Re: [Qemu-devel] [PATCH 20/22] tcg-i386: Tidy lea.

[Aurelien Jarno <aurelien@aurel32.net>]

On Wed, Apr 14, 2010 at 12:08:28PM -0700, Richard Henderson wrote:
> Implement full modrm+sib addressing mode processing.
> Use that in qemu_ld/st to output the LEA.
> 
> Signed-off-by: Richard Henderson <rth@twiddle.net>

Acked-by: Aurelien Jarno <aurelien@aurel32.net>

> ---
>  tcg/i386/tcg-target.c |   91 ++++++++++++++++++++++++++++++++-----------------
>  1 files changed, 60 insertions(+), 31 deletions(-)
> 
> diff --git a/tcg/i386/tcg-target.c b/tcg/i386/tcg-target.c
> index bf3c0d6..755d46d 100644
> --- a/tcg/i386/tcg-target.c
> +++ b/tcg/i386/tcg-target.c
> @@ -176,6 +176,7 @@ static inline int tcg_target_const_match(tcg_target_long val,
>  #define OPC_JCC_short	(0x70)		/* ... plus condition code */
>  #define OPC_JMP_long	(0xe9)
>  #define OPC_JMP_short	(0xeb)
> +#define OPC_LEA         (0x8d)
>  #define OPC_MOVB_EvGv	(0x88)		/* stores, more or less */
>  #define OPC_MOVL_EvGv	(0x89)		/* stores, more or less */
>  #define OPC_MOVL_GvEv	(0x8b)		/* loads, more or less */
> @@ -277,40 +278,70 @@ static inline void tcg_out_modrm(TCGContext *s, int opc, int r, int rm)
>      tcg_out8(s, 0xc0 | (r << 3) | rm);
>  }
>  
> -/* rm == -1 means no register index */
> -static inline void tcg_out_modrm_offset(TCGContext *s, int opc, int r, int rm, 
> -                                        int32_t offset)
> +/* Output an opcode with a full "rm + (index<<shift) + offset" address mode.  
> +   We handle either RM and INDEX missing with a -1 value.  */
> +
> +static void tcg_out_modrm_sib_offset(TCGContext *s, int opc, int r, int rm,
> +                                     int index, int shift, int32_t offset)
>  {
> +    int mod, len;
> +
> +    if (index == -1 && rm == -1) {
> +        /* Absolute address.  */
> +        tcg_out_opc(s, opc);
> +        tcg_out8(s, (r << 3) | 5);
> +        tcg_out32(s, offset);
> +        return;
> +    }
> +
>      tcg_out_opc(s, opc);
> +
> +    /* Find the length of the immediate addend.  Note that the encoding
> +       that would be used for (%ebp) indicates absolute addressing.  */
>      if (rm == -1) {
> -        tcg_out8(s, 0x05 | (r << 3));
> -        tcg_out32(s, offset);
> +        mod = 0, len = 4, rm = 5;
>      } else if (offset == 0 && rm != TCG_REG_EBP) {
> -        if (rm == TCG_REG_ESP) {
> -            tcg_out8(s, 0x04 | (r << 3));
> -            tcg_out8(s, 0x24);
> -        } else {
> -            tcg_out8(s, 0x00 | (r << 3) | rm);
> -        }
> -    } else if ((int8_t)offset == offset) {
> -        if (rm == TCG_REG_ESP) {
> -            tcg_out8(s, 0x44 | (r << 3));
> -            tcg_out8(s, 0x24);
> -        } else {
> -            tcg_out8(s, 0x40 | (r << 3) | rm);
> -        }
> -        tcg_out8(s, offset);
> +        mod = 0, len = 0;
> +    } else if (offset == (int8_t)offset) {
> +        mod = 0x40, len = 1;
>      } else {
> -        if (rm == TCG_REG_ESP) {
> -            tcg_out8(s, 0x84 | (r << 3));
> -            tcg_out8(s, 0x24);
> +        mod = 0x80, len = 4;
> +    }
> +
> +    /* Use a single byte MODRM format if possible.  Note that the encoding
> +       that would be used for %esp is the escape to the two byte form.  */
> +    if (index == -1 && rm != TCG_REG_ESP) {
> +        /* Single byte MODRM format.  */
> +        tcg_out8(s, mod | (r << 3) | rm);
> +    } else {
> +        /* Two byte MODRM+SIB format.  */
> +
> +        /* Note that the encoding that would place %esp into the index
> +           field indicates no index register.  */
> +        if (index == -1) {
> +            index = 4;
>          } else {
> -            tcg_out8(s, 0x80 | (r << 3) | rm);
> +            assert(index != TCG_REG_ESP);
>          }
> +
> +        tcg_out8(s, mod | (r << 3) | 4);
> +        tcg_out8(s, (shift << 6) | (index << 3) | rm);
> +    }
> +
> +    if (len == 1) {
> +        tcg_out8(s, offset);
> +    } else if (len == 4) {
>          tcg_out32(s, offset);
>      }
>  }
>  
> +/* rm == -1 means no register index */
> +static inline void tcg_out_modrm_offset(TCGContext *s, int opc, int r, int rm, 
> +                                        int32_t offset)
> +{
> +    tcg_out_modrm_sib_offset(s, opc, r, rm, -1, 0, offset);
> +}
> +
>  /* Generate dest op= src.  Uses the same ARITH_* codes as tgen_arithi.  */
>  static inline void tgen_arithr(TCGContext *s, int subop, int dest, int src)
>  {
> @@ -733,10 +764,9 @@ static void tcg_out_qemu_ld(TCGContext *s, const TCGArg *args,
>      tgen_arithi(s, ARITH_AND, r0, TARGET_PAGE_MASK | ((1 << s_bits) - 1), 0);
>      tgen_arithi(s, ARITH_AND, r1, (CPU_TLB_SIZE - 1) << CPU_TLB_ENTRY_BITS, 0);
>  
> -    tcg_out_opc(s, 0x8d); /* lea offset(r1, %ebp), r1 */
> -    tcg_out8(s, 0x80 | (r1 << 3) | 0x04);
> -    tcg_out8(s, (5 << 3) | r1);
> -    tcg_out32(s, offsetof(CPUState, tlb_table[mem_index][0].addr_read));
> +    tcg_out_modrm_sib_offset(s, OPC_LEA, r1, TCG_AREG0, r1, 0,
> +                             offsetof(CPUState,
> +                                      tlb_table[mem_index][0].addr_read));
>  
>      /* cmp 0(r1), r0 */
>      tcg_out_modrm_offset(s, OPC_CMP_GvEv, r0, r1, 0);
> @@ -924,10 +954,9 @@ static void tcg_out_qemu_st(TCGContext *s, const TCGArg *args,
>      tgen_arithi(s, ARITH_AND, r0, TARGET_PAGE_MASK | ((1 << s_bits) - 1), 0);
>      tgen_arithi(s, ARITH_AND, r1, (CPU_TLB_SIZE - 1) << CPU_TLB_ENTRY_BITS, 0);
>  
> -    tcg_out_opc(s, 0x8d); /* lea offset(r1, %ebp), r1 */
> -    tcg_out8(s, 0x80 | (r1 << 3) | 0x04);
> -    tcg_out8(s, (5 << 3) | r1);
> -    tcg_out32(s, offsetof(CPUState, tlb_table[mem_index][0].addr_write));
> +    tcg_out_modrm_sib_offset(s, OPC_LEA, r1, TCG_AREG0, r1, 0,
> +                             offsetof(CPUState,
> +                                      tlb_table[mem_index][0].addr_write));
>  
>      /* cmp 0(r1), r0 */
>      tcg_out_modrm_offset(s, OPC_CMP_GvEv, r0, r1, 0);
> -- 
> 1.6.6.1
> 
> 
> 
> 

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