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>
---
tcg/i386/tcg-target.c.inc | 50 +++++++++++++++++++++++++++++++++++++++
1 file changed, 50 insertions(+)
diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
index 1542afd94d..4d7b745a52 100644
--- a/tcg/i386/tcg-target.c.inc
+++ b/tcg/i386/tcg-target.c.inc
@@ -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);
--
2.34.1