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Diffstat (limited to 'mesalib/src/util/register_allocate.c')
| -rw-r--r-- | mesalib/src/util/register_allocate.c | 654 |
1 files changed, 654 insertions, 0 deletions
diff --git a/mesalib/src/util/register_allocate.c b/mesalib/src/util/register_allocate.c new file mode 100644 index 000000000..afab9ddd3 --- /dev/null +++ b/mesalib/src/util/register_allocate.c @@ -0,0 +1,654 @@ +/* + * Copyright © 2010 Intel Corporation + * + * 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. + * + * Authors: + * Eric Anholt <eric@anholt.net> + * + */ + +/** @file register_allocate.c + * + * Graph-coloring register allocator. + * + * The basic idea of graph coloring is to make a node in a graph for + * every thing that needs a register (color) number assigned, and make + * edges in the graph between nodes that interfere (can't be allocated + * to the same register at the same time). + * + * During the "simplify" process, any any node with fewer edges than + * there are registers means that that edge can get assigned a + * register regardless of what its neighbors choose, so that node is + * pushed on a stack and removed (with its edges) from the graph. + * That likely causes other nodes to become trivially colorable as well. + * + * Then during the "select" process, nodes are popped off of that + * stack, their edges restored, and assigned a color different from + * their neighbors. Because they were pushed on the stack only when + * they were trivially colorable, any color chosen won't interfere + * with the registers to be popped later. + * + * The downside to most graph coloring is that real hardware often has + * limitations, like registers that need to be allocated to a node in + * pairs, or aligned on some boundary. This implementation follows + * the paper "Retargetable Graph-Coloring Register Allocation for + * Irregular Architectures" by Johan Runeson and Sven-Olof Nyström. + * + * In this system, there are register classes each containing various + * registers, and registers may interfere with other registers. For + * example, one might have a class of base registers, and a class of + * aligned register pairs that would each interfere with their pair of + * the base registers. Each node has a register class it needs to be + * assigned to. Define p(B) to be the size of register class B, and + * q(B,C) to be the number of registers in B that the worst choice + * register in C could conflict with. Then, this system replaces the + * basic graph coloring test of "fewer edges from this node than there + * are registers" with "For this node of class B, the sum of q(B,C) + * for each neighbor node of class C is less than pB". + * + * A nice feature of the pq test is that q(B,C) can be computed once + * up front and stored in a 2-dimensional array, so that the cost of + * coloring a node is constant with the number of registers. We do + * this during ra_set_finalize(). + */ + +#include <stdbool.h> + +#include "ralloc.h" +#include "main/imports.h" +#include "main/macros.h" +#include "main/mtypes.h" +#include "main/bitset.h" +#include "register_allocate.h" + +#define NO_REG ~0 + +struct ra_reg { + BITSET_WORD *conflicts; + unsigned int *conflict_list; + unsigned int conflict_list_size; + unsigned int num_conflicts; +}; + +struct ra_regs { + struct ra_reg *regs; + unsigned int count; + + struct ra_class **classes; + unsigned int class_count; + + bool round_robin; +}; + +struct ra_class { + /** + * Bitset indicating which registers belong to this class. + * + * (If bit N is set, then register N belongs to this class.) + */ + BITSET_WORD *regs; + + /** + * p(B) in Runeson/Nyström paper. + * + * This is "how many regs are in the set." + */ + unsigned int p; + + /** + * q(B,C) (indexed by C, B is this register class) in + * Runeson/Nyström paper. This is "how many registers of B could + * the worst choice register from C conflict with". + */ + unsigned int *q; +}; + +struct ra_node { + /** @{ + * + * List of which nodes this node interferes with. This should be + * symmetric with the other node. + */ + BITSET_WORD *adjacency; + unsigned int *adjacency_list; + unsigned int adjacency_list_size; + unsigned int adjacency_count; + /** @} */ + + unsigned int class; + + /* Register, if assigned, or NO_REG. */ + unsigned int reg; + + /** + * Set when the node is in the trivially colorable stack. When + * set, the adjacency to this node is ignored, to implement the + * "remove the edge from the graph" in simplification without + * having to actually modify the adjacency_list. + */ + bool in_stack; + + /** + * The q total, as defined in the Runeson/Nyström paper, for all the + * interfering nodes not in the stack. + */ + unsigned int q_total; + + /* For an implementation that needs register spilling, this is the + * approximate cost of spilling this node. + */ + float spill_cost; +}; + +struct ra_graph { + struct ra_regs *regs; + /** + * the variables that need register allocation. + */ + struct ra_node *nodes; + unsigned int count; /**< count of nodes. */ + + unsigned int *stack; + unsigned int stack_count; +}; + +/** + * Creates a set of registers for the allocator. + * + * mem_ctx is a ralloc context for the allocator. The reg set may be freed + * using ralloc_free(). + */ +struct ra_regs * +ra_alloc_reg_set(void *mem_ctx, unsigned int count) +{ + unsigned int i; + struct ra_regs *regs; + + regs = rzalloc(mem_ctx, struct ra_regs); + regs->count = count; + regs->regs = rzalloc_array(regs, struct ra_reg, count); + + for (i = 0; i < count; i++) { + regs->regs[i].conflicts = rzalloc_array(regs->regs, BITSET_WORD, + BITSET_WORDS(count)); + BITSET_SET(regs->regs[i].conflicts, i); + + regs->regs[i].conflict_list = ralloc_array(regs->regs, unsigned int, 4); + regs->regs[i].conflict_list_size = 4; + regs->regs[i].conflict_list[0] = i; + regs->regs[i].num_conflicts = 1; + } + + return regs; +} + +/** + * The register allocator by default prefers to allocate low register numbers, + * since it was written for hardware (gen4/5 Intel) that is limited in its + * multithreadedness by the number of registers used in a given shader. + * + * However, for hardware without that restriction, densely packed register + * allocation can put serious constraints on instruction scheduling. This + * function tells the allocator to rotate around the registers if possible as + * it allocates the nodes. + */ +void +ra_set_allocate_round_robin(struct ra_regs *regs) +{ + regs->round_robin = true; +} + +static void +ra_add_conflict_list(struct ra_regs *regs, unsigned int r1, unsigned int r2) +{ + struct ra_reg *reg1 = ®s->regs[r1]; + + if (reg1->conflict_list_size == reg1->num_conflicts) { + reg1->conflict_list_size *= 2; + reg1->conflict_list = reralloc(regs->regs, reg1->conflict_list, + unsigned int, reg1->conflict_list_size); + } + reg1->conflict_list[reg1->num_conflicts++] = r2; + BITSET_SET(reg1->conflicts, r2); +} + +void +ra_add_reg_conflict(struct ra_regs *regs, unsigned int r1, unsigned int r2) +{ + if (!BITSET_TEST(regs->regs[r1].conflicts, r2)) { + ra_add_conflict_list(regs, r1, r2); + ra_add_conflict_list(regs, r2, r1); + } +} + +/** + * Adds a conflict between base_reg and reg, and also between reg and + * anything that base_reg conflicts with. + * + * This can simplify code for setting up multiple register classes + * which are aggregates of some base hardware registers, compared to + * explicitly using ra_add_reg_conflict. + */ +void +ra_add_transitive_reg_conflict(struct ra_regs *regs, + unsigned int base_reg, unsigned int reg) +{ + int i; + + ra_add_reg_conflict(regs, reg, base_reg); + + for (i = 0; i < regs->regs[base_reg].num_conflicts; i++) { + ra_add_reg_conflict(regs, reg, regs->regs[base_reg].conflict_list[i]); + } +} + +unsigned int +ra_alloc_reg_class(struct ra_regs *regs) +{ + struct ra_class *class; + + regs->classes = reralloc(regs->regs, regs->classes, struct ra_class *, + regs->class_count + 1); + + class = rzalloc(regs, struct ra_class); + regs->classes[regs->class_count] = class; + + class->regs = rzalloc_array(class, BITSET_WORD, BITSET_WORDS(regs->count)); + + return regs->class_count++; +} + +void +ra_class_add_reg(struct ra_regs *regs, unsigned int c, unsigned int r) +{ + struct ra_class *class = regs->classes[c]; + + BITSET_SET(class->regs, r); + class->p++; +} + +/** + * Returns true if the register belongs to the given class. + */ +static bool +reg_belongs_to_class(unsigned int r, struct ra_class *c) +{ + return BITSET_TEST(c->regs, r); +} + +/** + * Must be called after all conflicts and register classes have been + * set up and before the register set is used for allocation. + * To avoid costly q value computation, use the q_values paramater + * to pass precomputed q values to this function. + */ +void +ra_set_finalize(struct ra_regs *regs, unsigned int **q_values) +{ + unsigned int b, c; + + for (b = 0; b < regs->class_count; b++) { + regs->classes[b]->q = ralloc_array(regs, unsigned int, regs->class_count); + } + + if (q_values) { + for (b = 0; b < regs->class_count; b++) { + for (c = 0; c < regs->class_count; c++) { + regs->classes[b]->q[c] = q_values[b][c]; + } + } + return; + } + + /* Compute, for each class B and C, how many regs of B an + * allocation to C could conflict with. + */ + for (b = 0; b < regs->class_count; b++) { + for (c = 0; c < regs->class_count; c++) { + unsigned int rc; + int max_conflicts = 0; + + for (rc = 0; rc < regs->count; rc++) { + int conflicts = 0; + int i; + + if (!reg_belongs_to_class(rc, regs->classes[c])) + continue; + + for (i = 0; i < regs->regs[rc].num_conflicts; i++) { + unsigned int rb = regs->regs[rc].conflict_list[i]; + if (BITSET_TEST(regs->classes[b]->regs, rb)) + conflicts++; + } + max_conflicts = MAX2(max_conflicts, conflicts); + } + regs->classes[b]->q[c] = max_conflicts; + } + } +} + +static void +ra_add_node_adjacency(struct ra_graph *g, unsigned int n1, unsigned int n2) +{ + BITSET_SET(g->nodes[n1].adjacency, n2); + + if (n1 != n2) { + int n1_class = g->nodes[n1].class; + int n2_class = g->nodes[n2].class; + g->nodes[n1].q_total += g->regs->classes[n1_class]->q[n2_class]; + } + + if (g->nodes[n1].adjacency_count >= + g->nodes[n1].adjacency_list_size) { + g->nodes[n1].adjacency_list_size *= 2; + g->nodes[n1].adjacency_list = reralloc(g, g->nodes[n1].adjacency_list, + unsigned int, + g->nodes[n1].adjacency_list_size); + } + + g->nodes[n1].adjacency_list[g->nodes[n1].adjacency_count] = n2; + g->nodes[n1].adjacency_count++; +} + +struct ra_graph * +ra_alloc_interference_graph(struct ra_regs *regs, unsigned int count) +{ + struct ra_graph *g; + unsigned int i; + + g = rzalloc(regs, struct ra_graph); + g->regs = regs; + g->nodes = rzalloc_array(g, struct ra_node, count); + g->count = count; + + g->stack = rzalloc_array(g, unsigned int, count); + + for (i = 0; i < count; i++) { + int bitset_count = BITSET_WORDS(count); + g->nodes[i].adjacency = rzalloc_array(g, BITSET_WORD, bitset_count); + + g->nodes[i].adjacency_list_size = 4; + g->nodes[i].adjacency_list = + ralloc_array(g, unsigned int, g->nodes[i].adjacency_list_size); + g->nodes[i].adjacency_count = 0; + g->nodes[i].q_total = 0; + + ra_add_node_adjacency(g, i, i); + g->nodes[i].reg = NO_REG; + } + + return g; +} + +void +ra_set_node_class(struct ra_graph *g, + unsigned int n, unsigned int class) +{ + g->nodes[n].class = class; +} + +void +ra_add_node_interference(struct ra_graph *g, + unsigned int n1, unsigned int n2) +{ + if (!BITSET_TEST(g->nodes[n1].adjacency, n2)) { + ra_add_node_adjacency(g, n1, n2); + ra_add_node_adjacency(g, n2, n1); + } +} + +static bool +pq_test(struct ra_graph *g, unsigned int n) +{ + int n_class = g->nodes[n].class; + + return g->nodes[n].q_total < g->regs->classes[n_class]->p; +} + +static void +decrement_q(struct ra_graph *g, unsigned int n) +{ + unsigned int i; + int n_class = g->nodes[n].class; + + for (i = 0; i < g->nodes[n].adjacency_count; i++) { + unsigned int n2 = g->nodes[n].adjacency_list[i]; + unsigned int n2_class = g->nodes[n2].class; + + if (n != n2 && !g->nodes[n2].in_stack) { + assert(g->nodes[n2].q_total >= g->regs->classes[n2_class]->q[n_class]); + g->nodes[n2].q_total -= g->regs->classes[n2_class]->q[n_class]; + } + } +} + +/** + * Simplifies the interference graph by pushing all + * trivially-colorable nodes into a stack of nodes to be colored, + * removing them from the graph, and rinsing and repeating. + * + * If we encounter a case where we can't push any nodes on the stack, then + * we optimistically choose a node and push it on the stack. We heuristically + * push the node with the lowest total q value, since it has the fewest + * neighbors and therefore is most likely to be allocated. + */ +static void +ra_simplify(struct ra_graph *g) +{ + bool progress = true; + int i; + + while (progress) { + unsigned int best_optimistic_node = ~0; + unsigned int lowest_q_total = ~0; + + progress = false; + + for (i = g->count - 1; i >= 0; i--) { + if (g->nodes[i].in_stack || g->nodes[i].reg != NO_REG) + continue; + + if (pq_test(g, i)) { + decrement_q(g, i); + g->stack[g->stack_count] = i; + g->stack_count++; + g->nodes[i].in_stack = true; + progress = true; + } else { + unsigned int new_q_total = g->nodes[i].q_total; + if (new_q_total < lowest_q_total) { + best_optimistic_node = i; + lowest_q_total = new_q_total; + } + } + } + + if (!progress && best_optimistic_node != ~0) { + decrement_q(g, best_optimistic_node); + g->stack[g->stack_count] = best_optimistic_node; + g->stack_count++; + g->nodes[best_optimistic_node].in_stack = true; + progress = true; + } + } +} + +/** + * Pops nodes from the stack back into the graph, coloring them with + * registers as they go. + * + * If all nodes were trivially colorable, then this must succeed. If + * not (optimistic coloring), then it may return false; + */ +static bool +ra_select(struct ra_graph *g) +{ + int i; + int start_search_reg = 0; + + while (g->stack_count != 0) { + unsigned int ri; + unsigned int r = -1; + int n = g->stack[g->stack_count - 1]; + struct ra_class *c = g->regs->classes[g->nodes[n].class]; + + /* Find the lowest-numbered reg which is not used by a member + * of the graph adjacent to us. + */ + for (ri = 0; ri < g->regs->count; ri++) { + r = (start_search_reg + ri) % g->regs->count; + if (!reg_belongs_to_class(r, c)) + continue; + + /* Check if any of our neighbors conflict with this register choice. */ + for (i = 0; i < g->nodes[n].adjacency_count; i++) { + unsigned int n2 = g->nodes[n].adjacency_list[i]; + + if (!g->nodes[n2].in_stack && + BITSET_TEST(g->regs->regs[r].conflicts, g->nodes[n2].reg)) { + break; + } + } + if (i == g->nodes[n].adjacency_count) + break; + } + + /* set this to false even if we return here so that + * ra_get_best_spill_node() considers this node later. + */ + g->nodes[n].in_stack = false; + + if (ri == g->regs->count) + return false; + + g->nodes[n].reg = r; + g->stack_count--; + + if (g->regs->round_robin) + start_search_reg = r + 1; + } + + return true; +} + +bool +ra_allocate(struct ra_graph *g) +{ + ra_simplify(g); + return ra_select(g); +} + +unsigned int +ra_get_node_reg(struct ra_graph *g, unsigned int n) +{ + return g->nodes[n].reg; +} + +/** + * Forces a node to a specific register. This can be used to avoid + * creating a register class containing one node when handling data + * that must live in a fixed location and is known to not conflict + * with other forced register assignment (as is common with shader + * input data). These nodes do not end up in the stack during + * ra_simplify(), and thus at ra_select() time it is as if they were + * the first popped off the stack and assigned their fixed locations. + * Nodes that use this function do not need to be assigned a register + * class. + * + * Must be called before ra_simplify(). + */ +void +ra_set_node_reg(struct ra_graph *g, unsigned int n, unsigned int reg) +{ + g->nodes[n].reg = reg; + g->nodes[n].in_stack = false; +} + +static float +ra_get_spill_benefit(struct ra_graph *g, unsigned int n) +{ + int j; + float benefit = 0; + int n_class = g->nodes[n].class; + + /* Define the benefit of eliminating an interference between n, n2 + * through spilling as q(C, B) / p(C). This is similar to the + * "count number of edges" approach of traditional graph coloring, + * but takes classes into account. + */ + for (j = 0; j < g->nodes[n].adjacency_count; j++) { + unsigned int n2 = g->nodes[n].adjacency_list[j]; + if (n != n2) { + unsigned int n2_class = g->nodes[n2].class; + benefit += ((float)g->regs->classes[n_class]->q[n2_class] / + g->regs->classes[n_class]->p); + } + } + + return benefit; +} + +/** + * Returns a node number to be spilled according to the cost/benefit using + * the pq test, or -1 if there are no spillable nodes. + */ +int +ra_get_best_spill_node(struct ra_graph *g) +{ + unsigned int best_node = -1; + float best_benefit = 0.0; + unsigned int n; + + /* Consider any nodes that we colored successfully or the node we failed to + * color for spilling. When we failed to color a node in ra_select(), we + * only considered these nodes, so spilling any other ones would not result + * in us making progress. + */ + for (n = 0; n < g->count; n++) { + float cost = g->nodes[n].spill_cost; + float benefit; + + if (cost <= 0.0) + continue; + + if (g->nodes[n].in_stack) + continue; + + benefit = ra_get_spill_benefit(g, n); + + if (benefit / cost > best_benefit) { + best_benefit = benefit / cost; + best_node = n; + } + } + + return best_node; +} + +/** + * Only nodes with a spill cost set (cost != 0.0) will be considered + * for register spilling. + */ +void +ra_set_node_spill_cost(struct ra_graph *g, unsigned int n, float cost) +{ + g->nodes[n].spill_cost = cost; +} |