target/arm: Fix nregs computation in do_{ld,st}_zpa

The field is encoded as [0-3], which is convenient for
indexing our array of function pointers, but the true
value is [1-4].  Adjust before calling do_mem_zpa.

Add an assert, and move the comment re passing ZT to
the helper back next to the relevant code.

Cc: qemu-stable@nongnu.org
Fixes: 206adac ("target/arm: Add mte helpers for sve scalar + int loads")
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Gustavo Romero <gustavo.romero@linaro.org>
Message-id: 20240207025210.8837-3-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/tcg/translate-sve.c

@@ -4445,11 +4445,7 @@ static void do_mem_zpa(DisasContext *s, int zt, int pg, TCGv_i64 addr,
     TCGv_ptr t_pg;
     int desc = 0;
 
-    /*
-     * For e.g. LD4, there are not enough arguments to pass all 4
-     * registers as pointers, so encode the regno into the data field.
-     * For consistency, do this even for LD1.
-     */
+    assert(mte_n >= 1 && mte_n <= 4);
     if (s->mte_active[0]) {
         int msz = dtype_msz(dtype);
 
@@ -4463,6 +4459,11 @@ static void do_mem_zpa(DisasContext *s, int zt, int pg, TCGv_i64 addr,
         addr = clean_data_tbi(s, addr);
     }
 
+    /*
+     * For e.g. LD4, there are not enough arguments to pass all 4
+     * registers as pointers, so encode the regno into the data field.
+     * For consistency, do this even for LD1.
+     */
     desc = simd_desc(vsz, vsz, zt | desc);
     t_pg = tcg_temp_new_ptr();
 
@@ -4600,7 +4601,7 @@ static void do_ld_zpa(DisasContext *s, int zt, int pg,
      * accessible via the instruction encoding.
      */
     assert(fn != NULL);
-    do_mem_zpa(s, zt, pg, addr, dtype, nreg, false, fn);
+    do_mem_zpa(s, zt, pg, addr, dtype, nreg + 1, false, fn);
 }
 
 static bool trans_LD_zprr(DisasContext *s, arg_rprr_load *a)
@@ -5168,14 +5169,13 @@ static void do_st_zpa(DisasContext *s, int zt, int pg, TCGv_i64 addr,
     if (nreg == 0) {
         /* ST1 */
         fn = fn_single[s->mte_active[0]][be][msz][esz];
-        nreg = 1;
     } else {
         /* ST2, ST3, ST4 -- msz == esz, enforced by encoding */
         assert(msz == esz);
         fn = fn_multiple[s->mte_active[0]][be][nreg - 1][msz];
     }
     assert(fn != NULL);
-    do_mem_zpa(s, zt, pg, addr, msz_dtype(s, msz), nreg, true, fn);
+    do_mem_zpa(s, zt, pg, addr, msz_dtype(s, msz), nreg + 1, true, fn);
 }
 
 static bool trans_ST_zprr(DisasContext *s, arg_rprr_store *a)