LNO optimizing out operations it shouldn't?

[Timothy J.Wood <tjw at omnigroup dot com>]

  I just built up LNO for the first time last night and was surprised 
at its behavior with a simple example (based on one of the 
tree-ssa-vect tests):


#define VECTOR_SIZE 512

typedef float afloat __attribute__ ((__aligned__(16)));

extern void check(const afloat * __restrict__ x, const afloat * 
__restrict__ y, const afloat * __restrict__ out);

void mul(const afloat * __restrict__ x, const afloat * __restrict__ y, 
afloat * __restrict__ out)
{
    unsigned int i;
    for (i = 0; i < VECTOR_SIZE; i++)
	out[i] = x[i] * y[i];
    //check(x,y,out);
}


  build with:

$PREFIX/bin/gcc -O2 -ftree-vectorize -fdump-tree-vect-stats -maltivec 
-S test.c  -o test.s

  I get the following on Darwin:

.text
	.align 2
	.align 2
	.globl _mul
_mul:
	li r0,128
	mtctr r0
L2:
	bdnz L2
	blr

  If I remove the comment on the call to 'check', real code to do the 
'*' gets emitted.  This seems like a pretty obvious case, and in fact I 
see that tree-ssa-vect-1.c has this same sort of 'call to non-existant' 
function (and of course many of the other test have checking to verify 
the results...).

  This this seems obvious, but I don't see anything in bugzilla.

-tim