Experimental Physics and
Industrial Control System

"Lawrence T. Hoff" <[email protected]> · Wed, 29 Sep 2004 05:45:47 -0400

	Interesting. "my" compiler does not do that, therefore I 
cannot know for sure how to help out. In general, however, compilers
are free to treat memory locations in any way they see fit, unless
you use the "volatile" qualifier, which tells the compiler that
an address does *not* behave like a typical memory cell, and that
no assumptions can be made for purposes of optimization. I.e.
Try this instead (or compile with -fvolatile):

	static void copy4 (volatile int *p, volatile int *q, int n) {
	  while (n-- > 0) *q++ = *p++;
	}

	With my compiler it made no difference. All accesses were
32-bit.

HTH -- Larry

GNU C version gcc-2.96 (2.96+) 19990621 AltiVec (powerpc-wrs-vxworks)
compiled by GNU C version 2.96 20000731 (Red Hat Linux 7.3 2.96-113).

        .align 2
        .type    copy4,@function
copy4:
        mr 0,5
        cmpwi 0,0,0
        addi 5,5,-1
        bclr 4,1
.L5:
        mr 0,5
        lwz 9,0(3)
        cmpwi 0,0,0
        stw 9,0(4)
        addi 3,3,4
        addi 4,4,4
        addi 5,5,-1
        bc 12,1,.L5
        blr

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System