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tcg: Optimize half-dead add2/sub2

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When x86_64 guest is not in 64-bit mode, the high-part of the 64-bit
add is dead.  When the host is 32-bit, we can simplify to 32-bit
arithmetic.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This commit is contained in:
Richard Henderson 2012-10-02 11:32:29 -07:00 committed by Aurelien Jarno
parent 212c328d61
commit 1305c451e6
1 changed files with 33 additions and 1 deletions
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34
tcg/tcg.c
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@ -1307,8 +1307,39 @@ static void tcg_liveness_analysis(TCGContext *s)
break;
case INDEX_op_end:
break;
/* XXX: optimize by hardcoding common cases (e.g. triadic ops) */
case INDEX_op_add2_i32:
case INDEX_op_sub2_i32:
args -= 6;
nb_iargs = 4;
nb_oargs = 2;
/* Test if the high part of the operation is dead, but not
the low part. The result can be optimized to a simple
add or sub. This happens often for x86_64 guest when the
cpu mode is set to 32 bit. */
if (dead_temps[args[1]]) {
if (dead_temps[args[0]]) {
goto do_remove;
}
/* Create the single operation plus nop. */
if (op == INDEX_op_add2_i32) {
op = INDEX_op_add_i32;
} else {
op = INDEX_op_sub_i32;
}
gen_opc_buf[op_index] = op;
args[1] = args[2];
args[2] = args[4];
assert(gen_opc_buf[op_index + 1] == INDEX_op_nop);
tcg_set_nop(s, gen_opc_buf + op_index + 1, args + 3, 3);
/* Fall through and mark the single-word operation live. */
nb_iargs = 2;
nb_oargs = 1;
}
goto do_not_remove;
default:
/* XXX: optimize by hardcoding common cases (e.g. triadic ops) */
args -= def->nb_args;
nb_iargs = def->nb_iargs;
nb_oargs = def->nb_oargs;
@ -1322,6 +1353,7 @@ static void tcg_liveness_analysis(TCGContext *s)
if (!dead_temps[arg])
goto do_not_remove;
}
do_remove:
tcg_set_nop(s, gen_opc_buf + op_index, args, def->nb_args);
#ifdef CONFIG_PROFILER
s->del_op_count++;