Re: PR90724 - ICE with __sync_bool_compare_and_swap with -march=armv8.2-a

[Kyrill Tkachov <kyrylo.tkachov@foss.arm.com>]

Hi Prathamesh

On 7/10/19 12:24 PM, Prathamesh Kulkarni wrote:
> Hi,
> For following test-case,
> static long long AL[24];
>
> int
> check_ok (void)
> {
>   return (__sync_bool_compare_and_swap (AL+1, 0x200000003ll, 
> 0x1234567890ll));
> }
>
> Compiling with -O2 -march=armv8.2-a results in:
> pr90724.c: In function ‘check_ok’:
> pr90724.c:7:1: error: unrecognizable insn:
>     7 | }
>       | ^
> (insn 11 10 12 2 (set (reg:CC 66 cc)
>         (compare:CC (reg:DI 95)
>             (const_int 8589934595 [0x200000003]))) "pr90724.c":6:11 -1
>      (nil))
>
> IIUC, the issue is that 0x200000003 falls outside the range of
> allowable immediate in cmp ? If it's replaced by a small constant then 
> it works.
>
> The ICE results with -march=armv8.2-a because, we enter if
> (TARGET_LSE) { ... } condition
> in aarch64_expand_compare_and_swap, while with -march=armv8.a it goes 
> into else,
> which forces oldval into register if the predicate fails to match.
>
> The attached patch checks if y (oldval) satisfies aarch64_plus_operand
> predicate and if not, forces it to be in register, which resolves ICE.
> Does it look OK ?
>
> Bootstrap+testing in progress on aarch64-linux-gnu.
>
> PS: The issue has nothing to do with SVE, which I incorrectly
> mentioned in bug report.
>
This looks ok to me (but you'll need maintainer approval).

Does this fail on the branches as well?

Thanks,

Kyrill


> Thanks,
> Prathamesh