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

[via cfe-commits]

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

Refer: https://github.com/llvm/llvm-project/issues/192330

>From 9281c84db3bafa08c2d014428d1730a3292cdfcc 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

---
 clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp b/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp
index 75658b23790bf..edfaea83c1a7f 100644
--- a/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp
@@ -2069,8 +2069,9 @@ mlir::Value CIRGenItaniumCXXABI::getVirtualBaseClassOffset(
 
   mlir::Value vbaseOffset;
   if (cgm.getLangOpts().RelativeCXXABIVTables) {
-    assert(!cir::MissingFeatures::vtableRelativeLayout());
-    cgm.errorNYI(loc, "getVirtualBaseClassOffset: relative layout");
+    vbaseOffset = cgf.getBuilder().createLoad(
+        loc, Address(vbaseOffsetPtr, cgm.sInt32Ty,
+                     CharUnits::fromQuantity(4))); // vbase.offset
   } else {
     mlir::Value offsetPtr = builder.createBitcast(
         vbaseOffsetPtr, builder.getPointerTo(cgm.ptrDiffTy));