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Re: PATCH:[darwin] fix load of a misaligned double word
- From: Brad Lucier <lucier at math dot purdue dot edu>
- To: dje at watson dot ibm dot com (David Edelsohn)
- Cc: lucier at mailhost dot math dot purdue dot edu (Brad Lucier), fjahanian at apple dot com (fj), gcc-patches at gcc dot gnu dot org, feeley at iro dot umontreal dot ca
- Date: Sat, 27 Dec 2003 17:38:47 -0500 (EST)
- Subject: Re: PATCH:[darwin] fix load of a misaligned double word
David:
Thanks, this fixes the performance degradation I was seeing (to within
benchmark measurement error).
I'll have to think a bit more about how to implement data-tagged languages like
Lisp or Scheme on PPC64. A tag of 0 is too useful for fixnums to use it
for anything else, and if one uses two tag bits, then tags of 1, 2, or 3 for
memory-allocated objects will require an extra addition to clear the tag. So
it appears that for a 64-bit Scheme/Lisp on PPC64 one should use at least
three tag bits with a tag value of 4 for memory-allocated objects.
Brad