target/mips: Check nanoMIPS DSP MULT[U] accumulator with Release 6

Per the "MIPS Architecture Extension: nanoMIPS32 DSP TRM" rev 0.04,
MULT and MULTU opcodes:

  The value of ac selects an accumulator numbered from 0 to 3.
  When ac=0, this refers to the original HI/LO register pair of the
  MIPS32 architecture.

  In Release 6 of the MIPS Architecture, accumulators are eliminated
  from MIPS32.

Ensure pre-Release 6 is restricted to HI/LO registers pair.

Fixes: 8b3698b ("target/mips: Add emulation of DSP ASE for nanoMIPS - part 4")
Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>

Author: philmd

target/mips/tcg/nanomips_translate.c.inc

@@ -1868,6 +1868,9 @@ static void gen_pool32axf_2_nanomips_insn(DisasContext *ctx, uint32_t opc,
                 TCGv_i32 t2 = tcg_temp_new_i32();
                 TCGv_i32 t3 = tcg_temp_new_i32();
 
+                if (acc || ctx->insn_flags & ISA_MIPS_R6) {
+                    check_dsp_r2(ctx);
+                }
                 gen_load_gpr(t0, rs);
                 gen_load_gpr(t1, rt);
                 tcg_gen_trunc_tl_i32(t2, t0);
@@ -1925,6 +1928,9 @@ static void gen_pool32axf_2_nanomips_insn(DisasContext *ctx, uint32_t opc,
                 TCGv_i32 t2 = tcg_temp_new_i32();
                 TCGv_i32 t3 = tcg_temp_new_i32();
 
+                if (acc || ctx->insn_flags & ISA_MIPS_R6) {
+                    check_dsp_r2(ctx);
+                }
                 gen_load_gpr(t0, rs);
                 gen_load_gpr(t1, rt);
                 tcg_gen_trunc_tl_i32(t2, t0);