pratlucas added inline comments.
================
Comment at: clang/lib/CodeGen/CGBuiltin.cpp:10366
+ auto Alignment = CGM.getNaturalPointeeTypeAlignment(
+ E->getArg(0)->IgnoreParenCasts()->getType());
Ops[0] = Builder.CreateBitCast(Ops[0], llvm::PointerType::getUnqual(VTy));
----------------
LukeGeeson wrote:
> simon_tatham wrote:
> > What effect is this change of strategy having on the alignment computation,
> > for the already-supported instances of this builtin?
> >
> > It //looks// to me as if `__builtin_neon_vld1_v` with (say) a `uint8_t *`
> > pointer argument will now compute `Alignment=1` (the natural alignment of
> > the pointee type), whereas it would previously have computed `Alignment=8`
> > (the size of the whole vector being loaded or stored).
> >
> > Is that intentional? Or accidental? Or have I completely misunderstood
> > what's going on?
> >
> > (Whichever of the three, some discussion in the commit message would be a
> > good idea, explaining why this change does or does not make a difference,
> > as appropriate.)
> Clang was incorrectly assuming that all the pointers from which loads were
> being generated for vld1 intrinsics were aligned according to according to
> the intrinsics result type. This causes alignment faults on the code
> generated by the backend.
> This fixes the issue so that alignment is based on the type of the pointer
> provided to as input to the intrinsic.
>
> @pratlucas has done some work on this in parallel
> https://reviews.llvm.org/D79721 which has been approved and may overrule this
> particular line of code.
>
> I shall add a note to the commit message, and tentatively mark this as fixed,
> given it's liable to adopt the work of Lucas.
>
Hi @LukeGeeson ,
Just as a heads up, some changes to this implementations were requested on
D79721.
The usage of `CGM.getNaturalPointeeTypeAlignment` and `IgnoreParenCasts()` was
causing problems on certain argument types, so the alignment is now captured
from the expression itself when it is emitted.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D80716/new/
https://reviews.llvm.org/D80716
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