Re: [Qemu-devel] [4715] Emit trampolines manually in prologue

[Fabrice Bellard]

This code is too complicated. Please remove it and just call an helper
to do the division if you really need it. The division is a slow
operation so no optimization is needed at this point.

Moreover, as I said previously there is no point in implementing divu[2]
as no QEMU target directly needs it.

Fabrice.

malc wrote:
> Revision: 4715
>           http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=4715
> Author:   malc
> Date:     2008-06-09 19:57:36 +0000 (Mon, 09 Jun 2008)
> 
> Log Message:
> -----------
> Emit trampolines manually in prologue
> 
> Modified Paths:
> --------------
>     trunk/tcg/ppc/tcg-target.c
> 
> Modified: trunk/tcg/ppc/tcg-target.c
> ===================================================================
> --- trunk/tcg/ppc/tcg-target.c        2008-06-09 19:57:27 UTC (rev 4714)
> +++ trunk/tcg/ppc/tcg-target.c        2008-06-09 19:57:36 UTC (rev 4715)
> @@ -23,6 +23,8 @@
>   */
>  
>  static uint8_t *tb_ret_addr;
> +static uint8_t *udiv_addr;
> +static uint8_t *div_addr;
>  
>  #define FAST_PATH
>  #if TARGET_PHYS_ADDR_BITS <= 32
> @@ -118,7 +120,7 @@
>  };
>  
>  static const int tcg_target_callee_save_regs[] = {
> -    TCG_REG_R13,                /* sould r13 be saved? */
> +    TCG_REG_R13,                /* should r13 be saved? */
>      TCG_REG_R14,
>      TCG_REG_R15,
>      TCG_REG_R16,
> @@ -135,6 +137,22 @@
>      TCG_REG_R31
>  };
>  
> +static const int div_save_regs[] = {
> +    TCG_REG_R4,
> +    TCG_REG_R5,
> +    TCG_REG_R7,
> +    TCG_REG_R8,
> +    TCG_REG_R9,
> +    TCG_REG_R10,
> +    TCG_REG_R11,
> +    TCG_REG_R12,
> +    TCG_REG_R13,                /* should r13 be saved? */
> +    TCG_REG_R24,
> +    TCG_REG_R25,
> +    TCG_REG_R26,
> +    TCG_REG_R27,
> +};
> +
>  static uint32_t reloc_pc24_val (void *pc, tcg_target_long target)
>  {
>      tcg_target_long disp;
> @@ -799,9 +817,25 @@
>  #endif
>  }
>  
> +static uint64_t ppc_udiv_helper (uint64_t a, uint32_t b)
> +{
> +    uint64_t rem, quo;
> +    quo = a / b;
> +    rem = a % b;
> +    return (rem << 32) | (uint32_t) quo;
> +}
> +
> +static uint64_t ppc_div_helper (int64_t a, int32_t b)
> +{
> +    int64_t rem, quo;
> +    quo = a / b;
> +    rem = a % b;
> +    return (rem << 32) | (uint32_t) quo;
> +}
> +
>  void tcg_target_qemu_prologue (TCGContext *s)
>  {
> -    int i, frame_size;
> +    int i, j, frame_size;
>  
>      frame_size = 0
>          + 4                     /* back chain */
> @@ -837,6 +871,49 @@
>      tcg_out32 (s, MTSPR | RS (0) | LR);
>      tcg_out32 (s, ADDI | RT (1) | RA (1) | frame_size);
>      tcg_out32 (s, BCLR | BO_ALWAYS);
> +
> +    /* div trampolines */
> +    for (j = 0; j < 2; ++j) {
> +        tcg_target_long target;
> +
> +        frame_size = 8 + ARRAY_SIZE (div_save_regs) * 4;
> +        frame_size = (frame_size + 15) & ~15;
> +
> +        if (j == 0) {
> +            target = (tcg_target_long) ppc_udiv_helper;
> +            udiv_addr = s->code_ptr;
> +        }
> +        else {
> +            target = (tcg_target_long) ppc_div_helper;
> +            div_addr = s->code_ptr;
> +        }
> +
> +        tcg_out32 (s, MFSPR | RT (0) | LR);
> +        tcg_out32 (s, STWU | RS (1) | RA (1) | (-frame_size & 0xffff));
> +        for (i = 0; i < ARRAY_SIZE (div_save_regs); ++i)
> +            tcg_out32 (s, (STW
> +                           | RS (div_save_regs[i])
> +                           | RA (1)
> +                           | (i * 4 + 8)
> +                           )
> +                );
> +        tcg_out32 (s, STW | RS (0) | RA (1) | (frame_size - 4));
> +        tcg_out_mov (s, 4, 6);
> +        tcg_out_b (s, LK, target);
> +        tcg_out_mov (s, 6, 4);
> +
> +        for (i = 0; i < ARRAY_SIZE (div_save_regs); ++i)
> +            tcg_out32 (s, (LWZ
> +                           | RT (div_save_regs[i])
> +                           | RA (1)
> +                           | (i * 4 + 8)
> +                           )
> +                );
> +        tcg_out32 (s, LWZ | RT (0) | RA (1) | (frame_size - 4));
> +        tcg_out32 (s, MTSPR | RS (0) | LR);
> +        tcg_out32 (s, ADDI | RT (1) | RA (1) | frame_size);
> +        tcg_out32 (s, BCLR | BO_ALWAYS);
> +    }
>  }
>  
>  static void tcg_out_ld (TCGContext *s, TCGType type, int ret, int arg1,
> @@ -1018,41 +1095,6 @@
>      tcg_out_label(s, label_next, (tcg_target_long)s->code_ptr);
>  }
>  
> -static uint64_t __attribute ((used)) ppc_udiv_helper (uint64_t a, uint32_t b)
> -{
> -    uint64_t rem, quo;
> -    quo = a / b;
> -    rem = a % b;
> -    return (rem << 32) | (uint32_t) quo;
> -}
> -
> -static uint64_t __attribute ((used)) ppc_div_helper (int64_t a, int32_t b)
> -{
> -    int64_t rem, quo;
> -    quo = a / b;
> -    rem = a % b;
> -    return (rem << 32) | (uint32_t) quo;
> -}
> -
> -#define MAKE_TRAMPOLINE(name)                   \
> -extern void name##_trampoline (void);           \
> -asm (#name "_trampoline:\n"                     \
> -     " mflr 0\n"                                \
> -     " addi 1,1,-112\n"                         \
> -     " mr   4,6\n"                              \
> -     " stmw 7,0(1)\n"                           \
> -     " stw  0,108(0)\n"                         \
> -     " bl   ppc_" #name "_helper\n"             \
> -     " lmw  7,0(1)\n"                           \
> -     " lwz  0,108(0)\n"                         \
> -     " addi 1,1,112\n"                          \
> -     " mtlr 0\n"                                \
> -     " blr\n"                                   \
> -    )
> -
> -MAKE_TRAMPOLINE (div);
> -MAKE_TRAMPOLINE (udiv);
> -
>  static void tcg_out_div2 (TCGContext *s, int uns)
>  {
>      void *label1_ptr, *label2_ptr;
> @@ -1067,7 +1109,7 @@
>      label1_ptr = s->code_ptr;
>      tcg_out32 (s, BC | BI (7, CR_EQ) | BO_COND_TRUE);
>  
> -    tcg_out_b (s, LK, (tcg_target_long) (uns ? udiv_trampoline : 
> div_trampoline));
> +    tcg_out_b (s, LK, (tcg_target_long) (uns ? udiv_addr : div_addr));
>  
>      label2_ptr = s->code_ptr;
>      tcg_out32 (s, B);
> 
> 
> 
> 
>