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nir/sink: Don't sink load_ubo to outside of its defining loop

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Previously, this could have made the resource divergent in code like
that which is genereated by nir_lower_non_uniform_access.

Fixes: da8ed68a ('nir: replace nir_move_load_const() with nir_opt_sink()')
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
This commit is contained in:
Connor Abbott 2019-09-25 14:17:23 +02:00
parent af9296b8c0
commit 5ac32b2954
1 changed files with 32 additions and 5 deletions
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37
src/compiler/nir/nir_opt_sink.c
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@ -87,14 +87,26 @@ loop_contains_block(nir_loop *loop, nir_block *block)
/* Given the LCA of all uses and the definition, find a block on the path
* between them in the dominance tree that is outside of as many loops as
* possible.
* possible. If "sink_out_of_loops" is false, then we disallow sinking the
* definition outside of the loop it's defined in (if any).
*/
static nir_block *
adjust_block_for_loops(nir_block *use_block, nir_block *def_block)
adjust_block_for_loops(nir_block *use_block, nir_block *def_block,
bool sink_out_of_loops)
{
nir_loop *def_loop = NULL;
if (!sink_out_of_loops)
def_loop = get_innermost_loop(&def_block->cf_node);
for (nir_block *cur_block = use_block; cur_block != def_block->imm_dom;
cur_block = cur_block->imm_dom) {
if (!sink_out_of_loops && def_loop &&
!loop_contains_block(def_loop, use_block)) {
use_block = cur_block;
continue;
}
nir_cf_node *next = nir_cf_node_next(&cur_block->cf_node);
if (next && next->type == nir_cf_node_loop) {
nir_loop *following_loop = nir_cf_node_as_loop(next);
@ -115,7 +127,7 @@ adjust_block_for_loops(nir_block *use_block, nir_block *def_block)
* the uses
*/
static nir_block *
get_preferred_block(nir_ssa_def *def, bool sink_into_loops)
get_preferred_block(nir_ssa_def *def, bool sink_into_loops, bool sink_out_of_loops)
{
nir_block *lca = NULL;
@ -158,8 +170,14 @@ get_preferred_block(nir_ssa_def *def, bool sink_into_loops)
* in as we can go is probably worth it for register pressure.
*/
if (!sink_into_loops) {
lca = adjust_block_for_loops(lca, def->parent_instr->block);
lca = adjust_block_for_loops(lca, def->parent_instr->block,
sink_out_of_loops);
assert(nir_block_dominates(def->parent_instr->block, lca));
} else {
/* sink_into_loops = true and sink_out_of_loops = false isn't
* implemented yet because it's not used.
*/
assert(sink_out_of_loops);
}
@ -204,8 +222,17 @@ nir_opt_sink(nir_shader *shader, nir_move_options options)
continue;
nir_ssa_def *def = nir_instr_ssa_def(instr);
bool sink_into_loops = instr->type != nir_instr_type_intrinsic;
/* Don't sink load_ubo out of loops because that can make its
* resource divergent and break code like that which is generated
* by nir_lower_non_uniform_access.
*/
bool sink_out_of_loops =
instr->type != nir_instr_type_intrinsic ||
nir_instr_as_intrinsic(instr)->intrinsic != nir_intrinsic_load_ubo;
nir_block *use_block =
get_preferred_block(def, instr->type != nir_instr_type_intrinsic);
get_preferred_block(def, sink_into_loops, sink_out_of_loops);
if (!use_block || use_block == instr->block)
continue;