[PATCH] D75423: [OpenCL] Mark pointers to constant address space as invariant

Mon Mar 2 09:55:35 PST 2020

rjmccall added a comment.

In D75423#1901348 <https://reviews.llvm.org/D75423#1901348>, @yaxunl wrote:

> In D75423#1901254 <https://reviews.llvm.org/D75423#1901254>, @rjmccall wrote:
>
> > In D75423#1901206 <https://reviews.llvm.org/D75423#1901206>, @hliao wrote:
> >
> > > invariant checking already takes account of loading from constant address space or memory (AA::pointsToConstantMemory), that's almost equivalent to adding invariant attributes. Why do we mark these constant loads with additional attributes?
> >
> >
> > If alias analysis already knows that all memory in the constant address space is immutable,  I agree that should be sufficient, at least on targets where the constant address space is actually a different address space in LLVM IR.  If it only knows that when it can resolve an access down to a specific `constant` global variable, this patch is still providing value because it applies even for accesses through a pointer.
>
>
> There is plan for amdgcn target to drop constant address space in IR and use global address space instead.
>
> Also, currently there are targets (e.g. x86_64) supporting OpenCL which does not have constant address space in IR.

Okay, then I have no problem taking a patch for this into IRGen.  But I think it should be fine to do this by adding the invariant-load metadata when loading from an l-value instead of injecting invariant-groups into l-value emission.

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https://reviews.llvm.org/D75423