Revert: r343521 and r343541: [globalisel] Add a combiner helpers for extending loads and use them in a pre-legalize combiner for AArch64

There's a strange assertion on two of the Green Dragon bots that goes away when
this is reverted. The assertion is in RegBankAlloc and if it is this commit then
-verify-machine-instrs should have caught it earlier in the pipeline.

llvm-svn: 343546

6 files changed, 4 insertions, 361 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/Combiner.cpp b/llvm/lib/CodeGen/GlobalISel/Combiner.cpp
index f3f075af486..0bc5b87de15 100644
--- a/llvm/lib/CodeGen/GlobalISel/Combiner.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/Combiner.cpp
@@ -25,34 +25,6 @@
 
 using namespace llvm;
 
-namespace {
-/// This class acts as the glue the joins the CombinerHelper to the overall
-/// Combine algorithm. The CombinerHelper is intended to report the
-/// modifications it makes to the MIR to the CombinerChangeObserver and the
-/// observer subclass will act on these events. In this case, instruction
-/// erasure will cancel any future visits to the erased instruction and
-/// instruction creation will schedule that instruction for a future visit.
-/// Other Combiner implementations may require more complex behaviour from
-/// their CombinerChangeObserver subclass.
-class WorkListMaintainer : public CombinerChangeObserver {
-  using WorkListTy = GISelWorkList<512>;
-  WorkListTy &WorkList;
-
-public:
-  WorkListMaintainer(WorkListTy &WorkList) : WorkList(WorkList) {}
-  virtual ~WorkListMaintainer() {}
-
-  void erasedInstr(MachineInstr &MI) override {
-    LLVM_DEBUG(dbgs() << "Erased: "; MI.print(dbgs()); dbgs() << "\n");
-    WorkList.remove(&MI);
-  }
-  void createdInstr(MachineInstr &MI) override {
-    LLVM_DEBUG(dbgs() << "Created: "; MI.print(dbgs()); dbgs() << "\n");
-    WorkList.insert(&MI);
-  }
-};
-}
-
 Combiner::Combiner(CombinerInfo &Info, const TargetPassConfig *TPC)
     : CInfo(Info), TPC(TPC) {
   (void)this->TPC; // FIXME: Remove when used.
@@ -81,7 +53,6 @@ bool Combiner::combineMachineInstrs(MachineFunction &MF) {
     // down RPOT.
     Changed = false;
     GISelWorkList<512> WorkList;
-    WorkListMaintainer Observer(WorkList);
     for (MachineBasicBlock *MBB : post_order(&MF)) {
       if (MBB->empty())
         continue;
@@ -101,7 +72,7 @@ bool Combiner::combineMachineInstrs(MachineFunction &MF) {
     while (!WorkList.empty()) {
       MachineInstr *CurrInst = WorkList.pop_back_val();
       LLVM_DEBUG(dbgs() << "Try combining " << *CurrInst << "\n";);
-      Changed |= CInfo.combine(Observer, *CurrInst, Builder);
+      Changed |= CInfo.combine(*CurrInst, Builder);
     }
     MFChanged |= Changed;
   } while (Changed);
diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
index f593a5b2570..44e904a6391 100644
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -6,28 +6,18 @@
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
-#include "llvm/CodeGen/GlobalISel/Combiner.h"
 #include "llvm/CodeGen/GlobalISel/CombinerHelper.h"
 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
 #include "llvm/CodeGen/GlobalISel/Utils.h"
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
-#include "llvm/CodeGen/TargetInstrInfo.h"
 
 #define DEBUG_TYPE "gi-combine"
 
 using namespace llvm;
 
-CombinerHelper::CombinerHelper(CombinerChangeObserver &Observer,
-                               MachineIRBuilder &B)
-    : Builder(B), MRI(Builder.getMF().getRegInfo()), Observer(Observer) {}
-
-void CombinerHelper::eraseInstr(MachineInstr &MI) {
-  Observer.erasedInstr(MI);
-}
-void CombinerHelper::scheduleForVisit(MachineInstr &MI) {
-  Observer.createdInstr(MI);
-}
+CombinerHelper::CombinerHelper(MachineIRBuilder &B) :
+  Builder(B), MRI(Builder.getMF().getRegInfo()) {}
 
 bool CombinerHelper::tryCombineCopy(MachineInstr &MI) {
   if (MI.getOpcode() != TargetOpcode::COPY)
@@ -46,207 +36,6 @@ bool CombinerHelper::tryCombineCopy(MachineInstr &MI) {
   return false;
 }
 
-namespace {
-struct PreferredTuple {
-  LLT Ty;                // The result type of the extend.
-  unsigned ExtendOpcode; // G_ANYEXT/G_SEXT/G_ZEXT
-  MachineInstr *MI;
-};
-
-/// Select a preference between two uses. CurrentUse is the current preference
-/// while *ForCandidate is attributes of the candidate under consideration.
-PreferredTuple ChoosePreferredUse(PreferredTuple &CurrentUse,
-                                  const LLT &TyForCandidate,
-                                  unsigned OpcodeForCandidate,
-                                  MachineInstr *MIForCandidate) {
-  if (!CurrentUse.Ty.isValid()) {
-    if (CurrentUse.ExtendOpcode == OpcodeForCandidate)
-      return {TyForCandidate, OpcodeForCandidate, MIForCandidate};
-    if (CurrentUse.ExtendOpcode == TargetOpcode::G_ANYEXT &&
-        (OpcodeForCandidate == TargetOpcode::G_SEXT ||
-         OpcodeForCandidate == TargetOpcode::G_ZEXT ||
-         OpcodeForCandidate == TargetOpcode::G_ANYEXT))
-      return {TyForCandidate, OpcodeForCandidate, MIForCandidate};
-    return CurrentUse;
-  }
-
-  // We permit the extend to hoist through basic blocks but this is only
-  // sensible if the target has extending loads. If you end up lowering back
-  // into a load and extend during the legalizer then the end result is
-  // hoisting the extend up to the load.
-
-  // Prefer defined extensions to undefined extensions as these are more
-  // likely to reduce the number of instructions.
-  if (OpcodeForCandidate == TargetOpcode::G_ANYEXT &&
-      CurrentUse.ExtendOpcode != TargetOpcode::G_ANYEXT)
-    return CurrentUse;
-  else if (CurrentUse.ExtendOpcode == TargetOpcode::G_ANYEXT &&
-           OpcodeForCandidate != TargetOpcode::G_ANYEXT)
-    return {TyForCandidate, OpcodeForCandidate, MIForCandidate};
-
-  // Prefer sign extensions to zero extensions as sign-extensions tend to be
-  // more expensive.
-  if (CurrentUse.Ty == TyForCandidate) {
-    if (CurrentUse.ExtendOpcode == TargetOpcode::G_SEXT &&
-        OpcodeForCandidate == TargetOpcode::G_ZEXT)
-      return CurrentUse;
-    else if (CurrentUse.ExtendOpcode == TargetOpcode::G_ZEXT &&
-             OpcodeForCandidate == TargetOpcode::G_SEXT)
-      return {TyForCandidate, OpcodeForCandidate, MIForCandidate};
-  }
-
-  // This is potentially target specific. We've chosen the largest type
-  // because G_TRUNC is usually free. One potential catch with this is that
-  // some targets have a reduced number of larger registers than smaller
-  // registers and this choice potentially increases the live-range for the
-  // larger value.
-  if (TyForCandidate.getSizeInBits() > CurrentUse.Ty.getSizeInBits()) {
-    return {TyForCandidate, OpcodeForCandidate, MIForCandidate};
-  }
-  return CurrentUse;
-};
-} // end anonymous namespace
-
-bool CombinerHelper::tryCombineExtendingLoads(MachineInstr &MI) {
-  // We match the loads and follow the uses to the extend instead of matching
-  // the extends and following the def to the load. This is because the load
-  // must remain in the same position for correctness (unless we also add code
-  // to find a safe place to sink it) whereas the extend is freely movable.
-  // It also prevents us from duplicating the load for the volatile case or just
-  // for performance.
-
-  if (MI.getOpcode() != TargetOpcode::G_LOAD &&
-      MI.getOpcode() != TargetOpcode::G_SEXTLOAD &&
-      MI.getOpcode() != TargetOpcode::G_ZEXTLOAD)
-    return false;
-
-  auto &LoadValue = MI.getOperand(0);
-  assert(LoadValue.isReg() && "Result wasn't a register?");
-
-  LLT LoadValueTy = MRI.getType(LoadValue.getReg());
-  if (!LoadValueTy.isScalar())
-    return false;
-
-  // Find the preferred type aside from the any-extends (unless it's the only
-  // one) and non-extending ops. We'll emit an extending load to that type and
-  // and emit a variant of (extend (trunc X)) for the others according to the
-  // relative type sizes. At the same time, pick an extend to use based on the
-  // extend involved in the chosen type.
-  unsigned PreferredOpcode = MI.getOpcode() == TargetOpcode::G_LOAD
-                                 ? TargetOpcode::G_ANYEXT
-                                 : MI.getOpcode() == TargetOpcode::G_SEXTLOAD
-                                       ? TargetOpcode::G_SEXT
-                                       : TargetOpcode::G_ZEXT;
-  PreferredTuple Preferred = {LLT(), PreferredOpcode, nullptr};
-  for (auto &UseMI : MRI.use_instructions(LoadValue.getReg())) {
-    if (UseMI.getOpcode() == TargetOpcode::G_SEXT ||
-        UseMI.getOpcode() == TargetOpcode::G_ZEXT || !Preferred.Ty.isValid())
-      Preferred = ChoosePreferredUse(Preferred,
-                                     MRI.getType(UseMI.getOperand(0).getReg()),
-                                     UseMI.getOpcode(), &UseMI);
-  }
-
-  // There were no extends
-  if (!Preferred.MI)
-    return false;
-  // It should be impossible to chose an extend without selecting a different
-  // type since by definition the result of an extend is larger.
-  assert(Preferred.Ty != LoadValueTy && "Extending to same type?");
-
-  // Rewrite the load and schedule the canonical use for erasure.
-  const auto TruncateUse = [](MachineIRBuilder &Builder, MachineOperand &UseMO,
-                              unsigned DstReg, unsigned SrcReg) {
-    MachineInstr &UseMI = *UseMO.getParent();
-    MachineBasicBlock &UseMBB = *UseMI.getParent();
-
-    Builder.setInsertPt(UseMBB, MachineBasicBlock::iterator(UseMI));
-    Builder.buildTrunc(DstReg, SrcReg);
-  };
-
-  // Rewrite the load to the chosen extending load.
-  unsigned ChosenDstReg = Preferred.MI->getOperand(0).getReg();
-  MI.setDesc(
-      Builder.getTII().get(Preferred.ExtendOpcode == TargetOpcode::G_SEXT
-                               ? TargetOpcode::G_SEXTLOAD
-                               : Preferred.ExtendOpcode == TargetOpcode::G_ZEXT
-                                     ? TargetOpcode::G_ZEXTLOAD
-                                     : TargetOpcode::G_LOAD));
-
-  // Rewrite all the uses to fix up the types.
-  SmallVector<MachineInstr *, 1> ScheduleForErase;
-  for (auto &UseMO : MRI.use_operands(LoadValue.getReg())) {
-    MachineInstr *UseMI = UseMO.getParent();
-
-    // If the extend is compatible with the preferred extend then we should fix
-    // up the type and extend so that it uses the preferred use.
-    if (UseMI->getOpcode() == Preferred.ExtendOpcode ||
-        UseMI->getOpcode() == TargetOpcode::G_ANYEXT) {
-      unsigned UseDstReg = UseMI->getOperand(0).getReg();
-      unsigned UseSrcReg = UseMI->getOperand(1).getReg();
-      const LLT &UseDstTy = MRI.getType(UseDstReg);
-      if (UseDstReg != ChosenDstReg) {
-        if (Preferred.Ty == UseDstTy) {
-          // If the use has the same type as the preferred use, then merge
-          // the vregs and erase the extend. For example:
-          //    %1:_(s8) = G_LOAD ...
-          //    %2:_(s32) = G_SEXT %1(s8)
-          //    %3:_(s32) = G_ANYEXT %1(s8)
-          //    ... = ... %3(s32)
-          // rewrites to:
-          //    %2:_(s32) = G_SEXTLOAD ...
-          //    ... = ... %2(s32)
-          MRI.replaceRegWith(UseDstReg, ChosenDstReg);
-          ScheduleForErase.push_back(UseMO.getParent());
-          Observer.erasedInstr(*UseMO.getParent());
-        } else if (Preferred.Ty.getSizeInBits() < UseDstTy.getSizeInBits()) {
-          // If the preferred size is smaller, then keep the extend but extend
-          // from the result of the extending load. For example:
-          //    %1:_(s8) = G_LOAD ...
-          //    %2:_(s32) = G_SEXT %1(s8)
-          //    %3:_(s64) = G_ANYEXT %1(s8)
-          //    ... = ... %3(s64)
-          /// rewrites to:
-          //    %2:_(s32) = G_SEXTLOAD ...
-          //    %3:_(s64) = G_ANYEXT %2:_(s32)
-          //    ... = ... %3(s64)
-          MRI.replaceRegWith(UseSrcReg, ChosenDstReg);
-        } else {
-          // If the preferred size is large, then insert a truncate. For
-          // example:
-          //    %1:_(s8) = G_LOAD ...
-          //    %2:_(s64) = G_SEXT %1(s8)
-          //    %3:_(s32) = G_ZEXT %1(s8)
-          //    ... = ... %3(s32)
-          /// rewrites to:
-          //    %2:_(s64) = G_SEXTLOAD ...
-          //    %4:_(s8) = G_TRUNC %2:_(s32)
-          //    %3:_(s64) = G_ZEXT %2:_(s8)
-          //    ... = ... %3(s64)
-          TruncateUse(Builder, UseMO, MI.getOperand(0).getReg(), ChosenDstReg);
-        }
-        continue;
-      }
-      // The use is (one of) the uses of the preferred use we chose earlier.
-      // We're going to update the load to def this value later so just erase
-      // the old extend.
-      ScheduleForErase.push_back(UseMO.getParent());
-      Observer.erasedInstr(*UseMO.getParent());
-      continue;
-    }
-
-    // The use isn't an extend. Truncate back to the type we originally loaded.
-    // This is free on many targets.
-    TruncateUse(Builder, UseMO, MI.getOperand(0).getReg(), ChosenDstReg);
-  }
-  for (auto &EraseMI : ScheduleForErase)
-    EraseMI->eraseFromParent();
-  MI.getOperand(0).setReg(ChosenDstReg);
-
-  return true;
-}
-
 bool CombinerHelper::tryCombine(MachineInstr &MI) {
-  if (tryCombineCopy(MI))
-    return true;
-  return tryCombineExtendingLoads(MI);
+  return tryCombineCopy(MI);
 }
diff --git a/llvm/lib/Target/AArch64/AArch64.h b/llvm/lib/Target/AArch64/AArch64.h
index 74f22e287f8..edda13ce97e 100644
--- a/llvm/lib/Target/AArch64/AArch64.h
+++ b/llvm/lib/Target/AArch64/AArch64.h
@@ -53,7 +53,6 @@ FunctionPass *createAArch64CollectLOHPass();
 InstructionSelector *
 createAArch64InstructionSelector(const AArch64TargetMachine &,
                                  AArch64Subtarget &, AArch64RegisterBankInfo &);
-FunctionPass *createAArch64PreLegalizeCombiner();
 
 void initializeAArch64A53Fix835769Pass(PassRegistry&);
 void initializeAArch64A57FPLoadBalancingPass(PassRegistry&);
@@ -66,7 +65,6 @@ void initializeAArch64DeadRegisterDefinitionsPass(PassRegistry&);
 void initializeAArch64ExpandPseudoPass(PassRegistry&);
 void initializeAArch64LoadStoreOptPass(PassRegistry&);
 void initializeAArch64SIMDInstrOptPass(PassRegistry&);
-void initializeAArch64PreLegalizerCombinerPass(PassRegistry&);
 void initializeAArch64PromoteConstantPass(PassRegistry&);
 void initializeAArch64RedundantCopyEliminationPass(PassRegistry&);
 void initializeAArch64StorePairSuppressPass(PassRegistry&);
diff --git a/llvm/lib/Target/AArch64/AArch64PreLegalizerCombiner.cpp b/llvm/lib/Target/AArch64/AArch64PreLegalizerCombiner.cpp
deleted file mode 100644
index 32487b9ccc3..00000000000
--- a/llvm/lib/Target/AArch64/AArch64PreLegalizerCombiner.cpp
+++ /dev/null
@@ -1,108 +0,0 @@
-//=== lib/CodeGen/GlobalISel/AArch64PreLegalizerCombiner.cpp --------------===//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This pass does combining of machine instructions at the generic MI level,
-// before the legalizer.
-//
-//===----------------------------------------------------------------------===//
-
-#include "AArch64TargetMachine.h"
-#include "llvm/CodeGen/GlobalISel/Combiner.h"
-#include "llvm/CodeGen/GlobalISel/CombinerHelper.h"
-#include "llvm/CodeGen/GlobalISel/CombinerInfo.h"
-#include "llvm/CodeGen/GlobalISel/MIPatternMatch.h"
-#include "llvm/CodeGen/MachineFunctionPass.h"
-#include "llvm/CodeGen/TargetPassConfig.h"
-#include "llvm/Support/Debug.h"
-
-#define DEBUG_TYPE "aarch64-prelegalizer-combiner"
-
-using namespace llvm;
-using namespace MIPatternMatch;
-
-namespace {
-class AArch64PreLegalizerCombinerInfo : public CombinerInfo {
-public:
-  AArch64PreLegalizerCombinerInfo()
-      : CombinerInfo(/*AllowIllegalOps*/ true, /*ShouldLegalizeIllegal*/ false,
-                     /*LegalizerInfo*/ nullptr) {}
-  virtual bool combine(CombinerChangeObserver &Observer, MachineInstr &MI,
-                       MachineIRBuilder &B) const override;
-};
-
-bool AArch64PreLegalizerCombinerInfo::combine(CombinerChangeObserver &Observer,
-                                              MachineInstr &MI,
-                                              MachineIRBuilder &B) const {
-  CombinerHelper Helper(Observer, B);
-
-  switch (MI.getOpcode()) {
-  default:
-    return false;
-  case TargetOpcode::G_LOAD:
-  case TargetOpcode::G_SEXTLOAD:
-  case TargetOpcode::G_ZEXTLOAD:
-    return Helper.tryCombineExtendingLoads(MI);
-  }
-
-  return false;
-}
-
-// Pass boilerplate
-// ================
-
-class AArch64PreLegalizerCombiner : public MachineFunctionPass {
-public:
-  static char ID;
-
-  AArch64PreLegalizerCombiner();
-
-  StringRef getPassName() const override { return "AArch64PreLegalizerCombiner"; }
-
-  bool runOnMachineFunction(MachineFunction &MF) override;
-
-  void getAnalysisUsage(AnalysisUsage &AU) const override;
-};
-}
-
-void AArch64PreLegalizerCombiner::getAnalysisUsage(AnalysisUsage &AU) const {
-  AU.addRequired<TargetPassConfig>();
-  AU.setPreservesCFG();
-  getSelectionDAGFallbackAnalysisUsage(AU);
-  MachineFunctionPass::getAnalysisUsage(AU);
-}
-
-AArch64PreLegalizerCombiner::AArch64PreLegalizerCombiner() : MachineFunctionPass(ID) {
-  initializeAArch64PreLegalizerCombinerPass(*PassRegistry::getPassRegistry());
-}
-
-bool AArch64PreLegalizerCombiner::runOnMachineFunction(MachineFunction &MF) {
-  if (MF.getProperties().hasProperty(
-          MachineFunctionProperties::Property::FailedISel))
-    return false;
-  auto *TPC = &getAnalysis<TargetPassConfig>();
-  AArch64PreLegalizerCombinerInfo PCInfo;
-  Combiner C(PCInfo, TPC);
-  return C.combineMachineInstrs(MF);
-}
-
-char AArch64PreLegalizerCombiner::ID = 0;
-INITIALIZE_PASS_BEGIN(AArch64PreLegalizerCombiner, DEBUG_TYPE,
-                      "Combine AArch64 machine instrs before legalization",
-                      false, false)
-INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
-INITIALIZE_PASS_END(AArch64PreLegalizerCombiner, DEBUG_TYPE,
-                    "Combine AArch64 machine instrs before legalization", false,
-                    false)
-
-
-namespace llvm {
-FunctionPass *createAArch64PreLegalizeCombiner() {
-  return new AArch64PreLegalizerCombiner();
-}
-} // end namespace llvm
diff --git a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
index a66f5277f24..c4b9b45f67b 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
@@ -158,7 +158,6 @@ extern "C" void LLVMInitializeAArch64Target() {
   initializeAArch64ExpandPseudoPass(*PR);
   initializeAArch64LoadStoreOptPass(*PR);
   initializeAArch64SIMDInstrOptPass(*PR);
-  initializeAArch64PreLegalizerCombinerPass(*PR);
   initializeAArch64PromoteConstantPass(*PR);
   initializeAArch64RedundantCopyEliminationPass(*PR);
   initializeAArch64StorePairSuppressPass(*PR);
@@ -349,7 +348,6 @@ public:
   bool addPreISel() override;
   bool addInstSelector() override;
   bool addIRTranslator() override;
-  void addPreLegalizeMachineIR() override;
   bool addLegalizeMachineIR() override;
   bool addRegBankSelect() override;
   void addPreGlobalInstructionSelect() override;
@@ -451,10 +449,6 @@ bool AArch64PassConfig::addIRTranslator() {
   return false;
 }
 
-void AArch64PassConfig::addPreLegalizeMachineIR() {
-  addPass(createAArch64PreLegalizeCombiner());
-}
-
 bool AArch64PassConfig::addLegalizeMachineIR() {
   addPass(new Legalizer());
   return false;
diff --git a/llvm/lib/Target/AArch64/CMakeLists.txt b/llvm/lib/Target/AArch64/CMakeLists.txt
index e6ca69c1971..d9a00512f71 100644
--- a/llvm/lib/Target/AArch64/CMakeLists.txt
+++ b/llvm/lib/Target/AArch64/CMakeLists.txt
@@ -43,7 +43,6 @@ add_llvm_target(AArch64CodeGen
   AArch64LoadStoreOptimizer.cpp
   AArch64MacroFusion.cpp
   AArch64MCInstLower.cpp
-  AArch64PreLegalizerCombiner.cpp
   AArch64PromoteConstant.cpp
   AArch64PBQPRegAlloc.cpp
   AArch64RegisterBankInfo.cpp