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PPCFrameLowering.cpp
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PPCFrameLowering.cpp
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//===-- PPCFrameLowering.cpp - PPC Frame Information ----------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file contains the PPC implementation of TargetFrameLowering class.
//
//===----------------------------------------------------------------------===//
#include "PPCFrameLowering.h"
#include "PPCInstrBuilder.h"
#include "PPCInstrInfo.h"
#include "PPCMachineFunctionInfo.h"
#include "PPCSubtarget.h"
#include "PPCTargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/IR/Function.h"
#include "llvm/Target/TargetOptions.h"
using namespace llvm;
#define DEBUG_TYPE "framelowering"
STATISTIC(NumPESpillVSR, "Number of spills to vector in prologue");
STATISTIC(NumPEReloadVSR, "Number of reloads from vector in epilogue");
static cl::opt<bool>
EnablePEVectorSpills("ppc-enable-pe-vector-spills",
cl::desc("Enable spills in prologue to vector registers."),
cl::init(false), cl::Hidden);
/// VRRegNo - Map from a numbered VR register to its enum value.
///
static const MCPhysReg VRRegNo[] = {
PPC::V0 , PPC::V1 , PPC::V2 , PPC::V3 , PPC::V4 , PPC::V5 , PPC::V6 , PPC::V7 ,
PPC::V8 , PPC::V9 , PPC::V10, PPC::V11, PPC::V12, PPC::V13, PPC::V14, PPC::V15,
PPC::V16, PPC::V17, PPC::V18, PPC::V19, PPC::V20, PPC::V21, PPC::V22, PPC::V23,
PPC::V24, PPC::V25, PPC::V26, PPC::V27, PPC::V28, PPC::V29, PPC::V30, PPC::V31
};
static unsigned computeReturnSaveOffset(const PPCSubtarget &STI) {
if (STI.isAIXABI())
return STI.isPPC64() ? 16 : 8;
// SVR4 ABI:
return STI.isPPC64() ? 16 : 4;
}
static unsigned computeTOCSaveOffset(const PPCSubtarget &STI) {
if (STI.isAIXABI())
return STI.isPPC64() ? 40 : 20;
return STI.isELFv2ABI() ? 24 : 40;
}
static unsigned computeFramePointerSaveOffset(const PPCSubtarget &STI) {
// First slot in the general register save area.
return STI.isPPC64() ? -8U : -4U;
}
static unsigned computeLinkageSize(const PPCSubtarget &STI) {
if (STI.isAIXABI() || STI.isPPC64())
return (STI.isELFv2ABI() ? 4 : 6) * (STI.isPPC64() ? 8 : 4);
// 32-bit SVR4 ABI:
return 8;
}
static unsigned computeBasePointerSaveOffset(const PPCSubtarget &STI) {
// SVR4 ABI: First slot in the general register save area.
return STI.isPPC64()
? -16U
: STI.getTargetMachine().isPositionIndependent() ? -12U : -8U;
}
static unsigned computeCRSaveOffset(const PPCSubtarget &STI) {
return (STI.isAIXABI() && !STI.isPPC64()) ? 4 : 8;
}
PPCFrameLowering::PPCFrameLowering(const PPCSubtarget &STI)
: TargetFrameLowering(TargetFrameLowering::StackGrowsDown,
STI.getPlatformStackAlignment(), 0),
Subtarget(STI), ReturnSaveOffset(computeReturnSaveOffset(Subtarget)),
TOCSaveOffset(computeTOCSaveOffset(Subtarget)),
FramePointerSaveOffset(computeFramePointerSaveOffset(Subtarget)),
LinkageSize(computeLinkageSize(Subtarget)),
BasePointerSaveOffset(computeBasePointerSaveOffset(Subtarget)),
CRSaveOffset(computeCRSaveOffset(Subtarget)) {}
// With the SVR4 ABI, callee-saved registers have fixed offsets on the stack.
const PPCFrameLowering::SpillSlot *PPCFrameLowering::getCalleeSavedSpillSlots(
unsigned &NumEntries) const {
// Early exit if not using the SVR4 ABI.
if (!Subtarget.isSVR4ABI()) {
NumEntries = 0;
return nullptr;
}
// Floating-point register save area offsets.
#define CALLEE_SAVED_FPRS \
{PPC::F31, -8}, \
{PPC::F30, -16}, \
{PPC::F29, -24}, \
{PPC::F28, -32}, \
{PPC::F27, -40}, \
{PPC::F26, -48}, \
{PPC::F25, -56}, \
{PPC::F24, -64}, \
{PPC::F23, -72}, \
{PPC::F22, -80}, \
{PPC::F21, -88}, \
{PPC::F20, -96}, \
{PPC::F19, -104}, \
{PPC::F18, -112}, \
{PPC::F17, -120}, \
{PPC::F16, -128}, \
{PPC::F15, -136}, \
{PPC::F14, -144}
// 32-bit general purpose register save area offsets.
#define CALLEE_SAVED_GPRS32 \
{PPC::R31, -4}, \
{PPC::R30, -8}, \
{PPC::R29, -12}, \
{PPC::R28, -16}, \
{PPC::R27, -20}, \
{PPC::R26, -24}, \
{PPC::R25, -28}, \
{PPC::R24, -32}, \
{PPC::R23, -36}, \
{PPC::R22, -40}, \
{PPC::R21, -44}, \
{PPC::R20, -48}, \
{PPC::R19, -52}, \
{PPC::R18, -56}, \
{PPC::R17, -60}, \
{PPC::R16, -64}, \
{PPC::R15, -68}, \
{PPC::R14, -72}
// 64-bit general purpose register save area offsets.
#define CALLEE_SAVED_GPRS64 \
{PPC::X31, -8}, \
{PPC::X30, -16}, \
{PPC::X29, -24}, \
{PPC::X28, -32}, \
{PPC::X27, -40}, \
{PPC::X26, -48}, \
{PPC::X25, -56}, \
{PPC::X24, -64}, \
{PPC::X23, -72}, \
{PPC::X22, -80}, \
{PPC::X21, -88}, \
{PPC::X20, -96}, \
{PPC::X19, -104}, \
{PPC::X18, -112}, \
{PPC::X17, -120}, \
{PPC::X16, -128}, \
{PPC::X15, -136}, \
{PPC::X14, -144}
// Vector register save area offsets.
#define CALLEE_SAVED_VRS \
{PPC::V31, -16}, \
{PPC::V30, -32}, \
{PPC::V29, -48}, \
{PPC::V28, -64}, \
{PPC::V27, -80}, \
{PPC::V26, -96}, \
{PPC::V25, -112}, \
{PPC::V24, -128}, \
{PPC::V23, -144}, \
{PPC::V22, -160}, \
{PPC::V21, -176}, \
{PPC::V20, -192}
// Note that the offsets here overlap, but this is fixed up in
// processFunctionBeforeFrameFinalized.
static const SpillSlot Offsets[] = {
CALLEE_SAVED_FPRS,
CALLEE_SAVED_GPRS32,
// CR save area offset. We map each of the nonvolatile CR fields
// to the slot for CR2, which is the first of the nonvolatile CR
// fields to be assigned, so that we only allocate one save slot.
// See PPCRegisterInfo::hasReservedSpillSlot() for more information.
{PPC::CR2, -4},
// VRSAVE save area offset.
{PPC::VRSAVE, -4},
CALLEE_SAVED_VRS,
// SPE register save area (overlaps Vector save area).
{PPC::S31, -8},
{PPC::S30, -16},
{PPC::S29, -24},
{PPC::S28, -32},
{PPC::S27, -40},
{PPC::S26, -48},
{PPC::S25, -56},
{PPC::S24, -64},
{PPC::S23, -72},
{PPC::S22, -80},
{PPC::S21, -88},
{PPC::S20, -96},
{PPC::S19, -104},
{PPC::S18, -112},
{PPC::S17, -120},
{PPC::S16, -128},
{PPC::S15, -136},
{PPC::S14, -144}};
static const SpillSlot Offsets64[] = {
CALLEE_SAVED_FPRS,
CALLEE_SAVED_GPRS64,
// VRSAVE save area offset.
{PPC::VRSAVE, -4},
CALLEE_SAVED_VRS
};
if (Subtarget.isPPC64()) {
NumEntries = array_lengthof(Offsets64);
return Offsets64;
} else {
NumEntries = array_lengthof(Offsets);
return Offsets;
}
}
/// RemoveVRSaveCode - We have found that this function does not need any code
/// to manipulate the VRSAVE register, even though it uses vector registers.
/// This can happen when the only registers used are known to be live in or out
/// of the function. Remove all of the VRSAVE related code from the function.
/// FIXME: The removal of the code results in a compile failure at -O0 when the
/// function contains a function call, as the GPR containing original VRSAVE
/// contents is spilled and reloaded around the call. Without the prolog code,
/// the spill instruction refers to an undefined register. This code needs
/// to account for all uses of that GPR.
static void RemoveVRSaveCode(MachineInstr &MI) {
MachineBasicBlock *Entry = MI.getParent();
MachineFunction *MF = Entry->getParent();
// We know that the MTVRSAVE instruction immediately follows MI. Remove it.
MachineBasicBlock::iterator MBBI = MI;
++MBBI;
assert(MBBI != Entry->end() && MBBI->getOpcode() == PPC::MTVRSAVE);
MBBI->eraseFromParent();
bool RemovedAllMTVRSAVEs = true;
// See if we can find and remove the MTVRSAVE instruction from all of the
// epilog blocks.
for (MachineFunction::iterator I = MF->begin(), E = MF->end(); I != E; ++I) {
// If last instruction is a return instruction, add an epilogue
if (I->isReturnBlock()) {
bool FoundIt = false;
for (MBBI = I->end(); MBBI != I->begin(); ) {
--MBBI;
if (MBBI->getOpcode() == PPC::MTVRSAVE) {
MBBI->eraseFromParent(); // remove it.
FoundIt = true;
break;
}
}
RemovedAllMTVRSAVEs &= FoundIt;
}
}
// If we found and removed all MTVRSAVE instructions, remove the read of
// VRSAVE as well.
if (RemovedAllMTVRSAVEs) {
MBBI = MI;
assert(MBBI != Entry->begin() && "UPDATE_VRSAVE is first instr in block?");
--MBBI;
assert(MBBI->getOpcode() == PPC::MFVRSAVE && "VRSAVE instrs wandered?");
MBBI->eraseFromParent();
}
// Finally, nuke the UPDATE_VRSAVE.
MI.eraseFromParent();
}
// HandleVRSaveUpdate - MI is the UPDATE_VRSAVE instruction introduced by the
// instruction selector. Based on the vector registers that have been used,
// transform this into the appropriate ORI instruction.
static void HandleVRSaveUpdate(MachineInstr &MI, const TargetInstrInfo &TII) {
MachineFunction *MF = MI.getParent()->getParent();
const TargetRegisterInfo *TRI = MF->getSubtarget().getRegisterInfo();
DebugLoc dl = MI.getDebugLoc();
const MachineRegisterInfo &MRI = MF->getRegInfo();
unsigned UsedRegMask = 0;
for (unsigned i = 0; i != 32; ++i)
if (MRI.isPhysRegModified(VRRegNo[i]))
UsedRegMask |= 1 << (31-i);
// Live in and live out values already must be in the mask, so don't bother
// marking them.
for (std::pair<unsigned, unsigned> LI : MF->getRegInfo().liveins()) {
unsigned RegNo = TRI->getEncodingValue(LI.first);
if (VRRegNo[RegNo] == LI.first) // If this really is a vector reg.
UsedRegMask &= ~(1 << (31-RegNo)); // Doesn't need to be marked.
}
// Live out registers appear as use operands on return instructions.
for (MachineFunction::const_iterator BI = MF->begin(), BE = MF->end();
UsedRegMask != 0 && BI != BE; ++BI) {
const MachineBasicBlock &MBB = *BI;
if (!MBB.isReturnBlock())
continue;
const MachineInstr &Ret = MBB.back();
for (unsigned I = 0, E = Ret.getNumOperands(); I != E; ++I) {
const MachineOperand &MO = Ret.getOperand(I);
if (!MO.isReg() || !PPC::VRRCRegClass.contains(MO.getReg()))
continue;
unsigned RegNo = TRI->getEncodingValue(MO.getReg());
UsedRegMask &= ~(1 << (31-RegNo));
}
}
// If no registers are used, turn this into a copy.
if (UsedRegMask == 0) {
// Remove all VRSAVE code.
RemoveVRSaveCode(MI);
return;
}
Register SrcReg = MI.getOperand(1).getReg();
Register DstReg = MI.getOperand(0).getReg();
if ((UsedRegMask & 0xFFFF) == UsedRegMask) {
if (DstReg != SrcReg)
BuildMI(*MI.getParent(), MI, dl, TII.get(PPC::ORI), DstReg)
.addReg(SrcReg)
.addImm(UsedRegMask);
else
BuildMI(*MI.getParent(), MI, dl, TII.get(PPC::ORI), DstReg)
.addReg(SrcReg, RegState::Kill)
.addImm(UsedRegMask);
} else if ((UsedRegMask & 0xFFFF0000) == UsedRegMask) {
if (DstReg != SrcReg)
BuildMI(*MI.getParent(), MI, dl, TII.get(PPC::ORIS), DstReg)
.addReg(SrcReg)
.addImm(UsedRegMask >> 16);
else
BuildMI(*MI.getParent(), MI, dl, TII.get(PPC::ORIS), DstReg)
.addReg(SrcReg, RegState::Kill)
.addImm(UsedRegMask >> 16);
} else {
if (DstReg != SrcReg)
BuildMI(*MI.getParent(), MI, dl, TII.get(PPC::ORIS), DstReg)
.addReg(SrcReg)
.addImm(UsedRegMask >> 16);
else
BuildMI(*MI.getParent(), MI, dl, TII.get(PPC::ORIS), DstReg)
.addReg(SrcReg, RegState::Kill)
.addImm(UsedRegMask >> 16);
BuildMI(*MI.getParent(), MI, dl, TII.get(PPC::ORI), DstReg)
.addReg(DstReg, RegState::Kill)
.addImm(UsedRegMask & 0xFFFF);
}
// Remove the old UPDATE_VRSAVE instruction.
MI.eraseFromParent();
}
static bool spillsCR(const MachineFunction &MF) {
const PPCFunctionInfo *FuncInfo = MF.getInfo<PPCFunctionInfo>();
return FuncInfo->isCRSpilled();
}
static bool spillsVRSAVE(const MachineFunction &MF) {
const PPCFunctionInfo *FuncInfo = MF.getInfo<PPCFunctionInfo>();
return FuncInfo->isVRSAVESpilled();
}
static bool hasSpills(const MachineFunction &MF) {
const PPCFunctionInfo *FuncInfo = MF.getInfo<PPCFunctionInfo>();
return FuncInfo->hasSpills();
}
static bool hasNonRISpills(const MachineFunction &MF) {
const PPCFunctionInfo *FuncInfo = MF.getInfo<PPCFunctionInfo>();
return FuncInfo->hasNonRISpills();
}
/// MustSaveLR - Return true if this function requires that we save the LR
/// register onto the stack in the prolog and restore it in the epilog of the
/// function.
static bool MustSaveLR(const MachineFunction &MF, unsigned LR) {
const PPCFunctionInfo *MFI = MF.getInfo<PPCFunctionInfo>();
// We need a save/restore of LR if there is any def of LR (which is
// defined by calls, including the PIC setup sequence), or if there is
// some use of the LR stack slot (e.g. for builtin_return_address).
// (LR comes in 32 and 64 bit versions.)
MachineRegisterInfo::def_iterator RI = MF.getRegInfo().def_begin(LR);
return RI !=MF.getRegInfo().def_end() || MFI->isLRStoreRequired();
}
/// determineFrameLayoutAndUpdate - Determine the size of the frame and maximum
/// call frame size. Update the MachineFunction object with the stack size.
unsigned
PPCFrameLowering::determineFrameLayoutAndUpdate(MachineFunction &MF,
bool UseEstimate) const {
unsigned NewMaxCallFrameSize = 0;
unsigned FrameSize = determineFrameLayout(MF, UseEstimate,
&NewMaxCallFrameSize);
MF.getFrameInfo().setStackSize(FrameSize);
MF.getFrameInfo().setMaxCallFrameSize(NewMaxCallFrameSize);
return FrameSize;
}
/// determineFrameLayout - Determine the size of the frame and maximum call
/// frame size.
unsigned
PPCFrameLowering::determineFrameLayout(const MachineFunction &MF,
bool UseEstimate,
unsigned *NewMaxCallFrameSize) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
const PPCFunctionInfo *FI = MF.getInfo<PPCFunctionInfo>();
// Get the number of bytes to allocate from the FrameInfo
unsigned FrameSize =
UseEstimate ? MFI.estimateStackSize(MF) : MFI.getStackSize();
// Get stack alignments. The frame must be aligned to the greatest of these:
Align TargetAlign = getStackAlign(); // alignment required per the ABI
Align MaxAlign = MFI.getMaxAlign(); // algmt required by data in frame
Align Alignment = std::max(TargetAlign, MaxAlign);
const PPCRegisterInfo *RegInfo = Subtarget.getRegisterInfo();
unsigned LR = RegInfo->getRARegister();
bool DisableRedZone = MF.getFunction().hasFnAttribute(Attribute::NoRedZone);
bool CanUseRedZone = !MFI.hasVarSizedObjects() && // No dynamic alloca.
!MFI.adjustsStack() && // No calls.
!MustSaveLR(MF, LR) && // No need to save LR.
!FI->mustSaveTOC() && // No need to save TOC.
!RegInfo->hasBasePointer(MF); // No special alignment.
// Note: for PPC32 SVR4ABI (Non-DarwinABI), we can still generate stackless
// code if all local vars are reg-allocated.
bool FitsInRedZone = FrameSize <= Subtarget.getRedZoneSize();
// Check whether we can skip adjusting the stack pointer (by using red zone)
if (!DisableRedZone && CanUseRedZone && FitsInRedZone) {
// No need for frame
return 0;
}
// Get the maximum call frame size of all the calls.
unsigned maxCallFrameSize = MFI.getMaxCallFrameSize();
// Maximum call frame needs to be at least big enough for linkage area.
unsigned minCallFrameSize = getLinkageSize();
maxCallFrameSize = std::max(maxCallFrameSize, minCallFrameSize);
// If we have dynamic alloca then maxCallFrameSize needs to be aligned so
// that allocations will be aligned.
if (MFI.hasVarSizedObjects())
maxCallFrameSize = alignTo(maxCallFrameSize, Alignment);
// Update the new max call frame size if the caller passes in a valid pointer.
if (NewMaxCallFrameSize)
*NewMaxCallFrameSize = maxCallFrameSize;
// Include call frame size in total.
FrameSize += maxCallFrameSize;
// Make sure the frame is aligned.
FrameSize = alignTo(FrameSize, Alignment);
return FrameSize;
}
// hasFP - Return true if the specified function actually has a dedicated frame
// pointer register.
bool PPCFrameLowering::hasFP(const MachineFunction &MF) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
// FIXME: This is pretty much broken by design: hasFP() might be called really
// early, before the stack layout was calculated and thus hasFP() might return
// true or false here depending on the time of call.
return (MFI.getStackSize()) && needsFP(MF);
}
// needsFP - Return true if the specified function should have a dedicated frame
// pointer register. This is true if the function has variable sized allocas or
// if frame pointer elimination is disabled.
bool PPCFrameLowering::needsFP(const MachineFunction &MF) const {
const MachineFrameInfo &MFI = MF.getFrameInfo();
// Naked functions have no stack frame pushed, so we don't have a frame
// pointer.
if (MF.getFunction().hasFnAttribute(Attribute::Naked))
return false;
return MF.getTarget().Options.DisableFramePointerElim(MF) ||
MFI.hasVarSizedObjects() || MFI.hasStackMap() || MFI.hasPatchPoint() ||
(MF.getTarget().Options.GuaranteedTailCallOpt &&
MF.getInfo<PPCFunctionInfo>()->hasFastCall());
}
void PPCFrameLowering::replaceFPWithRealFP(MachineFunction &MF) const {
bool is31 = needsFP(MF);
unsigned FPReg = is31 ? PPC::R31 : PPC::R1;
unsigned FP8Reg = is31 ? PPC::X31 : PPC::X1;
const PPCRegisterInfo *RegInfo = Subtarget.getRegisterInfo();
bool HasBP = RegInfo->hasBasePointer(MF);
unsigned BPReg = HasBP ? (unsigned) RegInfo->getBaseRegister(MF) : FPReg;
unsigned BP8Reg = HasBP ? (unsigned) PPC::X30 : FP8Reg;
for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
BI != BE; ++BI)
for (MachineBasicBlock::iterator MBBI = BI->end(); MBBI != BI->begin(); ) {
--MBBI;
for (unsigned I = 0, E = MBBI->getNumOperands(); I != E; ++I) {
MachineOperand &MO = MBBI->getOperand(I);
if (!MO.isReg())
continue;
switch (MO.getReg()) {
case PPC::FP:
MO.setReg(FPReg);
break;
case PPC::FP8:
MO.setReg(FP8Reg);
break;
case PPC::BP:
MO.setReg(BPReg);
break;
case PPC::BP8:
MO.setReg(BP8Reg);
break;
}
}
}
}
/* This function will do the following:
- If MBB is an entry or exit block, set SR1 and SR2 to R0 and R12
respectively (defaults recommended by the ABI) and return true
- If MBB is not an entry block, initialize the register scavenger and look
for available registers.
- If the defaults (R0/R12) are available, return true
- If TwoUniqueRegsRequired is set to true, it looks for two unique
registers. Otherwise, look for a single available register.
- If the required registers are found, set SR1 and SR2 and return true.
- If the required registers are not found, set SR2 or both SR1 and SR2 to
PPC::NoRegister and return false.
Note that if both SR1 and SR2 are valid parameters and TwoUniqueRegsRequired
is not set, this function will attempt to find two different registers, but
still return true if only one register is available (and set SR1 == SR2).
*/
bool
PPCFrameLowering::findScratchRegister(MachineBasicBlock *MBB,
bool UseAtEnd,
bool TwoUniqueRegsRequired,
unsigned *SR1,
unsigned *SR2) const {
RegScavenger RS;
unsigned R0 = Subtarget.isPPC64() ? PPC::X0 : PPC::R0;
unsigned R12 = Subtarget.isPPC64() ? PPC::X12 : PPC::R12;
// Set the defaults for the two scratch registers.
if (SR1)
*SR1 = R0;
if (SR2) {
assert (SR1 && "Asking for the second scratch register but not the first?");
*SR2 = R12;
}
// If MBB is an entry or exit block, use R0 and R12 as the scratch registers.
if ((UseAtEnd && MBB->isReturnBlock()) ||
(!UseAtEnd && (&MBB->getParent()->front() == MBB)))
return true;
RS.enterBasicBlock(*MBB);
if (UseAtEnd && !MBB->empty()) {
// The scratch register will be used at the end of the block, so must
// consider all registers used within the block
MachineBasicBlock::iterator MBBI = MBB->getFirstTerminator();
// If no terminator, back iterator up to previous instruction.
if (MBBI == MBB->end())
MBBI = std::prev(MBBI);
if (MBBI != MBB->begin())
RS.forward(MBBI);
}
// If the two registers are available, we're all good.
// Note that we only return here if both R0 and R12 are available because
// although the function may not require two unique registers, it may benefit
// from having two so we should try to provide them.
if (!RS.isRegUsed(R0) && !RS.isRegUsed(R12))
return true;
// Get the list of callee-saved registers for the target.
const PPCRegisterInfo *RegInfo = Subtarget.getRegisterInfo();
const MCPhysReg *CSRegs = RegInfo->getCalleeSavedRegs(MBB->getParent());
// Get all the available registers in the block.
BitVector BV = RS.getRegsAvailable(Subtarget.isPPC64() ? &PPC::G8RCRegClass :
&PPC::GPRCRegClass);
// We shouldn't use callee-saved registers as scratch registers as they may be
// available when looking for a candidate block for shrink wrapping but not
// available when the actual prologue/epilogue is being emitted because they
// were added as live-in to the prologue block by PrologueEpilogueInserter.
for (int i = 0; CSRegs[i]; ++i)
BV.reset(CSRegs[i]);
// Set the first scratch register to the first available one.
if (SR1) {
int FirstScratchReg = BV.find_first();
*SR1 = FirstScratchReg == -1 ? (unsigned)PPC::NoRegister : FirstScratchReg;
}
// If there is another one available, set the second scratch register to that.
// Otherwise, set it to either PPC::NoRegister if this function requires two
// or to whatever SR1 is set to if this function doesn't require two.
if (SR2) {
int SecondScratchReg = BV.find_next(*SR1);
if (SecondScratchReg != -1)
*SR2 = SecondScratchReg;
else
*SR2 = TwoUniqueRegsRequired ? (unsigned)PPC::NoRegister : *SR1;
}
// Now that we've done our best to provide both registers, double check
// whether we were unable to provide enough.
if (BV.count() < (TwoUniqueRegsRequired ? 2U : 1U))
return false;
return true;
}
// We need a scratch register for spilling LR and for spilling CR. By default,
// we use two scratch registers to hide latency. However, if only one scratch
// register is available, we can adjust for that by not overlapping the spill
// code. However, if we need to realign the stack (i.e. have a base pointer)
// and the stack frame is large, we need two scratch registers.
bool
PPCFrameLowering::twoUniqueScratchRegsRequired(MachineBasicBlock *MBB) const {
const PPCRegisterInfo *RegInfo = Subtarget.getRegisterInfo();
MachineFunction &MF = *(MBB->getParent());
bool HasBP = RegInfo->hasBasePointer(MF);
unsigned FrameSize = determineFrameLayout(MF);
int NegFrameSize = -FrameSize;
bool IsLargeFrame = !isInt<16>(NegFrameSize);
MachineFrameInfo &MFI = MF.getFrameInfo();
Align MaxAlign = MFI.getMaxAlign();
bool HasRedZone = Subtarget.isPPC64() || !Subtarget.isSVR4ABI();
return (IsLargeFrame || !HasRedZone) && HasBP && MaxAlign > 1;
}
bool PPCFrameLowering::canUseAsPrologue(const MachineBasicBlock &MBB) const {
MachineBasicBlock *TmpMBB = const_cast<MachineBasicBlock *>(&MBB);
return findScratchRegister(TmpMBB, false,
twoUniqueScratchRegsRequired(TmpMBB));
}
bool PPCFrameLowering::canUseAsEpilogue(const MachineBasicBlock &MBB) const {
MachineBasicBlock *TmpMBB = const_cast<MachineBasicBlock *>(&MBB);
return findScratchRegister(TmpMBB, true);
}
bool PPCFrameLowering::stackUpdateCanBeMoved(MachineFunction &MF) const {
const PPCRegisterInfo *RegInfo = Subtarget.getRegisterInfo();
PPCFunctionInfo *FI = MF.getInfo<PPCFunctionInfo>();
// Abort if there is no register info or function info.
if (!RegInfo || !FI)
return false;
// Only move the stack update on ELFv2 ABI and PPC64.
if (!Subtarget.isELFv2ABI() || !Subtarget.isPPC64())
return false;
// Check the frame size first and return false if it does not fit the
// requirements.
// We need a non-zero frame size as well as a frame that will fit in the red
// zone. This is because by moving the stack pointer update we are now storing
// to the red zone until the stack pointer is updated. If we get an interrupt
// inside the prologue but before the stack update we now have a number of
// stores to the red zone and those stores must all fit.
MachineFrameInfo &MFI = MF.getFrameInfo();
unsigned FrameSize = MFI.getStackSize();
if (!FrameSize || FrameSize > Subtarget.getRedZoneSize())
return false;
// Frame pointers and base pointers complicate matters so don't do anything
// if we have them. For example having a frame pointer will sometimes require
// a copy of r1 into r31 and that makes keeping track of updates to r1 more
// difficult.
if (hasFP(MF) || RegInfo->hasBasePointer(MF))
return false;
// Calls to fast_cc functions use different rules for passing parameters on
// the stack from the ABI and using PIC base in the function imposes
// similar restrictions to using the base pointer. It is not generally safe
// to move the stack pointer update in these situations.
if (FI->hasFastCall() || FI->usesPICBase())
return false;
// Finally we can move the stack update if we do not require register
// scavenging. Register scavenging can introduce more spills and so
// may make the frame size larger than we have computed.
return !RegInfo->requiresFrameIndexScavenging(MF);
}
void PPCFrameLowering::emitPrologue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
MachineBasicBlock::iterator MBBI = MBB.begin();
MachineFrameInfo &MFI = MF.getFrameInfo();
const PPCInstrInfo &TII = *Subtarget.getInstrInfo();
const PPCRegisterInfo *RegInfo = Subtarget.getRegisterInfo();
MachineModuleInfo &MMI = MF.getMMI();
const MCRegisterInfo *MRI = MMI.getContext().getRegisterInfo();
DebugLoc dl;
// AIX assembler does not support cfi directives.
const bool needsCFI = MF.needsFrameMoves() && !Subtarget.isAIXABI();
// Get processor type.
bool isPPC64 = Subtarget.isPPC64();
// Get the ABI.
bool isSVR4ABI = Subtarget.isSVR4ABI();
bool isAIXABI = Subtarget.isAIXABI();
bool isELFv2ABI = Subtarget.isELFv2ABI();
assert((isSVR4ABI || isAIXABI) && "Unsupported PPC ABI.");
// Scan the prolog, looking for an UPDATE_VRSAVE instruction. If we find it,
// process it.
if (!isSVR4ABI)
for (unsigned i = 0; MBBI != MBB.end(); ++i, ++MBBI) {
if (MBBI->getOpcode() == PPC::UPDATE_VRSAVE) {
if (isAIXABI)
report_fatal_error("UPDATE_VRSAVE is unexpected on AIX.");
HandleVRSaveUpdate(*MBBI, TII);
break;
}
}
// Move MBBI back to the beginning of the prologue block.
MBBI = MBB.begin();
// Work out frame sizes.
unsigned FrameSize = determineFrameLayoutAndUpdate(MF);
int NegFrameSize = -FrameSize;
if (!isInt<32>(NegFrameSize))
llvm_unreachable("Unhandled stack size!");
if (MFI.isFrameAddressTaken())
replaceFPWithRealFP(MF);
// Check if the link register (LR) must be saved.
PPCFunctionInfo *FI = MF.getInfo<PPCFunctionInfo>();
bool MustSaveLR = FI->mustSaveLR();
bool MustSaveTOC = FI->mustSaveTOC();
const SmallVectorImpl<unsigned> &MustSaveCRs = FI->getMustSaveCRs();
bool MustSaveCR = !MustSaveCRs.empty();
// Do we have a frame pointer and/or base pointer for this function?
bool HasFP = hasFP(MF);
bool HasBP = RegInfo->hasBasePointer(MF);
bool HasRedZone = isPPC64 || !isSVR4ABI;
unsigned SPReg = isPPC64 ? PPC::X1 : PPC::R1;
Register BPReg = RegInfo->getBaseRegister(MF);
unsigned FPReg = isPPC64 ? PPC::X31 : PPC::R31;
unsigned LRReg = isPPC64 ? PPC::LR8 : PPC::LR;
unsigned TOCReg = isPPC64 ? PPC::X2 : PPC::R2;
unsigned ScratchReg = 0;
unsigned TempReg = isPPC64 ? PPC::X12 : PPC::R12; // another scratch reg
// ...(R12/X12 is volatile in both Darwin & SVR4, & can't be a function arg.)
const MCInstrDesc& MFLRInst = TII.get(isPPC64 ? PPC::MFLR8
: PPC::MFLR );
const MCInstrDesc& StoreInst = TII.get(isPPC64 ? PPC::STD
: PPC::STW );
const MCInstrDesc& StoreUpdtInst = TII.get(isPPC64 ? PPC::STDU
: PPC::STWU );
const MCInstrDesc& StoreUpdtIdxInst = TII.get(isPPC64 ? PPC::STDUX
: PPC::STWUX);
const MCInstrDesc& LoadImmShiftedInst = TII.get(isPPC64 ? PPC::LIS8
: PPC::LIS );
const MCInstrDesc& OrImmInst = TII.get(isPPC64 ? PPC::ORI8
: PPC::ORI );
const MCInstrDesc& OrInst = TII.get(isPPC64 ? PPC::OR8
: PPC::OR );
const MCInstrDesc& SubtractCarryingInst = TII.get(isPPC64 ? PPC::SUBFC8
: PPC::SUBFC);
const MCInstrDesc& SubtractImmCarryingInst = TII.get(isPPC64 ? PPC::SUBFIC8
: PPC::SUBFIC);
const MCInstrDesc &MoveFromCondRegInst = TII.get(isPPC64 ? PPC::MFCR8
: PPC::MFCR);
const MCInstrDesc &StoreWordInst = TII.get(isPPC64 ? PPC::STW8 : PPC::STW);
// Regarding this assert: Even though LR is saved in the caller's frame (i.e.,
// LROffset is positive), that slot is callee-owned. Because PPC32 SVR4 has no
// Red Zone, an asynchronous event (a form of "callee") could claim a frame &
// overwrite it, so PPC32 SVR4 must claim at least a minimal frame to save LR.
assert((isPPC64 || !isSVR4ABI || !(!FrameSize && (MustSaveLR || HasFP))) &&
"FrameSize must be >0 to save/restore the FP or LR for 32-bit SVR4.");
// Using the same bool variable as below to suppress compiler warnings.
bool SingleScratchReg =
findScratchRegister(&MBB, false, twoUniqueScratchRegsRequired(&MBB),
&ScratchReg, &TempReg);
assert(SingleScratchReg &&
"Required number of registers not available in this block");
SingleScratchReg = ScratchReg == TempReg;
int LROffset = getReturnSaveOffset();
int FPOffset = 0;
if (HasFP) {
if (isSVR4ABI) {
MachineFrameInfo &MFI = MF.getFrameInfo();
int FPIndex = FI->getFramePointerSaveIndex();
assert(FPIndex && "No Frame Pointer Save Slot!");
FPOffset = MFI.getObjectOffset(FPIndex);
} else {
FPOffset = getFramePointerSaveOffset();
}
}
int BPOffset = 0;
if (HasBP) {
if (isSVR4ABI) {
MachineFrameInfo &MFI = MF.getFrameInfo();
int BPIndex = FI->getBasePointerSaveIndex();
assert(BPIndex && "No Base Pointer Save Slot!");
BPOffset = MFI.getObjectOffset(BPIndex);
} else {
BPOffset = getBasePointerSaveOffset();
}
}
int PBPOffset = 0;
if (FI->usesPICBase()) {
MachineFrameInfo &MFI = MF.getFrameInfo();
int PBPIndex = FI->getPICBasePointerSaveIndex();
assert(PBPIndex && "No PIC Base Pointer Save Slot!");
PBPOffset = MFI.getObjectOffset(PBPIndex);
}
// Get stack alignments.
Align MaxAlign = MFI.getMaxAlign();
if (HasBP && MaxAlign > 1)
assert(Log2(MaxAlign) < 16 && "Invalid alignment!");
// Frames of 32KB & larger require special handling because they cannot be
// indexed into with a simple STDU/STWU/STD/STW immediate offset operand.
bool isLargeFrame = !isInt<16>(NegFrameSize);
// Check if we can move the stack update instruction (stdu) down the prologue
// past the callee saves. Hopefully this will avoid the situation where the
// saves are waiting for the update on the store with update to complete.
MachineBasicBlock::iterator StackUpdateLoc = MBBI;
bool MovingStackUpdateDown = false;
// Check if we can move the stack update.
if (stackUpdateCanBeMoved(MF)) {
const std::vector<CalleeSavedInfo> &Info = MFI.getCalleeSavedInfo();
for (CalleeSavedInfo CSI : Info) {
int FrIdx = CSI.getFrameIdx();
// If the frame index is not negative the callee saved info belongs to a
// stack object that is not a fixed stack object. We ignore non-fixed
// stack objects because we won't move the stack update pointer past them.
if (FrIdx >= 0)
continue;
if (MFI.isFixedObjectIndex(FrIdx) && MFI.getObjectOffset(FrIdx) < 0) {
StackUpdateLoc++;
MovingStackUpdateDown = true;
} else {
// We need all of the Frame Indices to meet these conditions.
// If they do not, abort the whole operation.
StackUpdateLoc = MBBI;
MovingStackUpdateDown = false;
break;
}
}
// If the operation was not aborted then update the object offset.
if (MovingStackUpdateDown) {
for (CalleeSavedInfo CSI : Info) {
int FrIdx = CSI.getFrameIdx();
if (FrIdx < 0)
MFI.setObjectOffset(FrIdx, MFI.getObjectOffset(FrIdx) + NegFrameSize);
}
}
}
// Where in the prologue we move the CR fields depends on how many scratch
// registers we have, and if we need to save the link register or not. This
// lambda is to avoid duplicating the logic in 2 places.
auto BuildMoveFromCR = [&]() {
if (isELFv2ABI && MustSaveCRs.size() == 1) {
// In the ELFv2 ABI, we are not required to save all CR fields.
// If only one CR field is clobbered, it is more efficient to use
// mfocrf to selectively save just that field, because mfocrf has short
// latency compares to mfcr.
assert(isPPC64 && "V2 ABI is 64-bit only.");
MachineInstrBuilder MIB =
BuildMI(MBB, MBBI, dl, TII.get(PPC::MFOCRF8), TempReg);
MIB.addReg(MustSaveCRs[0], RegState::Kill);
} else {
MachineInstrBuilder MIB =
BuildMI(MBB, MBBI, dl, MoveFromCondRegInst, TempReg);
for (unsigned CRfield : MustSaveCRs)
MIB.addReg(CRfield, RegState::ImplicitKill);
}
};
// If we need to spill the CR and the LR but we don't have two separate
// registers available, we must spill them one at a time
if (MustSaveCR && SingleScratchReg && MustSaveLR) {
BuildMoveFromCR();
BuildMI(MBB, MBBI, dl, StoreWordInst)
.addReg(TempReg, getKillRegState(true))
.addImm(CRSaveOffset)
.addReg(SPReg);
}
if (MustSaveLR)
BuildMI(MBB, MBBI, dl, MFLRInst, ScratchReg);
if (MustSaveCR && !(SingleScratchReg && MustSaveLR))
BuildMoveFromCR();
if (HasRedZone) {
if (HasFP)
BuildMI(MBB, MBBI, dl, StoreInst)
.addReg(FPReg)
.addImm(FPOffset)
.addReg(SPReg);
if (FI->usesPICBase())
BuildMI(MBB, MBBI, dl, StoreInst)
.addReg(PPC::R30)
.addImm(PBPOffset)
.addReg(SPReg);
if (HasBP)
BuildMI(MBB, MBBI, dl, StoreInst)
.addReg(BPReg)
.addImm(BPOffset)
.addReg(SPReg);
}
if (MustSaveLR)
BuildMI(MBB, StackUpdateLoc, dl, StoreInst)
.addReg(ScratchReg, getKillRegState(true))
.addImm(LROffset)
.addReg(SPReg);
if (MustSaveCR &&
!(SingleScratchReg && MustSaveLR)) {
assert(HasRedZone && "A red zone is always available on PPC64");
BuildMI(MBB, MBBI, dl, StoreWordInst)
.addReg(TempReg, getKillRegState(true))
.addImm(CRSaveOffset)
.addReg(SPReg);
}
// Skip the rest if this is a leaf function & all spills fit in the Red Zone.
if (!FrameSize)
return;
// Adjust stack pointer: r1 += NegFrameSize.
// If there is a preferred stack alignment, align R1 now
if (HasBP && HasRedZone) {
// Save a copy of r1 as the base pointer.
BuildMI(MBB, MBBI, dl, OrInst, BPReg)
.addReg(SPReg)
.addReg(SPReg);
}