[globalisel][combine] Split existing rules into a match and apply step

[dsanders]

Summary

The declarative tablegen definitions split rules into match and apply steps.
Prepare for that by doing the same in the C++ implementations. This aids
some of the migration effort while the tablegen version is incomplete.

[aditya_nandakumar]

Seems reasonable.

llvm/trunk/include/llvm/CodeGen/GlobalISel/CombinerHelper.h

 /// tryCombine which invokes all transformations. All of the transformations
 /// return true if the MachineInstruction changed and false otherwise.
 //
 //===--------------------------------------------------------------------===//
 
 #ifndef LLVM_CODEGEN_GLOBALISEL_COMBINER_HELPER_H
 #define LLVM_CODEGEN_GLOBALISEL_COMBINER_HELPER_H
 
+#include "llvm/CodeGen/LowLevelType.h"
+
 namespace llvm {
 
 class GISelChangeObserver;
 class MachineIRBuilder;
 class MachineRegisterInfo;
 class MachineInstr;
 class MachineOperand;
 
+struct PreferredTuple {
+  LLT Ty;                // The result type of the extend.
+  unsigned ExtendOpcode; // G_ANYEXT/G_SEXT/G_ZEXT
+  MachineInstr *MI;
+};
+
 class CombinerHelper {
   MachineIRBuilder &Builder;
   MachineRegisterInfo &MRI;
   GISelChangeObserver &Observer;
 
 public:
   CombinerHelper(GISelChangeObserver &Observer, MachineIRBuilder &B);
 
   /// MachineRegisterInfo::replaceRegWith() and inform the observer of the changes
   void replaceRegWith(MachineRegisterInfo &MRI, unsigned FromReg, unsigned ToReg) const;
 
   /// Replace a single register operand with a new register and inform the
   /// observer of the changes.
   void replaceRegOpWith(MachineRegisterInfo &MRI, MachineOperand &FromRegOp,
                         unsigned ToReg) const;
 
   /// If \p MI is COPY, try to combine it.
   /// Returns true if MI changed.
   bool tryCombineCopy(MachineInstr &MI);
+  bool matchCombineCopy(MachineInstr &MI);
+  void applyCombineCopy(MachineInstr &MI);
 
   /// If \p MI is extend that consumes the result of a load, try to combine it.
   /// Returns true if MI changed.
   bool tryCombineExtendingLoads(MachineInstr &MI);
+  bool matchCombineExtendingLoads(MachineInstr &MI, PreferredTuple &MatchInfo);
+  void applyCombineExtendingLoads(MachineInstr &MI, PreferredTuple &MatchInfo);
 
   /// Try to transform \p MI by using all of the above
   /// combine functions. Returns true if changed.
   bool tryCombine(MachineInstr &MI);
 };
 } // namespace llvm
 
 #endif

llvm/trunk/lib/CodeGen/GlobalISel/CombinerHelper.cpp

void CombinerHelper::replaceRegOpWith(MachineRegisterInfo &MRI,
   Observer.changingInstr(*FromRegOp.getParent());
 
   FromRegOp.setReg(ToReg);
 
   Observer.changedInstr(*FromRegOp.getParent());
 }
 
 bool CombinerHelper::tryCombineCopy(MachineInstr &MI) {
+  if (matchCombineCopy(MI)) {
+    applyCombineCopy(MI);
+    return true;
+  }
+  return false;
+}
+bool CombinerHelper::matchCombineCopy(MachineInstr &MI) {
   if (MI.getOpcode() != TargetOpcode::COPY)
     return false;
   unsigned DstReg = MI.getOperand(0).getReg();
   unsigned SrcReg = MI.getOperand(1).getReg();
   LLT DstTy = MRI.getType(DstReg);
   LLT SrcTy = MRI.getType(SrcReg);
   // Simple Copy Propagation.
   // a(sx) = COPY b(sx) -> Replace all uses of a with b.
-  if (DstTy.isValid() && SrcTy.isValid() && DstTy == SrcTy) {
-    MI.eraseFromParent();
-    replaceRegWith(MRI, DstReg, SrcReg);
+  if (DstTy.isValid() && SrcTy.isValid() && DstTy == SrcTy)
     return true;
-  }
   return false;
 }
+void CombinerHelper::applyCombineCopy(MachineInstr &MI) {
+  unsigned DstReg = MI.getOperand(0).getReg();
+  unsigned SrcReg = MI.getOperand(1).getReg();
+  MI.eraseFromParent();
+  replaceRegWith(MRI, DstReg, SrcReg);
+}
 
 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()) {
static void InsertInsnsWithoutSideEffectsBeforeUse(
   }
 
   // Otherwise we want the start of the BB
   Inserter(InsertBB, InsertBB->getFirstNonPHI());
 }
 } // end anonymous namespace
 
 bool CombinerHelper::tryCombineExtendingLoads(MachineInstr &MI) {
-  struct InsertionPoint {
-    MachineOperand *UseMO;
-    MachineBasicBlock *InsertIntoBB;
-    MachineBasicBlock::iterator InsertBefore;
-    InsertionPoint(MachineOperand *UseMO, MachineBasicBlock *InsertIntoBB,
-                   MachineBasicBlock::iterator InsertBefore)
-        : UseMO(UseMO), InsertIntoBB(InsertIntoBB), InsertBefore(InsertBefore) {
-    }
-  };
+  PreferredTuple Preferred;
+  if (matchCombineExtendingLoads(MI, Preferred)) {
+    applyCombineExtendingLoads(MI, Preferred);
+    return true;
+  }
+  return false;
 
+bool CombinerHelper::matchCombineExtendingLoads(MachineInstr &MI,
+                                                PreferredTuple &Preferred) {
   // 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 &&
bool CombinerHelper::matchCombineExtendingLoads(MachineInstr &MI,
   // 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};
+  Preferred = {LLT(), PreferredOpcode, nullptr};
   for (auto &UseMI : MRI.use_instructions(LoadValue.getReg())) {
     if (UseMI.getOpcode() == TargetOpcode::G_SEXT ||
         UseMI.getOpcode() == TargetOpcode::G_ZEXT ||
         UseMI.getOpcode() == TargetOpcode::G_ANYEXT) {
       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?");
 
   LLVM_DEBUG(dbgs() << "Preferred use is: " << *Preferred.MI);
+  return true;
+}
+
+void CombinerHelper::applyCombineExtendingLoads(MachineInstr &MI,
+                                                PreferredTuple &Preferred) {
+  struct InsertionPoint {
+    MachineOperand *UseMO;
+    MachineBasicBlock *InsertIntoBB;
+    MachineBasicBlock::iterator InsertBefore;
+    InsertionPoint(MachineOperand *UseMO, MachineBasicBlock *InsertIntoBB,
+                   MachineBasicBlock::iterator InsertBefore)
+        : UseMO(UseMO), InsertIntoBB(InsertIntoBB), InsertBefore(InsertBefore) {
+    }
+  };
 
   // Rewrite the load to the chosen extending load.
   unsigned ChosenDstReg = Preferred.MI->getOperand(0).getReg();
   Observer.changingInstr(MI);
   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;
   SmallVector<InsertionPoint, 4> ScheduleForInsert;
+  auto &LoadValue = MI.getOperand(0);
   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();
for (auto &InsertionInfo : ScheduleForInsert) {
     replaceRegOpWith(MRI, *UseMO, NewDstReg);
   }
   for (auto &EraseMI : ScheduleForErase) {
     Observer.erasingInstr(*EraseMI);
     EraseMI->eraseFromParent();
   }
   MI.getOperand(0).setReg(ChosenDstReg);
   Observer.changedInstr(MI);
-
-  return true;
 }
 
 bool CombinerHelper::tryCombine(MachineInstr &MI) {
   if (tryCombineCopy(MI))
     return true;
   return tryCombineExtendingLoads(MI);
 }