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Re: [Qemu-devel] [PATCH 1/2] tcg-x86_64: Special-case all 32-bit AND ope
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] tcg-x86_64: Special-case all 32-bit AND operands. |
Date: |
Thu, 14 Jan 2010 16:57:27 +0100 |
User-agent: |
Mutt/1.5.20 (2009-06-14) |
On Tue, Jan 05, 2010 at 04:03:00PM -0800, Richard Henderson wrote:
> This avoids an unnecessary REX.W prefix when dealing with AND
> operands that fit into a 32-bit quantity. The most common change
> actually seen is movz[wb]q -> movz[wb]l.
>
> Similarly, avoid REXW in ext{8,16}u_i64 tcg opcodes.
>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
> tcg/x86_64/tcg-target.c | 26 ++++++++------------------
> 1 files changed, 8 insertions(+), 18 deletions(-)
>
> diff --git a/tcg/x86_64/tcg-target.c b/tcg/x86_64/tcg-target.c
> index 2339091..f584c94 100644
> --- a/tcg/x86_64/tcg-target.c
> +++ b/tcg/x86_64/tcg-target.c
> @@ -426,24 +426,18 @@ static inline void tgen_arithi64(TCGContext *s, int c,
> int r0, int64_t val)
> } else if ((c == ARITH_ADD && val == -1) || (c == ARITH_SUB && val ==
> 1)) {
> /* dec */
> tcg_out_modrm(s, 0xff | P_REXW, 1, r0);
> - } else if (val == (int8_t)val) {
> - tcg_out_modrm(s, 0x83 | P_REXW, c, r0);
> - tcg_out8(s, val);
> - } else if (c == ARITH_AND && val == 0xffu) {
> - /* movzbl */
> - tcg_out_modrm(s, 0xb6 | P_EXT | P_REXW, r0, r0);
> - } else if (c == ARITH_AND && val == 0xffffu) {
> - /* movzwl */
> - tcg_out_modrm(s, 0xb7 | P_EXT | P_REXW, r0, r0);
> } else if (c == ARITH_AND && val == 0xffffffffu) {
> /* 32-bit mov zero extends */
> tcg_out_modrm(s, 0x8b, r0, r0);
> + } else if (c == ARITH_AND && (uint64_t)val <= 0xffffffffu) {
> + /* AND with no high bits set can use a 32-bit operation. */
> + tgen_arithi32(s, c, r0, val);
Do we really want to call tgen_arithi32() here, that will redo part of
the above tests again? It might be better to simply remove the REX.W
prefix above instead.
> + } else if (val == (int8_t)val) {
> + tcg_out_modrm(s, 0x83 | P_REXW, c, r0);
> + tcg_out8(s, val);
> } else if (val == (int32_t)val) {
> tcg_out_modrm(s, 0x81 | P_REXW, c, r0);
> tcg_out32(s, val);
> - } else if (c == ARITH_AND && val == (uint32_t)val) {
> - tcg_out_modrm(s, 0x81, c, r0);
> - tcg_out32(s, val);
> } else {
> tcg_abort();
> }
> @@ -1182,16 +1176,12 @@ static inline void tcg_out_op(TCGContext *s, int opc,
> const TCGArg *args,
> tcg_out_modrm(s, 0x63 | P_REXW, args[0], args[1]);
> break;
> case INDEX_op_ext8u_i32:
> + case INDEX_op_ext8u_i64:
> tcg_out_modrm(s, 0xb6 | P_EXT | P_REXB, args[0], args[1]);
> break;
> case INDEX_op_ext16u_i32:
> - tcg_out_modrm(s, 0xb7 | P_EXT, args[0], args[1]);
> - break;
> - case INDEX_op_ext8u_i64:
> - tcg_out_modrm(s, 0xb6 | P_EXT | P_REXW, args[0], args[1]);
> - break;
> case INDEX_op_ext16u_i64:
> - tcg_out_modrm(s, 0xb7 | P_EXT | P_REXW, args[0], args[1]);
> + tcg_out_modrm(s, 0xb7 | P_EXT, args[0], args[1]);
> break;
> case INDEX_op_ext32u_i64:
> tcg_out_modrm(s, 0x8b, args[0], args[1]);
This part looks fine.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
address@hidden http://www.aurel32.net