This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]

Re: Patch for h8300 port


On Fri, Oct 06, 2000 at 07:03:58PM -0400, Kazu Hirata wrote:
> A friend of mine on some mailing list was about to submit a very similar
> patch, where he was trying to change "2,4" to "2,6".  What a coincidence!

Oh, I see -- the h8 isn't a fixed-width architecture.
We are misjudging the length of the mov.w instruction.

Looking at the movhi pattern, I see that indeed moves
from memory may be either 2 or 4 bytes on h8300h or
h8300s.  So "2,6" would be the correct conservative
estimate, though splitting the input to "0,>,g" would
give the more accurate "2,4,6".

> By the way, as far as the comments I've read somewhere, the 2nd
> alternative, suggested to be deleted by the patch, is for optimization
> purpose, where -O0 generates a horibly long sequence of insns.

A very plausable explanation.  It would be still be
interesting to know how removing the memory alternative
affects optimized code, however.


r~

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]