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Re: long long / long long
- To: Linus Torvalds <torvalds at transmeta dot com>
- Subject: Re: long long / long long
- From: David Edelsohn <dje at watson dot ibm dot com>
- Date: Mon, 10 Sep 2001 13:38:21 -0400
- cc: jbuck at synopsys dot COM, gcc at gcc dot gnu dot org
Some of the problems have to do with value range propagation
optimizations which GCC currently does not have. The VRP patch under
development is far too over-engineered, IMHO.
What matters is whether the register will have a zero or non-zero
value. Or at best, whether the subreg bytes will be zero or not. Knowing
that the value will be between 33 and 34066415 really doesn't matter at
that level of detail. For DImode as a pair of 32-bit registers, knowing
that one register will be zero allows a lot of simplifications to be
propagated throughout the computation.
David