[clang] [CIR] Upstream missing support for vtables and virtual bases (PR #192617)

[via cfe-commits]

https://github.com/xiongzile updated https://github.com/llvm/llvm-project/pull/192617

>From 82966edf6179a0faf2c9c89eecfa960cf14e9782 Mon Sep 17 00:00:00 2001
From: Zile Xiong <xiongzile at bytedance.com>
Date: Fri, 17 Apr 2026 17:18:23 +0800
Subject: [PATCH] [CIR] getVirtualBaseClassOffset &&
 ApplyNonVirtualAndVirtualOffset

---
 clang/lib/CIR/CodeGen/CIRGenClass.cpp         | 12 ++++++++----
 clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp |  8 ++++++--
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/clang/lib/CIR/CodeGen/CIRGenClass.cpp b/clang/lib/CIR/CodeGen/CIRGenClass.cpp
index 5f9fdfba9d31b..9755acb883675 100644
--- a/clang/lib/CIR/CodeGen/CIRGenClass.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenClass.cpp
@@ -399,10 +399,14 @@ static Address applyNonVirtualAndVirtualOffset(
   mlir::Value baseOffset;
   if (!nonVirtualOffset.isZero()) {
     if (virtualOffset) {
-      cgf.cgm.errorNYI(
-          loc,
-          "applyNonVirtualAndVirtualOffset: virtual and non-virtual offset");
-      return Address::invalid();
+      mlir::Type offsetType =
+          (cgf.cgm.getTarget().getCXXABI().isItaniumFamily() &&
+           cgf.cgm.getLangOpts().RelativeCXXABIVTables)
+              ? cgf.sInt32Ty
+              : cgf.ptrDiffTy;
+      baseOffset = cgf.getBuilder().getConstInt(loc, offsetType,
+                                                nonVirtualOffset.getQuantity());
+      baseOffset = cgf.getBuilder().createAdd(loc, virtualOffset, baseOffset);
     } else {
       assert(baseValueTy && "expected base type");
       // If no virtualOffset is present this is the final stop.
diff --git a/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp b/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp
index 75658b23790bf..982349abb48c4 100644
--- a/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp
@@ -2056,6 +2056,7 @@ bool CIRGenItaniumCXXABI::isVirtualOffsetNeededForVTableField(
 mlir::Value CIRGenItaniumCXXABI::getVirtualBaseClassOffset(
     mlir::Location loc, CIRGenFunction &cgf, Address thisAddr,
     const CXXRecordDecl *classDecl, const CXXRecordDecl *baseClassDecl) {
+
   CIRGenBuilderTy &builder = cgf.getBuilder();
   mlir::Value vtablePtr = cgf.getVTablePtr(loc, thisAddr, classDecl);
   mlir::Value vtableBytePtr = builder.createBitcast(vtablePtr, cgm.uInt8PtrTy);
@@ -2069,8 +2070,11 @@ mlir::Value CIRGenItaniumCXXABI::getVirtualBaseClassOffset(
 
   mlir::Value vbaseOffset;
   if (cgm.getLangOpts().RelativeCXXABIVTables) {
-    assert(!cir::MissingFeatures::vtableRelativeLayout());
-    cgm.errorNYI(loc, "getVirtualBaseClassOffset: relative layout");
+    mlir::Value offsetPtr = builder.createBitcast(
+        vbaseOffsetPtr, builder.getPointerTo(cgm.sInt32Ty));
+    vbaseOffset = cgf.getBuilder().createLoad(
+        loc, Address(offsetPtr, cgm.sInt32Ty,
+                     CharUnits::fromQuantity(4))); // vbase.offset
   } else {
     mlir::Value offsetPtr = builder.createBitcast(
         vbaseOffsetPtr, builder.getPointerTo(cgm.ptrDiffTy));