ok for google/main.
David
On Thu, Jun 2, 2011 at 11:00 AM, Martin Thuresson <mart...@google.com> wrote:
> This patch from Neil Vachharajani and Dehao Chen improves mcf by using
> minimum cost circulation instead of minimum cost flow to smooth profiles.
> It also introduces a parameter for controlling running time of the algorithm.
> This was what was originally presented in the academic work and handles
> certain cases where the function entry and exit have incorrect profile
> weights.
>
> For now, this is for google/main. Once I have collected performance results
> from SPEC I will propose this patch for trunk as well.
>
> Bootstraps and no test regressions. Ok for google/main?
>
> 2011-06-02 Neil Vachharajani <nvach...@gmail.com>, Dehao Chen
> <daniel...@gmail.com>
>
> * gcc/doc/invoke.texi (min-mcf-cancel-iters): Document.
> * gcc/mcf.c (MAX_ITER): Use new param PARAM_MIN_MCF_CANCEL_ITERS.
> (edge_type): Add SINK_SOURCE_EDGE.
> (dump_fixup_edge): Handle SINK_SOURCE_EDGE.
> (create_fixup_graph): Make problem miminum cost circulation.
> (cancel_negative_cycle): Update handling of infinite capacity.
> (compute_residual_flow): Update handling of infinite capacity.
> (find_max_flow): Update handling of infinite capacity.
> (modify_sink_source_capacity): New function.
> (find_minimum_cost_flow): Make problem miminum cost circulation.
> Use param PARAM_MIN_MCF_CANCEL_ITERS.
> * gcc/params.def (PARAM_MIN_MCF_CANCEL_ITERS): Define.
>
> Index: gcc/doc/invoke.texi
> ===================================================================
> --- gcc/doc/invoke.texi (revision 174456)
> +++ gcc/doc/invoke.texi (working copy)
> @@ -8341,6 +8341,12 @@ whether the result of a complex multipli
>
> The default is @option{-fno-cx-fortran-rules}.
>
> +@item min-mcf-cancel-iters
> +The minimum number of iterations of negative cycle cancellation during
> +MCF profile correction before early termination. This parameter is
> +only useful when using @option{-fprofile-correction}.
> +
> +
> @end table
>
> The following options control optimizations that may improve
> Index: gcc/mcf.c
> ===================================================================
> --- gcc/mcf.c (revision 174456)
> +++ gcc/mcf.c (working copy)
> @@ -52,6 +52,8 @@ along with GCC; see the file COPYING3.
> #include "langhooks.h"
> #include "tree.h"
> #include "gcov-io.h"
> +#include "params.h"
> +#include "diagnostic-core.h"
>
> #include "profile.h"
>
> @@ -64,15 +66,18 @@ along with GCC; see the file COPYING3.
> #define COST(k, w) ((k) / mcf_ln ((w) + 2))
> /* Limit the number of iterations for cancel_negative_cycles() to ensure
> reasonable compile time. */
> -#define MAX_ITER(n, e) 10 + (1000000 / ((n) * (e)))
> +#define MAX_ITER(n, e) (PARAM_VALUE (PARAM_MIN_MCF_CANCEL_ITERS) + \
> + (1000000 / ((n) * (e))))
> +
> typedef enum
> {
> - INVALID_EDGE,
> + INVALID_EDGE = 0,
> VERTEX_SPLIT_EDGE, /* Edge to represent vertex with w(e) = w(v). */
> REDIRECT_EDGE, /* Edge after vertex transformation. */
> REVERSE_EDGE,
> SOURCE_CONNECT_EDGE, /* Single edge connecting to single source. */
> SINK_CONNECT_EDGE, /* Single edge connecting to single sink. */
> + SINK_SOURCE_EDGE, /* Single edge connecting sink to source. */
> BALANCE_EDGE, /* Edge connecting with source/sink: cp(e)
> = 0. */
> REDIRECT_NORMALIZED_EDGE, /* Normalized edge for a redirect edge. */
> REVERSE_NORMALIZED_EDGE /* Normalized edge for a reverse edge. */
> @@ -250,6 +255,10 @@ dump_fixup_edge (FILE *file, fixup_graph
> fputs (" @SINK_CONNECT_EDGE", file);
> break;
>
> + case SINK_SOURCE_EDGE:
> + fputs (" @SINK_SOURCE_EDGE", file);
> + break;
> +
> case REVERSE_EDGE:
> fputs (" @REVERSE_EDGE", file);
> break;
> @@ -465,7 +474,7 @@ create_fixup_graph (fixup_graph_type *fi
> double k_neg = 0;
> /* Vector to hold D(v) = sum_out_edges(v) - sum_in_edges(v). */
> gcov_type *diff_out_in = NULL;
> - gcov_type supply_value = 1, demand_value = 0;
> + gcov_type supply_value = 0, demand_value = 0;
> gcov_type fcost = 0;
> int new_entry_index = 0, new_exit_index = 0;
> int i = 0, j = 0;
> @@ -486,14 +495,15 @@ create_fixup_graph (fixup_graph_type *fi
> fnum_vertices_after_transform + n_edges + n_basic_blocks + 2;
>
> /* In create_fixup_graph: Each basic block and edge can be split into 3
> - edges. Number of balance edges = n_basic_blocks. So after
> - create_fixup_graph:
> - max_edges = 4 * n_basic_blocks + 3 * n_edges
> + edges. Number of balance edges = n_basic_blocks - 1. And there is 1 edge
> + connecting new_entry and new_exit, and 2 edges connecting new_entry to
> + entry, and exit to new_exit. So after create_fixup_graph:
> + max_edges = 4 * n_basic_blocks + 3 * n_edges + 2
> Accounting for residual flow edges
> - max_edges = 2 * (4 * n_basic_blocks + 3 * n_edges)
> - = 8 * n_basic_blocks + 6 * n_edges
> - < 8 * n_basic_blocks + 8 * n_edges. */
> - int fmax_num_edges = 8 * (n_basic_blocks + n_edges);
> + max_edges = 2 * (4 * n_basic_blocks + 3 * n_edges + 2)
> + = 8 * n_basic_blocks + 6 * n_edges + 4
> + < 8 * n_basic_blocks + 8 * n_edges + 8. */
> + int fmax_num_edges = 8 * (n_basic_blocks + n_edges + 1);
>
> /* Initial num of vertices in the fixup graph. */
> fixup_graph->num_vertices = n_basic_blocks;
> @@ -512,7 +522,7 @@ create_fixup_graph (fixup_graph_type *fi
>
> /* Compute constants b, k_pos, k_neg used in the cost function calculation.
> b = sqrt(avg_vertex_weight(cfg)); k_pos = b; k_neg = 50b. */
> - FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
> + FOR_ALL_BB (bb)
> total_vertex_weight += bb->count;
>
> sqrt_avg_vertex_weight = mcf_sqrt (total_vertex_weight / n_basic_blocks);
> @@ -526,10 +536,11 @@ create_fixup_graph (fixup_graph_type *fi
> if (dump_file)
> fprintf (dump_file, "\nVertex transformation:\n");
>
> - FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
> + FOR_ALL_BB (bb)
> {
> /* v'->v'': index1->(index1+1). */
> i = 2 * bb->index;
> +
> fcost = (gcov_type) COST (k_pos, bb->count);
> add_fixup_edge (fixup_graph, i, i + 1, VERTEX_SPLIT_EDGE, bb->count,
> fcost, CAP_INFINITY);
> @@ -593,23 +604,45 @@ create_fixup_graph (fixup_graph_type *fi
>
> new_entry_index = fixup_graph->new_entry_index = fixup_graph->num_vertices;
> fixup_graph->num_vertices++;
> - /* Set supply_value to 1 to avoid zero count function ENTRY. */
> - add_fixup_edge (fixup_graph, new_entry_index, ENTRY_BLOCK,
> SOURCE_CONNECT_EDGE,
> - 1 /* supply_value */, 0, 1 /* supply_value */);
> + /* Set capacity to 0 initially, it will be updated after
> + supply_value is computed. */
> + add_fixup_edge (fixup_graph, new_entry_index, ENTRY_BLOCK,
> + SOURCE_CONNECT_EDGE, 0 /* supply_value */, 0,
> + 0 /* supply_value */);
> + add_fixup_edge (fixup_graph, ENTRY_BLOCK, new_entry_index,
> + SOURCE_CONNECT_EDGE, 0 /* supply_value */, 0,
> + 0 /* supply_value */);
>
> - /* Create new exit with EXIT_BLOCK as single pred. */
> +
> + /* Set capacity to 0 initially, it will be updated after
> + demand_value is computed. */
> new_exit_index = fixup_graph->new_exit_index = fixup_graph->num_vertices;
> fixup_graph->num_vertices++;
> add_fixup_edge (fixup_graph, 2 * EXIT_BLOCK + 1, new_exit_index,
> SINK_CONNECT_EDGE,
> 0 /* demand_value */, 0, 0 /* demand_value */);
> + add_fixup_edge (fixup_graph, new_exit_index, 2 * EXIT_BLOCK + 1,
> + SINK_CONNECT_EDGE,
> + 0 /* demand_value */, 0, 0 /* demand_value */);
> +
> +
> + /* Create a back edge from the new_exit to the new_entry.
> + Initially, its capacity will be set to 0 so that it does not
> + affect max flow, but later its capacity will be changed to
> + infinity to cancel negative cycles. */
> + add_fixup_edge (fixup_graph, new_exit_index, new_entry_index,
> + SINK_SOURCE_EDGE, 0, 0, 0);
> +
> +
>
> /* Connect vertices with unbalanced D(v) to source/sink. */
> if (dump_file)
> fprintf (dump_file, "\nD(v) balance:\n");
> - /* Skip vertices for ENTRY (0, 1) and EXIT (2,3) blocks, so start with i =
> 4.
> - diff_out_in[v''] will be 0, so skip v'' vertices, hence i += 2. */
> - for (i = 4; i < new_entry_index; i += 2)
> +
> + /* Skip vertices for ENTRY (0, 1) and EXIT (2,3) blocks, so start
> + with i = 4. diff_out_in[v''] should be 0, but may not be due to
> + rounding error. So here we consider all vertices. */
> + for (i = 4; i < new_entry_index; i += 1)
> {
> if (diff_out_in[i] > 0)
> {
> @@ -674,7 +707,6 @@ create_fixup_graph (fixup_graph_type *fi
> fprintf (dump_file, "------------------\n");
> }
>
> - pfedge->cost /= 2;
> pfedge->norm_vertex_index = new_index;
> if (dump_file)
> {
> @@ -684,7 +716,7 @@ create_fixup_graph (fixup_graph_type *fi
>
> /* Add a new fixup edge: new_index->src. */
> add_fixup_edge (fixup_graph, new_index, pfedge->src,
> - REVERSE_NORMALIZED_EDGE, 0, r_pfedge->cost,
> + REVERSE_NORMALIZED_EDGE, 0, 0,
> r_pfedge->max_capacity);
> gcc_assert (fixup_graph->num_vertices <= fmax_num_vertices);
>
> @@ -692,7 +724,6 @@ create_fixup_graph (fixup_graph_type *fi
> ==> r_pfedge->src -> new_index. */
> r_pfedge->dest = new_index;
> r_pfedge->type = REVERSE_NORMALIZED_EDGE;
> - r_pfedge->cost = pfedge->cost;
> r_pfedge->max_capacity = pfedge->max_capacity;
> if (dump_file)
> dump_fixup_edge (dump_file, fixup_graph, r_pfedge);
> @@ -794,14 +825,12 @@ cancel_negative_cycle (fixup_graph_type
> bool found_cycle = false;
> int cycle_start = 0, cycle_end = 0;
> gcov_type sum_cost = 0, cycle_flow = 0;
> - int new_entry_index;
> bool propagated = false;
>
> gcc_assert (fixup_graph);
> fnum_vertices = fixup_graph->num_vertices;
> fnum_edges = fixup_graph->num_edges;
> fedge_list = fixup_graph->edge_list;
> - new_entry_index = fixup_graph->new_entry_index;
>
> /* Initialize. */
> /* Skip ENTRY. */
> @@ -820,8 +849,6 @@ cancel_negative_cycle (fixup_graph_type
> for (i = 0; i < fnum_edges; i++)
> {
> pfedge = fedge_list + i;
> - if (pfedge->src == new_entry_index)
> - continue;
> if (pfedge->is_rflow_valid && pfedge->rflow
> && d[pfedge->src] != CAP_INFINITY
> && (d[pfedge->dest] > d[pfedge->src] + pfedge->cost))
> @@ -843,8 +870,6 @@ cancel_negative_cycle (fixup_graph_type
> for (i = 0; i < fnum_edges; i++)
> {
> pfedge = fedge_list + i;
> - if (pfedge->src == new_entry_index)
> - continue;
> if (pfedge->is_rflow_valid && pfedge->rflow
> && d[pfedge->src] != CAP_INFINITY
> && (d[pfedge->dest] > d[pfedge->src] + pfedge->cost))
> @@ -912,10 +937,12 @@ cancel_negative_cycle (fixup_graph_type
> {
> pfedge = find_fixup_edge (fixup_graph, cycle[k + 1], cycle[k]);
> r_pfedge = find_fixup_edge (fixup_graph, cycle[k], cycle[k + 1]);
> - pfedge->rflow -= cycle_flow;
> + if (pfedge->rflow != CAP_INFINITY)
> + pfedge->rflow -= cycle_flow;
> if (pfedge->type)
> pfedge->flow += cycle_flow;
> - r_pfedge->rflow += cycle_flow;
> + if (r_pfedge->rflow != CAP_INFINITY)
> + r_pfedge->rflow += cycle_flow;
> if (r_pfedge->type)
> r_pfedge->flow -= cycle_flow;
> }
> @@ -945,7 +972,8 @@ compute_residual_flow (fixup_graph_type
> for (i = 0; i < fnum_edges; i++)
> {
> pfedge = fedge_list + i;
> - pfedge->rflow = pfedge->max_capacity - pfedge->flow;
> + pfedge->rflow = pfedge->max_capacity == CAP_INFINITY ?
> + CAP_INFINITY : pfedge->max_capacity - pfedge->flow;
> pfedge->is_rflow_valid = true;
> add_rfixup_edge (fixup_graph, pfedge->dest, pfedge->src, pfedge->flow,
> -pfedge->cost);
> @@ -1070,20 +1098,22 @@ find_max_flow (fixup_graph_type *fixup_g
> {
> pfedge = find_fixup_edge (fixup_graph, bb_pred[u], u);
> r_pfedge = find_fixup_edge (fixup_graph, u, bb_pred[u]);
> +
> + if (pfedge->rflow != CAP_INFINITY)
> + pfedge->rflow -= increment;
> + if (r_pfedge->rflow != CAP_INFINITY)
> + r_pfedge->rflow += increment;
> +
> if (pfedge->type)
> {
> /* forward edge. */
> pfedge->flow += increment;
> - pfedge->rflow -= increment;
> - r_pfedge->rflow += increment;
> }
> else
> {
> /* backward edge. */
> gcc_assert (r_pfedge->type);
> - r_pfedge->rflow += increment;
> r_pfedge->flow -= increment;
> - pfedge->rflow -= increment;
> }
> }
>
> @@ -1302,6 +1332,60 @@ adjust_cfg_counts (fixup_graph_type *fix
> }
>
>
> +/* Called before negative_cycle_cancellation, to form a cycle between
> + * new_exit to new_entry in FIXUP_GRAPH with capacity MAX_FLOW. We
> + * don't want the flow in the BALANCE_EDGE to be modified, so we set
> + * the residural flow of those edges to 0 */
> +
> +static void
> +modify_sink_source_capacity (fixup_graph_type *fixup_graph, gcov_type
> max_flow)
> +{
> + fixup_edge_p edge, r_edge;
> + int i;
> + int entry = ENTRY_BLOCK;
> + int exit = 2 * EXIT_BLOCK + 1;
> + int new_entry = fixup_graph->new_entry_index;
> + int new_exit = fixup_graph->new_exit_index;
> +
> + edge = find_fixup_edge (fixup_graph, new_entry, entry);
> + edge->max_capacity = CAP_INFINITY;
> + edge->rflow = CAP_INFINITY;
> +
> + edge = find_fixup_edge (fixup_graph, entry, new_entry);
> + edge->max_capacity = CAP_INFINITY;
> + edge->rflow = CAP_INFINITY;
> +
> + edge = find_fixup_edge (fixup_graph, exit, new_exit);
> + edge->max_capacity = CAP_INFINITY;
> + edge->rflow = CAP_INFINITY;
> +
> + edge = find_fixup_edge (fixup_graph, new_exit, exit);
> + edge->max_capacity = CAP_INFINITY;
> + edge->rflow = CAP_INFINITY;
> +
> + edge = find_fixup_edge (fixup_graph, new_exit, new_entry);
> + edge->max_capacity = CAP_INFINITY;
> + edge->flow = max_flow;
> + edge->rflow = CAP_INFINITY;
> +
> + r_edge = find_fixup_edge (fixup_graph, new_entry, new_exit);
> + r_edge->rflow = max_flow;
> +
> + /* Find all the backwards residual edges corresponding to
> + BALANCE_EDGEs and set their residual flow to 0 to enforce a
> + minimum flow constraint on these edges. */
> + for (i = 4; i < new_entry; i += 1)
> + {
> + edge = find_fixup_edge (fixup_graph, i, new_entry);
> + if (edge)
> + edge->rflow = 0;
> + edge = find_fixup_edge (fixup_graph, new_exit, i);
> + if (edge)
> + edge->rflow = 0;
> + }
> +}
> +
> +
> /* Implements the negative cycle canceling algorithm to compute a minimum
> cost
> flow.
> Algorithm:
> @@ -1330,13 +1414,18 @@ find_minimum_cost_flow (fixup_graph_type
> int fnum_vertices;
> int new_exit_index;
> int new_entry_index;
> + gcov_type max_flow;
>
> gcc_assert (fixup_graph);
> fnum_vertices = fixup_graph->num_vertices;
> new_exit_index = fixup_graph->new_exit_index;
> new_entry_index = fixup_graph->new_entry_index;
>
> - find_max_flow (fixup_graph, new_entry_index, new_exit_index);
> + max_flow = find_max_flow (fixup_graph, new_entry_index, new_exit_index);
> +
> + /* Adjust the fixup graph to translate things into a minimum cost
> + circulation problem. */
> + modify_sink_source_capacity (fixup_graph, max_flow);
>
> /* Initialize the structures for find_negative_cycle(). */
> pred = (int *) xcalloc (fnum_vertices, sizeof (int));
> @@ -1352,7 +1441,12 @@ find_minimum_cost_flow (fixup_graph_type
> iteration++;
> if (iteration > MAX_ITER (fixup_graph->num_vertices,
> fixup_graph->num_edges))
> - break;
> + {
> + inform (DECL_SOURCE_LOCATION (current_function_decl),
> + "Exiting profile correction early to avoid excessive "
> + "compile time");
> + break;
> + }
> }
>
> if (dump_file)
> Index: gcc/params.def
> ===================================================================
> --- gcc/params.def (revision 174456)
> +++ gcc/params.def (working copy)
> @@ -977,6 +977,12 @@ DEFPARAM (MIN_PARTITION_SIZE,
> "Size of minimal paritition for WHOPR (in estimated instructions)",
> 1000, 0, 0)
>
> +DEFPARAM (PARAM_MIN_MCF_CANCEL_ITERS,
> + "min-mcf-cancel-iters",
> + "the minimum number of iterations of negative cycle cancellation "
> + "in MCF",
> + 10, 1, 0)
> +
> /* Diagnostic parameters. */
>
> DEFPARAM (CXX_MAX_NAMESPACES_FOR_DIAGNOSTIC_HELP,
>
> --
> This patch is available for review at http://codereview.appspot.com/4536106
>
