[NFC][AMDGPU] Drop recursive types in LowerBufferFatPointers (#137735)

Now that IRMover and the rest of LLVM don't allow recursive types, drop
support for them from the clone of the IRMover code used when lowering
buffer fat pointer operations.

Author: krzysz00

llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp

@@ -267,7 +267,7 @@ namespace {
 class BufferFatPtrTypeLoweringBase : public ValueMapTypeRemapper {
   DenseMap<Type *, Type *> Map;
 
-  Type *remapTypeImpl(Type *Ty, SmallPtrSetImpl<StructType *> &Seen);
+  Type *remapTypeImpl(Type *Ty);
 
 protected:
   virtual Type *remapScalar(PointerType *PT) = 0;
@@ -305,8 +305,7 @@ class BufferFatPtrToStructTypeMap : public BufferFatPtrTypeLoweringBase {
 } // namespace
 
 // This code is adapted from the type remapper in lib/Linker/IRMover.cpp
-Type *BufferFatPtrTypeLoweringBase::remapTypeImpl(
-    Type *Ty, SmallPtrSetImpl<StructType *> &Seen) {
+Type *BufferFatPtrTypeLoweringBase::remapTypeImpl(Type *Ty) {
   Type **Entry = &Map[Ty];
   if (*Entry)
     return *Entry;
@@ -331,18 +330,11 @@ Type *BufferFatPtrTypeLoweringBase::remapTypeImpl(
   // require recursion.
   if (Ty->getNumContainedTypes() == 0 && IsUniqued)
     return *Entry = Ty;
-  if (!IsUniqued) {
-    // Create a dummy type for recursion purposes.
-    if (!Seen.insert(TyAsStruct).second) {
-      StructType *Placeholder = StructType::create(Ty->getContext());
-      return *Entry = Placeholder;
-    }
-  }
   bool Changed = false;
   SmallVector<Type *> ElementTypes(Ty->getNumContainedTypes(), nullptr);
   for (unsigned int I = 0, E = Ty->getNumContainedTypes(); I < E; ++I) {
     Type *OldElem = Ty->getContainedType(I);
-    Type *NewElem = remapTypeImpl(OldElem, Seen);
+    Type *NewElem = remapTypeImpl(OldElem);
     ElementTypes[I] = NewElem;
     Changed |= (OldElem != NewElem);
   }
@@ -366,22 +358,14 @@ Type *BufferFatPtrTypeLoweringBase::remapTypeImpl(
       return *Entry = StructType::get(Ty->getContext(), ElementTypes, IsPacked);
     SmallString<16> Name(STy->getName());
     STy->setName("");
-    Type **RecursionEntry = &Map[Ty];
-    if (*RecursionEntry) {
-      auto *Placeholder = cast<StructType>(*RecursionEntry);
-      Placeholder->setBody(ElementTypes, IsPacked);
-      Placeholder->setName(Name);
-      return *Entry = Placeholder;
-    }
     return *Entry = StructType::create(Ty->getContext(), ElementTypes, Name,
                                        IsPacked);
   }
   llvm_unreachable("Unknown type of type that contains elements");
 }
 
 Type *BufferFatPtrTypeLoweringBase::remapType(Type *SrcTy) {
-  SmallPtrSet<StructType *, 2> Visited;
-  return remapTypeImpl(SrcTy, Visited);
+  return remapTypeImpl(SrcTy);
 }
 
 Type *BufferFatPtrToStructTypeMap::remapScalar(PointerType *PT) {