[CIR] Add support for accessing members of base classes (#143195)

This change adds the support for accessing a member of a base class from
a derived class object.

1 files changed, 28 insertions, 0 deletions

diff --git a/clang/lib/CIR/CodeGen/CIRGenModule.cpp b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
index e5eae31..3d46c44 100644
--- a/clang/lib/CIR/CodeGen/CIRGenModule.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
@@ -19,6 +19,7 @@
 #include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclOpenACC.h"
 #include "clang/AST/GlobalDecl.h"
+#include "clang/AST/RecordLayout.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/CIR/Dialect/IR/CIRDialect.h"
 #include "clang/CIR/Interfaces/CIROpInterfaces.h"
@@ -1683,6 +1684,33 @@ bool CIRGenModule::verifyModule() const {
   return mlir::verify(theModule).succeeded();
 }
 
+// TODO(cir): this can be shared with LLVM codegen.
+CharUnits CIRGenModule::computeNonVirtualBaseClassOffset(
+    const CXXRecordDecl *derivedClass,
+    llvm::iterator_range<CastExpr::path_const_iterator> path) {
+  CharUnits offset = CharUnits::Zero();
+
+  const ASTContext &astContext = getASTContext();
+  const CXXRecordDecl *rd = derivedClass;
+
+  for (const CXXBaseSpecifier *base : path) {
+    assert(!base->isVirtual() && "Should not see virtual bases here!");
+
+    // Get the layout.
+    const ASTRecordLayout &layout = astContext.getASTRecordLayout(rd);
+
+    const auto *baseDecl = cast<CXXRecordDecl>(
+        base->getType()->castAs<clang::RecordType>()->getDecl());
+
+    // Add the offset.
+    offset += layout.getBaseClassOffset(baseDecl);
+
+    rd = baseDecl;
+  }
+
+  return offset;
+}
+
 DiagnosticBuilder CIRGenModule::errorNYI(SourceLocation loc,
                                          llvm::StringRef feature) {
   unsigned diagID = diags.getCustomDiagID(