Re: [patch] Cleanup and improvement of if-conversion for vectorization

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, May 24, 2010 at 11:29 AM, Sebastian Pop <sebpop@gmail.com> wrote:
> Hi,
>
> The attached patch-set cleans the code of the current if-conversion
> pass, separates the analysis of the basic block predicates from the
> transformation, and improves the if-conversion by transforming loops
> containing conditions with memory references. ?Conditional writes to
> memory are handled as non conditional writes by reading and writing
> back the same value, like this:
>
> +/* Predicate each write to memory in LOOP.
> +
> + ? Replace a statement "A[i] = foo" with "A[i] = cond ? foo : A[i]"
> + ? with the condition COND determined from the ->aux field of the
> + ? basic block containing the statement. ?*/
>
> With this patch set, I am XFAIL-ing vect-ifcvt-18.c that I am
> considering unsafe for the if-conversion as currently implemented in
> trunk. ?I am XFAIL-ing it until I get a patch that checks that a
> statically allocated data reference cannot trap in a loop accessed
> niter times. ?vect-ifcvt-18.c looks like the testcase of
> http://gcc.gnu.org/PR43423
>
> __attribute__ ((noinline)) void
> foo (int mid, int n)
> {
> ?int i;
>
> ?for (i = 0; i < n; i++)
> ? ?if (i < mid)
> ? ? ?A[i] = A[i] + B[i];
> ? ?else
> ? ? ?A[i] = A[i] + C[i];
> }
>
> After if-conversion the accesses to B and C would be executed for
> every iteration, and without proving that B and C have "n" elements,
> the if-converted code could trap.
>
> The patch-set passes test and bootstrap with BOOT_CFLAGS="-g -O3".
> Ok for trunk?
>

One of your changes caused:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44293

-- 
H.J.