Re: [PATCH v2 4/7] tcg/ppc: Use PLD in tcg_out_movi for constant pool

[Nicholas Piggin]

On Tue Aug 8, 2023 at 1:02 PM AEST, Richard Henderson wrote:
> The prefixed instruction has a pc-relative form to use here.

I don't understand this code very well but going by existing
relocs it looks okay.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/ppc/tcg-target.c.inc | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/tcg/ppc/tcg-target.c.inc b/tcg/ppc/tcg-target.c.inc
> index 61ae9d8ab7..b3b2e9874d 100644
> --- a/tcg/ppc/tcg-target.c.inc
> +++ b/tcg/ppc/tcg-target.c.inc
> @@ -101,6 +101,10 @@
>  #define ALL_GENERAL_REGS  0xffffffffu
>  #define ALL_VECTOR_REGS   0xffffffff00000000ull
>  
> +#ifndef R_PPC64_PCREL34
> +#define R_PPC64_PCREL34  132
> +#endif
> +
>  #define have_isel  (cpuinfo & CPUINFO_ISEL)
>  
>  #ifndef CONFIG_SOFTMMU
> @@ -260,6 +264,19 @@ static bool reloc_pc14(tcg_insn_unit *src_rw, const 
> tcg_insn_unit *target)
>      return false;
>  }
>  
> +static bool reloc_pc34(tcg_insn_unit *src_rw, const tcg_insn_unit *target)
> +{
> +    const tcg_insn_unit *src_rx = tcg_splitwx_to_rx(src_rw);
> +    ptrdiff_t disp = tcg_ptr_byte_diff(target, src_rx);
> +
> +    if (disp == sextract64(disp, 0, 34)) {
> +        src_rw[0] = (src_rw[0] & ~0x3ffff) | ((disp >> 16) & 0x3ffff);
> +        src_rw[1] = (src_rw[1] & ~0xffff) | (disp & 0xffff);
> +        return true;
> +    }
> +    return false;
> +}
> +
>  /* test if a constant matches the constraint */
>  static bool tcg_target_const_match(int64_t val, TCGType type, int ct)
>  {
> @@ -684,6 +701,8 @@ static bool patch_reloc(tcg_insn_unit *code_ptr, int type,
>          return reloc_pc14(code_ptr, target);
>      case R_PPC_REL24:
>          return reloc_pc24(code_ptr, target);
> +    case R_PPC64_PCREL34:
> +        return reloc_pc34(code_ptr, target);
>      case R_PPC_ADDR16:
>          /*
>           * We are (slightly) abusing this relocation type.  In particular,
> @@ -1111,6 +1130,11 @@ static void tcg_out_movi_int(TCGContext *s, TCGType 
> type, TCGReg ret,
>      }
>  
>      /* Use the constant pool, if possible.  */
> +    if (have_isa_3_10) {
> +        tcg_out_8ls_d(s, PLD, ret, 0, 0, 1);
> +        new_pool_label(s, arg, R_PPC64_PCREL34, s->code_ptr - 2, 0);
> +        return;
> +    }
>      if (!in_prologue && USE_REG_TB) {
>          new_pool_label(s, arg, R_PPC_ADDR16, s->code_ptr,
>                         tcg_tbrel_diff(s, NULL));