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

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

On Wed, Jun 9, 2010 at 3:07 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Thu, May 27, 2010 at 8:38 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> 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
>>
>
> One of your changes also caused:
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44483
>
>

One of your changes also caused:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45971


-- 
H.J.