On Fri, 15 Oct 2021, Tamar Christina wrote:
> > >
> > > +/* Fold (-x >> C) into x > 0 where C = precision(type) - 1. */ (for
> > > +cst (INTEGER_CST VECTOR_CST) (simplify
> > > + (rshift (negate:s @0) cst@1)
> > > + (if (!flag_wrapv)
> >
> > Don't test flag_wrapv directly, instead use the appropriate
> > TYPE_OVERFLOW_{UNDEFINED,WRAPS} predicates. But I'm not sure what
> > we are protecting against? Right-shift of signed integers is
> > implementation-
> > defined and GCC treats it as you'd expect, sign-extending the result.
> >
>
> It's protecting against the overflow of the negate on INT_MIN. When wrapping
> overflows are enabled the results would be wrong.
But -INT_MIN == INT_MIN in twos-complement so I fail to see the wrong
result? That is, both -INT_MIN >> 31 and INT_MIN >> 31 are -1.
> > > + (with { tree ctype = TREE_TYPE (@0);
> > > + tree stype = TREE_TYPE (@1);
> > > + tree bt = truth_type_for (ctype); }
> > > + (switch
> > > + /* Handle scalar case. */
> > > + (if (INTEGRAL_TYPE_P (ctype)
> > > + && !VECTOR_TYPE_P (ctype)
> > > + && !TYPE_UNSIGNED (ctype)
> > > + && canonicalize_math_after_vectorization_p ()
> > > + && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (stype) - 1))
> > > + (convert:bt (gt:bt @0 { build_zero_cst (stype); })))
> >
> > I'm not sure why the result is of type 'bt' rather than the original type
> > of the
> > expression?
>
> That was to satisfy some RTL check that expected results of comparisons to
> always
> be a Boolean, though for scalar that logically always is the case, I just
> added it
> for consistency.
>
> >
> > In that regard for non-vectors we'd have to add the sign extension from
> > unsigned bool, in the vector case we'd hope the type of the comparison is
> > correct. I think in both cases it might be convenient to use
> >
> > (cond (gt:bt @0 { build_zero_cst (ctype); }) { build_all_ones_cst
> > (ctype); }
> > { build_zero_cost (ctype); })
> >
> > to compute the correct result and rely on (cond ..) simplifications to
> > simplify
> > that if possible.
> >
> > Btw, 'stype' should be irrelevant - you need to look at the precision of
> > 'ctype',
> > no?
>
> I was working under the assumption that both input types must have the same
> precision, but turns out that assumption doesn't need to hold.
>
> New version attached.
>
> Bootstrapped Regtested on aarch64-none-linux-gnu,
> x86_64-pc-linux-gnu and no regressions.
>
> Ok for master?
>
> Thanks,
> Tamar
>
> gcc/ChangeLog:
>
> * match.pd: New negate+shift pattern.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/signbit-2.c: New test.
> * gcc.dg/signbit-3.c: New test.
> * gcc.target/aarch64/signbit-1.c: New test.
>
> --- inline copy of patch ---
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index
> 7d2a24dbc5e9644a09968f877e12a824d8ba1caa..9532cae582e152cae6e22fcce95a9744a844e3c2
> 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -38,7 +38,8 @@ along with GCC; see the file COPYING3. If not see
> uniform_integer_cst_p
> HONOR_NANS
> uniform_vector_p
> - bitmask_inv_cst_vector_p)
> + bitmask_inv_cst_vector_p
> + expand_vec_cmp_expr_p)
>
> /* Operator lists. */
> (define_operator_list tcc_comparison
> @@ -826,6 +827,42 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> { tree utype = unsigned_type_for (type); }
> (convert (rshift (lshift (convert:utype @0) @2) @3))))))
>
> +/* Fold (-x >> C) into x > 0 where C = precision(type) - 1. */
> +(for cst (INTEGER_CST VECTOR_CST)
> + (simplify
> + (rshift (negate:s @0) cst@1)
> + (if (!TYPE_OVERFLOW_WRAPS (type))
as said, I don't think that's necessary but at least it's now
written correctly ;)
> + (with { tree ctype = TREE_TYPE (@0);
Instead of 'ctype' you can use 'type' since the type of the expression
is the same as that of @0
> + tree stype = TREE_TYPE (@1);
> + tree bt = truth_type_for (ctype);
> + tree zeros = build_zero_cst (ctype); }
> + (switch
> + /* Handle scalar case. */
> + (if (INTEGRAL_TYPE_P (ctype)
> + && !VECTOR_TYPE_P (ctype)
INTEGRAL_TYPE_P does not include VECTOR_TYPE_P.
> + && !TYPE_UNSIGNED (ctype)
> + && canonicalize_math_after_vectorization_p ()
> + && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (ctype) - 1))
> + (cond (gt:bt @0 { zeros; }) { build_all_ones_cst (ctype); } { zeros;
> }))
> + /* Handle vector case with a scalar immediate. */
> + (if (VECTOR_INTEGER_TYPE_P (ctype)
> + && !VECTOR_TYPE_P (stype)
> + && !TYPE_UNSIGNED (ctype)
> + && expand_vec_cmp_expr_p (ctype, ctype, { GT_EXPR }))
> + (with { HOST_WIDE_INT bits = GET_MODE_UNIT_BITSIZE (TYPE_MODE
> (ctype)); }
> + (if (wi::eq_p (wi::to_wide (@1), bits - 1))
You can use element_precision (@0) - 1 in both the scalar and vector case.
> + (convert:bt (gt:bt @0 { zeros; })))))
> + /* Handle vector case with a vector immediate. */
> + (if (VECTOR_INTEGER_TYPE_P (ctype)
> + && VECTOR_TYPE_P (stype)
> + && !TYPE_UNSIGNED (ctype)
> + && uniform_vector_p (@1)
> + && expand_vec_cmp_expr_p (ctype, ctype, { GT_EXPR }))
> + (with { tree cst = vector_cst_elt (@1, 0);
> + HOST_WIDE_INT bits = GET_MODE_UNIT_BITSIZE (TYPE_MODE (ctype)); }
> + (if (wi::eq_p (wi::to_wide (cst), bits - 1))
> + (convert:bt (gt:bt @0 { zeros; }))))))))))
The (convert:bt are not necessary. Note that 'ctype' is not a valid
mask type but we eventually will be forgiving enough here. You are
computing thruth_type_for, asking for gt:bt but checking
expand_vec_cmp_expr_p (ctype, ctype, ...), that's inconsistent and
will lead to problems on targets with AVX512VL + AVX2 which will
have a AVX2 compare of say V4SImode producing a V4SImode mask
but thruth_type_for will give you a QImode vector type.
As said the most general transform would be to
(cond (gt:bt @0 { zeros; }) { build_zero_cst (ctype); } {
build_all_ones_cst (ctype); })
if you think that's not better than the negate + shift but only
when the compare will directly produce the desired result then
I think you have to either drop the truth_type_for and manually
build the truthtype or check that the mode of the truth type
and the value type match. And you need to produce
(view_convert:ctype (gt:bt @0 { zeros; }))
then.
> +
> /* Fold (C1/X)*C2 into (C1*C2)/X. */
> (simplify
> (mult (rdiv@3 REAL_CST@0 @1) REAL_CST@2)
> diff --git a/gcc/testsuite/gcc.dg/signbit-2.c
> b/gcc/testsuite/gcc.dg/signbit-2.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..fc0157cbc5c7996b481f2998bc30176c96a669bb
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/signbit-2.c
> @@ -0,0 +1,19 @@
> +/* { dg-do assemble } */
> +/* { dg-options "-O3 --save-temps -fdump-tree-optimized" } */
> +
> +#include <stdint.h>
> +
> +void fun1(int32_t *x, int n)
> +{
> + for (int i = 0; i < (n & -16); i++)
> + x[i] = (-x[i]) >> 31;
> +}
> +
> +void fun2(int32_t *x, int n)
> +{
> + for (int i = 0; i < (n & -16); i++)
> + x[i] = (-x[i]) >> 30;
> +}
> +
> +/* { dg-final { scan-tree-dump-times {\s+>\s+\{ 0, 0, 0, 0 \}} 1 optimized }
> } */
> +/* { dg-final { scan-tree-dump-not {\s+>>\s+31} optimized } } */
> diff --git a/gcc/testsuite/gcc.dg/signbit-3.c
> b/gcc/testsuite/gcc.dg/signbit-3.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..19e9c06c349b3287610f817628f00938ece60bf7
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/signbit-3.c
> @@ -0,0 +1,13 @@
> +/* { dg-do assemble } */
> +/* { dg-options "-O1 --save-temps -fdump-tree-optimized" } */
> +
> +#include <stdint.h>
> +
> +void fun1(int32_t *x, int n)
> +{
> + for (int i = 0; i < (n & -16); i++)
> + x[i] = (-x[i]) >> 31;
> +}
> +
> +/* { dg-final { scan-tree-dump-times {\s+>\s+0;} 1 optimized } } */
> +/* { dg-final { scan-tree-dump-not {\s+>>\s+31} optimized } } */
> diff --git a/gcc/testsuite/gcc.target/aarch64/signbit-1.c
> b/gcc/testsuite/gcc.target/aarch64/signbit-1.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..3ebfb0586f37de29cf58635b27fe48503714447e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/signbit-1.c
> @@ -0,0 +1,18 @@
> +/* { dg-do assemble } */
> +/* { dg-options "-O3 --save-temps" } */
> +
> +#include <stdint.h>
> +
> +void fun1(int32_t *x, int n)
> +{
> + for (int i = 0; i < (n & -16); i++)
> + x[i] = (-x[i]) >> 31;
> +}
> +
> +void fun2(int32_t *x, int n)
> +{
> + for (int i = 0; i < (n & -16); i++)
> + x[i] = (-x[i]) >> 30;
> +}
> +
> +/* { dg-final { scan-assembler-times {\tcmgt\t} 1 } } */
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
