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llvm/lib/CodeGen/PeepholeOptimizer.cpp
Benjamin Kramer 1bfcd1f675 Re-sort includes with sort-includes.py and insert raw_ostream.h where it's used. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232998 91177308-0d34-0410-b5e6-96231b3b80d8
2015-03-23 19:32:43 +00:00

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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 (more generally, target specific copies):
//
// 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/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
#include <utility>
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(false),
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(NumUncoalescableCopies, "Number of uncoalescable copies optimized");
STATISTIC(NumRewrittenCopies, "Number of copies rewritten");
namespace {
class PeepholeOptimizer : public MachineFunctionPass {
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
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,
SmallPtrSetImpl<MachineInstr*> &LocalMIs);
bool optimizeSelect(MachineInstr *MI,
SmallPtrSetImpl<MachineInstr *> &LocalMIs);
bool optimizeCondBranch(MachineInstr *MI);
bool optimizeCopyOrBitcast(MachineInstr *MI);
bool optimizeCoalescableCopy(MachineInstr *MI);
bool optimizeUncoalescableCopy(MachineInstr *MI,
SmallPtrSetImpl<MachineInstr *> &LocalMIs);
bool findNextSource(unsigned &Reg, unsigned &SubReg);
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 Check whether \p MI is understood by the register coalescer
/// but may require some rewriting.
bool isCoalescableCopy(const MachineInstr &MI) {
// SubregToRegs are not interesting, because they are already register
// coalescer friendly.
return MI.isCopy() || (!DisableAdvCopyOpt &&
(MI.isRegSequence() || MI.isInsertSubreg() ||
MI.isExtractSubreg()));
}
/// \brief Check whether \p MI is a copy like instruction that is
/// not recognized by the register coalescer.
bool isUncoalescableCopy(const MachineInstr &MI) {
return MI.isBitcast() ||
(!DisableAdvCopyOpt &&
(MI.isRegSequenceLike() || MI.isInsertSubregLike() ||
MI.isExtractSubregLike()));
}
};
/// \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;
/// MachineRegisterInfo used to perform tracking.
const MachineRegisterInfo &MRI;
/// Optional TargetInstrInfo used to perform some complex
/// tracking.
const TargetInstrInfo *TII;
/// \brief Dispatcher to the right underlying implementation of
/// getNextSource.
bool getNextSourceImpl(unsigned &SrcReg, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for Copy instructions.
bool getNextSourceFromCopy(unsigned &SrcReg, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for Bitcast instructions.
bool getNextSourceFromBitcast(unsigned &SrcReg, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for RegSequence
/// instructions.
bool getNextSourceFromRegSequence(unsigned &SrcReg, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for InsertSubreg
/// instructions.
bool getNextSourceFromInsertSubreg(unsigned &SrcReg, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for ExtractSubreg
/// instructions.
bool getNextSourceFromExtractSubreg(unsigned &SrcReg, unsigned &SrcSubReg);
/// \brief Specialized version of getNextSource for SubregToReg
/// instructions.
bool getNextSourceFromSubregToReg(unsigned &SrcReg, unsigned &SrcSubReg);
public:
/// \brief Create a ValueTracker instance for the value defined by \p Reg.
/// \p DefSubReg represents the sub register index the value tracker will
/// track. It does not need to match the sub register index used in the
/// definition of \p Reg.
/// \p UseAdvancedTracking specifies whether or not the value tracker looks
/// through complex instructions. By default (false), it handles only copy
/// and bitcast instructions.
/// If \p Reg is a physical register, a value tracker constructed with
/// this constructor will not find any alternative source.
/// Indeed, when \p Reg is a physical register that constructor does not
/// know which definition of \p Reg it should track.
/// Use the next constructor to track a physical register.
ValueTracker(unsigned Reg, unsigned DefSubReg,
const MachineRegisterInfo &MRI,
bool UseAdvancedTracking = false,
const TargetInstrInfo *TII = nullptr)
: Def(nullptr), DefIdx(0), DefSubReg(DefSubReg), Reg(Reg),
UseAdvancedTracking(UseAdvancedTracking), MRI(MRI), TII(TII) {
if (!TargetRegisterInfo::isPhysicalRegister(Reg)) {
Def = MRI.getVRegDef(Reg);
DefIdx = MRI.def_begin(Reg).getOperandNo();
}
}
/// \brief Create a ValueTracker instance for the value defined by
/// the pair \p MI, \p DefIdx.
/// Unlike the other constructor, the value tracker produced by this one
/// may be able to find a new source when the definition is a physical
/// register.
/// This could be useful to rewrite target specific instructions into
/// generic copy instructions.
ValueTracker(const MachineInstr &MI, unsigned DefIdx, unsigned DefSubReg,
const MachineRegisterInfo &MRI,
bool UseAdvancedTracking = false,
const TargetInstrInfo *TII = nullptr)
: Def(&MI), DefIdx(DefIdx), DefSubReg(DefSubReg),
UseAdvancedTracking(UseAdvancedTracking), MRI(MRI), TII(TII) {
assert(DefIdx < Def->getDesc().getNumDefs() &&
Def->getOperand(DefIdx).isReg() && "Invalid definition");
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, \p SrcReg gives the register
/// that contain the tracked value.
/// \note The sub register index returned in \p SrcSubReg must be used
/// on \p SrcReg to access the actual value.
/// \return Unless the returned value is nullptr (i.e., no source found),
/// \p SrcReg gives the register of the next source used in the returned
/// instruction and \p SrcSubReg the sub-register 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 &SrcReg, 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,
SmallPtrSetImpl<MachineInstr*> &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 = TRI->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 =
TRI->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.
Uses.append(ExtendedUses.begin(), ExtendedUses.end());
// 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,
SmallPtrSetImpl<MachineInstr *> &LocalMIs) {
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, LocalMIs))
return false;
MI->eraseFromParent();
++NumSelects;
return true;
}
/// \brief Check if a simpler conditional branch can be
// generated
bool PeepholeOptimizer::optimizeCondBranch(MachineInstr *MI) {
return TII->optimizeCondBranch(MI);
}
/// \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 Try to find the next source that share the same register file
/// for the value defined by \p Reg and \p SubReg.
/// When true is returned, \p Reg and \p SubReg are updated with the
/// register number and sub-register index of the new source.
/// \return False if no alternative sources are available. True otherwise.
bool PeepholeOptimizer::findNextSource(unsigned &Reg, unsigned &SubReg) {
// Do not try to find a new source for a physical register.
// So far we do not have any motivating example for doing that.
// Thus, instead of maintaining untested code, we will revisit that if
// that changes at some point.
if (TargetRegisterInfo::isPhysicalRegister(Reg))
return false;
const TargetRegisterClass *DefRC = MRI->getRegClass(Reg);
unsigned DefSubReg = SubReg;
unsigned Src;
unsigned SrcSubReg;
bool ShouldRewrite = false;
// Follow the chain of copies until we reach the top of the use-def chain
// or find a more suitable source.
ValueTracker ValTracker(Reg, DefSubReg, *MRI, !DisableAdvCopyOpt, TII);
do {
unsigned CopySrcReg, CopySrcSubReg;
if (!ValTracker.getNextSource(CopySrcReg, CopySrcSubReg))
break;
Src = CopySrcReg;
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 == Reg)
return false;
Reg = Src;
SubReg = SrcSubReg;
return true;
}
namespace {
/// \brief Helper class to rewrite the arguments of a copy-like instruction.
class CopyRewriter {
protected:
/// The copy-like instruction.
MachineInstr &CopyLike;
/// The index of the source being rewritten.
unsigned CurrentSrcIdx;
public:
CopyRewriter(MachineInstr &MI) : CopyLike(MI), CurrentSrcIdx(0) {}
virtual ~CopyRewriter() {}
/// \brief Get the next rewritable source (SrcReg, SrcSubReg) and
/// the related value that it affects (TrackReg, TrackSubReg).
/// A source is considered rewritable if its register class and the
/// register class of the related TrackReg may not be register
/// coalescer friendly. In other words, given a copy-like instruction
/// not all the arguments may be returned at rewritable source, since
/// some arguments are none to be register coalescer friendly.
///
/// Each call of this method moves the current source to the next
/// rewritable source.
/// For instance, let CopyLike be the instruction to rewrite.
/// CopyLike has one definition and one source:
/// dst.dstSubIdx = CopyLike src.srcSubIdx.
///
/// The first call will give the first rewritable source, i.e.,
/// the only source this instruction has:
/// (SrcReg, SrcSubReg) = (src, srcSubIdx).
/// This source defines the whole definition, i.e.,
/// (TrackReg, TrackSubReg) = (dst, dstSubIdx).
///
/// The second and subsequent calls will return false, has there is only one
/// rewritable source.
///
/// \return True if a rewritable source has been found, false otherwise.
/// The output arguments are valid if and only if true is returned.
virtual bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg,
unsigned &TrackReg,
unsigned &TrackSubReg) {
// If CurrentSrcIdx == 1, this means this function has already been
// called once. CopyLike has one defintiion and one argument, thus,
// there is nothing else to rewrite.
if (!CopyLike.isCopy() || CurrentSrcIdx == 1)
return false;
// This is the first call to getNextRewritableSource.
// Move the CurrentSrcIdx to remember that we made that call.
CurrentSrcIdx = 1;
// The rewritable source is the argument.
const MachineOperand &MOSrc = CopyLike.getOperand(1);
SrcReg = MOSrc.getReg();
SrcSubReg = MOSrc.getSubReg();
// What we track are the alternative sources of the definition.
const MachineOperand &MODef = CopyLike.getOperand(0);
TrackReg = MODef.getReg();
TrackSubReg = MODef.getSubReg();
return true;
}
/// \brief Rewrite the current source with \p NewReg and \p NewSubReg
/// if possible.
/// \return True if the rewritting was possible, false otherwise.
virtual bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) {
if (!CopyLike.isCopy() || CurrentSrcIdx != 1)
return false;
MachineOperand &MOSrc = CopyLike.getOperand(CurrentSrcIdx);
MOSrc.setReg(NewReg);
MOSrc.setSubReg(NewSubReg);
return true;
}
};
/// \brief Specialized rewriter for INSERT_SUBREG instruction.
class InsertSubregRewriter : public CopyRewriter {
public:
InsertSubregRewriter(MachineInstr &MI) : CopyRewriter(MI) {
assert(MI.isInsertSubreg() && "Invalid instruction");
}
/// \brief See CopyRewriter::getNextRewritableSource.
/// Here CopyLike has the following form:
/// dst = INSERT_SUBREG Src1, Src2.src2SubIdx, subIdx.
/// Src1 has the same register class has dst, hence, there is
/// nothing to rewrite.
/// Src2.src2SubIdx, may not be register coalescer friendly.
/// Therefore, the first call to this method returns:
/// (SrcReg, SrcSubReg) = (Src2, src2SubIdx).
/// (TrackReg, TrackSubReg) = (dst, subIdx).
///
/// Subsequence calls will return false.
bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg,
unsigned &TrackReg,
unsigned &TrackSubReg) override {
// If we already get the only source we can rewrite, return false.
if (CurrentSrcIdx == 2)
return false;
// We are looking at v2 = INSERT_SUBREG v0, v1, sub0.
CurrentSrcIdx = 2;
const MachineOperand &MOInsertedReg = CopyLike.getOperand(2);
SrcReg = MOInsertedReg.getReg();
SrcSubReg = MOInsertedReg.getSubReg();
const MachineOperand &MODef = CopyLike.getOperand(0);
// We want to track something that is compatible with the
// partial definition.
TrackReg = MODef.getReg();
if (MODef.getSubReg())
// Bails if we have to compose sub-register indices.
return false;
TrackSubReg = (unsigned)CopyLike.getOperand(3).getImm();
return true;
}
bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
if (CurrentSrcIdx != 2)
return false;
// We are rewriting the inserted reg.
MachineOperand &MO = CopyLike.getOperand(CurrentSrcIdx);
MO.setReg(NewReg);
MO.setSubReg(NewSubReg);
return true;
}
};
/// \brief Specialized rewriter for EXTRACT_SUBREG instruction.
class ExtractSubregRewriter : public CopyRewriter {
const TargetInstrInfo &TII;
public:
ExtractSubregRewriter(MachineInstr &MI, const TargetInstrInfo &TII)
: CopyRewriter(MI), TII(TII) {
assert(MI.isExtractSubreg() && "Invalid instruction");
}
/// \brief See CopyRewriter::getNextRewritableSource.
/// Here CopyLike has the following form:
/// dst.dstSubIdx = EXTRACT_SUBREG Src, subIdx.
/// There is only one rewritable source: Src.subIdx,
/// which defines dst.dstSubIdx.
bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg,
unsigned &TrackReg,
unsigned &TrackSubReg) override {
// If we already get the only source we can rewrite, return false.
if (CurrentSrcIdx == 1)
return false;
// We are looking at v1 = EXTRACT_SUBREG v0, sub0.
CurrentSrcIdx = 1;
const MachineOperand &MOExtractedReg = CopyLike.getOperand(1);
SrcReg = MOExtractedReg.getReg();
// If we have to compose sub-register indices, bails out.
if (MOExtractedReg.getSubReg())
return false;
SrcSubReg = CopyLike.getOperand(2).getImm();
// We want to track something that is compatible with the definition.
const MachineOperand &MODef = CopyLike.getOperand(0);
TrackReg = MODef.getReg();
TrackSubReg = MODef.getSubReg();
return true;
}
bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
// The only source we can rewrite is the input register.
if (CurrentSrcIdx != 1)
return false;
CopyLike.getOperand(CurrentSrcIdx).setReg(NewReg);
// If we find a source that does not require to extract something,
// rewrite the operation with a copy.
if (!NewSubReg) {
// Move the current index to an invalid position.
// We do not want another call to this method to be able
// to do any change.
CurrentSrcIdx = -1;
// Rewrite the operation as a COPY.
// Get rid of the sub-register index.
CopyLike.RemoveOperand(2);
// Morph the operation into a COPY.
CopyLike.setDesc(TII.get(TargetOpcode::COPY));
return true;
}
CopyLike.getOperand(CurrentSrcIdx + 1).setImm(NewSubReg);
return true;
}
};
/// \brief Specialized rewriter for REG_SEQUENCE instruction.
class RegSequenceRewriter : public CopyRewriter {
public:
RegSequenceRewriter(MachineInstr &MI) : CopyRewriter(MI) {
assert(MI.isRegSequence() && "Invalid instruction");
}
/// \brief See CopyRewriter::getNextRewritableSource.
/// Here CopyLike has the following form:
/// dst = REG_SEQUENCE Src1.src1SubIdx, subIdx1, Src2.src2SubIdx, subIdx2.
/// Each call will return a different source, walking all the available
/// source.
///
/// The first call returns:
/// (SrcReg, SrcSubReg) = (Src1, src1SubIdx).
/// (TrackReg, TrackSubReg) = (dst, subIdx1).
///
/// The second call returns:
/// (SrcReg, SrcSubReg) = (Src2, src2SubIdx).
/// (TrackReg, TrackSubReg) = (dst, subIdx2).
///
/// And so on, until all the sources have been traversed, then
/// it returns false.
bool getNextRewritableSource(unsigned &SrcReg, unsigned &SrcSubReg,
unsigned &TrackReg,
unsigned &TrackSubReg) override {
// We are looking at v0 = REG_SEQUENCE v1, sub1, v2, sub2, etc.
// If this is the first call, move to the first argument.
if (CurrentSrcIdx == 0) {
CurrentSrcIdx = 1;
} else {
// Otherwise, move to the next argument and check that it is valid.
CurrentSrcIdx += 2;
if (CurrentSrcIdx >= CopyLike.getNumOperands())
return false;
}
const MachineOperand &MOInsertedReg = CopyLike.getOperand(CurrentSrcIdx);
SrcReg = MOInsertedReg.getReg();
// If we have to compose sub-register indices, bails out.
if ((SrcSubReg = MOInsertedReg.getSubReg()))
return false;
// We want to track something that is compatible with the related
// partial definition.
TrackSubReg = CopyLike.getOperand(CurrentSrcIdx + 1).getImm();
const MachineOperand &MODef = CopyLike.getOperand(0);
TrackReg = MODef.getReg();
// If we have to compose sub-registers, bails.
return MODef.getSubReg() == 0;
}
bool RewriteCurrentSource(unsigned NewReg, unsigned NewSubReg) override {
// We cannot rewrite out of bound operands.
// Moreover, rewritable sources are at odd positions.
if ((CurrentSrcIdx & 1) != 1 || CurrentSrcIdx > CopyLike.getNumOperands())
return false;
MachineOperand &MO = CopyLike.getOperand(CurrentSrcIdx);
MO.setReg(NewReg);
MO.setSubReg(NewSubReg);
return true;
}
};
} // End namespace.
/// \brief Get the appropriated CopyRewriter for \p MI.
/// \return A pointer to a dynamically allocated CopyRewriter or nullptr
/// if no rewriter works for \p MI.
static CopyRewriter *getCopyRewriter(MachineInstr &MI,
const TargetInstrInfo &TII) {
switch (MI.getOpcode()) {
default:
return nullptr;
case TargetOpcode::COPY:
return new CopyRewriter(MI);
case TargetOpcode::INSERT_SUBREG:
return new InsertSubregRewriter(MI);
case TargetOpcode::EXTRACT_SUBREG:
return new ExtractSubregRewriter(MI, TII);
case TargetOpcode::REG_SEQUENCE:
return new RegSequenceRewriter(MI);
}
llvm_unreachable(nullptr);
}
/// \brief Optimize generic copy instructions to avoid cross
/// register bank copy. The optimization looks through a chain of
/// copies and tries 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 operands
/// when possible.
/// \pre isCoalescableCopy(*MI) is true.
/// \return True, when \p MI has been rewritten. False otherwise.
bool PeepholeOptimizer::optimizeCoalescableCopy(MachineInstr *MI) {
assert(MI && isCoalescableCopy(*MI) && "Invalid argument");
assert(MI->getDesc().getNumDefs() == 1 &&
"Coalescer can understand multiple defs?!");
const MachineOperand &MODef = MI->getOperand(0);
// Do not rewrite physical definitions.
if (TargetRegisterInfo::isPhysicalRegister(MODef.getReg()))
return false;
bool Changed = false;
// Get the right rewriter for the current copy.
std::unique_ptr<CopyRewriter> CpyRewriter(getCopyRewriter(*MI, *TII));
// If none exists, bails out.
if (!CpyRewriter)
return false;
// Rewrite each rewritable source.
unsigned SrcReg, SrcSubReg, TrackReg, TrackSubReg;
while (CpyRewriter->getNextRewritableSource(SrcReg, SrcSubReg, TrackReg,
TrackSubReg)) {
unsigned NewSrc = TrackReg;
unsigned NewSubReg = TrackSubReg;
// Try to find a more suitable source.
// If we failed to do so, or get the actual source,
// move to the next source.
if (!findNextSource(NewSrc, NewSubReg) || SrcReg == NewSrc)
continue;
// Rewrite source.
if (CpyRewriter->RewriteCurrentSource(NewSrc, NewSubReg)) {
// We may have extended the live-range of NewSrc, account for that.
MRI->clearKillFlags(NewSrc);
Changed = true;
}
}
// TODO: We could have a clean-up method to tidy the instruction.
// E.g., v0 = INSERT_SUBREG v1, v1.sub0, sub0
// => v0 = COPY v1
// Currently we haven't seen motivating example for that and we
// want to avoid untested code.
NumRewrittenCopies += Changed;
return Changed;
}
/// \brief Optimize copy-like instructions to create
/// register coalescer friendly instruction.
/// The optimization tries to kill-off the \p MI by looking
/// through a chain of copies to find a source that has a compatible
/// register class.
/// If such a source is found, it replace \p MI by a generic COPY
/// operation.
/// \pre isUncoalescableCopy(*MI) is true.
/// \return True, when \p MI has been optimized. In that case, \p MI has
/// been removed from its parent.
/// All COPY instructions created, are inserted in \p LocalMIs.
bool PeepholeOptimizer::optimizeUncoalescableCopy(
MachineInstr *MI, SmallPtrSetImpl<MachineInstr *> &LocalMIs) {
assert(MI && isUncoalescableCopy(*MI) && "Invalid argument");
// Check if we can rewrite all the values defined by this instruction.
SmallVector<
std::pair<TargetInstrInfo::RegSubRegPair, TargetInstrInfo::RegSubRegPair>,
4> RewritePairs;
for (const MachineOperand &MODef : MI->defs()) {
if (MODef.isDead())
// We can ignore those.
continue;
// If a physical register is here, this is probably for a good reason.
// Do not rewrite that.
if (TargetRegisterInfo::isPhysicalRegister(MODef.getReg()))
return false;
// If we do not know how to rewrite this definition, there is no point
// in trying to kill this instruction.
TargetInstrInfo::RegSubRegPair Def(MODef.getReg(), MODef.getSubReg());
TargetInstrInfo::RegSubRegPair Src = Def;
if (!findNextSource(Src.Reg, Src.SubReg))
return false;
RewritePairs.push_back(std::make_pair(Def, Src));
}
// The change is possible for all defs, do it.
for (const auto &PairDefSrc : RewritePairs) {
const auto &Def = PairDefSrc.first;
const auto &Src = PairDefSrc.second;
// Rewrite the "copy" in a way the register coalescer understands.
assert(!TargetRegisterInfo::isPhysicalRegister(Def.Reg) &&
"We do not rewrite physical registers");
const TargetRegisterClass *DefRC = MRI->getRegClass(Def.Reg);
unsigned NewVR = MRI->createVirtualRegister(DefRC);
MachineInstr *NewCopy = BuildMI(*MI->getParent(), MI, MI->getDebugLoc(),
TII->get(TargetOpcode::COPY),
NewVR).addReg(Src.Reg, 0, Src.SubReg);
NewCopy->getOperand(0).setSubReg(Def.SubReg);
if (Def.SubReg)
NewCopy->getOperand(0).setIsUndef();
LocalMIs.insert(NewCopy);
MRI->replaceRegWith(Def.Reg, NewVR);
MRI->clearKillFlags(NewVR);
// We extended the lifetime of Src.
// Clear the kill flags to account for that.
MRI->clearKillFlags(Src.Reg);
}
// MI is now dead.
MI->eraseFromParent();
++NumUncoalescableCopies;
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;
TII = MF.getSubtarget().getInstrInfo();
TRI = MF.getSubtarget().getRegisterInfo();
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;
// During this forward scan, at some point it needs to answer the question
// "given a pointer to an MI in the current BB, is it located before or
// after the current instruction".
// To perform this, the following set keeps track of the MIs already seen
// during the scan, if a MI is not in the set, it is assumed to be located
// after. Newly created MIs have to be inserted in the set as well.
SmallPtrSet<MachineInstr*, 16> 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 ((isUncoalescableCopy(*MI) &&
optimizeUncoalescableCopy(MI, LocalMIs)) ||
(MI->isCompare() && optimizeCmpInstr(MI, MBB)) ||
(MI->isSelect() && optimizeSelect(MI, LocalMIs))) {
// MI is deleted.
LocalMIs.erase(MI);
Changed = true;
continue;
}
if (MI->isConditionalBranch() && optimizeCondBranch(MI)) {
Changed = true;
continue;
}
if (isCoalescableCopy(*MI) && optimizeCoalescableCopy(MI)) {
// MI is just rewritten.
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 &SrcReg,
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->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.
const MachineOperand &Src = Def->getOperand(1);
SrcReg = Src.getReg();
SrcSubReg = Src.getSubReg();
return true;
}
bool ValueTracker::getNextSourceFromBitcast(unsigned &SrcReg,
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;
unsigned SrcIdx = Def->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;
}
const MachineOperand &Src = Def->getOperand(SrcIdx);
SrcReg = Src.getReg();
SrcSubReg = Src.getSubReg();
return true;
}
bool ValueTracker::getNextSourceFromRegSequence(unsigned &SrcReg,
unsigned &SrcSubReg) {
assert((Def->isRegSequence() || Def->isRegSequenceLike()) &&
"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;
if (!TII)
// We could handle the REG_SEQUENCE here, but we do not want to
// duplicate the code from the generic TII.
return false;
SmallVector<TargetInstrInfo::RegSubRegPairAndIdx, 8> RegSeqInputRegs;
if (!TII->getRegSequenceInputs(*Def, DefIdx, RegSeqInputRegs))
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 (auto &RegSeqInput : RegSeqInputRegs) {
if (RegSeqInput.SubIdx == DefSubReg) {
if (RegSeqInput.SubReg)
// Bails if we have to compose sub registers.
return false;
SrcReg = RegSeqInput.Reg;
SrcSubReg = RegSeqInput.SubReg;
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 &SrcReg,
unsigned &SrcSubReg) {
assert((Def->isInsertSubreg() || Def->isInsertSubregLike()) &&
"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;
if (!TII)
// We could handle the REG_SEQUENCE here, but we do not want to
// duplicate the code from the generic TII.
return false;
TargetInstrInfo::RegSubRegPair BaseReg;
TargetInstrInfo::RegSubRegPairAndIdx InsertedReg;
if (!TII->getInsertSubregInputs(*Def, DefIdx, BaseReg, InsertedReg))
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 required sub index.
if (InsertedReg.SubIdx == DefSubReg) {
SrcReg = InsertedReg.Reg;
SrcSubReg = InsertedReg.SubReg;
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).
const MachineOperand &MODef = Def->getOperand(DefIdx);
// 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(BaseReg.Reg) ||
BaseReg.SubReg)
return false;
// Get the TRI and check if the inserted sub-register overlaps with the
// sub-register we are tracking.
const TargetRegisterInfo *TRI = MRI.getTargetRegisterInfo();
if (!TRI ||
(TRI->getSubRegIndexLaneMask(DefSubReg) &
TRI->getSubRegIndexLaneMask(InsertedReg.SubIdx)) != 0)
return false;
// At this point, the value is available in v0 via the same subreg
// we used for Def.
SrcReg = BaseReg.Reg;
SrcSubReg = DefSubReg;
return true;
}
bool ValueTracker::getNextSourceFromExtractSubreg(unsigned &SrcReg,
unsigned &SrcSubReg) {
assert((Def->isExtractSubreg() ||
Def->isExtractSubregLike()) && "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;
if (!TII)
// We could handle the EXTRACT_SUBREG here, but we do not want to
// duplicate the code from the generic TII.
return false;
TargetInstrInfo::RegSubRegPairAndIdx ExtractSubregInputReg;
if (!TII->getExtractSubregInputs(*Def, DefIdx, ExtractSubregInputReg))
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 (ExtractSubregInputReg.SubReg)
return false;
// Otherwise, the value is available in the v0.sub0.
SrcReg = ExtractSubregInputReg.Reg;
SrcSubReg = ExtractSubregInputReg.SubIdx;
return true;
}
bool ValueTracker::getNextSourceFromSubregToReg(unsigned &SrcReg,
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;
SrcReg = Def->getOperand(2).getReg();
SrcSubReg = Def->getOperand(3).getImm();
return true;
}
bool ValueTracker::getNextSourceImpl(unsigned &SrcReg, 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(SrcReg, SrcSubReg);
if (Def->isBitcast())
return getNextSourceFromBitcast(SrcReg, 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() || Def->isRegSequenceLike())
return getNextSourceFromRegSequence(SrcReg, SrcSubReg);
if (Def->isInsertSubreg() || Def->isInsertSubregLike())
return getNextSourceFromInsertSubreg(SrcReg, SrcSubReg);
if (Def->isExtractSubreg() || Def->isExtractSubregLike())
return getNextSourceFromExtractSubreg(SrcReg, SrcSubReg);
if (Def->isSubregToReg())
return getNextSourceFromSubregToReg(SrcReg, SrcSubReg);
return false;
}
const MachineInstr *ValueTracker::getNextSource(unsigned &SrcReg,
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(SrcReg, SrcSubReg)) {
// Update definition, definition index, and subregister for the
// next call of getNextSource.
// Update the current register.
Reg = SrcReg;
// 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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