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nir/vars_to_ssa: Add phi sources for unreachable predecessors

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It is possible to end up with unreachable blocks if, for instance, you have
an "if (...) { break; } else { continue; } unreachable()".  In this case,
the unreachable block does not show up in the dominance tree so it never
gets visited.  Instead, we go and visit all of those in follow-on pass.
This commit is contained in:
Jason Ekstrand
2016-01-11 15:33:41 -08:00
parent c974b94578
commit fc3f659aa9
1 changed files with 46 additions and 0 deletions
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46
src/glsl/nir/nir_lower_vars_to_ssa.c
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@@ -581,6 +581,33 @@ add_phi_sources(nir_block *block, nir_block *pred,
}
}
static void
add_undef_phi_sources(nir_block *block, nir_block *pred,
struct lower_variables_state *state)
{
nir_foreach_instr(block, instr) {
if (instr->type != nir_instr_type_phi)
break;
nir_phi_instr *phi = nir_instr_as_phi(instr);
nir_ssa_undef_instr *undef =
nir_ssa_undef_instr_create(state->shader,
phi->dest.ssa.num_components);
nir_instr_insert(nir_before_cf_list(&state->impl->body), &undef->instr);
nir_phi_src *src = ralloc(phi, nir_phi_src);
src->pred = pred;
src->src.parent_instr = &phi->instr;
src->src.is_ssa = true;
src->src.ssa = &undef->def;
list_addtail(&src->src.use_link, &undef->def.uses);
exec_list_push_tail(&phi->srcs, &src->node);
}
}
/* Performs variable renaming by doing a DFS of the dominance tree
*
* This algorithm is very similar to the one outlined in "Efficiently
@@ -774,6 +801,23 @@ rename_variables_block(nir_block *block, struct lower_variables_state *state)
return true;
}
static bool
add_unreachable_phi_srcs_block(nir_block *block, void *void_state)
{
struct lower_variables_state *state = void_state;
/* Only run on unreachable blocks */
if (block->imm_dom || block == nir_start_block(state->impl))
return true;
if (block->successors[0])
add_undef_phi_sources(block->successors[0], block, state);
if (block->successors[1])
add_undef_phi_sources(block->successors[1], block, state);
return true;
}
/* Inserts phi nodes for all variables marked lower_to_ssa
*
* This is the same algorithm as presented in "Efficiently Computing Static
@@ -955,6 +999,8 @@ nir_lower_vars_to_ssa_impl(nir_function_impl *impl)
insert_phi_nodes(&state);
rename_variables_block(nir_start_block(impl), &state);
nir_foreach_block(impl, add_unreachable_phi_srcs_block, &state);
nir_metadata_preserve(impl, nir_metadata_block_index |
nir_metadata_dominance);