If I understand correctly:
Prop. of "0" causes simplfy-rtx to create NOP from OR Rx,0
This NOP (deletion?) creates another set of potential uses - as now
the prior RHS def now passes straight thru to a new set of uses - but
we miss those new uses. (which in the testcase are often 0)
I will try fwprop in a few different spots latter and see what, if any
changes occur.
thanks again
Andy
-----Original Message-----
From: Paolo Bonzini <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Cc: gcc@gcc.gnu.org
Sent: Thu, 21 Feb 2008 11:04 am
Subject: Re: Redundant logical operations left after early splitting
Putting fwprop after combine is no problem - but is too early - none
of > the patterns would be split at that time - preventing byte level >
propagations.
Yeah, I meant "after split" actually.
Anyway, the problem is that if the RHS becomes a constant, fwprop does
not propagate the LHS anymore. I can try to add some def->use
propagation.
(PS I was impressed by fwprop code, I actually stand a chance of >
understanding some of it)
Thanks (since I and Steven Bosscher wrote it) -- but I guess that's
what you can expect from optimization passes that can rely on a decent
framework (simplify-rtx.c and df-*.c).
Paolo
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