PATCH: SelectionDAG: Use MVT::i32 for vector indices

[Tom Stellard]

On Mon, Jul 29, 2013 at 08:22:24AM -0700, Tom Stellard wrote:
> On Mon, Jul 29, 2013 at 02:41:11PM +0200, Duncan Sands wrote:
> > Hi Tom,
> > 
> > >The attached patch ensures that the SelectionDAG always uses MVT::i32
> > >for the index operands of EXTRACT_VECTOR_ELT, INSERT_VECTOR_ELT,
> > >INSERT_SUBVECTOR, and EXTRACT_SUBVECTOR.  MVT::i32 was chosen because
> > >the LLVM IR specification uses i32 for all its vector instructions that
> > >take an index arguement.
> > 
> > I think this is a bad idea since it assumes that the i32 type is legal for
> > all platforms.
> >
> 
> The first version of this patch that I wrote:
> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20130715/181799.html
> added TargetLowering::getVectorIdxTy() which targets could use to specify
> whatever type the wanted.  What do you think of using the version one patch
> instead?
> 

Ping.

> 
> > >The previous code was using TargetLowering::getPointerTy() for vector
> > >indices.  I think the reason for this was to make it easier to handle
> > >non-constant vector indices, which required that the vector be
> > >stored in memory.
> > 
> > I think the real reason is that an integer type with the same size as a pointer
> > is required to be a legal type on all platforms.
> > 
> > >
> > >Using TargetLowering::getPointerTy() can be a problem for targets with
> > >pointer sizes that differ across address spaces, since the address space
> > >used to store the vector may have a different pointer size than the
> > >'zero' address space which is what TargetLowering::getPointerTy() uses.
> > 
> > I think this is a different issue to the one of always using an integer type
> > that is guaranteed to be legal.
> > 
> > Ciao, Duncan.
> > 
> > >
> > >There are two motivations for this patch, the first is to clean
> > >up some bad code that is generated when using dynamic indexing
> > >of vectors in the R600 target.  The second is to reduce the use of
> > >TargetLowering::getPointerTy() in the SelectionDAG code which will help
> > >anyone who is trying to improve support for targets with pointer sizes
> > >that differ across address spaces.
> > >
> > >Please Review.
> > >
> > >Thanks,
> > >Tom
> > >
> > >
> > >
> > >
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> > >
> > 
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