[AArch64] Split bitmask immediate of bitwise AND operation

MOVi32imm + ANDWrr ==> ANDWri + ANDWri
MOVi64imm + ANDXrr ==> ANDXri + ANDXri

The mov pseudo instruction could be expanded to multiple mov instructions later.
In this case, try to split the constant operand of mov instruction into two
bitmask immediates. It makes only two AND instructions intead of multiple
mov + and instructions.

Added a peephole optimization pass on MIR level to implement it.

Differential Revision: https://reviews.llvm.org/D109963

llvm/lib/Target/AArch64/AArch64.h

@@ -51,6 +51,7 @@ FunctionPass *createAArch64A53Fix835769();
 FunctionPass *createFalkorHWPFFixPass();
 FunctionPass *createFalkorMarkStridedAccessesPass();
 FunctionPass *createAArch64BranchTargetsPass();
+FunctionPass *createAArch64MIPeepholeOptPass();
 
 FunctionPass *createAArch64CleanupLocalDynamicTLSPass();
 
@@ -82,6 +83,7 @@ void initializeAArch64SLSHardeningPass(PassRegistry&);
 void initializeAArch64SpeculationHardeningPass(PassRegistry&);
 void initializeAArch64LoadStoreOptPass(PassRegistry&);
 void initializeAArch64LowerHomogeneousPrologEpilogPass(PassRegistry &);
+void initializeAArch64MIPeepholeOptPass(PassRegistry &);
 void initializeAArch64SIMDInstrOptPass(PassRegistry&);
 void initializeAArch64O0PreLegalizerCombinerPass(PassRegistry &);
 void initializeAArch64PreLegalizerCombinerPass(PassRegistry&);

llvm/lib/Target/AArch64/AArch64MIPeepholeOpt.cpp

@@ -0,0 +1,213 @@
+//===- AArch64MIPeepholeOpt.cpp - AArch64 MI peephole optimization pass ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs below peephole optimizations on MIR level.
+//
+// 1. MOVi32imm + ANDWrr ==> ANDWri + ANDWri
+//    MOVi64imm + ANDXrr ==> ANDXri + ANDXri
+//
+//    The mov pseudo instruction could be expanded to multiple mov instructions
+//    later. In this case, we could try to split the constant  operand of mov
+//    instruction into two bitmask immediates. It makes two AND instructions
+//    intead of multiple `mov` + `and` instructions.
+//===----------------------------------------------------------------------===//
+
+#include "AArch64ExpandImm.h"
+#include "AArch64InstrInfo.h"
+#include "MCTargetDesc/AArch64AddressingModes.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "aarch64-mi-peephole-opt"
+
+namespace {
+
+struct AArch64MIPeepholeOpt : public MachineFunctionPass {
+  static char ID;
+
+  AArch64MIPeepholeOpt() : MachineFunctionPass(ID) {
+    initializeAArch64MIPeepholeOptPass(*PassRegistry::getPassRegistry());
+  }
+
+  const AArch64InstrInfo *TII;
+  MachineLoopInfo *MLI;
+  MachineRegisterInfo *MRI;
+
+  template <typename T>
+  bool visitAND(MachineInstr &MI,
+                SmallSetVector<MachineInstr *, 8> &ToBeRemoved);
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  StringRef getPassName() const override {
+    return "AArch64 MI Peephole Optimization pass";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    AU.addRequired<MachineLoopInfo>();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+};
+
+char AArch64MIPeepholeOpt::ID = 0;
+
+} // end anonymous namespace
+
+INITIALIZE_PASS(AArch64MIPeepholeOpt, "aarch64-mi-peephole-opt",
+                "AArch64 MI Peephole Optimization", false, false)
+
+template <typename T>
+static bool splitBitmaskImm(T Imm, unsigned RegSize, T &Imm1Enc, T &Imm2Enc) {
+  T UImm = static_cast<T>(Imm);
+  if (AArch64_AM::isLogicalImmediate(UImm, RegSize))
+    return false;
+
+  // If this immediate can be handled by one instruction, do not split it.
+  SmallVector<AArch64_IMM::ImmInsnModel, 4> Insn;
+  AArch64_IMM::expandMOVImm(UImm, RegSize, Insn);
+  if (Insn.size() == 1)
+    return false;
+
+  // The bitmask immediate consists of consecutive ones.  Let's say there is
+  // constant 0b00000000001000000000010000000000 which does not consist of
+  // consecutive ones. We can split it in to two bitmask immediate like
+  // 0b00000000001111111111110000000000 and 0b11111111111000000000011111111111.
+  // If we do AND with these two bitmask immediate, we can see original one.
+  unsigned LowestBitSet = countTrailingZeros(UImm);
+  unsigned HighestBitSet = Log2_64(UImm);
+
+  // Create a mask which is filled with one from the position of lowest bit set
+  // to the position of highest bit set.
+  T NewImm1 = (static_cast<T>(2) << HighestBitSet) -
+              (static_cast<T>(1) << LowestBitSet);
+  // Create a mask which is filled with one outside the position of lowest bit
+  // set and the position of highest bit set.
+  T NewImm2 = UImm | ~NewImm1;
+
+  // If the splitted value is not valid bitmask immediate, do not split this
+  // constant.
+  if (!AArch64_AM::isLogicalImmediate(NewImm2, RegSize))
+    return false;
+
+  Imm1Enc = AArch64_AM::encodeLogicalImmediate(NewImm1, RegSize);
+  Imm2Enc = AArch64_AM::encodeLogicalImmediate(NewImm2, RegSize);
+  return true;
+}
+
+template <typename T>
+bool AArch64MIPeepholeOpt::visitAND(
+    MachineInstr &MI, SmallSetVector<MachineInstr *, 8> &ToBeRemoved) {
+  // Try below transformation.
+  //
+  // MOVi32imm + ANDWrr ==> ANDWri + ANDWri
+  // MOVi64imm + ANDXrr ==> ANDXri + ANDXri
+  //
+  // The mov pseudo instruction could be expanded to multiple mov instructions
+  // later. Let's try to split the constant operand of mov instruction into two
+  // bitmask immediates. It makes only two AND instructions intead of multiple
+  // mov + and instructions.
+
+  unsigned RegSize = sizeof(T) * 8;
+  assert((RegSize == 32 || RegSize == 64) &&
+         "Invalid RegSize for AND bitmask peephole optimization");
+
+  // Check whether AND's MBB is in loop and the AND is loop invariant.
+  MachineBasicBlock *MBB = MI.getParent();
+  MachineLoop *L = MLI->getLoopFor(MBB);
+  if (L && !L->isLoopInvariant(MI))
+    return false;
+
+  // Check whether AND's operand is MOV with immediate.
+  MachineInstr *MovMI = MRI->getUniqueVRegDef(MI.getOperand(2).getReg());
+  MachineInstr *SubregToRegMI = nullptr;
+  // If it is SUBREG_TO_REG, check its operand.
+  if (MovMI->getOpcode() == TargetOpcode::SUBREG_TO_REG) {
+    SubregToRegMI = MovMI;
+    MovMI = MRI->getUniqueVRegDef(MovMI->getOperand(2).getReg());
+  }
+
+  // If the MOV has multiple uses, do not split the immediate because it causes
+  // more instructions.
+  if (!MRI->hasOneUse(MovMI->getOperand(0).getReg()))
+    return false;
+
+  if (MovMI->getOpcode() != AArch64::MOVi32imm &&
+      MovMI->getOpcode() != AArch64::MOVi64imm)
+    return false;
+
+  // Split the bitmask immediate into two.
+  T UImm = static_cast<T>(MovMI->getOperand(1).getImm());
+  T Imm1Enc;
+  T Imm2Enc;
+  if (!splitBitmaskImm(UImm, RegSize, Imm1Enc, Imm2Enc))
+    return false;
+
+  // Create new AND MIs.
+  DebugLoc DL = MI.getDebugLoc();
+  Register DstReg = MI.getOperand(0).getReg();
+  Register SrcReg = MI.getOperand(1).getReg();
+  Register NewTmpReg = MRI->createVirtualRegister(MRI->getRegClass(DstReg));
+  unsigned Opcode = (RegSize == 32) ? AArch64::ANDWri : AArch64::ANDXri;
+
+  BuildMI(*MBB, MI, DL, TII->get(Opcode), NewTmpReg)
+      .addReg(SrcReg)
+      .addImm(Imm1Enc);
+
+  BuildMI(*MBB, MI, DL, TII->get(Opcode), DstReg)
+      .addReg(NewTmpReg)
+      .addImm(Imm2Enc);
+
+  ToBeRemoved.insert(&MI);
+  if (SubregToRegMI)
+    ToBeRemoved.insert(SubregToRegMI);
+  ToBeRemoved.insert(MovMI);
+
+  return true;
+}
+
+bool AArch64MIPeepholeOpt::runOnMachineFunction(MachineFunction &MF) {
+  if (skipFunction(MF.getFunction()))
+    return false;
+
+  TII = static_cast<const AArch64InstrInfo *>(MF.getSubtarget().getInstrInfo());
+  MLI = &getAnalysis<MachineLoopInfo>();
+  MRI = &MF.getRegInfo();
+
+  if (!MRI->isSSA())
+    return false;
+
+  bool Changed = false;
+  SmallSetVector<MachineInstr *, 8> ToBeRemoved;
+
+  for (MachineBasicBlock &MBB : MF) {
+    for (MachineInstr &MI : MBB) {
+      switch (MI.getOpcode()) {
+      default:
+        break;
+      case AArch64::ANDWrr:
+        Changed = visitAND<uint32_t>(MI, ToBeRemoved);
+        break;
+      case AArch64::ANDXrr:
+        Changed = visitAND<uint64_t>(MI, ToBeRemoved);
+        break;
+      }
+    }
+  }
+
+  for (MachineInstr *MI : ToBeRemoved)
+    MI->eraseFromParent();
+
+  return Changed;
+}
+
+FunctionPass *llvm::createAArch64MIPeepholeOptPass() {
+  return new AArch64MIPeepholeOpt();
+}

llvm/lib/Target/AArch64/AArch64TargetMachine.cpp

@@ -195,6 +195,7 @@ extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAArch64Target() {
   initializeAArch64DeadRegisterDefinitionsPass(*PR);
   initializeAArch64ExpandPseudoPass(*PR);
   initializeAArch64LoadStoreOptPass(*PR);
+  initializeAArch64MIPeepholeOptPass(*PR);
   initializeAArch64SIMDInstrOptPass(*PR);
   initializeAArch64O0PreLegalizerCombinerPass(*PR);
   initializeAArch64PreLegalizerCombinerPass(*PR);
@@ -479,6 +480,7 @@ class AArch64PassConfig : public TargetPassConfig {
   bool addRegBankSelect() override;
   void addPreGlobalInstructionSelect() override;
   bool addGlobalInstructionSelect() override;
+  void addMachineSSAOptimization() override;
   bool addILPOpts() override;
   void addPreRegAlloc() override;
   void addPostRegAlloc() override;
@@ -649,6 +651,14 @@ bool AArch64PassConfig::addGlobalInstructionSelect() {
   return false;
 }
 
+void AArch64PassConfig::addMachineSSAOptimization() {
+  // Run default MachineSSAOptimization first.
+  TargetPassConfig::addMachineSSAOptimization();
+
+  if (TM->getOptLevel() != CodeGenOpt::None)
+    addPass(createAArch64MIPeepholeOptPass());
+}
+
 bool AArch64PassConfig::addILPOpts() {
   if (EnableCondOpt)
     addPass(createAArch64ConditionOptimizerPass());

llvm/lib/Target/AArch64/CMakeLists.txt

@@ -66,6 +66,7 @@ add_llvm_target(AArch64CodeGen
   AArch64LowerHomogeneousPrologEpilog.cpp
   AArch64MachineFunctionInfo.cpp
   AArch64MacroFusion.cpp
+  AArch64MIPeepholeOpt.cpp
   AArch64MCInstLower.cpp
   AArch64PromoteConstant.cpp
   AArch64PBQPRegAlloc.cpp

llvm/lib/Target/AArch64/MCTargetDesc/AArch64AddressingModes.h

@@ -13,6 +13,7 @@
 #ifndef LLVM_LIB_TARGET_AARCH64_MCTARGETDESC_AARCH64ADDRESSINGMODES_H
 #define LLVM_LIB_TARGET_AARCH64_MCTARGETDESC_AARCH64ADDRESSINGMODES_H
 
+#include "AArch64ExpandImm.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/bit.h"

llvm/test/CodeGen/AArch64/O3-pipeline.ll

@@ -40,7 +40,7 @@
 ; CHECK-NEXT:         Induction Variable Users
 ; CHECK-NEXT:         Loop Strength Reduction
 ; CHECK-NEXT:       Basic Alias Analysis (stateless AA impl)
-; CHECK-NEXT:         Function Alias Analysis Results
+; CHECK-NEXT:       Function Alias Analysis Results
 ; CHECK-NEXT:       Merge contiguous icmps into a memcmp
 ; CHECK-NEXT:       Natural Loop Information
 ; CHECK-NEXT:       Lazy Branch Probability Analysis
@@ -131,6 +131,7 @@
 ; CHECK-NEXT:       Machine code sinking
 ; CHECK-NEXT:       Peephole Optimizations
 ; CHECK-NEXT:       Remove dead machine instructions
+; CHECK-NEXT:       AArch64 MI Peephole Optimization pass
 ; CHECK-NEXT:       AArch64 Dead register definitions
 ; CHECK-NEXT:       Detect Dead Lanes
 ; CHECK-NEXT:       Process Implicit Definitions