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tcg/x86_64: Avoid unnecessary REX.B prefixes.

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The existing P_REXB internal opcode flag unconditionally emits
the REX prefix.  Technically it's not needed if the register in
question is %al, %bl, %cl, %dl.

Eliding the prefix requires splitting the P_REXB flag into two,
in order to indicate whether the byte register in question is
in the REG or the R/M field.  Within TCG, the byte register is
in the REG field only for stores.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This commit is contained in:
Richard Henderson 2010-01-14 14:59:51 -08:00 committed by Aurelien Jarno
parent fccd2613d6
commit 09aac1266e
1 changed files with 30 additions and 16 deletions
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46
tcg/x86_64/tcg-target.c
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@ -217,9 +217,10 @@ static inline int tcg_target_const_match(tcg_target_long val,
#define JCC_JLE 0xe
#define JCC_JG 0xf
#define P_EXT 0x100 /* 0x0f opcode prefix */
#define P_REXW 0x200 /* set rex.w = 1 */
#define P_REXB 0x400 /* force rex use for byte registers */
#define P_EXT 0x100 /* 0x0f opcode prefix */
#define P_REXW 0x200 /* set rex.w = 1 */
#define P_REXB_R 0x400 /* REG field as byte register */
#define P_REXB_RM 0x800 /* R/M field as byte register */
static const uint8_t tcg_cond_to_jcc[10] = {
[TCG_COND_EQ] = JCC_JE,
@ -234,16 +235,29 @@ static const uint8_t tcg_cond_to_jcc[10] = {
[TCG_COND_GTU] = JCC_JA,
};
static inline void tcg_out_opc(TCGContext *s, int opc, int r, int rm, int x)
static void tcg_out_opc(TCGContext *s, int opc, int r, int rm, int x)
{
int rex;
rex = ((opc >> 6) & 0x8) | ((r >> 1) & 0x4) |
((x >> 2) & 2) | ((rm >> 3) & 1);
if (rex || (opc & P_REXB)) {
tcg_out8(s, rex | 0x40);
int rex = 0;
rex |= (opc & P_REXW) >> 6; /* REX.W */
rex |= (r & 8) >> 1; /* REX.R */
rex |= (x & 8) >> 2; /* REX.X */
rex |= (rm & 8) >> 3; /* REX.B */
/* P_REXB_{R,RM} indicates that the given register is the low byte.
For %[abcd]l we need no REX prefix, but for %{si,di,bp,sp}l we do,
as otherwise the encoding indicates %[abcd]h. Note that the values
that are ORed in merely indicate that the REX byte must be present;
those bits get discarded in output. */
rex |= opc & (r >= 4 ? P_REXB_R : 0);
rex |= opc & (rm >= 4 ? P_REXB_RM : 0);
if (rex) {
tcg_out8(s, (uint8_t)(rex | 0x40));
}
if (opc & P_EXT)
if (opc & P_EXT) {
tcg_out8(s, 0x0f);
}
tcg_out8(s, opc & 0xff);
}
@ -408,7 +422,7 @@ static inline void tgen_arithi32(TCGContext *s, int c, int r0, int32_t val)
tcg_out8(s, val);
} else if (c == ARITH_AND && val == 0xffu) {
/* movzbl */
tcg_out_modrm(s, 0xb6 | P_EXT | P_REXB, r0, r0);
tcg_out_modrm(s, 0xb6 | P_EXT | P_REXB_RM, r0, r0);
} else if (c == ARITH_AND && val == 0xffffu) {
/* movzwl */
tcg_out_modrm(s, 0xb7 | P_EXT, r0, r0);
@ -776,7 +790,7 @@ static void tcg_out_qemu_st(TCGContext *s, const TCGArg *args,
switch(opc) {
case 0:
/* movzbl */
tcg_out_modrm(s, 0xb6 | P_EXT | P_REXB, TCG_REG_RSI, data_reg);
tcg_out_modrm(s, 0xb6 | P_EXT | P_REXB_RM, TCG_REG_RSI, data_reg);
break;
case 1:
/* movzwl */
@ -829,7 +843,7 @@ static void tcg_out_qemu_st(TCGContext *s, const TCGArg *args,
switch(opc) {
case 0:
/* movb */
tcg_out_modrm_offset(s, 0x88 | P_REXB, data_reg, r0, offset);
tcg_out_modrm_offset(s, 0x88 | P_REXB_R, data_reg, r0, offset);
break;
case 1:
if (bswap) {
@ -964,7 +978,7 @@ static inline void tcg_out_op(TCGContext *s, int opc, const TCGArg *args,
case INDEX_op_st8_i32:
case INDEX_op_st8_i64:
/* movb */
tcg_out_modrm_offset(s, 0x88 | P_REXB, args[0], args[1], args[2]);
tcg_out_modrm_offset(s, 0x88 | P_REXB_R, args[0], args[1], args[2]);
break;
case INDEX_op_st16_i32:
case INDEX_op_st16_i64:
@ -1161,7 +1175,7 @@ static inline void tcg_out_op(TCGContext *s, int opc, const TCGArg *args,
break;
case INDEX_op_ext8s_i32:
tcg_out_modrm(s, 0xbe | P_EXT | P_REXB, args[0], args[1]);
tcg_out_modrm(s, 0xbe | P_EXT | P_REXB_RM, args[0], args[1]);
break;
case INDEX_op_ext16s_i32:
tcg_out_modrm(s, 0xbf | P_EXT, args[0], args[1]);
@ -1177,7 +1191,7 @@ static inline void tcg_out_op(TCGContext *s, int opc, const TCGArg *args,
break;
case INDEX_op_ext8u_i32:
case INDEX_op_ext8u_i64:
tcg_out_modrm(s, 0xb6 | P_EXT | P_REXB, args[0], args[1]);
tcg_out_modrm(s, 0xb6 | P_EXT | P_REXB_RM, args[0], args[1]);
break;
case INDEX_op_ext16u_i32:
case INDEX_op_ext16u_i64: