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Re: birthpoints in rtl.

From: Diego Novillo <dnovillo at google dot com>
To: Kenneth Zadeck <zadeck at naturalbridge dot com>
Cc: gcc <gcc at gcc dot gnu dot org>, "Bonzini, Paolo" <bonzini at gnu dot org>, "Park, Seongbae" <seongbae dot park at gmail dot com>, Ian Lance Taylor <iant at google dot com>, Richard Sandiford <rsandifo at nildram dot co dot uk>, Steven Bosscher <stevenb dot gcc at gmail dot com>
Date: Fri, 29 Feb 2008 17:51:23 -0500
Subject: Re: birthpoints in rtl.
References: <47C5EF2A.5020401@naturalbridge.com> <47C6B132.3090903@naturalbridge.com>

On 2/28/08 8:03 AM, Kenneth Zadeck wrote:

The big difference between what i am proposing with birthpoints and a
full blown ssa implementation is that i plan to do no rewriting since
there are no operands of the phis to support this.

You don't need to do a rewriting SSA implementation to have PHI nodes with operands. FUD chains fully support PHI nodes with operands.

I believe that what i am proposing is actually currently called (or at
least related to) factored use def chains, but i need to read up on the
literature to see if they really are the same.

Yes, they are. FUD chains are what I initially used on GIMPLE, but they do not allow overlapping live ranges for different SSA names of the same symbol, so for GIMPLE registers I implemented the basic rewriting form and for memory symbols I implemented FUD chains (the SSA web over VDEF/VUSEs are FUD chains).

If we are not going to use a rewriting SSA form, I believe that the original problems we had with RTL-SSA can be avoided.

Diego.

References:
- birthpoints in rtl.
  - From: Kenneth Zadeck
- Re: birthpoints in rtl.
  - From: Kenneth Zadeck

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