[MLIR] Add endianness accessors to the data layout (#87347)

This commit extends the data layout subsystem with accessors for the
endianness. The implementation follows the structure implemented for
alloca, global, and program memory spaces.

Author: Dinistro

mlir/include/mlir/Dialect/DLTI/DLTI.h

@@ -100,6 +100,9 @@ class DataLayoutSpecAttr
   /// Returns the list of entries.
   DataLayoutEntryListRef getEntries() const;
 
+  /// Returns the endiannes identifier.
+  StringAttr getEndiannessIdentifier(MLIRContext *context) const;
+
   /// Returns the alloca memory space identifier.
   StringAttr getAllocaMemorySpaceIdentifier(MLIRContext *context) const;
 

mlir/include/mlir/Interfaces/DataLayoutInterfaces.h

@@ -64,6 +64,10 @@ std::optional<uint64_t>
 getDefaultIndexBitwidth(Type type, const DataLayout &dataLayout,
                         ArrayRef<DataLayoutEntryInterface> params);
 
+/// Default handler for endianness request. Dispatches to the
+/// DataLayoutInterface if specified, otherwise returns the default.
+Attribute getDefaultEndianness(DataLayoutEntryInterface entry);
+
 /// Default handler for alloca memory space request. Dispatches to the
 /// DataLayoutInterface if specified, otherwise returns the default.
 Attribute getDefaultAllocaMemorySpace(DataLayoutEntryInterface entry);
@@ -192,6 +196,9 @@ class DataLayout {
   /// type is not a pointer-like type, it returns std::nullopt.
   std::optional<uint64_t> getTypeIndexBitwidth(Type t) const;
 
+  /// Returns the specified endianness.
+  Attribute getEndianness() const;
+
   /// Returns the memory space used for AllocaOps.
   Attribute getAllocaMemorySpace() const;
 
@@ -230,6 +237,8 @@ class DataLayout {
   mutable DenseMap<Type, uint64_t> preferredAlignments;
   mutable DenseMap<Type, std::optional<uint64_t>> indexBitwidths;
 
+  /// Cache for the endianness.
+  mutable std::optional<Attribute> endianness;
   /// Cache for alloca, global, and program memory spaces.
   mutable std::optional<Attribute> allocaMemorySpace;
   mutable std::optional<Attribute> programMemorySpace;

mlir/include/mlir/Interfaces/DataLayoutInterfaces.td

@@ -106,6 +106,12 @@ def DataLayoutSpecInterface : AttrInterface<"DataLayoutSpecInterface"> {
       /*methodName=*/"getEntries",
       /*args=*/(ins)
     >,
+    InterfaceMethod<
+      /*description=*/"Returns the endianness identifier.",
+      /*retTy=*/"::mlir::StringAttr",
+      /*methodName=*/"getEndiannessIdentifier",
+      /*args=*/(ins "::mlir::MLIRContext *":$context)
+    >,
     InterfaceMethod<
       /*description=*/"Returns the alloca memory space identifier.",
       /*retTy=*/"::mlir::StringAttr",
@@ -296,6 +302,18 @@ def DataLayoutOpInterface : OpInterface<"DataLayoutOpInterface"> {
                                                        params);
       }]
     >,
+    StaticInterfaceMethod<
+      /*description=*/"Returns the endianness used by the ABI computed "
+                      "using the relevant entries. The data layout object "
+                      "can be used for recursive queries.",
+      /*retTy=*/"::mlir::Attribute",
+      /*methodName=*/"getEndianness",
+      /*args=*/(ins "::mlir::DataLayoutEntryInterface":$entry),
+      /*methodBody=*/"",
+      /*defaultImplementation=*/[{
+        return ::mlir::detail::getDefaultEndianness(entry);
+      }]
+    >,
     StaticInterfaceMethod<
       /*description=*/"Returns the memory space used by the ABI computed "
                       "using the relevant entries. The data layout object "

mlir/lib/Dialect/DLTI/DLTI.cpp

@@ -281,6 +281,11 @@ DataLayoutEntryListRef DataLayoutSpecAttr::getEntries() const {
   return getImpl()->entries;
 }
 
+StringAttr
+DataLayoutSpecAttr::getEndiannessIdentifier(MLIRContext *context) const {
+  return Builder(context).getStringAttr(DLTIDialect::kDataLayoutEndiannessKey);
+}
+
 StringAttr
 DataLayoutSpecAttr::getAllocaMemorySpaceIdentifier(MLIRContext *context) const {
   return Builder(context).getStringAttr(

mlir/lib/Interfaces/DataLayoutInterfaces.cpp

@@ -234,6 +234,15 @@ std::optional<uint64_t> mlir::detail::getDefaultIndexBitwidth(
   return std::nullopt;
 }
 
+// Returns the endianness if specified in the given entry. If the entry is empty
+// the default endianness represented by an empty attribute is returned.
+Attribute mlir::detail::getDefaultEndianness(DataLayoutEntryInterface entry) {
+  if (entry == DataLayoutEntryInterface())
+    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.
@@ -548,6 +557,22 @@ std::optional<uint64_t> mlir::DataLayout::getTypeIndexBitwidth(Type t) const {
   });
 }
 
+mlir::Attribute mlir::DataLayout::getEndianness() const {
+  checkValid();
+  if (endianness)
+    return *endianness;
+  DataLayoutEntryInterface entry;
+  if (originalLayout)
+    entry = originalLayout.getSpecForIdentifier(
+        originalLayout.getEndiannessIdentifier(originalLayout.getContext()));
+
+  if (auto iface = dyn_cast_or_null<DataLayoutOpInterface>(scope))
+    endianness = iface.getEndianness(entry);
+  else
+    endianness = detail::getDefaultEndianness(entry);
+  return *endianness;
+}
+
 mlir::Attribute mlir::DataLayout::getAllocaMemorySpace() const {
   checkValid();
   if (allocaMemorySpace)

mlir/test/Dialect/LLVMIR/layout.mlir

@@ -6,6 +6,7 @@ module {
     // CHECK: alignment = 8
     // CHECK: alloca_memory_space = 0
     // CHECK: bitsize = 64
+    // CHECK: endianness = ""
     // CHECK: global_memory_space = 0
     // CHECK: index = 64
     // CHECK: preferred = 8
@@ -16,6 +17,7 @@ module {
     // CHECK: alignment = 8
     // CHECK: alloca_memory_space = 0
     // CHECK: bitsize = 64
+    // CHECK: endianness = ""
     // CHECK: global_memory_space = 0
     // CHECK: index = 64
     // CHECK: preferred = 8
@@ -26,6 +28,7 @@ module {
     // CHECK: alignment = 8
     // CHECK: alloca_memory_space = 0
     // CHECK: bitsize = 64
+    // CHECK: endianness = ""
     // CHECK: global_memory_space = 0
     // CHECK: index = 64
     // CHECK: preferred = 8
@@ -43,6 +46,7 @@ module attributes { dlti.dl_spec = #dlti.dl_spec<
   #dlti.dl_entry<!llvm.ptr, dense<[32, 32, 64]> : vector<3xi64>>,
   #dlti.dl_entry<!llvm.ptr<5>, dense<[64, 64, 64]> : vector<3xi64>>,
   #dlti.dl_entry<!llvm.ptr<4>, dense<[32, 64, 64, 24]> : vector<4xi64>>,
+  #dlti.dl_entry<"dlti.endianness", "little">,
   #dlti.dl_entry<"dlti.alloca_memory_space", 5 : ui64>,
   #dlti.dl_entry<"dlti.global_memory_space", 2 : ui64>,
   #dlti.dl_entry<"dlti.program_memory_space", 3 : ui64>,
@@ -53,6 +57,7 @@ module attributes { dlti.dl_spec = #dlti.dl_spec<
     // CHECK: alignment = 4
     // CHECK: alloca_memory_space = 5
     // CHECK: bitsize = 32
+    // CHECK: endianness = "little"
     // CHECK: global_memory_space = 2
     // CHECK: index = 32
     // CHECK: preferred = 8
@@ -63,6 +68,7 @@ module attributes { dlti.dl_spec = #dlti.dl_spec<
     // CHECK: alignment = 4
     // CHECK: alloca_memory_space = 5
     // CHECK: bitsize = 32
+    // CHECK: endianness = "little"
     // CHECK: global_memory_space = 2
     // CHECK: index = 32
     // CHECK: preferred = 8
@@ -73,6 +79,7 @@ module attributes { dlti.dl_spec = #dlti.dl_spec<
     // CHECK: alignment = 8
     // CHECK: alloca_memory_space = 5
     // CHECK: bitsize = 64
+    // CHECK: endianness = "little"
     // CHECK: global_memory_space = 2
     // CHECK: index = 64
     // CHECK: preferred = 8
@@ -83,6 +90,7 @@ module attributes { dlti.dl_spec = #dlti.dl_spec<
     // CHECK: alignment = 8
     // CHECK: alloca_memory_space = 5
     // CHECK: bitsize = 32
+    // CHECK: endianness = "little"
     // CHECK: global_memory_space = 2
     // CHECK: index = 24
     // CHECK: preferred = 8

mlir/test/lib/Dialect/DLTI/TestDataLayoutQuery.cpp

@@ -41,6 +41,7 @@ struct TestDataLayoutQuery
       uint64_t alignment = layout.getTypeABIAlignment(op.getType());
       uint64_t preferred = layout.getTypePreferredAlignment(op.getType());
       uint64_t index = layout.getTypeIndexBitwidth(op.getType()).value_or(0);
+      Attribute endianness = layout.getEndianness();
       Attribute allocaMemorySpace = layout.getAllocaMemorySpace();
       Attribute programMemorySpace = layout.getProgramMemorySpace();
       Attribute globalMemorySpace = layout.getGlobalMemorySpace();
@@ -51,6 +52,9 @@ struct TestDataLayoutQuery
            builder.getNamedAttr("alignment", builder.getIndexAttr(alignment)),
            builder.getNamedAttr("preferred", builder.getIndexAttr(preferred)),
            builder.getNamedAttr("index", builder.getIndexAttr(index)),
+           builder.getNamedAttr("endianness", endianness == Attribute()
+                                                  ? builder.getStringAttr("")
+                                                  : endianness),
            builder.getNamedAttr("alloca_memory_space",
                                 allocaMemorySpace == Attribute()
                                     ? builder.getUI32IntegerAttr(0)

mlir/unittests/Interfaces/DataLayoutInterfacesTest.cpp

@@ -22,6 +22,7 @@ using namespace mlir;
 
 namespace {
 constexpr static llvm::StringLiteral kAttrName = "dltest.layout";
+constexpr static llvm::StringLiteral kEndiannesKeyName = "dltest.endianness";
 constexpr static llvm::StringLiteral kAllocaKeyName =
     "dltest.alloca_memory_space";
 constexpr static llvm::StringLiteral kProgramKeyName =
@@ -73,6 +74,9 @@ struct CustomDataLayoutSpec
   }
   DataLayoutEntryListRef getEntries() const { return getImpl()->entries; }
   LogicalResult verifySpec(Location loc) { return success(); }
+  StringAttr getEndiannessIdentifier(MLIRContext *context) const {
+    return Builder(context).getStringAttr(kEndiannesKeyName);
+  }
   StringAttr getAllocaMemorySpaceIdentifier(MLIRContext *context) const {
     return Builder(context).getStringAttr(kAllocaKeyName);
   }
@@ -130,6 +134,15 @@ struct SingleQueryType
     return 4;
   }
 
+  Attribute getEndianness(DataLayoutEntryInterface entry) {
+    static bool executed = false;
+    if (executed)
+      llvm::report_fatal_error("repeated call");
+
+    executed = true;
+    return Attribute();
+  }
+
   Attribute getAllocaMemorySpace(DataLayoutEntryInterface entry) {
     static bool executed = false;
     if (executed)
@@ -317,6 +330,7 @@ module {}
   EXPECT_EQ(layout.getTypePreferredAlignment(IntegerType::get(&ctx, 42)), 8u);
   EXPECT_EQ(layout.getTypePreferredAlignment(Float16Type::get(&ctx)), 2u);
 
+  EXPECT_EQ(layout.getEndianness(), Attribute());
   EXPECT_EQ(layout.getAllocaMemorySpace(), Attribute());
   EXPECT_EQ(layout.getProgramMemorySpace(), Attribute());
   EXPECT_EQ(layout.getGlobalMemorySpace(), Attribute());
@@ -348,6 +362,7 @@ TEST(DataLayout, NullSpec) {
   EXPECT_EQ(layout.getTypeIndexBitwidth(Float16Type::get(&ctx)), std::nullopt);
   EXPECT_EQ(layout.getTypeIndexBitwidth(IndexType::get(&ctx)), 64u);
 
+  EXPECT_EQ(layout.getEndianness(), Attribute());
   EXPECT_EQ(layout.getAllocaMemorySpace(), Attribute());
   EXPECT_EQ(layout.getProgramMemorySpace(), Attribute());
   EXPECT_EQ(layout.getGlobalMemorySpace(), Attribute());
@@ -378,6 +393,7 @@ TEST(DataLayout, EmptySpec) {
   EXPECT_EQ(layout.getTypeIndexBitwidth(Float16Type::get(&ctx)), std::nullopt);
   EXPECT_EQ(layout.getTypeIndexBitwidth(IndexType::get(&ctx)), 64u);
 
+  EXPECT_EQ(layout.getEndianness(), Attribute());
   EXPECT_EQ(layout.getAllocaMemorySpace(), Attribute());
   EXPECT_EQ(layout.getProgramMemorySpace(), Attribute());
   EXPECT_EQ(layout.getGlobalMemorySpace(), Attribute());
@@ -390,6 +406,7 @@ TEST(DataLayout, SpecWithEntries) {
   #dlti.dl_entry<i42, 5>,
   #dlti.dl_entry<i16, 6>,
   #dlti.dl_entry<index, 42>,
+  #dlti.dl_entry<"dltest.endianness", "little">,
   #dlti.dl_entry<"dltest.alloca_memory_space", 5 : i32>,
   #dlti.dl_entry<"dltest.program_memory_space", 3 : i32>,
   #dlti.dl_entry<"dltest.global_memory_space", 2 : i32>,
@@ -425,6 +442,7 @@ TEST(DataLayout, SpecWithEntries) {
   EXPECT_EQ(layout.getTypePreferredAlignment(IntegerType::get(&ctx, 32)), 64u);
   EXPECT_EQ(layout.getTypePreferredAlignment(Float32Type::get(&ctx)), 64u);
 
+  EXPECT_EQ(layout.getEndianness(), Builder(&ctx).getStringAttr("little"));
   EXPECT_EQ(layout.getAllocaMemorySpace(), Builder(&ctx).getI32IntegerAttr(5));
   EXPECT_EQ(layout.getProgramMemorySpace(), Builder(&ctx).getI32IntegerAttr(3));
   EXPECT_EQ(layout.getGlobalMemorySpace(), Builder(&ctx).getI32IntegerAttr(2));