Re: [Qemu-devel] [PATCH 10/16] tcg: Avoid loops against variable bounds

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <rth@twiddle.net> writes:

> Copy s->nb_globals or s->nb_temps to a local variable for the purposes
> of iteration.  This should allow the compiler to use low-overhead
> looping constructs on some hosts.
>
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>  tcg/tcg.c | 27 ++++++++++-----------------
>  1 file changed, 10 insertions(+), 17 deletions(-)
>
> diff --git a/tcg/tcg.c b/tcg/tcg.c
> index e78140b..c228f1e 100644
> --- a/tcg/tcg.c
> +++ b/tcg/tcg.c
> @@ -943,23 +943,16 @@ void tcg_gen_callN(TCGContext *s, void *func, TCGArg ret,
>
>  static void tcg_reg_alloc_start(TCGContext *s)
>  {
> -    int i;
> +    int i, n;
>      TCGTemp *ts;
> -    for(i = 0; i < s->nb_globals; i++) {
> +
> +    for (i = 0, n = s->nb_globals; i < n; i++) {
>          ts = &s->temps[i];
> -        if (ts->fixed_reg) {
> -            ts->val_type = TEMP_VAL_REG;
> -        } else {
> -            ts->val_type = TEMP_VAL_MEM;
> -        }
> +        ts->val_type = (ts->fixed_reg ? TEMP_VAL_REG : TEMP_VAL_MEM);
>      }
> -    for(i = s->nb_globals; i < s->nb_temps; i++) {
> +    for (n = s->nb_temps; i < n; i++) {

A one line comment like /* i continues on from s->nb_globals above */
might prevent a momentary confusion when reading through.

>          ts = &s->temps[i];
> -        if (ts->temp_local) {
> -            ts->val_type = TEMP_VAL_MEM;
> -        } else {
> -            ts->val_type = TEMP_VAL_DEAD;
> -        }
> +        ts->val_type = (ts->temp_local ? TEMP_VAL_MEM : TEMP_VAL_DEAD);
>          ts->mem_allocated = 0;
>          ts->fixed_reg = 0;
>      }
> @@ -2050,9 +2043,9 @@ static void temp_save(TCGContext *s, TCGTemp *ts, TCGRegSet allocated_regs)
>     temporary registers needs to be allocated to store a constant. */
>  static void save_globals(TCGContext *s, TCGRegSet allocated_regs)
>  {
> -    int i;
> +    int i, n;
>
> -    for (i = 0; i < s->nb_globals; i++) {
> +    for (i = 0, n = s->nb_globals; i < n; i++) {
>          temp_save(s, &s->temps[i], allocated_regs);
>      }
>  }
> @@ -2062,9 +2055,9 @@ static void save_globals(TCGContext *s, TCGRegSet allocated_regs)
>     temporary registers needs to be allocated to store a constant. */
>  static void sync_globals(TCGContext *s, TCGRegSet allocated_regs)
>  {
> -    int i;
> +    int i, n;
>
> -    for (i = 0; i < s->nb_globals; i++) {
> +    for (i = 0, n = s->nb_globals; i < n; i++) {
>          TCGTemp *ts = &s->temps[i];
>          tcg_debug_assert(ts->val_type != TEMP_VAL_REG
>                           || ts->fixed_reg

Otherwise:

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

--
Alex Bennée