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Re: Dropping of old loop optimizer
- From: law at redhat dot com
- To: Jan Hubicka <jh at suse dot cz>
- Cc: Daniel Berlin <dberlin at dberlin dot org>, Pop Sébastian <pop at gauvain dot u-strasbg dot fr>, Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>, tm_gccmail at mail dot kloo dot net, gcc at gcc dot gnu dot org, m dot hayes at elec dot canterbury dot ac dot nz, rth at redhat dot com, dan at dberlin dot org
- Date: Fri, 28 Feb 2003 07:29:28 -0700
- Subject: Re: Dropping of old loop optimizer
- Reply-to: law at redhat dot com
In message <20030228095445 dot GD5431 at kam dot mff dot cuni dot cz>, Jan Hubicka writes:
>>
>> On Thursday, February 27, 2003, at 12:13 PM, Pop Sébastian wrote:
>>
>> >On Thu, Feb 27, 2003 at 05:39:17PM +0100, Zdenek Dvorak wrote:
>> >>
>> >>The problem I see is that rtl ssa is broken (or never worked?); but
>> >Last time I had a close look at rtl was about two years ago :-)
>> >Dan is the expert to ask about the status of SSA at rtl level (he
>> >adapted
>> >the CCP code from rtl to tree-ssa).
>> The problem with RTL SSA is hard registers and subregs.
>> There are hard registers assigned in certain cases during initial RTL
>> generation.
>> These can't be renamed, obviously.
>
>The tree-SSA represents the SSA form as datastructure on the top of the
>trees not modifying the trees themselves, right? Why it is not feasible
>for RTL (ie you won't need to rename the registers)
hard-regs and subregs really aren't really the problem with rtl-ssa,
they're both solvable. The first by ignoring them, the second with
some annoying, but not terribly difficult work in the ssa->normal
translator.
What is far more of a problem for rtl-ssa is the lack of any kind of
generic level rtl.
The tree-SSA branch using a rewriting SSA form now.
Jeff