[m-rev.] for review 1/4: Disable GCC Labels on RISC-V

[Julien Fischer]

On Sat, 18 Mar 2023, Paul Bone wrote:

> On Fri, 17 Mar 2023, at 3:03 PM, Julien Fischer wrote:
>> Hi Paul,
>>
>> On Fri, 17 Mar 2023, Paul Bone wrote:
>>
>>> The configure test runs an infinite loop on RISC-V, disable it.
>>
>> Aarch64 had the same issue, the solution there was to disable the GCC
>> option -ftree-dominator-opts.
>
> I saw that.  The code below that says that PIC is still a problem though.  I'm trying now with gcc 12 and -fno-tree-dominator-opts (I copied the code from the aarch64 section).  The configure script is happy but the runtime won't compile.  I'm hitting (unrelated?) GCC bugs, both GCC 12 and GCC 9:
>
> $ ../scripts/mgnuc --grade asm_fast.gc    --c-debug --no-ansi   --      -c mercury_engine.c -o mercury_engine.o
> mercury_engine.c: Assembler messages:
> mercury_engine.c:476: Error: junk at end of line, first unrecognized character is `/'
> mercury_engine.c:523: Error: junk at end of line, first unrecognized character is `/'

It is likely we may need to add some workarounds for RISC-V / PIC to
runtime/mercury_goto.h.

> What's interesting here is if I do:
>
> $ ../scripts/mgnuc --grade asm_fast.gc    --c-debug --no-ansi   --      -S mercury_engine.c -o mercury_engine.S
> $ ../scripts/mgnuc --grade asm_fast.gc    --c-debug --no-ansi   --      -c mercury_engine.S -o mercury_engine.o
>
> Then it works, well it builds the .o file but I don't know if it has valid code.

If you disable the use of shared libs, you should be able to check if it
works.

> Since I'm using gcc 12 (I have convenient access to 9, 10, 11 and 12) I may have the same problem on RISC-V.  But without getting really in-depth I won't know if a problem I'm having is because of PIC or because of -ftree-dominator-opts. 
>
> I don't want to spend more time chasing asm_fast right now.  So I'll update the comment and push the changes I made.

Sure, go ahead.

Julien.