I did have a couple of "real" comments on this one that I'd like to at
least see a reply to. Does look pretty good though.
On Sun, Dec 18, 2016 at 9:47 PM, Timothy Arceri <
timothy.arc...@collabora.com> wrote:
> From: Thomas Helland <thomashellan...@gmail.com>
>
> V2: Do a "depth first search" to convert to LCSSA
>
> V3: Small comment fixup
>
> V4: Rebase, adapt to removal of function overloads
>
> V5: Rebase, adapt to relocation of nir to compiler/nir
> Still need to adapt to potential if-uses
> Work around nir_validate issue
>
> V6 (Timothy):
> - tidy lcssa and stop leaking memory
> - dont rewrite the src for the lcssa phi node
> - validate lcssa phi srcs to avoid postvalidate assert
> - don't add new phi if one already exists
> - more lcssa phi validation fixes
> - Rather than marking ssa defs inside a loop just mark blocks inside
> a loop. This is simpler and fixes lcssa for intrinsics which do
> not have a destination.
> - don't create LCSSA phis for loops we won't unroll
> - require loop metadata for lcssa pass
> - handle case were the ssa defs use outside the loop is already a phi
>
> V7: (Timothy)
> - pass indirect mask to metadata call
>
> v8: (Timothy)
> - make convert to lcssa a helper function rather than a nir pass
> - replace inside loop bitset with on the fly block index logic.
> - remove lcssa phi validation special cases
> - inline code from useless helpers, suggested by Jason.
> - always do lcssa on loops, suggested by Jason.
> - stop making lcssa phis special. Add as many source as the block
> has predecessors, suggested by Jason.
>
> V9: (Timothy)
> - fix regression with the is_lcssa_phi field not being initialised
> to false now that ralloc() doesn't zero out memory.
>
> V10: (Timothy)
> - remove extra braces in SSA example, pointed out by Topi
>
> V11: (Timothy)
> - add missing support for LCSSA phis in if conditions.
> ---
> src/compiler/Makefile.sources | 1 +
> src/compiler/nir/nir.c | 1 +
> src/compiler/nir/nir.h | 4 +
> src/compiler/nir/nir_to_lcssa.c | 215 ++++++++++++++++++++++++++++++
> ++++++++++
> 4 files changed, 221 insertions(+)
> create mode 100644 src/compiler/nir/nir_to_lcssa.c
>
> diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
> index ca8a056..e8f7b02 100644
> --- a/src/compiler/Makefile.sources
> +++ b/src/compiler/Makefile.sources
> @@ -254,6 +254,7 @@ NIR_FILES = \
> nir/nir_split_var_copies.c \
> nir/nir_sweep.c \
> nir/nir_to_ssa.c \
> + nir/nir_to_lcssa.c \
> nir/nir_validate.c \
> nir/nir_vla.h \
> nir/nir_worklist.c \
> diff --git a/src/compiler/nir/nir.c b/src/compiler/nir/nir.c
> index 2c3531c..e522a67 100644
> --- a/src/compiler/nir/nir.c
> +++ b/src/compiler/nir/nir.c
> @@ -561,6 +561,7 @@ nir_phi_instr_create(nir_shader *shader)
> {
> nir_phi_instr *instr = ralloc(shader, nir_phi_instr);
> instr_init(&instr->instr, nir_instr_type_phi);
> + instr->is_lcssa_phi = false;
>
> dest_init(&instr->dest);
> exec_list_make_empty(&instr->srcs);
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index 28010aa..75a91ea 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -1360,6 +1360,8 @@ typedef struct {
> struct exec_list srcs; /** < list of nir_phi_src */
>
> nir_dest dest;
> +
> + bool is_lcssa_phi;
> } nir_phi_instr;
>
> typedef struct {
> @@ -2526,6 +2528,8 @@ void nir_convert_to_ssa(nir_shader *shader);
> bool nir_repair_ssa_impl(nir_function_impl *impl);
> bool nir_repair_ssa(nir_shader *shader);
>
> +void nir_convert_loop_to_lcssa(nir_loop *loop);
> +
> /* If phi_webs_only is true, only convert SSA values involved in phi
> nodes to
> * registers. If false, convert all values (even those not involved in a
> phi
> * node) to registers.
> diff --git a/src/compiler/nir/nir_to_lcssa.c b/src/compiler/nir/nir_to_
> lcssa.c
> new file mode 100644
> index 0000000..8afdc54
> --- /dev/null
> +++ b/src/compiler/nir/nir_to_lcssa.c
> @@ -0,0 +1,215 @@
> +/*
> + * Copyright © 2015 Thomas Helland
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the
> "Software"),
> + * to deal in the Software without restriction, including without
> limitation
> + * the rights to use, copy, modify, merge, publish, distribute,
> sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice (including the
> next
> + * paragraph) shall be included in all copies or substantial portions of
> the
> + * Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
> EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
> MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
> SHALL
> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
> OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> DEALINGS
> + * IN THE SOFTWARE.
> + */
> +
> +/*
> + * This pass converts the ssa-graph into "Loop Closed SSA form". This is
> + * done by placing phi nodes at the exits of the loop for all values
> + * that are used outside the loop. The result is it transforms:
> + *
> + * loop { -> loop {
> + * ssa2 = .... -> ssa2 = ...
> + * if (cond) -> if (cond)
> + * break; -> break;
> + * ssa3 = ssa2 * ssa4 -> ssa3 = ssa2 * ssa4
> + * } -> }
> + * ssa6 = ssa2 + 4 -> ssa5 = lcssa_phi(ssa2)
> + * ssa6 = ssa5 + 4
> + */
> +
> +#include "nir.h"
> +
> +typedef struct {
> + /* The nir_shader we are transforming */
> + nir_shader *shader;
> +
> + /* The loop we store information for */
> + nir_loop *loop;
> +
> +} lcssa_state;
> +
> +static bool
> +is_if_use_inside_loop(nir_src *use, nir_loop* loop)
> +{
> + nir_block *block_before_loop =
> + nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));
> + nir_block *block_after_loop =
> + nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node));
> +
> + nir_block *prev_block =
> + nir_cf_node_as_block(nir_cf_node_prev(&use->parent_if->cf_node));
> + if (prev_block->index <= block_before_loop->index ||
> + prev_block->index >= block_after_loop->index) {
>
I'm not sure you want "<=" and ">=" here. It seems like you either want <=
and nir_loop_first_block above or keep what you have above and use <. As
currently written, this will return true if it's used in the block before
or after the loop not just inside the loop.
> + return false;
> + }
> +
> + return true;
> +}
> +
> +static bool
> +is_use_inside_loop(nir_src *use, nir_loop* loop)
> +{
> + nir_block *block_before_loop =
> + nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));
> + nir_block *block_after_loop =
> + nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node));
> +
> + if (use->parent_instr->block->index <= block_before_loop->index ||
> + use->parent_instr->block->index >= block_after_loop->index) {
>
Same here
> + return false;
> + }
> +
> + return true;
> +}
> +
> +static bool
> +convert_loop_exit_for_ssa(nir_ssa_def *def, void *void_state)
> +{
> + lcssa_state *state = void_state;
> + bool all_uses_inside_loop = true;
> +
> + nir_block *block_after_loop =
> + nir_cf_node_as_block(nir_cf_node_next(&state->loop->cf_node));
> +
> + /* If a LCSSA-phi from a nested loop is use outside the parent loop
> there
> + * is no reason to create another LCSSA-phi for the parent loop.
> + */
>
I don't think this is true. The whole point of LCSSA is that no SSA def
declared inside a loop is able to escape the loop except through a phi in
the block after the loop. If it's an LCSSA phi from an inner loop, I think
you very much want it to have another phi for the outer loop.
> + if (def->parent_instr->type == nir_instr_type_phi &&
> + nir_instr_as_phi(def->parent_instr)->is_lcssa_phi) {
> + return true;
> + }
> +
> + nir_foreach_use(use, def) {
> + if (use->parent_instr->type == nir_instr_type_phi &&
> + block_after_loop == use->parent_instr->block) {
>
I'm silly but would you mind flipping this equality around? That way the
LHS is use->parent_instr->something for both clauses.
> + continue;
> + }
> +
> + if (!is_use_inside_loop(use, state->loop)) {
> + all_uses_inside_loop = false;
> + }
> + }
> +
> + nir_foreach_if_use(use, def) {
> + if (!is_if_use_inside_loop(use, state->loop)) {
> + all_uses_inside_loop = false;
> + }
> + }
> +
> + /* There where no sources that had defs outside the loop */
> + if (all_uses_inside_loop)
> + return true;
> +
> + /* Initialize a phi-instruction */
> + nir_phi_instr *phi = nir_phi_instr_create(state->shader);
> + phi->instr.block = block_after_loop;
>
You don't need this. nir_instr_insert will set it for you.
> + nir_ssa_dest_init(&phi->instr, &phi->dest,
> + def->num_components, def->bit_size, "LCSSA-phi");
> + phi->is_lcssa_phi = true;
> +
> + /* Create a phi node with as many sources pointing to the same ssa_def
> as
> + * the block has predecessors.
> + */
> + struct set_entry *entry;
> + set_foreach(block_after_loop->predecessors, entry) {
> + nir_phi_src *phi_src = ralloc(phi, nir_phi_src);
> + phi_src->src = nir_src_for_ssa(def);
> +
> + /* This is a lie to pass validation */
> + phi_src->pred = (nir_block *) entry->key;
>
This is not a lie. It really is the value we get coming in from that
predecessor.
> +
> + exec_list_push_tail(&phi->srcs, &phi_src->node);
> + }
> +
> + nir_instr_insert_before_block(phi->instr.block, &phi->instr);
> +
> + /* Run through all uses and rewrite those outside the loop to point to
> + * the phi instead of pointing to the ssa-def.
> + */
> + nir_foreach_use_safe(use, def) {
> + if (use->parent_instr->type == nir_instr_type_phi &&
> + block_after_loop == use->parent_instr->block) {
> + continue;
> + }
> +
> + if (!is_use_inside_loop(use, state->loop)) {
> + nir_instr_rewrite_src(use->parent_instr, use,
> + nir_src_for_ssa(&phi->dest.ssa));
> + }
> + }
> +
> + nir_foreach_if_use_safe(use, def) {
> + if (!is_if_use_inside_loop(use, state->loop)) {
> + nir_if_rewrite_condition(use->parent_if,
> + nir_src_for_ssa(&phi->dest.ssa));
> + }
> + }
> +
> + return true;
> +}
> +
> +static void
> +convert_to_lcssa(nir_cf_node *cf_node, lcssa_state *state)
> +{
> + switch (cf_node->type) {
> + case nir_cf_node_block:
> + nir_foreach_instr(instr, nir_cf_node_as_block(cf_node))
> + nir_foreach_ssa_def(instr, convert_loop_exit_for_ssa, state);
> + return;
> + case nir_cf_node_if: {
> + nir_if *if_stmt = nir_cf_node_as_if(cf_node);
> + foreach_list_typed(nir_cf_node, nested_node, node,
> &if_stmt->then_list)
> + convert_to_lcssa(nested_node, state);
> + foreach_list_typed(nir_cf_node, nested_node, node,
> &if_stmt->else_list)
> + convert_to_lcssa(nested_node, state);
> + return;
> + }
> + case nir_cf_node_loop: {
> + nir_loop *parent_loop = state->loop;
> + state->loop = nir_cf_node_as_loop(cf_node);
> +
> + foreach_list_typed(nir_cf_node, nested_node, node,
> &state->loop->body)
> + convert_to_lcssa(nested_node, state);
> +
> + state->loop = parent_loop;
> + return;
> + }
> + default:
> + unreachable("unknown cf node type");
> + }
>
+}
> +
> +void
> +nir_convert_loop_to_lcssa(nir_loop *loop) {
> + nir_function_impl *impl = nir_cf_node_get_function(&loop->cf_node);
> +
> + nir_metadata_require(impl, nir_metadata_block_index);
> +
> + lcssa_state *state = rzalloc(NULL, lcssa_state);
> + state->loop = loop;
> + state->shader = impl->function->shader;
> +
> + foreach_list_typed(nir_cf_node, node, node, &state->loop->body)
> + convert_to_lcssa(node, state);
>
We have better iterators now! This and the whole convert_to_lcssa function
can be replaced with
nir_foreach_block_in_cf_node(block, &loop->cf_node) {
nir_foreach_instr(instr, block)
nir_foreach_ssa_def(instr, convert_loop_exit_for_ssa, state);
}
Much simpler!
> +
> + ralloc_free(state);
> +}
> --
> 2.9.3
>
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