Hi,
David Edelsohn <dje....@gmail.com> writes:
> On Mon, Jun 12, 2023 at 11:30 PM Jiufu Guo <guoji...@linux.ibm.com> wrote:
>>
>>
>> Hi David,
>>
>> David Edelsohn <dje....@gmail.com> writes:
>> > On Wed, Jun 7, 2023 at 9:55 PM Jiufu Guo <guoji...@linux.ibm.com> wrote:
>> >
>> > Hi,
>> >
>> > This patch checks if a constant is possible to be rotated to/from a
>> > positive
>> > or negative value from "li". If so, we could use "li;rotldi" to build it.
>> >
>> > Bootstrap and regtest pass on ppc64{,le}.
>> > Is this ok for trunk?
>> >
>> > BR,
>> > Jeff (Jiufu)
>> >
>> > gcc/ChangeLog:
>> >
>> > * config/rs6000/rs6000.cc (can_be_rotated_to_positive_li): New
>> > function.
>> > (can_be_rotated_to_negative_li): New function.
>> > (can_be_built_by_li_and_rotldi): New function.
>> > (rs6000_emit_set_long_const): Call can_be_built_by_li_and_rotldi.
>> >
>> > gcc/testsuite/ChangeLog:
>> >
>> > * gcc.target/powerpc/const-build.c: New test.
>> > ---
>> > gcc/config/rs6000/rs6000.cc | 64 +++++++++++++++++--
>> > .../gcc.target/powerpc/const-build.c | 54 ++++++++++++++++
>> > 2 files changed, 112 insertions(+), 6 deletions(-)
>> > create mode 100644 gcc/testsuite/gcc.target/powerpc/const-build.c
>> >
>> > diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
>> > index 42f49e4a56b..1dd0072350a 100644
>> > --- a/gcc/config/rs6000/rs6000.cc
>> > +++ b/gcc/config/rs6000/rs6000.cc
>> > @@ -10258,6 +10258,48 @@ rs6000_emit_set_const (rtx dest, rtx source)
>> > return true;
>> > }
>> >
>> > +/* Check if C can be rotated to a positive value which 'li' instruction
>> > + is able to load. If so, set *ROT to the number by which C is rotated,
>> > + and return true. Return false otherwise. */
>> > +
>> > +static bool
>> > +can_be_rotated_to_positive_li (HOST_WIDE_INT c, int *rot)
>> > +{
>> > + /* 49 leading zeros and 15 low bits on the positive value
>> > + generated by 'li' instruction. */
>> > + return can_be_rotated_to_lowbits (c, 15, rot);
>> > +}
>> > +
>> > +/* Like can_be_rotated_to_positive_li, but check the negative value of
>> > 'li'. */
>> > +
>> > +static bool
>> > +can_be_rotated_to_negative_li (HOST_WIDE_INT c, int *rot)
>> > +{
>> > + return can_be_rotated_to_lowbits (~c, 15, rot);
>> > +}
>> > +
>> > +/* Check if value C can be built by 2 instructions: one is 'li', another
>> > is
>> > + rotldi.
>> > +
>> > + If so, *SHIFT is set to the shift operand of rotldi(rldicl), and *MASK
>> > + is set to -1, and return true. Return false otherwise. */
>> > +
>> >
>> > I look at this feature and it's good, but I don't fully understand the
>> > benefit of this level of abstraction. Ideally all of the above functions
>> > would
>> > be inlined. They aren't reused.
>> >
>> > +static bool
>> > +can_be_built_by_li_and_rotldi (HOST_WIDE_INT c, int *shift,
>> > + HOST_WIDE_INT *mask)
>> > +{
>> > + int n;
>> > + if (can_be_rotated_to_positive_li (c, &n)
>> > + || can_be_rotated_to_negative_li (c, &n))
>> >
>> > Why not
>> >
>> > /* Check if C or ~C can be rotated to a positive or negative value
>> > which 'li' instruction is able to load. */
>> > if (can_be_rotated_to_lowbits (c, 15, &n)
>> > || can_be_rotated_to_lowbits (~c, 15, &n))
>>
>>
>> Thanks a lot for your review!!
>>
>> Your suggestions could also achieve my goal of using a new function:
>> Using "can_be_rotated_to_positive_li" is just trying to get a
>> straightforward name. Like yours, the code's comments would also
>> make it easy to understand.
>
> I recognize that you are trying to be consistent with the other
> functions that you add in later patches, but it feels like overkill in
Yes :)
> abstraction to me. Or maybe combine postive_li and negative_li into a
> single function so that the abstraction serves a purpose other than a
> tail call and creating an alias for a specific invocation of
> can_be_rotated_to_lowbits.
Get it.
Thanks for your valuable suggestion!
BR,
Jeff (Jiufu Guo)
>
> Thanks, David
>
>>
>> BR,
>> Jeff (Jiufu Guo)
>> >
>> > ...
>> >
>> > This is a style of software engineering, but it seems overkill to me when
>> > the function is a single line that tail calls another function. Am I
>> > missing
>> > something?
>> >
>> > The rest of this patch looks good.
>> >
>> > Thanks, David
>> >
>> > + {
>> > + *mask = HOST_WIDE_INT_M1;
>> > + *shift = HOST_BITS_PER_WIDE_INT - n;
>> > + return true;
>> > + }
>> > +
>> > + return false;
>> > +}
>> > +
>> > /* Subroutine of rs6000_emit_set_const, handling PowerPC64 DImode.
>> > Output insns to set DEST equal to the constant C as a series of
>> > lis, ori and shl instructions. */
>> > @@ -10266,15 +10308,14 @@ static void
>> > rs6000_emit_set_long_const (rtx dest, HOST_WIDE_INT c)
>> > {
>> > rtx temp;
>> > + int shift;
>> > + HOST_WIDE_INT mask;
>> > HOST_WIDE_INT ud1, ud2, ud3, ud4;
>> >
>> > ud1 = c & 0xffff;
>> > - c = c >> 16;
>> > - ud2 = c & 0xffff;
>> > - c = c >> 16;
>> > - ud3 = c & 0xffff;
>> > - c = c >> 16;
>> > - ud4 = c & 0xffff;
>> > + ud2 = (c >> 16) & 0xffff;
>> > + ud3 = (c >> 32) & 0xffff;
>> > + ud4 = (c >> 48) & 0xffff;
>> >
>> > if ((ud4 == 0xffff && ud3 == 0xffff && ud2 == 0xffff && (ud1 & 0x8000))
>> > || (ud4 == 0 && ud3 == 0 && ud2 == 0 && ! (ud1 & 0x8000)))
>> > @@ -10305,6 +10346,17 @@ rs6000_emit_set_long_const (rtx dest,
>> > HOST_WIDE_INT c)
>> > emit_move_insn (dest, gen_rtx_XOR (DImode, temp,
>> > GEN_INT ((ud2 ^ 0xffff) << 16)));
>> > }
>> > + else if (can_be_built_by_li_and_rotldi (c, &shift, &mask))
>> > + {
>> > + temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode);
>> > + unsigned HOST_WIDE_INT imm = (c | ~mask);
>> > + imm = (imm >> shift) | (imm << (HOST_BITS_PER_WIDE_INT - shift));
>> > +
>> > + emit_move_insn (temp, GEN_INT (imm));
>> > + if (shift != 0)
>> > + temp = gen_rtx_ROTATE (DImode, temp, GEN_INT (shift));
>> > + emit_move_insn (dest, temp);
>> > + }
>> > else if (ud3 == 0 && ud4 == 0)
>> > {
>> > temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode);
>> > diff --git a/gcc/testsuite/gcc.target/powerpc/const-build.c
>> > b/gcc/testsuite/gcc.target/powerpc/const-build.c
>> > new file mode 100644
>> > index 00000000000..70f095f6bf2
>> > --- /dev/null
>> > +++ b/gcc/testsuite/gcc.target/powerpc/const-build.c
>> > @@ -0,0 +1,54 @@
>> > +/* { dg-do run } */
>> > +/* { dg-options "-O2 -save-temps" } */
>> > +/* { dg-require-effective-target has_arch_ppc64 } */
>> > +
>> > +#define NOIPA __attribute__ ((noipa))
>> > +
>> > +struct fun
>> > +{
>> > + long long (*f) (void);
>> > + long long val;
>> > +};
>> > +
>> > +long long NOIPA
>> > +li_rotldi_1 (void)
>> > +{
>> > + return 0x7531000000000LL;
>> > +}
>> > +
>> > +long long NOIPA
>> > +li_rotldi_2 (void)
>> > +{
>> > + return 0x2100000000000064LL;
>> > +}
>> > +
>> > +long long NOIPA
>> > +li_rotldi_3 (void)
>> > +{
>> > + return 0xffff8531ffffffffLL;
>> > +}
>> > +
>> > +long long NOIPA
>> > +li_rotldi_4 (void)
>> > +{
>> > + return 0x21ffffffffffff94LL;
>> > +}
>> > +
>> > +struct fun arr[] = {
>> > + {li_rotldi_1, 0x7531000000000LL},
>> > + {li_rotldi_2, 0x2100000000000064LL},
>> > + {li_rotldi_3, 0xffff8531ffffffffLL},
>> > + {li_rotldi_4, 0x21ffffffffffff94LL},
>> > +};
>> > +
>> > +/* { dg-final { scan-assembler-times {\mrotldi\M} 4 } } */
>> > +
>> > +int
>> > +main ()
>> > +{
>> > + for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
>> > + if ((*arr[i].f) () != arr[i].val)
>> > + __builtin_abort ();
>> > +
>> > + return 0;
>> > +}
>> > --
>> > 2.39.1
