target-arm: A64: Add support for floating point conditional compare

This adds decoding support for C3.6.23 FP Conditional Compare.
Signed-off-by: NClaudio Fontana <claudio.fontana@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <rth@twiddle.net>

target-arm/translate-a64.c

@@ -3268,7 +3268,40 @@ static void disas_fp_compare(DisasContext *s, uint32_t insn)
  */
 static void disas_fp_ccomp(DisasContext *s, uint32_t insn)
 {
-    unsupported_encoding(s, insn);
+    unsigned int mos, type, rm, cond, rn, op, nzcv;
+    TCGv_i64 tcg_flags;
+    int label_continue = -1;
+
+    mos = extract32(insn, 29, 3);
+    type = extract32(insn, 22, 2); /* 0 = single, 1 = double */
+    rm = extract32(insn, 16, 5);
+    cond = extract32(insn, 12, 4);
+    rn = extract32(insn, 5, 5);
+    op = extract32(insn, 4, 1);
+    nzcv = extract32(insn, 0, 4);
+
+    if (mos || type > 1) {
+        unallocated_encoding(s);
+        return;
+    }
+
+    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_flags = tcg_const_i64(nzcv << 28);
+        gen_set_nzcv(tcg_flags);
+        tcg_temp_free_i64(tcg_flags);
+        tcg_gen_br(label_continue);
+        gen_set_label(label_match);
+    }
+
+    handle_fp_compare(s, type, rn, rm, false, op);
+
+    if (cond < 0x0e) {
+        gen_set_label(label_continue);
+    }
 }
 
 /* C3.6.24 Floating point conditional select