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llvm-6502/lib/Target/ARM64/ARM64LoadStoreOptimizer.cpp
Chad Rosier 8f0f458824 [ARM64][fast-isel] Disable target specific optimizations at -O0. Functionally, 
this patch disables the dead register elimination pass and the load/store pair
optimization pass at -O0.  The ILP optimizations don't require the optimization
level to be checked because the call to addILPOpts is predicated with the
necessary check.  The AdvSIMDScalar pass is disabled by default at all
optimization levels.  This patch leaves that pass disabled by default.

Also, move command-line options into ARM64TargetMachine.cpp and add a few
additional flags to aid in debugging.  This fixes an issue with the
-debug-pass=Structure flag where passes were printed, but not actually run
(i.e., AdvSIMDScalar pass).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208223 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-07 16:41:55 +00:00

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//===-- ARM64LoadStoreOptimizer.cpp - ARM64 load/store opt. pass --*- C++ -*-=//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains a pass that performs load / store related peephole
// optimizations. This pass should be run after register allocation.
//
//===----------------------------------------------------------------------===//
#include "ARM64InstrInfo.h"
#include "MCTargetDesc/ARM64AddressingModes.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
#define DEBUG_TYPE "arm64-ldst-opt"
/// ARM64AllocLoadStoreOpt - Post-register allocation pass to combine
/// load / store instructions to form ldp / stp instructions.
STATISTIC(NumPairCreated, "Number of load/store pair instructions generated");
STATISTIC(NumPostFolded, "Number of post-index updates folded");
STATISTIC(NumPreFolded, "Number of pre-index updates folded");
STATISTIC(NumUnscaledPairCreated,
"Number of load/store from unscaled generated");
static cl::opt<unsigned> ScanLimit("arm64-load-store-scan-limit", cl::init(20),
cl::Hidden);
// Place holder while testing unscaled load/store combining
static cl::opt<bool>
EnableARM64UnscaledMemOp("arm64-unscaled-mem-op", cl::Hidden,
cl::desc("Allow ARM64 unscaled load/store combining"),
cl::init(true));
namespace {
struct ARM64LoadStoreOpt : public MachineFunctionPass {
static char ID;
ARM64LoadStoreOpt() : MachineFunctionPass(ID) {}
const ARM64InstrInfo *TII;
const TargetRegisterInfo *TRI;
// Scan the instructions looking for a load/store that can be combined
// with the current instruction into a load/store pair.
// Return the matching instruction if one is found, else MBB->end().
// If a matching instruction is found, mergeForward is set to true if the
// merge is to remove the first instruction and replace the second with
// a pair-wise insn, and false if the reverse is true.
MachineBasicBlock::iterator findMatchingInsn(MachineBasicBlock::iterator I,
bool &mergeForward,
unsigned Limit);
// Merge the two instructions indicated into a single pair-wise instruction.
// If mergeForward is true, erase the first instruction and fold its
// operation into the second. If false, the reverse. Return the instruction
// following the first instruction (which may change during processing).
MachineBasicBlock::iterator
mergePairedInsns(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Paired, bool mergeForward);
// Scan the instruction list to find a base register update that can
// be combined with the current instruction (a load or store) using
// pre or post indexed addressing with writeback. Scan forwards.
MachineBasicBlock::iterator
findMatchingUpdateInsnForward(MachineBasicBlock::iterator I, unsigned Limit,
int Value);
// Scan the instruction list to find a base register update that can
// be combined with the current instruction (a load or store) using
// pre or post indexed addressing with writeback. Scan backwards.
MachineBasicBlock::iterator
findMatchingUpdateInsnBackward(MachineBasicBlock::iterator I, unsigned Limit);
// Merge a pre-index base register update into a ld/st instruction.
MachineBasicBlock::iterator
mergePreIdxUpdateInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update);
// Merge a post-index base register update into a ld/st instruction.
MachineBasicBlock::iterator
mergePostIdxUpdateInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update);
bool optimizeBlock(MachineBasicBlock &MBB);
bool runOnMachineFunction(MachineFunction &Fn) override;
const char *getPassName() const override {
return "ARM64 load / store optimization pass";
}
private:
int getMemSize(MachineInstr *MemMI);
};
char ARM64LoadStoreOpt::ID = 0;
}
static bool isUnscaledLdst(unsigned Opc) {
switch (Opc) {
default:
return false;
case ARM64::STURSi:
return true;
case ARM64::STURDi:
return true;
case ARM64::STURQi:
return true;
case ARM64::STURWi:
return true;
case ARM64::STURXi:
return true;
case ARM64::LDURSi:
return true;
case ARM64::LDURDi:
return true;
case ARM64::LDURQi:
return true;
case ARM64::LDURWi:
return true;
case ARM64::LDURXi:
return true;
}
}
// Size in bytes of the data moved by an unscaled load or store
int ARM64LoadStoreOpt::getMemSize(MachineInstr *MemMI) {
switch (MemMI->getOpcode()) {
default:
llvm_unreachable("Opcode has has unknown size!");
case ARM64::STRSui:
case ARM64::STURSi:
return 4;
case ARM64::STRDui:
case ARM64::STURDi:
return 8;
case ARM64::STRQui:
case ARM64::STURQi:
return 16;
case ARM64::STRWui:
case ARM64::STURWi:
return 4;
case ARM64::STRXui:
case ARM64::STURXi:
return 8;
case ARM64::LDRSui:
case ARM64::LDURSi:
return 4;
case ARM64::LDRDui:
case ARM64::LDURDi:
return 8;
case ARM64::LDRQui:
case ARM64::LDURQi:
return 16;
case ARM64::LDRWui:
case ARM64::LDURWi:
return 4;
case ARM64::LDRXui:
case ARM64::LDURXi:
return 8;
}
}
static unsigned getMatchingPairOpcode(unsigned Opc) {
switch (Opc) {
default:
llvm_unreachable("Opcode has no pairwise equivalent!");
case ARM64::STRSui:
case ARM64::STURSi:
return ARM64::STPSi;
case ARM64::STRDui:
case ARM64::STURDi:
return ARM64::STPDi;
case ARM64::STRQui:
case ARM64::STURQi:
return ARM64::STPQi;
case ARM64::STRWui:
case ARM64::STURWi:
return ARM64::STPWi;
case ARM64::STRXui:
case ARM64::STURXi:
return ARM64::STPXi;
case ARM64::LDRSui:
case ARM64::LDURSi:
return ARM64::LDPSi;
case ARM64::LDRDui:
case ARM64::LDURDi:
return ARM64::LDPDi;
case ARM64::LDRQui:
case ARM64::LDURQi:
return ARM64::LDPQi;
case ARM64::LDRWui:
case ARM64::LDURWi:
return ARM64::LDPWi;
case ARM64::LDRXui:
case ARM64::LDURXi:
return ARM64::LDPXi;
}
}
static unsigned getPreIndexedOpcode(unsigned Opc) {
switch (Opc) {
default:
llvm_unreachable("Opcode has no pre-indexed equivalent!");
case ARM64::STRSui: return ARM64::STRSpre;
case ARM64::STRDui: return ARM64::STRDpre;
case ARM64::STRQui: return ARM64::STRQpre;
case ARM64::STRWui: return ARM64::STRWpre;
case ARM64::STRXui: return ARM64::STRXpre;
case ARM64::LDRSui: return ARM64::LDRSpre;
case ARM64::LDRDui: return ARM64::LDRDpre;
case ARM64::LDRQui: return ARM64::LDRQpre;
case ARM64::LDRWui: return ARM64::LDRWpre;
case ARM64::LDRXui: return ARM64::LDRXpre;
}
}
static unsigned getPostIndexedOpcode(unsigned Opc) {
switch (Opc) {
default:
llvm_unreachable("Opcode has no post-indexed wise equivalent!");
case ARM64::STRSui:
return ARM64::STRSpost;
case ARM64::STRDui:
return ARM64::STRDpost;
case ARM64::STRQui:
return ARM64::STRQpost;
case ARM64::STRWui:
return ARM64::STRWpost;
case ARM64::STRXui:
return ARM64::STRXpost;
case ARM64::LDRSui:
return ARM64::LDRSpost;
case ARM64::LDRDui:
return ARM64::LDRDpost;
case ARM64::LDRQui:
return ARM64::LDRQpost;
case ARM64::LDRWui:
return ARM64::LDRWpost;
case ARM64::LDRXui:
return ARM64::LDRXpost;
}
}
MachineBasicBlock::iterator
ARM64LoadStoreOpt::mergePairedInsns(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Paired,
bool mergeForward) {
MachineBasicBlock::iterator NextI = I;
++NextI;
// If NextI is the second of the two instructions to be merged, we need
// to skip one further. Either way we merge will invalidate the iterator,
// and we don't need to scan the new instruction, as it's a pairwise
// instruction, which we're not considering for further action anyway.
if (NextI == Paired)
++NextI;
bool IsUnscaled = isUnscaledLdst(I->getOpcode());
int OffsetStride = IsUnscaled && EnableARM64UnscaledMemOp ? getMemSize(I) : 1;
unsigned NewOpc = getMatchingPairOpcode(I->getOpcode());
// Insert our new paired instruction after whichever of the paired
// instructions mergeForward indicates.
MachineBasicBlock::iterator InsertionPoint = mergeForward ? Paired : I;
// Also based on mergeForward is from where we copy the base register operand
// so we get the flags compatible with the input code.
MachineOperand &BaseRegOp =
mergeForward ? Paired->getOperand(1) : I->getOperand(1);
// Which register is Rt and which is Rt2 depends on the offset order.
MachineInstr *RtMI, *Rt2MI;
if (I->getOperand(2).getImm() ==
Paired->getOperand(2).getImm() + OffsetStride) {
RtMI = Paired;
Rt2MI = I;
} else {
RtMI = I;
Rt2MI = Paired;
}
// Handle Unscaled
int OffsetImm = RtMI->getOperand(2).getImm();
if (IsUnscaled && EnableARM64UnscaledMemOp)
OffsetImm /= OffsetStride;
// Construct the new instruction.
MachineInstrBuilder MIB = BuildMI(*I->getParent(), InsertionPoint,
I->getDebugLoc(), TII->get(NewOpc))
.addOperand(RtMI->getOperand(0))
.addOperand(Rt2MI->getOperand(0))
.addOperand(BaseRegOp)
.addImm(OffsetImm);
(void)MIB;
// FIXME: Do we need/want to copy the mem operands from the source
// instructions? Probably. What uses them after this?
DEBUG(dbgs() << "Creating pair load/store. Replacing instructions:\n ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG(Paired->print(dbgs()));
DEBUG(dbgs() << " with instruction:\n ");
DEBUG(((MachineInstr *)MIB)->print(dbgs()));
DEBUG(dbgs() << "\n");
// Erase the old instructions.
I->eraseFromParent();
Paired->eraseFromParent();
return NextI;
}
/// trackRegDefsUses - Remember what registers the specified instruction uses
/// and modifies.
static void trackRegDefsUses(MachineInstr *MI, BitVector &ModifiedRegs,
BitVector &UsedRegs,
const TargetRegisterInfo *TRI) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isRegMask())
ModifiedRegs.setBitsNotInMask(MO.getRegMask());
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (MO.isDef()) {
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
ModifiedRegs.set(*AI);
} else {
assert(MO.isUse() && "Reg operand not a def and not a use?!?");
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
UsedRegs.set(*AI);
}
}
}
static bool inBoundsForPair(bool IsUnscaled, int Offset, int OffsetStride) {
if (!IsUnscaled && (Offset > 63 || Offset < -64))
return false;
if (IsUnscaled) {
// Convert the byte-offset used by unscaled into an "element" offset used
// by the scaled pair load/store instructions.
int elemOffset = Offset / OffsetStride;
if (elemOffset > 63 || elemOffset < -64)
return false;
}
return true;
}
// Do alignment, specialized to power of 2 and for signed ints,
// avoiding having to do a C-style cast from uint_64t to int when
// using RoundUpToAlignment from include/llvm/Support/MathExtras.h.
// FIXME: Move this function to include/MathExtras.h?
static int alignTo(int Num, int PowOf2) {
return (Num + PowOf2 - 1) & ~(PowOf2 - 1);
}
/// findMatchingInsn - Scan the instructions looking for a load/store that can
/// be combined with the current instruction into a load/store pair.
MachineBasicBlock::iterator
ARM64LoadStoreOpt::findMatchingInsn(MachineBasicBlock::iterator I,
bool &mergeForward, unsigned Limit) {
MachineBasicBlock::iterator E = I->getParent()->end();
MachineBasicBlock::iterator MBBI = I;
MachineInstr *FirstMI = I;
++MBBI;
int Opc = FirstMI->getOpcode();
bool mayLoad = FirstMI->mayLoad();
bool IsUnscaled = isUnscaledLdst(Opc);
unsigned Reg = FirstMI->getOperand(0).getReg();
unsigned BaseReg = FirstMI->getOperand(1).getReg();
int Offset = FirstMI->getOperand(2).getImm();
// Early exit if the first instruction modifies the base register.
// e.g., ldr x0, [x0]
// Early exit if the offset if not possible to match. (6 bits of positive
// range, plus allow an extra one in case we find a later insn that matches
// with Offset-1
if (FirstMI->modifiesRegister(BaseReg, TRI))
return E;
int OffsetStride =
IsUnscaled && EnableARM64UnscaledMemOp ? getMemSize(FirstMI) : 1;
if (!inBoundsForPair(IsUnscaled, Offset, OffsetStride))
return E;
// Track which registers have been modified and used between the first insn
// (inclusive) and the second insn.
BitVector ModifiedRegs, UsedRegs;
ModifiedRegs.resize(TRI->getNumRegs());
UsedRegs.resize(TRI->getNumRegs());
for (unsigned Count = 0; MBBI != E && Count < Limit; ++MBBI) {
MachineInstr *MI = MBBI;
// Skip DBG_VALUE instructions. Otherwise debug info can affect the
// optimization by changing how far we scan.
if (MI->isDebugValue())
continue;
// Now that we know this is a real instruction, count it.
++Count;
if (Opc == MI->getOpcode() && MI->getOperand(2).isImm()) {
// If we've found another instruction with the same opcode, check to see
// if the base and offset are compatible with our starting instruction.
// These instructions all have scaled immediate operands, so we just
// check for +1/-1. Make sure to check the new instruction offset is
// actually an immediate and not a symbolic reference destined for
// a relocation.
//
// Pairwise instructions have a 7-bit signed offset field. Single insns
// have a 12-bit unsigned offset field. To be a valid combine, the
// final offset must be in range.
unsigned MIBaseReg = MI->getOperand(1).getReg();
int MIOffset = MI->getOperand(2).getImm();
if (BaseReg == MIBaseReg && ((Offset == MIOffset + OffsetStride) ||
(Offset + OffsetStride == MIOffset))) {
int MinOffset = Offset < MIOffset ? Offset : MIOffset;
// If this is a volatile load/store that otherwise matched, stop looking
// as something is going on that we don't have enough information to
// safely transform. Similarly, stop if we see a hint to avoid pairs.
if (MI->hasOrderedMemoryRef() || TII->isLdStPairSuppressed(MI))
return E;
// If the resultant immediate offset of merging these instructions
// is out of range for a pairwise instruction, bail and keep looking.
bool MIIsUnscaled = isUnscaledLdst(MI->getOpcode());
if (!inBoundsForPair(MIIsUnscaled, MinOffset, OffsetStride)) {
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
continue;
}
// If the alignment requirements of the paired (scaled) instruction
// can't express the offset of the unscaled input, bail and keep
// looking.
if (IsUnscaled && EnableARM64UnscaledMemOp &&
(alignTo(MinOffset, OffsetStride) != MinOffset)) {
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
continue;
}
// If the destination register of the loads is the same register, bail
// and keep looking. A load-pair instruction with both destination
// registers the same is UNPREDICTABLE and will result in an exception.
if (mayLoad && Reg == MI->getOperand(0).getReg()) {
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
continue;
}
// If the Rt of the second instruction was not modified or used between
// the two instructions, we can combine the second into the first.
if (!ModifiedRegs[MI->getOperand(0).getReg()] &&
!UsedRegs[MI->getOperand(0).getReg()]) {
mergeForward = false;
return MBBI;
}
// Likewise, if the Rt of the first instruction is not modified or used
// between the two instructions, we can combine the first into the
// second.
if (!ModifiedRegs[FirstMI->getOperand(0).getReg()] &&
!UsedRegs[FirstMI->getOperand(0).getReg()]) {
mergeForward = true;
return MBBI;
}
// Unable to combine these instructions due to interference in between.
// Keep looking.
}
}
// If the instruction wasn't a matching load or store, but does (or can)
// modify memory, stop searching, as we don't have alias analysis or
// anything like that to tell us whether the access is tromping on the
// locations we care about. The big one we want to catch is calls.
//
// FIXME: Theoretically, we can do better than that for SP and FP based
// references since we can effectively know where those are touching. It's
// unclear if it's worth the extra code, though. Most paired instructions
// will be sequential, perhaps with a few intervening non-memory related
// instructions.
if (MI->mayStore() || MI->isCall())
return E;
// Likewise, if we're matching a store instruction, we don't want to
// move across a load, as it may be reading the same location.
if (FirstMI->mayStore() && MI->mayLoad())
return E;
// Update modified / uses register lists.
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
// Otherwise, if the base register is modified, we have no match, so
// return early.
if (ModifiedRegs[BaseReg])
return E;
}
return E;
}
MachineBasicBlock::iterator
ARM64LoadStoreOpt::mergePreIdxUpdateInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update) {
assert((Update->getOpcode() == ARM64::ADDXri ||
Update->getOpcode() == ARM64::SUBXri) &&
"Unexpected base register update instruction to merge!");
MachineBasicBlock::iterator NextI = I;
// Return the instruction following the merged instruction, which is
// the instruction following our unmerged load. Unless that's the add/sub
// instruction we're merging, in which case it's the one after that.
if (++NextI == Update)
++NextI;
int Value = Update->getOperand(2).getImm();
assert(ARM64_AM::getShiftValue(Update->getOperand(3).getImm()) == 0 &&
"Can't merge 1 << 12 offset into pre-indexed load / store");
if (Update->getOpcode() == ARM64::SUBXri)
Value = -Value;
unsigned NewOpc = getPreIndexedOpcode(I->getOpcode());
MachineInstrBuilder MIB =
BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
.addOperand(I->getOperand(0))
.addOperand(I->getOperand(1))
.addImm(Value);
(void)MIB;
DEBUG(dbgs() << "Creating pre-indexed load/store.");
DEBUG(dbgs() << " Replacing instructions:\n ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG(Update->print(dbgs()));
DEBUG(dbgs() << " with instruction:\n ");
DEBUG(((MachineInstr *)MIB)->print(dbgs()));
DEBUG(dbgs() << "\n");
// Erase the old instructions for the block.
I->eraseFromParent();
Update->eraseFromParent();
return NextI;
}
MachineBasicBlock::iterator
ARM64LoadStoreOpt::mergePostIdxUpdateInsn(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator Update) {
assert((Update->getOpcode() == ARM64::ADDXri ||
Update->getOpcode() == ARM64::SUBXri) &&
"Unexpected base register update instruction to merge!");
MachineBasicBlock::iterator NextI = I;
// Return the instruction following the merged instruction, which is
// the instruction following our unmerged load. Unless that's the add/sub
// instruction we're merging, in which case it's the one after that.
if (++NextI == Update)
++NextI;
int Value = Update->getOperand(2).getImm();
assert(ARM64_AM::getShiftValue(Update->getOperand(3).getImm()) == 0 &&
"Can't merge 1 << 12 offset into post-indexed load / store");
if (Update->getOpcode() == ARM64::SUBXri)
Value = -Value;
unsigned NewOpc = getPostIndexedOpcode(I->getOpcode());
MachineInstrBuilder MIB =
BuildMI(*I->getParent(), I, I->getDebugLoc(), TII->get(NewOpc))
.addOperand(I->getOperand(0))
.addOperand(I->getOperand(1))
.addImm(Value);
(void)MIB;
DEBUG(dbgs() << "Creating post-indexed load/store.");
DEBUG(dbgs() << " Replacing instructions:\n ");
DEBUG(I->print(dbgs()));
DEBUG(dbgs() << " ");
DEBUG(Update->print(dbgs()));
DEBUG(dbgs() << " with instruction:\n ");
DEBUG(((MachineInstr *)MIB)->print(dbgs()));
DEBUG(dbgs() << "\n");
// Erase the old instructions for the block.
I->eraseFromParent();
Update->eraseFromParent();
return NextI;
}
static bool isMatchingUpdateInsn(MachineInstr *MI, unsigned BaseReg,
int Offset) {
switch (MI->getOpcode()) {
default:
break;
case ARM64::SUBXri:
// Negate the offset for a SUB instruction.
Offset *= -1;
// FALLTHROUGH
case ARM64::ADDXri:
// Make sure it's a vanilla immediate operand, not a relocation or
// anything else we can't handle.
if (!MI->getOperand(2).isImm())
break;
// Watch out for 1 << 12 shifted value.
if (ARM64_AM::getShiftValue(MI->getOperand(3).getImm()))
break;
// If the instruction has the base register as source and dest and the
// immediate will fit in a signed 9-bit integer, then we have a match.
if (MI->getOperand(0).getReg() == BaseReg &&
MI->getOperand(1).getReg() == BaseReg &&
MI->getOperand(2).getImm() <= 255 &&
MI->getOperand(2).getImm() >= -256) {
// If we have a non-zero Offset, we check that it matches the amount
// we're adding to the register.
if (!Offset || Offset == MI->getOperand(2).getImm())
return true;
}
break;
}
return false;
}
MachineBasicBlock::iterator
ARM64LoadStoreOpt::findMatchingUpdateInsnForward(MachineBasicBlock::iterator I,
unsigned Limit, int Value) {
MachineBasicBlock::iterator E = I->getParent()->end();
MachineInstr *MemMI = I;
MachineBasicBlock::iterator MBBI = I;
const MachineFunction &MF = *MemMI->getParent()->getParent();
unsigned DestReg = MemMI->getOperand(0).getReg();
unsigned BaseReg = MemMI->getOperand(1).getReg();
int Offset = MemMI->getOperand(2).getImm() *
TII->getRegClass(MemMI->getDesc(), 0, TRI, MF)->getSize();
// If the base register overlaps the destination register, we can't
// merge the update.
if (DestReg == BaseReg || TRI->isSubRegister(BaseReg, DestReg))
return E;
// Scan forward looking for post-index opportunities.
// Updating instructions can't be formed if the memory insn already
// has an offset other than the value we're looking for.
if (Offset != Value)
return E;
// Track which registers have been modified and used between the first insn
// (inclusive) and the second insn.
BitVector ModifiedRegs, UsedRegs;
ModifiedRegs.resize(TRI->getNumRegs());
UsedRegs.resize(TRI->getNumRegs());
++MBBI;
for (unsigned Count = 0; MBBI != E; ++MBBI) {
MachineInstr *MI = MBBI;
// Skip DBG_VALUE instructions. Otherwise debug info can affect the
// optimization by changing how far we scan.
if (MI->isDebugValue())
continue;
// Now that we know this is a real instruction, count it.
++Count;
// If we found a match, return it.
if (isMatchingUpdateInsn(MI, BaseReg, Value))
return MBBI;
// Update the status of what the instruction clobbered and used.
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
// Otherwise, if the base register is used or modified, we have no match, so
// return early.
if (ModifiedRegs[BaseReg] || UsedRegs[BaseReg])
return E;
}
return E;
}
MachineBasicBlock::iterator
ARM64LoadStoreOpt::findMatchingUpdateInsnBackward(MachineBasicBlock::iterator I,
unsigned Limit) {
MachineBasicBlock::iterator B = I->getParent()->begin();
MachineBasicBlock::iterator E = I->getParent()->end();
MachineInstr *MemMI = I;
MachineBasicBlock::iterator MBBI = I;
const MachineFunction &MF = *MemMI->getParent()->getParent();
unsigned DestReg = MemMI->getOperand(0).getReg();
unsigned BaseReg = MemMI->getOperand(1).getReg();
int Offset = MemMI->getOperand(2).getImm();
unsigned RegSize = TII->getRegClass(MemMI->getDesc(), 0, TRI, MF)->getSize();
// If the load/store is the first instruction in the block, there's obviously
// not any matching update. Ditto if the memory offset isn't zero.
if (MBBI == B || Offset != 0)
return E;
// If the base register overlaps the destination register, we can't
// merge the update.
if (DestReg == BaseReg || TRI->isSubRegister(BaseReg, DestReg))
return E;
// Track which registers have been modified and used between the first insn
// (inclusive) and the second insn.
BitVector ModifiedRegs, UsedRegs;
ModifiedRegs.resize(TRI->getNumRegs());
UsedRegs.resize(TRI->getNumRegs());
--MBBI;
for (unsigned Count = 0; MBBI != B; --MBBI) {
MachineInstr *MI = MBBI;
// Skip DBG_VALUE instructions. Otherwise debug info can affect the
// optimization by changing how far we scan.
if (MI->isDebugValue())
continue;
// Now that we know this is a real instruction, count it.
++Count;
// If we found a match, return it.
if (isMatchingUpdateInsn(MI, BaseReg, RegSize))
return MBBI;
// Update the status of what the instruction clobbered and used.
trackRegDefsUses(MI, ModifiedRegs, UsedRegs, TRI);
// Otherwise, if the base register is used or modified, we have no match, so
// return early.
if (ModifiedRegs[BaseReg] || UsedRegs[BaseReg])
return E;
}
return E;
}
bool ARM64LoadStoreOpt::optimizeBlock(MachineBasicBlock &MBB) {
bool Modified = false;
// Two tranformations to do here:
// 1) Find loads and stores that can be merged into a single load or store
// pair instruction.
// e.g.,
// ldr x0, [x2]
// ldr x1, [x2, #8]
// ; becomes
// ldp x0, x1, [x2]
// 2) Find base register updates that can be merged into the load or store
// as a base-reg writeback.
// e.g.,
// ldr x0, [x2]
// add x2, x2, #4
// ; becomes
// ldr x0, [x2], #4
for (MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
MBBI != E;) {
MachineInstr *MI = MBBI;
switch (MI->getOpcode()) {
default:
// Just move on to the next instruction.
++MBBI;
break;
case ARM64::STRSui:
case ARM64::STRDui:
case ARM64::STRQui:
case ARM64::STRXui:
case ARM64::STRWui:
case ARM64::LDRSui:
case ARM64::LDRDui:
case ARM64::LDRQui:
case ARM64::LDRXui:
case ARM64::LDRWui:
// do the unscaled versions as well
case ARM64::STURSi:
case ARM64::STURDi:
case ARM64::STURQi:
case ARM64::STURWi:
case ARM64::STURXi:
case ARM64::LDURSi:
case ARM64::LDURDi:
case ARM64::LDURQi:
case ARM64::LDURWi:
case ARM64::LDURXi: {
// If this is a volatile load/store, don't mess with it.
if (MI->hasOrderedMemoryRef()) {
++MBBI;
break;
}
// Make sure this is a reg+imm (as opposed to an address reloc).
if (!MI->getOperand(2).isImm()) {
++MBBI;
break;
}
// Check if this load/store has a hint to avoid pair formation.
// MachineMemOperands hints are set by the ARM64StorePairSuppress pass.
if (TII->isLdStPairSuppressed(MI)) {
++MBBI;
break;
}
// Look ahead up to ScanLimit instructions for a pairable instruction.
bool mergeForward = false;
MachineBasicBlock::iterator Paired =
findMatchingInsn(MBBI, mergeForward, ScanLimit);
if (Paired != E) {
// Merge the loads into a pair. Keeping the iterator straight is a
// pain, so we let the merge routine tell us what the next instruction
// is after it's done mucking about.
MBBI = mergePairedInsns(MBBI, Paired, mergeForward);
Modified = true;
++NumPairCreated;
if (isUnscaledLdst(MI->getOpcode()))
++NumUnscaledPairCreated;
break;
}
++MBBI;
break;
}
// FIXME: Do the other instructions.
}
}
for (MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end();
MBBI != E;) {
MachineInstr *MI = MBBI;
// Do update merging. It's simpler to keep this separate from the above
// switch, though not strictly necessary.
int Opc = MI->getOpcode();
switch (Opc) {
default:
// Just move on to the next instruction.
++MBBI;
break;
case ARM64::STRSui:
case ARM64::STRDui:
case ARM64::STRQui:
case ARM64::STRXui:
case ARM64::STRWui:
case ARM64::LDRSui:
case ARM64::LDRDui:
case ARM64::LDRQui:
case ARM64::LDRXui:
case ARM64::LDRWui:
// do the unscaled versions as well
case ARM64::STURSi:
case ARM64::STURDi:
case ARM64::STURQi:
case ARM64::STURWi:
case ARM64::STURXi:
case ARM64::LDURSi:
case ARM64::LDURDi:
case ARM64::LDURQi:
case ARM64::LDURWi:
case ARM64::LDURXi: {
// Make sure this is a reg+imm (as opposed to an address reloc).
if (!MI->getOperand(2).isImm()) {
++MBBI;
break;
}
// Look ahead up to ScanLimit instructions for a mergable instruction.
MachineBasicBlock::iterator Update =
findMatchingUpdateInsnForward(MBBI, ScanLimit, 0);
if (Update != E) {
// Merge the update into the ld/st.
MBBI = mergePostIdxUpdateInsn(MBBI, Update);
Modified = true;
++NumPostFolded;
break;
}
// Don't know how to handle pre/post-index versions, so move to the next
// instruction.
if (isUnscaledLdst(Opc)) {
++MBBI;
break;
}
// Look back to try to find a pre-index instruction. For example,
// add x0, x0, #8
// ldr x1, [x0]
// merged into:
// ldr x1, [x0, #8]!
Update = findMatchingUpdateInsnBackward(MBBI, ScanLimit);
if (Update != E) {
// Merge the update into the ld/st.
MBBI = mergePreIdxUpdateInsn(MBBI, Update);
Modified = true;
++NumPreFolded;
break;
}
// Look forward to try to find a post-index instruction. For example,
// ldr x1, [x0, #64]
// add x0, x0, #64
// merged into:
// ldr x1, [x0], #64
// The immediate in the load/store is scaled by the size of the register
// being loaded. The immediate in the add we're looking for,
// however, is not, so adjust here.
int Value = MI->getOperand(2).getImm() *
TII->getRegClass(MI->getDesc(), 0, TRI, *(MBB.getParent()))
->getSize();
Update = findMatchingUpdateInsnForward(MBBI, ScanLimit, Value);
if (Update != E) {
// Merge the update into the ld/st.
MBBI = mergePreIdxUpdateInsn(MBBI, Update);
Modified = true;
++NumPreFolded;
break;
}
// Nothing found. Just move to the next instruction.
++MBBI;
break;
}
// FIXME: Do the other instructions.
}
}
return Modified;
}
bool ARM64LoadStoreOpt::runOnMachineFunction(MachineFunction &Fn) {
const TargetMachine &TM = Fn.getTarget();
TII = static_cast<const ARM64InstrInfo *>(TM.getInstrInfo());
TRI = TM.getRegisterInfo();
bool Modified = false;
for (auto &MBB : Fn)
Modified |= optimizeBlock(MBB);
return Modified;
}
// FIXME: Do we need/want a pre-alloc pass like ARM has to try to keep
// loads and stores near one another?
/// createARMLoadStoreOptimizationPass - returns an instance of the load / store
/// optimization pass.
FunctionPass *llvm::createARM64LoadStoreOptimizationPass() {
return new ARM64LoadStoreOpt();
}
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