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

[Richard Henderson <rth@twiddle.net>]

Ping.

r~

On 11/19/2013 07:57 PM, Richard Henderson wrote:
> 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 <rth@twiddle.net>
>> ---
>>  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;
>>
>