On Thu, Jun 2, 2011 at 11:05 AM, Xinliang David Li <davi...@google.com> wrote:
>
> Smoothing works for sample FDO and profile data from multi-threaded
> programs. You won't see any difference in SPEC.
Dehao reported some performance improvements from the algorithmic improvements
he added in terms of extra fixup edges and handling of infinite capacity.
Martin
>
> 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
> >
