &ST,
const MachineFunction &MF) {
return makeArrayRef(AMDGPU::SGPR_32RegClass.begin(),
ST.getMaxNumSGPRs(MF));
}
void SIFrameLowering::emitFlatScratchInit(const GCNSubtarget &ST,
MachineFunction &MF,
MachineBasicBlock &MBB) const {
const SIInstrInfo *TII = ST.getInstrInfo();
const SIRegisterInfo* TRI = &TII->getRegisterInfo();
const SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
// We don't need this if we only have spills since there is no user facing
// scratch.
// TODO: If we know we don't have flat instructions earlier, we can omit
// this from the input registers.
//
// TODO: We only need to know if we access scratch space through a flat
// pointer. Because we only detect if flat instructions are used at all,
// this will be used more often than necessary on VI.
// Debug location must be unknown since the first debug location is used to
// determine the end of the prologue.
DebugLoc DL;
MachineBasicBlock::iterator I = MBB.begin();
unsigned FlatScratchInitReg
= MFI->getPreloadedReg(AMDGPUFunctionArgInfo::FLAT_SCRATCH_INIT);
MachineRegisterInfo &MRI = MF.getRegInfo();
MRI.addLiveIn(FlatScratchInitReg);
MBB.addLiveIn(FlatScratchInitReg);
unsigned FlatScrInitLo = TRI->getSubReg(FlatScratchInitReg, AMDGPU::sub0);
unsigned FlatScrInitHi = TRI->getSubReg(FlatScratchInitReg, AMDGPU::sub1);
unsigned ScratchWaveOffsetReg = MFI->getScratchWaveOffsetReg();
// Do a 64-bit pointer add.
if (ST.flatScratchIsPointer()) {
if (ST.getGeneration() >= AMDGPUSubtarget::GFX10) {
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_ADD_U32), FlatScrInitLo)
.addReg(FlatScrInitLo)
.addReg(ScratchWaveOffsetReg);
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_ADDC_U32), FlatScrInitHi)
.addReg(FlatScrInitHi)
.addImm(0);
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_SETREG_B32)).
addReg(FlatScrInitLo).
addImm(int16_t(AMDGPU::Hwreg::ID_FLAT_SCR_LO |
(31 << AMDGPU::Hwreg::WIDTH_M1_SHIFT_)));
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_SETREG_B32)).
addReg(FlatScrInitHi).
addImm(int16_t(AMDGPU::Hwreg::ID_FLAT_SCR_HI |
(31 << AMDGPU::Hwreg::WIDTH_M1_SHIFT_)));
return;
}
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_ADD_U32), AMDGPU::FLAT_SCR_LO)
.addReg(FlatScrInitLo)
.addReg(ScratchWaveOffsetReg);
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_ADDC_U32), AMDGPU::FLAT_SCR_HI)
.addReg(FlatScrInitHi)
.addImm(0);
return;
}
assert(ST.getGeneration() < AMDGPUSubtarget::GFX10);
// Copy the size in bytes.
BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), AMDGPU::FLAT_SCR_LO)
.addReg(FlatScrInitHi, RegState::Kill);
// Add wave offset in bytes to private base offset.
// See comment in AMDKernelCodeT.h for enable_sgpr_flat_scratch_init.
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_ADD_U32), FlatScrInitLo)
.addReg(FlatScrInitLo)
.addReg(ScratchWaveOffsetReg);
// Convert offset to 256-byte units.
BuildMI(MBB, I, DL, TII->get(AMDGPU::S_LSHR_B32), AMDGPU::FLAT_SCR_HI)
.addReg(FlatScrInitLo, RegState::Kill)
.addImm(8);
}
unsigned SIFrameLowering::getReservedPrivateSegmentBufferReg(
const GCNSubtarget &ST,
const SIInstrInfo *TII,
const SIRegisterInfo *TRI,
SIMachineFunctionInfo *MFI,
MachineFunction &MF) const {
MachineRegisterInfo &MRI = MF.getRegInfo();
// We need to insert initialization of the scratch resource descriptor.
unsigned ScratchRsrcReg = MFI->getScratchRSrcReg();
if (ScratchRsrcReg == AMDGPU::NoRegister ||
!MRI.isPhysRegUsed(ScratchRsrcReg))
return AMDGPU::NoRegister;
if (ST.hasSGPRInitBug() ||
ScratchRsrcReg != TRI->reservedPrivateSegmentBufferReg(MF))
return ScratchRsrcReg;
// We reserved the last registers for this. Shift it down to the end of those
// which were actually used.
//
// FIXME: It might be safer to use a pseudoregister before replacement.
// FIXME: We should be able to eliminate unused input registers. We only
// cannot do this for the resources required for scratch access. For now we
// skip over user SGPRs and may leave unused holes.
// We find the resource first because it has an alignment requirement.
unsigned NumPreloaded = (MFI->getNumPreloadedSGPRs() + 3) / 4;
ArrayRef<MCPhysReg> AllSGPR128s = getAllSGPR128(ST, MF);
AllSGPR128s = AllSGPR128s.slice(std::min(static_cast<unsigned>(AllSGPR128s.size()), NumPreloaded));
// Skip the last N reserved elements because they should have already been
// reserved for VCC etc.
for (MCPhysReg Reg : AllSGPR128s) {
// Pick the first unallocated one. Make sure we don't clobber the other
// reserved input we needed.
if (!MRI.isPhysRegUsed(Reg) && MRI.isAllocatable(Reg)) {
MRI.replaceRegWith(ScratchRsrcReg, Reg);
MFI->setScratchRSrcReg(Reg);
return Reg;
}
}
return ScratchRsrcReg;
}
// Shift down registers reserved for the scratch wave offset and stack pointer
// SGPRs.
std::pair<unsigned, unsigned>
SIFrameLowering::getReservedPrivateSegmentWaveByteOffsetReg(
const GCNSubtarget &ST,
const SIInstrInfo *TII,
const SIRegisterInfo *TRI,
SIMachineFunctionInfo *MFI,
MachineFunction &MF) const {
MachineRegisterInfo &MRI = MF.getRegInfo();
unsigned ScratchWaveOffsetReg = MFI->getScratchWaveOffsetReg();
// No replacement necessary.
if (ScratchWaveOffsetReg == AMDGPU::NoRegister ||
!MRI.isPhysRegUsed(ScratchWaveOffsetReg)) {
assert(MFI->getStackPtrOffsetReg() == AMDGPU::SP_REG);
return std::make_pair(AMDGPU::NoRegister, AMDGPU::NoRegister);
}
unsigned SPReg = MFI->getStackPtrOffsetReg();
if (ST.hasSGPRInitBug())
return std::make_pair(ScratchWaveOffsetReg, SPReg);
unsigned NumPreloaded = MFI->getNumPreloadedSGPRs();
ArrayRef<MCPhysReg> AllSGPRs = getAllSGPRs(ST, MF);
if (NumPreloaded > AllSGPRs.size())
return std::make_pair(ScratchWaveOffsetReg, SPReg);
AllSGPRs = AllSGPRs.slice(NumPreloaded);
// We need to drop register from the end of the list that we cannot use
// for the scratch wave offset.
// + 2 s102 and s103 do not exist on VI.
// + 2 for vcc
// + 2 for xnack_mask
// + 2 for flat_scratch
// + 4 for registers reserved for scratch resource register
// + 1 for register reserved for scratch wave offset. (By exluding this
// register from the list to consider, it means that when this
// register is being used for the scratch wave offset and there
// are no other free SGPRs, then the value will stay in this register.
// + 1 if stack pointer is used.
// ----
// 13 (+1)
unsigned ReservedRegCount = 13;
if (AllSGPRs.size() < ReservedRegCount)
return std::make_pair(ScratchWaveOffsetReg, SPReg);
bool HandledScratchWaveOffsetReg =
ScratchWaveOffsetReg != TRI->reservedPrivateSegmentWaveByteOffsetReg(MF);
for (MCPhysReg Reg : AllSGPRs.drop_back(ReservedRegCount)) {
// Pick the first unallocated SGPR. Be careful not to pick an alias of the
// scratch descriptor, since we haven’t added its uses yet.
if (!MRI.isPhysRegUsed(Reg) && MRI.isAllocatable(Reg)) {
if (!HandledScratchWaveOffsetReg) {
HandledScratchWaveOffsetReg = true;
MRI.replaceRegWith(ScratchWaveOffsetReg, Reg);
MFI->setScratchWaveOffsetReg(Reg);
ScratchWaveOffsetReg = Reg;
break;
}
}
}
return std::make_pair(ScratchWaveOffsetReg, SPReg);
}
void SIFrameLowering::emitEntryFunctionPrologue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
// If we only have SGPR spills, we won't actually be using scratch memory
// since these spill to VGPRs.
//
// FIXME: We should be cleaning up these unused SGPR spill frame indices
// somewhere.
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
const SIInstrInfo *TII = ST.getInstrInfo();
const SIRegisterInfo *TRI = &TII->getRegisterInfo();
MachineRegisterInfo &MRI = MF.getRegInfo();
const Function &F = MF.getFunction();
// We need to do the replacement of the private segment buffer and wave offset
// register even if there are no stack objects. There could be stores to undef
// or a constant without an associated object.
// FIXME: We still have implicit uses on SGPR spill instructions in case they
// need to spill to vector memory. It's likely that will not happen, but at
// this point it appears we need the setup. This part of the prolog should be
// emitted after frame indices are eliminated.
if (MFI->hasFlatScratchInit())
emitFlatScratchInit(ST, MF, MBB);
unsigned SPReg = MFI->getStackPtrOffsetReg();
if (SPReg != AMDGPU::SP_REG) {
assert(MRI.isReserved(SPReg) && "SPReg used but not reserved");
DebugLoc DL;
const MachineFrameInfo &FrameInfo = MF.getFrameInfo();
int64_t StackSize = FrameInfo.getStackSize();
if (StackSize == 0) {
BuildMI(MBB, MBB.begin(), DL, TII->get(AMDGPU::COPY), SPReg)
.addReg(MFI->getScratchWaveOffsetReg());
} else {
BuildMI(MBB, MBB.begin(), DL, TII->get(AMDGPU::S_ADD_U32), SPReg)
.addReg(MFI->getScratchWaveOffsetReg())
.addImm(StackSize * ST.getWavefrontSize());
}
}
unsigned ScratchRsrcReg
= getReservedPrivateSegmentBufferReg(ST, TII, TRI, MFI, MF);
unsigned ScratchWaveOffsetReg;
std::tie(ScratchWaveOffsetReg, SPReg)
= getReservedPrivateSegmentWaveByteOffsetReg(ST, TII, TRI, MFI, MF);
// It's possible to have uses of only ScratchWaveOffsetReg without
// ScratchRsrcReg if it's only used for the initialization of flat_scratch,
// but the inverse is not true.
if (ScratchWaveOffsetReg == AMDGPU::NoRegister) {
assert(ScratchRsrcReg == AMDGPU::NoRegister);
return;
}
// We need to insert initialization of the scratch resource descriptor.
unsigned PreloadedScratchWaveOffsetReg = MFI->getPreloadedReg(
AMDGPUFunctionArgInfo::PRIVATE_SEGMENT_WAVE_BYTE_OFFSET);
unsigned PreloadedPrivateBufferReg = AMDGPU::NoRegister;
if (ST.isAmdHsaOrMesa(F)) {
PreloadedPrivateBufferReg = MFI->getPreloadedReg(
AMDGPUFunctionArgInfo::PRIVATE_SEGMENT_BUFFER);
}
bool OffsetRegUsed = MRI.isPhysRegUsed(ScratchWaveOffsetReg);
bool ResourceRegUsed = ScratchRsrcReg != AMDGPU::NoRegister &&
MRI.isPhysRegUsed(ScratchRsrcReg);
// We added live-ins during argument lowering, but since they were not used
// they were deleted. We're adding the uses now, so add them back.
if (OffsetRegUsed) {
assert(PreloadedScratchWaveOffsetReg != AMDGPU::NoRegister &&
"scratch wave offset input is required");
MRI.addLiveIn(PreloadedScratchWaveOffsetReg);
MBB.addLiveIn(PreloadedScratchWaveOffsetReg);
}
if (ResourceRegUsed && PreloadedPrivateBufferReg != AMDGPU::NoRegister) {
assert(ST.isAmdHsaOrMesa(F) || ST.isMesaGfxShader(F));
MRI.addLiveIn(PreloadedPrivateBufferReg);
MBB.addLiveIn(PreloadedPrivateBufferReg);
}
// Make the register selected live throughout the function.
for (MachineBasicBlock &OtherBB : MF) {
if (&OtherBB == &MBB)
continue;
if (OffsetRegUsed)
OtherBB.addLiveIn(ScratchWaveOffsetReg);
if (ResourceRegUsed)
OtherBB.addLiveIn(ScratchRsrcReg);
}
DebugLoc DL;
MachineBasicBlock::iterator I = MBB.begin();
// If we reserved the original input registers, we don't need to copy to the
// reserved registers.
bool CopyBuffer = ResourceRegUsed &&
PreloadedPrivateBufferReg != AMDGPU::NoRegister &&
ST.isAmdHsaOrMesa(F) &&
ScratchRsrcReg != PreloadedPrivateBufferReg;
// This needs to be careful of the copying order to avoid overwriting one of
// the input registers before it's been copied to it's final
// destination. Usually the offset should be copied first.
bool CopyBufferFirst = TRI->isSubRegisterEq(PreloadedPrivateBufferReg,
ScratchWaveOffsetReg);
if (CopyBuffer && CopyBufferFirst) {
BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), ScratchRsrcReg)
.addReg(PreloadedPrivateBufferReg, RegState::Kill);
}
if (OffsetRegUsed &&
PreloadedScratchWaveOffsetReg != ScratchWaveOffsetReg) {
BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), ScratchWaveOffsetReg)
.addReg(PreloadedScratchWaveOffsetReg,
MRI.isPhysRegUsed(ScratchWaveOffsetReg) ? 0 : RegState::Kill);
}
if (CopyBuffer && !CopyBufferFirst) {
BuildMI(MBB, I, DL, TII->get(AMDGPU::COPY), ScratchRsrcReg)
.addReg(PreloadedPrivateBufferReg, RegState::Kill);
}
if (ResourceRegUsed)
emitEntryFunctionScratchSetup(ST, MF, MBB, MFI, I,
PreloadedPrivateBufferReg, ScratchRsrcReg);
}
// Emit scratch setup code for AMDPAL or Mesa, assuming ResourceRegUsed is set.
void SIFrameLowering::emitEntryFunctionScratchSetup(const GCNSubtarget &ST,
MachineFunction &MF, MachineBasicBlock &MBB, SIMachineFunctionInfo *MFI,
MachineBasicBlock::iterator I, unsigned PreloadedPrivateBufferReg,
unsigned ScratchRsrcReg) const {
const SIInstrInfo *TII = ST.getInstrInfo();
const SIRegisterInfo *TRI = &TII->getRegisterInfo();
const Function &Fn = MF.getFunction();
DebugLoc DL;
if (ST.isAmdPalOS()) {
// The pointer to the GIT is formed from the offset passed in and either
// the amdgpu-git-ptr-high function attribute or the top part of the PC
unsigned RsrcLo = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub0);
unsigned RsrcHi = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub1);
unsigned Rsrc01 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub0_sub1);
const MCInstrDesc &SMovB32 = TII->get(AMDGPU::S_MOV_B32);
if (MFI->getGITPtrHigh() != 0xffffffff) {
BuildMI(MBB, I, DL, SMovB32, RsrcHi)
.addImm(MFI->getGITPtrHigh())
.addReg(ScratchRsrcReg, RegState::ImplicitDefine);
} else {
const MCInstrDesc &GetPC64 = TII->get(AMDGPU::S_GETPC_B64);
BuildMI(MBB, I, DL, GetPC64, Rsrc01);
}
auto GitPtrLo = AMDGPU::SGPR0; // Low GIT address passed in
if (ST.hasMergedShaders()) {
switch (MF.getFunction().getCallingConv()) {
case CallingConv::AMDGPU_HS:
case CallingConv::AMDGPU_GS:
// Low GIT address is passed in s8 rather than s0 for an LS+HS or
// ES+GS merged shader on gfx9+.
GitPtrLo = AMDGPU::SGPR8;
break;
default:
break;
}
}
MF.getRegInfo().addLiveIn(GitPtrLo);
MF.front().addLiveIn(GitPtrLo);
BuildMI(MBB, I, DL, SMovB32, RsrcLo)
.addReg(GitPtrLo)
.addReg(ScratchRsrcReg, RegState::ImplicitDefine);
// We now have the GIT ptr - now get the scratch descriptor from the entry
// at offset 0 (or offset 16 for a compute shader).
PointerType *PtrTy =
PointerType::get(Type::getInt64Ty(MF.getFunction().getContext()),
AMDGPUAS::CONSTANT_ADDRESS);
MachinePointerInfo PtrInfo(UndefValue::get(PtrTy));
const MCInstrDesc &LoadDwordX4 = TII->get(AMDGPU::S_LOAD_DWORDX4_IMM);
auto MMO = MF.getMachineMemOperand(PtrInfo,
MachineMemOperand::MOLoad |
MachineMemOperand::MOInvariant |
MachineMemOperand::MODereferenceable,
16, 4);
unsigned Offset = Fn.getCallingConv() == CallingConv::AMDGPU_CS ? 16 : 0;
const GCNSubtarget &Subtarget = MF.getSubtarget<GCNSubtarget>();
unsigned EncodedOffset = AMDGPU::getSMRDEncodedOffset(Subtarget, Offset);
BuildMI(MBB, I, DL, LoadDwordX4, ScratchRsrcReg)
.addReg(Rsrc01)
.addImm(EncodedOffset) // offset
.addImm(0) // glc
.addImm(0) // dlc
.addReg(ScratchRsrcReg, RegState::ImplicitDefine)
.addMemOperand(MMO);
return;
}
if (ST.isMesaGfxShader(Fn)
|| (PreloadedPrivateBufferReg == AMDGPU::NoRegister)) {
assert(!ST.isAmdHsaOrMesa(Fn));
const MCInstrDesc &SMovB32 = TII->get(AMDGPU::S_MOV_B32);
unsigned Rsrc2 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub2);
unsigned Rsrc3 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub3);
// Use relocations to get the pointer, and setup the other bits manually.
uint64_t Rsrc23 = TII->getScratchRsrcWords23();
if (MFI->hasImplicitBufferPtr()) {
unsigned Rsrc01 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub0_sub1);
if (AMDGPU::isCompute(MF.getFunction().getCallingConv())) {
const MCInstrDesc &Mov64 = TII->get(AMDGPU::S_MOV_B64);
BuildMI(MBB, I, DL, Mov64, Rsrc01)
.addReg(MFI->getImplicitBufferPtrUserSGPR())
.addReg(ScratchRsrcReg, RegState::ImplicitDefine);
} else {
const MCInstrDesc &LoadDwordX2 = TII->get(AMDGPU::S_LOAD_DWORDX2_IMM);
PointerType *PtrTy =
PointerType::get(Type::getInt64Ty(MF.getFunction().getContext()),
AMDGPUAS::CONSTANT_ADDRESS);
MachinePointerInfo PtrInfo(UndefValue::get(PtrTy));
auto MMO = MF.getMachineMemOperand(PtrInfo,
MachineMemOperand::MOLoad |
MachineMemOperand::MOInvariant |
MachineMemOperand::MODereferenceable,
8, 4);
BuildMI(MBB, I, DL, LoadDwordX2, Rsrc01)
.addReg(MFI->getImplicitBufferPtrUserSGPR())
.addImm(0) // offset
.addImm(0) // glc
.addImm(0) // dlc
.addMemOperand(MMO)
.addReg(ScratchRsrcReg, RegState::ImplicitDefine);
}
} else {
unsigned Rsrc0 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub0);
unsigned Rsrc1 = TRI->getSubReg(ScratchRsrcReg, AMDGPU::sub1);
BuildMI(MBB, I, DL, SMovB32, Rsrc0)
.addExternalSymbol("SCRATCH_RSRC_DWORD0")
.addReg(ScratchRsrcReg, RegState::ImplicitDefine);
BuildMI(MBB, I, DL, SMovB32, Rsrc1)
.addExternalSymbol("SCRATCH_RSRC_DWORD1")
.addReg(ScratchRsrcReg, RegState::ImplicitDefine);
}
BuildMI(MBB, I, DL, SMovB32, Rsrc2)
.addImm(Rsrc23 & 0xffffffff)
.addReg(ScratchRsrcReg, RegState::ImplicitDefine);
BuildMI(MBB, I, DL, SMovB32, Rsrc3)
.addImm(Rsrc23 >> 32)
.addReg(ScratchRsrcReg, RegState::ImplicitDefine);
}
}
// Find a scratch register that we can use at the start of the prologue to
// re-align the stack pointer. We avoid using callee-save registers since they
// may appear to be free when this is called from canUseAsPrologue (during
// shrink wrapping), but then no longer be free when this is called from
// emitPrologue.
//
// FIXME: This is a bit conservative, since in the above case we could use one
// of the callee-save registers as a scratch temp to re-align the stack pointer,
// but we would then have to make sure that we were in fact saving at least one
// callee-save register in the prologue, which is additional complexity that
// doesn't seem worth the benefit.
static unsigned findScratchNonCalleeSaveRegister(MachineBasicBlock &MBB) {
MachineFunction *MF = MBB.getParent();
const GCNSubtarget &Subtarget = MF->getSubtarget<GCNSubtarget>();
const SIRegisterInfo &TRI = *Subtarget.getRegisterInfo();
LivePhysRegs LiveRegs(TRI);
LiveRegs.addLiveIns(MBB);
// Mark callee saved registers as used so we will not choose them.
const MCPhysReg *CSRegs = TRI.getCalleeSavedRegs(MF);
for (unsigned i = 0; CSRegs[i]; ++i)
LiveRegs.addReg(CSRegs[i]);
MachineRegisterInfo &MRI = MF->getRegInfo();
for (unsigned Reg : AMDGPU::SReg_32_XM0RegClass) {
if (LiveRegs.available(MRI, Reg))
return Reg;
}
return AMDGPU::NoRegister;
}
void SIFrameLowering::emitPrologue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
SIMachineFunctionInfo *FuncInfo = MF.getInfo<SIMachineFunctionInfo>();
if (FuncInfo->isEntryFunction()) {
emitEntryFunctionPrologue(MF, MBB);
return;
}
const MachineFrameInfo &MFI = MF.getFrameInfo();
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
const SIInstrInfo *TII = ST.getInstrInfo();
const SIRegisterInfo &TRI = TII->getRegisterInfo();
unsigned StackPtrReg = FuncInfo->getStackPtrOffsetReg();
unsigned FramePtrReg = FuncInfo->getFrameOffsetReg();
MachineBasicBlock::iterator MBBI = MBB.begin();
DebugLoc DL;
// XXX - Is this the right predicate?
bool NeedFP = hasFP(MF);
uint32_t NumBytes = MFI.getStackSize();
uint32_t RoundedSize = NumBytes;
const bool NeedsRealignment = TRI.needsStackRealignment(MF);
if (NeedsRealignment) {
assert(NeedFP);
const unsigned Alignment = MFI.getMaxAlignment();
RoundedSize += Alignment;
unsigned ScratchSPReg = findScratchNonCalleeSaveRegister(MBB);
assert(ScratchSPReg != AMDGPU::NoRegister);
// s_add_u32 tmp_reg, s32, NumBytes
// s_and_b32 s32, tmp_reg, 0b111...0000
BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::S_ADD_U32), ScratchSPReg)
.addReg(StackPtrReg)
.addImm((Alignment - 1) * ST.getWavefrontSize())
.setMIFlag(MachineInstr::FrameSetup);
BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::S_AND_B32), FramePtrReg)
.addReg(ScratchSPReg, RegState::Kill)
.addImm(-Alignment * ST.getWavefrontSize())
.setMIFlag(MachineInstr::FrameSetup);
FuncInfo->setIsStackRealigned(true);
} else if (NeedFP) {
// If we need a base pointer, set it up here. It's whatever the value of
// the stack pointer is at this point. Any variable size objects will be
// allocated after this, so we can still use the base pointer to reference
// locals.
BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::COPY), FramePtrReg)
.addReg(StackPtrReg)
.setMIFlag(MachineInstr::FrameSetup);
}
if (RoundedSize != 0 && hasSP(MF)) {
BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::S_ADD_U32), StackPtrReg)
.addReg(StackPtrReg)
.addImm(RoundedSize * ST.getWavefrontSize())
.setMIFlag(MachineInstr::FrameSetup);
}
for (const SIMachineFunctionInfo::SGPRSpillVGPRCSR &Reg
: FuncInfo->getSGPRSpillVGPRs()) {
if (!Reg.FI.hasValue())
continue;
TII->storeRegToStackSlot(MBB, MBBI, Reg.VGPR, true,
Reg.FI.getValue(), &AMDGPU::VGPR_32RegClass,
&TII->getRegisterInfo());
}
}
void SIFrameLowering::emitEpilogue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
const SIMachineFunctionInfo *FuncInfo = MF.getInfo<SIMachineFunctionInfo>();
if (FuncInfo->isEntryFunction())
return;
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
const SIInstrInfo *TII = ST.getInstrInfo();
MachineBasicBlock::iterator MBBI = MBB.getFirstTerminator();
for (const SIMachineFunctionInfo::SGPRSpillVGPRCSR &Reg
: FuncInfo->getSGPRSpillVGPRs()) {
if (!Reg.FI.hasValue())
continue;
TII->loadRegFromStackSlot(MBB, MBBI, Reg.VGPR,
Reg.FI.getValue(), &AMDGPU::VGPR_32RegClass,
&TII->getRegisterInfo());
}
unsigned StackPtrReg = FuncInfo->getStackPtrOffsetReg();
if (StackPtrReg == AMDGPU::NoRegister)
return;
const MachineFrameInfo &MFI = MF.getFrameInfo();
uint32_t NumBytes = MFI.getStackSize();
DebugLoc DL;
// FIXME: Clarify distinction between no set SP and SP. For callee functions,
// it's really whether we need SP to be accurate or not.
if (NumBytes != 0 && hasSP(MF)) {
uint32_t RoundedSize = FuncInfo->isStackRealigned() ?
NumBytes + MFI.getMaxAlignment() : NumBytes;
BuildMI(MBB, MBBI, DL, TII->get(AMDGPU::S_SUB_U32), StackPtrReg)
.addReg(StackPtrReg)
.addImm(RoundedSize * ST.getWavefrontSize());
}
}
static bool allStackObjectsAreDead(const MachineFrameInfo &MFI) {
for (int I = MFI.getObjectIndexBegin(), E = MFI.getObjectIndexEnd();
I != E; ++I) {
if (!MFI.isDeadObjectIndex(I))
return false;
}
return true;
}
int SIFrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
unsigned &FrameReg) const {
const SIRegisterInfo *RI = MF.getSubtarget<GCNSubtarget>().getRegisterInfo();
FrameReg = RI->getFrameRegister(MF);
return MF.getFrameInfo().getObjectOffset(FI);
}
void SIFrameLowering::processFunctionBeforeFrameFinalized(
MachineFunction &MF,
RegScavenger *RS) const {
MachineFrameInfo &MFI = MF.getFrameInfo();
if (!MFI.hasStackObjects())
return;
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
const SIInstrInfo *TII = ST.getInstrInfo();
const SIRegisterInfo &TRI = TII->getRegisterInfo();
SIMachineFunctionInfo *FuncInfo = MF.getInfo<SIMachineFunctionInfo>();
bool AllSGPRSpilledToVGPRs = false;
if (TRI.spillSGPRToVGPR() && FuncInfo->hasSpilledSGPRs()) {
AllSGPRSpilledToVGPRs = true;
// Process all SGPR spills before frame offsets are finalized. Ideally SGPRs
// are spilled to VGPRs, in which case we can eliminate the stack usage.
//
// XXX - This operates under the assumption that only other SGPR spills are
// users of the frame index. I'm not 100% sure this is correct. The
// StackColoring pass has a comment saying a future improvement would be to
// merging of allocas with spill slots, but for now according to
// MachineFrameInfo isSpillSlot can't alias any other object.
for (MachineBasicBlock &MBB : MF) {
MachineBasicBlock::iterator Next;
for (auto I = MBB.begin(), E = MBB.end(); I != E; I = Next) {
MachineInstr &MI = *I;
Next = std::next(I);
if (TII->isSGPRSpill(MI)) {
int FI = TII->getNamedOperand(MI, AMDGPU::OpName::addr)->getIndex();
assert(MFI.getStackID(FI) == SIStackID::SGPR_SPILL);
if (FuncInfo->allocateSGPRSpillToVGPR(MF, FI)) {
bool Spilled = TRI.eliminateSGPRToVGPRSpillFrameIndex(MI, FI, RS);
(void)Spilled;
assert(Spilled && "failed to spill SGPR to VGPR when allocated");
} else
AllSGPRSpilledToVGPRs = false;
}
}
}
}
FuncInfo->removeSGPRToVGPRFrameIndices(MFI);
// FIXME: The other checks should be redundant with allStackObjectsAreDead,
// but currently hasNonSpillStackObjects is set only from source
// allocas. Stack temps produced from legalization are not counted currently.
if (FuncInfo->hasNonSpillStackObjects() || FuncInfo->hasSpilledVGPRs() ||
!AllSGPRSpilledToVGPRs || !allStackObjectsAreDead(MFI)) {
assert(RS && "RegScavenger required if spilling");
// We force this to be at offset 0 so no user object ever has 0 as an
// address, so we may use 0 as an invalid pointer value. This is because
// LLVM assumes 0 is an invalid pointer in address space 0. Because alloca
// is required to be address space 0, we are forced to accept this for
// now. Ideally we could have the stack in another address space with 0 as a
// valid pointer, and -1 as the null value.
//
// This will also waste additional space when user stack objects require > 4
// byte alignment.
//
// The main cost here is losing the offset for addressing modes. However
// this also ensures we shouldn't need a register for the offset when
// emergency scavenging.
int ScavengeFI = MFI.CreateFixedObject(
TRI.getSpillSize(AMDGPU::SGPR_32RegClass), 0, false);
RS->addScavengingFrameIndex(ScavengeFI);
}
}
void SIFrameLowering::determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
RegScavenger *RS) const {
TargetFrameLowering::determineCalleeSaves(MF, SavedRegs, RS);
const SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
// The SP is specifically managed and we don't want extra spills of it.
SavedRegs.reset(MFI->getStackPtrOffsetReg());
}
MachineBasicBlock::iterator SIFrameLowering::eliminateCallFramePseudoInstr(
MachineFunction &MF,
MachineBasicBlock &MBB,
MachineBasicBlock::iterator I) const {
int64_t Amount = I->getOperand(0).getImm();
if (Amount == 0)
return MBB.erase(I);
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
const SIInstrInfo *TII = ST.getInstrInfo();
const DebugLoc &DL = I->getDebugLoc();
unsigned Opc = I->getOpcode();
bool IsDestroy = Opc == TII->getCallFrameDestroyOpcode();
uint64_t CalleePopAmount = IsDestroy ? I->getOperand(1).getImm() : 0;
const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
if (!TFI->hasReservedCallFrame(MF)) {
unsigned Align = getStackAlignment();
Amount = alignTo(Amount, Align);
assert(isUInt<32>(Amount) && "exceeded stack address space size");
const SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
unsigned SPReg = MFI->getStackPtrOffsetReg();
unsigned Op = IsDestroy ? AMDGPU::S_SUB_U32 : AMDGPU::S_ADD_U32;
BuildMI(MBB, I, DL, TII->get(Op), SPReg)
.addReg(SPReg)
.addImm(Amount * ST.getWavefrontSize());
} else if (CalleePopAmount != 0) {
llvm_unreachable("is this used?");
}
return MBB.erase(I);
}
bool SIFrameLowering::hasFP(const MachineFunction &MF) const {
// All stack operations are relative to the frame offset SGPR.
// TODO: Still want to eliminate sometimes.
const MachineFrameInfo &MFI = MF.getFrameInfo();
// XXX - Is this only called after frame is finalized? Should be able to check
// frame size.
return MFI.hasStackObjects() && !allStackObjectsAreDead(MFI);
}
bool SIFrameLowering::hasSP(const MachineFunction &MF) const {
const SIRegisterInfo *TRI = MF.getSubtarget<GCNSubtarget>().getRegisterInfo();
// All stack operations are relative to the frame offset SGPR.
const MachineFrameInfo &MFI = MF.getFrameInfo();
return MFI.hasCalls() || MFI.hasVarSizedObjects() || TRI->needsStackRealignment(MF);
}
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