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Re: [tree-ssa] Copy prop into virtual operands
- From: law at redhat dot com
- To: Diego Novillo <dnovillo at redhat dot com>
- Cc: Andrew Macleod <amacleod at redhat dot com>, gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 29 Jul 2003 09:25:45 -0600
- Subject: Re: [tree-ssa] Copy prop into virtual operands
- Reply-to: law at redhat dot com
In message <1059491832.3164.36.camel@frodo.toronto.redhat.com>, Diego Novillo w
rites:
>On Tue, 2003-07-29 at 11:14, Andrew MacLeod wrote:
>
>> > Right. But I don't see how we would get into this situation. After
>> > all, we only do constant propagation on real operands.
>> >
>> How do you know what a real operand is now? you don't have a flag any
>> more...
>>
>CCP only propagates from def_ops() into use_ops(). We only follow
>use-def chains on real operands, not virtual. And any definition coming
>from anything but the LHS of a MODIFY_EXPR is considered VARYING.
This is not in CCP. This is in the dominator optimizer. If you wait
until CCP, then you'll get little/no benefit from propagating into
virtual operands.
jeff