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Re: [ping][PATCH][1 of 2] Add value range info to SSA_NAME for zero sign extension elimination in RTL

On Tue, Sep 10, 2013 at 03:17:50PM +0200, Richard Biener wrote:
> > unsigned short s;
> > s.1_3 = (short unsigned int) l.0_2;
> > l.0_2: VARYING
> > s.1_3: [0, +INF]
> Note that [0, +INF] is the same as VARYING and [-INF, +INF] and VARYING for
> l.0_2 is the same as [-INF, +INF].

Yeah, I don't see much value in differentiating between VR_VARYING and
VR_RANGE [TYPE_MIN_VALUE, TYPE_MAX_VALUE] (perhaps a question is what to do
for types with precisions different from TYPE_MODE's bitsize, if we should
store for VARYING/UNDEFINED a range of all possible values in the mode).
Unsigned type will be always >= 0, even if it is VARYING or UNDEFINED.
What is the valid bit good for?  Is it meant just for integrals with >
2*HOST_BITS_PER_WIDE_INT precision, which we can't represent in double_int?
I'd say we just don't want to keep track on the value ranges for those.
And, do we need to distinguish between VR_RANGE and VR_ANTI_RANGE?
I mean, can't we always store the range in VR_RANGE format?  Instead of
-[3,7] we'd store [8,2] and define that if the min double_int is bigger than
max double_int, then it is [min,+infinity] merged with [-infinity,max] range
(i.e. -[max+1,min-1])?

> Micha just suggested
>   union vrp_info_type {
>     /* Pointer attributes used for alias analysis.  */
>     struct GTY ((tag ("0"))) ptr_info_def *ptr_info;
>     /* Value range attributes used for zero/sign extension elimination.  
> */
>     struct GTY ((tag ("1"))) range_info_def *range_info;
>   } GTY ((desc ("%1.typed.type ? !POINTER_TYPE_P (TREE_TYPE 

Why not TREE_TYPE(&%1) here and why the (tree) cast?


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