On Tue, 22 Aug 2023 at 10:51, Philippe Mathieu-Daudé <phi...@linaro.org> wrote:
>
> When clearing a bitfield we don't need to lead the
"load" ?
> source register. Use deposit_z_i32() with the BFC
> opcode to save a load_reg() call.
>
> Signed-off-by: Philippe Mathieu-Daudé <phi...@linaro.org>
> ---
> target/arm/tcg/translate.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/target/arm/tcg/translate.c b/target/arm/tcg/translate.c
> index b71ac2d0d5..1a6938d1b3 100644
> --- a/target/arm/tcg/translate.c
> +++ b/target/arm/tcg/translate.c
> @@ -7255,7 +7255,7 @@ static bool trans_UBFX(DisasContext *s, arg_UBFX *a)
> static bool trans_BFCI(DisasContext *s, arg_BFCI *a)
> {
> int msb = a->msb, lsb = a->lsb;
> - TCGv_i32 t_in, t_rd;
> + TCGv_i32 t_rd;
> int width;
>
> if (!ENABLE_ARCH_6T2) {
> @@ -7268,15 +7268,14 @@ static bool trans_BFCI(DisasContext *s, arg_BFCI *a)
> }
>
> width = msb + 1 - lsb;
> + t_rd = load_reg(s, a->rd);
> if (a->rn == 15) {
> /* BFC */
> - t_in = tcg_constant_i32(0);
> + tcg_gen_deposit_z_i32(t_rd, t_rd, lsb, width);
> } else {
> /* BFI */
> - t_in = load_reg(s, a->rn);
> + tcg_gen_deposit_i32(t_rd, t_rd, load_reg(s, a->rn), lsb, width);
> }
> - t_rd = load_reg(s, a->rd);
> - tcg_gen_deposit_i32(t_rd, t_rd, t_in, lsb, width);
> store_reg(s, a->rd, t_rd);
> return true;
The comment says we are saving a load_reg() call, but the
code change doesn't seem to do that. Before the change:
* for BFC we call load_reg for rd
* for BFI we call load_reg for rn and rd
After the change:
* for BFC we call load_reg for rd
* for BFI we call load_reg for rn and rd
So we're not saving any load_reg() calls as far as I can see ?
-- PMM
