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nir/repair_ssa: Replace the unreachable check with the phi builder

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In a3268599f3, I attempted to fix nir_repair_ssa for unreachable
blocks.  However, that commit missed the possibility that the use is in
a block which, itself, is unreachable.  In this case, we can end up in
an infinite loop trying to replace a def with itself.  Even though a
no-op replacement is a fine operation, it keeps extending the end of the
uses list as we're walking it.  Instead of explicitly checking for the
group of conditions, just check if the phi builder gives us a different
def.  That's guaranteed to be 100% reliable and, while it lacks symmetry
with the is_valid checks, should be more reliable.

Fixes: a3268599 "nir/repair_ssa: Repair dominance for unreachable..."
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
This commit is contained in:
Jason Ekstrand 2019-09-09 13:38:37 -05:00
parent 2c050b49b3
commit d63162cff0
1 changed files with 44 additions and 35 deletions
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79
src/compiler/nir/nir_repair_ssa.c
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@ -103,48 +103,57 @@ repair_ssa_def(nir_ssa_def *def, void *void_state)
nir_foreach_use_safe(src, def) {
nir_block *src_block = get_src_block(src);
if (nir_block_is_unreachable(src_block) ||
!nir_block_dominates(def->parent_instr->block, src_block)) {
nir_ssa_def *block_def =
nir_phi_builder_value_get_block_def(val, src_block);
/* If def was a deref and the use we're looking at is a deref that
* isn't a cast, we need to wrap it in a cast so we don't loose any
* deref information.
*/
if (def->parent_instr->type == nir_instr_type_deref &&
src->parent_instr->type == nir_instr_type_deref &&
nir_instr_as_deref(src->parent_instr)->deref_type != nir_deref_type_cast) {
nir_deref_instr *cast =
nir_deref_instr_create(state->impl->function->shader,
nir_deref_type_cast);
nir_deref_instr *deref = nir_instr_as_deref(def->parent_instr);
cast->mode = deref->mode;
cast->type = deref->type;
cast->parent = nir_src_for_ssa(block_def);
cast->cast.ptr_stride = nir_deref_instr_ptr_as_array_stride(deref);
nir_ssa_dest_init(&cast->instr, &cast->dest,
def->num_components, def->bit_size, NULL);
nir_instr_insert(nir_before_instr(src->parent_instr),
&cast->instr);
block_def = &cast->dest.ssa;
}
nir_instr_rewrite_src(src->parent_instr, src,
nir_src_for_ssa(block_def));
if (src_block == def->parent_instr->block) {
assert(nir_phi_builder_value_get_block_def(val, src_block) == def);
continue;
}
nir_ssa_def *block_def =
nir_phi_builder_value_get_block_def(val, src_block);
if (block_def == def)
continue;
/* If def was a deref and the use we're looking at is a deref that
* isn't a cast, we need to wrap it in a cast so we don't loose any
* deref information.
*/
if (def->parent_instr->type == nir_instr_type_deref &&
src->parent_instr->type == nir_instr_type_deref &&
nir_instr_as_deref(src->parent_instr)->deref_type != nir_deref_type_cast) {
nir_deref_instr *cast =
nir_deref_instr_create(state->impl->function->shader,
nir_deref_type_cast);
nir_deref_instr *deref = nir_instr_as_deref(def->parent_instr);
cast->mode = deref->mode;
cast->type = deref->type;
cast->parent = nir_src_for_ssa(block_def);
cast->cast.ptr_stride = nir_deref_instr_ptr_as_array_stride(deref);
nir_ssa_dest_init(&cast->instr, &cast->dest,
def->num_components, def->bit_size, NULL);
nir_instr_insert(nir_before_instr(src->parent_instr),
&cast->instr);
block_def = &cast->dest.ssa;
}
nir_instr_rewrite_src(src->parent_instr, src, nir_src_for_ssa(block_def));
}
nir_foreach_if_use_safe(src, def) {
nir_block *block_before_if =
nir_cf_node_as_block(nir_cf_node_prev(&src->parent_if->cf_node));
if (nir_block_is_unreachable(block_before_if) ||
!nir_block_dominates(def->parent_instr->block, block_before_if)) {
nir_if_rewrite_condition(src->parent_if, nir_src_for_ssa(
nir_phi_builder_value_get_block_def(val, block_before_if)));
if (block_before_if == def->parent_instr->block) {
assert(nir_phi_builder_value_get_block_def(val, block_before_if) == def);
continue;
}
nir_ssa_def *block_def =
nir_phi_builder_value_get_block_def(val, block_before_if);
if (block_def == def)
continue;
nir_if_rewrite_condition(src->parent_if, nir_src_for_ssa(block_def));
}
return true;