GC improvement

[Henry Cejtin]

I  did  a  quick  hack  changing  gc.h  to  use my wordAlign() definition and
changing forward() in gc.c to  actually  test  to  make  sure  that  all  the
alignments  were  satisfied  and  to  then  just loop moving words instead of
calling memmove().  The result in a self compile was that GC  time  decreased
by 27% on a Red Hat 6.2 machine.  Not huge, but definitely not bad.  The most
extreme case is going to be  when  the  live  data  consists  of  many  small
objects.  I don't know if this is the case with the self compile or not.

Any way, here are the changes to the two files.  I will probably do some more
serious hacking on the gc, but if you agree that the relevant alignments  are
all  true  in  the copy loop, then you should replace the check with assert's
and put it in the official source.  Also, if the memmove()  in  copyStack  is
for non-overlapping regions, you should change it to a memcpy().

*** gc.orig.h	Thu Apr 19 17:37:11 2001
--- gc.h	Wed Jun 27 02:01:24 2001
***************
*** 85,91 ****
--- 85,95 ----
  }
  
  static inline uint wordAlign(uint p) {
+ #if 1	/* HCC */
+ 	return ((p + 3) & ~ 3);
+ #else
  	return ((1 + ((p - 1) >> 2)) << 2);
+ #endif
  }
  
  /* ------------------------------------------------- */
diff -c gc.orig.c gc.c
*** gc.orig.c	Fri Jun 22 11:45:56 2001
--- gc.c	Wed Jun 27 02:11:49 2001
***************
*** 965,971 ****
--- 965,989 ----
  		if (s->back + size + skip > s->toLimit)
  			die("Out of memory.");
  		/* Copy the object. */
+ #if 1	/* HCC */
+ 		{
+ 			uint	*to,
+ 				*from,
+ 				*limit;
+ 
+ 			to = (uint *)s->back;
+ 			from = (uint *)(p - headerBytes);
+ 			if ((size & 3)
+ 			or  ((uint)to & 3)
+ 			or  ((uint)from & 3))
+ 				die("Henry: you blew it");
+ 			limit = (uint *)((char *)from + size);
+ 			until (from == limit)
+ 				*to++ = *from++;
+ 		}
+ #else
  		memmove(s->back, p - headerBytes, size);
+ #endif
   		/* Store the forwarding pointer in the old object. */
  		*(word*)(p - WORD_SIZE) = FORWARDED;
  		*(pointer*)p = s->back + headerBytes;