Re: [gofrontend-dev] Re: Go patch committed: Intrinsify runtime/internal/atomic functions

[Ian Lance Taylor <iant@golang.org>]

On Wed, May 22, 2019 at 9:36 PM Cherry Zhang <cherryyz@google.com> wrote:
>
> Jim, thank you for the fix! The patch looks good to me. Maybe we should also apply this to __atomic_add_fetch_4 and __atomic_add_fetch_8?
>
> Thanks,
> Cherry
>
>
>
> On Tue, May 21, 2019 at 11:25 PM Jim Wilson <jimw@sifive.com> wrote:
>>
>> On Sun, May 19, 2019 at 5:22 AM Andreas Schwab <schwab@linux-m68k.org> wrote:
>> > ../../../libgo/go/runtime/mbitmap.go: In function ‘runtime.setMarked.runtime.markBits’:
>> > ../../../libgo/go/runtime/mbitmap.go:291:9: internal compiler error: Segmentation fault
>> >   291 |  atomic.Or8(m.bytep, m.mask)
>> >       |         ^
>>
>> This is failing for RISC-V because __atomic_or_fetch_1 isn't a
>> built-in function that can be expanded inline.  You have to call the
>> library function in libatomic.  The C front-end is registering all of
>> the built-in functions, but it looks like the go front-end is only
>> registering functions it thinks it needs and this list is incomplete.
>> In expand_builtin, case BUILT_IN_ATOMIC_OR_FETCH_1, the external
>> library call for this gets set to BUILT_IN_ATOMIC_FETCH_OR_1.  Then in
>> expand_builtin_atomic_fetch_op when we call builtin_decl_explicit
>> (ext_call) it returns NULL.  This is because the go front end
>> registered BUILT_IN_ATOMIC_OR_FETCH_1 as a built-in, but did not
>> register BUILT_IN_ATOMIC_FETCH_OR_1 as a built-in.  The NULL return
>> from builtin_decl_explicit gives us an ADDR_EXPR with a NULL operand
>> which eventually causes the internal compiler error.  It looks like
>> the same thing is done with all of the op_fetch built-ins, so use of
>> any of them means that the fetch_op built-in also has to be
>> registered.  I verified with a quick hack that I need both
>> BUILT_IN_ATOMIC_FETCH_OR_1 and BUILT_IN_ATOMIC_FETCH_AND_1 defined as
>> built-ins to make a RISC-V go build work.  I haven't done any testing
>> yet.

Jim, you can go ahead and commit that patch with a ChangeLog entry.
(The files in go/gcc but not in go/gcc/gofrontend) are under normal
GCC rules.)  Thanks.

Ian