Re: [nvptx, committed] Disable -gstatement-frontiers for nvptx

[Tom de Vries <Tom_deVries at mentor dot com>]

On 12/29/2017 05:12 AM, Alexandre Oliva wrote:
> On Dec 27, 2017, Tom de Vries <Tom_deVries@mentor.com> wrote:
>
> > .loc file_index line_number column_position
>
> > so this causes ptxas errors when compiling something for nvptx with
> > -g, which breaks the nvptx build.
>
> What do the errors look like?

The nvptx-none build breaks in libgcc:
...
configure:3706: error: in 
`/home/vries/nvptx/mainkernel-2/build-gcc/nvptx-none/libgcc':
configure:3709: error: cannot compute suffix of object files: cannot compile
...

For this conftest.c:
...
#define PACKAGE_NAME "GNU C Runtime Library"
#define PACKAGE_TARNAME "libgcc"
#define PACKAGE_VERSION "1.0"
#define PACKAGE_STRING "GNU C Runtime Library 1.0"
#define PACKAGE_BUGREPORT ""
#define PACKAGE_URL "http://www.gnu.org/software/libgcc/";
/* end confdefs.h.  */

int
main ()
{

  ;
  return 0;
}
...

We get this error:
...
$ build-gcc/gcc/xgcc -Bbuild-gcc/gcc -c -g -O2 conftest.c
ptxas conftest.o, line 17; fatal   : Parsing error near 'st': syntax error
ptxas fatal   : Ptx assembly aborted due to errors
nvptx-as: ptxas returned 255 exit status
...

By using -Wa,--no-verify, we can see the ptxas input:
...
$ cat -n conftest.o
    ...
    15  mov.u32 %value,0;
    16  .loc 1 15 1 is_stmt 0
    17  st.param.u32 [%value_out],%value;
    18  ret;
    19  }
...

With -gno-statement-frontiers, we have this instead:
...
    ...
    13  mov.u32 %value,0;
    14  .loc 1 15 1
    15  st.param.u32 [%value_out],%value;
    16  ret;
    17  }
...
and ptxas is able to parse the input.

> I ask because the patches that actually change the generated debug info,
> adding view to .loc lines when the assembler supports them, are yet to
> be installed, in the patches that introduces LVUs.  No significant
> changes have been made to dwarf2out in the SFN patchset so far.
>
> Furthermore, even with the LVU patch, .loc directives with view numbers
> would only be used if the assembler is detected as supporting them at
> compiler build time.

If you point me to the location of a configure test that is supposed to 
file, I can try to find out why it passes.

Thanks,
- Tom