Hi!
On Mon, Jul 25, 2022 at 09:29:22PM +0800, Jiufu Guo wrote:
> When checking eq/neq with a constant which has only 16bits, it can be
> optimized to check the rotated data. By this, the constant building
> is optimized.
"ne", not "neq".
> gcc/ChangeLog:
>
> * config/rs6000/rs6000-protos.h (rotate_from_leading_zeros_const):
> New decl.
"New declaration." or just "New". Also, don't break lines early please,
especially if that means ending a line in a colon, which then looks as
if you forgot to write something there.
> * config/rs6000/rs6000.cc (rotate_from_leading_zeros_const): New
> define for checking simply rotated constant.
"New." or "New definition." or such.
> +/* Check if C can be rotated from an immediate which contains leading
> + zeros at least CLZ.
"Which starts (as 64 bit integer) with at least CLZ bits zero" or such.
> + /* xx0..0xx: rotate enough bits firstly, then check case a. */
> + const int rot_bits = HOST_BITS_PER_WIDE_INT - clz + 1;
> + unsigned HOST_WIDE_INT rc = (c >> rot_bits) | (c << (clz - 1));
> + tz = ctz_hwi (rc);
> + if (clz_hwi (rc) + tz >= clz)
> + return tz + rot_bits;
This could use some more explanation.
> +(define_code_iterator eqne [eq ne])
> +;; "i == C" ==> "rotl(i,N) == rotl(C,N)"
> +(define_insn_and_split "*rotate_on_cmpdi"
> + [(set (pc)
> + (if_then_else (eqne (match_operand:DI 1 "gpc_reg_operand" "r")
Wrong indentation. The ( should be in the same column as the preceding (
it matches.
Setting "pc" to either 0 or 1 is never correct.
> + "TARGET_POWERPC64 && !reload_completed && can_create_pseudo_p ()
reload_completed in splitters is almost always wrong. It isn't any
better if it is in the insn condition of a define_insn_and_split :-)
> + && num_insns_constant (operands[2], DImode) > 1
> + && (rotate_from_leading_zeros_const (~UINTVAL (operands[2]), 49) > 0
> + || rotate_from_leading_zeros_const (UINTVAL (operands[2]), 48) > 0)"
There must be a better way to describe this.
> + if (rot < 0)
> + {
> + sgn = true;
> + rot = rotate_from_leading_zeros_const (~C, 49);
> + }
Bad indentation.
> + rtx cmp = ne ? gen_rtx_NE (CCmode, cc, const0_rtx)
> + : gen_rtx_EQ (CCmode, cc, const0_rtx);
rtx cmp = gen_rtx_<EQNE> (...);
(and define a code_attr EQNE to just output the uppercase EQ or NE).
Why is this doing a conditional branch at all? Unpredictable
conditional branches are extremely costly.
> +/* { dg-require-effective-target lp64 } */
arch_ppc64
> +/* { dg-final { scan-assembler-times "cmpldi" 10 } } */
> +/* { dg-final { scan-assembler-times "cmpdi" 4 } } */
> +/* { dg-final { scan-assembler-times "rotldi" 14 } } */
Please use \m and \M .
Thanks,
Segher
