Re: [PATCH] Fix aarch64_compare_and_swap* constraints (PR target/87839)

[Kyrill Tkachov <kyrylo dot tkachov at foss dot arm dot com>]

Hi Jakub,

On 13/11/18 09:28, Jakub Jelinek wrote:
> Hi!
>
> The following testcase ICEs because the predicate and constraints on one of
> the operands of @aarch64_compare_and_swapdi aren't consistent.  The RA which
> goes according to constraints
> (insn 15 13 16 2 (set (reg:DI 104)
>         (const_int 8589934595 [0x200000003])) "pr87839.c":15:3 47 {*movdi_aarch64}
>      (expr_list:REG_EQUIV (const_int 8589934595 [0x200000003])
>         (nil)))
> (insn 16 15 21 2 (parallel [
>             (set (reg:CC 66 cc)
>                 (unspec_volatile:CC [
>                         (const_int 0 [0])
>                     ] UNSPECV_ATOMIC_CMPSW))
>             (set (reg:DI 101)
>                 (mem/v:DI (reg/f:DI 99) [-1  S8 A64]))
>             (set (mem/v:DI (reg/f:DI 99) [-1  S8 A64])
>                 (unspec_volatile:DI [
>                         (reg:DI 104)
>                         (reg:DI 103)
>                         (const_int 0 [0])
>                         (const_int 32773 [0x8005]) repeated x2
>                     ] UNSPECV_ATOMIC_CMPSW))
>             (clobber (scratch:SI))
>         ]) "pr87839.c":15:3 3532 {aarch64_compare_and_swapdi}
>      (expr_list:REG_UNUSED (reg:DI 101)
>         (expr_list:REG_UNUSED (reg:CC 66 cc)
>             (nil))))
> when seeing n constraint puts the 0x200000003 constant directly into the
> atomic instruction, but the predicate requires that it is either a register,
> or shifted positive or negative 12-bit constant and so it fails to split.
> The positive shifted constant apparently has I constraint and negative one
> J, and other uses of aarch64_plus_operand that have some constraint use
> rIJ (or r):
> config/aarch64/aarch64.md: (match_operand:GPI 2 "aarch64_plus_operand" "r,I,J"))
> config/aarch64/aarch64.md:                (match_operand:SI 2 "aarch64_plus_operand" "r,I,J"))
> config/aarch64/aarch64.md: (match_operand:GPI 1 "aarch64_plus_operand" "r,I,J"))
> config/aarch64/aarch64.md: (match_operand:GPI 1 "aarch64_plus_operand" "r"))
> config/aarch64/aarch64.md: (match_operand:GPI 1 "aarch64_plus_operand" "r,I,J")))]
>
> I don't have a setup to easily bootstrap/regtest aarch64-linux ATM, could
> somebody please include it in their bootstrap/regtest? Thanks.
>
> 2018-11-13  Jakub Jelinek  <jakub@redhat.com>
>
>         PR target/87839
>         * config/aarch64/atomics.md (@aarch64_compare_and_swap<mode>): Use
>         rIJ constraint for aarch64_plus_operand rather than rn.
>
>         * gcc.target/aarch64/pr87839.c: New test.

This passes bootstrap and regtesting shows no problems on aarch64-none-linux-gnu.
The change looks good to me but you'll still need maintainer approval.

Thanks,
Kyrill

> --- gcc/config/aarch64/atomics.md.jj    2018-11-01 12:06:43.469963662 +0100
> +++ gcc/config/aarch64/atomics.md       2018-11-13 09:59:35.660185116 +0100
> @@ -71,7 +71,7 @@ (define_insn_and_split "@aarch64_compare
>      (match_operand:GPI 1 "aarch64_sync_memory_operand" "+Q"))   ;; memory
>     (set (match_dup 1)
>      (unspec_volatile:GPI
> -      [(match_operand:GPI 2 "aarch64_plus_operand" "rn")       ;; expect
> +      [(match_operand:GPI 2 "aarch64_plus_operand" "rIJ")      ;; expect
>         (match_operand:GPI 3 "aarch64_reg_or_zero" "rZ")                ;; desired
>         (match_operand:SI 4 "const_int_operand")                        ;; is_weak
>         (match_operand:SI 5 "const_int_operand")                        ;; mod_s
> --- gcc/testsuite/gcc.target/aarch64/pr87839.c.jj 2018-11-13 10:13:44.353309416 +0100
> +++ gcc/testsuite/gcc.target/aarch64/pr87839.c  2018-11-13 10:13:05.496944699 +0100
> @@ -0,0 +1,29 @@
> +/* PR target/87839 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -w" } */
> +
> +long long b[64];
> +void foo (void);
> +int bar (void (*) (void));
> +void qux (long long *, long long) __attribute__((noreturn));
> +void quux (long long *, long long);
> +
> +void
> +baz (void)
> +{
> +  __sync_val_compare_and_swap (b, 4294967298LL, 78187493520LL);
> +  __sync_bool_compare_and_swap (b + 1, 8589934595LL, 21474836489LL);
> +  __sync_fetch_and_xor (b, 60129542145LL);
> +  quux (b, 42949672967LL);
> +  __sync_xor_and_fetch (b + 22, 60129542145LL);
> +  quux (b + 23, 42949672967LL);
> +  if (bar (baz))
> +    __builtin_abort ();
> +  foo ();
> +  __sync_val_compare_and_swap (b, 4294967298LL, 0);
> +  __sync_bool_compare_and_swap (b + 1, 8589934595LL, 78187493520LL);
> +  if (__sync_or_and_fetch (b, 21474836489LL) != 21474836489LL)
> +    qux (b + 22, 60129542145LL);
> +  __atomic_fetch_nand (b + 23, 42949672967LL, __ATOMIC_RELAXED);
> +  bar (baz);
> +}
>
>         Jakub