question about rtl loop-iv analysis

[Bernd Schmidt]

Michael Matz wrote:
> 
> Apart from that I agree that in the case of conditional defs multiple ones 
> might reach a use.  I disagree for partial defs, if one dominates the 
> other.  For most cases (except register allocation) a partial def is just 
> a complete killing def, which happens to leave some contents unchanged (by 
> conceptually copying that part from what was in there before, hence the 
> usual read-mod-write dependency from a partial def which generates also a 
> use).  But the use doesn't care for this, for all it knows that def is the 
> one changing the contents, hence a use-def chain should not contain a def 
> dominating other defs (partial or not).  The relationship between both 
> defs will be described by the use-def chain hanging off the implicit use 
> generated by the partial def.

I completely agree, and I've tried very hard to argue that with Kenneth 
last year when I spotted this kind of bogosity in the dataflow code, but 
I got nowhere.  I wish you better luck.


Bernd
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