Re: SPARC code generation references

There's a more general technique that, at the expense of code space, is
faster most of the time. You compile one version of the code that assumes
it's wrapped in a save/restore. Then you start compiling, outside-in, a
version that does not use save-restore. Every time you find you need to use
save-restore, you insert it and branch to the corresponding location in the
wrapped version.


This copes with such annoying cases as


void bufferchars(const char *s)
{
register char c;
while (c = *s++) {
*buf++ = c;
if (buf >= buflim) {
flushbuf(buf, buflim-bufbase);
buf = bufbase;
}
}
}


If you have a string that fits in the buffer, no save/restores are generated;
but if the string is many times larger than the buffer, you still only get
one save/restore.


I have glossed over many issues, mostly in that word "corresponding", as if
the optimal code didn't depend on how many registers you have free. But the
idea is there - postpone the save as long as possible, then do it and use an
alternate code sequence.


(Of course, do dead-code elimination, and move code around to turn jumps into
fallthroughs.)
--
-Colin


--

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