Re: [RFC] Add support for vectors in comparisons (like the C++ frontend does)

[Paul Iannetta <piannetta@kalrayinc.com>]

On Mon, Oct 10, 2022 at 11:07:06PM +0000, Joseph Myers wrote:
> On Mon, 10 Oct 2022, Paul Iannetta via Gcc-patches wrote:
> 
> > I have a patch to bring this feature to the C front-end as well, and
> > would like to hear your opinion on it, especially since it may affect
> > the feature-set of the objc front-end as well.
> 
> > Currently, this is only a tentative patch and I did not add any tests
> > to the testsuite.
> 
> I think tests (possibly existing C++ tests moved to c-c++-common?) are 
> necessary to judge such a feature; it could better be judged based on 
> tests without implementation than based on implementation without tests.

Currently, this feature has the following tests in g++.dg/ext/
  - vector9.C
  - vector19.C
  - vector21.C
  - vector22.C
  - vector23.C
  - vector27.C
  - vector28.C
provided by Marc Glisse when he implemented the feature for C++.

They are all handled by my mirror implementation (after removing
C++-only features), save for a case in vector19.C ( v ? '1' : '2',
where v is a vector of unsigned char, but '1' and '2' are considered
as int, which results in a type mismatch.)

I'll move those tests to c-c++-common tomorrow, but will duplicate
vector19.C and vector23.C which rely on C++-only features.

During my tests, I've been using variations around this:

typedef int v2si __attribute__((__vector_size__ (2 * sizeof(int))));

v2si f (v2si a, v2si b, v2si c)
{
  v2si d = a + !b;
  v2si e = a || b;
  return c ? (a + !b) && (c - e && a) : (!!b ^ c && e);
}

It is already possible to express much of the same thing without the
syntactic sugar but is is barely legible

typedef int v2si __attribute__((__vector_size__ (2 * sizeof(int))));

v2si f (v2si a, v2si b, v2si c)
{
  v2si d = a + (b == 0);
  v2si e = (a != 0) | (b != 0);
  return ((c != 0) & (((a + (b == 0)) != 0) & (((c - e) != 0) & (a != 0))))
       | ((c == 0) & (((((b == 0) == 0) ^ c) != 0) & (e != 0)));
}

Paul