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

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//===- 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "codegen-cp"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Pass.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumDeletes, "Number of dead copies deleted");
namespace {
class MachineCopyPropagation : public MachineFunctionPass {
const TargetRegisterInfo *TRI;
BitVector ReservedRegs;
public:
static char ID; // Pass identification, replacement for typeid
MachineCopyPropagation() : MachineFunctionPass(ID) {
initializeMachineCopyPropagationPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnMachineFunction(MachineFunction &MF);
private:
void SourceNoLongerAvailable(unsigned Reg,
DenseMap<unsigned, unsigned> &SrcMap,
DenseMap<unsigned, MachineInstr*> &AvailCopyMap);
bool CopyPropagateBlock(MachineBasicBlock &MBB);
};
}
char MachineCopyPropagation::ID = 0;
char &llvm::MachineCopyPropagationID = MachineCopyPropagation::ID;
INITIALIZE_PASS(MachineCopyPropagation, "machine-cp",
"Machine Copy Propagation Pass", false, false)
void
MachineCopyPropagation::SourceNoLongerAvailable(unsigned Reg,
DenseMap<unsigned, unsigned> &SrcMap,
DenseMap<unsigned, MachineInstr*> &AvailCopyMap) {
DenseMap<unsigned, unsigned>::iterator SI = SrcMap.find(Reg);
if (SI != SrcMap.end()) {
unsigned MappedDef = SI->second;
// Source of copy is no longer available for propagation.
if (AvailCopyMap.erase(MappedDef)) {
for (const uint16_t *SR = TRI->getSubRegisters(MappedDef); *SR; ++SR)
AvailCopyMap.erase(*SR);
}
}
for (const uint16_t *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
SI = SrcMap.find(*AS);
if (SI != SrcMap.end()) {
unsigned MappedDef = SI->second;
if (AvailCopyMap.erase(MappedDef)) {
for (const uint16_t *SR = TRI->getSubRegisters(MappedDef); *SR; ++SR)
AvailCopyMap.erase(*SR);
}
}
}
}
static bool NoInterveningSideEffect(const MachineInstr *CopyMI,
const MachineInstr *MI) {
const MachineBasicBlock *MBB = CopyMI->getParent();
if (MI->getParent() != MBB)
return false;
MachineBasicBlock::const_iterator I = CopyMI;
MachineBasicBlock::const_iterator E = MBB->end();
MachineBasicBlock::const_iterator E2 = MI;
++I;
while (I != E && I != E2) {
if (I->hasUnmodeledSideEffects() || I->isCall() ||
I->isTerminator())
return false;
++I;
}
return true;
}
/// isNopCopy - Return true if the specified copy is really a nop. That is
/// if the source of the copy is the same of the definition of the copy that
/// supplied the source. If the source of the copy is a sub-register than it
/// must check the sub-indices match. e.g.
/// ecx = mov eax
/// al = mov cl
/// But not
/// ecx = mov eax
/// al = mov ch
static bool isNopCopy(MachineInstr *CopyMI, unsigned Def, unsigned Src,
const TargetRegisterInfo *TRI) {
unsigned SrcSrc = CopyMI->getOperand(1).getReg();
if (Def == SrcSrc)
return true;
if (TRI->isSubRegister(SrcSrc, Def)) {
unsigned SrcDef = CopyMI->getOperand(0).getReg();
unsigned SubIdx = TRI->getSubRegIndex(SrcSrc, Def);
if (!SubIdx)
return false;
return SubIdx == TRI->getSubRegIndex(SrcDef, Src);
}
return false;
}
bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
SmallSetVector<MachineInstr*, 8> MaybeDeadCopies; // Candidates for deletion
DenseMap<unsigned, MachineInstr*> AvailCopyMap; // Def -> available copies map
DenseMap<unsigned, MachineInstr*> CopyMap; // Def -> copies map
DenseMap<unsigned, unsigned> SrcMap; // Src -> Def map
bool Changed = false;
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();
if (TargetRegisterInfo::isVirtualRegister(Def) ||
TargetRegisterInfo::isVirtualRegister(Src))
report_fatal_error("MachineCopyPropagation should be run after"
" register allocation!");
DenseMap<unsigned, MachineInstr*>::iterator CI = AvailCopyMap.find(Src);
if (CI != AvailCopyMap.end()) {
MachineInstr *CopyMI = CI->second;
if (!ReservedRegs.test(Def) &&
(!ReservedRegs.test(Src) || NoInterveningSideEffect(CopyMI, MI)) &&
isNopCopy(CopyMI, Def, Src, TRI)) {
// 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<kill>
// ... nothing clobbered EAX.
// %EAX<def> = COPY %ECX
// =>
// %ECX<def> = COPY %EAX
//
// Also avoid eliminating a copy from reserved registers unless the
// definition is proven not clobbered. e.g.
// %RSP<def> = COPY %RAX
// CALL
// %RAX<def> = COPY %RSP
// Clear any kills of Def between CopyMI and MI. This extends the
// live range.
for (MachineBasicBlock::iterator I = CopyMI, E = MI; I != E; ++I)
I->clearRegisterKills(Def, TRI);
MI->eraseFromParent();
Changed = true;
++NumDeletes;
continue;
}
}
// If Src is defined by a previous copy, it cannot be eliminated.
CI = CopyMap.find(Src);
if (CI != CopyMap.end())
MaybeDeadCopies.remove(CI->second);
for (const uint16_t *AS = TRI->getAliasSet(Src); *AS; ++AS) {
CI = CopyMap.find(*AS);
if (CI != CopyMap.end())
MaybeDeadCopies.remove(CI->second);
}
// Copy is now a candidate for deletion.
MaybeDeadCopies.insert(MI);
// If 'Src' 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
SourceNoLongerAvailable(Def, SrcMap, AvailCopyMap);
// Remember Def is defined by the copy.
// ... Make sure to clear the def maps of aliases first.
for (const uint16_t *AS = TRI->getAliasSet(Def); *AS; ++AS) {
CopyMap.erase(*AS);
AvailCopyMap.erase(*AS);
}
CopyMap[Def] = MI;
AvailCopyMap[Def] = MI;
for (const uint16_t *SR = TRI->getSubRegisters(Def); *SR; ++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.
SrcMap[Src] = Def;
continue;
}
// Not a copy.
SmallVector<unsigned, 2> Defs;
int RegMaskOpNum = -1;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isRegMask())
RegMaskOpNum = i;
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (!Reg)
continue;
if (TargetRegisterInfo::isVirtualRegister(Reg))
report_fatal_error("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.
DenseMap<unsigned, MachineInstr*>::iterator CI = CopyMap.find(Reg);
if (CI != CopyMap.end())
MaybeDeadCopies.remove(CI->second);
for (const uint16_t *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
CI = CopyMap.find(*AS);
if (CI != CopyMap.end())
MaybeDeadCopies.remove(CI->second);
}
}
// The instruction has a register mask operand which means that it clobbers
// a large set of registers. It is possible to use the register mask to
// prune the available copies, but treat it like a basic block boundary for
// now.
if (RegMaskOpNum >= 0) {
// Erase any MaybeDeadCopies whose destination register is clobbered.
const MachineOperand &MaskMO = MI->getOperand(RegMaskOpNum);
for (SmallSetVector<MachineInstr*, 8>::iterator
DI = MaybeDeadCopies.begin(), DE = MaybeDeadCopies.end();
DI != DE; ++DI) {
unsigned Reg = (*DI)->getOperand(0).getReg();
if (ReservedRegs.test(Reg) || !MaskMO.clobbersPhysReg(Reg))
continue;
(*DI)->eraseFromParent();
Changed = true;
++NumDeletes;
}
// Clear all data structures as if we were beginning a new basic block.
MaybeDeadCopies.clear();
AvailCopyMap.clear();
CopyMap.clear();
SrcMap.clear();
continue;
}
for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
unsigned Reg = Defs[i];
// No longer defined by a copy.
CopyMap.erase(Reg);
AvailCopyMap.erase(Reg);
for (const uint16_t *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
CopyMap.erase(*AS);
AvailCopyMap.erase(*AS);
}
// If 'Reg' is previously source of a copy, it is no longer available for
// copy propagation.
SourceNoLongerAvailable(Reg, SrcMap, AvailCopyMap);
}
}
// 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 (SmallSetVector<MachineInstr*, 8>::iterator
DI = MaybeDeadCopies.begin(), DE = MaybeDeadCopies.end();
DI != DE; ++DI) {
if (!ReservedRegs.test((*DI)->getOperand(0).getReg())) {
(*DI)->eraseFromParent();
Changed = true;
++NumDeletes;
}
}
}
return Changed;
}
bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
bool Changed = false;
TRI = MF.getTarget().getRegisterInfo();
ReservedRegs = TRI->getReservedRegs(MF);
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
Changed |= CopyPropagateBlock(*I);
return Changed;
}
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