[CIR] Extend StructLayoutAttr to support querying offset for members

Testcase not added because we are not using the printers and parsers,
but upcoming atomic work will exercise the path and testcases.

Author: bcardosolopes

clang/include/clang/CIR/Dialect/IR/CIRAttrs.td

@@ -521,28 +521,31 @@ def VTableAttr : CIR_Attr<"VTable", "vtable", [TypedAttrInterface]> {
 def StructLayoutAttr : CIR_Attr<"StructLayout", "struct_layout"> {
   let summary = "ABI specific information about a struct layout";
   let description = [{
+    Holds layout information often queried by !cir.struct users
+    during lowering passes and optimizations.
   }];
 
   let parameters = (ins "unsigned":$size,
                         "unsigned":$alignment,
                         "bool":$padded,
-                        "mlir::Type":$largest_member);
+                        "mlir::Type":$largest_member,
+                        "mlir::ArrayAttr":$offsets);
 
   let builders = [
     AttrBuilderWithInferredContext<(ins "unsigned":$size,
                                         "unsigned":$alignment,
                                         "bool":$padded,
-                                        "mlir::Type":$largest_member
-                                        ), [{
+                                        "mlir::Type":$largest_member,
+                                        "mlir::ArrayAttr":$offsets), [{
       return $_get(largest_member.getContext(), size, alignment, padded,
-                   largest_member);
+                   largest_member, offsets);
     }]>,
   ];
 
   let genVerifyDecl = 1;
   let assemblyFormat = [{
     `<`
-      struct($size, $alignment, $padded, $largest_member)
+      struct($size, $alignment, $padded, $largest_member, $offsets)
     `>`
   }];
 }

clang/include/clang/CIR/Dialect/IR/CIRTypes.h

@@ -172,6 +172,8 @@ class StructType
   // instead.
   mutable mlir::Attribute layoutInfo;
   bool isPadded(const DataLayout &dataLayout) const;
+  uint64_t getElementOffset(const DataLayout &dataLayout, unsigned idx) const;
+
   void computeSizeAndAlignment(const DataLayout &dataLayout) const;
 };
 

clang/lib/CIR/Dialect/IR/CIRAttrs.cpp

@@ -167,7 +167,13 @@ LogicalResult ConstStructAttr::verify(
 
 LogicalResult StructLayoutAttr::verify(
     ::llvm::function_ref<::mlir::InFlightDiagnostic()> emitError, unsigned size,
-    unsigned alignment, bool padded, mlir::Type largest_member) {
+    unsigned alignment, bool padded, mlir::Type largest_member,
+    mlir::ArrayAttr offsets) {
+  if (not std::all_of(offsets.begin(), offsets.end(), [](mlir::Attribute attr) {
+        return attr.isa<mlir::IntegerAttr>();
+      })) {
+    return emitError() << "all index values must be integers";
+  }
   return success();
 }
 

clang/lib/CIR/Dialect/IR/CIRTypes.cpp

@@ -498,6 +498,16 @@ bool StructType::isPadded(const ::mlir::DataLayout &dataLayout) const {
   return layoutInfo.cast<mlir::cir::StructLayoutAttr>().getPadded();
 }
 
+uint64_t StructType::getElementOffset(const ::mlir::DataLayout &dataLayout,
+                                      unsigned idx) const {
+  assert(idx < getMembers().size() && "access not valid");
+  if (!layoutInfo)
+    computeSizeAndAlignment(dataLayout);
+  auto offsets = layoutInfo.cast<mlir::cir::StructLayoutAttr>().getOffsets();
+  auto intAttr = offsets[idx].cast<mlir::IntegerAttr>();
+  return intAttr.getInt();
+}
+
 void StructType::computeSizeAndAlignment(
     const ::mlir::DataLayout &dataLayout) const {
   assert(isComplete() && "Cannot get layout of incomplete structs");
@@ -513,8 +523,10 @@ void StructType::computeSizeAndAlignment(
   auto members = getMembers();
   mlir::Type largestMember;
   unsigned largestMemberSize = 0;
+  SmallVector<mlir::Attribute, 4> memberOffsets;
 
   // Loop over each of the elements, placing them in memory.
+  memberOffsets.reserve(numElements);
   for (unsigned i = 0, e = numElements; i != e; ++i) {
     auto ty = members[i];
 
@@ -544,8 +556,9 @@ void StructType::computeSizeAndAlignment(
     // Keep track of maximum alignment constraint.
     structAlignment = std::max(tyAlign, structAlignment);
 
-    // FIXME: track struct size up to each element.
-    // getMemberOffsets()[i] = structSize;
+    // Struct size up to each element is the element offset.
+    memberOffsets.push_back(mlir::IntegerAttr::get(
+        mlir::IntegerType::get(getContext(), 32), structSize));
 
     // Consume space for this data item
     structSize += dataLayout.getTypeSize(ty);
@@ -564,9 +577,10 @@ void StructType::computeSizeAndAlignment(
     }
   }
 
-  layoutInfo = mlir::cir::StructLayoutAttr::get(getContext(), structSize,
-                                                structAlignment.value(),
-                                                isPadded, largestMember);
+  auto offsets = mlir::ArrayAttr::get(getContext(), memberOffsets);
+  layoutInfo = mlir::cir::StructLayoutAttr::get(
+      getContext(), structSize, structAlignment.value(), isPadded,
+      largestMember, offsets);
 }
 
 //===----------------------------------------------------------------------===//