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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.
+//
+//===----------------------------------------------------------------------===//
+
+#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/ErrorHandling.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 {
+ class MachineCopyPropagation : public MachineFunctionPass {
+ const TargetRegisterInfo *TRI;
+ const TargetInstrInfo *TII;
+ MachineRegisterInfo *MRI;
+
+ public:
+ static char ID; // Pass identification, replacement for typeid
+ MachineCopyPropagation() : MachineFunctionPass(ID) {
+ initializeMachineCopyPropagationPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnMachineFunction(MachineFunction &MF) override;
+
+ private:
+ typedef SmallVector<unsigned, 4> DestList;
+ typedef DenseMap<unsigned, DestList> SourceMap;
+
+ void SourceNoLongerAvailable(unsigned Reg,
+ SourceMap &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,
+ SourceMap &SrcMap,
+ DenseMap<unsigned, MachineInstr*> &AvailCopyMap) {
+ for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
+ SourceMap::iterator SI = SrcMap.find(*AI);
+ if (SI != SrcMap.end()) {
+ const DestList& Defs = SI->second;
+ for (DestList::const_iterator I = Defs.begin(), E = Defs.end();
+ I != E; ++I) {
+ unsigned MappedDef = *I;
+ // Source of copy is no longer available for propagation.
+ AvailCopyMap.erase(MappedDef);
+ for (MCSubRegIterator SR(MappedDef, TRI); SR.isValid(); ++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
+ SourceMap SrcMap; // Src -> Def map
+
+ DEBUG(dbgs() << "MCP: CopyPropagateBlock " << MBB.getName() << "\n");
+
+ 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 (!MRI->isReserved(Def) &&
+ (!MRI->isReserved(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
+
+ DEBUG(dbgs() << "MCP: copy is a NOP, removing: "; MI->dump());
+
+ // 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.
+ for (MCRegAliasIterator AI(Src, TRI, true); AI.isValid(); ++AI) {
+ 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.
+ 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 (MCRegAliasIterator AI(Def, TRI, false); AI.isValid(); ++AI) {
+ CopyMap.erase(*AI);
+ AvailCopyMap.erase(*AI);
+ }
+ 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.
+ if (std::find(SrcMap[Src].begin(), SrcMap[Src].end(), Def) ==
+ SrcMap[Src].end()) {
+ SrcMap[Src].push_back(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.
+ for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
+ DenseMap<unsigned, MachineInstr*>::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. 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 (MRI->isReserved(Reg) || !MaskMO.clobbersPhysReg(Reg))
+ continue;
+ DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
+ (*DI)->dump());
+ (*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.
+ for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
+ CopyMap.erase(*AI);
+ AvailCopyMap.erase(*AI);
+ }
+
+ // 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 (!MRI->isReserved((*DI)->getOperand(0).getReg())) {
+ (*DI)->eraseFromParent();
+ Changed = true;
+ ++NumDeletes;
+ }
+ }
+ }
+
+ return Changed;
+}
+
+bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
+ if (skipOptnoneFunction(*MF.getFunction()))
+ return false;
+
+ bool Changed = false;
+
+ TRI = MF.getSubtarget().getRegisterInfo();
+ TII = MF.getSubtarget().getInstrInfo();
+ MRI = &MF.getRegInfo();
+
+ for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
+ Changed |= CopyPropagateBlock(*I);
+
+ return Changed;
+}
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