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.
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
