Re: [Qemu-devel] [PATCH v2 2/7] tcg-i386: Don't perform GETPC adjustment in TCG code

[Aurelien Jarno]

On Thu, Aug 29, 2013 at 03:05:56PM -0700, Richard Henderson wrote:
> Since we now perform it inside the helper, no need to do it here.
> This also lets us perform a tail-call from the store slow path to
> the helper.
> 
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  tcg/i386/tcg-target.c | 34 ++++++++++++++--------------------
>  1 file changed, 14 insertions(+), 20 deletions(-)
> 
> diff --git a/tcg/i386/tcg-target.c b/tcg/i386/tcg-target.c
> index 12a7ca3..84f17fe 100644
> --- a/tcg/i386/tcg-target.c
> +++ b/tcg/i386/tcg-target.c
> @@ -1470,12 +1470,6 @@ static void add_qemu_ldst_label(TCGContext *s,
>      }
>  }
>  
> -/* See the GETPC definition in include/exec/exec-all.h.  */
> -static inline uintptr_t do_getpc(uint8_t *raddr)
> -{
> -    return (uintptr_t)raddr - 1;
> -}
> -
>  /*
>   * Generate code for the slow path for a load at the end of block
>   */
> @@ -1509,14 +1503,14 @@ static void tcg_out_qemu_ld_slow_path(TCGContext *s, 
> TCGLabelQemuLdst *l)
>          tcg_out_sti(s, TCG_TYPE_I32, TCG_REG_ESP, ofs, l->mem_index);
>          ofs += 4;
>  
> -        tcg_out_sti(s, TCG_TYPE_I32, TCG_REG_ESP, ofs, do_getpc(l->raddr));
> +        tcg_out_sti(s, TCG_TYPE_I32, TCG_REG_ESP, ofs, (uintptr_t)l->raddr);
>      } else {
>          tcg_out_mov(s, TCG_TYPE_PTR, tcg_target_call_iarg_regs[0], 
> TCG_AREG0);
>          /* The second argument is already loaded with addrlo.  */
>          tcg_out_movi(s, TCG_TYPE_I32, tcg_target_call_iarg_regs[2],
>                       l->mem_index);
>          tcg_out_movi(s, TCG_TYPE_PTR, tcg_target_call_iarg_regs[3],
> -                     do_getpc(l->raddr));
> +                     (uintptr_t)l->raddr);
>      }
>  
>      tcg_out_calli(s, (tcg_target_long)qemu_ld_helpers[s_bits]);
> @@ -1571,6 +1565,7 @@ static void tcg_out_qemu_st_slow_path(TCGContext *s, 
> TCGLabelQemuLdst *l)
>      int opc = l->opc;
>      int s_bits = opc & 3;
>      uint8_t **label_ptr = &l->label_ptr[0];
> +    TCGReg retaddr;
>  
>      /* resolve label address */
>      *(uint32_t *)label_ptr[0] = (uint32_t)(s->code_ptr - label_ptr[0] - 4);
> @@ -1603,10 +1598,10 @@ static void tcg_out_qemu_st_slow_path(TCGContext *s, 
> TCGLabelQemuLdst *l)
>          tcg_out_sti(s, TCG_TYPE_I32, TCG_REG_ESP, ofs, l->mem_index);
>          ofs += 4;
>  
> -        tcg_out_sti(s, TCG_TYPE_I32, TCG_REG_ESP, ofs, do_getpc(l->raddr));
> +        retaddr = TCG_REG_EAX;
> +        tcg_out_movi(s, TCG_TYPE_I32, retaddr, (uintptr_t)l->raddr);
> +        tcg_out_st(s, TCG_TYPE_I32, retaddr, TCG_REG_ESP, ofs);
>      } else {
> -        uintptr_t pc;
> -
>          tcg_out_mov(s, TCG_TYPE_PTR, tcg_target_call_iarg_regs[0], 
> TCG_AREG0);
>          /* The second argument is already loaded with addrlo.  */
>          tcg_out_mov(s, (opc == 3 ? TCG_TYPE_I64 : TCG_TYPE_I32),
> @@ -1614,20 +1609,19 @@ static void tcg_out_qemu_st_slow_path(TCGContext *s, 
> TCGLabelQemuLdst *l)
>          tcg_out_movi(s, TCG_TYPE_I32, tcg_target_call_iarg_regs[3],
>                       l->mem_index);
>  
> -        pc = do_getpc(l->raddr);
>          if (ARRAY_SIZE(tcg_target_call_iarg_regs) > 4) {
> -            tcg_out_movi(s, TCG_TYPE_PTR, tcg_target_call_iarg_regs[4], pc);
> -        } else if (pc == (int32_t)pc) {
> -            tcg_out_sti(s, TCG_TYPE_PTR, TCG_REG_ESP, 0, pc);
> +            retaddr = tcg_target_call_iarg_regs[4];
> +            tcg_out_movi(s, TCG_TYPE_PTR, retaddr, (uintptr_t)l->raddr);
>          } else {
> -            tcg_out_movi(s, TCG_TYPE_PTR, TCG_REG_RAX, pc);
> -            tcg_out_st(s, TCG_TYPE_PTR, TCG_REG_RAX, TCG_REG_ESP, 0);
> +            retaddr = TCG_REG_RAX;
> +            tcg_out_movi(s, TCG_TYPE_PTR, retaddr, (uintptr_t)l->raddr);
> +            tcg_out_st(s, TCG_TYPE_PTR, retaddr, TCG_REG_ESP, 0);
>          }
>      }
>  
> -    tcg_out_calli(s, (tcg_target_long)qemu_st_helpers[s_bits]);
> -
> -    tcg_out_jmp(s, (tcg_target_long)l->raddr);
> +    /* "Tail call" to the helper, with the return address back inline.  */
> +    tcg_out_push(s, retaddr);
> +    tcg_out_jmp(s, (tcg_target_long)qemu_st_helpers[s_bits]);
>  }

Reviewed-by: Aurelien Jarno <address@hidden>


-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net