llvm dev - Jan 2012 - [LLVMdev] truncstore fails in PTX backend

From what I can tell, the truncstore paths all fail instruction selection in the
current PTX backend. This is easy to work around for int types >= 16 bits by
setting the truncstore action to expand in PTXISelLowering.cpp, but this cannot
handle i8 values, since the PTX backend has no register representation for i8s.
As a result of all this, it is not possible to store to i8 pointers at all.

PTX does support truncating stores, including to i8s. (ld/st and cvt are the
only ops which work with i8 types.)

Is this a known issue?

I'm far from a master of the SelectionDAG infrastructure, though this seems
like it should not be a terribly hard addition.
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On Tue, Jan 10, 2012 at 1:28 PM, Jonathan Ragan-Kelley <jrk at
csail.mit.edu>wrote:
> From what I can tell, the truncstore paths all fail instruction selection
> in the current PTX backend. This is easy to work around for int types >=
16
> bits by setting the truncstore action to expand in PTXISelLowering.cpp, but
> this cannot handle i8 values, since the PTX backend has no register
> representation for i8s. As a result of all this, it is not possible to
> store to i8 pointers at all.
>
> PTX does support truncating stores, including to i8s. (ld/st and cvt are
> the only ops which work with i8 types.)
>
> Is this a known issue?
>
Yes, this is known.  I've been too swamped with (mostly) unrelated work the
last month or so.  It's on my to-do list, but patches are always welcome. :)

>
> I'm far from a master of the SelectionDAG infrastructure, though this
> seems like it should not be a terribly hard addition.
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>
>

-- 

Thanks,

Justin Holewinski
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