GISel/Combiner: maintain created instructions in a SetVector

[nhaehnle]

Summary

This is not a correctness fix because the set is only used for debug
output. However, it helps avoid noise when looking at diffs between
compiler runs.

The set is only maintained with debug output enabled, so the added cost
should be acceptable.

[foad]

LGTM. Could put the declaration inside #ifndef NDEBUG.

[nhaehnle]

In D139465#3977195, @foad wrote:

LGTM. Could put the declaration inside #ifndef NDEBUG.

This is in a .cpp file, so not part of the ABI, so that seems perfectly safe. Good idea!

llvm/lib/CodeGen/GlobalISel/Combiner.cpp

 //===-- lib/CodeGen/GlobalISel/Combiner.cpp -------------------------------===//
 //
 // 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 file constains common code to combine machine functions at generic
 // level.
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/GlobalISel/Combiner.h"
 #include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/CodeGen/GlobalISel/CSEInfo.h"
 #include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
 #include "llvm/CodeGen/GlobalISel/CombinerInfo.h"
 #include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
 #include "llvm/CodeGen/GlobalISel/GISelWorkList.h"
 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
 #include "llvm/CodeGen/GlobalISel/Utils.h"
 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"

 /// instruction creation will schedule that instruction for a future visit.
 /// Other Combiner implementations may require more complex behaviour from
 /// their GISelChangeObserver subclass.
 class WorkListMaintainer : public GISelChangeObserver {
   using WorkListTy = GISelWorkList<512>;
   WorkListTy &WorkList;
   /// The instructions that have been created but we want to report once they
   /// have their operands. This is only maintained if debug output is requested.
-  SmallPtrSet<const MachineInstr *, 4> CreatedInstrs;
+#ifndef NDEBUG
+  SetVector<const MachineInstr *> CreatedInstrs;
+#endif
 
 public:
   WorkListMaintainer(WorkListTy &WorkList) : WorkList(WorkList) {}
   virtual ~WorkListMaintainer() = default;
 
   void erasingInstr(MachineInstr &MI) override {
     LLVM_DEBUG(dbgs() << "Erasing: " << MI << "\n");
     WorkList.remove(&MI);