On Tue, 5 Dec 2023, Jakub Jelinek wrote:
> Hi!
>
> A zero or sign extension from result of some upwards_2limb operation
> is implemented in lower_mergeable_stmt as an extra loop which fills in
> the extra bits with 0s or 1s.
> If the delta of extended vs. unextended bit count is small, the code
> doesn't use a loop and emits up to a couple of stores to constant indexes,
> but if the delta is large, it uses
> cnt = (bo_bit != 0) + 1 + (rem != 0);
> statements. bo_bit is non-zero for bit-field loads and is done in that
> case as straight line, the unconditional 1 in there is for a loop which
> handles most of the limbs in the delta and finally (rem != 0) is for the
> case when the extended precision is not a multiple of limb_prec and is
> again done in straight line code (after the loop).
> The testcase ICEs because the decision what idx to use was incorrect
> for kind == bitint_prec_huge (i.e. when the precision delta is very large)
> and rem == 0 (i.e. the extended precision is multiple of limb_prec).
> In that case cnt is either 1 (if bo_bit == 0) or 2, and idx should
> be either first size_int (start) and then result of create_loop (for bo_bit
> != 0) or just result of create_loop, but by mistake the last case
> was size_int (end), which means when precision is multiple of limb_prec
> storing above the precision (which ICEs; but also not emitting the loop
> which is needed).
>
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok
> for trunk?
OK.
> 2023-12-05 Jakub Jelinek
>
> PR tree-optimization/112809
> * gimple-lower-bitint.cc (bitint_large_huge::lower_mergeable_stmt): For
> separate_ext in kind == bitint_prec_huge mode if rem == 0, create for
> i == cnt - 1 the loop rather than using size_int (end).
>
> * gcc.dg/bitint-48.c: New test.
>
> --- gcc/gimple-lower-bitint.cc.jj 2023-12-05 09:48:14.0 +0100
> +++ gcc/gimple-lower-bitint.cc2023-12-05 18:55:58.996323144 +0100
> @@ -2624,7 +2624,7 @@ bitint_large_huge::lower_mergeable_stmt
> {
> if (kind == bitint_prec_large || (i == 0 && bo_bit != 0))
> idx = size_int (start + i);
> - else if (i == cnt - 1)
> + else if (i == cnt - 1 && (rem != 0))
> idx = size_int (end);
> else if (i == (bo_bit != 0))
> idx = create_loop (size_int (start + i), _next);
> --- gcc/testsuite/gcc.dg/bitint-48.c.jj 2023-12-05 19:00:19.593664966
> +0100
> +++ gcc/testsuite/gcc.dg/bitint-48.c 2023-12-05 19:00:14.599735086 +0100
> @@ -0,0 +1,23 @@
> +/* PR tree-optimization/112809 */
> +/* { dg-do compile { target bitint } } */
> +/* { dg-options "-O2" } */
> +
> +#if __BITINT_MAXWIDTH__ >= 512
> +_BitInt (512) a;
> +_BitInt (256) b;
> +_BitInt (256) c;
> +
> +int
> +foo (void)
> +{
> + return a == (b | c);
> +}
> +
> +void
> +bar (void)
> +{
> + a /= b - 2;
> +}
> +#else
> +int i;
> +#endif
>
> Jakub
>
>
--
Richard Biener
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
