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Re: Using shifts by 1 on K6,K7 and i386
- To: "Martin Erhardsen" <MartinErhardsen at mail dot tele dot dk>
- Subject: Re: Using shifts by 1 on K6,K7 and i386
- From: Jeffrey A Law <law at cygnus dot com>
- Date: Wed, 05 Jul 2000 19:06:47 -0600
- cc: gcc at gcc dot gnu dot org
- Reply-To: law at cygnus dot com
In message <000701bfe33f$1e751e60$b495f9c3@mincomputer>you write:
> Why doesn't gcc use logical shifts, arithmetric shifts and rotates by 1
> instead of immediate operands on the K6,K7 and i386.
Because nobody's told us what is best for this case on the K6, K7 and
i386.
> It saves a byte and has the same latency (except on i486,
> where it uses an extra cycle). I have measured this on
> my K6-2 and looked it up for K7 and i386
OK.
> I propose that the current predicate for using shifts
> and rotates by 1
So, submit a patch which changes i386.md appropriately.
THanks,
jeff