aarch64: Fix vector-to-vector vec_extract

The documentation says:

-------------------------------------------------------------------------
@cindex @code{vec_extract@var{m}@var{n}} instruction pattern
@item @samp{vec_extract@var{m}@var{n}}
Extract given field from the vector value.  [...]  The
@var{n} mode is the mode of the field or vector of fields that should be
extracted, [...]
If @var{n} is a vector mode, the index is counted in units of that mode.
-------------------------------------------------------------------------

However, Robin pointed out that, in practice, the index is counted
in whole multiples of @var{n}.  These are the semantics that x86
and target-independent code follow.

This patch updates the aarch64 pattern to match, which also removes
the FAIL.  I think Robin has patches that update the documentation
and make more use of the de facto semantics.

I haven't found an existing testcase that shows the difference.
We do now use the pattern for:

union u { int32x4_t x; int32x2_t y[2]; };
int32x2_t f(int32x4_t x) { union u u = { x }; return u.y[1]; }

but we were already generating perfect code for it.  Because of that,
it didn't really seem worth adding a specific dump test.

gcc/
	* config/aarch64/aarch64-simd.md (vec_extract<mode><Vhalf>): Expect
	the index to be 0 or 1.

0 files changed, 0 insertions, 0 deletions