On Wed, 1 Feb 2023, Jakub Jelinek wrote:
> Hi!
>
> The PR78437 r7-4871 changes made combine_reaching_defs punt on
> WORD_REGISTER_OPERATIONS targets if a setter of smaller than word
> register has wider uses. This unfortunately breaks -fcompare-debug,
> because if such a use appears only in DEBUG_INSN(s), while all other
> uses aren't wider than the setter, we can REE optimize it without -g
> and not with -g.
>
> Such decisions shouldn't be based on debug instructions. We could try
> to reset them or adjust in some other way after we decide to perform the
> change, but at least on the testcase which used to fail on riscv64-linux
> the
> (debug_insn 8 7 9 2 (var_location:HI s (minus:HI (subreg:HI (and:DI (reg:DI
> 10 a0 [160])
> (const_int 1 [0x1])) 0)
> (subreg:HI (ashiftrt:DI (reg/v:DI 9 s1 [orig:151 l ] [151])
> (debug_expr:SI D#1)) 0))) "pr108573.c":12:5 -1
> (nil))
> clearly doesn't care about the upper bits and I have hard time imaging how
> could one end up with DEBUG_INSN which actually cares about those upper
> bits.
>
> So, the following patch just ignores uses on DEBUG_INSNs in this case,
> if we run into something where we'd need to do something further later on,
> let's deal with it when we have a testcase for it.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux (admittedly
> non-WORD_REGISTER_OPERATIONS targets) and tested using a cross to
> riscv64-linux on the testcase, ok for trunk?
OK.
Richard.
> 2023-02-01 Jakub Jelinek <ja...@redhat.com>
>
> PR debug/108573
> * ree.cc (combine_reaching_defs): Don't return false for paradoxical
> subregs in DEBUG_INSNs.
>
> * gcc.dg/pr108573.c: New test.
>
> --- gcc/ree.cc.jj 2023-02-01 10:19:22.833436546 +0100
> +++ gcc/ree.cc 2023-02-01 12:25:57.468252609 +0100
> @@ -875,7 +875,8 @@ combine_reaching_defs (ext_cand *cand, c
>
> for (df_link *use = uses; use; use = use->next)
> if (paradoxical_subreg_p (GET_MODE (*DF_REF_LOC (use->ref)),
> - GET_MODE (SET_DEST (*dest_sub_rtx))))
> + GET_MODE (SET_DEST (*dest_sub_rtx)))
> + && !DEBUG_INSN_P (DF_REF_INSN (use->ref)))
> return false;
> }
>
> @@ -963,7 +964,8 @@ combine_reaching_defs (ext_cand *cand, c
> rtx dest2 = SET_DEST (*dest_sub_rtx2);
> for (use = uses; use; use = use->next)
> if (paradoxical_subreg_p (GET_MODE (*DF_REF_LOC (use->ref)),
> - GET_MODE (dest2)))
> + GET_MODE (dest2))
> + && !DEBUG_INSN_P (DF_REF_INSN (use->ref)))
> break;
> if (use)
> break;
> --- gcc/testsuite/gcc.dg/pr108573.c.jj 2023-02-01 12:15:20.476577340
> +0100
> +++ gcc/testsuite/gcc.dg/pr108573.c 2023-02-01 12:15:03.044832520 +0100
> @@ -0,0 +1,18 @@
> +/* PR debug/108573 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fcompare-debug" } */
> +
> +unsigned g;
> +
> +int bar (void);
> +int baz (int);
> +
> +void
> +foo (unsigned short s, long l)
> +{
> + unsigned u = bar ();
> + s &= __builtin_add_overflow_p (0, u, 0);
> + s %= g;
> + s -= l >> s;
> + baz (s);
> +}
>
> 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)
