[mlir][DataLayout] Add a default memory space entry to the data layout. (#127416)

This patch adds a default memory space attribute to the DL and adds
methods to query the attribute. This is required as MLIR has no well
defined default memory space unlike LLVM which has 0. While `nullptr` is
a candidate for default memory space, the `ptr` dialect will remove the
possibility for `nullptr` memory spaces to avoid undefined semantics.

This patch also modifies the `DataLayoutTypeInterface::areCompatible` to
include the new DL spec and merged entries, as it is needed to query the default memory
space.

---------

Co-authored-by: Christian Ulmann <[email protected]>

Author: fabianmcg

mlir/include/mlir/Dialect/DLTI/DLTIAttrs.td

@@ -74,6 +74,9 @@ def DLTI_DataLayoutSpecAttr :
     /// Returns the endiannes identifier.
     StringAttr getEndiannessIdentifier(MLIRContext *context) const;
 
+    /// Returns the default memory space identifier.
+    StringAttr getDefaultMemorySpaceIdentifier(MLIRContext *context) const;
+
     /// Returns the alloca memory space identifier.
     StringAttr getAllocaMemorySpaceIdentifier(MLIRContext *context) const;
 

mlir/include/mlir/Dialect/DLTI/DLTIBase.td

@@ -53,6 +53,9 @@ def DLTI_Dialect : Dialect {
     constexpr const static ::llvm::StringLiteral
     kDataLayoutManglingModeKey = "dlti.mangling_mode";
 
+    constexpr const static ::llvm::StringLiteral
+    kDataLayoutDefaultMemorySpaceKey = "dlti.default_memory_space";
+
     constexpr const static ::llvm::StringLiteral
     kDataLayoutAllocaMemorySpaceKey = "dlti.alloca_memory_space";
 

mlir/include/mlir/Interfaces/DataLayoutInterfaces.h

@@ -34,6 +34,8 @@ using DataLayoutEntryList = llvm::SmallVector<DataLayoutEntryInterface, 4>;
 using DataLayoutEntryListRef = llvm::ArrayRef<DataLayoutEntryInterface>;
 using TargetDeviceSpecListRef = llvm::ArrayRef<TargetDeviceSpecInterface>;
 using TargetDeviceSpecEntry = std::pair<StringAttr, TargetDeviceSpecInterface>;
+using DataLayoutIdentifiedEntryMap =
+    ::llvm::DenseMap<::mlir::StringAttr, ::mlir::DataLayoutEntryInterface>;
 class DataLayoutOpInterface;
 class DataLayoutSpecInterface;
 class ModuleOp;
@@ -74,6 +76,10 @@ getDefaultIndexBitwidth(Type type, const DataLayout &dataLayout,
 /// DataLayoutInterface if specified, otherwise returns the default.
 Attribute getDefaultEndianness(DataLayoutEntryInterface entry);
 
+/// Default handler for the default memory space request. Dispatches to the
+/// DataLayoutInterface if specified, otherwise returns the default.
+Attribute getDefaultMemorySpace(DataLayoutEntryInterface entry);
+
 /// Default handler for alloca memory space request. Dispatches to the
 /// DataLayoutInterface if specified, otherwise returns the default.
 Attribute getDefaultAllocaMemorySpace(DataLayoutEntryInterface entry);
@@ -231,6 +237,9 @@ class DataLayout {
   /// Returns the specified endianness.
   Attribute getEndianness() const;
 
+  /// Returns the default memory space used for memory operations.
+  Attribute getDefaultMemorySpace() const;
+
   /// Returns the memory space used for AllocaOps.
   Attribute getAllocaMemorySpace() const;
 
@@ -285,7 +294,8 @@ class DataLayout {
   mutable std::optional<Attribute> endianness;
   /// Cache for the mangling mode.
   mutable std::optional<Attribute> manglingMode;
-  /// Cache for alloca, global, and program memory spaces.
+  /// Cache for default, alloca, global, and program memory spaces.
+  mutable std::optional<Attribute> defaultMemorySpace;
   mutable std::optional<Attribute> allocaMemorySpace;
   mutable std::optional<Attribute> programMemorySpace;
   mutable std::optional<Attribute> globalMemorySpace;

mlir/include/mlir/Interfaces/DataLayoutInterfaces.td

@@ -135,6 +135,12 @@ def DataLayoutSpecInterface : AttrInterface<"DataLayoutSpecInterface", [DLTIQuer
       /*methodName=*/"getEndiannessIdentifier",
       /*args=*/(ins "::mlir::MLIRContext *":$context)
     >,
+    InterfaceMethod<
+      /*description=*/"Returns the default memory space identifier.",
+      /*retTy=*/"::mlir::StringAttr",
+      /*methodName=*/"getDefaultMemorySpaceIdentifier",
+      /*args=*/(ins "::mlir::MLIRContext *":$context)
+    >,
     InterfaceMethod<
       /*description=*/"Returns the alloca memory space identifier.",
       /*retTy=*/"::mlir::StringAttr",
@@ -475,6 +481,18 @@ def DataLayoutOpInterface : OpInterface<"DataLayoutOpInterface"> {
         return ::mlir::detail::getDefaultEndianness(entry);
       }]
     >,
+    StaticInterfaceMethod<
+      /*description=*/"Returns the memory space used by the ABI computed "
+                      "using the relevant entries. The data layout object "
+                      "can be used for recursive queries.",
+      /*retTy=*/"::mlir::Attribute",
+      /*methodName=*/"getDefaultMemorySpace",
+      /*args=*/(ins "::mlir::DataLayoutEntryInterface":$entry),
+      /*methodBody=*/"",
+      /*defaultImplementation=*/[{
+        return ::mlir::detail::getDefaultMemorySpace(entry);
+      }]
+    >,
     StaticInterfaceMethod<
       /*description=*/"Returns the memory space used by the ABI computed "
                       "using the relevant entries. The data layout object "
@@ -637,11 +655,16 @@ def DataLayoutTypeInterface : TypeInterface<"DataLayoutTypeInterface"> {
     InterfaceMethod<
       /*desc=*/"Returns true if the two lists of entries are compatible, that "
                "is, that `newLayout` spec entries can be nested in an op with "
-               "`oldLayout` spec entries.",
+               "`oldLayout` spec entries. `newSpec` and `identified` are"
+               "provided to further query data from the combined spec, e.g.,"
+               "the default address space. TODO: Revisit this method once"
+               "https://github.com/llvm/llvm-project/issues/130321 gets solved",
       /*retTy=*/"bool",
       /*methodName=*/"areCompatible",
       /*args=*/(ins "::mlir::DataLayoutEntryListRef":$oldLayout,
-                    "::mlir::DataLayoutEntryListRef":$newLayout),
+                    "::mlir::DataLayoutEntryListRef":$newLayout,
+                    "::mlir::DataLayoutSpecInterface":$newSpec,
+                    "const ::mlir::DataLayoutIdentifiedEntryMap&":$identified),
       /*methodBody=*/"",
       /*defaultImplementation=*/[{ return true; }]
     >,

mlir/lib/Dialect/DLTI/DLTI.cpp

@@ -305,25 +305,8 @@ combineOneSpec(DataLayoutSpecInterface spec,
   DenseMap<StringAttr, DataLayoutEntryInterface> newEntriesForID;
   spec.bucketEntriesByType(newEntriesForType, newEntriesForID);
 
-  // Try overwriting the old entries with the new ones.
-  for (auto &kvp : newEntriesForType) {
-    if (!entriesForType.count(kvp.first)) {
-      entriesForType[kvp.first] = std::move(kvp.second);
-      continue;
-    }
-
-    Type typeSample = cast<Type>(kvp.second.front().getKey());
-    assert(&typeSample.getDialect() !=
-               typeSample.getContext()->getLoadedDialect<BuiltinDialect>() &&
-           "unexpected data layout entry for built-in type");
-
-    auto interface = cast<DataLayoutTypeInterface>(typeSample);
-    if (!interface.areCompatible(entriesForType.lookup(kvp.first), kvp.second))
-      return failure();
-
-    overwriteDuplicateEntries(entriesForType[kvp.first], kvp.second);
-  }
-
+  // Combine non-Type DL entries first so they are visible to the
+  // `type.areCompatible` method, allowing to query global properties.
   for (const auto &kvp : newEntriesForID) {
     StringAttr id = cast<StringAttr>(kvp.second.getKey());
     Dialect *dialect = id.getReferencedDialect();
@@ -332,7 +315,7 @@ combineOneSpec(DataLayoutSpecInterface spec,
       continue;
     }
 
-    // Attempt to combine the enties using the dialect interface. If the
+    // Attempt to combine the entries using the dialect interface. If the
     // dialect is not loaded for some reason, use the default combinator
     // that conservatively accepts identical entries only.
     entriesForID[id] =
@@ -344,6 +327,28 @@ combineOneSpec(DataLayoutSpecInterface spec,
       return failure();
   }
 
+  // Try overwriting the old entries with the new ones.
+  for (auto &kvp : newEntriesForType) {
+    if (!entriesForType.count(kvp.first)) {
+      entriesForType[kvp.first] = std::move(kvp.second);
+      continue;
+    }
+
+    Type typeSample = cast<Type>(kvp.second.front().getKey());
+    assert(&typeSample.getDialect() !=
+               typeSample.getContext()->getLoadedDialect<BuiltinDialect>() &&
+           "unexpected data layout entry for built-in type");
+
+    auto interface = cast<DataLayoutTypeInterface>(typeSample);
+    // TODO: Revisit this method and call once
+    // https://github.com/llvm/llvm-project/issues/130321 gets resolved.
+    if (!interface.areCompatible(entriesForType.lookup(kvp.first), kvp.second,
+                                 spec, entriesForID))
+      return failure();
+
+    overwriteDuplicateEntries(entriesForType[kvp.first], kvp.second);
+  }
+
   return success();
 }
 
@@ -379,6 +384,12 @@ DataLayoutSpecAttr::getEndiannessIdentifier(MLIRContext *context) const {
   return Builder(context).getStringAttr(DLTIDialect::kDataLayoutEndiannessKey);
 }
 
+StringAttr DataLayoutSpecAttr::getDefaultMemorySpaceIdentifier(
+    MLIRContext *context) const {
+  return Builder(context).getStringAttr(
+      DLTIDialect::kDataLayoutDefaultMemorySpaceKey);
+}
+
 StringAttr
 DataLayoutSpecAttr::getAllocaMemorySpaceIdentifier(MLIRContext *context) const {
   return Builder(context).getStringAttr(
@@ -609,7 +620,8 @@ class TargetDataLayoutInterface : public DataLayoutDialectInterface {
                             << DLTIDialect::kDataLayoutEndiannessBig << "' or '"
                             << DLTIDialect::kDataLayoutEndiannessLittle << "'";
     }
-    if (entryName == DLTIDialect::kDataLayoutAllocaMemorySpaceKey ||
+    if (entryName == DLTIDialect::kDataLayoutDefaultMemorySpaceKey ||
+        entryName == DLTIDialect::kDataLayoutAllocaMemorySpaceKey ||
         entryName == DLTIDialect::kDataLayoutProgramMemorySpaceKey ||
         entryName == DLTIDialect::kDataLayoutGlobalMemorySpaceKey ||
         entryName == DLTIDialect::kDataLayoutStackAlignmentKey ||

mlir/lib/Dialect/LLVMIR/IR/LLVMTypes.cpp

@@ -349,8 +349,10 @@ LLVMPointerType::getIndexBitwidth(const DataLayout &dataLayout,
   return dataLayout.getTypeIndexBitwidth(get(getContext()));
 }
 
-bool LLVMPointerType::areCompatible(DataLayoutEntryListRef oldLayout,
-                                    DataLayoutEntryListRef newLayout) const {
+bool LLVMPointerType::areCompatible(
+    DataLayoutEntryListRef oldLayout, DataLayoutEntryListRef newLayout,
+    DataLayoutSpecInterface newSpec,
+    const DataLayoutIdentifiedEntryMap &map) const {
   for (DataLayoutEntryInterface newEntry : newLayout) {
     if (!newEntry.isTypeEntry())
       continue;
@@ -597,8 +599,10 @@ static uint64_t extractStructSpecValue(Attribute attr, StructDLEntryPos pos) {
       .getValues<uint64_t>()[static_cast<size_t>(pos)];
 }
 
-bool LLVMStructType::areCompatible(DataLayoutEntryListRef oldLayout,
-                                   DataLayoutEntryListRef newLayout) const {
+bool LLVMStructType::areCompatible(
+    DataLayoutEntryListRef oldLayout, DataLayoutEntryListRef newLayout,
+    DataLayoutSpecInterface newSpec,
+    const DataLayoutIdentifiedEntryMap &map) const {
   for (DataLayoutEntryInterface newEntry : newLayout) {
     if (!newEntry.isTypeEntry())
       continue;

mlir/lib/Dialect/Ptr/IR/PtrTypes.cpp

@@ -23,13 +23,12 @@ using namespace mlir::ptr;
 
 constexpr const static unsigned kDefaultPointerSizeBits = 64;
 constexpr const static unsigned kBitsInByte = 8;
-constexpr const static unsigned kDefaultPointerAlignment = 8;
-
-static Attribute getDefaultMemorySpace(PtrType ptr) { return nullptr; }
+constexpr const static unsigned kDefaultPointerAlignmentBits = 8;
 
 /// Searches the data layout for the pointer spec, returns nullptr if it is not
 /// found.
-static SpecAttr getPointerSpec(DataLayoutEntryListRef params, PtrType type) {
+static SpecAttr getPointerSpec(DataLayoutEntryListRef params, PtrType type,
+                               Attribute defaultMemorySpace) {
   for (DataLayoutEntryInterface entry : params) {
     if (!entry.isTypeEntry())
       continue;
@@ -41,20 +40,22 @@ static SpecAttr getPointerSpec(DataLayoutEntryListRef params, PtrType type) {
   }
   // If not found, and this is the pointer to the default memory space, assume
   // 64-bit pointers.
-  if (type.getMemorySpace() == getDefaultMemorySpace(type))
+  if (type.getMemorySpace() == defaultMemorySpace)
     return SpecAttr::get(type.getContext(), kDefaultPointerSizeBits,
-                         kDefaultPointerAlignment, kDefaultPointerAlignment,
-                         kDefaultPointerSizeBits);
+                         kDefaultPointerAlignmentBits,
+                         kDefaultPointerAlignmentBits, kDefaultPointerSizeBits);
   return nullptr;
 }
 
 bool PtrType::areCompatible(DataLayoutEntryListRef oldLayout,
-                            DataLayoutEntryListRef newLayout) const {
+                            DataLayoutEntryListRef newLayout,
+                            DataLayoutSpecInterface newSpec,
+                            const DataLayoutIdentifiedEntryMap &map) const {
   for (DataLayoutEntryInterface newEntry : newLayout) {
     if (!newEntry.isTypeEntry())
       continue;
     uint32_t size = kDefaultPointerSizeBits;
-    uint32_t abi = kDefaultPointerAlignment;
+    uint32_t abi = kDefaultPointerAlignmentBits;
     auto newType = llvm::cast<PtrType>(llvm::cast<Type>(newEntry.getKey()));
     const auto *it =
         llvm::find_if(oldLayout, [&](DataLayoutEntryInterface entry) {
@@ -65,10 +66,12 @@ bool PtrType::areCompatible(DataLayoutEntryListRef oldLayout,
           return false;
         });
     if (it == oldLayout.end()) {
+      Attribute defaultMemorySpace = mlir::detail::getDefaultMemorySpace(
+          map.lookup(newSpec.getDefaultMemorySpaceIdentifier(getContext())));
       it = llvm::find_if(oldLayout, [&](DataLayoutEntryInterface entry) {
         if (auto type = llvm::dyn_cast_if_present<Type>(entry.getKey())) {
           auto ptrTy = llvm::cast<PtrType>(type);
-          return ptrTy.getMemorySpace() == getDefaultMemorySpace(ptrTy);
+          return ptrTy.getMemorySpace() == defaultMemorySpace;
         }
         return false;
       });
@@ -90,43 +93,44 @@ bool PtrType::areCompatible(DataLayoutEntryListRef oldLayout,
 
 uint64_t PtrType::getABIAlignment(const DataLayout &dataLayout,
                                   DataLayoutEntryListRef params) const {
-  if (SpecAttr spec = getPointerSpec(params, *this))
+  Attribute defaultMemorySpace = dataLayout.getDefaultMemorySpace();
+  if (SpecAttr spec = getPointerSpec(params, *this, defaultMemorySpace))
     return spec.getAbi() / kBitsInByte;
 
-  return dataLayout.getTypeABIAlignment(
-      get(getContext(), getDefaultMemorySpace(*this)));
+  return dataLayout.getTypeABIAlignment(get(getContext(), defaultMemorySpace));
 }
 
 std::optional<uint64_t>
 PtrType::getIndexBitwidth(const DataLayout &dataLayout,
                           DataLayoutEntryListRef params) const {
-  if (SpecAttr spec = getPointerSpec(params, *this)) {
+  Attribute defaultMemorySpace = dataLayout.getDefaultMemorySpace();
+  if (SpecAttr spec = getPointerSpec(params, *this, defaultMemorySpace)) {
     return spec.getIndex() == SpecAttr::kOptionalSpecValue ? spec.getSize()
                                                            : spec.getIndex();
   }
 
-  return dataLayout.getTypeIndexBitwidth(
-      get(getContext(), getDefaultMemorySpace(*this)));
+  return dataLayout.getTypeIndexBitwidth(get(getContext(), defaultMemorySpace));
 }
 
 llvm::TypeSize PtrType::getTypeSizeInBits(const DataLayout &dataLayout,
                                           DataLayoutEntryListRef params) const {
-  if (SpecAttr spec = getPointerSpec(params, *this))
+  Attribute defaultMemorySpace = dataLayout.getDefaultMemorySpace();
+  if (SpecAttr spec = getPointerSpec(params, *this, defaultMemorySpace))
     return llvm::TypeSize::getFixed(spec.getSize());
 
   // For other memory spaces, use the size of the pointer to the default memory
   // space.
-  return dataLayout.getTypeSizeInBits(
-      get(getContext(), getDefaultMemorySpace(*this)));
+  return dataLayout.getTypeSizeInBits(get(getContext(), defaultMemorySpace));
 }
 
 uint64_t PtrType::getPreferredAlignment(const DataLayout &dataLayout,
                                         DataLayoutEntryListRef params) const {
-  if (SpecAttr spec = getPointerSpec(params, *this))
+  Attribute defaultMemorySpace = dataLayout.getDefaultMemorySpace();
+  if (SpecAttr spec = getPointerSpec(params, *this, defaultMemorySpace))
     return spec.getPreferred() / kBitsInByte;
 
   return dataLayout.getTypePreferredAlignment(
-      get(getContext(), getDefaultMemorySpace(*this)));
+      get(getContext(), defaultMemorySpace));
 }
 
 LogicalResult PtrType::verifyEntries(DataLayoutEntryListRef entries,

mlir/lib/Interfaces/DataLayoutInterfaces.cpp

@@ -246,6 +246,16 @@ Attribute mlir::detail::getDefaultEndianness(DataLayoutEntryInterface entry) {
   return entry.getValue();
 }
 
+// Returns the default memory space if specified in the given entry. If the
+// entry is empty the default memory space represented by an empty attribute is
+// returned.
+Attribute mlir::detail::getDefaultMemorySpace(DataLayoutEntryInterface entry) {
+  if (!entry)
+    return Attribute();
+
+  return entry.getValue();
+}
+
 // Returns the memory space used for alloca operations if specified in the
 // given entry. If the entry is empty the default memory space represented by
 // an empty attribute is returned.
@@ -605,6 +615,22 @@ mlir::Attribute mlir::DataLayout::getEndianness() const {
   return *endianness;
 }
 
+mlir::Attribute mlir::DataLayout::getDefaultMemorySpace() const {
+  checkValid();
+  if (defaultMemorySpace)
+    return *defaultMemorySpace;
+  DataLayoutEntryInterface entry;
+  if (originalLayout)
+    entry = originalLayout.getSpecForIdentifier(
+        originalLayout.getDefaultMemorySpaceIdentifier(
+            originalLayout.getContext()));
+  if (auto iface = dyn_cast_or_null<DataLayoutOpInterface>(scope))
+    defaultMemorySpace = iface.getDefaultMemorySpace(entry);
+  else
+    defaultMemorySpace = detail::getDefaultMemorySpace(entry);
+  return *defaultMemorySpace;
+}
+
 mlir::Attribute mlir::DataLayout::getAllocaMemorySpace() const {
   checkValid();
   if (allocaMemorySpace)