On Fri, Feb 3, 2023 at 8:34 AM Richard Biener
<richard.guent...@gmail.com> wrote:
>
> On Thu, Feb 2, 2023 at 6:39 PM Michael Meissner via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > The new __dmr type that is being added as a possible future PowerPC
> > instruction
>
> "is being added" means this feature is already in GCC 13?
>
> > set bumps into a structure field size issue. The size of the __dmr type is
> > 1024 bits.
> > The precision field in tree_type_common is currently 10 bits, so if you
> > store
> > 1,024 into field, you get a 0 back. When you get 0 in the precision field,
> > the
> > ccp pass passes this 0 to sext_hwi in hwint.h. That function in turn
> > generates
> > a shift that is equal to the host wide int bit size, which is undefined as
> > machine dependent for shifting in C/C++.
> >
> > int shift = HOST_BITS_PER_WIDE_INT - prec;
> > return ((HOST_WIDE_INT) ((unsigned HOST_WIDE_INT) src << shift)) >>
> > shift;
> >
> > It turns out the x86_64 where I first did my tests returns the original
> > input
> > before the two shifts, while the PowerPC always returns 0. In the ccp
> > pass, the
> > original input is -1, and so it worked. When I did the runs on the
> > PowerPC, the
> > result was 0, which ultimately led to the failure.
> >
> > In addition, once the precision field is larger, it will help PR C/102989
> > (C2x
> > _BigInt) as well as the implementation of the SET_TYPE_VECTOR_SUBPARTS
> > macro.
> >
> > I bootstraped various PowerPC compilers (power10 LE, power9 LE, power8 BE)
> > along with an x86_64 build. There were no regressions. My proposed patches
> > for the __dmr type now run fine. Can I install this into the master branch
> > for
> > GCC 13?
>
> ... because since we're in stage4 this should fix a regression or at least a
> bug that's like ice-on-valid or wrong-code?
>
> Definitely OK for stage1.
I have pushed this now after bootstrapping / testing on
x86_64-unknown-linux-gnu.
Richard.
> Thanks,
> Richard.
>
> > 2023-02-02 Richard Biener <rguent...@suse.de>
> > Michael Meissner <meiss...@linux.ibm.com>
> >
> > gcc/
> >
> > PR middle-end/108623
> > * hwint.h (sext_hwi): Add assertion against precision 0.
> > * tree-core.h (tree_type_common): Bump up precision field to 16
> > bits.
> > Align bit fields > 1 bit to at least an 8-bit boundary.
> > ---
> > gcc/hwint.h | 1 +
> > gcc/tree-core.h | 24 ++++++++++++------------
> > 2 files changed, 13 insertions(+), 12 deletions(-)
> >
> > diff --git a/gcc/hwint.h b/gcc/hwint.h
> > index e31aa006fa4..ba92efbfc25 100644
> > --- a/gcc/hwint.h
> > +++ b/gcc/hwint.h
> > @@ -277,6 +277,7 @@ ctz_or_zero (unsigned HOST_WIDE_INT x)
> > static inline HOST_WIDE_INT
> > sext_hwi (HOST_WIDE_INT src, unsigned int prec)
> > {
> > + gcc_checking_assert (prec != 0);
> > if (prec == HOST_BITS_PER_WIDE_INT)
> > return src;
> > else
> > diff --git a/gcc/tree-core.h b/gcc/tree-core.h
> > index 8124a1328d4..b71748c6c02 100644
> > --- a/gcc/tree-core.h
> > +++ b/gcc/tree-core.h
> > @@ -1686,18 +1686,8 @@ struct GTY(()) tree_type_common {
> > tree attributes;
> > unsigned int uid;
> >
> > - unsigned int precision : 10;
> > - unsigned no_force_blk_flag : 1;
> > - unsigned needs_constructing_flag : 1;
> > - unsigned transparent_aggr_flag : 1;
> > - unsigned restrict_flag : 1;
> > - unsigned contains_placeholder_bits : 2;
> > -
> > + unsigned int precision : 16;
> > ENUM_BITFIELD(machine_mode) mode : 8;
> > -
> > - /* TYPE_STRING_FLAG for INTEGER_TYPE and ARRAY_TYPE.
> > - TYPE_CXX_ODR_P for RECORD_TYPE and UNION_TYPE. */
> > - unsigned string_flag : 1;
> > unsigned lang_flag_0 : 1;
> > unsigned lang_flag_1 : 1;
> > unsigned lang_flag_2 : 1;
> > @@ -1713,12 +1703,22 @@ struct GTY(()) tree_type_common {
> > so we need to store the value 32 (not 31, as we need the zero
> > as well), hence six bits. */
> > unsigned align : 6;
> > + /* TYPE_STRING_FLAG for INTEGER_TYPE and ARRAY_TYPE.
> > + TYPE_CXX_ODR_P for RECORD_TYPE and UNION_TYPE. */
> > + unsigned string_flag : 1;
> > + unsigned no_force_blk_flag : 1;
> > +
> > unsigned warn_if_not_align : 6;
> > + unsigned needs_constructing_flag : 1;
> > + unsigned transparent_aggr_flag : 1;
> > +
> > + unsigned contains_placeholder_bits : 2;
> > + unsigned restrict_flag : 1;
> > unsigned typeless_storage : 1;
> > unsigned empty_flag : 1;
> > unsigned indivisible_p : 1;
> > unsigned no_named_args_stdarg_p : 1;
> > - unsigned spare : 15;
> > + unsigned spare : 9;
> >
> > alias_set_type alias_set;
> > tree pointer_to;
> > --
> > 2.39.1
> >
> >
> > --
> > Michael Meissner, IBM
> > PO Box 98, Ayer, Massachusetts, USA, 01432
> > email: meiss...@linux.ibm.com
