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Re: [tree-ssa] CCP and variable reference fixes [patch]


On Thu, 07 Nov 2002, Jason Merrill wrote:

> On Thu, 7 Nov 2002 07:36:17 -0500, Diego Novillo <dnovillo@redhat.com> wrote:
> 
> > - Removes unnecessary fields from tree_ref structure.  We don't
> >   need to keep pointers into the expression nor operand for each
> >   reference.  This makes it possible for a pass to replicate a
> >   statement and replace references from the original statement
> >   into the copy.
> 
> When rth and I were talking about this later, it occurred to me that if we
> can have an expression with uses of two different defs of the same variable
> in a single stmt, then we do need a use to refer directly to its instance
> of the variable within the statement.
> 
Impossible.  If you have two uses of the same variable coming
from different definitions, then your SSA information is
completely broken.  It's actually not possible for the SSA
builder to create such a thing (it keeps a single instance of
'current definition').


Diego.


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