yaxunl added inline comments.
================
Comment at: lib/CodeGen/TargetInfo.cpp:7296
+ unsigned getASTAllocaAddressSpace() const override {
+ return LangAS::Count + getABIInfo().getDataLayout().getAllocaAddrSpace();
+ }
----------------
rjmccall wrote:
> yaxunl wrote:
> > rjmccall wrote:
> > > Can we rename LangAS::Count to something more meaningful like
> > > LangAS::FirstTargetAddressSpace? I think this would clarify a lot of
> > > code.
> > >
> > > Is the OpenCL special case in ASTContext::getTargetAddressSpace still
> > > correct with this patch? A pointer in LangAS::Default should be lowered
> > > as a generic pointer instead of a pointer into the alloca address space,
> > > right?
> > Will do.
> >
> > The OpenCL special case in ASTContext::getTargetAddressSpace is still
> > correct with this patch. In OpenCL private address space is still
> > represented in AST by LangAS::Default, so a pointer in LangAS::Default
> > should be lowered as a pointer to alloca address space.
> Then I don't understand. If __private is always the alloca address space,
> why does IRGen have to add addrspace casts after allocating local variables
> in it? IRGen's invariant is that the value stored in LocalDeclMap for a
> variable of AST type T is a value of type [[T]] addrspace([[AS]]) *, where
> [[T]] is the lowered IR type for T and [[AS]] is the target address space of
> the variable. For auto variables, AS is always LangAS::Default, which
> according to you means that [[AS]] is always LLVM's notion of the alloca
> address space, which is exactly the type produced by alloca. So why is there
> ever a cast?
>
> My understanding was that, on your target, __private is (at least sometimes)
> a 64-bit extension of the alloca address space, which is 32-bit. But that
> makes __private a different address space from the alloca address space, so
> the special case in getTargetAddressSpace is still wrong, because that
> special case means that a pointer-to-__private type will be lowered to be a
> 32-bit pointer type.
>
> Also, I'm not sure why the normal AddrSpaceMap mechanism isn't sufficient for
> mapping LangAS::Default.
This work is mostly for C++.
For OpenCL, the default address space is mapped to alloca address space (5),
there is no address space cast inserted.
For C++, the default address space is mapped to generic address space (0),
therefore the address space cast is needed.
https://reviews.llvm.org/D32248
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