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nir/from_ssa: Don't lower constant SSA values to registers

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Backends want to be able to do special things with constant values such as
put them into immediates or make decisions based on whether or not a value
is constant.  Before, constants always got lowered to a load_const into a
register and then a register use.  Now we leave constants as SSA values so
backends can special-case them if they want.  Since handling constant SSA
values is trivial, this shouldn't be a problem for backends.

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
This commit is contained in:
Jason Ekstrand 2015-01-14 11:19:41 -08:00
parent c2abfc0b86
commit 5690c2b54c
1 changed files with 32 additions and 8 deletions
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40
src/glsl/nir/nir_from_ssa.c
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@ -465,6 +465,12 @@ get_register_for_ssa_def(nir_ssa_def *def, struct from_ssa_state *state)
if (entry) {
return (nir_register *)entry->data;
} else {
/* We leave load_const SSA values alone. They act as immediates to
* the backend. If it got coalesced into a phi, that's ok.
*/
if (def->parent_instr->type == nir_instr_type_load_const)
return NULL;
nir_register *reg = nir_local_reg_create(state->impl);
reg->name = def->name;
reg->num_components = def->num_components;
@ -481,12 +487,18 @@ rewrite_ssa_src(nir_src *src, void *void_state)
struct from_ssa_state *state = void_state;
if (src->is_ssa) {
/* We don't need to remove it from the uses set because that is going
* away. We just need to add it to the one for the register. */
nir_register *reg = get_register_for_ssa_def(src->ssa, state);
if (reg == NULL) {
assert(src->ssa->parent_instr->type == nir_instr_type_load_const);
return true;
}
memset(src, 0, sizeof *src);
src->reg.reg = reg;
/* We don't need to remove it from the uses set because that is going
* away. We just need to add it to the one for the register. */
_mesa_set_add(reg->uses, _mesa_hash_pointer(state->instr), state->instr);
}
@ -499,10 +511,16 @@ rewrite_ssa_dest(nir_dest *dest, void *void_state)
struct from_ssa_state *state = void_state;
if (dest->is_ssa) {
nir_register *reg = get_register_for_ssa_def(&dest->ssa, state);
if (reg == NULL) {
assert(dest->ssa.parent_instr->type == nir_instr_type_load_const);
return true;
}
_mesa_set_destroy(dest->ssa.uses, NULL);
_mesa_set_destroy(dest->ssa.if_uses, NULL);
nir_register *reg = get_register_for_ssa_def(&dest->ssa, state);
memset(dest, 0, sizeof *dest);
dest->reg.reg = reg;
@ -529,7 +547,6 @@ resolve_registers_block(nir_block *block, void *void_state)
instr->type == nir_instr_type_phi) {
nir_instr_remove(instr);
ralloc_steal(state->dead_ctx, instr);
continue;
}
}
state->instr = NULL;
@ -538,11 +555,18 @@ resolve_registers_block(nir_block *block, void *void_state)
if (following_if && following_if->condition.is_ssa) {
nir_register *reg = get_register_for_ssa_def(following_if->condition.ssa,
state);
memset(&following_if->condition, 0, sizeof following_if->condition);
following_if->condition.reg.reg = reg;
if (reg) {
memset(&following_if->condition, 0, sizeof following_if->condition);
following_if->condition.reg.reg = reg;
_mesa_set_add(reg->if_uses, _mesa_hash_pointer(following_if),
following_if);
_mesa_set_add(reg->if_uses, _mesa_hash_pointer(following_if),
following_if);
} else {
/* FIXME: We really shouldn't hit this. We should be doing
* constant control flow propagation.
*/
assert(following_if->condition.ssa->parent_instr->type == nir_instr_type_load_const);
}
}
return true;