Re: [PATCH]rs6000: Load high and low part of 64bit constant independently

["Kewen.Lin" <linkw@linux.ibm.com>]

Hi Jeff,

Sorry for the late review.

on 2022/9/15 16:30, Jiufu Guo wrote:
> Hi,
> 
> For a complicate 64bit constant, blow is one instruction-sequence to
> build:
> 	lis 9,0x800a
> 	ori 9,9,0xabcd
> 	sldi 9,9,32
> 	oris 9,9,0xc167
> 	ori 9,9,0xfa16
> 
> while we can also use below sequence to build:
> 	lis 9,0xc167
> 	lis 10,0x800a
> 	ori 9,9,0xfa16
> 	ori 10,10,0xabcd
> 	rldimi 9,10,32,0
> This sequence is using 2 registers to build high and low part firstly,
> and then merge them.
> In parallel aspect, this sequence would be faster. (Ofcause, using 1 more
> register with potential register pressure).
> 
> Bootstrap and regtest pass on ppc64le.
> Is this ok for trunk?
> 
> 
> BR,
> Jeff(Jiufu)
> 
> 
> gcc/ChangeLog:
> 
> 	* config/rs6000/rs6000.cc (rs6000_emit_set_long_const): Update 64bit
> 	constant build.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.target/powerpc/parall_5insn_const.c: New test.
> 
> ---
>  gcc/config/rs6000/rs6000.cc                   | 45 +++++++++++--------
>  .../gcc.target/powerpc/parall_5insn_const.c   | 27 +++++++++++
>  2 files changed, 53 insertions(+), 19 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/powerpc/parall_5insn_const.c
> 
> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> index a656cb32a47..759c6309677 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -10180,26 +10180,33 @@ rs6000_emit_set_long_const (rtx dest, HOST_WIDE_INT c)
>      }
>    else
>      {
> -      temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode);
> -
> -      emit_move_insn (copy_rtx (temp),
> -		      GEN_INT (((ud4 << 16) ^ 0x80000000) - 0x80000000));
> -      if (ud3 != 0)
> -	emit_move_insn (copy_rtx (temp),
> -			gen_rtx_IOR (DImode, copy_rtx (temp),
> -				     GEN_INT (ud3)));
> +      if (can_create_pseudo_p ())
> +	{
> +	  /* lis A,U4; ori A,U3; lis B,U2; ori B,U1; rldimi A,B,32,0.  */

Nit: A, B are supposed to be H, L?

> +	  rtx H = gen_reg_rtx (DImode);
> +	  rtx L = gen_reg_rtx (DImode);
> +	  HOST_WIDE_INT num = (ud2 << 16) | ud1;
> +	  rs6000_emit_set_long_const (L, (num ^ 0x80000000) - 0x80000000);
> +	  num = (ud4 << 16) | ud3;
> +	  rs6000_emit_set_long_const (H, (num ^ 0x80000000) - 0x80000000);
> +	  emit_insn (gen_rotldi3_insert_3 (dest, H, GEN_INT (32), L,
> +					   GEN_INT (0xffffffff)));
> +	}
> +      else
> +	{
> +	  /* lis A, U4; ori A,U3; rotl A,32; oris A,U2; ori A,U1.  */
                   ~~~ unexpected space?

> +	  emit_move_insn (dest,
> +			  GEN_INT (((ud4 << 16) ^ 0x80000000) - 0x80000000));
> +	  if (ud3 != 0)
> +	    emit_move_insn (dest, gen_rtx_IOR (DImode, dest, GEN_INT (ud3)));
> 
> -      emit_move_insn (ud2 != 0 || ud1 != 0 ? copy_rtx (temp) : dest,
> -		      gen_rtx_ASHIFT (DImode, copy_rtx (temp),
> -				      GEN_INT (32)));
> -      if (ud2 != 0)
> -	emit_move_insn (ud1 != 0 ? copy_rtx (temp) : dest,
> -			gen_rtx_IOR (DImode, copy_rtx (temp),
> -				     GEN_INT (ud2 << 16)));
> -      if (ud1 != 0)
> -	emit_move_insn (dest,
> -			gen_rtx_IOR (DImode, copy_rtx (temp),
> -				     GEN_INT (ud1)));
> +	  emit_move_insn (dest, gen_rtx_ASHIFT (DImode, dest, GEN_INT (32)));
> +	  if (ud2 != 0)
> +	    emit_move_insn (dest,
> +			    gen_rtx_IOR (DImode, dest, GEN_INT (ud2 << 16)));
> +	  if (ud1 != 0)
> +	    emit_move_insn (dest, gen_rtx_IOR (DImode, dest, GEN_INT (ud1)));
> +	}
>      }
>  }
> 
> diff --git a/gcc/testsuite/gcc.target/powerpc/parall_5insn_const.c b/gcc/testsuite/gcc.target/powerpc/parall_5insn_const.c
> new file mode 100644
> index 00000000000..ed8ccc73378
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/parall_5insn_const.c
> @@ -0,0 +1,27 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -mdejagnu-cpu=power7  -save-temps" } */

Why do we need power7 here?

> +/* { dg-require-effective-target has_arch_ppc64 } */
> +
> +/* { dg-final { scan-assembler-times {\mlis\M} 4 } } */
> +/* { dg-final { scan-assembler-times {\mori\M} 4 } } */
> +/* { dg-final { scan-assembler-times {\mrldimi\M} 2 } } */
> +
> +void __attribute__ ((noinline)) foo (unsigned long long *a)
> +{
> +  /* 2lis+2ori+1rldimi for each constant.  */

Nit: seems better to read with "/* 2 lis + 2 ori + 1 rldimi for ..."

BR,
Kewen