[RFC C++ / PR51033 ] Handle __builtin_shuffle in constexpr properly in the C++ frontend.

[Ramana Radhakrishnan]

Hi,

This patch following on from the fix for turning on __builtin_shuffle
for c++ , enables folding of vec_perm_exprs in the front-end for
constexpr and constructor style values.  I was originally going to go
with Marc's patch but then took a look at what it would take to
support this properly which appeared to me to be just calling fold
with the right parameters.

With simple tests based on variations from c-c++-common/vshuf*.c using
constexpr execution tests appear to pass - There is still an issue
with the compiler giving an error on seeing a subscript operation with
a __builtin_shuffle - I'm going to let that one for someone else to
pick up because I don't have the time to pick this up right at this
minute and the fact is that folks could use an extra vector for the
time being.

Regression tested with a bootstrap and testrun on powerpc /
x86_64-linux-gnu and cross-tested on arm-linux-gnueabi

Thoughts  ?

regards,
Ramana

cp/

        PR C++/51033
        * semantics.c (constexpr_call): Fix typo in comment.
        (cxx_eval_vec_perm_expr): New.
        (cxx_eval_constant_expression): Fold VEC_PERM_EXPRs.

testsuite/


        * g++.dg/torture/vshuf-16.inc: New test.
        * g++.dg/torture/vshuf-2.inc: New test.
        * g++.dg/torture/vshuf-4.inc: New test.
        * g++.dg/torture/vshuf-8.inc: New test.
        * g++.dg/torture/vshuf-main.inc: New test.
        * g++.dg/torture/vshuf-v16hi.C: New test.
        * g++.dg/torture/vshuf-v16qi.C: New test.
        * g++.dg/torture/vshuf-v2df.C: New test.
        * g++.dg/torture/vshuf-v2di.C: New test.
        * g++.dg/torture/vshuf-v2sf.C: New test.
        * g++.dg/torture/vshuf-v2si.C: New test.
        * g++.dg/torture/vshuf-v4df.C: New test.
        * g++.dg/torture/vshuf-v4di.C: New test.
        * g++.dg/torture/vshuf-v4sf.C: New test.
        * g++.dg/torture/vshuf-v4si.C: New test.
        * g++.dg/torture/vshuf-v8hi.C: New test.
        * g++.dg/torture/vshuf-v8qi.C: New test.
        * g++.dg/torture/vshuf-v8si.C: New test.

constexpr-vshuf.patch
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