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llvm-project/llvm/lib/Target/AArch64/AArch64CollectLOH.cpp

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//===---------- AArch64CollectLOH.cpp - AArch64 collect LOH pass --*- C++ -*-=//
//
// 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 a pass that collect the Linker Optimization Hint (LOH).
// This pass should be run at the very end of the compilation flow, just before
// assembly printer.
// To be useful for the linker, the LOH must be printed into the assembly file.
//
// A LOH describes a sequence of instructions that may be optimized by the
// linker.
// This same sequence cannot be optimized by the compiler because some of
// the information will be known at link time.
// For instance, consider the following sequence:
// L1: adrp xA, sym@PAGE
// L2: add xB, xA, sym@PAGEOFF
// L3: ldr xC, [xB, #imm]
// This sequence can be turned into:
// A literal load if sym@PAGE + sym@PAGEOFF + #imm - address(L3) is < 1MB:
// L3: ldr xC, sym+#imm
// It may also be turned into either the following more efficient
// code sequences:
// - If sym@PAGEOFF + #imm fits the encoding space of L3.
// L1: adrp xA, sym@PAGE
// L3: ldr xC, [xB, sym@PAGEOFF + #imm]
// - If sym@PAGE + sym@PAGEOFF - address(L1) < 1MB:
// L1: adr xA, sym
// L3: ldr xC, [xB, #imm]
//
// To be valid a LOH must meet all the requirements needed by all the related
// possible linker transformations.
// For instance, using the running example, the constraints to emit
// ".loh AdrpAddLdr" are:
// - L1, L2, and L3 instructions are of the expected type, i.e.,
// respectively ADRP, ADD (immediate), and LD.
// - The result of L1 is used only by L2.
// - The register argument (xA) used in the ADD instruction is defined
// only by L1.
// - The result of L2 is used only by L3.
// - The base address (xB) in L3 is defined only L2.
// - The ADRP in L1 and the ADD in L2 must reference the same symbol using
// @PAGE/@PAGEOFF with no additional constants
//
// Currently supported LOHs are:
// * So called non-ADRP-related:
// - .loh AdrpAddLdr L1, L2, L3:
// L1: adrp xA, sym@PAGE
// L2: add xB, xA, sym@PAGEOFF
// L3: ldr xC, [xB, #imm]
// - .loh AdrpLdrGotLdr L1, L2, L3:
// L1: adrp xA, sym@GOTPAGE
// L2: ldr xB, [xA, sym@GOTPAGEOFF]
// L3: ldr xC, [xB, #imm]
// - .loh AdrpLdr L1, L3:
// L1: adrp xA, sym@PAGE
// L3: ldr xC, [xA, sym@PAGEOFF]
// - .loh AdrpAddStr L1, L2, L3:
// L1: adrp xA, sym@PAGE
// L2: add xB, xA, sym@PAGEOFF
// L3: str xC, [xB, #imm]
// - .loh AdrpLdrGotStr L1, L2, L3:
// L1: adrp xA, sym@GOTPAGE
// L2: ldr xB, [xA, sym@GOTPAGEOFF]
// L3: str xC, [xB, #imm]
// - .loh AdrpAdd L1, L2:
// L1: adrp xA, sym@PAGE
// L2: add xB, xA, sym@PAGEOFF
// For all these LOHs, L1, L2, L3 form a simple chain:
// L1 result is used only by L2 and L2 result by L3.
// L3 LOH-related argument is defined only by L2 and L2 LOH-related argument
// by L1.
// All these LOHs aim at using more efficient load/store patterns by folding
// some instructions used to compute the address directly into the load/store.
//
// * So called ADRP-related:
// - .loh AdrpAdrp L2, L1:
// L2: ADRP xA, sym1@PAGE
// L1: ADRP xA, sym2@PAGE
// L2 dominates L1 and xA is not redifined between L2 and L1
// This LOH aims at getting rid of redundant ADRP instructions.
//
// The overall design for emitting the LOHs is:
// 1. AArch64CollectLOH (this pass) records the LOHs in the AArch64FunctionInfo.
// 2. AArch64AsmPrinter reads the LOHs from AArch64FunctionInfo and it:
// 1. Associates them a label.
// 2. Emits them in a MCStreamer (EmitLOHDirective).
// - The MCMachOStreamer records them into the MCAssembler.
// - The MCAsmStreamer prints them.
// - Other MCStreamers ignore them.
// 3. Closes the MCStreamer:
// - The MachObjectWriter gets them from the MCAssembler and writes
// them in the object file.
// - Other ObjectWriters ignore them.
//===----------------------------------------------------------------------===//
#include "AArch64.h"
#include "AArch64InstrInfo.h"
#include "AArch64MachineFunctionInfo.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
#define DEBUG_TYPE "aarch64-collect-loh"
STATISTIC(NumADRPSimpleCandidate,
"Number of simplifiable ADRP dominate by another");
STATISTIC(NumADDToSTR, "Number of simplifiable STR reachable by ADD");
STATISTIC(NumLDRToSTR, "Number of simplifiable STR reachable by LDR");
STATISTIC(NumADDToLDR, "Number of simplifiable LDR reachable by ADD");
STATISTIC(NumLDRToLDR, "Number of simplifiable LDR reachable by LDR");
STATISTIC(NumADRPToLDR, "Number of simplifiable LDR reachable by ADRP");
STATISTIC(NumADRSimpleCandidate, "Number of simplifiable ADRP + ADD");
#define AARCH64_COLLECT_LOH_NAME "AArch64 Collect Linker Optimization Hint (LOH)"
namespace {
struct AArch64CollectLOH : public MachineFunctionPass {
static char ID;
AArch64CollectLOH() : MachineFunctionPass(ID) {}
bool runOnMachineFunction(MachineFunction &MF) override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
MachineFunctionProperties::Property::NoVRegs);
}
StringRef getPassName() const override { return AARCH64_COLLECT_LOH_NAME; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
MachineFunctionPass::getAnalysisUsage(AU);
AU.setPreservesAll();
}
};
char AArch64CollectLOH::ID = 0;
} // end anonymous namespace.
INITIALIZE_PASS(AArch64CollectLOH, "aarch64-collect-loh",
AARCH64_COLLECT_LOH_NAME, false, false)
static bool canAddBePartOfLOH(const MachineInstr &MI) {
// Check immediate to see if the immediate is an address.
switch (MI.getOperand(2).getType()) {
default:
return false;
case MachineOperand::MO_GlobalAddress:
case MachineOperand::MO_JumpTableIndex:
case MachineOperand::MO_ConstantPoolIndex:
case MachineOperand::MO_BlockAddress:
return true;
}
}
/// Answer the following question: Can Def be one of the definition
/// involved in a part of a LOH?
static bool canDefBePartOfLOH(const MachineInstr &MI) {
// Accept ADRP, ADDLow and LOADGot.
switch (MI.getOpcode()) {
default:
return false;
case AArch64::ADRP:
return true;
case AArch64::ADDXri:
return canAddBePartOfLOH(MI);
case AArch64::LDRXui:
case AArch64::LDRWui:
// Check immediate to see if the immediate is an address.
switch (MI.getOperand(2).getType()) {
default:
return false;
case MachineOperand::MO_GlobalAddress:
return MI.getOperand(2).getTargetFlags() & AArch64II::MO_GOT;
}
}
}
/// Check whether the given instruction can the end of a LOH chain involving a
/// store.
static bool isCandidateStore(const MachineInstr &MI, const MachineOperand &MO) {
switch (MI.getOpcode()) {
default:
return false;
case AArch64::STRBBui:
case AArch64::STRHHui:
case AArch64::STRBui:
case AArch64::STRHui:
case AArch64::STRWui:
case AArch64::STRXui:
case AArch64::STRSui:
case AArch64::STRDui:
case AArch64::STRQui:
// We can only optimize the index operand.
// In case we have str xA, [xA, #imm], this is two different uses
// of xA and we cannot fold, otherwise the xA stored may be wrong,
// even if #imm == 0.
return MI.getOperandNo(&MO) == 1 &&
MI.getOperand(0).getReg() != MI.getOperand(1).getReg();
}
}
/// Check whether the given instruction can be the end of a LOH chain
/// involving a load.
static bool isCandidateLoad(const MachineInstr &MI) {
switch (MI.getOpcode()) {
default:
return false;
case AArch64::LDRSBWui:
case AArch64::LDRSBXui:
case AArch64::LDRSHWui:
case AArch64::LDRSHXui:
case AArch64::LDRSWui:
case AArch64::LDRBui:
case AArch64::LDRHui:
case AArch64::LDRWui:
case AArch64::LDRXui:
case AArch64::LDRSui:
case AArch64::LDRDui:
case AArch64::LDRQui:
return !(MI.getOperand(2).getTargetFlags() & AArch64II::MO_GOT);
}
}
/// Check whether the given instruction can load a litteral.
static bool supportLoadFromLiteral(const MachineInstr &MI) {
switch (MI.getOpcode()) {
default:
return false;
case AArch64::LDRSWui:
case AArch64::LDRWui:
case AArch64::LDRXui:
case AArch64::LDRSui:
case AArch64::LDRDui:
case AArch64::LDRQui:
return true;
}
}
/// Number of GPR registers traked by mapRegToGPRIndex()
static const unsigned N_GPR_REGS = 31;
/// Map register number to index from 0-30.
static int mapRegToGPRIndex(MCPhysReg Reg) {
static_assert(AArch64::X28 - AArch64::X0 + 3 == N_GPR_REGS, "Number of GPRs");
static_assert(AArch64::W30 - AArch64::W0 + 1 == N_GPR_REGS, "Number of GPRs");
if (AArch64::X0 <= Reg && Reg <= AArch64::X28)
return Reg - AArch64::X0;
if (AArch64::W0 <= Reg && Reg <= AArch64::W30)
return Reg - AArch64::W0;
// TableGen gives "FP" and "LR" an index not adjacent to X28 so we have to
// handle them as special cases.
if (Reg == AArch64::FP)
return 29;
if (Reg == AArch64::LR)
return 30;
return -1;
}
/// State tracked per register.
/// The main algorithm walks backwards over a basic block maintaining this
/// datastructure for each tracked general purpose register.
struct LOHInfo {
MCLOHType Type : 8; ///< "Best" type of LOH possible.
bool IsCandidate : 1; ///< Possible LOH candidate.
bool OneUser : 1; ///< Found exactly one user (yet).
bool MultiUsers : 1; ///< Found multiple users.
const MachineInstr *MI0; ///< First instruction involved in the LOH.
const MachineInstr *MI1; ///< Second instruction involved in the LOH
/// (if any).
const MachineInstr *LastADRP; ///< Last ADRP in same register.
};
/// Update state \p Info given \p MI uses the tracked register.
static void handleUse(const MachineInstr &MI, const MachineOperand &MO,
LOHInfo &Info) {
// We have multiple uses if we already found one before.
if (Info.MultiUsers || Info.OneUser) {
Info.IsCandidate = false;
Info.MultiUsers = true;
return;
}
Info.OneUser = true;
// Start new LOHInfo if applicable.
if (isCandidateLoad(MI)) {
Info.Type = MCLOH_AdrpLdr;
Info.IsCandidate = true;
Info.MI0 = &MI;
// Note that even this is AdrpLdr now, we can switch to a Ldr variant
// later.
} else if (isCandidateStore(MI, MO)) {
Info.Type = MCLOH_AdrpAddStr;
Info.IsCandidate = true;
Info.MI0 = &MI;
Info.MI1 = nullptr;
} else if (MI.getOpcode() == AArch64::ADDXri) {
Info.Type = MCLOH_AdrpAdd;
Info.IsCandidate = true;
Info.MI0 = &MI;
} else if ((MI.getOpcode() == AArch64::LDRXui ||
MI.getOpcode() == AArch64::LDRWui) &&
MI.getOperand(2).getTargetFlags() & AArch64II::MO_GOT) {
Info.Type = MCLOH_AdrpLdrGot;
Info.IsCandidate = true;
Info.MI0 = &MI;
}
}
/// Update state \p Info given the tracked register is clobbered.
static void handleClobber(LOHInfo &Info) {
Info.IsCandidate = false;
Info.OneUser = false;
Info.MultiUsers = false;
Info.LastADRP = nullptr;
}
/// Update state \p Info given that \p MI is possibly the middle instruction
/// of an LOH involving 3 instructions.
static bool handleMiddleInst(const MachineInstr &MI, LOHInfo &DefInfo,
LOHInfo &OpInfo) {
if (!DefInfo.IsCandidate || (&DefInfo != &OpInfo && OpInfo.OneUser))
return false;
// Copy LOHInfo for dest register to LOHInfo for source register.
if (&DefInfo != &OpInfo) {
OpInfo = DefInfo;
// Invalidate \p DefInfo because we track it in \p OpInfo now.
handleClobber(DefInfo);
} else
DefInfo.LastADRP = nullptr;
// Advance state machine.
assert(OpInfo.IsCandidate && "Expect valid state");
if (MI.getOpcode() == AArch64::ADDXri && canAddBePartOfLOH(MI)) {
if (OpInfo.Type == MCLOH_AdrpLdr) {
OpInfo.Type = MCLOH_AdrpAddLdr;
OpInfo.IsCandidate = true;
OpInfo.MI1 = &MI;
return true;
} else if (OpInfo.Type == MCLOH_AdrpAddStr && OpInfo.MI1 == nullptr) {
OpInfo.Type = MCLOH_AdrpAddStr;
OpInfo.IsCandidate = true;
OpInfo.MI1 = &MI;
return true;
}
} else {
assert((MI.getOpcode() == AArch64::LDRXui ||
MI.getOpcode() == AArch64::LDRWui) &&
"Expect LDRXui or LDRWui");
assert((MI.getOperand(2).getTargetFlags() & AArch64II::MO_GOT) &&
"Expected GOT relocation");
if (OpInfo.Type == MCLOH_AdrpAddStr && OpInfo.MI1 == nullptr) {
OpInfo.Type = MCLOH_AdrpLdrGotStr;
OpInfo.IsCandidate = true;
OpInfo.MI1 = &MI;
return true;
} else if (OpInfo.Type == MCLOH_AdrpLdr) {
OpInfo.Type = MCLOH_AdrpLdrGotLdr;
OpInfo.IsCandidate = true;
OpInfo.MI1 = &MI;
return true;
}
}
return false;
}
/// Update state when seeing and ADRP instruction.
static void handleADRP(const MachineInstr &MI, AArch64FunctionInfo &AFI,
LOHInfo &Info) {
if (Info.LastADRP != nullptr) {
LLVM_DEBUG(dbgs() << "Adding MCLOH_AdrpAdrp:\n"
<< '\t' << MI << '\t' << *Info.LastADRP);
AFI.addLOHDirective(MCLOH_AdrpAdrp, {&MI, Info.LastADRP});
++NumADRPSimpleCandidate;
}
// Produce LOH directive if possible.
if (Info.IsCandidate) {
switch (Info.Type) {
case MCLOH_AdrpAdd:
LLVM_DEBUG(dbgs() << "Adding MCLOH_AdrpAdd:\n"
<< '\t' << MI << '\t' << *Info.MI0);
AFI.addLOHDirective(MCLOH_AdrpAdd, {&MI, Info.MI0});
++NumADRSimpleCandidate;
break;
case MCLOH_AdrpLdr:
if (supportLoadFromLiteral(*Info.MI0)) {
LLVM_DEBUG(dbgs() << "Adding MCLOH_AdrpLdr:\n"
<< '\t' << MI << '\t' << *Info.MI0);
AFI.addLOHDirective(MCLOH_AdrpLdr, {&MI, Info.MI0});
++NumADRPToLDR;
}
break;
case MCLOH_AdrpAddLdr:
LLVM_DEBUG(dbgs() << "Adding MCLOH_AdrpAddLdr:\n"
<< '\t' << MI << '\t' << *Info.MI1 << '\t'
<< *Info.MI0);
AFI.addLOHDirective(MCLOH_AdrpAddLdr, {&MI, Info.MI1, Info.MI0});
++NumADDToLDR;
break;
case MCLOH_AdrpAddStr:
if (Info.MI1 != nullptr) {
LLVM_DEBUG(dbgs() << "Adding MCLOH_AdrpAddStr:\n"
<< '\t' << MI << '\t' << *Info.MI1 << '\t'
<< *Info.MI0);
AFI.addLOHDirective(MCLOH_AdrpAddStr, {&MI, Info.MI1, Info.MI0});
++NumADDToSTR;
}
break;
case MCLOH_AdrpLdrGotLdr:
LLVM_DEBUG(dbgs() << "Adding MCLOH_AdrpLdrGotLdr:\n"
<< '\t' << MI << '\t' << *Info.MI1 << '\t'
<< *Info.MI0);
AFI.addLOHDirective(MCLOH_AdrpLdrGotLdr, {&MI, Info.MI1, Info.MI0});
++NumLDRToLDR;
break;
case MCLOH_AdrpLdrGotStr:
LLVM_DEBUG(dbgs() << "Adding MCLOH_AdrpLdrGotStr:\n"
<< '\t' << MI << '\t' << *Info.MI1 << '\t'
<< *Info.MI0);
AFI.addLOHDirective(MCLOH_AdrpLdrGotStr, {&MI, Info.MI1, Info.MI0});
++NumLDRToSTR;
break;
case MCLOH_AdrpLdrGot:
LLVM_DEBUG(dbgs() << "Adding MCLOH_AdrpLdrGot:\n"
<< '\t' << MI << '\t' << *Info.MI0);
AFI.addLOHDirective(MCLOH_AdrpLdrGot, {&MI, Info.MI0});
break;
case MCLOH_AdrpAdrp:
llvm_unreachable("MCLOH_AdrpAdrp not used in state machine");
}
}
handleClobber(Info);
Info.LastADRP = &MI;
}
static void handleRegMaskClobber(const uint32_t *RegMask, MCPhysReg Reg,
LOHInfo *LOHInfos) {
if (!MachineOperand::clobbersPhysReg(RegMask, Reg))
return;
int Idx = mapRegToGPRIndex(Reg);
if (Idx >= 0)
handleClobber(LOHInfos[Idx]);
}
static void handleNormalInst(const MachineInstr &MI, LOHInfo *LOHInfos) {
// Handle defs and regmasks.
for (const MachineOperand &MO : MI.operands()) {
if (MO.isRegMask()) {
const uint32_t *RegMask = MO.getRegMask();
for (MCPhysReg Reg : AArch64::GPR32RegClass)
handleRegMaskClobber(RegMask, Reg, LOHInfos);
for (MCPhysReg Reg : AArch64::GPR64RegClass)
handleRegMaskClobber(RegMask, Reg, LOHInfos);
continue;
}
if (!MO.isReg() || !MO.isDef())
continue;
int Idx = mapRegToGPRIndex(MO.getReg());
if (Idx < 0)
continue;
handleClobber(LOHInfos[Idx]);
}
// Handle uses.
SmallSet<int, 4> UsesSeen;
for (const MachineOperand &MO : MI.uses()) {
if (!MO.isReg() || !MO.readsReg())
continue;
int Idx = mapRegToGPRIndex(MO.getReg());
if (Idx < 0)
continue;
// Multiple uses of the same register within a single instruction don't
// count as MultiUser or block optimization. This is especially important on
// arm64_32, where any memory operation is likely to be an explicit use of
// xN and an implicit use of wN (the base address register).
if (!UsesSeen.count(Idx)) {
handleUse(MI, MO, LOHInfos[Idx]);
UsesSeen.insert(Idx);
}
}
}
bool AArch64CollectLOH::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
return false;
LLVM_DEBUG(dbgs() << "********** AArch64 Collect LOH **********\n"
<< "Looking in function " << MF.getName() << '\n');
LOHInfo LOHInfos[N_GPR_REGS];
AArch64FunctionInfo &AFI = *MF.getInfo<AArch64FunctionInfo>();
for (const MachineBasicBlock &MBB : MF) {
// Reset register tracking state.
memset(LOHInfos, 0, sizeof(LOHInfos));
// Live-out registers are used.
for (const MachineBasicBlock *Succ : MBB.successors()) {
for (const auto &LI : Succ->liveins()) {
int RegIdx = mapRegToGPRIndex(LI.PhysReg);
if (RegIdx >= 0)
LOHInfos[RegIdx].OneUser = true;
}
}
// Walk the basic block backwards and update the per register state machine
// in the process.
for (const MachineInstr &MI : make_range(MBB.rbegin(), MBB.rend())) {
unsigned Opcode = MI.getOpcode();
switch (Opcode) {
case AArch64::ADDXri:
case AArch64::LDRXui:
case AArch64::LDRWui:
if (canDefBePartOfLOH(MI)) {
const MachineOperand &Def = MI.getOperand(0);
const MachineOperand &Op = MI.getOperand(1);
assert(Def.isReg() && Def.isDef() && "Expected reg def");
assert(Op.isReg() && Op.isUse() && "Expected reg use");
int DefIdx = mapRegToGPRIndex(Def.getReg());
int OpIdx = mapRegToGPRIndex(Op.getReg());
if (DefIdx >= 0 && OpIdx >= 0 &&
handleMiddleInst(MI, LOHInfos[DefIdx], LOHInfos[OpIdx]))
continue;
}
break;
case AArch64::ADRP:
const MachineOperand &Op0 = MI.getOperand(0);
int Idx = mapRegToGPRIndex(Op0.getReg());
if (Idx >= 0) {
handleADRP(MI, AFI, LOHInfos[Idx]);
continue;
}
break;
}
handleNormalInst(MI, LOHInfos);
}
}
// Return "no change": The pass only collects information.
return false;
}
FunctionPass *llvm::createAArch64CollectLOHPass() {
return new AArch64CollectLOH();
}
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