[LLVMdev] (GEP) Index validity

[Matthijs Kooijman]

Hi Chris & Evan,

On Sun, Jul 13, 2008 at 03:34:03PM -0700, Chris Lattner wrote:
> Why?  What value does that provide?  Struct indices are not allowed to  
> be variable, so picking any width constant (that isn't too small) is  
> fine.  What problem are you trying to solve here?
The current code only allows 32 bit constants. My patch allows any width
constant to be used, but it seems Evan doesn't agree with that.

On Fri, Jul 11, 2008 at 10:56:16AM -0700, Evan Cheng wrote:
> >> I don't think this is right. According to llvm documentation:
> >>
> >> The index types specified for the 'getelementptr' instruction  depend on
> >> the pointer type that is being indexed into. Pointer and array types  can
> >> use a 32-bit or 64-bit integer type but the value will always be sign
> >> extended to 64-bits. Structure and packed structure types require i32
> >> constants.
> > That's correct. I'm not saying to allow other integer types for GEP
> > instructions. The first two methods below are methods in StructType  and
> > SequentialType. Regardless of any limitations posed by a GEP  instruction,
> > I argue that "i8 2" is a perfectly valid index for a struct. The fact
> > that it is not valid for a GEP instruction, should be checked somewhere
> > else  (GEPInst constructor or GEPInst::getIndexedValue probably).
> That's what the documentation is saying though. Struct and packed  
> structure types require i32 constants. Perhaps I am misunderstanding  
> something?
Ah, I did miss the "only 32 bit" limitation for structs, which makes my
current argpromotion fix wrong. However, I still think that that is a GEP
limitation, that does not belong with StructType. Or is there some other piece
of documentation you are referring to?

Gr.

Matthijs