[clang] [CIR] Relative vtable layout for virtual base offset (PR #195025)

[via cfe-commits]

https://github.com/xiongzile updated https://github.com/llvm/llvm-project/pull/195025

>From e465a414191fd0468b545e52637aa5a0257eae73 Mon Sep 17 00:00:00 2001
From: Zile Xiong <xiongzile at bytedance.com>
Date: Thu, 30 Apr 2026 15:14:45 +0800
Subject: [PATCH] [CIR] Relative vtable layout for virtual base offset

---
 clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp b/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp
index 946739d4e1702..f56f291c70772 100644
--- a/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp
@@ -2057,8 +2057,10 @@ 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));