#pragma GCC unroll support

[Mike Stump <mikestump at comcast dot net>]

So, I have a rough cut of a new feature to add pragma GCC unroll support to gcc.  It is safe wrt the test suite and code-gen, but there are some corners that I need help or suggestions on how to round off nicely.

Things to think about, can we put this in even if we have TODO support for C++ template support?  I think that is only 2-5 lines away from completion, but one needs to play peak-a-boo with some data (the unroll count) and I wanted to let pt fingers decide where to hide the data.  See RANGE_FOR_IVDEP for how I want to do it.

Can I increase the size of all annotations to 3 from 2?  It seemed safer, easier than trying to subdivide it.

I didn’t engineer ivdeps and unroll together.  Does it sound reasonable to allow both to be used at the same time on the same loop?  If so, I can add the two other cases, presently I just handle one of them then the loop.

Fortran support is left to the fortran people, if they want to do it.  I wired it up tantalizingly close for them to complete.

See ICK in the code.  I was unsure how to resolve that code.

Does unroll 8 mean that the loop is repeated 8 times?

Can I turn on peeling in try_peel_loop by simply wanted to do it for 1 loop?

I support using -1 for a directive that says, don’t peel, don’t unroll.  As a UI issue, I think this is wrong.  I want to to be either 0 or 1, those two seem better.  But, not sure which is the right one of the two.  Which number says, don’t unroll, I’m smarter than you think.

If we have a loop that we know can only be unroll 7 times, and the user says unroll 8, should we unroll it 7 times?  Presently I do.  The other option, is to ignore the directive when we know it is non-sensicle.

Yes, I’m aware that this isn’t the right phase for this, but such are business cycles.  It would not go in until we reenter stage 1.  I see no value in trying to squeeze it in past stage 1.

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