Re: [Qemu-devel] [PATCH v2 05/29] tcg: Assert fixed_reg is read-only

[Alex Bennée]

Richard Henderson <address@hidden> writes:

> The only fixed_reg is cpu_env, and it should not be modified
> during any TB.  Therefore code that tries to special-case moves
> into a fixed_reg is dead.  Remove it.
>
> Reviewed-by: David Hildenbrand <address@hidden>
> Signed-off-by: Richard Henderson <address@hidden>

Reviewed-by: Alex Bennée <address@hidden>

> ---
>  tcg/tcg.c | 87 +++++++++++++++++++++++++------------------------------
>  1 file changed, 40 insertions(+), 47 deletions(-)
>
> diff --git a/tcg/tcg.c b/tcg/tcg.c
> index f7bef51de8..70ca113c26 100644
> --- a/tcg/tcg.c
> +++ b/tcg/tcg.c
> @@ -3274,11 +3274,8 @@ static void tcg_reg_alloc_do_movi(TCGContext *s, 
> TCGTemp *ots,
>                                    tcg_target_ulong val, TCGLifeData arg_life,
>                                    TCGRegSet preferred_regs)
>  {
> -    if (ots->fixed_reg) {
> -        /* For fixed registers, we do not do any constant propagation.  */
> -        tcg_out_movi(s, ots->type, ots->reg, val);
> -        return;
> -    }
> +    /* ENV should not be modified.  */
> +    tcg_debug_assert(!ots->fixed_reg);
>
>      /* The movi is not explicitly generated here.  */
>      if (ots->val_type == TEMP_VAL_REG) {
> @@ -3314,6 +3311,9 @@ static void tcg_reg_alloc_mov(TCGContext *s, const 
> TCGOp *op)
>      ots = arg_temp(op->args[0]);
>      ts = arg_temp(op->args[1]);
>
> +    /* ENV should not be modified.  */
> +    tcg_debug_assert(!ots->fixed_reg);
> +
>      /* Note that otype != itype for no-op truncation.  */
>      otype = ots->type;
>      itype = ts->type;
> @@ -3338,7 +3338,7 @@ static void tcg_reg_alloc_mov(TCGContext *s, const 
> TCGOp *op)
>      }
>
>      tcg_debug_assert(ts->val_type == TEMP_VAL_REG);
> -    if (IS_DEAD_ARG(0) && !ots->fixed_reg) {
> +    if (IS_DEAD_ARG(0)) {
>          /* mov to a non-saved dead register makes no sense (even with
>             liveness analysis disabled). */
>          tcg_debug_assert(NEED_SYNC_ARG(0));
> @@ -3351,7 +3351,7 @@ static void tcg_reg_alloc_mov(TCGContext *s, const 
> TCGOp *op)
>          }
>          temp_dead(s, ots);
>      } else {
> -        if (IS_DEAD_ARG(1) && !ts->fixed_reg && !ots->fixed_reg) {
> +        if (IS_DEAD_ARG(1) && !ts->fixed_reg) {
>              /* the mov can be suppressed */
>              if (ots->val_type == TEMP_VAL_REG) {
>                  s->reg_to_temp[ots->reg] = NULL;
> @@ -3504,6 +3504,10 @@ static void tcg_reg_alloc_op(TCGContext *s, const 
> TCGOp *op)
>              arg = op->args[i];
>              arg_ct = &def->args_ct[i];
>              ts = arg_temp(arg);
> +
> +            /* ENV should not be modified.  */
> +            tcg_debug_assert(!ts->fixed_reg);
> +
>              if ((arg_ct->ct & TCG_CT_ALIAS)
>                  && !const_args[arg_ct->alias_index]) {
>                  reg = new_args[arg_ct->alias_index];
> @@ -3512,29 +3516,21 @@ static void tcg_reg_alloc_op(TCGContext *s, const 
> TCGOp *op)
>                                      i_allocated_regs | o_allocated_regs,
>                                      op->output_pref[k], ts->indirect_base);
>              } else {
> -                /* if fixed register, we try to use it */
> -                reg = ts->reg;
> -                if (ts->fixed_reg &&
> -                    tcg_regset_test_reg(arg_ct->u.regs, reg)) {
> -                    goto oarg_end;
> -                }
>                  reg = tcg_reg_alloc(s, arg_ct->u.regs, o_allocated_regs,
>                                      op->output_pref[k], ts->indirect_base);
>              }
>              tcg_regset_set_reg(o_allocated_regs, reg);
> -            /* if a fixed register is used, then a move will be done 
> afterwards */
> -            if (!ts->fixed_reg) {
> -                if (ts->val_type == TEMP_VAL_REG) {
> -                    s->reg_to_temp[ts->reg] = NULL;
> -                }
> -                ts->val_type = TEMP_VAL_REG;
> -                ts->reg = reg;
> -                /* temp value is modified, so the value kept in memory is
> -                   potentially not the same */
> -                ts->mem_coherent = 0;
> -                s->reg_to_temp[reg] = ts;
> +            if (ts->val_type == TEMP_VAL_REG) {
> +                s->reg_to_temp[ts->reg] = NULL;
>              }
> -        oarg_end:
> +            ts->val_type = TEMP_VAL_REG;
> +            ts->reg = reg;
> +            /*
> +             * Temp value is modified, so the value kept in memory is
> +             * potentially not the same.
> +             */
> +            ts->mem_coherent = 0;
> +            s->reg_to_temp[reg] = ts;
>              new_args[i] = reg;
>          }
>      }
> @@ -3550,10 +3546,10 @@ static void tcg_reg_alloc_op(TCGContext *s, const 
> TCGOp *op)
>      /* move the outputs in the correct register if needed */
>      for(i = 0; i < nb_oargs; i++) {
>          ts = arg_temp(op->args[i]);
> -        reg = new_args[i];
> -        if (ts->fixed_reg && ts->reg != reg) {
> -            tcg_out_mov(s, ts->type, ts->reg, reg);
> -        }
> +
> +        /* ENV should not be modified.  */
> +        tcg_debug_assert(!ts->fixed_reg);
> +
>          if (NEED_SYNC_ARG(i)) {
>              temp_sync(s, ts, o_allocated_regs, 0, IS_DEAD_ARG(i));
>          } else if (IS_DEAD_ARG(i)) {
> @@ -3674,26 +3670,23 @@ static void tcg_reg_alloc_call(TCGContext *s, TCGOp 
> *op)
>      for(i = 0; i < nb_oargs; i++) {
>          arg = op->args[i];
>          ts = arg_temp(arg);
> +
> +        /* ENV should not be modified.  */
> +        tcg_debug_assert(!ts->fixed_reg);
> +
>          reg = tcg_target_call_oarg_regs[i];
>          tcg_debug_assert(s->reg_to_temp[reg] == NULL);
> -
> -        if (ts->fixed_reg) {
> -            if (ts->reg != reg) {
> -                tcg_out_mov(s, ts->type, ts->reg, reg);
> -            }
> -        } else {
> -            if (ts->val_type == TEMP_VAL_REG) {
> -                s->reg_to_temp[ts->reg] = NULL;
> -            }
> -            ts->val_type = TEMP_VAL_REG;
> -            ts->reg = reg;
> -            ts->mem_coherent = 0;
> -            s->reg_to_temp[reg] = ts;
> -            if (NEED_SYNC_ARG(i)) {
> -                temp_sync(s, ts, allocated_regs, 0, IS_DEAD_ARG(i));
> -            } else if (IS_DEAD_ARG(i)) {
> -                temp_dead(s, ts);
> -            }
> +        if (ts->val_type == TEMP_VAL_REG) {
> +            s->reg_to_temp[ts->reg] = NULL;
> +        }
> +        ts->val_type = TEMP_VAL_REG;
> +        ts->reg = reg;
> +        ts->mem_coherent = 0;
> +        s->reg_to_temp[reg] = ts;
> +        if (NEED_SYNC_ARG(i)) {
> +            temp_sync(s, ts, allocated_regs, 0, IS_DEAD_ARG(i));
> +        } else if (IS_DEAD_ARG(i)) {
> +            temp_dead(s, ts);
>          }
>      }
>  }


--
Alex Bennée