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tree-ssa.texi (Preserving the virtual ssa form): New subsection. 

2006-04-04  Daniel Berlin  <dberlin@dberlin.org>

	* doc/tree-ssa.texi (Preserving the virtual ssa form): New
	subsection.

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@ -1,3 +1,8 @@
2006-04-04 Daniel Berlin <dberlin@dberlin.org>
* doc/tree-ssa.texi (Preserving the virtual ssa form): New
subsection.
2006-04-04 Matthias Klose <doko@debian.org>
* Makefile.in (unprotoize.o): Same dependencies as for protoize.o.

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gcc/doc/tree-ssa.texi
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@ -1384,6 +1384,26 @@ There are several @code{TODO} flags that control the behavior of
renaming are processed@.
@end itemize
@subsection Preserving the virtual SSA form
@cindex preserving virtual SSA form
The virtual SSA form is harder to preserve than the non-virtual SSA form
mainly because the set of virtual operands for a statement may change at
what some would consider unexpected times. In general, any time you
have modified a statement that has virtual operands, you should verify
whether the list of virtual operands has changed, and if so, mark the
newly exposed symbols by callnig @code{mark_new_vars_to_rename}.
There is one additional caveat to preserving virtual SSA form. When the
entire set of virtual operands may be eliminated due to better
disambiguation, a bare SMT will be added to the list of virtual
operands, to signify the non-visible aliases that the are still being
referenced. If the set of bare SMT's may change,
@code{TODO_update_smt_usage} should be added to the todo flags.
With the current pruning code, this can only occur when constants are
propagated into array references that were previously non-constant, or
address expressions are propagated into their uses.
@subsection Examining @code{SSA_NAME} nodes
@cindex examining SSA_NAMEs