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


On Wed, 17 Jul 2019 at 13:45, Kyrill Tkachov
<kyrylo.tkachov@foss.arm.com> wrote:
>
> 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?
Hi Kyrill,
Thanks for the review. The test also fails on gcc-9-branch (but not on gcc-8).

Thanks,
Prathamesh
>
> Thanks,
>
> Kyrill
>
>
> > Thanks,
> > Prathamesh


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