Ramana,
could you review this?

original thread https://gcc.gnu.org/ml/gcc-patches/2016-05/msg00630.html, 
reproduced below:


currently, the documentation for -mno-pic-data-is-text-relative (-mno-PDITR) says
'Assume that each data segments are relative to text segment at load time.
  Therefore, it permits addressing data using PC-relative operations.
  This option is on by default for targets other than VxWorks RTP.'

However, if you use just this option, you still end up with a pic-register init 
sequence that presumes a fixed mapping. That's a surprise. Joey tells me its 
expected use is with -msingle-pic-base (-mSPB), which reserves a global register 
to point at the (single) GOT. That's what I had expected the -mno-PDITR option 
to have implied.

Apparently there are legitimate reasons one might want the -mno-PDITR behaviour 
without -mSPB. I don't know what those are though.

Anyway, IMHO that is the rare case and the more common case is that one would 
want to have -mnoPDITR imply -mSPB. (The reverse probably doesn't apply.)

This patch does 3 things.
1) have -mno-PDITR imply -mSPB, unless one has explicitly provided -m[no-]SPB.
2) clarified  the -m[no-]PDITR documentation.
3) Added some testcases -- there didn't appear to be any.

ok?

nathan