Re: [PATCH 14/18] target/i386: move 60-BF opcodes to new decoder

[Richard Henderson]

On 10/14/23 03:01, Paolo Bonzini wrote:

@@ -179,6 +180,9 @@
 #define p_66_f3_f2    .valid_prefix = P_66 | P_F3 | P_F2,
 #define p_00_66_f3_f2 .valid_prefix = P_00 | P_66 | P_F3 | P_F2,

+static X86OpEntry illegal_opcode =

+    X86_OP_ENTRY0(illegal);

const.

+static void gen_ARPL(DisasContext *s, CPUX86State *env, X86DecodedInsn *decode)
+{
+    TCGLabel *label1 = gen_new_label();
+    TCGv rpl_adj = tcg_temp_new();
+
+    gen_mov_eflags(s, s->tmp4);
+    tcg_gen_andi_tl(s->tmp4, s->tmp4, ~CC_Z);
+
+    /* Compute dest[rpl] - src[rpl], adjust if result <0.  */
+    tcg_gen_andi_tl(rpl_adj, s->T0, 3);
+    tcg_gen_andi_tl(s->T1, s->T1, 3);
+    tcg_gen_sub_tl(rpl_adj, rpl_adj, s->T1);
+
+    tcg_gen_brcondi_tl(TCG_COND_LT, rpl_adj, 0, label1);
+
+    /* Subtract dest[rpl] - src[rpl] to set dest[rpl] = src[rpl].  */
+    tcg_gen_sub_tl(s->T0, s->T0, rpl_adj);
+    tcg_gen_ori_tl(s->tmp4, s->tmp4, CC_Z);
+    gen_set_label(label1);
+
+    decode->cc_src = s->tmp4;
+    set_cc_op(s, CC_OP_EFLAGS);
+}

If you're going to adjust the algorithm here,
you might as well make it branchless:

    tcg_gen_negsetcond_tl(TCG_COND_GE, mask, rpl_adj, tcg_constant_tl(0));
    tcg_gen_and_tl(rpl_adj, rpl_adj, mask);
    tcg_gen_sub_tl(t0, t0, rpl_adj);
    tcg_gen_andi_tl(mask, mask, CC_Z);
    tcg_gen_or_tl(tmp4, tmp4, mask);

+static void gen_CBW(DisasContext *s, CPUX86State *env, X86DecodedInsn *decode)
+{
+    switch(decode->op[0].ot) {
+#ifdef TARGET_X86_64
+        case MO_64:
+            tcg_gen_ext32s_tl(s->T0, s->T0);
+            break;
+#endif
+        case MO_32:
+            tcg_gen_ext16s_tl(s->T0, s->T0);
+            break;
+        case MO_16:
+            tcg_gen_ext8s_tl(s->T0, s->T0);
+            break;
+        default:
+            abort();
+    }
+}

Reuse gen_ext_tl(t0, t0, (ot - 1) | MO_SIGN)?

+static void gen_CWD(DisasContext *s, CPUX86State *env, X86DecodedInsn *decode)
+{
+    int shift = 8 << decode->op[0].ot;
+    switch (shift) {
+    case 64:
+        break;
+    case 32:
+        tcg_gen_ext32s_tl(s->T0, s->T0);
+        break;
+    case 16:
+        tcg_gen_ext16s_tl(s->T0, s->T0);
+        break;
+    default:
+        abort();
+    }
+    tcg_gen_sari_tl(s->T0, s->T0, shift - 1);

Better as

  tcg_gen_sextract_tl(t0, t0, shift - 1, 1)

to just extract and replicate the one bit you wanted.


r~