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llvm-project/llvm/lib/Target/Mips/MipsBranchExpansion.cpp

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//===----------------------- MipsBranchExpansion.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
//
//===----------------------------------------------------------------------===//
/// \file
///
/// This pass do two things:
/// - it expands a branch or jump instruction into a long branch if its offset
/// is too large to fit into its immediate field,
/// - it inserts nops to prevent forbidden slot hazards.
///
/// The reason why this pass combines these two tasks is that one of these two
/// tasks can break the result of the previous one.
///
/// Example of that is a situation where at first, no branch should be expanded,
/// but after adding at least one nop somewhere in the code to prevent a
/// forbidden slot hazard, offset of some branches may go out of range. In that
/// case it is necessary to check again if there is some branch that needs
/// expansion. On the other hand, expanding some branch may cause a control
/// transfer instruction to appear in the forbidden slot, which is a hazard that
/// should be fixed. This pass alternates between this two tasks untill no
/// changes are made. Only then we can be sure that all branches are expanded
/// properly, and no hazard situations exist.
///
/// Regarding branch expanding:
///
/// When branch instruction like beqzc or bnezc has offset that is too large
/// to fit into its immediate field, it has to be expanded to another
/// instruction or series of instructions.
///
/// FIXME: Fix pc-region jump instructions which cross 256MB segment boundaries.
/// TODO: Handle out of range bc, b (pseudo) instructions.
///
/// Regarding compact branch hazard prevention:
///
/// Hazards handled: forbidden slots for MIPSR6.
///
/// A forbidden slot hazard occurs when a compact branch instruction is executed
/// and the adjacent instruction in memory is a control transfer instruction
/// such as a branch or jump, ERET, ERETNC, DERET, WAIT and PAUSE.
///
/// For example:
///
/// 0x8004 bnec a1,v0,<P+0x18>
/// 0x8008 beqc a1,a2,<P+0x54>
///
/// In such cases, the processor is required to signal a Reserved Instruction
/// exception.
///
/// Here, if the instruction at 0x8004 is executed, the processor will raise an
/// exception as there is a control transfer instruction at 0x8008.
///
/// There are two sources of forbidden slot hazards:
///
/// A) A previous pass has created a compact branch directly.
/// B) Transforming a delay slot branch into compact branch. This case can be
/// difficult to process as lookahead for hazards is insufficient, as
/// backwards delay slot fillling can also produce hazards in previously
/// processed instuctions.
///
/// In future this pass can be extended (or new pass can be created) to handle
/// other pipeline hazards, such as various MIPS1 hazards, processor errata that
/// require instruction reorganization, etc.
///
/// This pass has to run after the delay slot filler as that pass can introduce
/// pipeline hazards such as compact branch hazard, hence the existing hazard
/// recognizer is not suitable.
///
//===----------------------------------------------------------------------===//
#include "MCTargetDesc/MipsABIInfo.h"
#include "MCTargetDesc/MipsBaseInfo.h"
#include "MCTargetDesc/MipsMCNaCl.h"
#include "MCTargetDesc/MipsMCTargetDesc.h"
#include "Mips.h"
#include "MipsInstrInfo.h"
#include "MipsMachineFunction.h"
#include "MipsSubtarget.h"
#include "MipsTargetMachine.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Target/TargetMachine.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <iterator>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "mips-branch-expansion"
STATISTIC(NumInsertedNops, "Number of nops inserted");
STATISTIC(LongBranches, "Number of long branches.");
static cl::opt<bool>
SkipLongBranch("skip-mips-long-branch", cl::init(false),
cl::desc("MIPS: Skip branch expansion pass."), cl::Hidden);
static cl::opt<bool>
ForceLongBranch("force-mips-long-branch", cl::init(false),
cl::desc("MIPS: Expand all branches to long format."),
cl::Hidden);
namespace {
using Iter = MachineBasicBlock::iterator;
using ReverseIter = MachineBasicBlock::reverse_iterator;
struct MBBInfo {
uint64_t Size = 0;
bool HasLongBranch = false;
MachineInstr *Br = nullptr;
uint64_t Offset = 0;
MBBInfo() = default;
};
class MipsBranchExpansion : public MachineFunctionPass {
public:
static char ID;
MipsBranchExpansion() : MachineFunctionPass(ID), ABI(MipsABIInfo::Unknown()) {
initializeMipsBranchExpansionPass(*PassRegistry::getPassRegistry());
}
StringRef getPassName() const override {
return "Mips Branch Expansion Pass";
}
bool runOnMachineFunction(MachineFunction &F) override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
MachineFunctionProperties::Property::NoVRegs);
}
private:
void splitMBB(MachineBasicBlock *MBB);
void initMBBInfo();
int64_t computeOffset(const MachineInstr *Br);
uint64_t computeOffsetFromTheBeginning(int MBB);
void replaceBranch(MachineBasicBlock &MBB, Iter Br, const DebugLoc &DL,
MachineBasicBlock *MBBOpnd);
bool buildProperJumpMI(MachineBasicBlock *MBB,
MachineBasicBlock::iterator Pos, DebugLoc DL);
void expandToLongBranch(MBBInfo &Info);
bool handleForbiddenSlot();
bool handlePossibleLongBranch();
const MipsSubtarget *STI;
const MipsInstrInfo *TII;
MachineFunction *MFp;
SmallVector<MBBInfo, 16> MBBInfos;
bool IsPIC;
MipsABIInfo ABI;
bool ForceLongBranchFirstPass = false;
};
} // end of anonymous namespace
char MipsBranchExpansion::ID = 0;
INITIALIZE_PASS(MipsBranchExpansion, DEBUG_TYPE,
"Expand out of range branch instructions and fix forbidden"
" slot hazards",
false, false)
/// Returns a pass that clears pipeline hazards.
FunctionPass *llvm::createMipsBranchExpansion() {
return new MipsBranchExpansion();
}
// Find the next real instruction from the current position in current basic
// block.
static Iter getNextMachineInstrInBB(Iter Position) {
Iter I = Position, E = Position->getParent()->end();
I = std::find_if_not(I, E,
[](const Iter &Insn) { return Insn->isTransient(); });
return I;
}
// Find the next real instruction from the current position, looking through
// basic block boundaries.
static std::pair<Iter, bool> getNextMachineInstr(Iter Position,
MachineBasicBlock *Parent) {
if (Position == Parent->end()) {
do {
MachineBasicBlock *Succ = Parent->getNextNode();
if (Succ != nullptr && Parent->isSuccessor(Succ)) {
Position = Succ->begin();
Parent = Succ;
} else {
return std::make_pair(Position, true);
}
} while (Parent->empty());
}
Iter Instr = getNextMachineInstrInBB(Position);
if (Instr == Parent->end()) {
return getNextMachineInstr(Instr, Parent);
}
return std::make_pair(Instr, false);
}
/// Iterate over list of Br's operands and search for a MachineBasicBlock
/// operand.
static MachineBasicBlock *getTargetMBB(const MachineInstr &Br) {
for (unsigned I = 0, E = Br.getDesc().getNumOperands(); I < E; ++I) {
const MachineOperand &MO = Br.getOperand(I);
if (MO.isMBB())
return MO.getMBB();
}
llvm_unreachable("This instruction does not have an MBB operand.");
}
// Traverse the list of instructions backwards until a non-debug instruction is
// found or it reaches E.
static ReverseIter getNonDebugInstr(ReverseIter B, const ReverseIter &E) {
for (; B != E; ++B)
if (!B->isDebugInstr())
return B;
return E;
}
// Split MBB if it has two direct jumps/branches.
void MipsBranchExpansion::splitMBB(MachineBasicBlock *MBB) {
ReverseIter End = MBB->rend();
ReverseIter LastBr = getNonDebugInstr(MBB->rbegin(), End);
// Return if MBB has no branch instructions.
if ((LastBr == End) ||
(!LastBr->isConditionalBranch() && !LastBr->isUnconditionalBranch()))
return;
ReverseIter FirstBr = getNonDebugInstr(std::next(LastBr), End);
// MBB has only one branch instruction if FirstBr is not a branch
// instruction.
if ((FirstBr == End) ||
(!FirstBr->isConditionalBranch() && !FirstBr->isUnconditionalBranch()))
return;
assert(!FirstBr->isIndirectBranch() && "Unexpected indirect branch found.");
// Create a new MBB. Move instructions in MBB to the newly created MBB.
MachineBasicBlock *NewMBB =
MFp->CreateMachineBasicBlock(MBB->getBasicBlock());
// Insert NewMBB and fix control flow.
MachineBasicBlock *Tgt = getTargetMBB(*FirstBr);
NewMBB->transferSuccessors(MBB);
if (Tgt != getTargetMBB(*LastBr))
NewMBB->removeSuccessor(Tgt, true);
MBB->addSuccessor(NewMBB);
MBB->addSuccessor(Tgt);
MFp->insert(std::next(MachineFunction::iterator(MBB)), NewMBB);
NewMBB->splice(NewMBB->end(), MBB, LastBr.getReverse(), MBB->end());
}
// Fill MBBInfos.
void MipsBranchExpansion::initMBBInfo() {
// Split the MBBs if they have two branches. Each basic block should have at
// most one branch after this loop is executed.
for (auto &MBB : *MFp)
splitMBB(&MBB);
MFp->RenumberBlocks();
MBBInfos.clear();
MBBInfos.resize(MFp->size());
for (unsigned I = 0, E = MBBInfos.size(); I < E; ++I) {
MachineBasicBlock *MBB = MFp->getBlockNumbered(I);
// Compute size of MBB.
for (MachineBasicBlock::instr_iterator MI = MBB->instr_begin();
MI != MBB->instr_end(); ++MI)
MBBInfos[I].Size += TII->getInstSizeInBytes(*MI);
}
}
// Compute offset of branch in number of bytes.
int64_t MipsBranchExpansion::computeOffset(const MachineInstr *Br) {
int64_t Offset = 0;
int ThisMBB = Br->getParent()->getNumber();
int TargetMBB = getTargetMBB(*Br)->getNumber();
// Compute offset of a forward branch.
if (ThisMBB < TargetMBB) {
for (int N = ThisMBB + 1; N < TargetMBB; ++N)
Offset += MBBInfos[N].Size;
return Offset + 4;
}
// Compute offset of a backward branch.
for (int N = ThisMBB; N >= TargetMBB; --N)
Offset += MBBInfos[N].Size;
return -Offset + 4;
}
// Returns the distance in bytes up until MBB
uint64_t MipsBranchExpansion::computeOffsetFromTheBeginning(int MBB) {
uint64_t Offset = 0;
for (int N = 0; N < MBB; ++N)
Offset += MBBInfos[N].Size;
return Offset;
}
// Replace Br with a branch which has the opposite condition code and a
// MachineBasicBlock operand MBBOpnd.
void MipsBranchExpansion::replaceBranch(MachineBasicBlock &MBB, Iter Br,
const DebugLoc &DL,
MachineBasicBlock *MBBOpnd) {
unsigned NewOpc = TII->getOppositeBranchOpc(Br->getOpcode());
const MCInstrDesc &NewDesc = TII->get(NewOpc);
MachineInstrBuilder MIB = BuildMI(MBB, Br, DL, NewDesc);
for (unsigned I = 0, E = Br->getDesc().getNumOperands(); I < E; ++I) {
MachineOperand &MO = Br->getOperand(I);
if (!MO.isReg()) {
assert(MO.isMBB() && "MBB operand expected.");
break;
}
MIB.addReg(MO.getReg());
}
MIB.addMBB(MBBOpnd);
if (Br->hasDelaySlot()) {
// Bundle the instruction in the delay slot to the newly created branch
// and erase the original branch.
assert(Br->isBundledWithSucc());
MachineBasicBlock::instr_iterator II = Br.getInstrIterator();
MIBundleBuilder(&*MIB).append((++II)->removeFromBundle());
}
Br->eraseFromParent();
}
bool MipsBranchExpansion::buildProperJumpMI(MachineBasicBlock *MBB,
MachineBasicBlock::iterator Pos,
DebugLoc DL) {
bool HasR6 = ABI.IsN64() ? STI->hasMips64r6() : STI->hasMips32r6();
bool AddImm = HasR6 && !STI->useIndirectJumpsHazard();
unsigned JR = ABI.IsN64() ? Mips::JR64 : Mips::JR;
unsigned JIC = ABI.IsN64() ? Mips::JIC64 : Mips::JIC;
unsigned JR_HB = ABI.IsN64() ? Mips::JR_HB64 : Mips::JR_HB;
unsigned JR_HB_R6 = ABI.IsN64() ? Mips::JR_HB64_R6 : Mips::JR_HB_R6;
unsigned JumpOp;
if (STI->useIndirectJumpsHazard())
JumpOp = HasR6 ? JR_HB_R6 : JR_HB;
else
JumpOp = HasR6 ? JIC : JR;
if (JumpOp == Mips::JIC && STI->inMicroMipsMode())
JumpOp = Mips::JIC_MMR6;
unsigned ATReg = ABI.IsN64() ? Mips::AT_64 : Mips::AT;
MachineInstrBuilder Instr =
BuildMI(*MBB, Pos, DL, TII->get(JumpOp)).addReg(ATReg);
if (AddImm)
Instr.addImm(0);
return !AddImm;
}
// Expand branch instructions to long branches.
// TODO: This function has to be fixed for beqz16 and bnez16, because it
// currently assumes that all branches have 16-bit offsets, and will produce
// wrong code if branches whose allowed offsets are [-128, -126, ..., 126]
// are present.
void MipsBranchExpansion::expandToLongBranch(MBBInfo &I) {
MachineBasicBlock::iterator Pos;
MachineBasicBlock *MBB = I.Br->getParent(), *TgtMBB = getTargetMBB(*I.Br);
DebugLoc DL = I.Br->getDebugLoc();
const BasicBlock *BB = MBB->getBasicBlock();
MachineFunction::iterator FallThroughMBB = ++MachineFunction::iterator(MBB);
MachineBasicBlock *LongBrMBB = MFp->CreateMachineBasicBlock(BB);
MFp->insert(FallThroughMBB, LongBrMBB);
MBB->replaceSuccessor(TgtMBB, LongBrMBB);
if (IsPIC) {
MachineBasicBlock *BalTgtMBB = MFp->CreateMachineBasicBlock(BB);
MFp->insert(FallThroughMBB, BalTgtMBB);
LongBrMBB->addSuccessor(BalTgtMBB);
BalTgtMBB->addSuccessor(TgtMBB);
// We must select between the MIPS32r6/MIPS64r6 BALC (which is a normal
// instruction) and the pre-MIPS32r6/MIPS64r6 definition (which is an
// pseudo-instruction wrapping BGEZAL).
const unsigned BalOp =
STI->hasMips32r6()
? STI->inMicroMipsMode() ? Mips::BALC_MMR6 : Mips::BALC
: STI->inMicroMipsMode() ? Mips::BAL_BR_MM : Mips::BAL_BR;
if (!ABI.IsN64()) {
// Pre R6:
// $longbr:
// addiu $sp, $sp, -8
// sw $ra, 0($sp)
// lui $at, %hi($tgt - $baltgt)
// bal $baltgt
// addiu $at, $at, %lo($tgt - $baltgt)
// $baltgt:
// addu $at, $ra, $at
// lw $ra, 0($sp)
// jr $at
// addiu $sp, $sp, 8
// $fallthrough:
//
// R6:
// $longbr:
// addiu $sp, $sp, -8
// sw $ra, 0($sp)
// lui $at, %hi($tgt - $baltgt)
// addiu $at, $at, %lo($tgt - $baltgt)
// balc $baltgt
// $baltgt:
// addu $at, $ra, $at
// lw $ra, 0($sp)
// addiu $sp, $sp, 8
// jic $at, 0
// $fallthrough:
Pos = LongBrMBB->begin();
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::ADDiu), Mips::SP)
.addReg(Mips::SP)
.addImm(-8);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::SW))
.addReg(Mips::RA)
.addReg(Mips::SP)
.addImm(0);
// LUi and ADDiu instructions create 32-bit offset of the target basic
// block from the target of BAL(C) instruction. We cannot use immediate
// value for this offset because it cannot be determined accurately when
// the program has inline assembly statements. We therefore use the
// relocation expressions %hi($tgt-$baltgt) and %lo($tgt-$baltgt) which
// are resolved during the fixup, so the values will always be correct.
//
// Since we cannot create %hi($tgt-$baltgt) and %lo($tgt-$baltgt)
// expressions at this point (it is possible only at the MC layer),
// we replace LUi and ADDiu with pseudo instructions
// LONG_BRANCH_LUi and LONG_BRANCH_ADDiu, and add both basic
// blocks as operands to these instructions. When lowering these pseudo
// instructions to LUi and ADDiu in the MC layer, we will create
// %hi($tgt-$baltgt) and %lo($tgt-$baltgt) expressions and add them as
// operands to lowered instructions.
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_LUi), Mips::AT)
.addMBB(TgtMBB, MipsII::MO_ABS_HI)
.addMBB(BalTgtMBB);
MachineInstrBuilder BalInstr =
BuildMI(*MFp, DL, TII->get(BalOp)).addMBB(BalTgtMBB);
MachineInstrBuilder ADDiuInstr =
BuildMI(*MFp, DL, TII->get(Mips::LONG_BRANCH_ADDiu), Mips::AT)
.addReg(Mips::AT)
.addMBB(TgtMBB, MipsII::MO_ABS_LO)
.addMBB(BalTgtMBB);
if (STI->hasMips32r6()) {
LongBrMBB->insert(Pos, ADDiuInstr);
LongBrMBB->insert(Pos, BalInstr);
} else {
LongBrMBB->insert(Pos, BalInstr);
LongBrMBB->insert(Pos, ADDiuInstr);
LongBrMBB->rbegin()->bundleWithPred();
}
Pos = BalTgtMBB->begin();
BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::ADDu), Mips::AT)
.addReg(Mips::RA)
.addReg(Mips::AT);
BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::LW), Mips::RA)
.addReg(Mips::SP)
.addImm(0);
if (STI->isTargetNaCl())
// Bundle-align the target of indirect branch JR.
TgtMBB->setAlignment(MIPS_NACL_BUNDLE_ALIGN);
// In NaCl, modifying the sp is not allowed in branch delay slot.
// For MIPS32R6, we can skip using a delay slot branch.
bool hasDelaySlot = buildProperJumpMI(BalTgtMBB, Pos, DL);
if (STI->isTargetNaCl() || !hasDelaySlot) {
BuildMI(*BalTgtMBB, std::prev(Pos), DL, TII->get(Mips::ADDiu), Mips::SP)
.addReg(Mips::SP)
.addImm(8);
}
if (hasDelaySlot) {
if (STI->isTargetNaCl()) {
BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::NOP));
} else {
BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::ADDiu), Mips::SP)
.addReg(Mips::SP)
.addImm(8);
}
BalTgtMBB->rbegin()->bundleWithPred();
}
} else {
// Pre R6:
// $longbr:
// daddiu $sp, $sp, -16
// sd $ra, 0($sp)
// daddiu $at, $zero, %hi($tgt - $baltgt)
// dsll $at, $at, 16
// bal $baltgt
// daddiu $at, $at, %lo($tgt - $baltgt)
// $baltgt:
// daddu $at, $ra, $at
// ld $ra, 0($sp)
// jr64 $at
// daddiu $sp, $sp, 16
// $fallthrough:
// R6:
// $longbr:
// daddiu $sp, $sp, -16
// sd $ra, 0($sp)
// daddiu $at, $zero, %hi($tgt - $baltgt)
// dsll $at, $at, 16
// daddiu $at, $at, %lo($tgt - $baltgt)
// balc $baltgt
// $baltgt:
// daddu $at, $ra, $at
// ld $ra, 0($sp)
// daddiu $sp, $sp, 16
// jic $at, 0
// $fallthrough:
// We assume the branch is within-function, and that offset is within
// +/- 2GB. High 32 bits will therefore always be zero.
// Note that this will work even if the offset is negative, because
// of the +1 modification that's added in that case. For example, if the
// offset is -1MB (0xFFFFFFFFFFF00000), the computation for %higher is
//
// 0xFFFFFFFFFFF00000 + 0x80008000 = 0x000000007FF08000
//
// and the bits [47:32] are zero. For %highest
//
// 0xFFFFFFFFFFF00000 + 0x800080008000 = 0x000080007FF08000
//
// and the bits [63:48] are zero.
Pos = LongBrMBB->begin();
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::DADDiu), Mips::SP_64)
.addReg(Mips::SP_64)
.addImm(-16);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::SD))
.addReg(Mips::RA_64)
.addReg(Mips::SP_64)
.addImm(0);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_DADDiu),
Mips::AT_64)
.addReg(Mips::ZERO_64)
.addMBB(TgtMBB, MipsII::MO_ABS_HI)
.addMBB(BalTgtMBB);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::DSLL), Mips::AT_64)
.addReg(Mips::AT_64)
.addImm(16);
MachineInstrBuilder BalInstr =
BuildMI(*MFp, DL, TII->get(BalOp)).addMBB(BalTgtMBB);
MachineInstrBuilder DADDiuInstr =
BuildMI(*MFp, DL, TII->get(Mips::LONG_BRANCH_DADDiu), Mips::AT_64)
.addReg(Mips::AT_64)
.addMBB(TgtMBB, MipsII::MO_ABS_LO)
.addMBB(BalTgtMBB);
if (STI->hasMips32r6()) {
LongBrMBB->insert(Pos, DADDiuInstr);
LongBrMBB->insert(Pos, BalInstr);
} else {
LongBrMBB->insert(Pos, BalInstr);
LongBrMBB->insert(Pos, DADDiuInstr);
LongBrMBB->rbegin()->bundleWithPred();
}
Pos = BalTgtMBB->begin();
BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::DADDu), Mips::AT_64)
.addReg(Mips::RA_64)
.addReg(Mips::AT_64);
BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::LD), Mips::RA_64)
.addReg(Mips::SP_64)
.addImm(0);
bool hasDelaySlot = buildProperJumpMI(BalTgtMBB, Pos, DL);
// If there is no delay slot, Insert stack adjustment before
if (!hasDelaySlot) {
BuildMI(*BalTgtMBB, std::prev(Pos), DL, TII->get(Mips::DADDiu),
Mips::SP_64)
.addReg(Mips::SP_64)
.addImm(16);
} else {
BuildMI(*BalTgtMBB, Pos, DL, TII->get(Mips::DADDiu), Mips::SP_64)
.addReg(Mips::SP_64)
.addImm(16);
BalTgtMBB->rbegin()->bundleWithPred();
}
}
} else { // Not PIC
Pos = LongBrMBB->begin();
LongBrMBB->addSuccessor(TgtMBB);
// Compute the position of the potentiall jump instruction (basic blocks
// before + 4 for the instruction)
uint64_t JOffset = computeOffsetFromTheBeginning(MBB->getNumber()) +
MBBInfos[MBB->getNumber()].Size + 4;
uint64_t TgtMBBOffset = computeOffsetFromTheBeginning(TgtMBB->getNumber());
// If it's a forward jump, then TgtMBBOffset will be shifted by two
// instructions
if (JOffset < TgtMBBOffset)
TgtMBBOffset += 2 * 4;
// Compare 4 upper bits to check if it's the same segment
bool SameSegmentJump = JOffset >> 28 == TgtMBBOffset >> 28;
if (STI->hasMips32r6() && TII->isBranchOffsetInRange(Mips::BC, I.Offset)) {
// R6:
// $longbr:
// bc $tgt
// $fallthrough:
//
BuildMI(*LongBrMBB, Pos, DL,
TII->get(STI->inMicroMipsMode() ? Mips::BC_MMR6 : Mips::BC))
.addMBB(TgtMBB);
} else if (SameSegmentJump) {
// Pre R6:
// $longbr:
// j $tgt
// nop
// $fallthrough:
//
MIBundleBuilder(*LongBrMBB, Pos)
.append(BuildMI(*MFp, DL, TII->get(Mips::J)).addMBB(TgtMBB))
.append(BuildMI(*MFp, DL, TII->get(Mips::NOP)));
} else {
// At this point, offset where we need to branch does not fit into
// immediate field of the branch instruction and is not in the same
// segment as jump instruction. Therefore we will break it into couple
// instructions, where we first load the offset into register, and then we
// do branch register.
if (ABI.IsN64()) {
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_LUi2Op_64),
Mips::AT_64)
.addMBB(TgtMBB, MipsII::MO_HIGHEST);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_DADDiu2Op),
Mips::AT_64)
.addReg(Mips::AT_64)
.addMBB(TgtMBB, MipsII::MO_HIGHER);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::DSLL), Mips::AT_64)
.addReg(Mips::AT_64)
.addImm(16);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_DADDiu2Op),
Mips::AT_64)
.addReg(Mips::AT_64)
.addMBB(TgtMBB, MipsII::MO_ABS_HI);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::DSLL), Mips::AT_64)
.addReg(Mips::AT_64)
.addImm(16);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_DADDiu2Op),
Mips::AT_64)
.addReg(Mips::AT_64)
.addMBB(TgtMBB, MipsII::MO_ABS_LO);
} else {
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_LUi2Op),
Mips::AT)
.addMBB(TgtMBB, MipsII::MO_ABS_HI);
BuildMI(*LongBrMBB, Pos, DL, TII->get(Mips::LONG_BRANCH_ADDiu2Op),
Mips::AT)
.addReg(Mips::AT)
.addMBB(TgtMBB, MipsII::MO_ABS_LO);
}
buildProperJumpMI(LongBrMBB, Pos, DL);
}
}
if (I.Br->isUnconditionalBranch()) {
// Change branch destination.
assert(I.Br->getDesc().getNumOperands() == 1);
I.Br->RemoveOperand(0);
I.Br->addOperand(MachineOperand::CreateMBB(LongBrMBB));
} else
// Change branch destination and reverse condition.
replaceBranch(*MBB, I.Br, DL, &*FallThroughMBB);
}
static void emitGPDisp(MachineFunction &F, const MipsInstrInfo *TII) {
MachineBasicBlock &MBB = F.front();
MachineBasicBlock::iterator I = MBB.begin();
DebugLoc DL = MBB.findDebugLoc(MBB.begin());
BuildMI(MBB, I, DL, TII->get(Mips::LUi), Mips::V0)
.addExternalSymbol("_gp_disp", MipsII::MO_ABS_HI);
BuildMI(MBB, I, DL, TII->get(Mips::ADDiu), Mips::V0)
.addReg(Mips::V0)
.addExternalSymbol("_gp_disp", MipsII::MO_ABS_LO);
MBB.removeLiveIn(Mips::V0);
}
bool MipsBranchExpansion::handleForbiddenSlot() {
// Forbidden slot hazards are only defined for MIPSR6 but not microMIPSR6.
if (!STI->hasMips32r6() || STI->inMicroMipsMode())
return false;
bool Changed = false;
for (MachineFunction::iterator FI = MFp->begin(); FI != MFp->end(); ++FI) {
for (Iter I = FI->begin(); I != FI->end(); ++I) {
// Forbidden slot hazard handling. Use lookahead over state.
if (!TII->HasForbiddenSlot(*I))
continue;
Iter Inst;
bool LastInstInFunction =
std::next(I) == FI->end() && std::next(FI) == MFp->end();
if (!LastInstInFunction) {
std::pair<Iter, bool> Res = getNextMachineInstr(std::next(I), &*FI);
LastInstInFunction |= Res.second;
Inst = Res.first;
}
if (LastInstInFunction || !TII->SafeInForbiddenSlot(*Inst)) {
MachineBasicBlock::instr_iterator Iit = I->getIterator();
if (std::next(Iit) == FI->end() ||
std::next(Iit)->getOpcode() != Mips::NOP) {
Changed = true;
MIBundleBuilder(&*I).append(
BuildMI(*MFp, I->getDebugLoc(), TII->get(Mips::NOP)));
NumInsertedNops++;
}
}
}
}
return Changed;
}
bool MipsBranchExpansion::handlePossibleLongBranch() {
if (STI->inMips16Mode() || !STI->enableLongBranchPass())
return false;
if (SkipLongBranch)
return false;
bool EverMadeChange = false, MadeChange = true;
while (MadeChange) {
MadeChange = false;
initMBBInfo();
for (unsigned I = 0, E = MBBInfos.size(); I < E; ++I) {
MachineBasicBlock *MBB = MFp->getBlockNumbered(I);
// Search for MBB's branch instruction.
ReverseIter End = MBB->rend();
ReverseIter Br = getNonDebugInstr(MBB->rbegin(), End);
if ((Br != End) && Br->isBranch() && !Br->isIndirectBranch() &&
(Br->isConditionalBranch() ||
(Br->isUnconditionalBranch() && IsPIC))) {
int64_t Offset = computeOffset(&*Br);
if (STI->isTargetNaCl()) {
// The offset calculation does not include sandboxing instructions
// that will be added later in the MC layer. Since at this point we
// don't know the exact amount of code that "sandboxing" will add, we
// conservatively estimate that code will not grow more than 100%.
Offset *= 2;
}
if (ForceLongBranchFirstPass ||
!TII->isBranchOffsetInRange(Br->getOpcode(), Offset)) {
MBBInfos[I].Offset = Offset;
MBBInfos[I].Br = &*Br;
}
}
} // End for
ForceLongBranchFirstPass = false;
SmallVectorImpl<MBBInfo>::iterator I, E = MBBInfos.end();
for (I = MBBInfos.begin(); I != E; ++I) {
// Skip if this MBB doesn't have a branch or the branch has already been
// converted to a long branch.
if (!I->Br)
continue;
expandToLongBranch(*I);
++LongBranches;
EverMadeChange = MadeChange = true;
}
MFp->RenumberBlocks();
}
return EverMadeChange;
}
bool MipsBranchExpansion::runOnMachineFunction(MachineFunction &MF) {
const TargetMachine &TM = MF.getTarget();
IsPIC = TM.isPositionIndependent();
ABI = static_cast<const MipsTargetMachine &>(TM).getABI();
STI = &static_cast<const MipsSubtarget &>(MF.getSubtarget());
TII = static_cast<const MipsInstrInfo *>(STI->getInstrInfo());
if (IsPIC && ABI.IsO32() &&
MF.getInfo<MipsFunctionInfo>()->globalBaseRegSet())
emitGPDisp(MF, TII);
MFp = &MF;
ForceLongBranchFirstPass = ForceLongBranch;
// Run these two at least once
bool longBranchChanged = handlePossibleLongBranch();
bool forbiddenSlotChanged = handleForbiddenSlot();
bool Changed = longBranchChanged || forbiddenSlotChanged;
// Then run them alternatively while there are changes
while (forbiddenSlotChanged) {
longBranchChanged = handlePossibleLongBranch();
if (!longBranchChanged)
break;
forbiddenSlotChanged = handleForbiddenSlot();
}
return Changed;
}
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