I sent this reply on Saturday however is seems something went wrong and
it didn't make it out so here it is again.
On Fri, 2016-09-16 at 15:25 -0700, Jason Ekstrand wrote:
> On Thu, Sep 15, 2016 at 12:03 AM, Timothy Arceri <timothy.arceri@coll
> abora.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?
No really sure. There is other stuff I've removed from this pass Thomas
may have had other ideas for this or just never cleaned it up. Will see
if I can combine them.
>
> > +
> > + /* 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.
Sure.
>
> > +} 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.
Sure.
>
> > +{
> > + 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"?
No sure. This is just they way Thomas did it. If that makes sense also
I'll make the change.
>
> > +
> > + 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.
>
> > +
> > + 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...
ok thats interesting, out of interest why do we do that? And in what
pass is this done? Also I think I should probably add support for other
ops I believe I've seen shaders that use either / or * possibly both.
>
> 1) You don't handle swizzles at all
I recall there being a TODO for this originally. Probably a dumb
question but can you give a small shader example? I wasn't sure what I
need to handle exactly.
> 2) You don't handle things other than 64 or 16-bit. Those are
> coming soon; they need to be supported.
Do we need this for the initial implementation though?
>
> > + 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.
It would we trip_count - 1 but yes we should be able to do that.
>
> > + }
> > +
> > + 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.
I started out trying to do that but ended up at this. I think my
concern was that the initial value could be negative so we need to
handle that somehow. This seemed slightly nicer than doing "int32_t
iadd = mul + initial_val;" in each struct case.
>
> > + }
> > + 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.
I think I was seeing things like this get cleaned up by the dead cf
pass.
>
> > + 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.
Seems reasonable.
> For that matter, it could just produce a hash map from induction
> variables to the loop for which they are an induction variable.
I guess so but the above suggestion seems simpler.
> You could also just record the trip count per-loop.
No sure what you mean as we do this already.
> 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.
Thanks for taking a look.
>
> --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
> >
>
> _______________________________________________
> mesa-dev mailing list
> mesa-dev@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
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