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tcg/i386: Use CMP+SBB in tcg_out_setcond

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Use the carry bit to optimize some forms of setcond.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2023-08-05 15:43:23 -07:00
parent 78ddf0dc75
commit 6950f68b62
1 changed files with 50 additions and 0 deletions
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50
tcg/i386/tcg-target.c.inc
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@ -1531,6 +1531,56 @@ static void tcg_out_setcond(TCGContext *s, int rexw, TCGCond cond,
TCGArg dest, TCGArg arg1, TCGArg arg2,
int const_arg2)
{
bool inv = false;
switch (cond) {
case TCG_COND_NE:
inv = true;
/* fall through */
case TCG_COND_EQ:
/* If arg2 is 0, convert to LTU/GEU vs 1. */
if (const_arg2 && arg2 == 0) {
arg2 = 1;
goto do_ltu;
}
break;
case TCG_COND_LEU:
inv = true;
/* fall through */
case TCG_COND_GTU:
/* If arg2 is a register, swap for LTU/GEU. */
if (!const_arg2) {
TCGReg t = arg1;
arg1 = arg2;
arg2 = t;
goto do_ltu;
}
break;
case TCG_COND_GEU:
inv = true;
/* fall through */
case TCG_COND_LTU:
do_ltu:
/*
* Relying on the carry bit, use SBB to produce -1 if LTU, 0 if GEU.
* We can then use NEG or INC to produce the desired result.
* This is always smaller than the SETCC expansion.
*/
tcg_out_cmp(s, arg1, arg2, const_arg2, rexw);
tgen_arithr(s, ARITH_SBB, dest, dest); /* T:-1 F:0 */
if (inv) {
tgen_arithi(s, ARITH_ADD, dest, 1, 0); /* T:0 F:1 */
} else {
tcg_out_modrm(s, OPC_GRP3_Ev, EXT3_NEG, dest); /* T:1 F:0 */
}
return;
default:
break;
}
tcg_out_cmp(s, arg1, arg2, const_arg2, rexw);
tcg_out_modrm(s, OPC_SETCC | tcg_cond_to_jcc[cond], 0, dest);
tcg_out_ext8u(s, dest, dest);