> Am 27.01.2024 um 09:18 schrieb Jakub Jelinek <ja...@redhat.com>:
>
> Hi!
>
> The following testcase is miscompiled, because some narrower value
> is sign-extended to wider unsigned _BitInt used as division operand.
> handle_operand_addr for that case returns the narrower value and
> precision -prec_of_narrower_value. That works fine for multiplication
> (at least, normal multiplication, but we don't merge casts with
> .MUL_OVERFLOW or the ubsan multiplication right now), because the
> result is the same whether we treat the arguments as signed or unsigned.
> But is completely wrong for division/modulo or conversions to
> floating-point, if we pass negative prec for an input operand of a libgcc
> handler, those treat it like a negative number, not an unsigned one
> sign-extended from something smaller (and it doesn't know to what precision
> it has been extended).
>
> So, the following patch fixes it by making sure we don't merge such
> sign-extensions to unsigned _BitInt type with division, modulo or
> conversions to floating point.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Ok
Richard
> 2024-01-27 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/113614
> * gimple-lower-bitint.cc (gimple_lower_bitint): Don't merge
> widening casts from signed to unsigned types with TRUNC_DIV_EXPR,
> TRUNC_MOD_EXPR or FLOAT_EXPR uses.
>
> * gcc.dg/torture/bitint-54.c: New test.
>
> --- gcc/gimple-lower-bitint.cc.jj 2024-01-26 18:05:24.461891138 +0100
> +++ gcc/gimple-lower-bitint.cc 2024-01-26 19:04:07.948780942 +0100
> @@ -6102,17 +6102,27 @@ gimple_lower_bitint (void)
> && (TREE_CODE (rhs1) != SSA_NAME
> || !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs1)))
> {
> - if (TREE_CODE (TREE_TYPE (rhs1)) != BITINT_TYPE
> - || (bitint_precision_kind (TREE_TYPE (rhs1))
> - < bitint_prec_large))
> - continue;
> if (is_gimple_assign (use_stmt))
> switch (gimple_assign_rhs_code (use_stmt))
> {
> - case MULT_EXPR:
> case TRUNC_DIV_EXPR:
> case TRUNC_MOD_EXPR:
> case FLOAT_EXPR:
> + /* For division, modulo and casts to floating
> + point, avoid representing unsigned operands
> + using negative prec if they were sign-extended
> + from narrower precision. */
> + if (TYPE_UNSIGNED (TREE_TYPE (s))
> + && !TYPE_UNSIGNED (TREE_TYPE (rhs1))
> + && (TYPE_PRECISION (TREE_TYPE (s))
> + > TYPE_PRECISION (TREE_TYPE (rhs1))))
> + goto force_name;
> + /* FALLTHRU */
> + case MULT_EXPR:
> + if (TREE_CODE (TREE_TYPE (rhs1)) != BITINT_TYPE
> + || (bitint_precision_kind (TREE_TYPE (rhs1))
> + < bitint_prec_large))
> + continue;
> /* Uses which use handle_operand_addr can't
> deal with nested casts. */
> if (TREE_CODE (rhs1) == SSA_NAME
> @@ -6126,6 +6136,10 @@ gimple_lower_bitint (void)
> default:
> break;
> }
> + if (TREE_CODE (TREE_TYPE (rhs1)) != BITINT_TYPE
> + || (bitint_precision_kind (TREE_TYPE (rhs1))
> + < bitint_prec_large))
> + continue;
> if ((TYPE_PRECISION (TREE_TYPE (rhs1))
> >= TYPE_PRECISION (TREE_TYPE (s)))
> && mergeable_op (use_stmt))
> --- gcc/testsuite/gcc.dg/torture/bitint-54.c.jj 2024-01-26
> 19:09:01.436688318 +0100
> +++ gcc/testsuite/gcc.dg/torture/bitint-54.c 2024-01-26 19:16:24.908504368
> +0100
> @@ -0,0 +1,29 @@
> +/* PR tree-optimization/113614 */
> +/* { dg-do run { target bitint } } */
> +/* { dg-options "-std=c23 -pedantic-errors" } */
> +/* { dg-skip-if "" { ! run_expensive_tests } { "*" } { "-O0" "-O2" } } */
> +/* { dg-skip-if "" { ! run_expensive_tests } { "-flto" } { "" } } */
> +
> +_BitInt(8) a;
> +_BitInt(8) b;
> +_BitInt(8) c;
> +
> +#if __BITINT_MAXWIDTH__ >= 256
> +_BitInt(256)
> +foo (_BitInt(8) y, unsigned _BitInt(256) z)
> +{
> + unsigned _BitInt(256) d = -y;
> + z /= d;
> + return z + a + b + c;
> +}
> +#endif
> +
> +int
> +main ()
> +{
> +#if __BITINT_MAXWIDTH__ >= 256
> + if (foo (0xfwb, 0x24euwb))
> + __builtin_abort ();
> +#endif
> + return 0;
> +}
>
> Jakub
>
