Re: [Qemu-devel] [PATCH] tcg: Use bitmaps for free temporaries

[Richard Henderson]

Ping?

r~

On 09/20/2013 05:58 AM, Richard Henderson wrote:
> We previously allocated 32-bits per temp for the next_free_temp entry.
> We now allocate 4 bits per temp across the 4 bitmaps.
> 
> Using a linked list meant that if a translator is tweeked, resulting in
> temps being freed in a different order, that would have follow-on effects
> throughout the TB.  Always allocating the lowest free temp means that
> follow-on effects are minimized, which can make it easier to diff output
> when debugging the translators.
> 
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  tcg/tcg.c | 32 +++++++++++++++-----------------
>  tcg/tcg.h | 11 ++++++-----
>  2 files changed, 21 insertions(+), 22 deletions(-)
> 
> diff --git a/tcg/tcg.c b/tcg/tcg.c
> index fd7fb6b..41ed8b0 100644
> --- a/tcg/tcg.c
> +++ b/tcg/tcg.c
> @@ -316,11 +316,12 @@ void tcg_set_frame(TCGContext *s, int reg, intptr_t 
> start, intptr_t size)
>  
>  void tcg_func_start(TCGContext *s)
>  {
> -    int i;
>      tcg_pool_reset(s);
>      s->nb_temps = s->nb_globals;
> -    for(i = 0; i < (TCG_TYPE_COUNT * 2); i++)
> -        s->first_free_temp[i] = -1;
> +
> +    /* No temps have been previously allocated for size or locality.  */
> +    memset(s->free_temps, 0, sizeof(s->free_temps));
> +
>      s->labels = tcg_malloc(sizeof(TCGLabel) * TCG_MAX_LABELS);
>      s->nb_labels = 0;
>      s->current_frame_offset = s->frame_start;
> @@ -468,16 +469,15 @@ static inline int tcg_temp_new_internal(TCGType type, 
> int temp_local)
>      TCGTemp *ts;
>      int idx, k;
>  
> -    k = type;
> -    if (temp_local)
> -        k += TCG_TYPE_COUNT;
> -    idx = s->first_free_temp[k];
> -    if (idx != -1) {
> -        /* There is already an available temp with the
> -           right type */
> +    k = type + (temp_local ? TCG_TYPE_COUNT : 0);
> +    idx = find_first_bit(s->free_temps[k].l, TCG_MAX_TEMPS);
> +    if (idx < TCG_MAX_TEMPS) {
> +        /* There is already an available temp with the right type.  */
> +        clear_bit(idx, s->free_temps[k].l);
> +
>          ts = &s->temps[idx];
> -        s->first_free_temp[k] = ts->next_free_temp;
>          ts->temp_allocated = 1;
> +        assert(ts->base_type == type);
>          assert(ts->temp_local == temp_local);
>      } else {
>          idx = s->nb_temps;
> @@ -533,7 +533,7 @@ TCGv_i64 tcg_temp_new_internal_i64(int temp_local)
>      return MAKE_TCGV_I64(idx);
>  }
>  
> -static inline void tcg_temp_free_internal(int idx)
> +static void tcg_temp_free_internal(int idx)
>  {
>      TCGContext *s = &tcg_ctx;
>      TCGTemp *ts;
> @@ -550,11 +550,9 @@ static inline void tcg_temp_free_internal(int idx)
>      ts = &s->temps[idx];
>      assert(ts->temp_allocated != 0);
>      ts->temp_allocated = 0;
> -    k = ts->base_type;
> -    if (ts->temp_local)
> -        k += TCG_TYPE_COUNT;
> -    ts->next_free_temp = s->first_free_temp[k];
> -    s->first_free_temp[k] = idx;
> +
> +    k = ts->type + (ts->temp_local ? TCG_TYPE_COUNT : 0);
> +    set_bit(idx, s->free_temps[k].l);
>  }
>  
>  void tcg_temp_free_i32(TCGv_i32 arg)
> diff --git a/tcg/tcg.h b/tcg/tcg.h
> index 902c751..c45e41b 100644
> --- a/tcg/tcg.h
> +++ b/tcg/tcg.h
> @@ -26,7 +26,7 @@
>  #define TCG_H
>  
>  #include "qemu-common.h"
> -
> +#include "qemu/bitops.h"
>  #include "tcg-target.h"
>  
>  /* Default target word size to pointer size.  */
> @@ -400,8 +400,6 @@ typedef struct TCGTemp {
>                                    basic blocks. Otherwise, it is not
>                                    preserved across basic blocks. */
>      unsigned int temp_allocated:1; /* never used for code gen */
> -    /* index of next free temp of same base type, -1 if end */
> -    int next_free_temp;
>      const char *name;
>  } TCGTemp;
>  
> @@ -412,6 +410,10 @@ typedef struct TCGHelperInfo {
>  
>  typedef struct TCGContext TCGContext;
>  
> +typedef struct TCGTempSet {
> +    unsigned long l[BITS_TO_LONGS(TCG_MAX_TEMPS)];
> +} TCGTempSet;
> +
>  struct TCGContext {
>      uint8_t *pool_cur, *pool_end;
>      TCGPool *pool_first, *pool_current, *pool_first_large;
> @@ -419,8 +421,6 @@ struct TCGContext {
>      int nb_labels;
>      int nb_globals;
>      int nb_temps;
> -    /* index of free temps, -1 if none */
> -    int first_free_temp[TCG_TYPE_COUNT * 2]; 
>  
>      /* goto_tb support */
>      uint8_t *code_buf;
> @@ -446,6 +446,7 @@ struct TCGContext {
>  
>      uint8_t *code_ptr;
>      TCGTemp temps[TCG_MAX_TEMPS]; /* globals first, temps after */
> +    TCGTempSet free_temps[TCG_TYPE_COUNT * 2];
>  
>      TCGHelperInfo *helpers;
>      int nb_helpers;
>