On Wed, 6 Aug 2025, Jakub Jelinek wrote:
> Hi!
>
> handle_operand_addr (used for the cases where we use libgcc APIs, so
> multiplication, division, modulo, casts of _BitInt to float/dfp) when it
> sees default definition of an SSA_NAME which is not PARM_DECL (i.e.
> uninitialized one) just allocates single uninitialized limb, there is no
> need to waste more memory on it, it can just tell libgcc that it has
> 64-bit precision, not say 1024 bit etc.
> Unfortunately, doing this runs into some asserts when we have a narrowing
> cast of the uninitialized SSA_NAME (but still large/huge _BitInt).
>
> The following patch fixes that by using a magic value in *prec_stored
> for the uninitialized cases (0) and just don't do any *prec tweaks for
> narrowing casts from that. precs still needs to be maintained as before,
> that one is used for big endian adjustment.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
> 2025-08-06 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/121127
> * gimple-lower-bitint.cc (bitint_large_huge::handle_operand_addr): For
> uninitialized SSA_NAME, set *prec_stored to 0 rather than *prec.
> Handle that case in narrowing casts. If prec_stored is non-NULL, set
> *prec_stored to prec_stored_val.
>
> * gcc.dg/bitint-125.c: New test.
>
> --- gcc/gimple-lower-bitint.cc.jj 2025-05-22 11:01:04.820035770 +0200
> +++ gcc/gimple-lower-bitint.cc 2025-08-05 11:15:31.597227618 +0200 @@
> -2373,7 +2373,7 @@ range_to_prec (tree op, gimple *stmt)
> from that precision, if it is negative, the operand is sign-extended
> from -*PREC. If PREC_STORED is NULL, it is the toplevel call,
> otherwise *PREC_STORED is prec from the innermost call without
> - range optimizations. */
> + range optimizations (0 for uninitialized SSA_NAME). */
>
> tree
> bitint_large_huge::handle_operand_addr (tree op, gimple *stmt,
> @@ -2481,7 +2481,7 @@ bitint_large_huge::handle_operand_addr (
> *prec = TYPE_UNSIGNED (TREE_TYPE (op)) ? limb_prec : -limb_prec;
> precs = *prec;
> if (prec_stored)
> - *prec_stored = precs;
> + *prec_stored = 0;
> tree var = create_tmp_var (m_limb_type);
> TREE_ADDRESSABLE (var) = 1;
> ret = build_fold_addr_expr (var);
> @@ -2510,6 +2510,13 @@ bitint_large_huge::handle_operand_addr (
> int prec_stored_val = 0;
> ret = handle_operand_addr (rhs1, g, &prec_stored_val, prec);
> precs = prec_stored_val;
> + if (prec_stored)
> + *prec_stored = prec_stored_val;
> + if (precs == 0)
> + {
> + gcc_assert (*prec == limb_prec || *prec == -limb_prec);
> + precs = *prec;
> + }
> if (TYPE_PRECISION (lhs_type) > TYPE_PRECISION (rhs_type))
> {
> if (TYPE_UNSIGNED (lhs_type)
> @@ -2518,7 +2525,9 @@ bitint_large_huge::handle_operand_addr (
> }
> else
> {
> - if (*prec > 0 && *prec < TYPE_PRECISION (lhs_type))
> + if (prec_stored_val == 0)
> + /* Non-widening cast of uninitialized value. */;
> + else if (*prec > 0 && *prec < TYPE_PRECISION (lhs_type))
> ;
> else if (TYPE_UNSIGNED (lhs_type))
> {
> --- gcc/testsuite/gcc.dg/bitint-125.c.jj 2025-08-05 11:17:26.297717091
> +0200
> +++ gcc/testsuite/gcc.dg/bitint-125.c 2025-08-05 11:17:17.262836076 +0200
> @@ -0,0 +1,15 @@
> +/* PR tree-optimization/121127 */
> +/* { dg-do compile { target bitint } } */
> +/* { dg-options "-O2 -w" } */
> +
> +#if __BITINT_MAXWIDTH__ >= 576
> +_BitInt(575)
> +foo (void)
> +{
> + _BitInt(576) d;
> + _BitInt(575) e = d * 42wb;
> + return e;
> +}
> +#else
> +int i;
> +#endif
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
