Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> The following adjusts the tree.def documentation about VEC_PERM_EXPR
> which wasn't adjusted when the restrictions of permutes with constant
> mask were relaxed.
I was going to complain about having two copies of the documentation,
but then I realised that generic.texi doesn't document VEC_PERM_EXPR.
So... oops.
>
> OK?
>
> Thanks,
> Richard.
>
> PR middle-end/110541
> * tree.def (VEC_PERM_EXPR): Adjust documentation to reflect
> reality.
> ---
> gcc/tree.def | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/gcc/tree.def b/gcc/tree.def
> index 1fc2ca7a724..9e1a54ac2f9 100644
> --- a/gcc/tree.def
> +++ b/gcc/tree.def
> @@ -565,13 +565,20 @@ DEFTREECODE (VEC_COND_EXPR, "vec_cond_expr",
> tcc_expression, 3)
>
> N = length(mask)
> foreach i in N:
> - M = mask[i] % (2*N)
> - A = M < N ? v0[M] : v1[M-N]
> + M = mask[i] % (length(v0) + length(v1))
> + A[i] = M < length(v0) ? v0[M] : v1[M - length(v0)]
>
> - V0 and V1 are vectors of the same type. MASK is an integer-typed
> - vector. The number of MASK elements must be the same with the
> - number of elements in V0 and V1. The size of the inner type
> - of the MASK and of the V0 and V1 must be the same.
> + V0 and V1 are vectors of the same type.
> +
> + When MASK is not constant:
> + MASK is an integer-typed vector. The number of MASK elements must
> + be the same with the number of elements in V0 and V1. The size of
Preexisting, but s/same with/same as/
> + the inner type of the MASK and of the V0 and V1 must be the same.
> +
> + When MASK is constant:
> + MASK is an integer-typed vector. MASK elements outside of
> + [0, length(V0) + length(V1) - 1] invoke undefined behavior (the
> + modulo operation above doesn't apply).
I don't remember the last rule. I thought the modulo did still apply.
(But the canonical form is to remove obvious modulo opportunities.)
E.g. a VLA reverse-and-rotate pattern might have { N-2, N-3, N-4, ... }.
That will wrap at the final position to 2N-1, but that seems OK.
LGTM otherwise FWIW.
Thanks,
Richard
