target-arm: A64: add support for conditional compare insns

this patch adds support for C3.5.4 - C3.5.5
Conditional compare (both immediate and register)

Signed-off-by: Claudio Fontana <claudio.fontana@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>

target-arm/translate-a64.c

@@ -2483,16 +2483,67 @@ static void disas_adc_sbc(DisasContext *s, uint32_t insn)
     }
 }
 
-/* Conditional compare (immediate) */
+/* C3.5.4 - C3.5.5 Conditional compare (immediate / register)
-static void disas_cc_imm(DisasContext *s, uint32_t insn)
+ *  31 30 29 28 27 26 25 24 23 22 21  20    16 15  12  11  10  9   5  4 3   0
+ * +--+--+--+------------------------+--------+------+----+--+------+--+-----+
+ * |sf|op| S| 1  1  0  1  0  0  1  0 |imm5/rm | cond |i/r |o2|  Rn  |o3|nzcv |
+ * +--+--+--+------------------------+--------+------+----+--+------+--+-----+
+ *        [1]                             y                [0]       [0]
+ */
+static void disas_cc(DisasContext *s, uint32_t insn)
 {
-    unsupported_encoding(s, insn);
+    unsigned int sf, op, y, cond, rn, nzcv, is_imm;
-}
+    int label_continue = -1;
+    TCGv_i64 tcg_tmp, tcg_y, tcg_rn;
 
-/* Conditional compare (register) */
+    if (!extract32(insn, 29, 1)) {
-static void disas_cc_reg(DisasContext *s, uint32_t insn)
+        unallocated_encoding(s);
-{
+        return;
-    unsupported_encoding(s, insn);
+    }
+    if (insn & (1 << 10 | 1 << 4)) {
+        unallocated_encoding(s);
+        return;
+    }
+    sf = extract32(insn, 31, 1);
+    op = extract32(insn, 30, 1);
+    is_imm = extract32(insn, 11, 1);
+    y = extract32(insn, 16, 5); /* y = rm (reg) or imm5 (imm) */
+    cond = extract32(insn, 12, 4);
+    rn = extract32(insn, 5, 5);
+    nzcv = extract32(insn, 0, 4);
+
+    if (cond < 0x0e) { /* not always */
+        int label_match = gen_new_label();
+        label_continue = gen_new_label();
+        arm_gen_test_cc(cond, label_match);
+        /* nomatch: */
+        tcg_tmp = tcg_temp_new_i64();
+        tcg_gen_movi_i64(tcg_tmp, nzcv << 28);
+        gen_set_nzcv(tcg_tmp);
+        tcg_temp_free_i64(tcg_tmp);
+        tcg_gen_br(label_continue);
+        gen_set_label(label_match);
+    }
+    /* match, or condition is always */
+    if (is_imm) {
+        tcg_y = new_tmp_a64(s);
+        tcg_gen_movi_i64(tcg_y, y);
+    } else {
+        tcg_y = cpu_reg(s, y);
+    }
+    tcg_rn = cpu_reg(s, rn);
+
+    tcg_tmp = tcg_temp_new_i64();
+    if (op) {
+        gen_sub_CC(sf, tcg_tmp, tcg_rn, tcg_y);
+    } else {
+        gen_add_CC(sf, tcg_tmp, tcg_rn, tcg_y);
+    }
+    tcg_temp_free_i64(tcg_tmp);
+
+    if (cond < 0x0e) { /* continue */
+        gen_set_label(label_continue);
+    }
 }
 
 /* C3.5.6 Conditional select
@@ -2846,11 +2897,7 @@ static void disas_data_proc_reg(DisasContext *s, uint32_t insn)
             disas_adc_sbc(s, insn);
             break;
         case 0x2: /* Conditional compare */
-            if (insn & (1 << 11)) { /* (immediate) */
+            disas_cc(s, insn); /* both imm and reg forms */
-                disas_cc_imm(s, insn);
-            } else {            /* (register) */
-                disas_cc_reg(s, insn);
-            }
             break;
         case 0x4: /* Conditional select */
             disas_cond_select(s, insn);