[tree-ssa] reaching def. question

[law@redhat.com]

In message <1079481013.3173.481.camel@localhost.localdomain>, Diego Novillo wri
tes:
 >On Tue, 2004-03-16 at 18:42, law@redhat.com wrote:
 >
 >> It seems to me that to do that he must first take the affected variables
 >> out of SSA form.  Otherwise how does the renamer know which instance of
 >> "a" ought to be used?
 >> 
 >If you mark a _DECL to be renamed, the renamer itself strips the
 >SSA_NAME wrappers.
Which is not a safe thing to do if you've done things like copy propagation
since you can have overlapping lifetimes.

You also have to be damn careful about marking something to be rewritten
which is used in a mixed PHI node.  ie

a_3 = PHI (a_2, b_1)

Marking just a or b to be written is a recipe for disaster.


 > Or you mean *really* taking the variable out of SSA form?
If you've done things like copy propagation and the like, then yes,  you
really need to take it out of SSA form.


jeff