Re: [Qemu-devel] [PATCH 06/16] tcg: Add temp_global bit to TCGTemp

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

Richard Henderson <rth@twiddle.net> writes:

> This avoids needing to test the index of a temp against nb_globals.
>
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>  tcg/optimize.c | 15 ++++++++-------
>  tcg/tcg.c      | 11 ++++++++---
>  tcg/tcg.h      | 12 ++++++++----
>  3 files changed, 24 insertions(+), 14 deletions(-)
>
> diff --git a/tcg/optimize.c b/tcg/optimize.c
> index d8c3a7e..55f9e83 100644
> --- a/tcg/optimize.c
> +++ b/tcg/optimize.c
> @@ -116,25 +116,26 @@ static TCGOpcode op_to_movi(TCGOpcode op)
>      }
>  }
>
> -static TCGArg find_better_copy(TCGContext *s, TCGArg temp)
> +static TCGArg find_better_copy(TCGContext *s, TCGArg arg)
>  {
> +    TCGTemp *ts = arg_temp(arg);
>      TCGArg i;
>
>      /* If this is already a global, we can't do better. */
> -    if (temp < s->nb_globals) {
> -        return temp;
> +    if (ts->temp_global) {
> +        return arg;
>      }
>
>      /* Search for a global first. */
> -    for (i = temps[temp].next_copy ; i != temp ; i = temps[i].next_copy) {
> +    for (i = temps[arg].next_copy ; i != arg; i = temps[i].next_copy) {
>          if (i < s->nb_globals) {
>              return i;
>          }
>      }
>
>      /* If it is a temp, search for a temp local. */
> -    if (!arg_temp(temp)->temp_local) {
> -        for (i = temps[temp].next_copy ; i != temp ; i = temps[i].next_copy) {
> +    if (!ts->temp_local) {
> +        for (i = temps[arg].next_copy ; i != arg; i = temps[i].next_copy) {
>              if (s->temps[i].temp_local) {
>                  return i;
>              }
> @@ -142,7 +143,7 @@ static TCGArg find_better_copy(TCGContext *s, TCGArg temp)
>      }
>
>      /* Failure to find a better representation, return the same temp. */
> -    return temp;
> +    return arg;
>  }
>
>  static bool temps_are_copies(TCGArg arg1, TCGArg arg2)
> diff --git a/tcg/tcg.c b/tcg/tcg.c
> index 068ac51..0bb88b1 100644
> --- a/tcg/tcg.c
> +++ b/tcg/tcg.c
> @@ -489,9 +489,14 @@ static inline TCGTemp *tcg_temp_alloc(TCGContext *s)
>
>  static inline TCGTemp *tcg_global_alloc(TCGContext *s)
>  {
> +    TCGTemp *ts;
> +
>      tcg_debug_assert(s->nb_globals == s->nb_temps);
>      s->nb_globals++;
> -    return tcg_temp_alloc(s);
> +    ts = tcg_temp_alloc(s);
> +    ts->temp_global = 1;
> +
> +    return ts;
>  }
>
>  static int tcg_global_reg_new_internal(TCGContext *s, TCGType type,
> @@ -967,7 +972,7 @@ static char *tcg_get_arg_str_ptr(TCGContext *s, char *buf, int buf_size,
>  {
>      int idx = temp_idx(s, ts);
>
> -    if (idx < s->nb_globals) {
> +    if (ts->temp_global) {
>          pstrcpy(buf, buf_size, ts->name);
>      } else if (ts->temp_local) {
>          snprintf(buf, buf_size, "loc%d", idx - s->nb_globals);
> @@ -1905,7 +1910,7 @@ static void temp_free_or_dead(TCGContext *s, TCGTemp *ts, int free_or_dead)
>      }
>      ts->val_type = (free_or_dead < 0
>                      || ts->temp_local
> -                    || temp_idx(s, ts) < s->nb_globals
> +                    || ts->temp_global
>                      ? TEMP_VAL_MEM : TEMP_VAL_DEAD);
>  }
>
> diff --git a/tcg/tcg.h b/tcg/tcg.h
> index 70d9fda..3b35344 100644
> --- a/tcg/tcg.h
> +++ b/tcg/tcg.h
> @@ -586,10 +586,14 @@ typedef struct TCGTemp {
>      unsigned int indirect_base:1;
>      unsigned int mem_coherent:1;
>      unsigned int mem_allocated:1;
> -    unsigned int temp_local:1; /* If true, the temp is saved across
> -                                  basic blocks. Otherwise, it is not
> -                                  preserved across basic blocks. */
> -    unsigned int temp_allocated:1; /* never used for code gen */
> +    /* If true, the temp is saved across both basic blocks and
> +       translation blocks.  */
> +    unsigned int temp_global:1;
> +    /* If true, the temp is saved across basic blocks but dead
> +       at the end of translation blocks.  If false, the temp is
> +       dead at the end of basic blocks.  */
> +    unsigned int temp_local:1;
> +    unsigned int temp_allocated:1;

This is where my knowledge of the TCG internals gets slightly confused.
As far as I'm aware all our TranslationBlocks are Basic Blocks - they
don't have any branches until the end of the block. What is the
distinction here?

Is a temp_global truly global? I thought the guest state was fully
rectified by the time we leave the basic block.

>
>      tcg_target_long val;
>      struct TCGTemp *mem_base;


--
Alex Bennée