On Thu, Jul 30, 2020 at 9:49 AM Marc Glisse <marc.gli...@inria.fr> wrote:
>
> When vector comparisons were forced to use vec_cond_expr, we lost a number
> of optimizations (my fault for not adding enough testcases to prevent
> that). This patch tries to unwrap vec_cond_expr a bit so some
> optimizations can still happen.
>
> I wasn't planning to add all those transformations together, but adding
> one caused a regression, whose fix introduced a second regression, etc.
>
> Using a simple fold_binary internally looks like an ok compromise to me.
> It remains cheap enough (not recursive, and vector instructions are not
> that frequent), while still allowing more than const_binop (X|0 or X&X for
> instance). The transformations are quite conservative with :s and folding
> only if everything simplifies, we may want to relax this later. And of
> course we are going to miss things like a?b:c + a?c:b -> b+c.
>
> In terms of number of operations, some transformations turning 2
> VEC_COND_EXPR into VEC_COND_EXPR + BIT_IOR_EXPR + BIT_NOT_EXPR might not
> look like a gain... I expect the bit_not disappears in most cases, and
> VEC_COND_EXPR looks more costly than a simpler BIT_IOR_EXPR.
>
> I am a bit confused that with avx512 we get types like "vector(4)
> <signed-boolean:2>" with :2 and not :1 (is it a hack so true is 1 and not
> -1?), but that doesn't matter for this patch.
>
> Regtest+bootstrap on x86_64-pc-linux-gnu
+ (with
+ {
+ tree rhs1, rhs2 = NULL;
+ rhs1 = fold_binary (op, type, @1, @3);
+ if (rhs1 && is_gimple_val (rhs1))
+ rhs2 = fold_binary (op, type, @2, @3);
ICK. I guess a more match-and-simplify way would be
(with
{
tree rhs1, rhs2;
gimple_match_op op (gimple_match_cond::UNCOND, op,
type, @1, @3);
if (op.resimplify (NULL, valueize)
&& gimple_simplified_result_is_gimple_val (op))
{
rhs1 = op.ops[0];
... other operand ...
}
now in theory we could invent some new syntax for this, like
(simplify
(op (vec_cond:s @0 @1 @2) @3)
(vec_cond @0 (op:x @1 @3) (op:x @2 @3)))
and pick something better instead of :x (:s is taken,
would be 'simplified', :c is taken would be 'constexpr', ...).
_Maybe_ just
(simplify
(op (vec_cond:s @0 @1 @2) @3)
(vec_cond:x @0 (op @1 @3) (op @2 @3)))
which would have the same practical meaning as passing
NULL for the seq argument to simplification - do not allow
any intermediate stmt to be generated.
The other "simple" patterns look good, you can commit
them separately if you like.
Richard.
> 2020-07-30 Marc Glisse <marc.gli...@inria.fr>
>
> PR tree-optimization/95906
> PR target/70314
> * match.pd ((c ? a : b) op d, (c ? a : b) op (c ? d : e),
> (v ? w : 0) ? a : b, c1 ? c2 ? a : b : b): New transformations.
>
> * gcc.dg/tree-ssa/andnot-2.c: New file.
> * gcc.dg/tree-ssa/pr95906.c: Likewise.
> * gcc.target/i386/pr70314.c: Likewise.
>
> --
> Marc Glisse
