On Wed, Aug 06, 2025 at 05:57:51PM +0800, Yang Yujie wrote:
> A widening cast from a signed _BitInt operand to an unsigned _BitInt
> type involves filling the extra limb(s) with sign extension.
> On a target that wants _BitInts extended in memory, if this unsigned
> type has a partial limb, the unused part of it should be zeroed.
>
> e.g. Assuming limb_mode == E_DImode, at the end of
>
> void
> test (unsigned _BitInt(519) *t, _BitInt(512) x)
> {
> *t = -x;
> }
>
> the most significant limb of *t should be masked with 0x7f.
>
> This patch also fixes gcc.dg/torture/bitint-16.c, which aborts at -O2
> when the extension on load is optimized away.
>
> gcc/ChangeLog:
>
> * gimple-lower-bitint.cc (bitint_large_huge::lower_mergeable_stmt):
> Zero-extend the partial limb of any unsigned _BitInt LHS assigned
> with a widening sign-extension.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/torture/bitint-83.c: New test.
Ok.
Jakub
