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Re: [tree-ssa] Copy prop into virtual operands


On Tue, 2003-07-29 at 11:25, law@redhat.com wrote:
> 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.
> 
Similar principle, the dominator optimizers don't pick up constant
values from VDEFs, do they?  If 'a' is aliased:

	a_2 = VDEF <a_1>
	a = 3;

we won't register the tuple <a_2, '3'> in const_and_copies, correct?


Diego.


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