[clang] abe8b35 - Fix vtbl field addr space

[Yaxun Liu via cfe-commits]

Author: Yaxun (Sam) Liu
Date: 2021-09-16T10:57:31-04:00
New Revision: abe8b354e37d8d6a163a6402d8e68ddcfc462dfc

URL: https://github.com/llvm/llvm-project/commit/abe8b354e37d8d6a163a6402d8e68ddcfc462dfc
DIFF: https://github.com/llvm/llvm-project/commit/abe8b354e37d8d6a163a6402d8e68ddcfc462dfc.diff

LOG: Fix vtbl field addr space

Storing the vtable field of an object should use the same address space as
the this pointer. Currently it is assumed to be addr space 0 but this may not
be true.

This assumption (added in 054cc3b1b469de4b0cb25d1dc3af43c679c5dc44) caused
issues for the out-of-tree CHERI targets.

Reviewed by: John McCall, Alexander Richardson

Differential Revision: https://reviews.llvm.org/D109841

Added: 
    

Modified: 
    clang/lib/CodeGen/CGClass.cpp

Removed: 
    


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diff  --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 9895a23b7093..828dd7147da5 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -2502,6 +2502,8 @@ void CodeGenFunction::InitializeVTablePointer(const VPtr &Vptr) {
 
   // Apply the offsets.
   Address VTableField = LoadCXXThisAddress();
+  unsigned ThisAddrSpace =
+      VTableField.getPointer()->getType()->getPointerAddressSpace();
 
   if (!NonVirtualOffset.isZero() || VirtualOffset)
     VTableField = ApplyNonVirtualAndVirtualOffset(
@@ -2516,12 +2518,11 @@ void CodeGenFunction::InitializeVTablePointer(const VPtr &Vptr) {
       llvm::FunctionType::get(CGM.Int32Ty, /*isVarArg=*/true)
           ->getPointerTo(ProgAS)
           ->getPointerTo(GlobalsAS);
-  // vtable field is is derived from `this` pointer, therefore it should be in
-  // default address space.
-  VTableField = Builder.CreatePointerBitCastOrAddrSpaceCast(
-      VTableField, VTablePtrTy->getPointerTo());
-  VTableAddressPoint = Builder.CreatePointerBitCastOrAddrSpaceCast(
-      VTableAddressPoint, VTablePtrTy);
+  // vtable field is is derived from `this` pointer, therefore they should be in
+  // the same addr space. Note that this might not be LLVM address space 0.
+  VTableField = Builder.CreateBitCast(VTableField,
+                                      VTablePtrTy->getPointerTo(ThisAddrSpace));
+  VTableAddressPoint = Builder.CreateBitCast(VTableAddressPoint, VTablePtrTy);
 
   llvm::StoreInst *Store = Builder.CreateStore(VTableAddressPoint, VTableField);
   TBAAAccessInfo TBAAInfo = CGM.getTBAAVTablePtrAccessInfo(VTablePtrTy);