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961f3df27b
As part of the unification of the debug format and the MIR format, always print registers as lowercase. * Only debug printing is affected. It now follows MIR. Differential Revision: https://reviews.llvm.org/D40417 llvm-svn: 319187
396 lines
13 KiB
C++
396 lines
13 KiB
C++
//===- MachineCopyPropagation.cpp - Machine Copy Propagation Pass ---------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This is an extremely simple MachineInstr-level copy propagation pass.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/iterator_range.h"
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineOperand.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/TargetInstrInfo.h"
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#include "llvm/CodeGen/TargetRegisterInfo.h"
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#include "llvm/CodeGen/TargetSubtargetInfo.h"
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#include "llvm/MC/MCRegisterInfo.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include <cassert>
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#include <iterator>
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using namespace llvm;
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#define DEBUG_TYPE "machine-cp"
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STATISTIC(NumDeletes, "Number of dead copies deleted");
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namespace {
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using RegList = SmallVector<unsigned, 4>;
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using SourceMap = DenseMap<unsigned, RegList>;
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using Reg2MIMap = DenseMap<unsigned, MachineInstr *>;
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class MachineCopyPropagation : public MachineFunctionPass {
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const TargetRegisterInfo *TRI;
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const TargetInstrInfo *TII;
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const MachineRegisterInfo *MRI;
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public:
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static char ID; // Pass identification, replacement for typeid
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MachineCopyPropagation() : MachineFunctionPass(ID) {
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initializeMachineCopyPropagationPass(*PassRegistry::getPassRegistry());
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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bool runOnMachineFunction(MachineFunction &MF) override;
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MachineFunctionProperties getRequiredProperties() const override {
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return MachineFunctionProperties().set(
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MachineFunctionProperties::Property::NoVRegs);
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}
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private:
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void ClobberRegister(unsigned Reg);
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void ReadRegister(unsigned Reg);
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void CopyPropagateBlock(MachineBasicBlock &MBB);
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bool eraseIfRedundant(MachineInstr &Copy, unsigned Src, unsigned Def);
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/// Candidates for deletion.
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SmallSetVector<MachineInstr*, 8> MaybeDeadCopies;
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/// Def -> available copies map.
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Reg2MIMap AvailCopyMap;
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/// Def -> copies map.
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Reg2MIMap CopyMap;
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/// Src -> Def map
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SourceMap SrcMap;
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bool Changed;
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};
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} // end anonymous namespace
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char MachineCopyPropagation::ID = 0;
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char &llvm::MachineCopyPropagationID = MachineCopyPropagation::ID;
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INITIALIZE_PASS(MachineCopyPropagation, DEBUG_TYPE,
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"Machine Copy Propagation Pass", false, false)
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/// Remove any entry in \p Map where the register is a subregister or equal to
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/// a register contained in \p Regs.
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static void removeRegsFromMap(Reg2MIMap &Map, const RegList &Regs,
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const TargetRegisterInfo &TRI) {
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for (unsigned Reg : Regs) {
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// Source of copy is no longer available for propagation.
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for (MCSubRegIterator SR(Reg, &TRI, true); SR.isValid(); ++SR)
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Map.erase(*SR);
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}
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}
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/// Remove any entry in \p Map that is marked clobbered in \p RegMask.
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/// The map will typically have a lot fewer entries than the regmask clobbers,
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/// so this is more efficient than iterating the clobbered registers and calling
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/// ClobberRegister() on them.
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static void removeClobberedRegsFromMap(Reg2MIMap &Map,
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const MachineOperand &RegMask) {
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for (Reg2MIMap::iterator I = Map.begin(), E = Map.end(), Next; I != E;
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I = Next) {
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Next = std::next(I);
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unsigned Reg = I->first;
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if (RegMask.clobbersPhysReg(Reg))
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Map.erase(I);
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}
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}
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void MachineCopyPropagation::ClobberRegister(unsigned Reg) {
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for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
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CopyMap.erase(*AI);
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AvailCopyMap.erase(*AI);
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SourceMap::iterator SI = SrcMap.find(*AI);
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if (SI != SrcMap.end()) {
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removeRegsFromMap(AvailCopyMap, SI->second, *TRI);
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SrcMap.erase(SI);
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}
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}
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}
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void MachineCopyPropagation::ReadRegister(unsigned Reg) {
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// If 'Reg' is defined by a copy, the copy is no longer a candidate
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// for elimination.
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for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
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Reg2MIMap::iterator CI = CopyMap.find(*AI);
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if (CI != CopyMap.end()) {
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DEBUG(dbgs() << "MCP: Copy is used - not dead: "; CI->second->dump());
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MaybeDeadCopies.remove(CI->second);
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}
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}
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}
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/// Return true if \p PreviousCopy did copy register \p Src to register \p Def.
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/// This fact may have been obscured by sub register usage or may not be true at
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/// all even though Src and Def are subregisters of the registers used in
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/// PreviousCopy. e.g.
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/// isNopCopy("ecx = COPY eax", AX, CX) == true
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/// isNopCopy("ecx = COPY eax", AH, CL) == false
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static bool isNopCopy(const MachineInstr &PreviousCopy, unsigned Src,
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unsigned Def, const TargetRegisterInfo *TRI) {
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unsigned PreviousSrc = PreviousCopy.getOperand(1).getReg();
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unsigned PreviousDef = PreviousCopy.getOperand(0).getReg();
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if (Src == PreviousSrc) {
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assert(Def == PreviousDef);
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return true;
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}
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if (!TRI->isSubRegister(PreviousSrc, Src))
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return false;
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unsigned SubIdx = TRI->getSubRegIndex(PreviousSrc, Src);
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return SubIdx == TRI->getSubRegIndex(PreviousDef, Def);
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}
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/// Remove instruction \p Copy if there exists a previous copy that copies the
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/// register \p Src to the register \p Def; This may happen indirectly by
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/// copying the super registers.
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bool MachineCopyPropagation::eraseIfRedundant(MachineInstr &Copy, unsigned Src,
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unsigned Def) {
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// Avoid eliminating a copy from/to a reserved registers as we cannot predict
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// the value (Example: The sparc zero register is writable but stays zero).
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if (MRI->isReserved(Src) || MRI->isReserved(Def))
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return false;
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// Search for an existing copy.
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Reg2MIMap::iterator CI = AvailCopyMap.find(Def);
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if (CI == AvailCopyMap.end())
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return false;
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// Check that the existing copy uses the correct sub registers.
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MachineInstr &PrevCopy = *CI->second;
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if (PrevCopy.getOperand(0).isDead())
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return false;
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if (!isNopCopy(PrevCopy, Src, Def, TRI))
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return false;
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DEBUG(dbgs() << "MCP: copy is a NOP, removing: "; Copy.dump());
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// Copy was redundantly redefining either Src or Def. Remove earlier kill
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// flags between Copy and PrevCopy because the value will be reused now.
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assert(Copy.isCopy());
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unsigned CopyDef = Copy.getOperand(0).getReg();
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assert(CopyDef == Src || CopyDef == Def);
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for (MachineInstr &MI :
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make_range(PrevCopy.getIterator(), Copy.getIterator()))
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MI.clearRegisterKills(CopyDef, TRI);
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Copy.eraseFromParent();
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Changed = true;
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++NumDeletes;
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return true;
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}
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void MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
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DEBUG(dbgs() << "MCP: CopyPropagateBlock " << MBB.getName() << "\n");
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for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ) {
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MachineInstr *MI = &*I;
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++I;
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if (MI->isCopy()) {
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unsigned Def = MI->getOperand(0).getReg();
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unsigned Src = MI->getOperand(1).getReg();
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assert(!TargetRegisterInfo::isVirtualRegister(Def) &&
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!TargetRegisterInfo::isVirtualRegister(Src) &&
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"MachineCopyPropagation should be run after register allocation!");
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// The two copies cancel out and the source of the first copy
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// hasn't been overridden, eliminate the second one. e.g.
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// %ecx<def> = COPY %eax
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// ... nothing clobbered eax.
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// %eax<def> = COPY %ecx
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// =>
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// %ecx<def> = COPY %eax
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//
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// or
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//
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// %ecx<def> = COPY %eax
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// ... nothing clobbered eax.
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// %ecx<def> = COPY %eax
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// =>
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// %ecx<def> = COPY %eax
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if (eraseIfRedundant(*MI, Def, Src) || eraseIfRedundant(*MI, Src, Def))
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continue;
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// If Src is defined by a previous copy, the previous copy cannot be
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// eliminated.
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ReadRegister(Src);
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for (const MachineOperand &MO : MI->implicit_operands()) {
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if (!MO.isReg() || !MO.readsReg())
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continue;
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unsigned Reg = MO.getReg();
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if (!Reg)
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continue;
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ReadRegister(Reg);
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}
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DEBUG(dbgs() << "MCP: Copy is a deletion candidate: "; MI->dump());
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// Copy is now a candidate for deletion.
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if (!MRI->isReserved(Def))
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MaybeDeadCopies.insert(MI);
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// If 'Def' is previously source of another copy, then this earlier copy's
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// source is no longer available. e.g.
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// %xmm9<def> = copy %xmm2
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// ...
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// %xmm2<def> = copy %xmm0
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// ...
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// %xmm2<def> = copy %xmm9
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ClobberRegister(Def);
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for (const MachineOperand &MO : MI->implicit_operands()) {
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if (!MO.isReg() || !MO.isDef())
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continue;
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unsigned Reg = MO.getReg();
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if (!Reg)
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continue;
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ClobberRegister(Reg);
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}
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// Remember Def is defined by the copy.
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for (MCSubRegIterator SR(Def, TRI, /*IncludeSelf=*/true); SR.isValid();
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++SR) {
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CopyMap[*SR] = MI;
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AvailCopyMap[*SR] = MI;
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}
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// Remember source that's copied to Def. Once it's clobbered, then
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// it's no longer available for copy propagation.
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RegList &DestList = SrcMap[Src];
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if (!is_contained(DestList, Def))
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DestList.push_back(Def);
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continue;
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}
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// Not a copy.
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SmallVector<unsigned, 2> Defs;
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const MachineOperand *RegMask = nullptr;
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for (const MachineOperand &MO : MI->operands()) {
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if (MO.isRegMask())
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RegMask = &MO;
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if (!MO.isReg())
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continue;
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unsigned Reg = MO.getReg();
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if (!Reg)
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continue;
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assert(!TargetRegisterInfo::isVirtualRegister(Reg) &&
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"MachineCopyPropagation should be run after register allocation!");
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if (MO.isDef()) {
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Defs.push_back(Reg);
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continue;
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} else if (MO.readsReg())
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ReadRegister(Reg);
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}
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// The instruction has a register mask operand which means that it clobbers
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// a large set of registers. Treat clobbered registers the same way as
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// defined registers.
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if (RegMask) {
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// Erase any MaybeDeadCopies whose destination register is clobbered.
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for (SmallSetVector<MachineInstr *, 8>::iterator DI =
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MaybeDeadCopies.begin();
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DI != MaybeDeadCopies.end();) {
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MachineInstr *MaybeDead = *DI;
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unsigned Reg = MaybeDead->getOperand(0).getReg();
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assert(!MRI->isReserved(Reg));
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if (!RegMask->clobbersPhysReg(Reg)) {
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++DI;
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continue;
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}
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DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
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MaybeDead->dump());
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// erase() will return the next valid iterator pointing to the next
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// element after the erased one.
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DI = MaybeDeadCopies.erase(DI);
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MaybeDead->eraseFromParent();
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Changed = true;
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++NumDeletes;
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}
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removeClobberedRegsFromMap(AvailCopyMap, *RegMask);
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removeClobberedRegsFromMap(CopyMap, *RegMask);
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for (SourceMap::iterator I = SrcMap.begin(), E = SrcMap.end(), Next;
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I != E; I = Next) {
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Next = std::next(I);
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if (RegMask->clobbersPhysReg(I->first)) {
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removeRegsFromMap(AvailCopyMap, I->second, *TRI);
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SrcMap.erase(I);
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}
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}
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}
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// Any previous copy definition or reading the Defs is no longer available.
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for (unsigned Reg : Defs)
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ClobberRegister(Reg);
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}
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// If MBB doesn't have successors, delete the copies whose defs are not used.
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// If MBB does have successors, then conservative assume the defs are live-out
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// since we don't want to trust live-in lists.
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if (MBB.succ_empty()) {
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for (MachineInstr *MaybeDead : MaybeDeadCopies) {
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assert(!MRI->isReserved(MaybeDead->getOperand(0).getReg()));
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MaybeDead->eraseFromParent();
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Changed = true;
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++NumDeletes;
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}
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}
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MaybeDeadCopies.clear();
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AvailCopyMap.clear();
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CopyMap.clear();
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SrcMap.clear();
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}
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bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
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if (skipFunction(*MF.getFunction()))
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return false;
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Changed = false;
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TRI = MF.getSubtarget().getRegisterInfo();
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TII = MF.getSubtarget().getInstrInfo();
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MRI = &MF.getRegInfo();
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for (MachineBasicBlock &MBB : MF)
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CopyPropagateBlock(MBB);
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return Changed;
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}
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