kovdan01 wrote:
> I think you should be able to avoid constructing the initializer twice if you
> restructure the code a bit to just construct the global before the call to
> BuildVTablePointer. I added GlobalVariable::replaceInitializer because I was
> looking at this review: it lets you construct the global before the
> initializer, without having to do awkward things with RAUW.
@efriedma-quic Sorry, I'm not sure if I got your point correctly.
The issue with enabling address discrimination for signed vtable pointers is
that it requires self-references - see, for example,
llvm/test/CodeGen/AArch64/ptrauth-type-info-vptr-discr.ll:
```
@_ZTI10TestStruct = constant { ptr, ptr } {
ptr ptrauth (
ptr getelementptr inbounds ( ; <== raw unsigned pointer
ptr,
ptr @_ZTVN10__cxxabiv117__class_type_infoE,
i64 2),
i32 2, ; <== key
i64 [[STDTYPEINFO_DISC]], ; <== constant discr
; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ptr @_ZTI10TestStruct), ; <== address discr
; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ptr @_ZTS10TestStruct
}
```
As far as I understand, the correct way of creating such structures which
contain self-references, is to use `ConstantInitBuilder` and
`getAddrOfCurrentPosition`. As far as I see from its source code, it handles
self-references specially. With `ConstantInitBuilder`, we'll not end up with a
vector of elements to be passed as struct initializer (`Fields` in our case) -
instead, we'll need to call `finishAndSetAsInitializer` on the builder object.
As for `replaceInitializer` - sure, we can use it in existing code below, where
we have `if (OldGV) { /* ... */ }`. But I'm not sure how it this newly proposed
function can help us in context of this particular patch.
Do I miss smth? Can we somehow differently handle self-references and avoid
using `ConstantInitBuilder`? Thanks in advance!
https://github.com/llvm/llvm-project/pull/102199
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