Robin Dapp via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> Hi,
>
> as Juzhe noticed in gcc.dg/pr92301.c there was still something missing in
> the last patch. The attached v2 makes sure we always have a COND_LEN
> operation
> before returning true and initializes len and bias even if they are unused.
>
> Bootstrapped and regtested on aarch64 and x86.
Sorry for the slow review. I was hoping Richi would take it,
but I see he was hoping the same from me.
> Regards
> Robin
>
> Subject: [PATCH v2] gimple-match: Do not try UNCOND optimization with
> COND_LEN.
>
> On riscv we mis-optimize conditional (length) operations into
> unconditional operations e.g. in slp-reduc-7.c and
> gcc.dg/pr92301.c.
>
> This patch prevents optimizing e.g.
> COND_LEN_ADD ({-1, ... }, a, 0, c, len, bias)
> unconditionally into just "a".
>
> Currently, we assume that COND_LEN operations can be optimized similarly
> to COND operations. As the length is part of the mask (and usually not
> compile-time constant), we must not perform any optimization that relies
> on just the mask being "true". This patch ensures that we still have a
> COND_LEN pattern after optimization.
>
> gcc/ChangeLog:
>
> PR target/111311
> * gimple-match-exports.cc (maybe_resimplify_conditional_op):
> Check for length masking.
> (try_conditional_simplification): Check that the result is still
> length masked.
> ---
> gcc/gimple-match-exports.cc | 38 ++++++++++++++++++++++++++++++-------
> gcc/gimple-match.h | 3 ++-
> 2 files changed, 33 insertions(+), 8 deletions(-)
>
> diff --git a/gcc/gimple-match-exports.cc b/gcc/gimple-match-exports.cc
> index b36027b0bad..d41de98a3d3 100644
> --- a/gcc/gimple-match-exports.cc
> +++ b/gcc/gimple-match-exports.cc
> @@ -262,7 +262,8 @@ maybe_resimplify_conditional_op (gimple_seq *seq,
> gimple_match_op *res_op,
> if (!res_op->cond.cond)
> return false;
>
> - if (!res_op->cond.else_value
> + if (!res_op->cond.len
> + && !res_op->cond.else_value
> && res_op->code.is_tree_code ())
> {
> /* The "else" value doesn't matter. If the "then" value is a
Why are the contents of this if statement wrong for COND_LEN?
If the "else" value doesn't matter, then the masked form can use
the "then" value for all elements. I would have expected the same
thing to be true of COND_LEN.
> @@ -301,9 +302,12 @@ maybe_resimplify_conditional_op (gimple_seq *seq,
> gimple_match_op *res_op,
>
> /* If the "then" value is a gimple value and the "else" value matters,
> create a VEC_COND_EXPR between them, then see if it can be further
> - simplified. */
> + simplified.
> + Don't do this if we have a COND_LEN_ as that would make us lose the
> + length masking. */
> gimple_match_op new_op;
> - if (res_op->cond.else_value
> + if (!res_op->cond.len
> + && res_op->cond.else_value
> && VECTOR_TYPE_P (res_op->type)
> && gimple_simplified_result_is_gimple_val (res_op))
> {
The change LGTM, but it would be nice to phrase the comment to avoid
the "Do A. Don't do A if B" pattern. Maybe:
/* If the condition represents MASK ? THEN : ELSE, where THEN is a gimple
value and ELSE matters, create a VEC_COND_EXPR between them, then see
if it can be further simplified. */
> @@ -314,7 +318,7 @@ maybe_resimplify_conditional_op (gimple_seq *seq,
> gimple_match_op *res_op,
> return gimple_resimplify3 (seq, res_op, valueize);
> }
>
> - /* Otherwise try rewriting the operation as an IFN_COND_* call.
> + /* Otherwise try rewriting the operation as an IFN_COND_(LEN_)* call.
> Again, this isn't a simplification in itself, since it's what
> RES_OP already described. */
> if (convert_conditional_op (res_op, &new_op))
> @@ -386,9 +390,29 @@ try_conditional_simplification (internal_fn ifn,
> gimple_match_op *res_op,
> default:
> gcc_unreachable ();
> }
> - *res_op = cond_op;
> - maybe_resimplify_conditional_op (seq, res_op, valueize);
> - return true;
> +
> + if (len)
> + {
> + /* If we had a COND_LEN before we need to ensure that it stays that
> + way. */
> + gimple_match_op old_op = *res_op;
> + *res_op = cond_op;
> + maybe_resimplify_conditional_op (seq, res_op, valueize);
> +
> + auto cfn = combined_fn (res_op->code);
> + if (internal_fn_p (cfn)
> + && internal_fn_len_index (as_internal_fn (cfn)) != -1)
> + return true;
Why isn't it enough to check the result of maybe_resimplify_conditional_op?
Thanks,
Richard
> +
> + *res_op = old_op;
> + return false;
> + }
> + else
> + {
> + *res_op = cond_op;
> + maybe_resimplify_conditional_op (seq, res_op, valueize);
> + return true;
> + }
> }
>
> /* Helper for the autogenerated code, valueize OP. */
> diff --git a/gcc/gimple-match.h b/gcc/gimple-match.h
> index bec3ff42e3e..d192b7dae3e 100644
> --- a/gcc/gimple-match.h
> +++ b/gcc/gimple-match.h
> @@ -56,7 +56,8 @@ public:
>
> inline
> gimple_match_cond::gimple_match_cond (tree cond_in, tree else_value_in)
> - : cond (cond_in), else_value (else_value_in)
> + : cond (cond_in), else_value (else_value_in), len (NULL_TREE),
> + bias (NULL_TREE)
> {
> }
