Re: Autoincrement examples

["Rask Ingemann Lambertsen" <rask at kampsax dot k-net dot dk>]

Den 22-Sep-99 11:08:25 skrev Bernd Schmidt fĝlgende om "Autoincrement examples":

> If someone has (preferrably small) example code (for any target), which
> shows how the compiler generates auto-increments either very well or very
> badly,

   This particular example has long been a pet peeve of mine wrt. GCC code
generation on m68k:

void stringcopy (const char *src, char *dest)
{
	while (*dest++ = *src++)
		;
}

   GCC 2.95.1 generates this code for the loop body:

L5:
	moveb a1@+,a0@
	tstb a0@+
	jne L5

   That sort of code will give any m68k programmer red eyes, since the tstb
instruction is unneeded. The loop body should be just

L5:
	moveb a1@+,a0@+
	jne L5

   In particular on the 68010, the latter loop should be quite a bit
faster (2*strlen(src) + 2 memory accesses instead of 5*strlen(src) memory
accesses.

Regards,

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