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1 /* The tracer pass for the GNU compiler.
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2 Contributed by Jan Hubicka, SuSE Labs.
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3 Adapted to work on GIMPLE instead of RTL by Robert Kidd, UIUC.
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4 Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
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5 Free Software Foundation, Inc.
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6
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7 This file is part of GCC.
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8
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9 GCC is free software; you can redistribute it and/or modify it
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10 under the terms of the GNU General Public License as published by
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11 the Free Software Foundation; either version 3, or (at your option)
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12 any later version.
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13
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14 GCC is distributed in the hope that it will be useful, but WITHOUT
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15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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16 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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17 License for more details.
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18
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19 You should have received a copy of the GNU General Public License
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20 along with GCC; see the file COPYING3. If not see
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21 <http://www.gnu.org/licenses/>. */
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22
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23 /* This pass performs the tail duplication needed for superblock formation.
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24 For more information see:
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25
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26 Design and Analysis of Profile-Based Optimization in Compaq's
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27 Compilation Tools for Alpha; Journal of Instruction-Level
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28 Parallelism 3 (2000) 1-25
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29
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30 Unlike Compaq's implementation we don't do the loop peeling as most
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31 probably a better job can be done by a special pass and we don't
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32 need to worry too much about the code size implications as the tail
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33 duplicates are crossjumped again if optimizations are not
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34 performed. */
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35
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36
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37 #include "config.h"
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38 #include "system.h"
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39 #include "coretypes.h"
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40 #include "tm.h"
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41 #include "tree.h"
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42 #include "rtl.h"
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43 #include "hard-reg-set.h"
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44 #include "basic-block.h"
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45 #include "output.h"
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46 #include "cfglayout.h"
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47 #include "fibheap.h"
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48 #include "flags.h"
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49 #include "timevar.h"
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50 #include "params.h"
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51 #include "coverage.h"
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52 #include "tree-pass.h"
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53 #include "tree-flow.h"
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54 #include "tree-inline.h"
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55
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56 static int count_insns (basic_block);
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57 static bool ignore_bb_p (const_basic_block);
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58 static bool better_p (const_edge, const_edge);
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59 static edge find_best_successor (basic_block);
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60 static edge find_best_predecessor (basic_block);
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61 static int find_trace (basic_block, basic_block *);
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62 static void tail_duplicate (void);
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63
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64 /* Minimal outgoing edge probability considered for superblock formation. */
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65 static int probability_cutoff;
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66 static int branch_ratio_cutoff;
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67
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68 /* A bit BB->index is set if BB has already been seen, i.e. it is
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69 connected to some trace already. */
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70 sbitmap bb_seen;
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71
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72 static inline void
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73 mark_bb_seen (basic_block bb)
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74 {
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75 unsigned int size = SBITMAP_SIZE_BYTES (bb_seen) * 8;
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76
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77 if ((unsigned int)bb->index >= size)
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78 bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
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79
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80 SET_BIT (bb_seen, bb->index);
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81 }
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82
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83 static inline bool
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84 bb_seen_p (basic_block bb)
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85 {
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86 return TEST_BIT (bb_seen, bb->index);
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87 }
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88
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89 /* Return true if we should ignore the basic block for purposes of tracing. */
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90 static bool
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91 ignore_bb_p (const_basic_block bb)
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92 {
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93 if (bb->index < NUM_FIXED_BLOCKS)
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94 return true;
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95 if (optimize_bb_for_size_p (bb))
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96 return true;
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97 return false;
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98 }
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99
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100 /* Return number of instructions in the block. */
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101
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102 static int
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103 count_insns (basic_block bb)
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104 {
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105 gimple_stmt_iterator gsi;
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106 gimple stmt;
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107 int n = 0;
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108
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109 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
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110 {
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111 stmt = gsi_stmt (gsi);
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112 n += estimate_num_insns (stmt, &eni_size_weights);
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113 }
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114 return n;
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115 }
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116
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117 /* Return true if E1 is more frequent than E2. */
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118 static bool
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119 better_p (const_edge e1, const_edge e2)
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120 {
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121 if (e1->count != e2->count)
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122 return e1->count > e2->count;
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123 if (e1->src->frequency * e1->probability !=
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124 e2->src->frequency * e2->probability)
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125 return (e1->src->frequency * e1->probability
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126 > e2->src->frequency * e2->probability);
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127 /* This is needed to avoid changes in the decision after
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128 CFG is modified. */
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129 if (e1->src != e2->src)
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130 return e1->src->index > e2->src->index;
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131 return e1->dest->index > e2->dest->index;
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132 }
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133
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134 /* Return most frequent successor of basic block BB. */
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135
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136 static edge
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137 find_best_successor (basic_block bb)
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138 {
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139 edge e;
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140 edge best = NULL;
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141 edge_iterator ei;
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142
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143 FOR_EACH_EDGE (e, ei, bb->succs)
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144 if (!best || better_p (e, best))
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145 best = e;
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146 if (!best || ignore_bb_p (best->dest))
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147 return NULL;
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148 if (best->probability <= probability_cutoff)
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149 return NULL;
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150 return best;
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151 }
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152
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153 /* Return most frequent predecessor of basic block BB. */
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154
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155 static edge
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156 find_best_predecessor (basic_block bb)
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157 {
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158 edge e;
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159 edge best = NULL;
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160 edge_iterator ei;
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161
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162 FOR_EACH_EDGE (e, ei, bb->preds)
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163 if (!best || better_p (e, best))
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164 best = e;
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165 if (!best || ignore_bb_p (best->src))
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166 return NULL;
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167 if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
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168 < bb->frequency * branch_ratio_cutoff)
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169 return NULL;
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170 return best;
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171 }
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172
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173 /* Find the trace using bb and record it in the TRACE array.
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174 Return number of basic blocks recorded. */
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175
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176 static int
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177 find_trace (basic_block bb, basic_block *trace)
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178 {
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179 int i = 0;
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180 edge e;
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181
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182 if (dump_file)
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183 fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->frequency);
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184
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185 while ((e = find_best_predecessor (bb)) != NULL)
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186 {
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187 basic_block bb2 = e->src;
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188 if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
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189 || find_best_successor (bb2) != e)
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190 break;
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191 if (dump_file)
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192 fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
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193 bb = bb2;
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194 }
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195 if (dump_file)
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196 fprintf (dump_file, " forward %i [%i]", bb->index, bb->frequency);
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197 trace[i++] = bb;
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198
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199 /* Follow the trace in forward direction. */
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200 while ((e = find_best_successor (bb)) != NULL)
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201 {
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202 bb = e->dest;
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203 if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
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204 || find_best_predecessor (bb) != e)
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205 break;
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206 if (dump_file)
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207 fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
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208 trace[i++] = bb;
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209 }
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210 if (dump_file)
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211 fprintf (dump_file, "\n");
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212 return i;
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213 }
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214
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215 /* Look for basic blocks in frequency order, construct traces and tail duplicate
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216 if profitable. */
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217
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218 static void
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219 tail_duplicate (void)
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220 {
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221 fibnode_t *blocks = XCNEWVEC (fibnode_t, last_basic_block);
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222 basic_block *trace = XNEWVEC (basic_block, n_basic_blocks);
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223 int *counts = XNEWVEC (int, last_basic_block);
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224 int ninsns = 0, nduplicated = 0;
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225 gcov_type weighted_insns = 0, traced_insns = 0;
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226 fibheap_t heap = fibheap_new ();
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227 gcov_type cover_insns;
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228 int max_dup_insns;
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229 basic_block bb;
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230
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231 /* Create an oversized sbitmap to reduce the chance that we need to
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232 resize it. */
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233 bb_seen = sbitmap_alloc (last_basic_block * 2);
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234 sbitmap_zero (bb_seen);
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235 initialize_original_copy_tables ();
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236
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237 if (profile_info && flag_branch_probabilities)
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238 probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
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239 else
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240 probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
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241 probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
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242
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243 branch_ratio_cutoff =
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244 (REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
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245
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246 FOR_EACH_BB (bb)
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247 {
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248 int n = count_insns (bb);
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249 if (!ignore_bb_p (bb))
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250 blocks[bb->index] = fibheap_insert (heap, -bb->frequency,
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251 bb);
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252
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253 counts [bb->index] = n;
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254 ninsns += n;
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255 weighted_insns += n * bb->frequency;
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256 }
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257
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258 if (profile_info && flag_branch_probabilities)
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259 cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
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260 else
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261 cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
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262 cover_insns = (weighted_insns * cover_insns + 50) / 100;
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263 max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
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264
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265 while (traced_insns < cover_insns && nduplicated < max_dup_insns
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266 && !fibheap_empty (heap))
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267 {
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268 basic_block bb = (basic_block) fibheap_extract_min (heap);
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269 int n, pos;
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270
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271 if (!bb)
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272 break;
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273
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274 blocks[bb->index] = NULL;
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275
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276 if (ignore_bb_p (bb))
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277 continue;
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278 gcc_assert (!bb_seen_p (bb));
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279
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280 n = find_trace (bb, trace);
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281
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282 bb = trace[0];
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283 traced_insns += bb->frequency * counts [bb->index];
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284 if (blocks[bb->index])
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285 {
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286 fibheap_delete_node (heap, blocks[bb->index]);
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287 blocks[bb->index] = NULL;
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288 }
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289
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290 for (pos = 1; pos < n; pos++)
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291 {
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292 basic_block bb2 = trace[pos];
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293
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294 if (blocks[bb2->index])
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295 {
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296 fibheap_delete_node (heap, blocks[bb2->index]);
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297 blocks[bb2->index] = NULL;
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298 }
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299 traced_insns += bb2->frequency * counts [bb2->index];
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300 if (EDGE_COUNT (bb2->preds) > 1
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301 && can_duplicate_block_p (bb2))
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302 {
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303 edge e;
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304 basic_block copy;
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305
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306 nduplicated += counts [bb2->index];
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307
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308 e = find_edge (bb, bb2);
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309
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310 copy = duplicate_block (bb2, e, bb);
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311 flush_pending_stmts (e);
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312
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313 add_phi_args_after_copy (©, 1, NULL);
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314
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315 /* Reconsider the original copy of block we've duplicated.
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316 Removing the most common predecessor may make it to be
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317 head. */
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318 blocks[bb2->index] =
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319 fibheap_insert (heap, -bb2->frequency, bb2);
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320
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321 if (dump_file)
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322 fprintf (dump_file, "Duplicated %i as %i [%i]\n",
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323 bb2->index, copy->index, copy->frequency);
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324
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325 bb2 = copy;
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326 }
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327 mark_bb_seen (bb2);
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328 bb = bb2;
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329 /* In case the trace became infrequent, stop duplicating. */
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330 if (ignore_bb_p (bb))
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331 break;
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332 }
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333 if (dump_file)
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334 fprintf (dump_file, " covered now %.1f\n\n",
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335 traced_insns * 100.0 / weighted_insns);
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336 }
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337 if (dump_file)
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338 fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
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339 nduplicated * 100 / ninsns);
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340
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341 free_original_copy_tables ();
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342 sbitmap_free (bb_seen);
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343 free (blocks);
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344 free (trace);
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345 free (counts);
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346 fibheap_delete (heap);
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347 }
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348
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349 /* Main entry point to this file. */
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350
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351 static unsigned int
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352 tracer (void)
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353 {
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354 gcc_assert (current_ir_type () == IR_GIMPLE);
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355
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356 if (n_basic_blocks <= NUM_FIXED_BLOCKS + 1)
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357 return 0;
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358
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359 mark_dfs_back_edges ();
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360 if (dump_file)
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361 dump_flow_info (dump_file, dump_flags);
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362
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363 /* Trace formation is done on the fly inside tail_duplicate */
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364 tail_duplicate ();
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365
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366 /* FIXME: We really only need to do this when we know tail duplication
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367 has altered the CFG. */
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368 free_dominance_info (CDI_DOMINATORS);
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369 if (dump_file)
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370 dump_flow_info (dump_file, dump_flags);
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371
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372 return 0;
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373 }
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374
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375 static bool
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376 gate_tracer (void)
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377 {
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378 return (optimize > 0 && flag_tracer && flag_reorder_blocks);
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379 }
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380
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381 struct gimple_opt_pass pass_tracer =
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382 {
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383 {
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384 GIMPLE_PASS,
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385 "tracer", /* name */
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386 gate_tracer, /* gate */
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387 tracer, /* execute */
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388 NULL, /* sub */
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389 NULL, /* next */
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390 0, /* static_pass_number */
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391 TV_TRACER, /* tv_id */
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392 0, /* properties_required */
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393 0, /* properties_provided */
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394 0, /* properties_destroyed */
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395 0, /* todo_flags_start */
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396 TODO_dump_func
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397 | TODO_update_ssa
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398 | TODO_verify_ssa /* todo_flags_finish */
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399 }
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400 };
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