[PATCH][0/2] GIMPLE Frontend

[Richard Biener]

I've posted two patches implementing a GIMPLE Frontend to the extent
required for simple unit testing of GIMPLE passes.  The work was
mostly done by Prasad Ghangal during this years GSoC project.  I've
picked it up to ensure it would be ready for the end of stage1
even though the frontend itself can IMHO be developed throughout
stage3 where required.

https://gcc.gnu.org/ml/gcc-patches/2016-10/msg02336.html
https://gcc.gnu.org/ml/gcc-patches/2016-10/msg02335.html

The current status is that simple C testcases can be compiled
and dumped at some random pass with -gimple and that dump
output can be fed back into the GIMPLE frontend (by adding -fgimple
to the C compiler invocation).

Most syntax and semantic checking is only done by the GIMPLE
verification code we have in the middle-end as the parser is
modeled after the C one which usually accepts more complex input
as allowed by GIMPLE.

I expect there is syntax we still do not parse (MEM_REF comes to
my mind) plus on-the-side info that we either do not have a good
source representation for or that the parser does not yet parse
(generally EH info or things like range info or points-to info).

Currently what the parser emits is a mixed bag of low and high
gimple (it's technically high gimple as it still has the outer
gimple BIND).  It parses SSA form with PHIs being represented
as a function call to __PHI with pairs of label (comes-from)
and value.

A feature of the frontend is that it allows (or rather requires
for all declarations) mixing C with GIMPLE.  This means you
can write a single function in GIMPLE and surround it with
a (unit-)test harness written in C.

I hope we can get this into GCC 7, kind of as a preview as I expect
it will evolve once we get the first unit tests (I didn't try to
re-write existing tests).

Thanks,
Richard.