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llvm-project/llvm/lib/Target/PowerPC/PPCReduceCRLogicals.cpp

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//===---- PPCReduceCRLogicals.cpp - Reduce CR Bit Logical operations ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===---------------------------------------------------------------------===//
//
// This pass aims to reduce the number of logical operations on bits in the CR
// register. These instructions have a fairly high latency and only a single
// pipeline at their disposal in modern PPC cores. Furthermore, they have a
// tendency to occur in fairly small blocks where there's little opportunity
// to hide the latency between the CR logical operation and its user.
//
//===---------------------------------------------------------------------===//
#include "PPCInstrInfo.h"
#include "PPC.h"
#include "PPCTargetMachine.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
#define DEBUG_TYPE "ppc-reduce-cr-ops"
#include "PPCMachineBasicBlockUtils.h"
STATISTIC(NumContainedSingleUseBinOps,
"Number of single-use binary CR logical ops contained in a block");
STATISTIC(NumToSplitBlocks,
"Number of binary CR logical ops that can be used to split blocks");
STATISTIC(TotalCRLogicals, "Number of CR logical ops.");
STATISTIC(TotalNullaryCRLogicals,
"Number of nullary CR logical ops (CRSET/CRUNSET).");
STATISTIC(TotalUnaryCRLogicals, "Number of unary CR logical ops.");
STATISTIC(TotalBinaryCRLogicals, "Number of CR logical ops.");
STATISTIC(NumBlocksSplitOnBinaryCROp,
"Number of blocks split on CR binary logical ops.");
STATISTIC(NumNotSplitIdenticalOperands,
"Number of blocks not split due to operands being identical.");
STATISTIC(NumNotSplitChainCopies,
"Number of blocks not split due to operands being chained copies.");
STATISTIC(NumNotSplitWrongOpcode,
"Number of blocks not split due to the wrong opcode.");
namespace llvm {
void initializePPCReduceCRLogicalsPass(PassRegistry&);
}
namespace {
static bool isBinary(MachineInstr &MI) {
return MI.getNumOperands() == 3;
}
static bool isNullary(MachineInstr &MI) {
return MI.getNumOperands() == 1;
}
/// Given a CR logical operation \p CROp, branch opcode \p BROp as well as
/// a flag to indicate if the first operand of \p CROp is used as the
/// SplitBefore operand, determines whether either of the branches are to be
/// inverted as well as whether the new target should be the original
/// fall-through block.
static void
computeBranchTargetAndInversion(unsigned CROp, unsigned BROp, bool UsingDef1,
bool &InvertNewBranch, bool &InvertOrigBranch,
bool &TargetIsFallThrough) {
// The conditions under which each of the output operands should be [un]set
// can certainly be written much more concisely with just 3 if statements or
// ternary expressions. However, this provides a much clearer overview to the
// reader as to what is set for each <CROp, BROp, OpUsed> combination.
if (BROp == PPC::BC || BROp == PPC::BCLR) {
// Regular branches.
switch (CROp) {
default:
llvm_unreachable("Don't know how to handle this CR logical.");
case PPC::CROR:
InvertNewBranch = false;
InvertOrigBranch = false;
TargetIsFallThrough = false;
return;
case PPC::CRAND:
InvertNewBranch = true;
InvertOrigBranch = false;
TargetIsFallThrough = true;
return;
case PPC::CRNAND:
InvertNewBranch = true;
InvertOrigBranch = true;
TargetIsFallThrough = false;
return;
case PPC::CRNOR:
InvertNewBranch = false;
InvertOrigBranch = true;
TargetIsFallThrough = true;
return;
case PPC::CRORC:
InvertNewBranch = UsingDef1;
InvertOrigBranch = !UsingDef1;
TargetIsFallThrough = false;
return;
case PPC::CRANDC:
InvertNewBranch = !UsingDef1;
InvertOrigBranch = !UsingDef1;
TargetIsFallThrough = true;
return;
}
} else if (BROp == PPC::BCn || BROp == PPC::BCLRn) {
// Negated branches.
switch (CROp) {
default:
llvm_unreachable("Don't know how to handle this CR logical.");
case PPC::CROR:
InvertNewBranch = true;
InvertOrigBranch = false;
TargetIsFallThrough = true;
return;
case PPC::CRAND:
InvertNewBranch = false;
InvertOrigBranch = false;
TargetIsFallThrough = false;
return;
case PPC::CRNAND:
InvertNewBranch = false;
InvertOrigBranch = true;
TargetIsFallThrough = true;
return;
case PPC::CRNOR:
InvertNewBranch = true;
InvertOrigBranch = true;
TargetIsFallThrough = false;
return;
case PPC::CRORC:
InvertNewBranch = !UsingDef1;
InvertOrigBranch = !UsingDef1;
TargetIsFallThrough = true;
return;
case PPC::CRANDC:
InvertNewBranch = UsingDef1;
InvertOrigBranch = !UsingDef1;
TargetIsFallThrough = false;
return;
}
} else
llvm_unreachable("Don't know how to handle this branch.");
}
class PPCReduceCRLogicals : public MachineFunctionPass {
public:
static char ID;
struct CRLogicalOpInfo {
MachineInstr *MI;
// FIXME: If chains of copies are to be handled, this should be a vector.
std::pair<MachineInstr*, MachineInstr*> CopyDefs;
std::pair<MachineInstr*, MachineInstr*> TrueDefs;
unsigned IsBinary : 1;
unsigned IsNullary : 1;
unsigned ContainedInBlock : 1;
unsigned FeedsISEL : 1;
unsigned FeedsBR : 1;
unsigned FeedsLogical : 1;
unsigned SingleUse : 1;
unsigned DefsSingleUse : 1;
unsigned SubregDef1;
unsigned SubregDef2;
CRLogicalOpInfo() : MI(nullptr), IsBinary(0), IsNullary(0),
ContainedInBlock(0), FeedsISEL(0), FeedsBR(0),
FeedsLogical(0), SingleUse(0), DefsSingleUse(1),
SubregDef1(0), SubregDef2(0) { }
void dump();
};
private:
const PPCInstrInfo *TII;
MachineFunction *MF;
MachineRegisterInfo *MRI;
const MachineBranchProbabilityInfo *MBPI;
// A vector to contain all the CR logical operations
std::vector<CRLogicalOpInfo> AllCRLogicalOps;
void initialize(MachineFunction &MFParm);
void collectCRLogicals();
bool handleCROp(CRLogicalOpInfo &CRI);
bool splitBlockOnBinaryCROp(CRLogicalOpInfo &CRI);
static bool isCRLogical(MachineInstr &MI) {
unsigned Opc = MI.getOpcode();
return Opc == PPC::CRAND || Opc == PPC::CRNAND || Opc == PPC::CROR ||
Opc == PPC::CRXOR || Opc == PPC::CRNOR || Opc == PPC::CREQV ||
Opc == PPC::CRANDC || Opc == PPC::CRORC || Opc == PPC::CRSET ||
Opc == PPC::CRUNSET || Opc == PPC::CR6SET || Opc == PPC::CR6UNSET;
}
bool simplifyCode() {
bool Changed = false;
// Not using a range-based for loop here as the vector may grow while being
// operated on.
for (unsigned i = 0; i < AllCRLogicalOps.size(); i++)
Changed |= handleCROp(AllCRLogicalOps[i]);
return Changed;
}
public:
PPCReduceCRLogicals() : MachineFunctionPass(ID) {
initializePPCReduceCRLogicalsPass(*PassRegistry::getPassRegistry());
}
MachineInstr *lookThroughCRCopy(unsigned Reg, unsigned &Subreg,
MachineInstr *&CpDef);
bool runOnMachineFunction(MachineFunction &MF) override {
if (skipFunction(MF.getFunction()))
return false;
// If the subtarget doesn't use CR bits, there's nothing to do.
const PPCSubtarget &STI = MF.getSubtarget<PPCSubtarget>();
if (!STI.useCRBits())
return false;
initialize(MF);
collectCRLogicals();
return simplifyCode();
}
CRLogicalOpInfo createCRLogicalOpInfo(MachineInstr &MI);
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineBranchProbabilityInfo>();
AU.addRequired<MachineDominatorTree>();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void PPCReduceCRLogicals::CRLogicalOpInfo::dump() {
dbgs() << "CRLogicalOpMI: ";
MI->dump();
dbgs() << "IsBinary: " << IsBinary << ", FeedsISEL: " << FeedsISEL;
dbgs() << ", FeedsBR: " << FeedsBR << ", FeedsLogical: ";
dbgs() << FeedsLogical << ", SingleUse: " << SingleUse;
dbgs() << ", DefsSingleUse: " << DefsSingleUse;
dbgs() << ", SubregDef1: " << SubregDef1 << ", SubregDef2: ";
dbgs() << SubregDef2 << ", ContainedInBlock: " << ContainedInBlock;
if (!IsNullary) {
dbgs() << "\nDefs:\n";
TrueDefs.first->dump();
}
if (IsBinary)
TrueDefs.second->dump();
dbgs() << "\n";
if (CopyDefs.first) {
dbgs() << "CopyDef1: ";
CopyDefs.first->dump();
}
if (CopyDefs.second) {
dbgs() << "CopyDef2: ";
CopyDefs.second->dump();
}
}
#endif
PPCReduceCRLogicals::CRLogicalOpInfo
PPCReduceCRLogicals::createCRLogicalOpInfo(MachineInstr &MIParam) {
CRLogicalOpInfo Ret;
Ret.MI = &MIParam;
// Get the defs
if (isNullary(MIParam)) {
Ret.IsNullary = 1;
Ret.TrueDefs = std::make_pair(nullptr, nullptr);
Ret.CopyDefs = std::make_pair(nullptr, nullptr);
} else {
MachineInstr *Def1 = lookThroughCRCopy(MIParam.getOperand(1).getReg(),
Ret.SubregDef1, Ret.CopyDefs.first);
Ret.DefsSingleUse &=
MRI->hasOneNonDBGUse(Def1->getOperand(0).getReg());
Ret.DefsSingleUse &=
MRI->hasOneNonDBGUse(Ret.CopyDefs.first->getOperand(0).getReg());
assert(Def1 && "Must be able to find a definition of operand 1.");
if (isBinary(MIParam)) {
Ret.IsBinary = 1;
MachineInstr *Def2 = lookThroughCRCopy(MIParam.getOperand(2).getReg(),
Ret.SubregDef2,
Ret.CopyDefs.second);
Ret.DefsSingleUse &=
MRI->hasOneNonDBGUse(Def2->getOperand(0).getReg());
Ret.DefsSingleUse &=
MRI->hasOneNonDBGUse(Ret.CopyDefs.second->getOperand(0).getReg());
assert(Def2 && "Must be able to find a definition of operand 2.");
Ret.TrueDefs = std::make_pair(Def1, Def2);
} else {
Ret.TrueDefs = std::make_pair(Def1, nullptr);
Ret.CopyDefs.second = nullptr;
}
}
Ret.ContainedInBlock = 1;
// Get the uses
for (MachineInstr &UseMI :
MRI->use_nodbg_instructions(MIParam.getOperand(0).getReg())) {
unsigned Opc = UseMI.getOpcode();
if (Opc == PPC::ISEL || Opc == PPC::ISEL8)
Ret.FeedsISEL = 1;
if (Opc == PPC::BC || Opc == PPC::BCn || Opc == PPC::BCLR ||
Opc == PPC::BCLRn)
Ret.FeedsBR = 1;
Ret.FeedsLogical = isCRLogical(UseMI);
if (UseMI.getParent() != MIParam.getParent())
Ret.ContainedInBlock = 0;
}
Ret.SingleUse = MRI->hasOneNonDBGUse(MIParam.getOperand(0).getReg()) ? 1 : 0;
// We now know whether all the uses of the CR logical are in the same block.
if (!Ret.IsNullary) {
Ret.ContainedInBlock &=
(MIParam.getParent() == Ret.TrueDefs.first->getParent());
if (Ret.IsBinary)
Ret.ContainedInBlock &=
(MIParam.getParent() == Ret.TrueDefs.second->getParent());
}
DEBUG(Ret.dump());
if (Ret.IsBinary && Ret.ContainedInBlock && Ret.SingleUse) {
NumContainedSingleUseBinOps++;
if (Ret.FeedsBR && Ret.DefsSingleUse)
NumToSplitBlocks++;
}
return Ret;
}
/// Looks trhough a COPY instruction to the actual definition of the CR-bit
/// register and returns the instruction that defines it.
/// FIXME: This currently handles what is by-far the most common case:
/// an instruction that defines a CR field followed by a single copy of a bit
/// from that field into a virtual register. If chains of copies need to be
/// handled, this should have a loop until a non-copy instruction is found.
MachineInstr *PPCReduceCRLogicals::lookThroughCRCopy(unsigned Reg,
unsigned &Subreg,
MachineInstr *&CpDef) {
Subreg = -1;
if (!TargetRegisterInfo::isVirtualRegister(Reg))
return nullptr;
MachineInstr *Copy = MRI->getVRegDef(Reg);
CpDef = Copy;
if (!Copy->isCopy())
return Copy;
unsigned CopySrc = Copy->getOperand(1).getReg();
Subreg = Copy->getOperand(1).getSubReg();
if (!TargetRegisterInfo::isVirtualRegister(CopySrc)) {
const TargetRegisterInfo *TRI = &TII->getRegisterInfo();
// Set the Subreg
if (CopySrc == PPC::CR0EQ || CopySrc == PPC::CR6EQ)
Subreg = PPC::sub_eq;
if (CopySrc == PPC::CR0LT || CopySrc == PPC::CR6LT)
Subreg = PPC::sub_lt;
if (CopySrc == PPC::CR0GT || CopySrc == PPC::CR6GT)
Subreg = PPC::sub_gt;
if (CopySrc == PPC::CR0UN || CopySrc == PPC::CR6UN)
Subreg = PPC::sub_un;
// Loop backwards and return the first MI that modifies the physical CR Reg.
MachineBasicBlock::iterator Me = Copy, B = Copy->getParent()->begin();
while (Me != B)
if ((--Me)->modifiesRegister(CopySrc, TRI))
return &*Me;
return nullptr;
}
return MRI->getVRegDef(CopySrc);
}
void PPCReduceCRLogicals::initialize(MachineFunction &MFParam) {
MF = &MFParam;
MRI = &MF->getRegInfo();
TII = MF->getSubtarget<PPCSubtarget>().getInstrInfo();
MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
AllCRLogicalOps.clear();
}
/// Contains all the implemented transformations on CR logical operations.
/// For example, a binary CR logical can be used to split a block on its inputs,
/// a unary CR logical might be used to change the condition code on a
/// comparison feeding it. A nullary CR logical might simply be removable
/// if the user of the bit it [un]sets can be transformed.
bool PPCReduceCRLogicals::handleCROp(CRLogicalOpInfo &CRI) {
// We can definitely split a block on the inputs to a binary CR operation
// whose defs and (single) use are within the same block.
bool Changed = false;
if (CRI.IsBinary && CRI.ContainedInBlock && CRI.SingleUse && CRI.FeedsBR &&
CRI.DefsSingleUse) {
Changed = splitBlockOnBinaryCROp(CRI);
if (Changed)
NumBlocksSplitOnBinaryCROp++;
}
return Changed;
}
/// Splits a block that contains a CR-logical operation that feeds a branch
/// and whose operands are produced within the block.
/// Example:
/// %vr5<def> = CMPDI %vr2, 0; CRRC:%vr5 G8RC:%vr2
/// %vr6<def> = COPY %vr5:sub_eq; CRBITRC:%vr6 CRRC:%vr5
/// %vr7<def> = CMPDI %vr3, 0; CRRC:%vr7 G8RC:%vr3
/// %vr8<def> = COPY %vr7:sub_eq; CRBITRC:%vr8 CRRC:%vr7
/// %vr9<def> = CROR %vr6<kill>, %vr8<kill>; CRBITRC:%vr9,%vr6,%vr8
/// BC %vr9<kill>, <BB#2>; CRBITRC:%vr9
/// Becomes:
/// %vr5<def> = CMPDI %vr2, 0; CRRC:%vr5 G8RC:%vr2
/// %vr6<def> = COPY %vr5:sub_eq; CRBITRC:%vr6 CRRC:%vr5
/// BC %vr6<kill>, <BB#2>; CRBITRC:%vr6
///
/// %vr7<def> = CMPDI %vr3, 0; CRRC:%vr7 G8RC:%vr3
/// %vr8<def> = COPY %vr7:sub_eq; CRBITRC:%vr8 CRRC:%vr7
/// BC %vr9<kill>, <BB#2>; CRBITRC:%vr9
bool PPCReduceCRLogicals::splitBlockOnBinaryCROp(CRLogicalOpInfo &CRI) {
if (CRI.CopyDefs.first == CRI.CopyDefs.second) {
DEBUG(dbgs() << "Unable to split as the two operands are the same\n");
NumNotSplitIdenticalOperands++;
return false;
}
if (CRI.TrueDefs.first->isCopy() || CRI.TrueDefs.second->isCopy() ||
CRI.TrueDefs.first->isPHI() || CRI.TrueDefs.second->isPHI()) {
DEBUG(dbgs() << "Unable to split because one of the operands is a PHI or "
"chain of copies.\n");
NumNotSplitChainCopies++;
return false;
}
// Note: keep in sync with computeBranchTargetAndInversion().
if (CRI.MI->getOpcode() != PPC::CROR &&
CRI.MI->getOpcode() != PPC::CRAND &&
CRI.MI->getOpcode() != PPC::CRNOR &&
CRI.MI->getOpcode() != PPC::CRNAND &&
CRI.MI->getOpcode() != PPC::CRORC &&
CRI.MI->getOpcode() != PPC::CRANDC) {
DEBUG(dbgs() << "Unable to split blocks on this opcode.\n");
NumNotSplitWrongOpcode++;
return false;
}
DEBUG(dbgs() << "Splitting the following CR op:\n"; CRI.dump());
MachineBasicBlock::iterator Def1It = CRI.TrueDefs.first;
MachineBasicBlock::iterator Def2It = CRI.TrueDefs.second;
bool UsingDef1 = false;
MachineInstr *SplitBefore = &*Def2It;
for (auto E = CRI.MI->getParent()->end(); Def2It != E; ++Def2It) {
if (Def1It == Def2It) { // Def2 comes before Def1.
SplitBefore = &*Def1It;
UsingDef1 = true;
break;
}
}
DEBUG(dbgs() << "We will split the following block:\n";);
DEBUG(CRI.MI->getParent()->dump());
DEBUG(dbgs() << "Before instruction:\n"; SplitBefore->dump());
// Get the branch instruction.
MachineInstr *Branch =
MRI->use_nodbg_begin(CRI.MI->getOperand(0).getReg())->getParent();
// We want the new block to have no code in it other than the definition
// of the input to the CR logical and the CR logical itself. So we move
// those to the bottom of the block (just before the branch). Then we
// will split before the CR logical.
MachineBasicBlock *MBB = SplitBefore->getParent();
auto FirstTerminator = MBB->getFirstTerminator();
MachineBasicBlock::iterator FirstInstrToMove =
UsingDef1 ? CRI.TrueDefs.first : CRI.TrueDefs.second;
MachineBasicBlock::iterator SecondInstrToMove =
UsingDef1 ? CRI.CopyDefs.first : CRI.CopyDefs.second;
// The instructions that need to be moved are not guaranteed to be
// contiguous. Move them individually.
// FIXME: If one of the operands is a chain of (single use) copies, they
// can all be moved and we can still split.
MBB->splice(FirstTerminator, MBB, FirstInstrToMove);
if (FirstInstrToMove != SecondInstrToMove)
MBB->splice(FirstTerminator, MBB, SecondInstrToMove);
MBB->splice(FirstTerminator, MBB, CRI.MI);
unsigned Opc = CRI.MI->getOpcode();
bool InvertOrigBranch, InvertNewBranch, TargetIsFallThrough;
computeBranchTargetAndInversion(Opc, Branch->getOpcode(), UsingDef1,
InvertNewBranch, InvertOrigBranch,
TargetIsFallThrough);
MachineInstr *SplitCond =
UsingDef1 ? CRI.CopyDefs.second : CRI.CopyDefs.first;
DEBUG(dbgs() << "We will " << (InvertNewBranch ? "invert" : "copy"));
DEBUG(dbgs() << " the original branch and the target is the " <<
(TargetIsFallThrough ? "fallthrough block\n" : "orig. target block\n"));
DEBUG(dbgs() << "Original branch instruction: "; Branch->dump());
BlockSplitInfo BSI { Branch, SplitBefore, SplitCond, InvertNewBranch,
InvertOrigBranch, TargetIsFallThrough, MBPI, CRI.MI,
UsingDef1 ? CRI.CopyDefs.first : CRI.CopyDefs.second };
bool Changed = splitMBB(BSI);
// If we've split on a CR logical that is fed by a CR logical,
// recompute the source CR logical as it may be usable for splitting.
if (Changed) {
bool Input1CRlogical =
CRI.TrueDefs.first && isCRLogical(*CRI.TrueDefs.first);
bool Input2CRlogical =
CRI.TrueDefs.second && isCRLogical(*CRI.TrueDefs.second);
if (Input1CRlogical)
AllCRLogicalOps.push_back(createCRLogicalOpInfo(*CRI.TrueDefs.first));
if (Input2CRlogical)
AllCRLogicalOps.push_back(createCRLogicalOpInfo(*CRI.TrueDefs.second));
}
return Changed;
}
void PPCReduceCRLogicals::collectCRLogicals() {
for (MachineBasicBlock &MBB : *MF) {
for (MachineInstr &MI : MBB) {
if (isCRLogical(MI)) {
AllCRLogicalOps.push_back(createCRLogicalOpInfo(MI));
TotalCRLogicals++;
if (AllCRLogicalOps.back().IsNullary)
TotalNullaryCRLogicals++;
else if (AllCRLogicalOps.back().IsBinary)
TotalBinaryCRLogicals++;
else
TotalUnaryCRLogicals++;
}
}
}
}
} // end annonymous namespace
INITIALIZE_PASS_BEGIN(PPCReduceCRLogicals, DEBUG_TYPE,
"PowerPC Reduce CR logical Operation", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_END(PPCReduceCRLogicals, DEBUG_TYPE,
"PowerPC Reduce CR logical Operation", false, false)
char PPCReduceCRLogicals::ID = 0;
FunctionPass*
llvm::createPPCReduceCRLogicalsPass() { return new PPCReduceCRLogicals(); }
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