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Re: Combine versus volatile (Was: Re: Performance of Integer Multiplication on PIII)
- To: jh at suse dot cz
- Subject: Re: Combine versus volatile (Was: Re: Performance of Integer Multiplication on PIII)
- From: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- Date: Thu, 8 Nov 01 09:44:09 EST
- Cc: gcc at gcc dot gnu dot org, torvalds at transmeta dot com
Unfortunately I am not at all sure if it is needed in combine - I am
not able to come with counterexample where it can cause problems.
Combine, in worst case, IMO can change the size of memory read and I
am not quite sure if we require this to not change in our volatile
definition.
We do require this not to change.
There are also other more obscure cases, but I can't think of them just now.
I agree that we can *a bit* more in optimizing volatile references, but I
don't think we need to: they should be used very sparingly and we should treat
them quite conservatively.