On Tue, 21 Jun 2022, Jakub Jelinek wrote:
> Hi!
>
> noce_try_sign_mask as documented will optimize
> if (c < 0)
> x = t;
> else
> x = 0;
> into x = (c >> bitsm1) & t;
> The optimization is done if either t is unconditional
> (e.g. for
> x = t;
> if (c >= 0)
> x = 0;
> ) or if it is cheap. We already check that t doesn't have side-effects,
> but if t is conditional, we need to punt also if it may trap or fault,
> as we make it unconditional.
>
> I've briefly skimmed other noce_try* optimizations and didn't find one that
> would suffer from the same problem.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Thanks,
Richard.
> 2022-06-21 Jakub Jelinek <ja...@redhat.com>
>
> PR rtl-optimization/106032
> * ifcvt.cc (noce_try_sign_mask): Punt if !t_unconditional, and
> t may_trap_or_fault_p, even if it is cheap.
>
> * gcc.c-torture/execute/pr106032.c: New test.
>
> --- gcc/ifcvt.cc.jj 2022-04-26 10:11:51.951558338 +0200
> +++ gcc/ifcvt.cc 2022-06-20 17:44:18.638394338 +0200
> @@ -2833,18 +2833,19 @@ noce_try_sign_mask (struct noce_if_info
> return FALSE;
>
> /* This is only profitable if T is unconditionally executed/evaluated in
> the
> - original insn sequence or T is cheap. The former happens if B is the
> - non-zero (T) value and if INSN_B was taken from TEST_BB, or there was no
> - INSN_B which can happen for e.g. conditional stores to memory. For the
> - cost computation use the block TEST_BB where the evaluation will end up
> - after the transformation. */
> + original insn sequence or T is cheap and can't trap or fault. The
> former
> + happens if B is the non-zero (T) value and if INSN_B was taken from
> + TEST_BB, or there was no INSN_B which can happen for e.g. conditional
> + stores to memory. For the cost computation use the block TEST_BB where
> + the evaluation will end up after the transformation. */
> t_unconditional
> = (t == if_info->b
> && (if_info->insn_b == NULL_RTX
> || BLOCK_FOR_INSN (if_info->insn_b) == if_info->test_bb));
> if (!(t_unconditional
> - || (set_src_cost (t, mode, if_info->speed_p)
> - < COSTS_N_INSNS (2))))
> + || ((set_src_cost (t, mode, if_info->speed_p)
> + < COSTS_N_INSNS (2))
> + && !may_trap_or_fault_p (t))))
> return FALSE;
>
> if (!noce_can_force_operand (t))
> --- gcc/testsuite/gcc.c-torture/execute/pr106032.c.jj 2022-06-20
> 18:00:01.064352904 +0200
> +++ gcc/testsuite/gcc.c-torture/execute/pr106032.c 2022-06-20
> 17:59:41.714600349 +0200
> @@ -0,0 +1,21 @@
> +/* PR rtl-optimization/106032 */
> +
> +__attribute__((noipa)) int
> +foo (int x, int *y)
> +{
> + int a = 0;
> + if (x < 0)
> + a = *y;
> + return a;
> +}
> +
> +int
> +main ()
> +{
> + int a = 42;
> + if (foo (0, 0) != 0 || foo (1, 0) != 0)
> + __builtin_abort ();
> + if (foo (-1, &a) != 42 || foo (-42, &a) != 42)
> + __builtin_abort ();
> + return 0;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstraße 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
