On Mon, 26 Jan 2015, Jakub Jelinek wrote:
> Hi!
>
> On the following testcase we generate wrong code, because
> apparently divmod_internal_2 relies on 0 being the topmost
> element (at b_dividend[m]):
> algorithm. M is the number of significant elements of U however
> there needs to be at least one extra element of B_DIVIDEND
> allocated, N is the number of elements of B_DIVISOR. */
> The comment talks just about allocation, but from the code
> it seems it really relies on it being 0.
> There is space for it:
> unsigned HOST_HALF_WIDE_INT
> b_dividend[(4 * MAX_BITSIZE_MODE_ANY_INT / HOST_BITS_PER_HALF_WIDE_INT) +
> 1];
> unsigned HOST_HALF_WIDE_INT
> b_divisor[4 * MAX_BITSIZE_MODE_ANY_INT / HOST_BITS_PER_HALF_WIDE_INT];
> (the + 1), and usually there already is a zero in there:
> m = dividend_blocks_needed;
> while (m > 1 && b_dividend[m - 1] == 0)
> m--;
> so the only problematic case is if m isn't decreased.
>
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,
> ok for trunk?
Ok.
Thanks,
Richard.
> 2015-01-26 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/64807
> * wide-int.cc (wi::divmod_internal): Clear
> b_dividend[dividend_blocks_needed].
>
> * gcc.dg/pr64807.c: New test.
>
> --- gcc/wide-int.cc.jj 2015-01-09 21:59:38.000000000 +0100
> +++ gcc/wide-int.cc 2015-01-26 19:21:56.114316481 +0100
> @@ -1819,6 +1819,7 @@ wi::divmod_internal (HOST_WIDE_INT *quot
> divisor_blocks_needed, divisor_prec, sgn);
>
> m = dividend_blocks_needed;
> + b_dividend[m] = 0;
> while (m > 1 && b_dividend[m - 1] == 0)
> m--;
>
> --- gcc/testsuite/gcc.dg/pr64807.c.jj 2015-01-26 19:24:13.612943033 +0100
> +++ gcc/testsuite/gcc.dg/pr64807.c 2015-01-26 19:32:34.502237566 +0100
> @@ -0,0 +1,19 @@
> +/* PR tree-optimization/64807 */
> +/* { dg-do run { target int128 } } */
> +/* { dg-options "-O2" } */
> +
> +__uint128_t
> +foo (void)
> +{
> + __uint128_t a = -1;
> + __uint128_t b = -1;
> + return a / b;
> +}
> +
> +int
> +main ()
> +{
> + if (foo () != 1)
> + __builtin_abort ();
> + return 0;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Jennifer Guild,
Dilip Upmanyu, Graham Norton HRB 21284 (AG Nuernberg)
