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lima/ppir: optimize branch comparison when possible

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The branch operation supports comparisons, so it may be possible to
merge a previous comparison operation with the branch operation.
There are several restrictions to do it at this stage, but it may save
instructions in many cases.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16163>
This commit is contained in:
Erico Nunes 2022-04-26 11:09:24 +02:00 • committed by Marge Bot
parent 5718629a70
commit c3f13ee551
1 changed files with 98 additions and 5 deletions
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103
src/gallium/drivers/lima/ir/pp/lower.c
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@ -322,6 +322,98 @@ static bool ppir_lower_sat(ppir_block *block, ppir_node *node)
return true;
}
static bool ppir_lower_branch_merge_condition(ppir_block *block, ppir_node *node)
{
/* Check if we can merge a condition with a branch instruction,
* removing the need for a select instruction */
assert(node->type == ppir_node_type_branch);
if (!ppir_node_has_single_pred(node))
return false;
ppir_node *pred = ppir_node_first_pred(node);
assert(pred);
if (pred->type != ppir_node_type_alu)
return false;
switch (pred->op)
{
case ppir_op_lt:
case ppir_op_gt:
case ppir_op_le:
case ppir_op_ge:
case ppir_op_eq:
case ppir_op_ne:
break;
default:
return false;
}
ppir_dest *dest = ppir_node_get_dest(pred);
if (!ppir_node_has_single_succ(pred) || dest->type != ppir_target_ssa)
return false;
ppir_alu_node *cond = ppir_node_to_alu(pred);
/* branch can't reference pipeline registers */
if (cond->src[0].type == ppir_target_pipeline ||
cond->src[1].type == ppir_target_pipeline)
return false;
/* branch can't use flags */
if (cond->src[0].negate || cond->src[0].absolute ||
cond->src[1].negate || cond->src[1].absolute)
return false;
/* at this point, it can be successfully be replaced. */
ppir_branch_node *branch = ppir_node_to_branch(node);
switch (pred->op)
{
case ppir_op_le:
branch->cond_gt = true;
break;
case ppir_op_lt:
branch->cond_eq = true;
branch->cond_gt = true;
break;
case ppir_op_ge:
branch->cond_lt = true;
break;
case ppir_op_gt:
branch->cond_eq = true;
branch->cond_lt = true;
break;
case ppir_op_eq:
branch->cond_lt = true;
branch->cond_gt = true;
break;
case ppir_op_ne:
branch->cond_eq = true;
break;
default:
assert(0);
break;
}
assert(cond->num_src == 2);
branch->num_src = 2;
branch->src[0] = cond->src[0];
branch->src[1] = cond->src[1];
/* for all nodes before the condition */
ppir_node_foreach_pred_safe(pred, dep) {
/* insert the branch node as successor */
ppir_node *p = dep->pred;
ppir_node_remove_dep(dep);
ppir_node_add_dep(node, p, ppir_dep_src);
}
ppir_node_delete(pred);
return true;
}
static bool ppir_lower_branch(ppir_block *block, ppir_node *node)
{
ppir_branch_node *branch = ppir_node_to_branch(node);
@ -330,6 +422,12 @@ static bool ppir_lower_branch(ppir_block *block, ppir_node *node)
if (branch->num_src == 0)
return true;
/* Check if we can merge a condition with the branch */
if (ppir_lower_branch_merge_condition(block, node))
return true;
/* If the condition cannot be merged, fall back to a
* comparison against zero */
ppir_const_node *zero = ppir_node_create(block, ppir_op_const, -1, 0);
if (!zero)
@ -342,11 +440,6 @@ static bool ppir_lower_branch(ppir_block *block, ppir_node *node)
zero->dest.ssa.num_components = 1;
zero->dest.write_mask = 0x01;
/* For now we're just comparing branch condition with 0,
* in future we should look whether it's possible to move
* comparision node into branch itself and use current
* way as a fallback for complex conditions.
*/
ppir_node_target_assign(&branch->src[1], &zero->node);
if (branch->negate)