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llvm-project/llvm/lib/CodeGen/PeepholeOptimizer.cpp

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//===-- PeepholeOptimizer.cpp - Peephole Optimizations --------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Perform peephole optimizations on the machine code:
//
// - Optimize Extensions
//
// Optimization of sign / zero extension instructions. It may be extended to
// handle other instructions with similar properties.
//
// On some targets, some instructions, e.g. X86 sign / zero extension, may
// leave the source value in the lower part of the result. This optimization
// will replace some uses of the pre-extension value with uses of the
// sub-register of the results.
//
// - Optimize Comparisons
//
// Optimization of comparison instructions. For instance, in this code:
//
// sub r1, 1
// cmp r1, 0
// bz L1
//
// If the "sub" instruction all ready sets (or could be modified to set) the
// same flag that the "cmp" instruction sets and that "bz" uses, then we can
// eliminate the "cmp" instruction.
//
// Another instance, in this code:
//
// sub r1, r3 | sub r1, imm
// cmp r3, r1 or cmp r1, r3 | cmp r1, imm
// bge L1
//
// If the branch instruction can use flag from "sub", then we can replace
// "sub" with "subs" and eliminate the "cmp" instruction.
//
// - Optimize Loads:
//
// Loads that can be folded into a later instruction. A load is foldable
// if it loads to virtual registers and the virtual register defined has
// a single use.
//
// - Optimize Copies and Bitcast:
//
// Rewrite copies and bitcasts to avoid cross register bank copies
// when possible.
// E.g., Consider the following example, where capital and lower
// letters denote different register file:
// b = copy A <-- cross-bank copy
// C = copy b <-- cross-bank copy
// =>
// b = copy A <-- cross-bank copy
// C = copy A <-- same-bank copy
//
// E.g., for bitcast:
// b = bitcast A <-- cross-bank copy
// C = bitcast b <-- cross-bank copy
// =>
// b = bitcast A <-- cross-bank copy
// C = copy A <-- same-bank copy
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Passes.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
using namespace llvm;
#define DEBUG_TYPE "peephole-opt"
// Optimize Extensions
static cl::opt<bool>
Aggressive("aggressive-ext-opt", cl::Hidden,
cl::desc("Aggressive extension optimization"));
static cl::opt<bool>
DisablePeephole("disable-peephole", cl::Hidden, cl::init(false),
cl::desc("Disable the peephole optimizer"));
static cl::opt<bool>
DisableAdvCopyOpt("disable-adv-copy-opt", cl::Hidden, cl::init(true),
cl::desc("Disable advanced copy optimization"));
STATISTIC(NumReuse, "Number of extension results reused");
STATISTIC(NumCmps, "Number of compares eliminated");
STATISTIC(NumImmFold, "Number of move immediate folded");
STATISTIC(NumLoadFold, "Number of loads folded");
STATISTIC(NumSelects, "Number of selects optimized");
STATISTIC(NumCopiesBitcasts, "Number of copies/bitcasts optimized");
namespace {
class PeepholeOptimizer : public MachineFunctionPass {
const TargetMachine *TM;
const TargetInstrInfo *TII;
MachineRegisterInfo *MRI;
MachineDominatorTree *DT; // Machine dominator tree
public:
static char ID; // Pass identification
PeepholeOptimizer() : MachineFunctionPass(ID) {
initializePeepholeOptimizerPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
if (Aggressive) {
AU.addRequired<MachineDominatorTree>();
AU.addPreserved<MachineDominatorTree>();
}
}
private:
bool optimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB);
bool optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &LocalMIs);
bool optimizeSelect(MachineInstr *MI);
bool optimizeCopyOrBitcast(MachineInstr *MI);
bool isMoveImmediate(MachineInstr *MI,
SmallSet<unsigned, 4> &ImmDefRegs,
DenseMap<unsigned, MachineInstr*> &ImmDefMIs);
bool foldImmediate(MachineInstr *MI, MachineBasicBlock *MBB,
SmallSet<unsigned, 4> &ImmDefRegs,
DenseMap<unsigned, MachineInstr*> &ImmDefMIs);
bool isLoadFoldable(MachineInstr *MI,
SmallSet<unsigned, 16> &FoldAsLoadDefCandidates);
};
/// \brief Helper class to track the possible sources of a value defined by
/// a (chain of) copy related instructions.
/// Given a definition (instruction and definition index), this class
/// follows the use-def chain to find successive suitable sources.
/// The given source can be used to rewrite the definition into
/// def = COPY src.
///
/// For instance, let us consider the following snippet:
/// v0 =
/// v2 = INSERT_SUBREG v1, v0, sub0
/// def = COPY v2.sub0
///
/// Using a ValueTracker for def = COPY v2.sub0 will give the following
/// suitable sources:
/// v2.sub0 and v0.
/// Then, def can be rewritten into def = COPY v0.
class ValueTracker {
private:
/// The current point into the use-def chain.
const MachineInstr *Def;
/// The index of the definition in Def.
unsigned DefIdx;
/// The sub register index of the definition.
unsigned DefSubReg;
/// The register where the value can be found.
unsigned Reg;
/// Specifiy whether or not the value tracking looks through
/// complex instructions. When this is false, the value tracker
/// bails on everything that is not a copy or a bitcast.
///
/// Note: This could have been implemented as a specialized version of
/// the ValueTracker class but that would have complicated the code of
/// the users of this class.
bool UseAdvancedTracking;
/// Optional MachineRegisterInfo used to perform some complex
/// tracking.
const MachineRegisterInfo *MRI;
/// \brief Dispatcher to the right underlying implementation of
/// getNextSource.
bool getNextSourceImpl(unsigned &SrcIdx, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for Copy instructions.
bool getNextSourceFromCopy(unsigned &SrcIdx, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for Bitcast instructions.
bool getNextSourceFromBitcast(unsigned &SrcIdx, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for RegSequence
/// instructions.
bool getNextSourceFromRegSequence(unsigned &SrcIdx, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for InsertSubreg
/// instructions.
bool getNextSourceFromInsertSubreg(unsigned &SrcIdx, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for ExtractSubreg
/// instructions.
bool getNextSourceFromExtractSubreg(unsigned &SrcIdx, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for SubregToReg
/// instructions.
bool getNextSourceFromSubregToReg(unsigned &SrcIdx, unsigned &SrcSubReg);
public:
/// \brief Create a ValueTracker instance for the value defines by \p MI
/// at the operand index \p DefIdx.
/// \p DefSubReg represents the sub register index the value tracker will
/// track. It does not need to match the sub register index used in \p MI.
/// \p UseAdvancedTracking specifies whether or not the value tracker looks
/// through complex instructions. By default (false), it handles only copy
/// and bitcast instructions.
/// \p MRI useful to perform some complex checks.
ValueTracker(const MachineInstr &MI, unsigned DefIdx, unsigned DefSubReg,
bool UseAdvancedTracking = false,
const MachineRegisterInfo *MRI = nullptr)
: Def(&MI), DefIdx(DefIdx), DefSubReg(DefSubReg),
UseAdvancedTracking(UseAdvancedTracking), MRI(MRI) {
assert(Def->getOperand(DefIdx).isDef() &&
Def->getOperand(DefIdx).isReg() &&
"Definition does not match machine instruction");
// Initially the value is in the defined register.
Reg = Def->getOperand(DefIdx).getReg();
}
/// \brief Following the use-def chain, get the next available source
/// for the tracked value.
/// When the returned value is not nullptr, getReg() gives the register
/// that contain the tracked value.
/// \note The sub register index returned in \p SrcSubReg must be used
/// on that getReg() to access the actual value.
/// \return Unless the returned value is nullptr (i.e., no source found),
/// \p SrcIdx gives the index of the next source in the returned
/// instruction and \p SrcSubReg the index to be used on that source to
/// get the tracked value. When nullptr is returned, no alternative source
/// has been found.
const MachineInstr *getNextSource(unsigned &SrcIdx, unsigned &SrcSubReg);
/// \brief Get the last register where the initial value can be found.
/// Initially this is the register of the definition.
/// Then, after each successful call to getNextSource, this is the
/// register of the last source.
unsigned getReg() const { return Reg; }
};
}
char PeepholeOptimizer::ID = 0;
char &llvm::PeepholeOptimizerID = PeepholeOptimizer::ID;
INITIALIZE_PASS_BEGIN(PeepholeOptimizer, "peephole-opts",
"Peephole Optimizations", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_END(PeepholeOptimizer, "peephole-opts",
"Peephole Optimizations", false, false)
/// optimizeExtInstr - If instruction is a copy-like instruction, i.e. it reads
/// a single register and writes a single register and it does not modify the
/// source, and if the source value is preserved as a sub-register of the
/// result, then replace all reachable uses of the source with the subreg of the
/// result.
///
/// Do not generate an EXTRACT that is used only in a debug use, as this changes
/// the code. Since this code does not currently share EXTRACTs, just ignore all
/// debug uses.
bool PeepholeOptimizer::
optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &LocalMIs) {
unsigned SrcReg, DstReg, SubIdx;
if (!TII->isCoalescableExtInstr(*MI, SrcReg, DstReg, SubIdx))
return false;
if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
TargetRegisterInfo::isPhysicalRegister(SrcReg))
return false;
if (MRI->hasOneNonDBGUse(SrcReg))
// No other uses.
return false;
// Ensure DstReg can get a register class that actually supports
// sub-registers. Don't change the class until we commit.
const TargetRegisterClass *DstRC = MRI->getRegClass(DstReg);
DstRC = TM->getRegisterInfo()->getSubClassWithSubReg(DstRC, SubIdx);
if (!DstRC)
return false;
// The ext instr may be operating on a sub-register of SrcReg as well.
// PPC::EXTSW is a 32 -> 64-bit sign extension, but it reads a 64-bit
// register.
// If UseSrcSubIdx is Set, SubIdx also applies to SrcReg, and only uses of
// SrcReg:SubIdx should be replaced.
bool UseSrcSubIdx = TM->getRegisterInfo()->
getSubClassWithSubReg(MRI->getRegClass(SrcReg), SubIdx) != nullptr;
// The source has other uses. See if we can replace the other uses with use of
// the result of the extension.
SmallPtrSet<MachineBasicBlock*, 4> ReachedBBs;
for (MachineInstr &UI : MRI->use_nodbg_instructions(DstReg))
ReachedBBs.insert(UI.getParent());
// Uses that are in the same BB of uses of the result of the instruction.
SmallVector<MachineOperand*, 8> Uses;
// Uses that the result of the instruction can reach.
SmallVector<MachineOperand*, 8> ExtendedUses;
bool ExtendLife = true;
for (MachineOperand &UseMO : MRI->use_nodbg_operands(SrcReg)) {
MachineInstr *UseMI = UseMO.getParent();
if (UseMI == MI)
continue;
if (UseMI->isPHI()) {
ExtendLife = false;
continue;
}
// Only accept uses of SrcReg:SubIdx.
if (UseSrcSubIdx && UseMO.getSubReg() != SubIdx)
continue;
// It's an error to translate this:
//
// %reg1025 = <sext> %reg1024
// ...
// %reg1026 = SUBREG_TO_REG 0, %reg1024, 4
//
// into this:
//
// %reg1025 = <sext> %reg1024
// ...
// %reg1027 = COPY %reg1025:4
// %reg1026 = SUBREG_TO_REG 0, %reg1027, 4
//
// The problem here is that SUBREG_TO_REG is there to assert that an
// implicit zext occurs. It doesn't insert a zext instruction. If we allow
// the COPY here, it will give us the value after the <sext>, not the
// original value of %reg1024 before <sext>.
if (UseMI->getOpcode() == TargetOpcode::SUBREG_TO_REG)
continue;
MachineBasicBlock *UseMBB = UseMI->getParent();
if (UseMBB == MBB) {
// Local uses that come after the extension.
if (!LocalMIs.count(UseMI))
Uses.push_back(&UseMO);
} else if (ReachedBBs.count(UseMBB)) {
// Non-local uses where the result of the extension is used. Always
// replace these unless it's a PHI.
Uses.push_back(&UseMO);
} else if (Aggressive && DT->dominates(MBB, UseMBB)) {
// We may want to extend the live range of the extension result in order
// to replace these uses.
ExtendedUses.push_back(&UseMO);
} else {
// Both will be live out of the def MBB anyway. Don't extend live range of
// the extension result.
ExtendLife = false;
break;
}
}
if (ExtendLife && !ExtendedUses.empty())
// Extend the liveness of the extension result.
std::copy(ExtendedUses.begin(), ExtendedUses.end(),
std::back_inserter(Uses));
// Now replace all uses.
bool Changed = false;
if (!Uses.empty()) {
SmallPtrSet<MachineBasicBlock*, 4> PHIBBs;
// Look for PHI uses of the extended result, we don't want to extend the
// liveness of a PHI input. It breaks all kinds of assumptions down
// stream. A PHI use is expected to be the kill of its source values.
for (MachineInstr &UI : MRI->use_nodbg_instructions(DstReg))
if (UI.isPHI())
PHIBBs.insert(UI.getParent());
const TargetRegisterClass *RC = MRI->getRegClass(SrcReg);
for (unsigned i = 0, e = Uses.size(); i != e; ++i) {
MachineOperand *UseMO = Uses[i];
MachineInstr *UseMI = UseMO->getParent();
MachineBasicBlock *UseMBB = UseMI->getParent();
if (PHIBBs.count(UseMBB))
continue;
// About to add uses of DstReg, clear DstReg's kill flags.
if (!Changed) {
MRI->clearKillFlags(DstReg);
MRI->constrainRegClass(DstReg, DstRC);
}
unsigned NewVR = MRI->createVirtualRegister(RC);
MachineInstr *Copy = BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
TII->get(TargetOpcode::COPY), NewVR)
.addReg(DstReg, 0, SubIdx);
// SubIdx applies to both SrcReg and DstReg when UseSrcSubIdx is set.
if (UseSrcSubIdx) {
Copy->getOperand(0).setSubReg(SubIdx);
Copy->getOperand(0).setIsUndef();
}
UseMO->setReg(NewVR);
++NumReuse;
Changed = true;
}
}
return Changed;
}
/// optimizeCmpInstr - If the instruction is a compare and the previous
/// instruction it's comparing against all ready sets (or could be modified to
/// set) the same flag as the compare, then we can remove the comparison and use
/// the flag from the previous instruction.
bool PeepholeOptimizer::optimizeCmpInstr(MachineInstr *MI,
MachineBasicBlock *MBB) {
// If this instruction is a comparison against zero and isn't comparing a
// physical register, we can try to optimize it.
unsigned SrcReg, SrcReg2;
int CmpMask, CmpValue;
if (!TII->analyzeCompare(MI, SrcReg, SrcReg2, CmpMask, CmpValue) ||
TargetRegisterInfo::isPhysicalRegister(SrcReg) ||
(SrcReg2 != 0 && TargetRegisterInfo::isPhysicalRegister(SrcReg2)))
return false;
// Attempt to optimize the comparison instruction.
if (TII->optimizeCompareInstr(MI, SrcReg, SrcReg2, CmpMask, CmpValue, MRI)) {
++NumCmps;
return true;
}
return false;
}
/// Optimize a select instruction.
bool PeepholeOptimizer::optimizeSelect(MachineInstr *MI) {
unsigned TrueOp = 0;
unsigned FalseOp = 0;
bool Optimizable = false;
SmallVector<MachineOperand, 4> Cond;
if (TII->analyzeSelect(MI, Cond, TrueOp, FalseOp, Optimizable))
return false;
if (!Optimizable)
return false;
if (!TII->optimizeSelect(MI))
return false;
MI->eraseFromParent();
++NumSelects;
return true;
}
/// \brief Check if the registers defined by the pair (RegisterClass, SubReg)
/// share the same register file.
static bool shareSameRegisterFile(const TargetRegisterInfo &TRI,
const TargetRegisterClass *DefRC,
unsigned DefSubReg,
const TargetRegisterClass *SrcRC,
unsigned SrcSubReg) {
// Same register class.
if (DefRC == SrcRC)
return true;
// Both operands are sub registers. Check if they share a register class.
unsigned SrcIdx, DefIdx;
if (SrcSubReg && DefSubReg)
return TRI.getCommonSuperRegClass(SrcRC, SrcSubReg, DefRC, DefSubReg,
SrcIdx, DefIdx) != nullptr;
// At most one of the register is a sub register, make it Src to avoid
// duplicating the test.
if (!SrcSubReg) {
std::swap(DefSubReg, SrcSubReg);
std::swap(DefRC, SrcRC);
}
// One of the register is a sub register, check if we can get a superclass.
if (SrcSubReg)
return TRI.getMatchingSuperRegClass(SrcRC, DefRC, SrcSubReg) != nullptr;
// Plain copy.
return TRI.getCommonSubClass(DefRC, SrcRC) != nullptr;
}
/// \brief Get the index of the definition and source for \p Copy
/// instruction.
/// \pre Copy.isCopy() or Copy.isBitcast().
/// \return True if the Copy instruction has only one register source
/// and one register definition. Otherwise, \p DefIdx and \p SrcIdx
/// are invalid.
static bool getCopyOrBitcastDefUseIdx(const MachineInstr &Copy,
unsigned &DefIdx, unsigned &SrcIdx) {
assert((Copy.isCopy() || Copy.isBitcast()) && "Wrong operation type.");
if (Copy.isCopy()) {
// Copy instruction are supposed to be: Def = Src.
if (Copy.getDesc().getNumOperands() != 2)
return false;
DefIdx = 0;
SrcIdx = 1;
assert(Copy.getOperand(DefIdx).isDef() && "Use comes before def!");
return true;
}
// Bitcast case.
// Bitcasts with more than one def are not supported.
if (Copy.getDesc().getNumDefs() != 1)
return false;
// Initialize SrcIdx to an undefined operand.
SrcIdx = Copy.getDesc().getNumOperands();
for (unsigned OpIdx = 0, EndOpIdx = SrcIdx; OpIdx != EndOpIdx; ++OpIdx) {
const MachineOperand &MO = Copy.getOperand(OpIdx);
if (!MO.isReg() || !MO.getReg())
continue;
if (MO.isDef())
DefIdx = OpIdx;
else if (SrcIdx != EndOpIdx)
// Multiple sources?
return false;
SrcIdx = OpIdx;
}
return true;
}
/// \brief Optimize a copy or bitcast instruction to avoid cross
/// register bank copy. The optimization looks through a chain of
/// copies and try to find a source that has a compatible register
/// class.
/// Two register classes are considered to be compatible if they share
/// the same register bank.
/// New copies issued by this optimization are register allocator
/// friendly. This optimization does not remove any copy as it may
/// overconstraint the register allocator, but replaces some when
/// possible.
/// \pre \p MI is a Copy (MI->isCopy() is true)
/// \return True, when \p MI has been optimized. In that case, \p MI has
/// been removed from its parent.
bool PeepholeOptimizer::optimizeCopyOrBitcast(MachineInstr *MI) {
unsigned DefIdx, SrcIdx;
if (!MI || !getCopyOrBitcastDefUseIdx(*MI, DefIdx, SrcIdx))
return false;
const MachineOperand &MODef = MI->getOperand(DefIdx);
assert(MODef.isReg() && "Copies must be between registers.");
unsigned Def = MODef.getReg();
if (TargetRegisterInfo::isPhysicalRegister(Def))
return false;
const TargetRegisterClass *DefRC = MRI->getRegClass(Def);
unsigned DefSubReg = MODef.getSubReg();
unsigned Src;
unsigned SrcSubReg;
bool ShouldRewrite = false;
const TargetRegisterInfo &TRI = *TM->getRegisterInfo();
// Follow the chain of copies until we reach the top of the use-def chain
// or find a more suitable source.
ValueTracker ValTracker(*MI, DefIdx, DefSubReg, !DisableAdvCopyOpt, MRI);
do {
unsigned CopySrcIdx, CopySrcSubReg;
if (!ValTracker.getNextSource(CopySrcIdx, CopySrcSubReg))
break;
Src = ValTracker.getReg();
SrcSubReg = CopySrcSubReg;
// Do not extend the live-ranges of physical registers as they add
// constraints to the register allocator.
// Moreover, if we want to extend the live-range of a physical register,
// unlike SSA virtual register, we will have to check that they are not
// redefine before the related use.
if (TargetRegisterInfo::isPhysicalRegister(Src))
break;
const TargetRegisterClass *SrcRC = MRI->getRegClass(Src);
// If this source does not incur a cross register bank copy, use it.
ShouldRewrite = shareSameRegisterFile(TRI, DefRC, DefSubReg, SrcRC,
SrcSubReg);
} while (!ShouldRewrite);
// If we did not find a more suitable source, there is nothing to optimize.
if (!ShouldRewrite || Src == MI->getOperand(SrcIdx).getReg())
return false;
// Rewrite the copy to avoid a cross register bank penalty.
unsigned NewVR = TargetRegisterInfo::isPhysicalRegister(Def) ? Def :
MRI->createVirtualRegister(DefRC);
MachineInstr *NewCopy = BuildMI(*MI->getParent(), MI, MI->getDebugLoc(),
TII->get(TargetOpcode::COPY), NewVR)
.addReg(Src, 0, SrcSubReg);
NewCopy->getOperand(0).setSubReg(DefSubReg);
MRI->replaceRegWith(Def, NewVR);
MRI->clearKillFlags(NewVR);
// We extended the lifetime of Src.
// Clear the kill flags to account for that.
MRI->clearKillFlags(Src);
MI->eraseFromParent();
++NumCopiesBitcasts;
return true;
}
/// isLoadFoldable - Check whether MI is a candidate for folding into a later
/// instruction. We only fold loads to virtual registers and the virtual
/// register defined has a single use.
bool PeepholeOptimizer::isLoadFoldable(
MachineInstr *MI,
SmallSet<unsigned, 16> &FoldAsLoadDefCandidates) {
if (!MI->canFoldAsLoad() || !MI->mayLoad())
return false;
const MCInstrDesc &MCID = MI->getDesc();
if (MCID.getNumDefs() != 1)
return false;
unsigned Reg = MI->getOperand(0).getReg();
// To reduce compilation time, we check MRI->hasOneNonDBGUse when inserting
// loads. It should be checked when processing uses of the load, since
// uses can be removed during peephole.
if (!MI->getOperand(0).getSubReg() &&
TargetRegisterInfo::isVirtualRegister(Reg) &&
MRI->hasOneNonDBGUse(Reg)) {
FoldAsLoadDefCandidates.insert(Reg);
return true;
}
return false;
}
bool PeepholeOptimizer::isMoveImmediate(MachineInstr *MI,
SmallSet<unsigned, 4> &ImmDefRegs,
DenseMap<unsigned, MachineInstr*> &ImmDefMIs) {
const MCInstrDesc &MCID = MI->getDesc();
if (!MI->isMoveImmediate())
return false;
if (MCID.getNumDefs() != 1)
return false;
unsigned Reg = MI->getOperand(0).getReg();
if (TargetRegisterInfo::isVirtualRegister(Reg)) {
ImmDefMIs.insert(std::make_pair(Reg, MI));
ImmDefRegs.insert(Reg);
return true;
}
return false;
}
/// foldImmediate - Try folding register operands that are defined by move
/// immediate instructions, i.e. a trivial constant folding optimization, if
/// and only if the def and use are in the same BB.
bool PeepholeOptimizer::foldImmediate(MachineInstr *MI, MachineBasicBlock *MBB,
SmallSet<unsigned, 4> &ImmDefRegs,
DenseMap<unsigned, MachineInstr*> &ImmDefMIs) {
for (unsigned i = 0, e = MI->getDesc().getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || MO.isDef())
continue;
unsigned Reg = MO.getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg))
continue;
if (ImmDefRegs.count(Reg) == 0)
continue;
DenseMap<unsigned, MachineInstr*>::iterator II = ImmDefMIs.find(Reg);
assert(II != ImmDefMIs.end());
if (TII->FoldImmediate(MI, II->second, Reg, MRI)) {
++NumImmFold;
return true;
}
}
return false;
}
bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
if (skipOptnoneFunction(*MF.getFunction()))
return false;
DEBUG(dbgs() << "********** PEEPHOLE OPTIMIZER **********\n");
DEBUG(dbgs() << "********** Function: " << MF.getName() << '\n');
if (DisablePeephole)
return false;
TM = &MF.getTarget();
TII = TM->getInstrInfo();
MRI = &MF.getRegInfo();
DT = Aggressive ? &getAnalysis<MachineDominatorTree>() : nullptr;
bool Changed = false;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *MBB = &*I;
bool SeenMoveImm = false;
SmallPtrSet<MachineInstr*, 8> LocalMIs;
SmallSet<unsigned, 4> ImmDefRegs;
DenseMap<unsigned, MachineInstr*> ImmDefMIs;
SmallSet<unsigned, 16> FoldAsLoadDefCandidates;
for (MachineBasicBlock::iterator
MII = I->begin(), MIE = I->end(); MII != MIE; ) {
MachineInstr *MI = &*MII;
// We may be erasing MI below, increment MII now.
++MII;
LocalMIs.insert(MI);
// Skip debug values. They should not affect this peephole optimization.
if (MI->isDebugValue())
continue;
// If there exists an instruction which belongs to the following
// categories, we will discard the load candidates.
if (MI->isPosition() || MI->isPHI() || MI->isImplicitDef() ||
MI->isKill() || MI->isInlineAsm() ||
MI->hasUnmodeledSideEffects()) {
FoldAsLoadDefCandidates.clear();
continue;
}
if (MI->mayStore() || MI->isCall())
FoldAsLoadDefCandidates.clear();
if (((MI->isBitcast() || MI->isCopy()) && optimizeCopyOrBitcast(MI)) ||
(MI->isCompare() && optimizeCmpInstr(MI, MBB)) ||
(MI->isSelect() && optimizeSelect(MI))) {
// MI is deleted.
LocalMIs.erase(MI);
Changed = true;
continue;
}
if (isMoveImmediate(MI, ImmDefRegs, ImmDefMIs)) {
SeenMoveImm = true;
} else {
Changed |= optimizeExtInstr(MI, MBB, LocalMIs);
// optimizeExtInstr might have created new instructions after MI
// and before the already incremented MII. Adjust MII so that the
// next iteration sees the new instructions.
MII = MI;
++MII;
if (SeenMoveImm)
Changed |= foldImmediate(MI, MBB, ImmDefRegs, ImmDefMIs);
}
// Check whether MI is a load candidate for folding into a later
// instruction. If MI is not a candidate, check whether we can fold an
// earlier load into MI.
if (!isLoadFoldable(MI, FoldAsLoadDefCandidates) &&
!FoldAsLoadDefCandidates.empty()) {
const MCInstrDesc &MIDesc = MI->getDesc();
for (unsigned i = MIDesc.getNumDefs(); i != MIDesc.getNumOperands();
++i) {
const MachineOperand &MOp = MI->getOperand(i);
if (!MOp.isReg())
continue;
unsigned FoldAsLoadDefReg = MOp.getReg();
if (FoldAsLoadDefCandidates.count(FoldAsLoadDefReg)) {
// We need to fold load after optimizeCmpInstr, since
// optimizeCmpInstr can enable folding by converting SUB to CMP.
// Save FoldAsLoadDefReg because optimizeLoadInstr() resets it and
// we need it for markUsesInDebugValueAsUndef().
unsigned FoldedReg = FoldAsLoadDefReg;
MachineInstr *DefMI = nullptr;
MachineInstr *FoldMI = TII->optimizeLoadInstr(MI, MRI,
FoldAsLoadDefReg,
DefMI);
if (FoldMI) {
// Update LocalMIs since we replaced MI with FoldMI and deleted
// DefMI.
DEBUG(dbgs() << "Replacing: " << *MI);
DEBUG(dbgs() << " With: " << *FoldMI);
LocalMIs.erase(MI);
LocalMIs.erase(DefMI);
LocalMIs.insert(FoldMI);
MI->eraseFromParent();
DefMI->eraseFromParent();
MRI->markUsesInDebugValueAsUndef(FoldedReg);
FoldAsLoadDefCandidates.erase(FoldedReg);
++NumLoadFold;
// MI is replaced with FoldMI.
Changed = true;
break;
}
}
}
}
}
}
return Changed;
}
bool ValueTracker::getNextSourceFromCopy(unsigned &SrcIdx,
unsigned &SrcSubReg) {
assert(Def->isCopy() && "Invalid definition");
// Copy instruction are supposed to be: Def = Src.
// If someone breaks this assumption, bad things will happen everywhere.
assert(Def->getDesc().getNumOperands() == 2 && "Invalid number of operands");
if (Def->getOperand(DefIdx).getSubReg() != DefSubReg)
// If we look for a different subreg, it means we want a subreg of src.
// Bails as we do not support composing subreg yet.
return false;
// Otherwise, we want the whole source.
SrcIdx = 1;
SrcSubReg = Def->getOperand(SrcIdx).getSubReg();
return true;
}
bool ValueTracker::getNextSourceFromBitcast(unsigned &SrcIdx,
unsigned &SrcSubReg) {
assert(Def->isBitcast() && "Invalid definition");
// Bail if there are effects that a plain copy will not expose.
if (Def->hasUnmodeledSideEffects())
return false;
// Bitcasts with more than one def are not supported.
if (Def->getDesc().getNumDefs() != 1)
return false;
if (Def->getOperand(DefIdx).getSubReg() != DefSubReg)
// If we look for a different subreg, it means we want a subreg of the src.
// Bails as we do not support composing subreg yet.
return false;
SrcIdx = Def->getDesc().getNumOperands();
for (unsigned OpIdx = DefIdx + 1, EndOpIdx = SrcIdx; OpIdx != EndOpIdx;
++OpIdx) {
const MachineOperand &MO = Def->getOperand(OpIdx);
if (!MO.isReg() || !MO.getReg())
continue;
assert(!MO.isDef() && "We should have skipped all the definitions by now");
if (SrcIdx != EndOpIdx)
// Multiple sources?
return false;
SrcIdx = OpIdx;
}
SrcSubReg = Def->getOperand(SrcIdx).getSubReg();
return true;
}
bool ValueTracker::getNextSourceFromRegSequence(unsigned &SrcIdx,
unsigned &SrcSubReg) {
assert(Def->isRegSequence() && "Invalid definition");
if (Def->getOperand(DefIdx).getSubReg())
// If we are composing subreg, bails out.
// The case we are checking is Def.<subreg> = REG_SEQUENCE.
// This should almost never happen as the SSA property is tracked at
// the register level (as opposed to the subreg level).
// I.e.,
// Def.sub0 =
// Def.sub1 =
// is a valid SSA representation for Def.sub0 and Def.sub1, but not for
// Def. Thus, it must not be generated.
// However, some code could theoretically generates a single
// Def.sub0 (i.e, not defining the other subregs) and we would
// have this case.
// If we can ascertain (or force) that this never happens, we could
// turn that into an assertion.
return false;
// We are looking at:
// Def = REG_SEQUENCE v0, sub0, v1, sub1, ...
// Check if one of the operand defines the subreg we are interested in.
for (unsigned OpIdx = DefIdx + 1, EndOpIdx = Def->getNumOperands();
OpIdx != EndOpIdx; OpIdx += 2) {
const MachineOperand &MOSubIdx = Def->getOperand(OpIdx + 1);
assert(MOSubIdx.isImm() &&
"One of the subindex of the reg_sequence is not an immediate");
if (MOSubIdx.getImm() == DefSubReg) {
assert(Def->getOperand(OpIdx).isReg() &&
"One of the source of the reg_sequence is not a register");
SrcIdx = OpIdx;
SrcSubReg = Def->getOperand(SrcIdx).getSubReg();
return true;
}
}
// If the subreg we are tracking is super-defined by another subreg,
// we could follow this value. However, this would require to compose
// the subreg and we do not do that for now.
return false;
}
bool ValueTracker::getNextSourceFromInsertSubreg(unsigned &SrcIdx,
unsigned &SrcSubReg) {
assert(Def->isInsertSubreg() && "Invalid definition");
if (Def->getOperand(DefIdx).getSubReg())
// If we are composing subreg, bails out.
// Same remark as getNextSourceFromRegSequence.
// I.e., this may be turned into an assert.
return false;
// We are looking at:
// Def = INSERT_SUBREG v0, v1, sub1
// There are two cases:
// 1. DefSubReg == sub1, get v1.
// 2. DefSubReg != sub1, the value may be available through v0.
// #1 Check if the inserted register matches the require sub index.
unsigned InsertedSubReg = Def->getOperand(3).getImm();
if (InsertedSubReg == DefSubReg) {
SrcIdx = 2;
SrcSubReg = Def->getOperand(SrcIdx).getSubReg();
return true;
}
// #2 Otherwise, if the sub register we are looking for is not partial
// defined by the inserted element, we can look through the main
// register (v0).
// To check the overlapping we need a MRI and a TRI.
if (!MRI)
return false;
const MachineOperand &MODef = Def->getOperand(DefIdx);
const MachineOperand &MOBase = Def->getOperand(1);
// If the result register (Def) and the base register (v0) do not
// have the same register class or if we have to compose
// subregisters, bails out.
if (MRI->getRegClass(MODef.getReg()) != MRI->getRegClass(MOBase.getReg()) ||
MOBase.getSubReg())
return false;
// Get the TRI and check if inserted sub register overlaps with the
// sub register we are tracking.
const TargetRegisterInfo *TRI = MRI->getTargetRegisterInfo();
if (!TRI ||
(TRI->getSubRegIndexLaneMask(DefSubReg) &
TRI->getSubRegIndexLaneMask(InsertedSubReg)) != 0)
return false;
// At this point, the value is available in v0 via the same subreg
// we used for Def.
SrcIdx = 1;
SrcSubReg = DefSubReg;
return true;
}
bool ValueTracker::getNextSourceFromExtractSubreg(unsigned &SrcIdx,
unsigned &SrcSubReg) {
assert(Def->isExtractSubreg() && "Invalid definition");
// We are looking at:
// Def = EXTRACT_SUBREG v0, sub0
// Bails if we have to compose sub registers.
// Indeed, if DefSubReg != 0, we would have to compose it with sub0.
if (DefSubReg)
return false;
// Bails if we have to compose sub registers.
// Likewise, if v0.subreg != 0, we would have to compose v0.subreg with sub0.
if (Def->getOperand(1).getSubReg())
return false;
// Otherwise, the value is available in the v0.sub0.
SrcIdx = 1;
SrcSubReg = Def->getOperand(2).getImm();
return true;
}
bool ValueTracker::getNextSourceFromSubregToReg(unsigned &SrcIdx,
unsigned &SrcSubReg) {
assert(Def->isSubregToReg() && "Invalid definition");
// We are looking at:
// Def = SUBREG_TO_REG Imm, v0, sub0
// Bails if we have to compose sub registers.
// If DefSubReg != sub0, we would have to check that all the bits
// we track are included in sub0 and if yes, we would have to
// determine the right subreg in v0.
if (DefSubReg != Def->getOperand(3).getImm())
return false;
// Bails if we have to compose sub registers.
// Likewise, if v0.subreg != 0, we would have to compose it with sub0.
if (Def->getOperand(2).getSubReg())
return false;
SrcIdx = 2;
SrcSubReg = Def->getOperand(3).getImm();
return true;
}
bool ValueTracker::getNextSourceImpl(unsigned &SrcIdx, unsigned &SrcSubReg) {
assert(Def && "This method needs a valid definition");
assert(
(DefIdx < Def->getDesc().getNumDefs() || Def->getDesc().isVariadic()) &&
Def->getOperand(DefIdx).isDef() && "Invalid DefIdx");
if (Def->isCopy())
return getNextSourceFromCopy(SrcIdx, SrcSubReg);
if (Def->isBitcast())
return getNextSourceFromBitcast(SrcIdx, SrcSubReg);
// All the remaining cases involve "complex" instructions.
// Bails if we did not ask for the advanced tracking.
if (!UseAdvancedTracking)
return false;
if (Def->isRegSequence())
return getNextSourceFromRegSequence(SrcIdx, SrcSubReg);
if (Def->isInsertSubreg())
return getNextSourceFromInsertSubreg(SrcIdx, SrcSubReg);
if (Def->isExtractSubreg())
return getNextSourceFromExtractSubreg(SrcIdx, SrcSubReg);
if (Def->isSubregToReg())
return getNextSourceFromSubregToReg(SrcIdx, SrcSubReg);
return false;
}
const MachineInstr *ValueTracker::getNextSource(unsigned &SrcIdx,
unsigned &SrcSubReg) {
// If we reach a point where we cannot move up in the use-def chain,
// there is nothing we can get.
if (!Def)
return nullptr;
const MachineInstr *PrevDef = nullptr;
// Try to find the next source.
if (getNextSourceImpl(SrcIdx, SrcSubReg)) {
// Update definition, definition index, and subregister for the
// next call of getNextSource.
const MachineOperand &MO = Def->getOperand(SrcIdx);
assert(MO.isReg() && !MO.isDef() && "Source is invalid");
// Update the current register.
Reg = MO.getReg();
// Update the return value before moving up in the use-def chain.
PrevDef = Def;
// If we can still move up in the use-def chain, move to the next
// defintion.
if (!TargetRegisterInfo::isPhysicalRegister(Reg)) {
Def = MRI->getVRegDef(Reg);
DefIdx = MRI->def_begin(Reg).getOperandNo();
DefSubReg = SrcSubReg;
return PrevDef;
}
}
// If we end up here, this means we will not be able to find another source
// for the next iteration.
// Make sure any new call to getNextSource bails out early by cutting the
// use-def chain.
Def = nullptr;
return PrevDef;
}
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