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111
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1 /* Back-propagation of usage information to definitions.
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2 Copyright (C) 2015-2017 Free Software Foundation, Inc.
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3
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4 This file is part of GCC.
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5
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6 GCC is free software; you can redistribute it and/or modify
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7 it under the terms of the GNU General Public License as published by
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8 the Free Software Foundation; either version 3, or (at your option)
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9 any later version.
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10
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11 GCC is distributed in the hope that it will be useful,
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12 but WITHOUT ANY WARRANTY; without even the implied warranty of
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13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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14 GNU General Public License for more details.
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15
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16 You should have received a copy of the GNU General Public License
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17 along with GCC; see the file COPYING3. If not see
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18 <http://www.gnu.org/licenses/>. */
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19
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20 /* This pass propagates information that is common to all uses of an SSA
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21 name back up through the sequence of statements that generate it,
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22 simplifying the statements where possible. Sometimes this can expose
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23 fully or partially dead code, but the main focus is simplifying
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24 computations.
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25
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26 At the moment the pass only handles one piece of information: whether the
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27 sign of a value matters, and therefore whether sign-changing operations
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28 can be skipped. The pass could be extended to more interesting
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29 information in future, such as which bits of an integer are significant.
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30
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31 For example, take the function:
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32
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33 double
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34 f (double *a, int n, double start)
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35 {
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36 double x = fabs (start);
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37 for (int i = 0; i < n; ++i)
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38 x *= a[i];
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39 return __builtin_cos (x);
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40 }
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41
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42 cos(x) == cos(-x), so the sign of the final x doesn't matter.
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43 That x is the result of a series of multiplications, and if
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44 the sign of the result of a multiplication doesn't matter,
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45 the signs of the inputs don't matter either.
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46
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47 The pass would replace the incoming value of x (i.e. fabs(start))
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48 with start. Since there are no other uses of the fabs result,
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49 the call would get deleted as dead.
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50
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51 The algorithm is:
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52
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53 (1) Do a post-order traversal of the blocks in the function, walking
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54 each block backwards. For each potentially-simplifiable statement
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55 that defines an SSA name X, examine all uses of X to see what
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56 information is actually significant. Record this as INFO_MAP[X].
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57 Optimistically ignore for now any back-edge references to
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58 unprocessed phis.
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59
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60 (An alternative would be to record each use when we visit its
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61 statement and take the intersection as we go along. However,
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62 this would lead to more SSA names being entered into INFO_MAP
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63 unnecessarily, only to be taken out again later. At the moment
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64 very few SSA names end up with useful information.)
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65
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66 (2) Iteratively reduce the optimistic result of (1) until we reach
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67 a maximal fixed point (which at the moment would mean revisiting
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68 statements at most once). First push all SSA names that used an
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69 optimistic assumption about a backedge phi onto a worklist.
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70 While the worklist is nonempty, pick off an SSA name X and recompute
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71 INFO_MAP[X]. If the value changes, push all SSA names used in the
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72 definition of X onto the worklist.
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73
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74 (3) Iterate over each SSA name X with info in INFO_MAP, in the
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75 opposite order to (1), i.e. a forward reverse-post-order walk.
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76 Try to optimize the definition of X using INFO_MAP[X] and fold
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77 the result. (This ensures that we fold definitions before uses.)
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78
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79 (4) Iterate over each SSA name X with info in INFO_MAP, in the same
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80 order as (1), and delete any statements that are now dead.
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81 (This ensures that if a sequence of statements is dead,
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82 we delete the last statement first.)
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83
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84 Note that this pass does not deal with direct redundancies,
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85 such as cos(-x)->cos(x). match.pd handles those cases instead. */
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86
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87 #include "config.h"
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88 #include "system.h"
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89 #include "coretypes.h"
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90 #include "backend.h"
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91 #include "tree.h"
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92 #include "gimple.h"
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93 #include "gimple-iterator.h"
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94 #include "ssa.h"
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95 #include "fold-const.h"
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96 #include "tree-pass.h"
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97 #include "cfganal.h"
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98 #include "gimple-pretty-print.h"
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99 #include "tree-cfg.h"
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100 #include "tree-ssa.h"
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101 #include "tree-ssa-propagate.h"
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102 #include "gimple-fold.h"
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103 #include "alloc-pool.h"
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104 #include "tree-hash-traits.h"
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105 #include "case-cfn-macros.h"
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106
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107 namespace {
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108
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109 /* Information about a group of uses of an SSA name. */
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110 struct usage_info
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111 {
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112 usage_info () : flag_word (0) {}
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113 usage_info &operator &= (const usage_info &);
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114 usage_info operator & (const usage_info &) const;
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115 bool operator == (const usage_info &) const;
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116 bool operator != (const usage_info &) const;
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117 bool is_useful () const;
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118
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119 static usage_info intersection_identity ();
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120
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121 union
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122 {
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123 struct
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124 {
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125 /* True if the uses treat x and -x in the same way. */
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126 unsigned int ignore_sign : 1;
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127 } flags;
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128 /* All the flag bits as a single int. */
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129 unsigned int flag_word;
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130 };
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131 };
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132
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133 /* Return an X such that X & Y == Y for all Y. This is the most
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134 optimistic assumption possible. */
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135
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136 usage_info
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137 usage_info::intersection_identity ()
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138 {
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139 usage_info ret;
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140 ret.flag_word = -1;
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141 return ret;
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142 }
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143
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144 /* Intersect *THIS with OTHER, so that *THIS describes all uses covered
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145 by the original *THIS and OTHER. */
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146
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147 usage_info &
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148 usage_info::operator &= (const usage_info &other)
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149 {
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150 flag_word &= other.flag_word;
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151 return *this;
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152 }
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153
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154 /* Return the intersection of *THIS and OTHER, i.e. a structure that
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155 describes all uses covered by *THIS and OTHER. */
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156
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157 usage_info
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158 usage_info::operator & (const usage_info &other) const
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159 {
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160 usage_info info (*this);
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161 info &= other;
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162 return info;
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163 }
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164
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165 bool
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166 usage_info::operator == (const usage_info &other) const
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167 {
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168 return flag_word == other.flag_word;
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169 }
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170
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171 bool
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172 usage_info::operator != (const usage_info &other) const
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173 {
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174 return !operator == (other);
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175 }
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176
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177 /* Return true if *THIS is not simply the default, safe assumption. */
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178
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179 bool
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180 usage_info::is_useful () const
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181 {
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182 return flag_word != 0;
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183 }
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184
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185 /* Start a dump line about SSA name VAR. */
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186
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187 static void
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188 dump_usage_prefix (FILE *file, tree var)
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189 {
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190 fprintf (file, " ");
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191 print_generic_expr (file, var);
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192 fprintf (file, ": ");
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193 }
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194
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195 /* Print INFO to FILE. */
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196
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197 static void
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198 dump_usage_info (FILE *file, tree var, usage_info *info)
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199 {
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200 if (info->flags.ignore_sign)
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201 {
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202 dump_usage_prefix (file, var);
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203 fprintf (file, "sign bit not important\n");
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204 }
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205 }
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206
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207 /* Represents one execution of the pass. */
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208 class backprop
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209 {
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210 public:
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211 backprop (function *);
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212 ~backprop ();
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213
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214 void execute ();
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215
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216 private:
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217 const usage_info *lookup_operand (tree);
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218
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219 void push_to_worklist (tree);
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220 tree pop_from_worklist ();
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221
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222 void process_builtin_call_use (gcall *, tree, usage_info *);
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223 void process_assign_use (gassign *, tree, usage_info *);
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224 void process_phi_use (gphi *, usage_info *);
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225 void process_use (gimple *, tree, usage_info *);
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226 bool intersect_uses (tree, usage_info *);
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227 void reprocess_inputs (gimple *);
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228 void process_var (tree);
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229 void process_block (basic_block);
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230
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231 void prepare_change (tree);
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232 void complete_change (gimple *);
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233 void optimize_builtin_call (gcall *, tree, const usage_info *);
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234 void replace_assign_rhs (gassign *, tree, tree, tree, tree);
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235 void optimize_assign (gassign *, tree, const usage_info *);
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236 void optimize_phi (gphi *, tree, const usage_info *);
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237
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238 typedef hash_map <tree_ssa_name_hash, usage_info *> info_map_type;
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239 typedef std::pair <tree, usage_info *> var_info_pair;
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240
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241 /* The function we're optimizing. */
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242 function *m_fn;
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243
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244 /* Pool for allocating usage_info structures. */
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245 object_allocator <usage_info> m_info_pool;
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246
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247 /* Maps an SSA name to a description of all uses of that SSA name.
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248 All the usage_infos satisfy is_useful.
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249
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250 We use a hash_map because the map is expected to be sparse
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251 (i.e. most SSA names won't have useful information attached to them).
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252 We could move to a directly-indexed array if that situation changes. */
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253 info_map_type m_info_map;
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254
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255 /* Post-ordered list of all potentially-interesting SSA names,
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256 along with information that describes all uses. */
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257 auto_vec <var_info_pair, 128> m_vars;
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258
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259 /* A bitmap of blocks that we have finished processing in the initial
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260 post-order walk. */
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261 auto_sbitmap m_visited_blocks;
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262
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263 /* A worklist of SSA names whose definitions need to be reconsidered. */
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264 auto_vec <tree, 64> m_worklist;
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265
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266 /* The SSA names in M_WORKLIST, identified by their SSA_NAME_VERSION.
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267 We use a bitmap rather than an sbitmap because most SSA names are
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268 never added to the worklist. */
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269 bitmap m_worklist_names;
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270 };
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271
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272 backprop::backprop (function *fn)
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273 : m_fn (fn),
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274 m_info_pool ("usage_info"),
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275 m_visited_blocks (last_basic_block_for_fn (m_fn)),
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276 m_worklist_names (BITMAP_ALLOC (NULL))
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277 {
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278 bitmap_clear (m_visited_blocks);
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279 }
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280
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281 backprop::~backprop ()
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282 {
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283 BITMAP_FREE (m_worklist_names);
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284 m_info_pool.release ();
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285 }
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286
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287 /* Return usage information for general operand OP, or null if none. */
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288
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289 const usage_info *
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290 backprop::lookup_operand (tree op)
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291 {
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292 if (op && TREE_CODE (op) == SSA_NAME)
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293 {
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294 usage_info **slot = m_info_map.get (op);
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295 if (slot)
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296 return *slot;
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297 }
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298 return NULL;
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299 }
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300
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301 /* Add SSA name VAR to the worklist, if it isn't on the worklist already. */
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302
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303 void
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304 backprop::push_to_worklist (tree var)
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305 {
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306 if (!bitmap_set_bit (m_worklist_names, SSA_NAME_VERSION (var)))
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307 return;
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308 m_worklist.safe_push (var);
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309 if (dump_file && (dump_flags & TDF_DETAILS))
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310 {
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311 fprintf (dump_file, "[WORKLIST] Pushing ");
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312 print_generic_expr (dump_file, var);
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313 fprintf (dump_file, "\n");
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314 }
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315 }
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316
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317 /* Remove and return the next SSA name from the worklist. The worklist
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318 is known to be nonempty. */
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319
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320 tree
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321 backprop::pop_from_worklist ()
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322 {
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323 tree var = m_worklist.pop ();
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324 bitmap_clear_bit (m_worklist_names, SSA_NAME_VERSION (var));
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325 if (dump_file && (dump_flags & TDF_DETAILS))
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326 {
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327 fprintf (dump_file, "[WORKLIST] Popping ");
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328 print_generic_expr (dump_file, var);
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329 fprintf (dump_file, "\n");
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330 }
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331 return var;
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332 }
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333
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334 /* Make INFO describe all uses of RHS in CALL, which is a call to a
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335 built-in function. */
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336
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337 void
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338 backprop::process_builtin_call_use (gcall *call, tree rhs, usage_info *info)
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339 {
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340 combined_fn fn = gimple_call_combined_fn (call);
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341 tree lhs = gimple_call_lhs (call);
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342 switch (fn)
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343 {
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344 case CFN_LAST:
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345 break;
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346
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347 CASE_CFN_COS:
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348 CASE_CFN_COSH:
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349 CASE_CFN_CCOS:
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350 CASE_CFN_CCOSH:
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351 CASE_CFN_HYPOT:
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352 /* The signs of all inputs are ignored. */
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353 info->flags.ignore_sign = true;
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354 break;
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355
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356 CASE_CFN_COPYSIGN:
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357 /* The sign of the first input is ignored. */
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358 if (rhs != gimple_call_arg (call, 1))
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359 info->flags.ignore_sign = true;
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360 break;
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361
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362 CASE_CFN_POW:
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363 {
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364 /* The sign of the first input is ignored as long as the second
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365 input is an even real. */
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366 tree power = gimple_call_arg (call, 1);
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367 HOST_WIDE_INT n;
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368 if (TREE_CODE (power) == REAL_CST
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369 && real_isinteger (&TREE_REAL_CST (power), &n)
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370 && (n & 1) == 0)
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371 info->flags.ignore_sign = true;
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372 break;
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373 }
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374
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375 CASE_CFN_FMA:
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376 /* In X * X + Y, where Y is distinct from X, the sign of X doesn't
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377 matter. */
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378 if (gimple_call_arg (call, 0) == rhs
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379 && gimple_call_arg (call, 1) == rhs
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380 && gimple_call_arg (call, 2) != rhs)
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381 info->flags.ignore_sign = true;
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382 break;
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383
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384 default:
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385 if (negate_mathfn_p (fn))
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386 {
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387 /* The sign of the (single) input doesn't matter provided
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388 that the sign of the output doesn't matter. */
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389 const usage_info *lhs_info = lookup_operand (lhs);
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390 if (lhs_info)
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391 info->flags.ignore_sign = lhs_info->flags.ignore_sign;
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392 }
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393 break;
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394 }
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395 }
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396
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397 /* Make INFO describe all uses of RHS in ASSIGN. */
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398
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399 void
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400 backprop::process_assign_use (gassign *assign, tree rhs, usage_info *info)
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401 {
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402 tree lhs = gimple_assign_lhs (assign);
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403 switch (gimple_assign_rhs_code (assign))
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404 {
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405 case ABS_EXPR:
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406 /* The sign of the input doesn't matter. */
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407 info->flags.ignore_sign = true;
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408 break;
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409
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410 case COND_EXPR:
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411 /* For A = B ? C : D, propagate information about all uses of A
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412 to C and D. */
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413 if (rhs != gimple_assign_rhs1 (assign))
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414 {
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415 const usage_info *lhs_info = lookup_operand (lhs);
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416 if (lhs_info)
|
|
|
417 *info = *lhs_info;
|
|
|
418 }
|
|
|
419 break;
|
|
|
420
|
|
|
421 case FMA_EXPR:
|
|
|
422 /* In X * X + Y, where Y is distinct from X, the sign of X doesn't
|
|
|
423 matter. */
|
|
|
424 if (gimple_assign_rhs1 (assign) == rhs
|
|
|
425 && gimple_assign_rhs2 (assign) == rhs
|
|
|
426 && gimple_assign_rhs3 (assign) != rhs)
|
|
|
427 info->flags.ignore_sign = true;
|
|
|
428 break;
|
|
|
429
|
|
|
430 case MULT_EXPR:
|
|
|
431 /* In X * X, the sign of X doesn't matter. */
|
|
|
432 if (gimple_assign_rhs1 (assign) == rhs
|
|
|
433 && gimple_assign_rhs2 (assign) == rhs)
|
|
|
434 info->flags.ignore_sign = true;
|
|
|
435 /* Fall through. */
|
|
|
436
|
|
|
437 case NEGATE_EXPR:
|
|
|
438 case RDIV_EXPR:
|
|
|
439 /* If the sign of the result doesn't matter, the sign of the inputs
|
|
|
440 doesn't matter either. */
|
|
|
441 if (FLOAT_TYPE_P (TREE_TYPE (rhs)))
|
|
|
442 {
|
|
|
443 const usage_info *lhs_info = lookup_operand (lhs);
|
|
|
444 if (lhs_info)
|
|
|
445 info->flags.ignore_sign = lhs_info->flags.ignore_sign;
|
|
|
446 }
|
|
|
447 break;
|
|
|
448
|
|
|
449 default:
|
|
|
450 break;
|
|
|
451 }
|
|
|
452 }
|
|
|
453
|
|
|
454 /* Make INFO describe the uses of PHI's result. */
|
|
|
455
|
|
|
456 void
|
|
|
457 backprop::process_phi_use (gphi *phi, usage_info *info)
|
|
|
458 {
|
|
|
459 tree result = gimple_phi_result (phi);
|
|
|
460 if (const usage_info *result_info = lookup_operand (result))
|
|
|
461 *info = *result_info;
|
|
|
462 }
|
|
|
463
|
|
|
464 /* Make INFO describe all uses of RHS in STMT. */
|
|
|
465
|
|
|
466 void
|
|
|
467 backprop::process_use (gimple *stmt, tree rhs, usage_info *info)
|
|
|
468 {
|
|
|
469 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
470 {
|
|
|
471 fprintf (dump_file, "[USE] ");
|
|
|
472 print_generic_expr (dump_file, rhs);
|
|
|
473 fprintf (dump_file, " in ");
|
|
|
474 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
|
|
|
475 }
|
|
|
476
|
|
|
477 if (gcall *call = dyn_cast <gcall *> (stmt))
|
|
|
478 process_builtin_call_use (call, rhs, info);
|
|
|
479 else if (gassign *assign = dyn_cast <gassign *> (stmt))
|
|
|
480 process_assign_use (assign, rhs, info);
|
|
|
481 else if (gphi *phi = dyn_cast <gphi *> (stmt))
|
|
|
482 process_phi_use (phi, info);
|
|
|
483
|
|
|
484 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
485 dump_usage_info (dump_file, rhs, info);
|
|
|
486 }
|
|
|
487
|
|
|
488 /* Make INFO describe all uses of VAR, returning true if the result
|
|
|
489 is useful. If the uses include phis that haven't been processed yet,
|
|
|
490 make the most optimistic assumption possible, so that we aim for
|
|
|
491 a maximum rather than a minimum fixed point. */
|
|
|
492
|
|
|
493 bool
|
|
|
494 backprop::intersect_uses (tree var, usage_info *info)
|
|
|
495 {
|
|
|
496 imm_use_iterator iter;
|
|
|
497 gimple *stmt;
|
|
|
498 *info = usage_info::intersection_identity ();
|
|
|
499 FOR_EACH_IMM_USE_STMT (stmt, iter, var)
|
|
|
500 {
|
|
|
501 if (is_gimple_debug (stmt))
|
|
|
502 continue;
|
|
|
503 if (is_a <gphi *> (stmt)
|
|
|
504 && !bitmap_bit_p (m_visited_blocks, gimple_bb (stmt)->index))
|
|
|
505 {
|
|
|
506 /* Skip unprocessed phis. */
|
|
|
507 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
508 {
|
|
|
509 fprintf (dump_file, "[BACKEDGE] ");
|
|
|
510 print_generic_expr (dump_file, var);
|
|
|
511 fprintf (dump_file, " in ");
|
|
|
512 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
|
|
|
513 }
|
|
|
514 }
|
|
|
515 else
|
|
|
516 {
|
|
|
517 usage_info subinfo;
|
|
|
518 process_use (stmt, var, &subinfo);
|
|
|
519 *info &= subinfo;
|
|
|
520 if (!info->is_useful ())
|
|
|
521 {
|
|
|
522 BREAK_FROM_IMM_USE_STMT (iter);
|
|
|
523 return false;
|
|
|
524 }
|
|
|
525 }
|
|
|
526 }
|
|
|
527 return true;
|
|
|
528 }
|
|
|
529
|
|
|
530 /* Queue for reconsideration any input of STMT that has information
|
|
|
531 associated with it. This is used if that information might be
|
|
|
532 too optimistic. */
|
|
|
533
|
|
|
534 void
|
|
|
535 backprop::reprocess_inputs (gimple *stmt)
|
|
|
536 {
|
|
|
537 use_operand_p use_p;
|
|
|
538 ssa_op_iter oi;
|
|
|
539 FOR_EACH_PHI_OR_STMT_USE (use_p, stmt, oi, SSA_OP_USE)
|
|
|
540 {
|
|
|
541 tree var = get_use_from_ptr (use_p);
|
|
|
542 if (lookup_operand (var))
|
|
|
543 push_to_worklist (var);
|
|
|
544 }
|
|
|
545 }
|
|
|
546
|
|
|
547 /* Say that we're recording INFO for SSA name VAR, or that we're deleting
|
|
|
548 existing information if INFO is null. INTRO describes the change. */
|
|
|
549
|
|
|
550 static void
|
|
|
551 dump_var_info (tree var, usage_info *info, const char *intro)
|
|
|
552 {
|
|
|
553 fprintf (dump_file, "[DEF] %s for ", intro);
|
|
|
554 print_gimple_stmt (dump_file, SSA_NAME_DEF_STMT (var), 0, TDF_SLIM);
|
|
|
555 if (info)
|
|
|
556 dump_usage_info (dump_file, var, info);
|
|
|
557 }
|
|
|
558
|
|
|
559 /* Process all uses of VAR and record or update the result in
|
|
|
560 M_INFO_MAP and M_VARS. */
|
|
|
561
|
|
|
562 void
|
|
|
563 backprop::process_var (tree var)
|
|
|
564 {
|
|
|
565 if (has_zero_uses (var))
|
|
|
566 return;
|
|
|
567
|
|
|
568 usage_info info;
|
|
|
569 intersect_uses (var, &info);
|
|
|
570
|
|
|
571 gimple *stmt = SSA_NAME_DEF_STMT (var);
|
|
|
572 if (info.is_useful ())
|
|
|
573 {
|
|
|
574 bool existed;
|
|
|
575 usage_info *&map_info = m_info_map.get_or_insert (var, &existed);
|
|
|
576 if (!existed)
|
|
|
577 {
|
|
|
578 /* Recording information about VAR for the first time. */
|
|
|
579 map_info = m_info_pool.allocate ();
|
|
|
580 *map_info = info;
|
|
|
581 m_vars.safe_push (var_info_pair (var, map_info));
|
|
|
582 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
583 dump_var_info (var, map_info, "Recording new information");
|
|
|
584
|
|
|
585 /* If STMT is a phi, reprocess any backedge uses. This is a
|
|
|
586 no-op for other uses, which won't have any information
|
|
|
587 associated with them. */
|
|
|
588 if (is_a <gphi *> (stmt))
|
|
|
589 reprocess_inputs (stmt);
|
|
|
590 }
|
|
|
591 else if (info != *map_info)
|
|
|
592 {
|
|
|
593 /* Recording information that is less optimistic than before. */
|
|
|
594 gcc_checking_assert ((info & *map_info) == info);
|
|
|
595 *map_info = info;
|
|
|
596 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
597 dump_var_info (var, map_info, "Updating information");
|
|
|
598 reprocess_inputs (stmt);
|
|
|
599 }
|
|
|
600 }
|
|
|
601 else
|
|
|
602 {
|
|
|
603 if (usage_info **slot = m_info_map.get (var))
|
|
|
604 {
|
|
|
605 /* Removing previously-recorded information. */
|
|
|
606 **slot = info;
|
|
|
607 m_info_map.remove (var);
|
|
|
608 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
609 dump_var_info (var, NULL, "Deleting information");
|
|
|
610 reprocess_inputs (stmt);
|
|
|
611 }
|
|
|
612 else
|
|
|
613 {
|
|
|
614 /* If STMT is a phi, remove any information recorded for
|
|
|
615 its arguments. */
|
|
|
616 if (is_a <gphi *> (stmt))
|
|
|
617 reprocess_inputs (stmt);
|
|
|
618 }
|
|
|
619 }
|
|
|
620 }
|
|
|
621
|
|
|
622 /* Process all statements and phis in BB, during the first post-order walk. */
|
|
|
623
|
|
|
624 void
|
|
|
625 backprop::process_block (basic_block bb)
|
|
|
626 {
|
|
|
627 for (gimple_stmt_iterator gsi = gsi_last_bb (bb); !gsi_end_p (gsi);
|
|
|
628 gsi_prev (&gsi))
|
|
|
629 {
|
|
|
630 tree lhs = gimple_get_lhs (gsi_stmt (gsi));
|
|
|
631 if (lhs && TREE_CODE (lhs) == SSA_NAME)
|
|
|
632 process_var (lhs);
|
|
|
633 }
|
|
|
634 for (gphi_iterator gpi = gsi_start_phis (bb); !gsi_end_p (gpi);
|
|
|
635 gsi_next (&gpi))
|
|
|
636 process_var (gimple_phi_result (gpi.phi ()));
|
|
|
637 }
|
|
|
638
|
|
|
639 /* Delete the definition of VAR, which has no uses. */
|
|
|
640
|
|
|
641 static void
|
|
|
642 remove_unused_var (tree var)
|
|
|
643 {
|
|
|
644 gimple *stmt = SSA_NAME_DEF_STMT (var);
|
|
|
645 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
646 {
|
|
|
647 fprintf (dump_file, "Deleting ");
|
|
|
648 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
|
|
|
649 }
|
|
|
650 gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
|
|
|
651 gsi_remove (&gsi, true);
|
|
|
652 release_defs (stmt);
|
|
|
653 }
|
|
|
654
|
|
|
655 /* Note that we're replacing OLD_RHS with NEW_RHS in STMT. */
|
|
|
656
|
|
|
657 static void
|
|
|
658 note_replacement (gimple *stmt, tree old_rhs, tree new_rhs)
|
|
|
659 {
|
|
|
660 fprintf (dump_file, "Replacing use of ");
|
|
|
661 print_generic_expr (dump_file, old_rhs);
|
|
|
662 fprintf (dump_file, " with ");
|
|
|
663 print_generic_expr (dump_file, new_rhs);
|
|
|
664 fprintf (dump_file, " in ");
|
|
|
665 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
|
|
|
666 }
|
|
|
667
|
|
|
668 /* If RHS is an SSA name whose definition just changes the sign of a value,
|
|
|
669 return that other value, otherwise return null. */
|
|
|
670
|
|
|
671 static tree
|
|
|
672 strip_sign_op_1 (tree rhs)
|
|
|
673 {
|
|
|
674 if (TREE_CODE (rhs) != SSA_NAME)
|
|
|
675 return NULL_TREE;
|
|
|
676
|
|
|
677 gimple *def_stmt = SSA_NAME_DEF_STMT (rhs);
|
|
|
678 if (gassign *assign = dyn_cast <gassign *> (def_stmt))
|
|
|
679 switch (gimple_assign_rhs_code (assign))
|
|
|
680 {
|
|
|
681 case ABS_EXPR:
|
|
|
682 case NEGATE_EXPR:
|
|
|
683 return gimple_assign_rhs1 (assign);
|
|
|
684
|
|
|
685 default:
|
|
|
686 break;
|
|
|
687 }
|
|
|
688 else if (gcall *call = dyn_cast <gcall *> (def_stmt))
|
|
|
689 switch (gimple_call_combined_fn (call))
|
|
|
690 {
|
|
|
691 CASE_CFN_COPYSIGN:
|
|
|
692 return gimple_call_arg (call, 0);
|
|
|
693
|
|
|
694 default:
|
|
|
695 break;
|
|
|
696 }
|
|
|
697
|
|
|
698 return NULL_TREE;
|
|
|
699 }
|
|
|
700
|
|
|
701 /* If RHS is an SSA name whose definition just changes the sign of a value,
|
|
|
702 strip all such operations and return the ultimate input to them.
|
|
|
703 Return null otherwise.
|
|
|
704
|
|
|
705 Although this could in principle lead to quadratic searching,
|
|
|
706 in practice a long sequence of sign manipulations should already
|
|
|
707 have been folded down. E.g. --x -> x, abs(-x) -> abs(x). We search
|
|
|
708 for more than one operation in order to catch cases like -abs(x). */
|
|
|
709
|
|
|
710 static tree
|
|
|
711 strip_sign_op (tree rhs)
|
|
|
712 {
|
|
|
713 tree new_rhs = strip_sign_op_1 (rhs);
|
|
|
714 if (!new_rhs)
|
|
|
715 return NULL_TREE;
|
|
|
716 while (tree next = strip_sign_op_1 (new_rhs))
|
|
|
717 new_rhs = next;
|
|
|
718 return new_rhs;
|
|
|
719 }
|
|
|
720
|
|
|
721 /* Start a change in the value of VAR that is suitable for all non-debug
|
|
|
722 uses of VAR. We need to make sure that debug statements continue to
|
|
|
723 use the original definition of VAR where possible, or are nullified
|
|
|
724 otherwise. */
|
|
|
725
|
|
|
726 void
|
|
|
727 backprop::prepare_change (tree var)
|
|
|
728 {
|
|
|
729 if (MAY_HAVE_DEBUG_STMTS)
|
|
|
730 insert_debug_temp_for_var_def (NULL, var);
|
|
|
731 reset_flow_sensitive_info (var);
|
|
|
732 }
|
|
|
733
|
|
|
734 /* STMT has been changed. Give the fold machinery a chance to simplify
|
|
|
735 and canonicalize it (e.g. by ensuring that commutative operands have
|
|
|
736 the right order), then record the updates. */
|
|
|
737
|
|
|
738 void
|
|
|
739 backprop::complete_change (gimple *stmt)
|
|
|
740 {
|
|
|
741 gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
|
|
|
742 if (fold_stmt (&gsi))
|
|
|
743 {
|
|
|
744 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
745 {
|
|
|
746 fprintf (dump_file, " which folds to: ");
|
|
|
747 print_gimple_stmt (dump_file, gsi_stmt (gsi), 0, TDF_SLIM);
|
|
|
748 }
|
|
|
749 }
|
|
|
750 update_stmt (gsi_stmt (gsi));
|
|
|
751 }
|
|
|
752
|
|
|
753 /* Optimize CALL, a call to a built-in function with lhs LHS, on the
|
|
|
754 basis that INFO describes all uses of LHS. */
|
|
|
755
|
|
|
756 void
|
|
|
757 backprop::optimize_builtin_call (gcall *call, tree lhs, const usage_info *info)
|
|
|
758 {
|
|
|
759 /* If we have an f such that -f(x) = f(-x), and if the sign of the result
|
|
|
760 doesn't matter, strip any sign operations from the input. */
|
|
|
761 if (info->flags.ignore_sign
|
|
|
762 && negate_mathfn_p (gimple_call_combined_fn (call)))
|
|
|
763 {
|
|
|
764 tree new_arg = strip_sign_op (gimple_call_arg (call, 0));
|
|
|
765 if (new_arg)
|
|
|
766 {
|
|
|
767 prepare_change (lhs);
|
|
|
768 gimple_call_set_arg (call, 0, new_arg);
|
|
|
769 complete_change (call);
|
|
|
770 }
|
|
|
771 }
|
|
|
772 }
|
|
|
773
|
|
|
774 /* Optimize ASSIGN, an assignment to LHS, by replacing rhs operand N
|
|
|
775 with RHS<N>, if RHS<N> is nonnull. This may change the value of LHS. */
|
|
|
776
|
|
|
777 void
|
|
|
778 backprop::replace_assign_rhs (gassign *assign, tree lhs, tree rhs1,
|
|
|
779 tree rhs2, tree rhs3)
|
|
|
780 {
|
|
|
781 if (!rhs1 && !rhs2 && !rhs3)
|
|
|
782 return;
|
|
|
783
|
|
|
784 prepare_change (lhs);
|
|
|
785 if (rhs1)
|
|
|
786 gimple_assign_set_rhs1 (assign, rhs1);
|
|
|
787 if (rhs2)
|
|
|
788 gimple_assign_set_rhs2 (assign, rhs2);
|
|
|
789 if (rhs3)
|
|
|
790 gimple_assign_set_rhs3 (assign, rhs3);
|
|
|
791 complete_change (assign);
|
|
|
792 }
|
|
|
793
|
|
|
794 /* Optimize ASSIGN, an assignment to LHS, on the basis that INFO
|
|
|
795 describes all uses of LHS. */
|
|
|
796
|
|
|
797 void
|
|
|
798 backprop::optimize_assign (gassign *assign, tree lhs, const usage_info *info)
|
|
|
799 {
|
|
|
800 switch (gimple_assign_rhs_code (assign))
|
|
|
801 {
|
|
|
802 case MULT_EXPR:
|
|
|
803 case RDIV_EXPR:
|
|
|
804 /* If the sign of the result doesn't matter, strip sign operations
|
|
|
805 from both inputs. */
|
|
|
806 if (info->flags.ignore_sign)
|
|
|
807 replace_assign_rhs (assign, lhs,
|
|
|
808 strip_sign_op (gimple_assign_rhs1 (assign)),
|
|
|
809 strip_sign_op (gimple_assign_rhs2 (assign)),
|
|
|
810 NULL_TREE);
|
|
|
811 break;
|
|
|
812
|
|
|
813 case COND_EXPR:
|
|
|
814 /* If the sign of A ? B : C doesn't matter, strip sign operations
|
|
|
815 from both B and C. */
|
|
|
816 if (info->flags.ignore_sign)
|
|
|
817 replace_assign_rhs (assign, lhs,
|
|
|
818 NULL_TREE,
|
|
|
819 strip_sign_op (gimple_assign_rhs2 (assign)),
|
|
|
820 strip_sign_op (gimple_assign_rhs3 (assign)));
|
|
|
821 break;
|
|
|
822
|
|
|
823 default:
|
|
|
824 break;
|
|
|
825 }
|
|
|
826 }
|
|
|
827
|
|
|
828 /* Optimize PHI, which defines VAR, on the basis that INFO describes all
|
|
|
829 uses of the result. */
|
|
|
830
|
|
|
831 void
|
|
|
832 backprop::optimize_phi (gphi *phi, tree var, const usage_info *info)
|
|
|
833 {
|
|
|
834 /* If the sign of the result doesn't matter, try to strip sign operations
|
|
|
835 from arguments. */
|
|
|
836 if (info->flags.ignore_sign)
|
|
|
837 {
|
|
|
838 basic_block bb = gimple_bb (phi);
|
|
|
839 use_operand_p use;
|
|
|
840 ssa_op_iter oi;
|
|
|
841 bool replaced = false;
|
|
|
842 FOR_EACH_PHI_ARG (use, phi, oi, SSA_OP_USE)
|
|
|
843 {
|
|
|
844 /* Propagating along abnormal edges is delicate, punt for now. */
|
|
|
845 const int index = PHI_ARG_INDEX_FROM_USE (use);
|
|
|
846 if (EDGE_PRED (bb, index)->flags & EDGE_ABNORMAL)
|
|
|
847 continue;
|
|
|
848
|
|
|
849 tree new_arg = strip_sign_op (USE_FROM_PTR (use));
|
|
|
850 if (new_arg)
|
|
|
851 {
|
|
|
852 if (!replaced)
|
|
|
853 prepare_change (var);
|
|
|
854 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
855 note_replacement (phi, USE_FROM_PTR (use), new_arg);
|
|
|
856 replace_exp (use, new_arg);
|
|
|
857 replaced = true;
|
|
|
858 }
|
|
|
859 }
|
|
|
860 }
|
|
|
861 }
|
|
|
862
|
|
|
863 void
|
|
|
864 backprop::execute ()
|
|
|
865 {
|
|
|
866 /* Phase 1: Traverse the function, making optimistic assumptions
|
|
|
867 about any phi whose definition we haven't seen. */
|
|
|
868 int *postorder = XNEWVEC (int, n_basic_blocks_for_fn (m_fn));
|
|
|
869 unsigned int postorder_num = post_order_compute (postorder, false, false);
|
|
|
870 for (unsigned int i = 0; i < postorder_num; ++i)
|
|
|
871 {
|
|
|
872 process_block (BASIC_BLOCK_FOR_FN (m_fn, postorder[i]));
|
|
|
873 bitmap_set_bit (m_visited_blocks, postorder[i]);
|
|
|
874 }
|
|
|
875 XDELETEVEC (postorder);
|
|
|
876
|
|
|
877 /* Phase 2: Use the initial (perhaps overly optimistic) information
|
|
|
878 to create a maximal fixed point solution. */
|
|
|
879 while (!m_worklist.is_empty ())
|
|
|
880 process_var (pop_from_worklist ());
|
|
|
881
|
|
|
882 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
883 fprintf (dump_file, "\n");
|
|
|
884
|
|
|
885 /* Phase 3: Do a reverse post-order walk, using information about
|
|
|
886 the uses of SSA names to optimize their definitions. */
|
|
|
887 for (unsigned int i = m_vars.length (); i-- > 0;)
|
|
|
888 {
|
|
|
889 usage_info *info = m_vars[i].second;
|
|
|
890 if (info->is_useful ())
|
|
|
891 {
|
|
|
892 tree var = m_vars[i].first;
|
|
|
893 gimple *stmt = SSA_NAME_DEF_STMT (var);
|
|
|
894 if (gcall *call = dyn_cast <gcall *> (stmt))
|
|
|
895 optimize_builtin_call (call, var, info);
|
|
|
896 else if (gassign *assign = dyn_cast <gassign *> (stmt))
|
|
|
897 optimize_assign (assign, var, info);
|
|
|
898 else if (gphi *phi = dyn_cast <gphi *> (stmt))
|
|
|
899 optimize_phi (phi, var, info);
|
|
|
900 }
|
|
|
901 }
|
|
|
902
|
|
|
903 /* Phase 4: Do a post-order walk, deleting statements that are no
|
|
|
904 longer needed. */
|
|
|
905 for (unsigned int i = 0; i < m_vars.length (); ++i)
|
|
|
906 {
|
|
|
907 tree var = m_vars[i].first;
|
|
|
908 if (has_zero_uses (var))
|
|
|
909 remove_unused_var (var);
|
|
|
910 }
|
|
|
911
|
|
|
912 if (dump_file && (dump_flags & TDF_DETAILS))
|
|
|
913 fprintf (dump_file, "\n");
|
|
|
914 }
|
|
|
915
|
|
|
916 const pass_data pass_data_backprop =
|
|
|
917 {
|
|
|
918 GIMPLE_PASS, /* type */
|
|
|
919 "backprop", /* name */
|
|
|
920 OPTGROUP_NONE, /* optinfo_flags */
|
|
|
921 TV_TREE_BACKPROP, /* tv_id */
|
|
|
922 ( PROP_cfg | PROP_ssa ), /* properties_required */
|
|
|
923 0, /* properties_provided */
|
|
|
924 0, /* properties_destroyed */
|
|
|
925 0, /* todo_flags_start */
|
|
|
926 0, /* todo_flags_finish */
|
|
|
927 };
|
|
|
928
|
|
|
929 class pass_backprop : public gimple_opt_pass
|
|
|
930 {
|
|
|
931 public:
|
|
|
932 pass_backprop (gcc::context *ctxt)
|
|
|
933 : gimple_opt_pass (pass_data_backprop, ctxt)
|
|
|
934 {}
|
|
|
935
|
|
|
936 /* opt_pass methods: */
|
|
|
937 opt_pass * clone () { return new pass_backprop (m_ctxt); }
|
|
|
938 virtual bool gate (function *) { return flag_ssa_backprop; }
|
|
|
939 virtual unsigned int execute (function *);
|
|
|
940
|
|
|
941 }; // class pass_backprop
|
|
|
942
|
|
|
943 unsigned int
|
|
|
944 pass_backprop::execute (function *fn)
|
|
|
945 {
|
|
|
946 backprop (fn).execute ();
|
|
|
947 return 0;
|
|
|
948 }
|
|
|
949
|
|
|
950 } // anon namespace
|
|
|
951
|
|
|
952 gimple_opt_pass *
|
|
|
953 make_pass_backprop (gcc::context *ctxt)
|
|
|
954 {
|
|
|
955 return new pass_backprop (ctxt);
|
|
|
956 }
|
