[Spill2Reg][2/9] This patch adds spill/reload collection.

[vporpo]

Summary

Walk through the code looking for spills and reloads and group them
per stack slot.

[vporpo]

[Spill2Reg] This patch adds spill/reload collection.

[vporpo]

Added a check that disables tha pass if NoImplicitFloat is set.

[arsenm]

llvm/lib/CodeGen/Spill2Reg.cpp

151

I wouldn't assume the memory size is the same as the register size

192

Typo spils

[vporpo]

Updated

[vporpo]

llvm/lib/CodeGen/Spill2Reg.cpp

151

Perhaps the variable name is bad. MemBits is the size of the register and we are using it later in the code generation phase to choose which insert/extract instruction to use.
Wdyt about renaming it to SpillBits ?

[vporpo]

Renamed MemBits to SpillBits and fixed typo.

[vporpo]

Ping

[Carrot]

llvm/lib/CodeGen/Spill2Reg.cpp

79

typo 'memoru'

llvm/lib/Target/X86/X86InstrInfo.cpp

9489

Instead of checking opcode, it's better to check register class.

[vporpo]

Updated isLegalToSpill2Reg() to take a reg argument instead of opcode.

[vporpo]

Rebased

[vporpo]

Replaced StackSlotDataEntry::getRegClass() with getSpilledReg().

[vporpo]

The patches have gone through a round of reviews by @Carrot . @arsenm could you also take a look ? Thanks!

[vporpo]

Rebased.

llvm/include/llvm/CodeGen/TargetInstrInfo.h

public:
   /// what the load does.
   virtual unsigned isLoadFromStackSlot(const MachineInstr &MI,
                                        int &FrameIndex,
                                        unsigned &MemBytes) const {
     MemBytes = 0;
     return isLoadFromStackSlot(MI, FrameIndex);
   }
 
+  virtual const MachineOperand *isLoadFromStackSlotMO(const MachineInstr &MI,
+                                                      int &FrameIndex) const {
+    llvm_unreachable("target did not implement");
+  }
+
   /// Check for post-frame ptr elimination stack locations as well.
   /// This uses a heuristic so it isn't reliable for correctness.
   virtual unsigned isLoadFromStackSlotPostFE(const MachineInstr &MI,
                                              int &FrameIndex) const {
     return 0;
   }
 
   /// If the specified machine instruction has a load from a stack slot,
public:
   /// the source reg along with the FrameIndex of the loaded stack slot.  If
   /// not, return 0.  This predicate must return 0 if the instruction has
   /// any side effects other than storing to the stack slot.
   virtual unsigned isStoreToStackSlot(const MachineInstr &MI,
                                       int &FrameIndex) const {
     return 0;
   }
 
+  virtual const MachineOperand *isStoreToStackSlotMO(const MachineInstr &MI,
+                                                     int &FrameIndex) const {
+    llvm_unreachable("target did not implement");
+  }
+
   /// Optional extension of isStoreToStackSlot that returns the number of
   /// bytes stored to the stack. This must be implemented if a backend
   /// supports partial stack slot spills/loads to further disambiguate
   /// what the store does.
   virtual unsigned isStoreToStackSlot(const MachineInstr &MI,
                                       int &FrameIndex,
                                       unsigned &MemBytes) const {
     MemBytes = 0;
virtual unsigned getTailDuplicateSize(CodeGenOpt::Level OptLevel) const {
     return OptLevel >= CodeGenOpt::Aggressive ? 4 : 2;
   }
 
   /// Returns the callee operand from the given \p MI.
   virtual const MachineOperand &getCalleeOperand(const MachineInstr &MI) const {
     return MI.getOperand(0);
   }
 
+  /// \Returns true if a spill/reload of \p Reg can be handled by Spill2Reg.
+  virtual bool isLegalToSpill2Reg(Register Reg, const TargetRegisterInfo *TRI,
+                                  const MachineRegisterInfo *MRI) const {
+    llvm_unreachable(
+        "Target didn't implement TargetInstrInfo::isLegalToSpill2Reg!");
+  }
+
+  virtual bool targetSupportsSpill2Reg(const TargetSubtargetInfo *STI) const {
+    return false;
+  }
+
 private:
   mutable std::unique_ptr<MIRFormatter> Formatter;
   unsigned CallFrameSetupOpcode, CallFrameDestroyOpcode;
   unsigned CatchRetOpcode;
   unsigned ReturnOpcode;
 };
 
 /// Provide DenseMapInfo for TargetInstrInfo::RegSubRegPair.

llvm/lib/CodeGen/Spill2Reg.cpp

 /// \file This file implements Spill2Reg, an optimization which selectively
 /// replaces spills/reloads to/from the stack with register copies to/from the
 /// vector register file. This works even on targets where load/stores have
 /// similar latency to register copies because it can free up memory units which
 /// helps avoid back-end stalls.
 ///
 //===----------------------------------------------------------------------===//
 
+#include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
+#include "llvm/CodeGen/TargetRegisterInfo.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
 
 using namespace llvm;
 
 namespace {
 
 class Spill2Reg : public MachineFunctionPass {
 public:
   static char ID;
   Spill2Reg() : MachineFunctionPass(ID) {
     initializeSpill2RegPass(*PassRegistry::getPassRegistry());
   }
   void getAnalysisUsage(AnalysisUsage &AU) const override;
   void releaseMemory() override;
   bool runOnMachineFunction(MachineFunction &) override;
+
+private:
+  /// Holds data for spills and reloads.
+  struct StackSlotDataEntry {
+    /// This is set to true to disable code generation for the spills/reloads
+    /// that we collected in this entry.
+    bool Disable = false;
+    /// Indentation for the dump() methods.
+    static constexpr const int DumpInd = 2;
+
+    /// The data held for each spill/reload.
+    struct MIData {
+      MIData(MachineInstr *MI, const MachineOperand *MO, unsigned SpillBits)
+          : MI(MI), MO(MO), SpillBits(SpillBits) {}
+      /// The Spill/Reload instruction.
+      MachineInstr *MI = nullptr;
+      /// The operand being spilled/reloaded.
+      const MachineOperand *MO = nullptr;
+      /// The size of the data spilled/reloaded in bits. This occasionally
+      /// differs across accesses to the same stack slot.
+      unsigned SpillBits = 0;
+#ifndef NDEBUG
+      LLVM_DUMP_METHOD void dump() const;
+#endif
+    };
+    SmallVector<MIData, 1> Spills;
+    SmallVector<MIData, 1> Reloads;
+
+    /// \Returns the register class of the register spilled/reloaded.
+    const TargetRegisterClass *getRegClass(MachineRegisterInfo *MRI) const {
+      Register SpillReg = Spills.front().MO->getReg();
+      return MRI->getRegClass(SpillReg);
+    }
+#ifndef NDEBUG
+    LLVM_DUMP_METHOD void dump() const;
+#endif
+  };
+  /// Look for candidates for spill2reg. These candidates are in places with
+  /// high memory unit contention. Fills in StackSlotData.
+  void collectSpillsAndReloads();
+  /// Replace spills to stack with spills to registers (same for reloads).
+  void generateCode();
+  /// Cleanup data structures once the pass is finished.
+  void cleanup();
+  /// The main entry point for this pass.
+  bool run();
+
+  /// Map from a stack slot to the corresponding spills and reloads.
+  DenseMap<int, StackSlotDataEntry> StackSlotData;
+
+  MachineFunction *MF = nullptr;
+  MachineRegisterInfo *MRI = nullptr;
+  MachineFrameInfo *MFI = nullptr;
+  const TargetInstrInfo *TII = nullptr;
+  const TargetRegisterInfo *TRI = nullptr;
 };
 
 } // namespace
 
 void Spill2Reg::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesCFG();
   MachineFunctionPass::getAnalysisUsage(AU);
 }
 
 void Spill2Reg::releaseMemory() {}
 
 bool Spill2Reg::runOnMachineFunction(MachineFunction &MFn) {
-  llvm_unreachable("Unimplemented");
+  // Disable if NoImplicitFloat to avoid emitting instrs that use vectors.
+  if (MFn.getFunction().hasFnAttribute(Attribute::NoImplicitFloat))
+    return false;
+
+  MF = &MFn;
+  MRI = &MF->getRegInfo();
+  MFI = &MF->getFrameInfo();
+  TII = MF->getSubtarget().getInstrInfo();
+  TRI = MF->getSubtarget().getRegisterInfo();
+  // Enable only if the target supports the appropriate vector instruction set.
+  if (!TII->targetSupportsSpill2Reg(&MF->getSubtarget()))
+    return false;
+
+  return run();
 }
 
 char Spill2Reg::ID = 0;
 
 char &llvm::Spill2RegID = Spill2Reg::ID;
 
+void Spill2Reg::collectSpillsAndReloads() {
+  /// The checks for collecting spills and reloads are identical, so we keep
+  /// them here in one place. Return true if we should not collect this.
+  auto SkipEntry = [this](int StackSlot, Register Reg) -> bool {
+    // If not a spill/reload stack slot.
+    if (!MFI->isSpillSlotObjectIndex(StackSlot))
+      return true;
+    // Check size in bits.
+    if (!TII->isLegalToSpill2Reg(Reg, TRI, MRI))
+      return true;
+    return false;
+  };
+
+  // Collect spills and reloads and associate them to stack slots.
+  // If any spill/reload for a stack slot is found not to be eligible for
+  // spill-to-reg, then that stack slot is disabled.
+  for (MachineBasicBlock &MBB : *MF) {
+    for (MachineInstr &MI : MBB) {
+      int StackSlot;
+      if (const MachineOperand *MO = TII->isStoreToStackSlotMO(MI, StackSlot)) {
+        MachineInstr *Spill = &MI;
+        auto &Entry = StackSlotData[StackSlot];
+        if (SkipEntry(StackSlot, MO->getReg())) {
+          Entry.Disable = true;
+          continue;
+        }
+        unsigned SpillBits = TRI->getRegSizeInBits(MO->getReg(), *MRI);
+        Entry.Spills.emplace_back(Spill, MO, SpillBits);
+      } else if (const MachineOperand *MO =
+                     TII->isLoadFromStackSlotMO(MI, StackSlot)) {
+        MachineInstr *Reload = &MI;
+        auto &Entry = StackSlotData[StackSlot];
+        if (SkipEntry(StackSlot, MO->getReg())) {
+          Entry.Disable = true;
+          continue;
+        }
+        assert(Reload->getRestoreSize(TII) && "Expected reload");
+        unsigned SpillBits = TRI->getRegSizeInBits(MO->getReg(), *MRI);
+        Entry.Reloads.emplace_back(Reload, MO, SpillBits);
+      } else {
+        // This should capture uses of the stack in instructions that access
+        // memory (e.g., folded spills/reloads) and non-memory instructions,
+        // like x86 LEA.
+        for (const MachineOperand &MO : MI.operands())
+          if (MO.isFI()) {
+            int StackSlot = MO.getIndex();
+            auto &Entry = StackSlotData[StackSlot];
+            Entry.Disable = true;
+          }
+      }
+    }
+  }
+}
+
+void Spill2Reg::generateCode() { llvm_unreachable("Unimplemented"); }
+
+void Spill2Reg::cleanup() { StackSlotData.clear(); }
+
+bool Spill2Reg::run() {
+  // Walk over each instruction in the code keeping track of the processor's
+  // port pressure and look for memory unit hot-spots.
+  collectSpillsAndReloads();
+
+  // Replace each spills/reloads to stack slots with register spills/reloads.
+  generateCode();
+
+  cleanup();
+  return true;
+}
+
+#ifndef NDEBUG
+void Spill2Reg::StackSlotDataEntry::MIData::dump() const {
+  dbgs() << "  (" << *MO << ") " << *MI;
+}
+
+void Spill2Reg::StackSlotDataEntry::dump() const {
+  dbgs().indent(DumpInd) << "Disable: " << Disable << "\n";
+  dbgs().indent(DumpInd) << "Spills:\n";
+  for (const MIData &Data : Spills)
+    Data.dump();
+  dbgs().indent(DumpInd) << "Reloads:\n";
+  for (const MIData &Data : Reloads)
+    Data.dump();
+}
+#endif
+
 INITIALIZE_PASS_BEGIN(Spill2Reg, "spill2reg", "Spill2Reg", false, false)
 INITIALIZE_PASS_END(Spill2Reg, "spill2reg", "Spill2Reg", false, false)

llvm/lib/Target/X86/X86InstrInfo.h

public:
   /// an indirect jump -- the destination is loaded into icache based on the
   /// bits set in the jump destination register.
   ///
   /// FIXME: This should become part of our instruction tables.
   static bool isDataInvariantLoad(MachineInstr &MI);
 
   unsigned isLoadFromStackSlot(const MachineInstr &MI,
                                int &FrameIndex) const override;
+
+  const MachineOperand *isLoadFromStackSlotMO(const MachineInstr &MI,
+                                              int &FrameIndex,
+                                              unsigned &MemBytes) const;
+
+  const MachineOperand *isLoadFromStackSlotMO(const MachineInstr &MI,
+                                              int &FrameIndex) const override;
+
   unsigned isLoadFromStackSlot(const MachineInstr &MI,
                                int &FrameIndex,
                                unsigned &MemBytes) const override;
   /// isLoadFromStackSlotPostFE - Check for post-frame ptr elimination
   /// stack locations as well.  This uses a heuristic so it isn't
   /// reliable for correctness.
   unsigned isLoadFromStackSlotPostFE(const MachineInstr &MI,
                                      int &FrameIndex) const override;
 
   unsigned isStoreToStackSlot(const MachineInstr &MI,
                               int &FrameIndex) const override;
+
+  const MachineOperand *isStoreToStackSlotMO(const MachineInstr &MI,
+                                             int &FrameIndex,
+                                             unsigned &MemBytes) const;
+
+  const MachineOperand *isStoreToStackSlotMO(const MachineInstr &MI,
+                                             int &FrameIndex) const override;
+
   unsigned isStoreToStackSlot(const MachineInstr &MI,
                               int &FrameIndex,
                               unsigned &MemBytes) const override;
   /// isStoreToStackSlotPostFE - Check for post-frame ptr elimination
   /// stack locations as well.  This uses a heuristic so it isn't
   /// reliable for correctness.
   unsigned isStoreToStackSlotPostFE(const MachineInstr &MI,
                                     int &FrameIndex) const override;
private:
   ///   CMP %1, 42   and  CMP %1, 42
   ///   CMP %1, %2   and  %3 = SUB %1, %2
   ///   TEST %1, %1  and  %2 = SUB %1, 0
   ///   CMP %1, %2   and  %3 = SUB %2, %1  ; IsSwapped=true
   bool isRedundantFlagInstr(const MachineInstr &FlagI, Register SrcReg,
                             Register SrcReg2, int64_t ImmMask, int64_t ImmValue,
                             const MachineInstr &OI, bool *IsSwapped,
                             int64_t *ImmDelta) const;
+
+  bool isLegalToSpill2Reg(Register Reg, const TargetRegisterInfo *TRI,
+                          const MachineRegisterInfo *MRI) const override;
+
+  bool targetSupportsSpill2Reg(const TargetSubtargetInfo *STI) const override;
 };
 
 } // namespace llvm
 
 #endif

llvm/lib/Target/X86/X86InstrInfo.cpp

 }
 
 unsigned X86InstrInfo::isLoadFromStackSlot(const MachineInstr &MI,
                                            int &FrameIndex) const {
   unsigned Dummy;
   return X86InstrInfo::isLoadFromStackSlot(MI, FrameIndex, Dummy);
 }
 
-unsigned X86InstrInfo::isLoadFromStackSlot(const MachineInstr &MI,
-                                           int &FrameIndex,
-                                           unsigned &MemBytes) const {
+const MachineOperand *
+X86InstrInfo::isLoadFromStackSlotMO(const MachineInstr &MI, int &FrameIndex,
   if (isFrameLoadOpcode(MI.getOpcode(), MemBytes))
     if (MI.getOperand(0).getSubReg() == 0 && isFrameOperand(MI, 1, FrameIndex))
-      return MI.getOperand(0).getReg();
-  return 0;
+      return &MI.getOperand(0);
+  return nullptr;
+}
+
+const MachineOperand *
+X86InstrInfo::isLoadFromStackSlotMO(const MachineInstr &MI,
+                                    int &FrameIndex) const {
+  unsigned UnusedMemBytes;
+  return isLoadFromStackSlotMO(MI, FrameIndex, UnusedMemBytes);
+}
+
+unsigned X86InstrInfo::isLoadFromStackSlot(const MachineInstr &MI,
+                                           int &FrameIndex,
+                                           unsigned &MemBytes) const {
+  const MachineOperand *MO = isLoadFromStackSlotMO(MI, FrameIndex, MemBytes);
+  return MO != nullptr ? (unsigned)MO->getReg() : 0;
 }
 
 unsigned X86InstrInfo::isLoadFromStackSlotPostFE(const MachineInstr &MI,
                                                  int &FrameIndex) const {
   unsigned Dummy;
   if (isFrameLoadOpcode(MI.getOpcode(), Dummy)) {
     unsigned Reg;
     if ((Reg = isLoadFromStackSlot(MI, FrameIndex)))

 }
 
 unsigned X86InstrInfo::isStoreToStackSlot(const MachineInstr &MI,
                                           int &FrameIndex) const {
   unsigned Dummy;
   return X86InstrInfo::isStoreToStackSlot(MI, FrameIndex, Dummy);
 }
 
-unsigned X86InstrInfo::isStoreToStackSlot(const MachineInstr &MI,
-                                          int &FrameIndex,
-                                          unsigned &MemBytes) const {
+const MachineOperand *
+X86InstrInfo::isStoreToStackSlotMO(const MachineInstr &MI, int &FrameIndex,
   if (isFrameStoreOpcode(MI.getOpcode(), MemBytes))
     if (MI.getOperand(X86::AddrNumOperands).getSubReg() == 0 &&
         isFrameOperand(MI, 0, FrameIndex))
-      return MI.getOperand(X86::AddrNumOperands).getReg();
-  return 0;
+      return &MI.getOperand(X86::AddrNumOperands);
+  return nullptr;
+}
+
+const MachineOperand *
+X86InstrInfo::isStoreToStackSlotMO(const MachineInstr &MI,
+                                   int &FrameIndex) const {
+  unsigned UnusedMemBytes;
+  return isStoreToStackSlotMO(MI, FrameIndex, UnusedMemBytes);
+}
+
+unsigned X86InstrInfo::isStoreToStackSlot(const MachineInstr &MI,
+                                          int &FrameIndex,
+                                          unsigned &MemBytes) const {
+  const MachineOperand *MO = isStoreToStackSlotMO(MI, FrameIndex, MemBytes);
+  return MO != nullptr ? (unsigned)MO->getReg() : 0;
 }
 
 unsigned X86InstrInfo::isStoreToStackSlotPostFE(const MachineInstr &MI,
                                                 int &FrameIndex) const {
   unsigned Dummy;
   if (isFrameStoreOpcode(MI.getOpcode(), Dummy)) {
     unsigned Reg;
     if ((Reg = isStoreToStackSlot(MI, FrameIndex)))
if (C.CallConstructionID == MachineOutlinerTailCall) {
     It = MBB.insert(It,
                   BuildMI(MF, DebugLoc(), get(X86::CALL64pcrel32))
                       .addGlobalAddress(M.getNamedValue(MF.getName())));
   }
 
   return It;
 }
 
+bool X86InstrInfo::isLegalToSpill2Reg(Register Reg,
+                                      const TargetRegisterInfo *TRI,
+                                      const MachineRegisterInfo *MRI) const {
+  // Skip instructions like `$k1 = KMOVWkm %stack.1` because replacing stack
+  // with xmm0 results in an illegal instruction `movq  %k1, %xmm0`.
+  if (X86::VK16RegClass.contains(Reg))
+    return false;
+
+  switch (unsigned Bits = TRI->getRegSizeInBits(Reg, *MRI)) {
+  case 64:
+  case 32:
+    return true;
+  }
+  return false;
+}
+
+bool X86InstrInfo::targetSupportsSpill2Reg(
+    const TargetSubtargetInfo *STI) const {
+  const X86Subtarget *X86STI = static_cast<const X86Subtarget *>(STI);
+  return X86STI->hasSSE41();
+}
+
 #define GET_INSTRINFO_HELPERS
 #include "X86GenInstrInfo.inc"