Imported Upstream version 5.18.0.179

Former-commit-id: 67aa10e65b237e1c4537630979ee99ebe1374215

external/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.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineOperand.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetRegisterInfo.h"
+#include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/MC/MCRegisterInfo.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include <cassert>
+#include <iterator>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "machine-cp"
+
+STATISTIC(NumDeletes, "Number of dead copies deleted");
+
+namespace {
+
+using RegList = SmallVector<unsigned, 4>;
+using SourceMap = DenseMap<unsigned, RegList>;
+using Reg2MIMap = DenseMap<unsigned, MachineInstr *>;
+
+  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());
+    }
+
+    void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.setPreservesCFG();
+      MachineFunctionPass::getAnalysisUsage(AU);
+    }
+
+    bool runOnMachineFunction(MachineFunction &MF) override;
+
+    MachineFunctionProperties getRequiredProperties() const override {
+      return MachineFunctionProperties().set(
+          MachineFunctionProperties::Property::NoVRegs);
+    }
+
+  private:
+    void ClobberRegister(unsigned Reg);
+    void ReadRegister(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;
+  };
+
+} // end anonymous namespace
+
+char MachineCopyPropagation::ID = 0;
+
+char &llvm::MachineCopyPropagationID = MachineCopyPropagation::ID;
+
+INITIALIZE_PASS(MachineCopyPropagation, DEBUG_TYPE,
+                "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);
+    }
+  }
+}
+
+void MachineCopyPropagation::ReadRegister(unsigned Reg) {
+  // 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);
+    }
+  }
+}
+
+/// 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 (PrevCopy.getOperand(0).isDead())
+    return false;
+  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 = COPY %eax
+      //  ... nothing clobbered eax.
+      //  %eax = COPY %ecx
+      // =>
+      //  %ecx = COPY %eax
+      //
+      // or
+      //
+      //  %ecx = COPY %eax
+      //  ... nothing clobbered eax.
+      //  %ecx = COPY %eax
+      // =>
+      //  %ecx = 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.
+      ReadRegister(Src);
+      for (const MachineOperand &MO : MI->implicit_operands()) {
+        if (!MO.isReg() || !MO.readsReg())
+          continue;
+        unsigned Reg = MO.getReg();
+        if (!Reg)
+          continue;
+        ReadRegister(Reg);
+      }
+
+      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 = copy %xmm2
+      // ...
+      // %xmm2 = copy %xmm0
+      // ...
+      // %xmm2 = copy %xmm9
+      ClobberRegister(Def);
+      for (const MachineOperand &MO : MI->implicit_operands()) {
+        if (!MO.isReg() || !MO.isDef())
+          continue;
+        unsigned Reg = MO.getReg();
+        if (!Reg)
+          continue;
+        ClobberRegister(Reg);
+      }
+
+      // 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 (!is_contained(DestList, Def))
+          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;
+      } else if (MO.readsReg())
+        ReadRegister(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 (skipFunction(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;
+}