367 lines
12 KiB
C++
367 lines
12 KiB
C++
//===- MachineCopyPropagation.cpp - Machine Copy Propagation Pass ---------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This is an extremely simple MachineInstr-level copy propagation pass.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/CodeGen/Passes.h"
|
|
#include "llvm/ADT/DenseMap.h"
|
|
#include "llvm/ADT/SetVector.h"
|
|
#include "llvm/ADT/SmallVector.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/CodeGen/MachineFunction.h"
|
|
#include "llvm/CodeGen/MachineFunctionPass.h"
|
|
#include "llvm/CodeGen/MachineRegisterInfo.h"
|
|
#include "llvm/Pass.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"
|
|
using namespace llvm;
|
|
|
|
#define DEBUG_TYPE "codegen-cp"
|
|
|
|
STATISTIC(NumDeletes, "Number of dead copies deleted");
|
|
|
|
namespace {
|
|
typedef SmallVector<unsigned, 4> RegList;
|
|
typedef DenseMap<unsigned, RegList> SourceMap;
|
|
typedef DenseMap<unsigned, MachineInstr*> Reg2MIMap;
|
|
|
|
class MachineCopyPropagation : public MachineFunctionPass {
|
|
const TargetRegisterInfo *TRI;
|
|
const TargetInstrInfo *TII;
|
|
const MachineRegisterInfo *MRI;
|
|
|
|
public:
|
|
static char ID; // Pass identification, replacement for typeid
|
|
MachineCopyPropagation() : MachineFunctionPass(ID) {
|
|
initializeMachineCopyPropagationPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
bool runOnMachineFunction(MachineFunction &MF) override;
|
|
|
|
MachineFunctionProperties getRequiredProperties() const override {
|
|
return MachineFunctionProperties().set(
|
|
MachineFunctionProperties::Property::AllVRegsAllocated);
|
|
}
|
|
|
|
private:
|
|
void ClobberRegister(unsigned Reg);
|
|
void CopyPropagateBlock(MachineBasicBlock &MBB);
|
|
bool eraseIfRedundant(MachineInstr &Copy, unsigned Src, unsigned Def);
|
|
|
|
/// Candidates for deletion.
|
|
SmallSetVector<MachineInstr*, 8> MaybeDeadCopies;
|
|
/// Def -> available copies map.
|
|
Reg2MIMap AvailCopyMap;
|
|
/// Def -> copies map.
|
|
Reg2MIMap CopyMap;
|
|
/// Src -> Def map
|
|
SourceMap SrcMap;
|
|
bool Changed;
|
|
};
|
|
}
|
|
char MachineCopyPropagation::ID = 0;
|
|
char &llvm::MachineCopyPropagationID = MachineCopyPropagation::ID;
|
|
|
|
INITIALIZE_PASS(MachineCopyPropagation, "machine-cp",
|
|
"Machine Copy Propagation Pass", false, false)
|
|
|
|
/// Remove any entry in \p Map where the register is a subregister or equal to
|
|
/// a register contained in \p Regs.
|
|
static void removeRegsFromMap(Reg2MIMap &Map, const RegList &Regs,
|
|
const TargetRegisterInfo &TRI) {
|
|
for (unsigned Reg : Regs) {
|
|
// Source of copy is no longer available for propagation.
|
|
for (MCSubRegIterator SR(Reg, &TRI, true); SR.isValid(); ++SR)
|
|
Map.erase(*SR);
|
|
}
|
|
}
|
|
|
|
/// Remove any entry in \p Map that is marked clobbered in \p RegMask.
|
|
/// The map will typically have a lot fewer entries than the regmask clobbers,
|
|
/// so this is more efficient than iterating the clobbered registers and calling
|
|
/// ClobberRegister() on them.
|
|
static void removeClobberedRegsFromMap(Reg2MIMap &Map,
|
|
const MachineOperand &RegMask) {
|
|
for (Reg2MIMap::iterator I = Map.begin(), E = Map.end(), Next; I != E;
|
|
I = Next) {
|
|
Next = std::next(I);
|
|
unsigned Reg = I->first;
|
|
if (RegMask.clobbersPhysReg(Reg))
|
|
Map.erase(I);
|
|
}
|
|
}
|
|
|
|
void MachineCopyPropagation::ClobberRegister(unsigned Reg) {
|
|
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
|
|
CopyMap.erase(*AI);
|
|
AvailCopyMap.erase(*AI);
|
|
|
|
SourceMap::iterator SI = SrcMap.find(*AI);
|
|
if (SI != SrcMap.end()) {
|
|
removeRegsFromMap(AvailCopyMap, SI->second, *TRI);
|
|
SrcMap.erase(SI);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Return true if \p PreviousCopy did copy register \p Src to register \p Def.
|
|
/// This fact may have been obscured by sub register usage or may not be true at
|
|
/// all even though Src and Def are subregisters of the registers used in
|
|
/// PreviousCopy. e.g.
|
|
/// isNopCopy("ecx = COPY eax", AX, CX) == true
|
|
/// isNopCopy("ecx = COPY eax", AH, CL) == false
|
|
static bool isNopCopy(const MachineInstr &PreviousCopy, unsigned Src,
|
|
unsigned Def, const TargetRegisterInfo *TRI) {
|
|
unsigned PreviousSrc = PreviousCopy.getOperand(1).getReg();
|
|
unsigned PreviousDef = PreviousCopy.getOperand(0).getReg();
|
|
if (Src == PreviousSrc) {
|
|
assert(Def == PreviousDef);
|
|
return true;
|
|
}
|
|
if (!TRI->isSubRegister(PreviousSrc, Src))
|
|
return false;
|
|
unsigned SubIdx = TRI->getSubRegIndex(PreviousSrc, Src);
|
|
return SubIdx == TRI->getSubRegIndex(PreviousDef, Def);
|
|
}
|
|
|
|
/// Remove instruction \p Copy if there exists a previous copy that copies the
|
|
/// register \p Src to the register \p Def; This may happen indirectly by
|
|
/// copying the super registers.
|
|
bool MachineCopyPropagation::eraseIfRedundant(MachineInstr &Copy, unsigned Src,
|
|
unsigned Def) {
|
|
// Avoid eliminating a copy from/to a reserved registers as we cannot predict
|
|
// the value (Example: The sparc zero register is writable but stays zero).
|
|
if (MRI->isReserved(Src) || MRI->isReserved(Def))
|
|
return false;
|
|
|
|
// Search for an existing copy.
|
|
Reg2MIMap::iterator CI = AvailCopyMap.find(Def);
|
|
if (CI == AvailCopyMap.end())
|
|
return false;
|
|
|
|
// Check that the existing copy uses the correct sub registers.
|
|
MachineInstr &PrevCopy = *CI->second;
|
|
if (!isNopCopy(PrevCopy, Src, Def, TRI))
|
|
return false;
|
|
|
|
DEBUG(dbgs() << "MCP: copy is a NOP, removing: "; Copy.dump());
|
|
|
|
// Copy was redundantly redefining either Src or Def. Remove earlier kill
|
|
// flags between Copy and PrevCopy because the value will be reused now.
|
|
assert(Copy.isCopy());
|
|
unsigned CopyDef = Copy.getOperand(0).getReg();
|
|
assert(CopyDef == Src || CopyDef == Def);
|
|
for (MachineInstr &MI :
|
|
make_range(PrevCopy.getIterator(), Copy.getIterator()))
|
|
MI.clearRegisterKills(CopyDef, TRI);
|
|
|
|
Copy.eraseFromParent();
|
|
Changed = true;
|
|
++NumDeletes;
|
|
return true;
|
|
}
|
|
|
|
void MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
|
|
DEBUG(dbgs() << "MCP: CopyPropagateBlock " << MBB.getName() << "\n");
|
|
|
|
for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ) {
|
|
MachineInstr *MI = &*I;
|
|
++I;
|
|
|
|
if (MI->isCopy()) {
|
|
unsigned Def = MI->getOperand(0).getReg();
|
|
unsigned Src = MI->getOperand(1).getReg();
|
|
|
|
assert(!TargetRegisterInfo::isVirtualRegister(Def) &&
|
|
!TargetRegisterInfo::isVirtualRegister(Src) &&
|
|
"MachineCopyPropagation should be run after register allocation!");
|
|
|
|
// The two copies cancel out and the source of the first copy
|
|
// hasn't been overridden, eliminate the second one. e.g.
|
|
// %ECX<def> = COPY %EAX
|
|
// ... nothing clobbered EAX.
|
|
// %EAX<def> = COPY %ECX
|
|
// =>
|
|
// %ECX<def> = COPY %EAX
|
|
//
|
|
// or
|
|
//
|
|
// %ECX<def> = COPY %EAX
|
|
// ... nothing clobbered EAX.
|
|
// %ECX<def> = COPY %EAX
|
|
// =>
|
|
// %ECX<def> = COPY %EAX
|
|
if (eraseIfRedundant(*MI, Def, Src) || eraseIfRedundant(*MI, Src, Def))
|
|
continue;
|
|
|
|
// If Src is defined by a previous copy, the previous copy cannot be
|
|
// eliminated.
|
|
for (MCRegAliasIterator AI(Src, TRI, true); AI.isValid(); ++AI) {
|
|
Reg2MIMap::iterator CI = CopyMap.find(*AI);
|
|
if (CI != CopyMap.end()) {
|
|
DEBUG(dbgs() << "MCP: Copy is no longer dead: "; CI->second->dump());
|
|
MaybeDeadCopies.remove(CI->second);
|
|
}
|
|
}
|
|
|
|
DEBUG(dbgs() << "MCP: Copy is a deletion candidate: "; MI->dump());
|
|
|
|
// Copy is now a candidate for deletion.
|
|
if (!MRI->isReserved(Def))
|
|
MaybeDeadCopies.insert(MI);
|
|
|
|
// If 'Def' is previously source of another copy, then this earlier copy's
|
|
// source is no longer available. e.g.
|
|
// %xmm9<def> = copy %xmm2
|
|
// ...
|
|
// %xmm2<def> = copy %xmm0
|
|
// ...
|
|
// %xmm2<def> = copy %xmm9
|
|
ClobberRegister(Def);
|
|
|
|
// Remember Def is defined by the copy.
|
|
for (MCSubRegIterator SR(Def, TRI, /*IncludeSelf=*/true); SR.isValid();
|
|
++SR) {
|
|
CopyMap[*SR] = MI;
|
|
AvailCopyMap[*SR] = MI;
|
|
}
|
|
|
|
// Remember source that's copied to Def. Once it's clobbered, then
|
|
// it's no longer available for copy propagation.
|
|
RegList &DestList = SrcMap[Src];
|
|
if (std::find(DestList.begin(), DestList.end(), Def) == DestList.end())
|
|
DestList.push_back(Def);
|
|
|
|
continue;
|
|
}
|
|
|
|
// Not a copy.
|
|
SmallVector<unsigned, 2> Defs;
|
|
const MachineOperand *RegMask = nullptr;
|
|
for (const MachineOperand &MO : MI->operands()) {
|
|
if (MO.isRegMask())
|
|
RegMask = &MO;
|
|
if (!MO.isReg())
|
|
continue;
|
|
unsigned Reg = MO.getReg();
|
|
if (!Reg)
|
|
continue;
|
|
|
|
assert(!TargetRegisterInfo::isVirtualRegister(Reg) &&
|
|
"MachineCopyPropagation should be run after register allocation!");
|
|
|
|
if (MO.isDef()) {
|
|
Defs.push_back(Reg);
|
|
continue;
|
|
}
|
|
|
|
// If 'Reg' is defined by a copy, the copy is no longer a candidate
|
|
// for elimination.
|
|
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
|
|
Reg2MIMap::iterator CI = CopyMap.find(*AI);
|
|
if (CI != CopyMap.end()) {
|
|
DEBUG(dbgs() << "MCP: Copy is used - not dead: "; CI->second->dump());
|
|
MaybeDeadCopies.remove(CI->second);
|
|
}
|
|
}
|
|
// Treat undef use like defs for copy propagation but not for
|
|
// dead copy. We would need to do a liveness check to be sure the copy
|
|
// is dead for undef uses.
|
|
// The backends are allowed to do whatever they want with undef value
|
|
// and we cannot be sure this register will not be rewritten to break
|
|
// some false dependencies for the hardware for instance.
|
|
if (MO.isUndef())
|
|
Defs.push_back(Reg);
|
|
}
|
|
|
|
// The instruction has a register mask operand which means that it clobbers
|
|
// a large set of registers. Treat clobbered registers the same way as
|
|
// defined registers.
|
|
if (RegMask) {
|
|
// Erase any MaybeDeadCopies whose destination register is clobbered.
|
|
for (SmallSetVector<MachineInstr *, 8>::iterator DI =
|
|
MaybeDeadCopies.begin();
|
|
DI != MaybeDeadCopies.end();) {
|
|
MachineInstr *MaybeDead = *DI;
|
|
unsigned Reg = MaybeDead->getOperand(0).getReg();
|
|
assert(!MRI->isReserved(Reg));
|
|
|
|
if (!RegMask->clobbersPhysReg(Reg)) {
|
|
++DI;
|
|
continue;
|
|
}
|
|
|
|
DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
|
|
MaybeDead->dump());
|
|
|
|
// erase() will return the next valid iterator pointing to the next
|
|
// element after the erased one.
|
|
DI = MaybeDeadCopies.erase(DI);
|
|
MaybeDead->eraseFromParent();
|
|
Changed = true;
|
|
++NumDeletes;
|
|
}
|
|
|
|
removeClobberedRegsFromMap(AvailCopyMap, *RegMask);
|
|
removeClobberedRegsFromMap(CopyMap, *RegMask);
|
|
for (SourceMap::iterator I = SrcMap.begin(), E = SrcMap.end(), Next;
|
|
I != E; I = Next) {
|
|
Next = std::next(I);
|
|
if (RegMask->clobbersPhysReg(I->first)) {
|
|
removeRegsFromMap(AvailCopyMap, I->second, *TRI);
|
|
SrcMap.erase(I);
|
|
}
|
|
}
|
|
}
|
|
|
|
// Any previous copy definition or reading the Defs is no longer available.
|
|
for (unsigned Reg : Defs)
|
|
ClobberRegister(Reg);
|
|
}
|
|
|
|
// If MBB doesn't have successors, delete the copies whose defs are not used.
|
|
// If MBB does have successors, then conservative assume the defs are live-out
|
|
// since we don't want to trust live-in lists.
|
|
if (MBB.succ_empty()) {
|
|
for (MachineInstr *MaybeDead : MaybeDeadCopies) {
|
|
assert(!MRI->isReserved(MaybeDead->getOperand(0).getReg()));
|
|
MaybeDead->eraseFromParent();
|
|
Changed = true;
|
|
++NumDeletes;
|
|
}
|
|
}
|
|
|
|
MaybeDeadCopies.clear();
|
|
AvailCopyMap.clear();
|
|
CopyMap.clear();
|
|
SrcMap.clear();
|
|
}
|
|
|
|
bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
|
|
if (skipOptnoneFunction(*MF.getFunction()))
|
|
return false;
|
|
|
|
Changed = false;
|
|
|
|
TRI = MF.getSubtarget().getRegisterInfo();
|
|
TII = MF.getSubtarget().getInstrInfo();
|
|
MRI = &MF.getRegInfo();
|
|
|
|
for (MachineBasicBlock &MBB : MF)
|
|
CopyPropagateBlock(MBB);
|
|
|
|
return Changed;
|
|
}
|
|
|