[Mesa-dev] [PATCH 03/13] nir: Add a loop analysis pass
Timothy Arceri
timothy.arceri at collabora.com
Mon Aug 29 04:59:11 UTC 2016
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.
- find induction var when copy propagation disabled
- fix iteration count bugs when induction var not on RHS of condition
- add FIXME for && conditions
- calculate trip count for unsigned induction/limit vars
---
src/compiler/Makefile.sources | 2 +
src/compiler/nir/nir.h | 77 +++
src/compiler/nir/nir_loop_analyze.c | 924 ++++++++++++++++++++++++++++++++++++
3 files changed, 1003 insertions(+)
create mode 100644 src/compiler/nir/nir_loop_analyze.c
diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
index edd683a..686e8a6 100644
--- a/src/compiler/Makefile.sources
+++ b/src/compiler/Makefile.sources
@@ -188,6 +188,8 @@ 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 7ff5394..491859e 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -1548,10 +1548,80 @@ nir_if_last_else_node(nir_if *if_stmt)
return exec_node_data(nir_cf_node, tail, node);
}
+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;
+
+ /* Link to the loop_variable list for the loop */
+ struct list_head loop_vars_link;
+
+ /* A link for a list of invariant variables */
+ struct list_head invariant_link;
+
+ /* A link for a list of induction variables */
+ struct list_head induction_link;
+
+ /* 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 {
+ nir_if *nif;
+
+ nir_instr *conditional_instr;
+
+ struct list_head loop_terminator_link;
+} nir_loop_terminator;
+
+typedef struct {
+ /* Loop_variable for all ssa_defs in loop */
+ struct list_head loop_vars_list;
+
+ /* How many times the loop is run (if known) */
+ uint32_t trip_count;
+ bool is_trip_count_known;
+
+ nir_loop_terminator *limiting_terminator;
+
+ /* A list of loop_terminators terminating this loop.
+ * XXX: These (apart from the limiting terminator) can be dead-code
+ * eliminated.
+ */
+ struct list_head loop_terminator_list;
+
+ /* The ssa_defs that are invariant */
+ struct list_head invariant_list;
+
+ struct hash_table *var_to_basic_ind;
+} 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 +1646,7 @@ 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 +1829,8 @@ 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 {
@@ -2553,6 +2626,10 @@ 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);
+void nir_loop_analyze(nir_shader *shader);
+
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..fc6464e
--- /dev/null
+++ b/src/compiler/nir/nir_loop_analyze.c
@@ -0,0 +1,924 @@
+/*
+ * 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 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;
+
+ /* A list of the loop_vars to analyze */
+ struct list_head process_list;
+
+ nir_loop_info *info;
+} 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));
+
+ 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)
+{
+ 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;
+
+ /* We disable copy propagation inside loops to simplify unrolling so
+ * follow moves when looking for induction variable.
+ */
+ bool copy_prop;
+ nir_alu_instr *alu = NULL;
+ do {
+ copy_prop = false;
+ if (!src_var->in_loop)
+ biv->def_outside_loop = src_var->nir_loop_var;
+
+ if (src_var->in_loop && is_var_alu(src_var) &&
+ !src_var->nir_loop_var->in_nested_loop &&
+ !src_var->nir_loop_var->in_conditional_block) {
+
+ alu = nir_instr_as_alu(src_var->nir_loop_var->def->parent_instr);
+
+ if (alu->op == nir_op_imov || alu->op == nir_op_fmov) {
+ src_var = get_loop_var(alu->src[0].src.ssa, state);
+ copy_prop = true;
+ }
+ }
+ } while (copy_prop);
+
+
+ if (src_var->in_loop && is_var_alu(src_var) &&
+ !src_var->nir_loop_var->in_nested_loop &&
+ !src_var->nir_loop_var->in_conditional_block) {
+ 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:
+
+ 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->info->var_to_basic_ind, biv->alu_def, biv);
+ _mesa_hash_table_insert(state->info->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)
+{
+ nir_block *block;
+
+ switch (node->type) {
+ case nir_cf_node_block:
+ block = nir_cf_node_as_block(node);
+ nir_foreach_instr(instr, block) {
+ 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;
+ }
+
+ 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;
+
+ 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->loop, 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->info->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)
+{
+ /* Superfluous assert */
+ 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))
+ 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;
+
+ 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;
+ }
+ 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)
+{
+ state->info->is_trip_count_known = false;
+ 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.
+ */
+ return;
+ }
+
+ 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;
+
+ /* FIXME: We should also be able to handle nir_op_iand for example
+ * if ((i >= minLights) && (i >= lightProps_count)) break;
+ */
+ 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)
+ return;
+
+ 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)
+ return;
+
+ /* 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);
+
+ /* If this is the first run then overwrite the value */
+ if (min_trip_count == -2)
+ min_trip_count = iterations;
+
+ /* Where we not able to calculate the iterations? */
+ if (iterations == -1)
+ return;
+
+ /* If we have found a smaller amount of iterations than previously
+ * that means we have identified a more limiting terminator
+ */
+ if (iterations < min_trip_count) {
+ min_trip_count = iterations;
+ limiting_terminator = terminator;
+ }
+ break;
+
+ default:
+ return;
+ }
+ }
+
+ state->info->is_trip_count_known = true;
+ state->info->trip_count = min_trip_count;
+ state->info->limiting_terminator = limiting_terminator;
+}
+
+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);
+}
+
+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);
+ LIST_INITHEAD(&state->info->loop_vars_list);
+
+ state->info->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)
+{
+ 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);
+ foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->else_list)
+ process_loops(nested_node);
+ 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);
+ 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);
+
+ get_loop_info(state, impl);
+
+ loop->info = state->info;
+
+ for (int i = 0; i < impl->ssa_alloc; i++) {
+ loop_variable *var = &state->loop_vars[i];
+ list_add(&var->nir_loop_var->loop_vars_link, &loop->info->loop_vars_list);
+ }
+
+ ralloc_free(mem_ctx);
+}
+
+void
+nir_loop_analyze_impl(nir_function_impl *impl)
+{
+ 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);
+}
+
+void
+nir_loop_analyze(nir_shader *shader)
+{
+ nir_foreach_function(func, shader) {
+ if (func->impl) {
+ nir_loop_analyze_impl(func->impl);
+ }
+ }
+}
--
2.7.4
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