Re: [RFC] Contributing tree-ssa to mainline

[law at redhat dot com]

In message <10401191507.AA28782@vlsi1.ultra.nyu.edu>, Richard Kenner writes:
 >Not necessarily.  If the front end is already tracking some dataflow for its
 >own purposes and can use that knowlege to eliminate a check, why would it be
 >better for it *not* to do so?  As I said, all over GCC we're doing
 >"duplicate" simplifications and the fact that we do so is one of the major
 >strengths of the compiler.
Certainly if you have information handy which allows you to create more
efficient code, then by all means use it.  But I wouldn't suggest tracking
dataflow in the front-end solely for the case of optimization purpose,
particularly for things like bounds checking since we really need to be
doing that in language independent ways given that every language can and
should be making use of those optimizers.


 >    There has been some discussion of perhaps lowering ARRAY_REFs.  But
 >    that would be done relatively late in the tree pipeline.
 >
 >Good, because that's my concern: the form of the subscript information is
 >critical to many high-level loop optimizations.  If you're going to have to
 >figure that out from an address computation, you're giving up much of the
 >benefit of doing that optimization on trees instead of RTL>
Agreed.   

jeff