On Fri, Sep 16, 2016 at 6:25 PM, Jason Ekstrand <ja...@jlekstrand.net> wrote:
> On Thu, Sep 15, 2016 at 12:03 AM, Timothy Arceri
> <timothy.arc...@collabora.com> wrote:
>>
>> From: Thomas Helland <thomashellan...@gmail.com>
>>
>> This pass detects induction variables and calculates the
>> trip count of loops to be used for loop unrolling.
>>
>> I've removed support for float induction values for now, for the
>> simple reason that they don't appear in my shader-db collection,
>> and so I don't see it as common enough that we want to pollute the
>> pass with this in the initial version.
>>
>> V2: Rebase, adapt to removal of function overloads
>>
>> V3: (Timothy Arceri)
>> - don't try to find trip count if loop terminator conditional is a phi
>> - fix trip count for do-while loops
>> - replace conditional type != alu assert with return
>> - disable unrolling of loops with continues
>> - multiple fixes to memory allocation, stop leaking and don't destroy
>> structs we want to use for unrolling.
>> - fix iteration count bugs when induction var not on RHS of condition
>> - add FIXME for && conditions
>> - calculate trip count for unsigned induction/limit vars
>>
>> V4:
>> - count instructions in a loop
>> - set the limiting_terminator even if we can't find the trip count for
>> all terminators. This is needed for complex unrolling where we handle
>> 2 terminators and the trip count is unknown for one of them.
>> - restruct structs so we don't keep information not required after
>> analysis and remove dead fields.
>> - force unrolling in some cases as per the rules in the GLSL IR pass
>> ---
>> src/compiler/Makefile.sources | 2 +
>> src/compiler/nir/nir.h | 36 +-
>> src/compiler/nir/nir_loop_analyze.c | 1012
>> +++++++++++++++++++++++++++++++++++
>> src/compiler/nir/nir_metadata.c | 8 +-
>> 4 files changed, 1056 insertions(+), 2 deletions(-)
>> create mode 100644 src/compiler/nir/nir_loop_analyze.c
>>
>> diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
>> index f5b4f9c..7ed26a9 100644
>> --- a/src/compiler/Makefile.sources
>> +++ b/src/compiler/Makefile.sources
>> @@ -190,6 +190,8 @@ NIR_FILES = \
>> nir/nir_intrinsics.c \
>> nir/nir_intrinsics.h \
>> nir/nir_liveness.c \
>> + nir/nir_loop_analyze.c \
>> + nir/nir_loop_analyze.h \
>> nir/nir_lower_alu_to_scalar.c \
>> nir/nir_lower_atomics.c \
>> nir/nir_lower_bitmap.c \
>> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
>> index ff7c422..49e8cd8 100644
>> --- a/src/compiler/nir/nir.h
>> +++ b/src/compiler/nir/nir.h
>> @@ -1549,9 +1549,36 @@ nir_if_last_else_node(nir_if *if_stmt)
>> }
>>
>> typedef struct {
>> + nir_if *nif;
>> +
>> + nir_instr *conditional_instr;
>> +
>> + struct list_head loop_terminator_link;
>> +} nir_loop_terminator;
>> +
>> +typedef struct {
>> + /* Number of instructions in the loop */
>> + unsigned num_instructions;
>> +
>> + /* How many times the loop is run (if known) */
>> + unsigned trip_count;
>> + bool is_trip_count_known;
>
>
> We could use 0 or -1 to indicate "I don't know trip count" instead of an
> extra boolean. Not sure that it matters much.
>
>>
>> +
>> + /* Unroll the loop regardless of its size */
>> + bool force_unroll;
>
>
> It seems a bit odd to have this decide to force-unroll. This is an analysis
> pass, not a "make decisions" pass.
>
>>
>> +
>> + nir_loop_terminator *limiting_terminator;
>> +
>> + /* A list of loop_terminators terminating this loop. */
>> + struct list_head loop_terminator_list;
>> +} nir_loop_info;
>> +
>> +typedef struct {
>> nir_cf_node cf_node;
>>
>> struct exec_list body; /** < list of nir_cf_node */
>> +
>> + nir_loop_info *info;
>> } nir_loop;
>>
>> static inline nir_cf_node *
>> @@ -1576,6 +1603,7 @@ typedef enum {
>> nir_metadata_dominance = 0x2,
>> nir_metadata_live_ssa_defs = 0x4,
>> nir_metadata_not_properly_reset = 0x8,
>> + nir_metadata_loop_analysis = 0x16,
>> } nir_metadata;
>>
>> typedef struct {
>> @@ -1758,6 +1786,8 @@ typedef struct nir_shader_compiler_options {
>> * information must be inferred from the list of input nir_variables.
>> */
>> bool use_interpolated_input_intrinsics;
>> +
>> + unsigned max_unroll_iterations;
>> } nir_shader_compiler_options;
>>
>> typedef struct nir_shader_info {
>> @@ -1962,7 +1992,7 @@ nir_loop *nir_loop_create(nir_shader *shader);
>> nir_function_impl *nir_cf_node_get_function(nir_cf_node *node);
>>
>> /** requests that the given pieces of metadata be generated */
>> -void nir_metadata_require(nir_function_impl *impl, nir_metadata
>> required);
>> +void nir_metadata_require(nir_function_impl *impl, nir_metadata required,
>> ...);
>> /** dirties all but the preserved metadata */
>> void nir_metadata_preserve(nir_function_impl *impl, nir_metadata
>> preserved);
>>
>> @@ -2559,6 +2589,10 @@ void nir_lower_double_pack(nir_shader *shader);
>> bool nir_normalize_cubemap_coords(nir_shader *shader);
>>
>> void nir_live_ssa_defs_impl(nir_function_impl *impl);
>> +
>> +void nir_loop_analyze_impl(nir_function_impl *impl,
>> + nir_variable_mode indirect_mask);
>> +
>> bool nir_ssa_defs_interfere(nir_ssa_def *a, nir_ssa_def *b);
>>
>> void nir_convert_to_ssa_impl(nir_function_impl *impl);
>> diff --git a/src/compiler/nir/nir_loop_analyze.c
>> b/src/compiler/nir/nir_loop_analyze.c
>> new file mode 100644
>> index 0000000..6bea9e5
>> --- /dev/null
>> +++ b/src/compiler/nir/nir_loop_analyze.c
>> @@ -0,0 +1,1012 @@
>> +/*
>> + * 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.
>> + */
>> +
>> +#include "nir.h"
>> +
>> +typedef enum {
>> + undefined,
>> + invariant,
>> + basic_induction
>> +} nir_loop_variable_type;
>> +
>> +typedef struct {
>> + /* The ssa_def associated with this info */
>> + nir_ssa_def *def;
>> +
>> + /* The type of this ssa_def */
>> + nir_loop_variable_type type;
>> +
>> + /* If the ssa-def is constant */
>> + bool is_constant;
>> +
>> + bool in_conditional_block;
>> +
>> + bool in_nested_loop;
>> +} nir_loop_variable;
>> +
>> +typedef struct {
>> + nir_op alu_op; /* The type of alu-operation
>> */
>> + nir_loop_variable *alu_def; /* The def of the
>> alu-operation */
>> + nir_loop_variable *invariant; /* The invariant alu-operand
>> */
>> + nir_loop_variable *phi; /* The other alu-operand
>> */
>> + nir_loop_variable *def_outside_loop; /* The phi-src outside the
>> loop */
>> +} nir_basic_induction_var;
>> +
>> +typedef struct {
>> + /* A link for the work list */
>> + struct list_head process_link;
>> +
>> + bool in_loop;
>> +
>> + nir_loop_variable *nir_loop_var;
>> +} loop_variable;
>> +
>> +typedef struct {
>> + bool contains_break;
>> + bool contains_continue;
>> +} loop_jumps;
>> +
>> +typedef struct {
>> + /* The loop we store information for */
>> + nir_loop *loop;
>> +
>> + /* Loop_variable for all ssa_defs in function */
>> + loop_variable *loop_vars;
>> +
>> + /* Loop_variable for all ssa_defs in function */
>> + nir_loop_variable *nir_loop_vars;
>
>
> Why are these two separate things? You have two arrays both indexed by
> nir_ssa_def::index and both called loop_vars and one has a pointer to the
> other. Can we just make 1 array?
>
>>
>> +
>> + /* A list of the loop_vars to analyze */
>> + struct list_head process_list;
>> +
>> + nir_loop_info *info;
>> +
>> + nir_variable_mode indirect_mask;
>> +
>> + struct hash_table *var_to_basic_ind;
>
>
> Also, this seems like an unneeded level of indirection. Just put a pointer
> in loop_variable that points to the induction var struct.
>
>>
>> +} loop_info_state;
>> +
>> +static loop_variable *
>> +get_loop_var(nir_ssa_def *value, loop_info_state *state)
>> +{
>> + return &(state->loop_vars[value->index]);
>> +}
>> +
>> +static nir_loop_variable *
>> +get_nir_loop_var(nir_ssa_def *value, loop_info_state *state)
>> +{
>> + return &(state->nir_loop_vars[value->index]);
>> +}
>> +
>> +typedef struct {
>> + loop_info_state *state;
>> + bool mark_nested;
>> + bool mark_in_conditional;
>> +} init_loop_state;
>> +
>> +static bool
>> +init_loop_def(nir_ssa_def *def, void *void_init_loop_state)
>> +{
>> + init_loop_state *loop_init_state = void_init_loop_state;
>> + loop_variable *var = get_loop_var(def, loop_init_state->state);
>> +
>> + /* Add to the tail of the list. That way we start at the beginning of
>> the
>> + * defs in the loop instead of the end when walking the list. This
>> means
>> + * less recursive calls. Only add defs that are not in nested loops or
>> + * conditional blocks.
>> + */
>> + if (!(loop_init_state->mark_in_conditional ||
>> + loop_init_state->mark_nested))
>> + LIST_ADDTAIL(&(var->process_link),
>> + &(loop_init_state->state->process_list));
>
>
> I have a mild preference for the lower-case variants. As I recall, they are
> more for legacy.
>
>>
>> +
>> + if (loop_init_state->mark_in_conditional)
>> + var->nir_loop_var->in_conditional_block = true;
>> +
>> + if (loop_init_state->mark_nested)
>> + var->nir_loop_var->in_nested_loop = true;
>> +
>> + var->in_loop = true;
>> +
>> + return true;
>> +}
>> +
>> +static bool
>> +init_loop_block(nir_block *block, void *void_init_loop_state)
>
>
> Can we make this function take the actual parameters and limit
> init_loop_state to being the thing we use for init_loop_def. Passing piles
> of pointers through made sense when Thomas originally wrote it but now that
> we have better loop iteration macros, we can just pass arguments.
>
>>
>> +{
>> + init_loop_state *loop_init_state = void_init_loop_state;
>> +
>> + nir_foreach_instr(instr, block)
>> + nir_foreach_ssa_def(instr, init_loop_def, loop_init_state);
>> +
>> + return true;
>> +}
>> +
>> +static inline bool
>> +is_var_alu(loop_variable *var)
>> +{
>> + return (var->nir_loop_var->def->parent_instr->type ==
>> nir_instr_type_alu);
>> +}
>> +
>> +static inline bool
>> +is_var_phi(loop_variable *var)
>> +{
>> + return (var->nir_loop_var->def->parent_instr->type ==
>> nir_instr_type_phi);
>> +}
>> +
>> +static inline bool
>> +is_ssa_def_invariant(nir_ssa_def *def, loop_info_state *state)
>> +{
>> + loop_variable *var = get_loop_var(def, state);
>> +
>> + if (var->nir_loop_var->type == invariant)
>> + return true;
>> +
>> + if (!var->in_loop) {
>> + var->nir_loop_var->type = invariant;
>> + return true;
>> + }
>> +
>> + if (var->nir_loop_var->type == basic_induction)
>> + return false;
>> +
>> + if (is_var_alu(var)) {
>> + nir_alu_instr *alu = nir_instr_as_alu(def->parent_instr);
>> +
>> + for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
>> + if (!is_ssa_def_invariant(alu->src[i].src.ssa, state))
>> + return false;
>> + }
>> + var->nir_loop_var->type = invariant;
>> + return true;
>> + }
>> +
>> + /* Phis shouldn't be invariant except if one operand is invariant, and
>> the
>> + * other is the phi itself. These should be removed by
>> opt_remove_phis.
>> + * load_consts are already set to invariant and constant during init,
>> + * and so should return earlier. Remaining op_codes are set undefined.
>> + */
>> + var->nir_loop_var->type = undefined;
>> + return false;
>> +}
>> +
>> +static void
>> +compute_invariance_information(loop_info_state *state)
>> +{
>> + /* An expression is invariant in a loop L if:
>> + * (base cases)
>> + * – it’s a constant
>> + * – it’s a variable use, all of whose single defs are outside of L
>> + * (inductive cases)
>> + * – it’s a pure computation all of whose args are loop invariant
>> + * – it’s a variable use whose single reaching def, and the
>> + * rhs of that def is loop-invariant
>> + */
>> + bool changes;
>> +
>> + do {
>> + changes = false;
>> + list_for_each_entry_safe(loop_variable, var,
>> + &state->process_list, process_link) {
>> +
>> + if (var->nir_loop_var->in_conditional_block ||
>> + var->nir_loop_var->in_nested_loop) {
>> + LIST_DEL(&var->process_link);
>> + continue;
>> + }
>> +
>> + if (is_ssa_def_invariant(var->nir_loop_var->def, state)) {
>> + LIST_DEL(&var->process_link);
>> + changes = true;
>> + }
>> + }
>> + } while (changes);
>> +}
>> +
>> +static inline bool
>> +is_var_basic_induction_var(loop_variable *var, loop_info_state *state)
>> +{
>> + if (var->nir_loop_var->type == basic_induction)
>> + return true;
>> +
>> + /* We are only interested in checking phi's for the basic induction
>> + * variable case as its simple to detect. All basic induction
>> variables
>> + * have a phi node
>> + */
>> + if (!is_var_phi(var))
>> + return false;
>> +
>> + nir_phi_instr *phi =
>> nir_instr_as_phi(var->nir_loop_var->def->parent_instr);
>> +
>> + nir_basic_induction_var *biv = rzalloc(state,
>> nir_basic_induction_var);
>> + biv->phi = var->nir_loop_var;
>> +
>> + nir_foreach_phi_src(src, phi) {
>> + loop_variable *src_var = get_loop_var(src->src.ssa, state);
>> +
>> + /* If one of the sources is in a conditional or nested block then
>> panic.
>> + */
>> + if (src_var->nir_loop_var->in_conditional_block ||
>> + src_var->nir_loop_var->in_nested_loop)
>> + break;
>> +
>> + if (!src_var->in_loop)
>> + biv->def_outside_loop = src_var->nir_loop_var;
>
>
> Could we assert biv->def_outside_loop == NULL
>
>>
>> +
>> + if (src_var->in_loop && is_var_alu(src_var)) {
>> + nir_alu_instr *alu =
>> + nir_instr_as_alu(src_var->nir_loop_var->def->parent_instr);
>> +
>> + switch (alu->op) {
>> + case nir_op_fadd: case nir_op_iadd: case
>> nir_op_uadd_carry:
>> + case nir_op_fsub: case nir_op_isub: case
>> nir_op_usub_borrow:
>> + case nir_op_fmul: case nir_op_imul: case nir_op_umul_high:
>> + case nir_op_fdiv: case nir_op_idiv: case nir_op_udiv:
>
>
> Is there a reason why this is an explicit list and not simply
> "nir_op_infos[alu->op].num_inputs == 2"?
>
>>
>> +
>> + biv->alu_def = src_var->nir_loop_var;
>> +
>> + for (unsigned i = 0; i < 2; i++) {
>> + /* Is one of the operands invariant, and the other the phi
>> */
>> + if (is_ssa_def_invariant(alu->src[i].src.ssa, state) &&
>> + alu->src[1-i].src.ssa->index == phi->dest.ssa.index)
>> + biv->invariant = get_nir_loop_var(alu->src[i].src.ssa,
>> + state);
>> + }
>> +
>> + biv->alu_op = alu->op;
>> + break;
>> + default:
>> + break;
>> + }
>> + }
>> + }
>> +
>> + if (biv->alu_def && biv->def_outside_loop && biv->invariant &&
>> biv->phi) {
>> + biv->alu_def->type = basic_induction;
>> + biv->phi->type = basic_induction;
>> + _mesa_hash_table_insert(state->var_to_basic_ind, biv->alu_def,
>> biv);
>> + _mesa_hash_table_insert(state->var_to_basic_ind, biv->phi, biv);
>> + return true;
>> + }
>> +
>> + /* The requirements for a basic induction variable are not fulfilled
>> */
>> + ralloc_free(biv);
>> + return false;
>> +}
>> +
>> +static bool
>> +compute_induction_information(loop_info_state *state)
>> +{
>> + bool changes;
>> + bool found_induction_var = false;
>> +
>> + do {
>> + changes = false;
>> + list_for_each_entry_safe(loop_variable, var,
>> + &state->process_list, process_link) {
>> +
>> + /* It can't be an induction variable if it is invariant. We
>> don't
>> + * want to deal with things in nested loops or conditionals.
>> + */
>> + if (var->nir_loop_var->type == invariant ||
>> + var->nir_loop_var->in_conditional_block ||
>> + var->nir_loop_var->in_nested_loop) {
>> + LIST_DEL(&(var->process_link));
>> + continue;
>> + }
>> +
>> + if (is_var_basic_induction_var(var, state)) {
>> + /* If a phi is marked basic_ind we also mark the alu_def
>> basic_ind
>> + * at the same time. It will then be detected as basic_ind
>> here,
>> + * on the second passing, and be removed from the list.
>> + */
>> + LIST_DEL(&(var->process_link));
>> + changes = true;
>> + found_induction_var = true;
>> + }
>> + }
>> + } while (changes);
>> +
>> + return found_induction_var;
>> +}
>> +
>> +static bool
>> +initialize_ssa_def(nir_ssa_def *def, void *void_state)
>> +{
>> + loop_info_state *state = void_state;
>> + loop_variable *var = get_loop_var(def, state);
>> +
>> + var->nir_loop_var = get_nir_loop_var(def, state);
>> +
>> + var->in_loop = false;
>> + var->nir_loop_var->def = def;
>> +
>> + if (def->parent_instr->type == nir_instr_type_load_const) {
>> + var->nir_loop_var->type = invariant;
>> + var->nir_loop_var->is_constant = true;
>> + } else {
>> + var->nir_loop_var->type = undefined;
>> + }
>> +
>> + return true;
>> +}
>> +
>> +static bool
>> +foreach_cf_node_ex_loop(nir_cf_node *node, void *state)
>
>
> There's no good reason for this to be a void *; it just leads to extra
> casting. Also, this function could use a better name. Maybe
> cf_node_find_loop_jumps?
>
>>
>> +{
>> + nir_block *block;
>> +
>> + switch (node->type) {
>> + case nir_cf_node_block:
>> + block = nir_cf_node_as_block(node);
>> + nir_foreach_instr(instr, block) {
>
>
> Jumps are always the last instruction in a block. There's no sense in
> walking all of them just to find the jump. Use nir_block_last_instr()
> instead.
>
>>
>> + if (instr->type == nir_instr_type_jump) {
>> + if (nir_instr_as_jump(instr)->type == nir_jump_break) {
>> + ((loop_jumps *) state)->contains_break = true;
>> + } else if (nir_instr_as_jump(instr)->type ==
>> nir_jump_continue) {
>> + ((loop_jumps *) state)->contains_continue = true;
>> + }
>> + }
>> + }
>> + return true;
>> +
>> + case nir_cf_node_if: {
>> + nir_if *if_stmt = nir_cf_node_as_if(node);
>> +
>> + foreach_list_typed_safe(nir_cf_node, node, node,
>> &if_stmt->then_list)
>> + if (!foreach_cf_node_ex_loop(node, state))
>> + return false;
>> +
>> + foreach_list_typed_safe(nir_cf_node, node, node,
>> &if_stmt->else_list)
>> + if (!foreach_cf_node_ex_loop(node, state))
>> + return false;
>> +
>> + break;
>> + }
>
>
> Maybe add an explicit case for nir_cf_node_loop with a comment that we don't
> care about inner loops.
>
>>
>> +
>> + default:
>> + break;
>> + }
>> +
>> + return false;
>> +}
>> +
>> +static bool
>> +is_trivial_loop_terminator(nir_if *nif)
>> +{
>> + /* If there is stuff in the else-block that means that this is not a
>> + * simple break on true if-statement and so we bail
>> + */
>> + foreach_list_typed_safe(nir_cf_node, node, node, &nif->else_list)
>> + if (node->type == nir_cf_node_block)
>> + nir_foreach_instr(instr, nir_cf_node_as_block(node))
>> + return false;
>
>
> How about "if (!exec_list_empty(&nif->else_list)) return false;"? That
> seems far simpler.
That won't work, since cf lists are never empty. I think the intent
was to check that the else branch consists of one empty basic block,
in which case it's broken -- it could have just a loop, for example,
and we wouldn't return false. I think what you want to do is get the
first node, cast it to a basic block, bail if it has any instructions,
and then bail if it doesn't equal the last node.
>
>>
>> +
>> + nir_cf_node *first_then = nir_if_first_then_node(nif);
>> + nir_block *first_then_block = nir_cf_node_as_block(first_then);
>> + nir_instr *first_instr = nir_block_first_instr(first_then_block);
>> +
>> + if (first_instr && first_instr->type == nir_instr_type_jump &&
>> + nir_instr_as_jump(first_instr)->type == nir_jump_break) {
>> + return true;
>> + }
>> +
>> + return false;
>> +}
>> +
>> +static bool
>> +find_loop_terminators(loop_info_state *state)
>> +{
>> + bool success = false;
>> + foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
>> + if (node->type == nir_cf_node_if) {
>> + nir_if *nif = nir_cf_node_as_if(node);
>> +
>> + /* Don't check the nested loops if there are breaks */
>> + loop_jumps lj;
>> + lj.contains_break = false;
>> + lj.contains_continue = false;
>> +
>> + foreach_cf_node_ex_loop(&nif->cf_node, &lj);
>> +
>> + if (lj.contains_continue)
>> + return false;
>> +
>> + if (!lj.contains_break)
>> + continue;
>> +
>> + /* If there is a break then we should find a terminator. If we
>> can
>> + * not find a loop terminator, but there is a break-statement
>> then
>> + * we should return false so that we do not try to find
>> trip-count
>> + */
>> + if (!is_trivial_loop_terminator(nif))
>> + return false;
>> +
>> + if (nif->condition.ssa->parent_instr->type ==
>> nir_instr_type_phi)
>> + return false;
>> +
>> + nir_loop_terminator *terminator =
>> + rzalloc(state->info, nir_loop_terminator);
>> +
>> + list_add(&terminator->loop_terminator_link,
>> + &state->info->loop_terminator_list);
>> +
>> + terminator->nif = nif;
>> + terminator->conditional_instr =
>> nif->condition.ssa->parent_instr;
>> +
>> + success = true;
>> + }
>> + }
>> +
>> + return success;
>> +}
>> +
>> +static nir_basic_induction_var *
>> +get_basic_ind_var_for_loop_var(loop_variable *var, loop_info_state
>> *state)
>> +{
>> + assert(var->nir_loop_var->type == basic_induction);
>> +
>> + struct hash_entry *entry =
>> + _mesa_hash_table_search(state->var_to_basic_ind,
>> var->nir_loop_var);
>> +
>> + return entry->data;
>> +}
>> +
>> +static int32_t
>> +get_iteration(nir_op cond_op, nir_const_value *initial, nir_const_value
>> *step,
>> + nir_const_value *limit, nir_alu_instr *alu, int32_t
>> *init_val,
>> + bool increment_before)
>> +{
>> + int32_t iter;
>> +
>> + switch (cond_op) {
>> + case nir_op_ige:
>> + case nir_op_ilt:
>> + case nir_op_ieq:
>> + case nir_op_ine: {
>> + int32_t initial_val = initial->i32[0];
>> + if (increment_before) {
>> + initial_val = alu->op == nir_op_iadd ?
>> + initial_val + step->i32[0] : initial_val - step->i32[0];
>> + }
>> +
>> + int32_t span = limit->i32[0] - initial_val;
>> + iter = span / step->i32[0];
>> + *init_val = initial_val;
>> + break;
>> + }
>> + case nir_op_uge:
>> + case nir_op_ult: {
>> + uint32_t initial_val = initial->u32[0];
>> + if (increment_before) {
>> + initial_val = alu->op == nir_op_iadd ?
>> + initial_val + step->u32[0] : initial_val - step->u32[0];
>> + }
>> +
>> + uint32_t span = limit->u32[0] - initial_val;
>> + iter = span / step->u32[0];
>> + *init_val = initial_val;
>> + break;
>> + }
>> + default:
>> + return -1;
>> + }
>> +
>> + return iter;
>> +}
>> +
>> +static uint32_t
>> +utest_interations(int32_t iter_int, nir_const_value *step,
>> + nir_const_value *limit, nir_op cond_op,
>> + uint32_t initial_val, bool limit_rhs)
>> +{
>> + bool valid_loop = false;
>> + uint32_t mul = iter_int * step->u32[0];
>> + uint32_t uadd = mul + initial_val;
>> +
>> + switch (cond_op) {
>> + case nir_op_uge:
>> + valid_loop = limit_rhs ? uadd >= limit->u32[0] : uadd <=
>> limit->u32[0];
>> + break;
>> + case nir_op_ult:
>> + valid_loop = limit_rhs ? uadd < limit->u32[0] : uadd >
>> limit->u32[0];
>> + break;
>> + default:
>> + unreachable("Unhandled loop condition!");
>> + }
>> +
>> + return valid_loop;
>> +}
>> +
>> +static int32_t
>> +itest_interations(int32_t iter_int, nir_const_value *step,
>> + nir_const_value *limit, nir_op cond_op,
>> + int32_t initial_val, bool limit_rhs)
>> +{
>> + bool valid_loop = false;
>> + int32_t mul = iter_int * step->i32[0];
>> + int32_t iadd = mul + initial_val;
>> +
>> + switch (cond_op) {
>> + case nir_op_ige:
>> + valid_loop = limit_rhs ? iadd >= limit->i32[0] : iadd <=
>> limit->i32[0];
>> + break;
>> + case nir_op_ilt:
>> + valid_loop = limit_rhs ? iadd < limit->i32[0] : iadd >
>> limit->i32[0];
>> + break;
>> + case nir_op_ieq:
>> + valid_loop = iadd == limit->i32[0];
>> + break;
>> + case nir_op_ine:
>> + valid_loop = iadd != limit->i32[0];
>> + break;
>> + default:
>> + unreachable("Unhandled loop condition!");
>> + }
>> +
>> + return valid_loop;
>> +}
>> +
>> +static int
>> +calculate_iterations(nir_const_value *initial, nir_const_value *step,
>> + nir_const_value *limit, nir_op cond_op,
>> + nir_loop_variable *alu_def, nir_alu_instr *cond_alu,
>> + bool limit_rhs)
>> +{
>> + assert(initial != NULL && step != NULL && limit != NULL);
>> +
>> + nir_alu_instr *alu = nir_instr_as_alu(alu_def->def->parent_instr);
>> +
>> + /* Unsupported alu operation */
>> + if (!(alu->op == nir_op_iadd || alu->op == nir_op_isub))
>
>
> You only allow iadd and isub except that we lower away isub so you'll never
> see it. Probably best to remove the dead code. Also...
>
> 1) You don't handle swizzles at all
> 2) You don't handle things other than 64 or 16-bit. Those are coming soon;
> they need to be supported.
>
>>
>> + return -1;
>> +
>> + /* do-while loops can increment the starting value before the
>> condition is
>> + * checked. e.g.
>> + *
>> + * do {
>> + * ndx++;
>> + * } while (ndx < 3);
>> + *
>> + * Here we check if the induction variable is used directly by the
>> loop
>> + * condition and if so we assume we need to step the initial value.
>> + */
>> + bool increment_before = false;
>> + if (cond_alu->src[0].src.ssa == alu_def->def ||
>> + cond_alu->src[1].src.ssa == alu_def->def) {
>> + increment_before = true;
>
>
> Is there a reason why this can't be handled as "trip_count + 1"? This seems
> way overcomplicated.
>
>>
>> + }
>> +
>> + int32_t initial_val;
>> + int iter_int = get_iteration(cond_op, initial, step, limit, alu,
>> + &initial_val, increment_before);
>> +
>> + /* If iter_int is negative the loop is ill-formed or is the
>> conditional is
>> + * unsigned with a huge iteration count so don't bother going any
>> further.
>> + */
>> + if (iter_int < 0)
>> + return -1;
>> +
>> + /* An explanation from the GLSL unrolling pass:
>> + *
>> + * Make sure that the calculated number of iterations satisfies the
>> exit
>> + * condition. This is needed to catch off-by-one errors and some
>> types of
>> + * ill-formed loops. For example, we need to detect that the
>> following
>> + * loop does not have a maximum iteration count.
>> + *
>> + * for (float x = 0.0; x != 0.9; x += 0.2);
>> + */
>> + const int bias[] = { -1, 1, 1 };
>> +
>> + for (unsigned i = 0; i < ARRAY_SIZE(bias); i++) {
>> + iter_int = iter_int + bias[i];
>> +
>> + switch (cond_op) {
>> + case nir_op_ige:
>> + case nir_op_ilt:
>> + case nir_op_ieq:
>> + case nir_op_ine:
>> + if (itest_interations(iter_int, step, limit, cond_op,
>> initial_val,
>> + limit_rhs)) {
>> + return iter_int;
>> + }
>> + break;
>> + case nir_op_uge:
>> + case nir_op_ult:
>> + if (utest_interations(iter_int, step, limit, cond_op,
>> + (uint32_t) initial_val, limit_rhs)) {
>> + return iter_int;
>
>
> I think it would be clearer if we combined these two functions.
>
>>
>> + }
>> + break;
>> + default:
>> + return -1;
>> + }
>> + }
>> +
>> + return -1;
>> +}
>> +
>> +/* Run through each of the terminators of the loop and try to infer a
>> possible
>> + * trip-count. We need to check them all, and set the lowest trip-count
>> as the
>> + * trip-count of our loop. If one of the terminators has an undecidable
>> + * trip-count we can not safely assume anything about the duration of the
>> + * loop.
>> + */
>> +static void
>> +find_trip_count(loop_info_state *state)
>> +{
>> + bool trip_count_known = true;
>> + nir_loop_terminator *limiting_terminator = NULL;
>> + int min_trip_count = -2;
>> +
>> + list_for_each_entry(nir_loop_terminator, terminator,
>> + &state->info->loop_terminator_list,
>> + loop_terminator_link) {
>> +
>> + if (terminator->conditional_instr->type != nir_instr_type_alu) {
>> + /* If we get here the loop is likely not really a loop and will
>> get
>> + * cleaned up elsewhere.
>> + */
>
>
> The if statement (and its contents) seem fine but the comment here seems
> sketchy.
>
>>
>> + trip_count_known = false;
>> + continue;
>> + }
>> +
>> + nir_alu_instr *alu =
>> nir_instr_as_alu(terminator->conditional_instr);
>> + loop_variable *basic_ind = NULL;
>> + loop_variable *limit = NULL;
>> + bool limit_rhs = true;
>> + nir_op cond_op;
>> +
>> + switch (alu->op) {
>> + case nir_op_fge: case nir_op_ige: case nir_op_uge:
>> + case nir_op_flt: case nir_op_ilt: case nir_op_ult:
>> + case nir_op_feq: case nir_op_ieq:
>> + case nir_op_fne: case nir_op_ine:
>> +
>> + /* We assume that the limit is the "right" operand */
>> + basic_ind = get_loop_var(alu->src[0].src.ssa, state);
>> + limit = get_loop_var(alu->src[1].src.ssa, state);
>> + cond_op = alu->op;
>> +
>> + if (basic_ind->nir_loop_var->type != basic_induction) {
>> + /* We had it the wrong way, flip things around */
>> + basic_ind = get_loop_var(alu->src[1].src.ssa, state);
>> + limit = get_loop_var(alu->src[0].src.ssa, state);
>> + limit_rhs = false;
>> + }
>> +
>> + /* The comparison has to have a basic induction variable
>> + * and a constant for us to be able to find trip counts
>> + */
>> + if (basic_ind->nir_loop_var->type != basic_induction ||
>> + !limit->nir_loop_var->is_constant) {
>> + trip_count_known = false;
>> + continue;
>> + }
>> +
>> + nir_basic_induction_var *ind =
>> + get_basic_ind_var_for_loop_var(basic_ind, state);
>> +
>> + if (!ind->def_outside_loop->is_constant ||
>> + !ind->invariant->is_constant) {
>> + trip_count_known = false;
>> + continue;
>> + }
>> +
>> + /* We have determined that we have the following constants:
>> + * (With the typical int i = 0; i < x; i++; as an example)
>> + * - Upper limit.
>> + * - Starting value
>> + * - Step / iteration size
>> + * Thats all thats needed to calculate the trip-count
>> + */
>> +
>> + nir_load_const_instr *initial_instr =
>> + nir_instr_as_load_const(
>> + ind->def_outside_loop->def->parent_instr);
>> +
>> + nir_const_value initial_val = initial_instr->value;
>> +
>> + nir_load_const_instr *step_instr =
>> + nir_instr_as_load_const(
>> + ind->invariant->def->parent_instr);
>> +
>> + nir_const_value step_val = step_instr->value;
>> +
>> + nir_load_const_instr *limit_instr =
>> + nir_instr_as_load_const(
>> + limit->nir_loop_var->def->parent_instr);
>> +
>> + nir_const_value limit_val = limit_instr->value;
>> +
>> + int iterations = calculate_iterations(&initial_val, &step_val,
>> + &limit_val, cond_op,
>> + ind->alu_def, alu,
>> limit_rhs);
>> +
>> + /* Where we not able to calculate the iteration count */
>> + if (iterations == -1) {
>> + trip_count_known = false;
>> + continue;
>> + }
>> +
>> + /* If this is the first run or we have found a smaller amount of
>> + * iterations than previously (we have identified a more
>> limiting
>> + * terminator) set the trip count and limiting terminator.
>> + */
>> + if (min_trip_count == -2 || iterations < min_trip_count) {
>
>
> Can we have a #define for -2 so that it has a name.
>
>>
>> + min_trip_count = iterations;
>> + limiting_terminator = terminator;
>> + }
>> + break;
>> +
>> + default:
>> + trip_count_known = false;
>> + }
>> + }
>> +
>> + state->info->is_trip_count_known = trip_count_known;
>> + if (min_trip_count > -2)
>> + state->info->trip_count = min_trip_count;
>> + state->info->limiting_terminator = limiting_terminator;
>> +}
>> +
>> +/* Checks if we should force the loop to be unrolled regardless of size
>> */
>> +static bool
>> +force_unroll(loop_info_state *state, nir_shader *ns, nir_deref_var
>> *variable)
>> +{
>> + nir_deref *tail = &variable->deref;
>> +
>> + while (tail->child != NULL) {
>> + tail = tail->child;
>> +
>> + if (tail->deref_type == nir_deref_type_array) {
>> +
>> + nir_deref_array *deref_array = nir_deref_as_array(tail);
>> + if (deref_array->deref_array_type !=
>> nir_deref_array_type_indirect)
>> + continue;
>> +
>> + nir_loop_variable *array_index =
>> + get_nir_loop_var(deref_array->indirect.ssa, state);
>> +
>> + if (array_index->type != basic_induction)
>> + continue;
>> +
>> + /* If an array is indexed by a loop induction variable, and the
>> + * array size is exactly the number of loop iterations, this is
>> + * probably a simple for-loop trying to access each element in
>> + * turn; the application may expect it to be unrolled.
>> + */
>> + if (glsl_get_length(tail->type) == state->info->trip_count) {
>> + state->info->force_unroll = true;
>> + return state->info->force_unroll;
>> + }
>> +
>> + if (variable->var->data.mode & state->indirect_mask) {
>> + state->info->force_unroll = true;
>> + return state->info->force_unroll;
>> + }
>
>
> Thinking a bit about analysis vs. lowering...
>
> I wonder if it wouldn't be better to make the loop anlaysis pass be a bit
> more informational and less decision making. For instance, it could record
> what all variable modes it has seen be indexed by an induction variable and
> let the pass using the analysis decide whether or not to force-unroll. For
> that matter, it could just produce a hash map from induction variables to
> the loop for which they are an induction variable. You could also just
> record the trip count per-loop. That all seems a bit more like things an
> analysis pass would do than just setting a force_unroll bit.
>
> Please don't feel like you need to make any changes in this direction yet.
> I'm mostly trying to open the discussion up a bit and feel out exactly how
> we want things to be structured.
>
> I think I've written you a long enough book for now. I'll try to look at
> the others as I get time.
>
> --Jason
>
>>
>> + }
>> + }
>> +
>> + return false;
>> +}
>> +
>> +static bool
>> +count_instructions(loop_info_state *state, nir_shader *ns, nir_block
>> *block)
>> +{
>> + nir_foreach_instr(instr, block) {
>> + if (instr->type == nir_instr_type_intrinsic ||
>> + instr->type == nir_instr_type_alu) {
>> + state->info->num_instructions++;
>> + }
>> +
>> + if (instr->type != nir_instr_type_intrinsic)
>> + continue;
>> +
>> + nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
>> +
>> + /* Check for arrays variably-indexed by a loop induction variable.
>> + * Unrolling the loop may convert that access into
>> constant-indexing.
>> + */
>> + if (intrin->intrinsic == nir_intrinsic_load_var ||
>> + intrin->intrinsic == nir_intrinsic_store_var ||
>> + intrin->intrinsic == nir_intrinsic_copy_var) {
>> + unsigned num_vars =
>> + nir_intrinsic_infos[intrin->intrinsic].num_variables;
>> + for (unsigned i = 0; i < num_vars; i++) {
>> + if (force_unroll(state, ns, intrin->variables[i]))
>> + return true;
>> + }
>> + }
>> + }
>> +
>> + return false;
>> +}
>> +
>> +static void
>> +get_loop_info(loop_info_state *state, nir_function_impl *impl)
>> +{
>> + /* Initialize all variables to "outside_loop". This also marks defs
>> + * invariant and constant if they are nir_instr_type_load_const's
>> + */
>> + nir_foreach_block(block, impl) {
>> + nir_foreach_instr(instr, block)
>> + nir_foreach_ssa_def(instr, initialize_ssa_def, state);
>> + }
>> +
>> + init_loop_state init_state = {.mark_in_conditional = false,
>> + .mark_nested = false, .state = state };
>> +
>> + /* Add all entries in the outermost part of the loop to the processing
>> list
>> + * Mark the entries in conditionals or in nested loops accordingly
>> + */
>> + foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
>> + switch (node->type) {
>> +
>> + case nir_cf_node_block:
>> + init_state.mark_in_conditional = false;
>> + init_state.mark_nested = false;
>> + init_loop_block(nir_cf_node_as_block(node), &init_state);
>> + break;
>> +
>> + case nir_cf_node_if:
>> + init_state.mark_in_conditional = true;
>> + init_state.mark_nested = false;
>> + nir_foreach_block_in_cf_node(block, node)
>> + init_loop_block(block, &init_state);
>> + break;
>> +
>> + case nir_cf_node_loop:
>> + init_state.mark_in_conditional = false;
>> + init_state.mark_nested = true;
>> + nir_foreach_block_in_cf_node(block, node) {
>> + init_loop_block(block, &init_state);
>> + }
>> + break;
>> +
>> + case nir_cf_node_function:
>> + break;
>> + }
>> + }
>> +
>> + /* Induction analysis needs invariance information so get that first
>> */
>> + compute_invariance_information(state);
>> +
>> + /* We may now have filled the process_list with instructions from
>> inside
>> + * the nested blocks in the loop. Remove all instructions from the
>> list
>> + * nir_foreach_block_in_cf_node before we start computing induction
>> + * information.
>> + */
>> + list_inithead(&state->process_list);
>> +
>> + /* Add all entries in the outermost part of the loop to the processing
>> list.
>> + * Don't include defs inn nested loops or in conditionals.
>> + */
>> + init_state.mark_in_conditional = false;
>> + init_state.mark_nested = false;
>> +
>> + foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body)
>> + if (node->type == nir_cf_node_block)
>> + init_loop_block(nir_cf_node_as_block(node), &init_state);
>> +
>> + /* We have invariance information so try to find induction variables
>> */
>> + if (!compute_induction_information(state))
>> + return;
>> +
>> + /* Try to find all simple terminators of the loop. If we can't find
>> any,
>> + * or we find possible terminators that have side effects then bail.
>> + */
>> + if (!find_loop_terminators(state))
>> + return;
>> +
>> + /* Run through each of the terminators and try to compute a trip-count
>> */
>> + find_trip_count(state);
>> +
>> + nir_shader *ns = impl->function->shader;
>> + foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
>> + if (node->type == nir_cf_node_block) {
>> + if (count_instructions(state, ns, nir_cf_node_as_block(node)))
>> + break;
>> + } else {
>> + nir_foreach_block_in_cf_node(block, node) {
>> + if (count_instructions(state, ns, block))
>> + break;
>> + }
>> + }
>> + }
>> +}
>> +
>> +static loop_info_state *
>> +initialize_loop_info_state(nir_loop *loop, void *mem_ctx,
>> nir_function_impl *impl)
>> +{
>> + loop_info_state *state = rzalloc(mem_ctx, loop_info_state);
>> + state->loop_vars = rzalloc_array(mem_ctx, loop_variable,
>> impl->ssa_alloc);
>> + state->loop = loop;
>> + state->nir_loop_vars = rzalloc_array(mem_ctx, nir_loop_variable,
>> + impl->ssa_alloc);
>> +
>> + LIST_INITHEAD(&state->process_list);
>> +
>> + if (loop->info)
>> + ralloc_free(loop->info);
>> +
>> + state->info = rzalloc(loop, nir_loop_info);
>> +
>> + LIST_INITHEAD(&state->info->loop_terminator_list);
>> +
>> + state->var_to_basic_ind =
>> + _mesa_hash_table_create(state->info, _mesa_hash_pointer,
>> + _mesa_key_pointer_equal);
>> +
>> + return state;
>> +}
>> +
>> +static void
>> +process_loops(nir_cf_node *cf_node, nir_variable_mode indirect_mask)
>> +{
>> + switch (cf_node->type) {
>> + case nir_cf_node_block:
>> + 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)
>> + process_loops(nested_node, indirect_mask);
>> + foreach_list_typed(nir_cf_node, nested_node, node,
>> &if_stmt->else_list)
>> + process_loops(nested_node, indirect_mask);
>> + return;
>> + }
>> + case nir_cf_node_loop: {
>> + nir_loop *loop = nir_cf_node_as_loop(cf_node);
>> + foreach_list_typed(nir_cf_node, nested_node, node, &loop->body)
>> + process_loops(nested_node, indirect_mask);
>> + break;
>> + }
>> + default:
>> + unreachable("unknown cf node type");
>> + }
>> +
>> + nir_loop *loop = nir_cf_node_as_loop(cf_node);
>> + nir_function_impl *impl = nir_cf_node_get_function(cf_node);
>> + void *mem_ctx = ralloc_context(NULL);
>> +
>> + loop_info_state *state = initialize_loop_info_state(loop, mem_ctx,
>> impl);
>> + state->indirect_mask = indirect_mask;
>> +
>> + get_loop_info(state, impl);
>> +
>> + loop->info = state->info;
>> +
>> + ralloc_free(mem_ctx);
>> +}
>> +
>> +void
>> +nir_loop_analyze_impl(nir_function_impl *impl,
>> + nir_variable_mode indirect_mask)
>> +{
>> + if (impl->function->shader->options->max_unroll_iterations == 0)
>> + return;
>> +
>> + nir_index_ssa_defs(impl);
>> + foreach_list_typed(nir_cf_node, node, node, &impl->body)
>> + process_loops(node, indirect_mask);
>> +}
>> diff --git a/src/compiler/nir/nir_metadata.c
>> b/src/compiler/nir/nir_metadata.c
>> index 9e1cff5..f71cf43 100644
>> --- a/src/compiler/nir/nir_metadata.c
>> +++ b/src/compiler/nir/nir_metadata.c
>> @@ -31,7 +31,7 @@
>> */
>>
>> void
>> -nir_metadata_require(nir_function_impl *impl, nir_metadata required)
>> +nir_metadata_require(nir_function_impl *impl, nir_metadata required, ...)
>> {
>> #define NEEDS_UPDATE(X) ((required & ~impl->valid_metadata) & (X))
>>
>> @@ -41,6 +41,12 @@ nir_metadata_require(nir_function_impl *impl,
>> nir_metadata required)
>> nir_calc_dominance_impl(impl);
>> if (NEEDS_UPDATE(nir_metadata_live_ssa_defs))
>> nir_live_ssa_defs_impl(impl);
>> + if (NEEDS_UPDATE(nir_metadata_loop_analysis)) {
>> + va_list ap;
>> + va_start(ap, required);
>> + nir_loop_analyze_impl(impl, va_arg(ap, nir_variable_mode));
>> + va_end(ap);
>> + }
>>
>> #undef NEEDS_UPDATE
>>
>> --
>> 2.7.4
>>
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
>
>
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> mesa-dev@lists.freedesktop.org
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