[PATCH 5/5] d3dcompiler: Allocate temporary registers for variables.

[Matteo Bruni]

On Mon, Mar 30, 2020 at 4:54 AM Zebediah Figura <z.figura12 at gmail.com> wrote:

Hi Zeb,

I have a number of questions / comments, inline.

> diff --git a/dlls/d3dcompiler_43/hlsl.y b/dlls/d3dcompiler_43/hlsl.y
> index d6c64edcace..f828e05e335 100644
> --- a/dlls/d3dcompiler_43/hlsl.y
> +++ b/dlls/d3dcompiler_43/hlsl.y
> @@ -2732,6 +2732,177 @@ static void compute_liveness(struct hlsl_ir_function_decl *entry_func)
>      compute_liveness_recurse(entry_func->body, 0, 0);
>  }
>
> +struct liveness_ctx
> +{
> +    size_t count;
> +    struct
> +    {
> +        /* 0 if not live yet. */
> +        unsigned int last_read;
> +    } *regs;
> +};
> +
> +static unsigned char get_dead_writemask(struct liveness_ctx *liveness,
> +        unsigned int first_write, unsigned int index, unsigned int components)

Maybe get_available_writemask()? Same for the other similarly named functions.

> +{
> +    unsigned char i, writemask = 0, count = 0;
> +
> +    for (i = 0; i < 4; ++i)
> +    {
> +        if (liveness->regs[index + i].last_read <= first_write)
> +        {
> +            writemask |= 1 << i;
> +            if (++count == components)
> +                return writemask;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
> +static struct hlsl_reg allocate_temp_register(struct liveness_ctx *liveness,
> +        unsigned int first_write, unsigned int last_read, unsigned char components)

How is this going to be different to the non-temp register allocation?

> +{
> +    struct hlsl_reg ret = {.allocated = TRUE};
> +    unsigned char writemask, i;
> +    unsigned int regnum;
> +
> +    for (regnum = 0; regnum < liveness->count; regnum += 4)
> +    {
> +        if ((writemask = get_dead_writemask(liveness, first_write, regnum, components)))
> +            break;
> +    }
> +    if (regnum == liveness->count)
> +    {
> +        liveness->count = max(liveness->count * 2, 32);
> +        liveness->regs = d3dcompiler_realloc(liveness->regs, liveness->count * sizeof(*liveness->regs));

Do we want to use array_reserve() here?

> +        writemask = (1 << components) - 1;
> +    }
> +    for (i = 0; i < 4; ++i)
> +    {
> +        if (writemask & (1 << i))
> +            liveness->regs[regnum + i].last_read = last_read;
> +    }
> +    ret.reg = regnum / 4;
> +    ret.writemask = writemask;
> +    return ret;
> +}
> +
> +static BOOL is_range_dead(struct liveness_ctx *liveness, unsigned int first_write,
> +        unsigned int index, unsigned int elements)
> +{
> +    unsigned int i;
> +
> +    for (i = 0; i < elements; i += 4)
> +    {
> +        if (!get_dead_writemask(liveness, first_write, index + i, 4))
> +            return FALSE;
> +    }
> +    return TRUE;
> +}
> +
> +/* "elements" is the total number of consecutive whole registers needed. */
> +static struct hlsl_reg allocate_temp_range(struct liveness_ctx *liveness,
> +        unsigned int first_write, unsigned int last_read, unsigned int elements)
> +{
> +    struct hlsl_reg ret = {.allocated = TRUE};
> +    unsigned int i, regnum;
> +
> +    elements *= 4;
> +
> +    for (regnum = 0; regnum < liveness->count; regnum += 4)
> +    {
> +        if (is_range_dead(liveness, first_write, regnum, min(elements, liveness->count - regnum)))
> +            break;
> +    }
> +    if (regnum + elements >= liveness->count)
> +    {
> +        liveness->count = max(liveness->count * 2, regnum + elements);
> +        liveness->regs = d3dcompiler_realloc(liveness->regs, liveness->count * sizeof(*liveness->regs));
> +    }
> +    for (i = 0; i < elements; ++i)
> +        liveness->regs[regnum + i].last_read = last_read;
> +    ret.reg = regnum / 4;
> +    return ret;

It feels like the for should execute elements * 4 iterations, instead.

> +}
> +
> +static void allocate_variable_temp_register(struct hlsl_ir_var *var, struct liveness_ctx *liveness)
> +{
> +    if (!var->reg.allocated && var->last_read)
> +    {
> +        if (var->data_type->reg_size > 1)
> +        {
> +            var->reg = allocate_temp_range(liveness, var->first_write,
> +                    var->last_read, var->data_type->reg_size);
> +            TRACE("Allocated r%u-r%u to %s (liveness %u-%u).\n", var->reg.reg,
> +                    var->reg.reg + var->data_type->reg_size - 1, var->name, var->first_write, var->last_read);
> +        }
> +        else
> +        {
> +            var->reg = allocate_temp_register(liveness, var->first_write,
> +                    var->last_read, var->data_type->dimx);
> +            TRACE("Allocated r%u%s to %s (liveness %u-%u).\n", var->reg.reg,
> +                    debug_writemask(var->reg.writemask), var->name, var->first_write, var->last_read);
> +        }
> +    }
> +}
> +
> +static void allocate_temp_registers_recurse(struct list *instrs, struct liveness_ctx *liveness)
> +{
> +    struct hlsl_ir_node *instr;
> +
> +    LIST_FOR_EACH_ENTRY(instr, instrs, struct hlsl_ir_node, entry)
> +    {
> +        switch (instr->type)
> +        {
> +        case HLSL_IR_ASSIGNMENT:
> +        {
> +            struct hlsl_ir_assignment *assignment = assignment_from_node(instr);
> +            allocate_variable_temp_register(hlsl_var_from_deref(&assignment->lhs), liveness);
> +            break;
> +        }
> +        case HLSL_IR_IF:
> +        {
> +            struct hlsl_ir_if *iff = if_from_node(instr);
> +            allocate_temp_registers_recurse(iff->then_instrs, liveness);
> +            if (iff->else_instrs)
> +                allocate_temp_registers_recurse(iff->else_instrs, liveness);
> +            break;
> +        }
> +        case HLSL_IR_LOOP:
> +        {
> +            struct hlsl_ir_loop *loop = loop_from_node(instr);
> +            allocate_temp_registers_recurse(loop->body, liveness);
> +            break;
> +        }
> +        default:
> +            break;
> +        }
> +    }
> +}

Do we need to allocate temporary registers for other instructions too,
like expressions?

> +
> +/* Simple greedy temporary register allocation pass that just assigns a unique
> + * index to all (simultaneously live) variables or intermediate values. Agnostic
> + * as to how many registers are actually available for the current backend, and
> + * does not handle constants. */
> +static void allocate_temp_registers(struct hlsl_ir_function_decl *entry_func)
> +{
> +    struct liveness_ctx liveness = {};

I'm pretty sure that this is a gcc extension: you want '{0}' instead.