On Fri, 1 Dec 2023, Jakub Jelinek wrote:
> Hi!
>
> The .{ADD,SUB}_OVERFLOW lowering is implemented by performing normal
> addition/subtraction (perhaps extended to even more bits than normally by
> continuing with extended values of operands after running of normal bits)
> and in addition to that trying to compute if certain sets of bits are either
> all zero or all sign extensions of the least significant bit.
>
> That code is in a lot of cases guarded just by a single condition (which
> can be idx > startlimb, idx >= startlimb or idx == startlimb) or by
> 2 conditions - if (idx >= startlimb) { if (idx == startlimb) ... else ... }
> Now, if_then_if_then_else when the second argument is NULL works just as
> if_then and sets m_gsi to be within the initially empty then block and that is
> where we emit code for constant tidx startlimb + (cmp_code == GT_EXPR).
> But in the 2 conditions case, m_gsi is set to the initially empty else
> block, so using EQ_EXPR for the condition was incorrect (and strangely
> nothing in the testsuite caught that), because the code for extracting the
> lowest set of bits (i.e. when tidx is startlimb) is then done when idx
> is not startlimb rather than when it is.
> The following patch fixes that.
>
> Note, when developing the lowering, I was using gcov to make sure all code
> is covered by the testsuite with minimum exceptions, so no idea how this
> slipped out.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Richard.
> 2023-12-01 Jakub Jelinek <ja...@redhat.com>
>
> PR middle-end/112750
> * gimple-lower-bitint.cc (bitint_large_huge::lower_addsub_overflow):
> Use NE_EXPR rather than EQ_EXPR for g2 if !single_comparison and
> adjust probabilities.
>
> * gcc.dg/bitint-41.c: Use -std=c23 rather than -std=c2x.
> * gcc.dg/torture/bitint-43.c: Likewise.
> * gcc.dg/torture/bitint-44.c: Likewise.
> * gcc.dg/torture/bitint-45.c: New test.
>
> --- gcc/gimple-lower-bitint.cc.jj 2023-11-24 11:30:24.416427246 +0100
> +++ gcc/gimple-lower-bitint.cc 2023-11-30 10:57:40.095555940 +0100
> @@ -4028,11 +4028,11 @@ bitint_large_huge::lower_addsub_overflow
> edge edge_true_true, edge_true_false, edge_false;
> gimple *g2 = NULL;
> if (!single_comparison)
> - g2 = gimple_build_cond (EQ_EXPR, idx,
> + g2 = gimple_build_cond (NE_EXPR, idx,
> size_int (startlimb), NULL_TREE,
> NULL_TREE);
> if_then_if_then_else (g, g2, profile_probability::likely (),
> - profile_probability::unlikely (),
> + profile_probability::likely (),
> edge_true_true, edge_true_false,
> edge_false);
> unsigned tidx = startlimb + (cmp_code == GT_EXPR);
> --- gcc/testsuite/gcc.dg/bitint-41.c.jj 2023-11-23 12:59:48.027443972
> +0100
> +++ gcc/testsuite/gcc.dg/bitint-41.c 2023-11-30 11:05:54.956550967 +0100
> @@ -1,6 +1,6 @@
> /* PR middle-end/112336 */
> /* { dg-do compile { target bitint } } */
> -/* { dg-options "-std=c2x" } */
> +/* { dg-options "-std=c23" } */
>
> unsigned _BitInt(1) v1;
> unsigned _BitInt(1) *p1 = &v1;
> --- gcc/testsuite/gcc.dg/torture/bitint-43.c.jj 2023-11-20
> 09:49:35.236668167 +0100
> +++ gcc/testsuite/gcc.dg/torture/bitint-43.c 2023-11-30 11:06:31.840028866
> +0100
> @@ -1,6 +1,6 @@
> /* PR c/111309 */
> /* { dg-do run { target bitint } } */
> -/* { dg-options "-std=c2x -pedantic-errors" } */
> +/* { dg-options "-std=c23 -pedantic-errors" } */
> /* { dg-skip-if "" { ! run_expensive_tests } { "*" } { "-O0" "-O2" } } */
> /* { dg-skip-if "" { ! run_expensive_tests } { "-flto" } { "" } } */
>
> --- gcc/testsuite/gcc.dg/torture/bitint-44.c.jj 2023-11-14
> 10:52:16.192276014 +0100
> +++ gcc/testsuite/gcc.dg/torture/bitint-44.c 2023-11-30 11:06:37.494948817
> +0100
> @@ -1,6 +1,6 @@
> /* PR c/111309 */
> /* { dg-do run { target bitint } } */
> -/* { dg-options "-std=c2x -pedantic-errors" } */
> +/* { dg-options "-std=c23 -pedantic-errors" } */
> /* { dg-skip-if "" { ! run_expensive_tests } { "*" } { "-O0" "-O2" } } */
> /* { dg-skip-if "" { ! run_expensive_tests } { "-flto" } { "" } } */
>
> --- gcc/testsuite/gcc.dg/torture/bitint-45.c.jj 2023-11-30
> 11:07:40.778053018 +0100
> +++ gcc/testsuite/gcc.dg/torture/bitint-45.c 2023-11-30 11:07:19.294357123
> +0100
> @@ -0,0 +1,32 @@
> +/* PR middle-end/112750 */
> +/* { 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" } { "" } } */
> +
> +#if __BITINT_MAXWIDTH__ >= 256
> +_BitInt(256) a = __INT_MAX__ + (_BitInt(256)) 1;
> +_BitInt(256) b = __INT_MAX__;
> +#endif
> +#if __BITINT_MAXWIDTH__ >= 512
> +_BitInt(512) c = 0x7fffffffffffffffffffffffffffffffffffffffwb +
> (_BitInt(512)) 1;
> +_BitInt(512) d = 0x7fffffffffffffffffffffffffffffffffffffffwb;
> +#endif
> +
> +int
> +main ()
> +{
> +#if __BITINT_MAXWIDTH__ >= 256
> + if (!__builtin_sub_overflow_p (a, 0, 0))
> + __builtin_abort ();
> + if (!__builtin_sub_overflow_p (b, -1, 0))
> + __builtin_abort ();
> +#endif
> +#if __BITINT_MAXWIDTH__ >= 512
> + if (!__builtin_sub_overflow_p (c, 0, (_BitInt(160)) 0))
> + __builtin_abort ();
> + if (!__builtin_sub_overflow_p (d, -1, 0))
> + __builtin_abort ();
> +#endif
> + return 0;
> +}
>
> 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)
