riscv: Add helper to make NaN-boxing for FP register

The function that makes NaN-boxing when a 32-bit value is assigned
to a 64-bit FP register is split out to a helper gen_nanbox_fpr().
Then it is applied in translating of the FLW instruction.

Signed-off-by: Ian Jiang <ianjiang.ict@gmail.com>
Message-Id: <20200128003707.17028-1-ianjiang.ict@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/insn_trans/trans_rvf.inc.c

@@ -23,6 +23,20 @@
         return false;                       \
 } while (0)
 
+/*
+ * RISC-V requires NaN-boxing of narrower width floating
+ * point values.  This applies when a 32-bit value is
+ * assigned to a 64-bit FP register.  Thus this does not
+ * apply when the RVD extension is not present.
+ */
+static void gen_nanbox_fpr(DisasContext *ctx, int regno)
+{
+    if (has_ext(ctx, RVD)) {
+        tcg_gen_ori_i64(cpu_fpr[regno], cpu_fpr[regno],
+                        MAKE_64BIT_MASK(32, 32));
+    }
+}
+
 static bool trans_flw(DisasContext *ctx, arg_flw *a)
 {
     TCGv t0 = tcg_temp_new();
@@ -32,8 +46,7 @@ static bool trans_flw(DisasContext *ctx, arg_flw *a)
     tcg_gen_addi_tl(t0, t0, a->imm);
 
     tcg_gen_qemu_ld_i64(cpu_fpr[a->rd], t0, ctx->mem_idx, MO_TEUL);
-    /* RISC-V requires NaN-boxing of narrower width floating point values */
-    tcg_gen_ori_i64(cpu_fpr[a->rd], cpu_fpr[a->rd], 0xffffffff00000000ULL);
+    gen_nanbox_fpr(ctx, a->rd);
 
     tcg_temp_free(t0);
     mark_fs_dirty(ctx);