[RFC][PR64946] "abs" vectorization fails for char/short types
Richard Biener
richard.guenther@gmail.com
Mon Jun 4 08:39:00 GMT 2018
On Mon, Jun 4, 2018 at 10:18 AM Kugan Vivekanandarajah
<kugan.vivekanandarajah@linaro.org> wrote:
>
> Hi Richard,
>
> Thanks for the review.
>
> On 1 June 2018 at 22:20, Richard Biener <richard.guenther@gmail.com> wrote:
> > On Fri, Jun 1, 2018 at 4:12 AM Kugan Vivekanandarajah
> > <kugan.vivekanandarajah@linaro.org> wrote:
> >>
> >> Hi Richard,
> >>
> >> This is the revised patch based on the review and the discussion in
> >> https://gcc.gnu.org/ml/gcc/2018-05/msg00179.html.
> >>
> >> In summary:
> >> - I skipped (element_precision (type) < element_precision (TREE_TYPE
> >> (@0))) in the match.pd pattern as this would prevent transformation
> >> for the case in PR.
> >> that is, I am interested in is something like:
> >> char t = (char) ABS_EXPR <(int) x>
> >> and I want to generate
> >> char t = (char) ABSU_EXPR <x>
> >>
> >> - I also haven't added all the necessary match.pd changes for
> >> ABSU_EXPR. I have a patch for that but will submit separately based on
> >> this reveiw.
> >>
> >> - I also tried to add ABSU_EXPRsupport in the places as necessary by
> >> grepping for ABS_EXPR.
> >>
> >> - I also had to add special casing in vectorizer for ABSU_EXP as its
> >> result is unsigned type.
> >>
> >> Is this OK. Patch bootstraps and the regression test is ongoing.
> >
> > The c/c-typeck.c:build_unary_op change looks unnecessary - the
> > C FE should never generate this directly (the c-common one might
> > be triggered by early folding I guess).
>
> The Gimple FE testcase is running into this.
Ah, OK then.
> >
> > @@ -1761,6 +1762,9 @@ const_unop (enum tree_code code, tree type, tree arg0)
> > if (TREE_CODE (arg0) == INTEGER_CST || TREE_CODE (arg0) == REAL_CST)
> > return fold_abs_const (arg0, type);
> > break;
> > + case ABSU_EXPR:
> > + return fold_convert (type, fold_abs_const (arg0,
> > + signed_type_for (type)));
> >
> > case CONJ_EXPR:
> >
> > I think this will get you bogus TREE_OVERFLOW flags set on ABSU (-INT_MIN).
> >
> > I think you want to change fold_abs_const to properly deal with arg0 being
> > signed and type unsigned. That is, sth like
> >
> > diff --git a/gcc/fold-const.c b/gcc/fold-const.c
> > index 6f80f1b1d69..f60f9c77e91 100644
> > --- a/gcc/fold-const.c
> > +++ b/gcc/fold-const.c
> > @@ -13843,18 +13843,19 @@ fold_abs_const (tree arg0, tree type)
> > {
> > /* If the value is unsigned or non-negative, then the absolute value
> > is the same as the ordinary value. */
> > - if (!wi::neg_p (wi::to_wide (arg0), TYPE_SIGN (type)))
> > - t = arg0;
> > + wide_int val = wi::to_wide (arg0);
> > + bool overflow = false;
> > + if (!wi::neg_p (val, TYPE_SIGN (TREE_TYPE (arg0))))
> > + ;
> >
> > /* If the value is negative, then the absolute value is
> > its negation. */
> > else
> > - {
> > - bool overflow;
> > - wide_int val = wi::neg (wi::to_wide (arg0), &overflow);
> > - t = force_fit_type (type, val, -1,
> > - overflow | TREE_OVERFLOW (arg0));
> > - }
> > + wide_int val = wi::neg (val, &overflow);
> > +
> > + /* Force to the destination type, set TREE_OVERFLOW for signed
> > + TYPE only. */
> > + t = force_fit_type (type, val, 1, overflow | TREE_OVERFLOW (arg0));
> > }
> > break;
> >
> > and then simply share the const_unop code with ABS_EXPR.
>
> Done.
>
> > diff --git a/gcc/match.pd b/gcc/match.pd
> > index 14386da..7d7c132 100644
> > --- a/gcc/match.pd
> > +++ b/gcc/match.pd
> > @@ -102,6 +102,14 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> > (match (nop_convert @0)
> > @0)
> >
> > +(simplify (abs (convert @0))
> > + (if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
> > + && !TYPE_UNSIGNED (TREE_TYPE (@0))
> > + && !TYPE_UNSIGNED (type))
> > + (with { tree utype = unsigned_type_for (TREE_TYPE (@0)); }
> > + (convert (absu:utype @0)))))
> > +
> > +
> >
> > please put a comment before the pattern. I believe there's no
> > need to check for !TYPE_UNSIGNED (type). Note this
> > also converts abs ((char)int-var) to (char)absu(int-var) which
> > doesn't make sense. The original issue you want to address
> > here is the case where TYPE_PRECISION of @0 is less than
> > the precision of type. That is, you want to remove language
> > introduced integer promotion of @0 which only is possible
> > with ABSU. So please do add such precision check
> > (I simply suggested the bogus direction of the test).
>
> Done.
> >
> > diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
> > index 68f4fd3..9b62583 100644
> > --- a/gcc/tree-cfg.c
> > +++ b/gcc/tree-cfg.c
> > @@ -3685,6 +3685,12 @@ verify_gimple_assign_unary (gassign *stmt)
> > case PAREN_EXPR:
> > case CONJ_EXPR:
> > break;
> > + case ABSU_EXPR:
> > + if (!TYPE_UNSIGNED (lhs_type)
> > + || !ANY_INTEGRAL_TYPE_P (rhs1_type))
> >
> > if (!ANY_INTEGRAL_TYPE_P (lhs_type)
> > || !TYPE_UNSIGNED (lhs_type)
> > || !ANY_INTEGRAL_TYPE_P (rhs1_type)
> > || TYPE_UNSIGNED (rhs1_type)
> > || element_precision (lhs_type) != element_precision (rhs1_type))
> > {
> > error ("invalid types for ABSU_EXPR");
> > debug_generic_expr (lhs_type);
> > debug_generic_expr (rhs1_type);
> > return true;
> > }
> >
^^^ you forgot this one.
> > + return true;
> > + return false;
> > + break;
> >
> > diff --git a/gcc/tree-eh.c b/gcc/tree-eh.c
> > index 30c6d9e..44b1399 100644
> > --- a/gcc/tree-eh.c
> > +++ b/gcc/tree-eh.c
> > @@ -2465,6 +2465,7 @@ operation_could_trap_helper_p (enum tree_code op,
> >
> > case NEGATE_EXPR:
> > case ABS_EXPR:
> > + case ABSU_EXPR:
> > case CONJ_EXPR:
> > /* These operations don't trap with floating point. */
> > if (honor_trapv)
> >
> > ABSU never traps. Please instead unconditionally return false.
> Done.
>
> >
> > diff --git a/gcc/tree-vect-stmts.c b/gcc/tree-vect-stmts.c
> > index 66c78de..b52d714 100644
> > --- a/gcc/tree-vect-stmts.c
> > +++ b/gcc/tree-vect-stmts.c
> > @@ -5995,7 +5995,11 @@ vectorizable_operation (gimple *stmt,
> > gimple_stmt_iterator *gsi,
> > "transform binary/unary operation.\n");
> >
> > /* Handle def. */
> > - vec_dest = vect_create_destination_var (scalar_dest, vectype);
> > + if (code == ABSU_EXPR)
> > + vec_dest = vect_create_destination_var (scalar_dest,
> > + unsigned_type_for (vectype));
> > + else
> > + vec_dest = vect_create_destination_var (scalar_dest, vectype);
> >
> > /* POINTER_DIFF_EXPR has pointer arguments which are vectorized as
> > vectors with unsigned elements, but the result is signed. So, we
> >
> > simply use vectype_out for creation of vec_dest.
> Done.
/* Handle def. */
- vec_dest = vect_create_destination_var (scalar_dest, vectype);
+ if (code == ABSU_EXPR)
+ vec_dest = vect_create_destination_var (scalar_dest, vectype_out);
+ else
+ vec_dest = vect_create_destination_var (scalar_dest, vectype);
I meant _always_ vectype_out. Thus unconditionally
vec_dest = vect_create_destination_var (scalar_dest, vectype_out);
OK with those two changes.
Thanks,
Richard.
> >
> > diff --git a/gcc/tree.def b/gcc/tree.def
> > index c660b2c..5fec781 100644
> > --- a/gcc/tree.def
> > +++ b/gcc/tree.def
> > @@ -760,6 +760,7 @@ DEFTREECODE (MAX_EXPR, "max_expr", tcc_binary, 2)
> > An ABS_EXPR must have either an INTEGER_TYPE or a REAL_TYPE. The
> > operand of the ABS_EXPR must have the same type. */
> > DEFTREECODE (ABS_EXPR, "abs_expr", tcc_unary, 1)
> > +DEFTREECODE (ABSU_EXPR, "absu_expr", tcc_unary, 1)
> >
> > /* Shift operations for shift and rotate.
> > Shift means logical shift if done on an
> >
> > You can clearly see that the comment before ABS_EXPR doesn't apply to ABSU_EXPR
> > so please add an appropriate one. I suggest
> >
> > /* Represents the unsigned absolute value of the operand.
> > An ABSU_EXPR must have unsigned INTEGER_TYPE. The operand of the ABSU_EXPR
> > must have the corresponding signed type. */
>
> Done.
>
> Here is the reviesed patch. Is this OK?
>
> Thanks,
> Kugan
>
> >
> > Otherwise looks OK. (I didn't explicitely check for missing ABSU_EXPR
> > handling this time)
> >
> > Thanks,
> > Richard.
> >
> >
> >> Thanks,
> >> Kugan
> >>
> >>
> >> On 18 May 2018 at 12:36, Kugan Vivekanandarajah
> >> <kugan.vivekanandarajah@linaro.org> wrote:
> >> > Hi Richard,
> >> >
> >> > Thanks for the review. I am revising the patch based on Andrew's comments too.
> >> >
> >> > On 17 May 2018 at 20:36, Richard Biener <richard.guenther@gmail.com> wrote:
> >> >> On Thu, May 17, 2018 at 4:56 AM Andrew Pinski <pinskia@gmail.com> wrote:
> >> >>
> >> >>> On Wed, May 16, 2018 at 7:14 PM, Kugan Vivekanandarajah
> >> >>> <kugan.vivekanandarajah@linaro.org> wrote:
> >> >>> > As mentioned in the PR, I am trying to add ABSU_EXPR to fix this
> >> >>> > issue. In the attached patch, in fold_cond_expr_with_comparison I am
> >> >>> > generating ABSU_EXPR for these cases. As I understand, absu_expr is
> >> >>> > well defined in RTL. So, the issue is generating absu_expr and
> >> >>> > transferring to RTL in the correct way. I am not sure I am not doing
> >> >>> > all that is needed. I will clean up and add more test-cases based on
> >> >>> > the feedback.
> >> >>
> >> >>
> >> >>> diff --git a/gcc/optabs-tree.c b/gcc/optabs-tree.c
> >> >>> index 71e172c..2b812e5 100644
> >> >>> --- a/gcc/optabs-tree.c
> >> >>> +++ b/gcc/optabs-tree.c
> >> >>> @@ -235,6 +235,7 @@ optab_for_tree_code (enum tree_code code, const_tree
> >> >> type,
> >> >>> return trapv ? negv_optab : neg_optab;
> >> >>
> >> >>> case ABS_EXPR:
> >> >>> + case ABSU_EXPR:
> >> >>> return trapv ? absv_optab : abs_optab;
> >> >>
> >> >>
> >> >>> This part is not correct, it should something like this:
> >> >>
> >> >>> case ABS_EXPR:
> >> >>> return trapv ? absv_optab : abs_optab;
> >> >>> + case ABSU_EXPR:
> >> >>> + return abs_optab ;
> >> >>
> >> >>> Because ABSU is not undefined at the TYPE_MAX.
> >> >>
> >> >> Also
> >> >>
> >> >> /* Unsigned abs is simply the operand. Testing here means we don't
> >> >> risk generating incorrect code below. */
> >> >> - if (TYPE_UNSIGNED (type))
> >> >> + if (TYPE_UNSIGNED (type)
> >> >> + && (code != ABSU_EXPR))
> >> >> return op0;
> >> >>
> >> >> is wrong. ABSU of an unsigned number is still just that number.
> >> >>
> >> >> The change to fold_cond_expr_with_comparison looks odd to me
> >> >> (premature optimization). It should be done separately - it seems
> >> >> you are doing
> >> >
> >> > FE seems to be using this to generate ABS_EXPR from
> >> > c_fully_fold_internal to fold_build3_loc and so on. I changed this to
> >> > generate ABSU_EXPR for the case in the testcase. So the question
> >> > should be, in what cases do we need ABS_EXPR and in what cases do we
> >> > need ABSU_EXPR. It is not very clear to me.
> >> >
> >> >
> >> >>
> >> >> (simplify (abs (convert @0)) (convert (absu @0)))
> >> >>
> >> >> here.
> >> >>
> >> >> You touch one other place in fold-const.c but there seem to be many
> >> >> more that need ABSU_EXPR handling (you touched the one needed
> >> >> for correctness) - esp. you should at least handle constant folding
> >> >> in const_unop and the nonnegative predicate.
> >> >
> >> > OK.
> >> >>
> >> >> @@ -3167,6 +3167,9 @@ verify_expr (tree *tp, int *walk_subtrees, void *data
> >> >> ATTRIBUTE_UNUSED)
> >> >> CHECK_OP (0, "invalid operand to unary operator");
> >> >> break;
> >> >>
> >> >> + case ABSU_EXPR:
> >> >> + break;
> >> >> +
> >> >> case REALPART_EXPR:
> >> >> case IMAGPART_EXPR:
> >> >>
> >> >> verify_expr is no more. Did you test this recently against trunk?
> >> >
> >> > This patch is against slightly older trunk. I will rebase it.
> >> >
> >> >>
> >> >> @@ -3937,6 +3940,9 @@ verify_gimple_assign_unary (gassign *stmt)
> >> >> case PAREN_EXPR:
> >> >> case CONJ_EXPR:
> >> >> break;
> >> >> + case ABSU_EXPR:
> >> >> + /* FIXME. */
> >> >> + return false;
> >> >>
> >> >> no - please not! Please add verification here - ABSU should be only
> >> >> called on INTEGRAL, vector or complex INTEGRAL types and the
> >> >> type of the LHS should be always the unsigned variant of the
> >> >> argument type.
> >> >
> >> > OK.
> >> >>
> >> >> if (is_gimple_val (cond_expr))
> >> >> return cond_expr;
> >> >>
> >> >> - if (TREE_CODE (cond_expr) == ABS_EXPR)
> >> >> + if (TREE_CODE (cond_expr) == ABS_EXPR
> >> >> + || TREE_CODE (cond_expr) == ABSU_EXPR)
> >> >> {
> >> >> rhs1 = TREE_OPERAND (cond_expr, 1);
> >> >> STRIP_USELESS_TYPE_CONVERSION (rhs1);
> >> >>
> >> >> err, but the next line just builds a ABS_EXPR ...
> >> >>
> >> >> How did you identify spots that need adjustment? I would expect that
> >> >> once folding generates ABSU_EXPR that you need to adjust frontends
> >> >> (C++ constexpr handling for example). Also I miss adjustments
> >> >> to gimple-pretty-print.c and the GIMPLE FE parser.
> >> >
> >> > I will add this.
> >> >>
> >> >> recursively grepping throughout the whole gcc/ tree doesn't reveal too many
> >> >> cases of ABS_EXPR so I think it's reasonable to audit all of them.
> >> >>
> >> >> I also miss some trivial absu simplifications in match.pd. There are not
> >> >> a lot of abs cases but similar ones would be good to have initially.
> >> >
> >> > I will add them in the next version.
> >> >
> >> > Thanks,
> >> > Kugan
> >> >
> >> >>
> >> >> Thanks for tackling this!
> >> >> Richard.
> >> >>
> >> >>> Thanks,
> >> >>> Andrew
> >> >>
> >> >>> >
> >> >>> > Thanks,
> >> >>> > Kugan
> >> >>> >
> >> >>> >
> >> >>> > gcc/ChangeLog:
> >> >>> >
> >> >>> > 2018-05-13 Kugan Vivekanandarajah <kugan.vivekanandarajah@linaro.org>
> >> >>> >
> >> >>> > * expr.c (expand_expr_real_2): Handle ABSU_EXPR.
> >> >>> > * fold-const.c (fold_cond_expr_with_comparison): Generate ABSU_EXPR
> >> >>> > (fold_unary_loc): Handle ABSU_EXPR.
> >> >>> > * optabs-tree.c (optab_for_tree_code): Likewise.
> >> >>> > * tree-cfg.c (verify_expr): Likewise.
> >> >>> > (verify_gimple_assign_unary): Likewise.
> >> >>> > * tree-if-conv.c (fold_build_cond_expr): Likewise.
> >> >>> > * tree-inline.c (estimate_operator_cost): Likewise.
> >> >>> > * tree-pretty-print.c (dump_generic_node): Likewise.
> >> >>> > * tree.def (ABSU_EXPR): New.
> >> >>> >
> >> >>> > gcc/testsuite/ChangeLog:
> >> >>> >
> >> >>> > 2018-05-13 Kugan Vivekanandarajah <kugan.vivekanandarajah@linaro.org>
> >> >>> >
> >> >>> > * gcc.dg/absu.c: New test.
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