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

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//===- ExecutionDepsFix.cpp - Fix execution dependecy issues ----*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the execution dependency fix pass.
//
// Some X86 SSE instructions like mov, and, or, xor are available in different
// variants for different operand types. These variant instructions are
// equivalent, but on Nehalem and newer cpus there is extra latency
// transferring data between integer and floating point domains. ARM cores
// have similar issues when they are configured with both VFP and NEON
// pipelines.
//
// This pass changes the variant instructions to minimize domain crossings.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "execution-fix"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
/// A DomainValue is a bit like LiveIntervals' ValNo, but it also keeps track
/// of execution domains.
///
/// An open DomainValue represents a set of instructions that can still switch
/// execution domain. Multiple registers may refer to the same open
/// DomainValue - they will eventually be collapsed to the same execution
/// domain.
///
/// A collapsed DomainValue represents a single register that has been forced
/// into one of more execution domains. There is a separate collapsed
/// DomainValue for each register, but it may contain multiple execution
/// domains. A register value is initially created in a single execution
/// domain, but if we were forced to pay the penalty of a domain crossing, we
/// keep track of the fact that the register is now available in multiple
/// domains.
namespace {
struct DomainValue {
// Basic reference counting.
unsigned Refs;
// Bitmask of available domains. For an open DomainValue, it is the still
// possible domains for collapsing. For a collapsed DomainValue it is the
// domains where the register is available for free.
unsigned AvailableDomains;
// Pointer to the next DomainValue in a chain. When two DomainValues are
// merged, Victim.Next is set to point to Victor, so old DomainValue
// references can be updated by folowing the chain.
DomainValue *Next;
// Twiddleable instructions using or defining these registers.
SmallVector<MachineInstr*, 8> Instrs;
// A collapsed DomainValue has no instructions to twiddle - it simply keeps
// track of the domains where the registers are already available.
bool isCollapsed() const { return Instrs.empty(); }
// Is domain available?
bool hasDomain(unsigned domain) const {
return AvailableDomains & (1u << domain);
}
// Mark domain as available.
void addDomain(unsigned domain) {
AvailableDomains |= 1u << domain;
}
// Restrict to a single domain available.
void setSingleDomain(unsigned domain) {
AvailableDomains = 1u << domain;
}
// Return bitmask of domains that are available and in mask.
unsigned getCommonDomains(unsigned mask) const {
return AvailableDomains & mask;
}
// First domain available.
unsigned getFirstDomain() const {
return CountTrailingZeros_32(AvailableDomains);
}
DomainValue() : Refs(0) { clear(); }
// Clear this DomainValue and point to next which has all its data.
void clear() {
AvailableDomains = 0;
Next = 0;
Instrs.clear();
}
};
}
namespace {
/// LiveReg - Information about a live register.
struct LiveReg {
/// Value currently in this register, or NULL when no value is being tracked.
/// This counts as a DomainValue reference.
DomainValue *Value;
/// Instruction that defined this register, relative to the beginning of the
/// current basic block. When a LiveReg is used to represent a live-out
/// register, this value is relative to the end of the basic block, so it
/// will be a negative number.
int Def;
};
} // anonynous namespace
namespace {
class ExeDepsFix : public MachineFunctionPass {
static char ID;
SpecificBumpPtrAllocator<DomainValue> Allocator;
SmallVector<DomainValue*,16> Avail;
const TargetRegisterClass *const RC;
MachineFunction *MF;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
std::vector<int> AliasMap;
const unsigned NumRegs;
LiveReg *LiveRegs;
typedef DenseMap<MachineBasicBlock*, LiveReg*> LiveOutMap;
LiveOutMap LiveOuts;
/// Current instruction number.
/// The first instruction in each basic block is 0.
int CurInstr;
/// True when the current block has a predecessor that hasn't been visited
/// yet.
bool SeenUnknownBackEdge;
public:
ExeDepsFix(const TargetRegisterClass *rc)
: MachineFunctionPass(ID), RC(rc), NumRegs(RC->getNumRegs()) {}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const {
return "Execution dependency fix";
}
private:
// Register mapping.
int regIndex(unsigned Reg);
// DomainValue allocation.
DomainValue *alloc(int domain = -1);
DomainValue *retain(DomainValue *DV) {
if (DV) ++DV->Refs;
return DV;
}
void release(DomainValue*);
DomainValue *resolve(DomainValue*&);
// LiveRegs manipulations.
void setLiveReg(int rx, DomainValue *DV);
void kill(int rx);
void force(int rx, unsigned domain);
void collapse(DomainValue *dv, unsigned domain);
bool merge(DomainValue *A, DomainValue *B);
void enterBasicBlock(MachineBasicBlock*);
void leaveBasicBlock(MachineBasicBlock*);
void visitInstr(MachineInstr*);
void processDefs(MachineInstr*, bool Kill);
void visitSoftInstr(MachineInstr*, unsigned mask);
void visitHardInstr(MachineInstr*, unsigned domain);
};
}
char ExeDepsFix::ID = 0;
/// Translate TRI register number to an index into our smaller tables of
/// interesting registers. Return -1 for boring registers.
int ExeDepsFix::regIndex(unsigned Reg) {
assert(Reg < AliasMap.size() && "Invalid register");
return AliasMap[Reg];
}
DomainValue *ExeDepsFix::alloc(int domain) {
DomainValue *dv = Avail.empty() ?
new(Allocator.Allocate()) DomainValue :
Avail.pop_back_val();
if (domain >= 0)
dv->addDomain(domain);
assert(dv->Refs == 0 && "Reference count wasn't cleared");
assert(!dv->Next && "Chained DomainValue shouldn't have been recycled");
return dv;
}
/// release - Release a reference to DV. When the last reference is released,
/// collapse if needed.
void ExeDepsFix::release(DomainValue *DV) {
while (DV) {
assert(DV->Refs && "Bad DomainValue");
if (--DV->Refs)
return;
// There are no more DV references. Collapse any contained instructions.
if (DV->AvailableDomains && !DV->isCollapsed())
collapse(DV, DV->getFirstDomain());
DomainValue *Next = DV->Next;
DV->clear();
Avail.push_back(DV);
// Also release the next DomainValue in the chain.
DV = Next;
}
}
/// resolve - Follow the chain of dead DomainValues until a live DomainValue is
/// reached. Update the referenced pointer when necessary.
DomainValue *ExeDepsFix::resolve(DomainValue *&DVRef) {
DomainValue *DV = DVRef;
if (!DV || !DV->Next)
return DV;
// DV has a chain. Find the end.
do DV = DV->Next;
while (DV->Next);
// Update DVRef to point to DV.
retain(DV);
release(DVRef);
DVRef = DV;
return DV;
}
/// Set LiveRegs[rx] = dv, updating reference counts.
void ExeDepsFix::setLiveReg(int rx, DomainValue *dv) {
assert(unsigned(rx) < NumRegs && "Invalid index");
assert(LiveRegs && "Must enter basic block first.");
if (LiveRegs[rx].Value == dv)
return;
if (LiveRegs[rx].Value)
release(LiveRegs[rx].Value);
LiveRegs[rx].Value = retain(dv);
}
// Kill register rx, recycle or collapse any DomainValue.
void ExeDepsFix::kill(int rx) {
assert(unsigned(rx) < NumRegs && "Invalid index");
assert(LiveRegs && "Must enter basic block first.");
if (!LiveRegs[rx].Value)
return;
release(LiveRegs[rx].Value);
LiveRegs[rx].Value = 0;
}
/// Force register rx into domain.
void ExeDepsFix::force(int rx, unsigned domain) {
assert(unsigned(rx) < NumRegs && "Invalid index");
assert(LiveRegs && "Must enter basic block first.");
if (DomainValue *dv = LiveRegs[rx].Value) {
if (dv->isCollapsed())
dv->addDomain(domain);
else if (dv->hasDomain(domain))
collapse(dv, domain);
else {
// This is an incompatible open DomainValue. Collapse it to whatever and
// force the new value into domain. This costs a domain crossing.
collapse(dv, dv->getFirstDomain());
assert(LiveRegs[rx].Value && "Not live after collapse?");
LiveRegs[rx].Value->addDomain(domain);
}
} else {
// Set up basic collapsed DomainValue.
setLiveReg(rx, alloc(domain));
}
}
/// Collapse open DomainValue into given domain. If there are multiple
/// registers using dv, they each get a unique collapsed DomainValue.
void ExeDepsFix::collapse(DomainValue *dv, unsigned domain) {
assert(dv->hasDomain(domain) && "Cannot collapse");
// Collapse all the instructions.
while (!dv->Instrs.empty())
TII->setExecutionDomain(dv->Instrs.pop_back_val(), domain);
dv->setSingleDomain(domain);
// If there are multiple users, give them new, unique DomainValues.
if (LiveRegs && dv->Refs > 1)
for (unsigned rx = 0; rx != NumRegs; ++rx)
if (LiveRegs[rx].Value == dv)
setLiveReg(rx, alloc(domain));
}
/// Merge - All instructions and registers in B are moved to A, and B is
/// released.
bool ExeDepsFix::merge(DomainValue *A, DomainValue *B) {
assert(!A->isCollapsed() && "Cannot merge into collapsed");
assert(!B->isCollapsed() && "Cannot merge from collapsed");
if (A == B)
return true;
// Restrict to the domains that A and B have in common.
unsigned common = A->getCommonDomains(B->AvailableDomains);
if (!common)
return false;
A->AvailableDomains = common;
A->Instrs.append(B->Instrs.begin(), B->Instrs.end());
// Clear the old DomainValue so we won't try to swizzle instructions twice.
B->clear();
// All uses of B are referred to A.
B->Next = retain(A);
for (unsigned rx = 0; rx != NumRegs; ++rx)
if (LiveRegs[rx].Value == B)
setLiveReg(rx, A);
return true;
}
// enterBasicBlock - Set up LiveRegs by merging predecessor live-out values.
void ExeDepsFix::enterBasicBlock(MachineBasicBlock *MBB) {
// Detect back-edges from predecessors we haven't processed yet.
SeenUnknownBackEdge = false;
// Reset instruction counter in each basic block.
CurInstr = 0;
// Set up LiveRegs to represent registers entering MBB.
if (!LiveRegs)
LiveRegs = new LiveReg[NumRegs];
// Default values are 'nothing happened a long time ago'.
for (unsigned rx = 0; rx != NumRegs; ++rx) {
LiveRegs[rx].Value = 0;
LiveRegs[rx].Def = -(1 << 20);
}
// This is the entry block.
if (MBB->pred_empty()) {
for (MachineBasicBlock::livein_iterator i = MBB->livein_begin(),
e = MBB->livein_end(); i != e; ++i) {
int rx = regIndex(*i);
if (rx < 0)
continue;
// Treat function live-ins as if they were defined just before the first
// instruction. Usually, function arguments are set up immediately
// before the call.
LiveRegs[rx].Def = -1;
}
DEBUG(dbgs() << "BB#" << MBB->getNumber() << ": entry\n");
return;
}
// Try to coalesce live-out registers from predecessors.
for (MachineBasicBlock::const_pred_iterator pi = MBB->pred_begin(),
pe = MBB->pred_end(); pi != pe; ++pi) {
LiveOutMap::const_iterator fi = LiveOuts.find(*pi);
if (fi == LiveOuts.end()) {
SeenUnknownBackEdge = true;
continue;
}
assert(fi->second && "Can't have NULL entries");
for (unsigned rx = 0; rx != NumRegs; ++rx) {
// Use the most recent predecessor def for each register.
LiveRegs[rx].Def = std::max(LiveRegs[rx].Def, fi->second[rx].Def);
DomainValue *pdv = resolve(fi->second[rx].Value);
if (!pdv)
continue;
if (!LiveRegs[rx].Value) {
setLiveReg(rx, pdv);
continue;
}
// We have a live DomainValue from more than one predecessor.
if (LiveRegs[rx].Value->isCollapsed()) {
// We are already collapsed, but predecessor is not. Force him.
unsigned Domain = LiveRegs[rx].Value->getFirstDomain();
if (!pdv->isCollapsed() && pdv->hasDomain(Domain))
collapse(pdv, Domain);
continue;
}
// Currently open, merge in predecessor.
if (!pdv->isCollapsed())
merge(LiveRegs[rx].Value, pdv);
else
force(rx, pdv->getFirstDomain());
}
}
DEBUG(dbgs() << "BB#" << MBB->getNumber()
<< (SeenUnknownBackEdge ? ": incomplete\n" : ": all preds known\n"));
}
void ExeDepsFix::leaveBasicBlock(MachineBasicBlock *MBB) {
assert(LiveRegs && "Must enter basic block first.");
// Save live registers at end of MBB - used by enterBasicBlock().
// Also use LiveOuts as a visited set to detect back-edges.
bool First = LiveOuts.insert(std::make_pair(MBB, LiveRegs)).second;
if (First) {
// LiveRegs was inserted in LiveOuts. Adjust all defs to be relative to
// the end of this block instead of the beginning.
for (unsigned i = 0, e = NumRegs; i != e; ++i)
LiveRegs[i].Def -= CurInstr;
} else {
// Insertion failed, this must be the second pass.
// Release all the DomainValues instead of keeping them.
for (unsigned i = 0, e = NumRegs; i != e; ++i)
release(LiveRegs[i].Value);
delete[] LiveRegs;
}
LiveRegs = 0;
}
void ExeDepsFix::visitInstr(MachineInstr *MI) {
if (MI->isDebugValue())
return;
// Update instructions with explicit execution domains.
std::pair<uint16_t, uint16_t> DomP = TII->getExecutionDomain(MI);
if (DomP.first) {
if (DomP.second)
visitSoftInstr(MI, DomP.second);
else
visitHardInstr(MI, DomP.first);
}
// Process defs to track register ages, and kill values clobbered by generic
// instructions.
processDefs(MI, !DomP.first);
}
// Update def-ages for registers defined by MI.
// If Kill is set, also kill off DomainValues clobbered by the defs.
void ExeDepsFix::processDefs(MachineInstr *MI, bool Kill) {
assert(!MI->isDebugValue() && "Won't process debug values");
const MCInstrDesc &MCID = MI->getDesc();
for (unsigned i = 0,
e = MI->isVariadic() ? MI->getNumOperands() : MCID.getNumDefs();
i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg())
continue;
if (MO.isImplicit())
break;
if (MO.isUse())
continue;
int rx = regIndex(MO.getReg());
if (rx < 0)
continue;
// This instruction explicitly defines rx.
DEBUG(dbgs() << TRI->getName(RC->getRegister(rx)) << ":\t" << CurInstr
<< '\t' << *MI);
// How many instructions since rx was last written?
unsigned Clearance = CurInstr - LiveRegs[rx].Def;
LiveRegs[rx].Def = CurInstr;
// Kill off domains redefined by generic instructions.
if (Kill)
kill(rx);
// Verify clearance before partial register updates.
unsigned Pref = TII->getPartialRegUpdateClearance(MI, i, TRI);
if (!Pref)
continue;
DEBUG(dbgs() << "Clearance: " << Clearance << ", want " << Pref);
if (Pref > Clearance) {
DEBUG(dbgs() << ": Break dependency.\n");
TII->breakPartialRegDependency(MI, i, TRI);
continue;
}
// The current clearance seems OK, but we may be ignoring a def from a
// back-edge.
if (!SeenUnknownBackEdge || Pref <= unsigned(CurInstr)) {
DEBUG(dbgs() << ": OK.\n");
continue;
}
// A def from an unprocessed back-edge may make us break this dependency.
DEBUG(dbgs() << ": Wait for back-edge to resolve.\n");
}
++CurInstr;
}
// A hard instruction only works in one domain. All input registers will be
// forced into that domain.
void ExeDepsFix::visitHardInstr(MachineInstr *mi, unsigned domain) {
// Collapse all uses.
for (unsigned i = mi->getDesc().getNumDefs(),
e = mi->getDesc().getNumOperands(); i != e; ++i) {
MachineOperand &mo = mi->getOperand(i);
if (!mo.isReg()) continue;
int rx = regIndex(mo.getReg());
if (rx < 0) continue;
force(rx, domain);
}
// Kill all defs and force them.
for (unsigned i = 0, e = mi->getDesc().getNumDefs(); i != e; ++i) {
MachineOperand &mo = mi->getOperand(i);
if (!mo.isReg()) continue;
int rx = regIndex(mo.getReg());
if (rx < 0) continue;
kill(rx);
force(rx, domain);
}
}
// A soft instruction can be changed to work in other domains given by mask.
void ExeDepsFix::visitSoftInstr(MachineInstr *mi, unsigned mask) {
// Bitmask of available domains for this instruction after taking collapsed
// operands into account.
unsigned available = mask;
// Scan the explicit use operands for incoming domains.
SmallVector<int, 4> used;
if (LiveRegs)
for (unsigned i = mi->getDesc().getNumDefs(),
e = mi->getDesc().getNumOperands(); i != e; ++i) {
MachineOperand &mo = mi->getOperand(i);
if (!mo.isReg()) continue;
int rx = regIndex(mo.getReg());
if (rx < 0) continue;
if (DomainValue *dv = LiveRegs[rx].Value) {
// Bitmask of domains that dv and available have in common.
unsigned common = dv->getCommonDomains(available);
// Is it possible to use this collapsed register for free?
if (dv->isCollapsed()) {
// Restrict available domains to the ones in common with the operand.
// If there are no common domains, we must pay the cross-domain
// penalty for this operand.
if (common) available = common;
} else if (common)
// Open DomainValue is compatible, save it for merging.
used.push_back(rx);
else
// Open DomainValue is not compatible with instruction. It is useless
// now.
kill(rx);
}
}
// If the collapsed operands force a single domain, propagate the collapse.
if (isPowerOf2_32(available)) {
unsigned domain = CountTrailingZeros_32(available);
TII->setExecutionDomain(mi, domain);
visitHardInstr(mi, domain);
return;
}
// Kill off any remaining uses that don't match available, and build a list of
// incoming DomainValues that we want to merge.
SmallVector<LiveReg, 4> Regs;
for (SmallVector<int, 4>::iterator i=used.begin(), e=used.end(); i!=e; ++i) {
int rx = *i;
const LiveReg &LR = LiveRegs[rx];
// This useless DomainValue could have been missed above.
if (!LR.Value->getCommonDomains(available)) {
kill(rx);
continue;
}
// Sorted insertion.
bool Inserted = false;
for (SmallVector<LiveReg, 4>::iterator i = Regs.begin(), e = Regs.end();
i != e && !Inserted; ++i) {
if (LR.Def < i->Def) {
Inserted = true;
Regs.insert(i, LR);
}
}
if (!Inserted)
Regs.push_back(LR);
}
// doms are now sorted in order of appearance. Try to merge them all, giving
// priority to the latest ones.
DomainValue *dv = 0;
while (!Regs.empty()) {
if (!dv) {
dv = Regs.pop_back_val().Value;
// Force the first dv to match the current instruction.
dv->AvailableDomains = dv->getCommonDomains(available);
assert(dv->AvailableDomains && "Domain should have been filtered");
continue;
}
DomainValue *Latest = Regs.pop_back_val().Value;
// Skip already merged values.
if (Latest == dv || Latest->Next)
continue;
if (merge(dv, Latest))
continue;
// If latest didn't merge, it is useless now. Kill all registers using it.
for (SmallVector<int,4>::iterator i=used.begin(), e=used.end(); i != e; ++i)
if (LiveRegs[*i].Value == Latest)
kill(*i);
}
// dv is the DomainValue we are going to use for this instruction.
if (!dv) {
dv = alloc();
dv->AvailableDomains = available;
}
dv->Instrs.push_back(mi);
// Finally set all defs and non-collapsed uses to dv.
for (unsigned i = 0, e = mi->getDesc().getNumOperands(); i != e; ++i) {
MachineOperand &mo = mi->getOperand(i);
if (!mo.isReg()) continue;
int rx = regIndex(mo.getReg());
if (rx < 0) continue;
if (!LiveRegs[rx].Value || (mo.isDef() && LiveRegs[rx].Value != dv)) {
kill(rx);
setLiveReg(rx, dv);
}
}
}
bool ExeDepsFix::runOnMachineFunction(MachineFunction &mf) {
MF = &mf;
TII = MF->getTarget().getInstrInfo();
TRI = MF->getTarget().getRegisterInfo();
LiveRegs = 0;
assert(NumRegs == RC->getNumRegs() && "Bad regclass");
DEBUG(dbgs() << "********** FIX EXECUTION DEPENDENCIES: "
<< RC->getName() << " **********\n");
// If no relevant registers are used in the function, we can skip it
// completely.
bool anyregs = false;
for (TargetRegisterClass::const_iterator I = RC->begin(), E = RC->end();
I != E; ++I)
if (MF->getRegInfo().isPhysRegOrOverlapUsed(*I)) {
anyregs = true;
break;
}
if (!anyregs) return false;
// Initialize the AliasMap on the first use.
if (AliasMap.empty()) {
// Given a PhysReg, AliasMap[PhysReg] is either the relevant index into RC,
// or -1.
AliasMap.resize(TRI->getNumRegs(), -1);
for (unsigned i = 0, e = RC->getNumRegs(); i != e; ++i)
for (const uint16_t *AI = TRI->getOverlaps(RC->getRegister(i)); *AI; ++AI)
AliasMap[*AI] = i;
}
MachineBasicBlock *Entry = MF->begin();
ReversePostOrderTraversal<MachineBasicBlock*> RPOT(Entry);
SmallVector<MachineBasicBlock*, 16> Loops;
for (ReversePostOrderTraversal<MachineBasicBlock*>::rpo_iterator
MBBI = RPOT.begin(), MBBE = RPOT.end(); MBBI != MBBE; ++MBBI) {
MachineBasicBlock *MBB = *MBBI;
enterBasicBlock(MBB);
if (SeenUnknownBackEdge)
Loops.push_back(MBB);
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
++I)
visitInstr(I);
leaveBasicBlock(MBB);
}
// Visit all the loop blocks again in order to merge DomainValues from
// back-edges.
for (unsigned i = 0, e = Loops.size(); i != e; ++i) {
MachineBasicBlock *MBB = Loops[i];
enterBasicBlock(MBB);
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
++I)
if (!I->isDebugValue())
processDefs(I, false);
leaveBasicBlock(MBB);
}
// Clear the LiveOuts vectors and collapse any remaining DomainValues.
for (ReversePostOrderTraversal<MachineBasicBlock*>::rpo_iterator
MBBI = RPOT.begin(), MBBE = RPOT.end(); MBBI != MBBE; ++MBBI) {
LiveOutMap::const_iterator FI = LiveOuts.find(*MBBI);
if (FI == LiveOuts.end() || !FI->second)
continue;
for (unsigned i = 0, e = NumRegs; i != e; ++i)
if (FI->second[i].Value)
release(FI->second[i].Value);
delete[] FI->second;
}
LiveOuts.clear();
Avail.clear();
Allocator.DestroyAll();
return false;
}
FunctionPass *
llvm::createExecutionDependencyFixPass(const TargetRegisterClass *RC) {
return new ExeDepsFix(RC);
}
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