[globalisel] Rename GISelChangeObserver's erasedInstr() to erasingInstr() and related nits. NFC

Summary:
There's little of interest that can be done to an already-erased instruction.
You can't inspect it, write it to a debug log, etc. It ought to be notification
that we're about to erase it. Rename the function to clarify the timing of the
event and reflect current usage.

Also fixed one case where we were trying to print an erased instruction.

Reviewers: aditya_nandakumar

Reviewed By: aditya_nandakumar

Subscribers: rovka, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D55611

llvm-svn: 348976

Author: dsandersllvm

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

@@ -30,7 +30,6 @@ class CombinerHelper {
   MachineRegisterInfo &MRI;
   GISelChangeObserver &Observer;
 
-  void eraseInstr(MachineInstr &MI);
   void scheduleForVisit(MachineInstr &MI);
 
 public:

llvm/include/llvm/CodeGen/GlobalISel/GISelChangeObserver.h

@@ -18,16 +18,16 @@
 namespace llvm {
 /// Abstract class that contains various methods for clients to notify about
 /// changes. This should be the preferred way for APIs to notify changes.
-/// Typically calling erasedInstr/createdInstr multiple times should not affect
+/// Typically calling erasingInstr/createdInstr multiple times should not affect
 /// the result. The observer would likely need to check if it was already
 /// notified earlier (consider using GISelWorkList).
 class MachineInstr;
 class GISelChangeObserver {
 public:
   virtual ~GISelChangeObserver() {}
 
-  /// An instruction was erased.
-  virtual void erasedInstr(MachineInstr &MI) = 0;
+  /// An instruction is about to be erased.
+  virtual void erasingInstr(MachineInstr &MI) = 0;
   /// An instruction was created and inserted into the function.
   virtual void createdInstr(MachineInstr &MI) = 0;
   /// This instruction was mutated in some way.

llvm/lib/CodeGen/GlobalISel/Combiner.cpp

@@ -43,7 +43,7 @@ class WorkListMaintainer : public GISelChangeObserver {
   WorkListMaintainer(WorkListTy &WorkList) : WorkList(WorkList) {}
   virtual ~WorkListMaintainer() {}
 
-  void erasedInstr(MachineInstr &MI) override {
+  void erasingInstr(MachineInstr &MI) override {
     LLVM_DEBUG(dbgs() << "Erased: "; MI.print(dbgs()); dbgs() << "\n");
     WorkList.remove(&MI);
   }

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

@@ -23,9 +23,6 @@ CombinerHelper::CombinerHelper(GISelChangeObserver &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);
 }
@@ -299,8 +296,8 @@ bool CombinerHelper::tryCombineExtendingLoads(MachineInstr &MI) {
     Observer.createdInstr(*NewMI);
   }
   for (auto &EraseMI : ScheduleForErase) {
+    Observer.erasingInstr(*EraseMI);
     EraseMI->eraseFromParent();
-    Observer.erasedInstr(*EraseMI);
   }
   MI.getOperand(0).setReg(ChosenDstReg);
 

llvm/lib/CodeGen/GlobalISel/Legalizer.cpp

@@ -94,7 +94,8 @@ class LegalizerWorkListManager : public GISelChangeObserver {
     LLVM_DEBUG(dbgs() << ".. .. New MI: " << MI;);
   }
 
-  void erasedInstr(MachineInstr &MI) override {
+  void erasingInstr(MachineInstr &MI) override {
+    LLVM_DEBUG(dbgs() << ".. .. Erasing: " << MI;);
     InstList.remove(&MI);
     ArtifactList.remove(&MI);
   }
@@ -146,7 +147,7 @@ bool Legalizer::runOnMachineFunction(MachineFunction &MF) {
   const LegalizerInfo &LInfo(Helper.getLegalizerInfo());
   LegalizationArtifactCombiner ArtCombiner(Helper.MIRBuilder, MF.getRegInfo(), LInfo);
   auto RemoveDeadInstFromLists = [&WorkListObserver](MachineInstr *DeadMI) {
-    WorkListObserver.erasedInstr(*DeadMI);
+    WorkListObserver.erasingInstr(*DeadMI);
   };
   bool Changed = false;
   do {
@@ -175,15 +176,15 @@ bool Legalizer::runOnMachineFunction(MachineFunction &MF) {
       MachineInstr &MI = *ArtifactList.pop_back_val();
       assert(isPreISelGenericOpcode(MI.getOpcode()) && "Expecting generic opcode");
       if (isTriviallyDead(MI, MRI)) {
-        LLVM_DEBUG(dbgs() << MI << "Is dead; erasing.\n");
+        LLVM_DEBUG(dbgs() << MI << "Is dead\n");
         RemoveDeadInstFromLists(&MI);
         MI.eraseFromParentAndMarkDBGValuesForRemoval();
         continue;
       }
       SmallVector<MachineInstr *, 4> DeadInstructions;
       if (ArtCombiner.tryCombineInstruction(MI, DeadInstructions)) {
         for (auto *DeadMI : DeadInstructions) {
-          LLVM_DEBUG(dbgs() << ".. Erasing Dead Instruction " << *DeadMI);
+          LLVM_DEBUG(dbgs() << *DeadMI << "Is dead\n");
           RemoveDeadInstFromLists(DeadMI);
           DeadMI->eraseFromParentAndMarkDBGValuesForRemoval();
         }

llvm/unittests/CodeGen/GlobalISel/LegalizerHelperTest.cpp

@@ -15,7 +15,7 @@ class DummyGISelObserver : public GISelChangeObserver {
 public:
   void changedInstr(MachineInstr &MI) override {}
   void createdInstr(MachineInstr &MI) override {}
-  void erasedInstr(MachineInstr &MI) override {}
+  void erasingInstr(MachineInstr &MI) override {}
 };
 
 // Test CTTZ expansion when CTTZ_ZERO_UNDEF is legal or custom,