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Re: RFC: using clz for comparing to zero on the tree level.
- From: Richard Henderson <rth at redhat dot com>
- To: David Edelsohn <dje at watson dot ibm dot com>
- Cc: Andrew Pinski <pinskia at physics dot uc dot edu>, gcc at gcc dot gnu dot org
- Date: Thu, 8 May 2003 10:54:25 -0700
- Subject: Re: RFC: using clz for comparing to zero on the tree level.
- References: <20030508162704.GB8330@redhat.com> <200305081636.MAA27134@makai.watson.ibm.com>
On Thu, May 08, 2003 at 12:36:35PM -0400, David Edelsohn wrote:
> Not Alpha and not ARM V5, which have single instruction clz?
PPC:
cntlz tmp, in
srwi out, tmp, 5
Alpha:
cmpeq in, 0, out
ARM:
cmp in, #0
movne out, #0
moveq out, #1
Hmm, so it might be a win for ARM. You'll have to work out
with Richard Earnshaw how you want to arrange these costs.
At the moment arm_rtx_costs doesn't tell you that the SEQ
operation takes 3 instructions.
r~