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1 /* Combine stack adjustments.
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2 Copyright (C) 1987, 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
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3 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
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4 Free Software Foundation, Inc.
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5
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6 This file is part of GCC.
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7
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8 GCC is free software; you can redistribute it and/or modify it under
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9 the terms of the GNU General Public License as published by the Free
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10 Software Foundation; either version 3, or (at your option) any later
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11 version.
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12
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13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
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15 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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16 for more details.
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17
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18 You should have received a copy of the GNU General Public License
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19 along with GCC; see the file COPYING3. If not see
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20 <http://www.gnu.org/licenses/>. */
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21
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22 /* Track stack adjustments and stack memory references. Attempt to
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23 reduce the number of stack adjustments by back-propagating across
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24 the memory references.
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25
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26 This is intended primarily for use with targets that do not define
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27 ACCUMULATE_OUTGOING_ARGS. It is of significantly more value to
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28 targets that define PREFERRED_STACK_BOUNDARY more aligned than
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29 STACK_BOUNDARY (e.g. x86), or if not all registers can be pushed
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30 (e.g. x86 fp regs) which would ordinarily have to be implemented
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31 as a sub/mov pair due to restrictions in calls.c.
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32
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33 Propagation stops when any of the insns that need adjusting are
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34 (a) no longer valid because we've exceeded their range, (b) a
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35 non-trivial push instruction, or (c) a call instruction.
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36
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37 Restriction B is based on the assumption that push instructions
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38 are smaller or faster. If a port really wants to remove all
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39 pushes, it should have defined ACCUMULATE_OUTGOING_ARGS. The
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40 one exception that is made is for an add immediately followed
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41 by a push. */
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42
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43 #include "config.h"
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44 #include "system.h"
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45 #include "coretypes.h"
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46 #include "tm.h"
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47 #include "rtl.h"
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48 #include "tm_p.h"
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49 #include "insn-config.h"
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50 #include "recog.h"
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51 #include "output.h"
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52 #include "regs.h"
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53 #include "hard-reg-set.h"
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54 #include "flags.h"
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55 #include "function.h"
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56 #include "expr.h"
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57 #include "basic-block.h"
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58 #include "df.h"
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59 #include "except.h"
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60 #include "toplev.h"
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61 #include "reload.h"
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62 #include "timevar.h"
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63 #include "tree-pass.h"
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64
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65
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66 /* Turn STACK_GROWS_DOWNWARD into a boolean. */
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67 #ifdef STACK_GROWS_DOWNWARD
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68 #undef STACK_GROWS_DOWNWARD
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69 #define STACK_GROWS_DOWNWARD 1
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70 #else
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71 #define STACK_GROWS_DOWNWARD 0
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72 #endif
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73
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74 /* This structure records stack memory references between stack adjusting
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75 instructions. */
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76
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77 struct csa_memlist
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78 {
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79 HOST_WIDE_INT sp_offset;
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80 rtx insn, *mem;
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81 struct csa_memlist *next;
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82 };
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83
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84 static int stack_memref_p (rtx);
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85 static rtx single_set_for_csa (rtx);
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86 static void free_csa_memlist (struct csa_memlist *);
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87 static struct csa_memlist *record_one_stack_memref (rtx, rtx *,
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88 struct csa_memlist *);
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89 static int try_apply_stack_adjustment (rtx, struct csa_memlist *,
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90 HOST_WIDE_INT, HOST_WIDE_INT);
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91 static void combine_stack_adjustments_for_block (basic_block);
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92 static int record_stack_memrefs (rtx *, void *);
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93
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94
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95 /* Main entry point for stack adjustment combination. */
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96
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97 static void
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98 combine_stack_adjustments (void)
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99 {
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100 basic_block bb;
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101
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102 FOR_EACH_BB (bb)
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103 combine_stack_adjustments_for_block (bb);
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104 }
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105
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106 /* Recognize a MEM of the form (sp) or (plus sp const). */
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107
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108 static int
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109 stack_memref_p (rtx x)
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110 {
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111 if (!MEM_P (x))
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112 return 0;
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113 x = XEXP (x, 0);
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114
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115 if (x == stack_pointer_rtx)
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116 return 1;
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117 if (GET_CODE (x) == PLUS
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118 && XEXP (x, 0) == stack_pointer_rtx
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119 && GET_CODE (XEXP (x, 1)) == CONST_INT)
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120 return 1;
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121
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122 return 0;
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123 }
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124
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125 /* Recognize either normal single_set or the hack in i386.md for
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126 tying fp and sp adjustments. */
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127
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128 static rtx
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129 single_set_for_csa (rtx insn)
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130 {
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131 int i;
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132 rtx tmp = single_set (insn);
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133 if (tmp)
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134 return tmp;
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135
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136 if (!NONJUMP_INSN_P (insn)
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137 || GET_CODE (PATTERN (insn)) != PARALLEL)
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138 return NULL_RTX;
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139
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140 tmp = PATTERN (insn);
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141 if (GET_CODE (XVECEXP (tmp, 0, 0)) != SET)
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142 return NULL_RTX;
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143
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144 for (i = 1; i < XVECLEN (tmp, 0); ++i)
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145 {
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146 rtx this_rtx = XVECEXP (tmp, 0, i);
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147
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148 /* The special case is allowing a no-op set. */
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149 if (GET_CODE (this_rtx) == SET
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150 && SET_SRC (this_rtx) == SET_DEST (this_rtx))
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151 ;
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152 else if (GET_CODE (this_rtx) != CLOBBER
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153 && GET_CODE (this_rtx) != USE)
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154 return NULL_RTX;
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155 }
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156
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157 return XVECEXP (tmp, 0, 0);
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158 }
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159
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160 /* Free the list of csa_memlist nodes. */
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161
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162 static void
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163 free_csa_memlist (struct csa_memlist *memlist)
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164 {
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165 struct csa_memlist *next;
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166 for (; memlist ; memlist = next)
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167 {
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168 next = memlist->next;
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169 free (memlist);
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170 }
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171 }
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172
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173 /* Create a new csa_memlist node from the given memory reference.
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174 It is already known that the memory is stack_memref_p. */
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175
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176 static struct csa_memlist *
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177 record_one_stack_memref (rtx insn, rtx *mem, struct csa_memlist *next_memlist)
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178 {
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179 struct csa_memlist *ml;
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180
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181 ml = XNEW (struct csa_memlist);
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182
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183 if (XEXP (*mem, 0) == stack_pointer_rtx)
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184 ml->sp_offset = 0;
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185 else
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186 ml->sp_offset = INTVAL (XEXP (XEXP (*mem, 0), 1));
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187
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188 ml->insn = insn;
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189 ml->mem = mem;
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190 ml->next = next_memlist;
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191
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192 return ml;
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193 }
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194
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195 /* Attempt to apply ADJUST to the stack adjusting insn INSN, as well
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196 as each of the memories in MEMLIST. Return true on success. */
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197
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198 static int
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199 try_apply_stack_adjustment (rtx insn, struct csa_memlist *memlist, HOST_WIDE_INT new_adjust,
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200 HOST_WIDE_INT delta)
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201 {
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202 struct csa_memlist *ml;
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203 rtx set;
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204
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205 set = single_set_for_csa (insn);
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206 validate_change (insn, &XEXP (SET_SRC (set), 1), GEN_INT (new_adjust), 1);
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207
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208 for (ml = memlist; ml ; ml = ml->next)
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209 validate_change
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210 (ml->insn, ml->mem,
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211 replace_equiv_address_nv (*ml->mem,
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212 plus_constant (stack_pointer_rtx,
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213 ml->sp_offset - delta)), 1);
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214
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215 if (apply_change_group ())
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216 {
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217 /* Succeeded. Update our knowledge of the memory references. */
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218 for (ml = memlist; ml ; ml = ml->next)
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219 ml->sp_offset -= delta;
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220
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221 return 1;
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222 }
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223 else
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224 return 0;
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225 }
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226
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227 /* Called via for_each_rtx and used to record all stack memory references in
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228 the insn and discard all other stack pointer references. */
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229 struct record_stack_memrefs_data
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230 {
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231 rtx insn;
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232 struct csa_memlist *memlist;
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233 };
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234
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235 static int
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236 record_stack_memrefs (rtx *xp, void *data)
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237 {
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238 rtx x = *xp;
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239 struct record_stack_memrefs_data *d =
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240 (struct record_stack_memrefs_data *) data;
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241 if (!x)
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242 return 0;
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243 switch (GET_CODE (x))
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244 {
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245 case MEM:
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246 if (!reg_mentioned_p (stack_pointer_rtx, x))
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247 return -1;
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248 /* We are not able to handle correctly all possible memrefs containing
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249 stack pointer, so this check is necessary. */
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250 if (stack_memref_p (x))
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251 {
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252 d->memlist = record_one_stack_memref (d->insn, xp, d->memlist);
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253 return -1;
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254 }
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255 return 1;
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256 case REG:
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257 /* ??? We want be able to handle non-memory stack pointer
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258 references later. For now just discard all insns referring to
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259 stack pointer outside mem expressions. We would probably
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260 want to teach validate_replace to simplify expressions first.
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261
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262 We can't just compare with STACK_POINTER_RTX because the
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263 reference to the stack pointer might be in some other mode.
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264 In particular, an explicit clobber in an asm statement will
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265 result in a QImode clobber. */
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266 if (REGNO (x) == STACK_POINTER_REGNUM)
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267 return 1;
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268 break;
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269 default:
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270 break;
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271 }
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272 return 0;
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273 }
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274
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275 /* Adjust or create REG_FRAME_RELATED_EXPR note when merging a stack
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276 adjustment into a frame related insn. */
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277
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278 static void
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279 adjust_frame_related_expr (rtx last_sp_set, rtx insn,
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280 HOST_WIDE_INT this_adjust)
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281 {
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282 rtx note = find_reg_note (last_sp_set, REG_FRAME_RELATED_EXPR, NULL_RTX);
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283 rtx new_expr = NULL_RTX;
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284
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285 if (note == NULL_RTX && RTX_FRAME_RELATED_P (insn))
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286 return;
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287
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288 if (note
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289 && GET_CODE (XEXP (note, 0)) == SEQUENCE
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290 && XVECLEN (XEXP (note, 0), 0) >= 2)
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291 {
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292 rtx expr = XEXP (note, 0);
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293 rtx last = XVECEXP (expr, 0, XVECLEN (expr, 0) - 1);
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294 int i;
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295
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296 if (GET_CODE (last) == SET
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297 && RTX_FRAME_RELATED_P (last) == RTX_FRAME_RELATED_P (insn)
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298 && SET_DEST (last) == stack_pointer_rtx
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299 && GET_CODE (SET_SRC (last)) == PLUS
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300 && XEXP (SET_SRC (last), 0) == stack_pointer_rtx
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301 && GET_CODE (XEXP (SET_SRC (last), 1)) == CONST_INT)
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302 {
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303 XEXP (SET_SRC (last), 1)
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304 = GEN_INT (INTVAL (XEXP (SET_SRC (last), 1)) + this_adjust);
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305 return;
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306 }
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307
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308 new_expr = gen_rtx_SEQUENCE (VOIDmode,
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309 rtvec_alloc (XVECLEN (expr, 0) + 1));
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310 for (i = 0; i < XVECLEN (expr, 0); i++)
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311 XVECEXP (new_expr, 0, i) = XVECEXP (expr, 0, i);
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312 }
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313 else
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314 {
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315 new_expr = gen_rtx_SEQUENCE (VOIDmode, rtvec_alloc (2));
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316 if (note)
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317 XVECEXP (new_expr, 0, 0) = XEXP (note, 0);
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318 else
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319 {
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320 rtx expr = copy_rtx (single_set_for_csa (last_sp_set));
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321
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322 XEXP (SET_SRC (expr), 1)
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323 = GEN_INT (INTVAL (XEXP (SET_SRC (expr), 1)) - this_adjust);
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324 RTX_FRAME_RELATED_P (expr) = 1;
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325 XVECEXP (new_expr, 0, 0) = expr;
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326 }
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327 }
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328
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329 XVECEXP (new_expr, 0, XVECLEN (new_expr, 0) - 1)
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330 = copy_rtx (single_set_for_csa (insn));
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331 RTX_FRAME_RELATED_P (XVECEXP (new_expr, 0, XVECLEN (new_expr, 0) - 1))
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332 = RTX_FRAME_RELATED_P (insn);
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333 if (note)
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334 XEXP (note, 0) = new_expr;
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335 else
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336 REG_NOTES (last_sp_set)
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337 = gen_rtx_EXPR_LIST (REG_FRAME_RELATED_EXPR, new_expr,
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338 REG_NOTES (last_sp_set));
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339 }
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340
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341 /* Subroutine of combine_stack_adjustments, called for each basic block. */
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342
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343 static void
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344 combine_stack_adjustments_for_block (basic_block bb)
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345 {
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346 HOST_WIDE_INT last_sp_adjust = 0;
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347 rtx last_sp_set = NULL_RTX;
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348 struct csa_memlist *memlist = NULL;
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349 rtx insn, next, set;
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350 struct record_stack_memrefs_data data;
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351 bool end_of_block = false;
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352
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353 for (insn = BB_HEAD (bb); !end_of_block ; insn = next)
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354 {
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355 end_of_block = insn == BB_END (bb);
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356 next = NEXT_INSN (insn);
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357
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358 if (! INSN_P (insn))
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359 continue;
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360
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361 set = single_set_for_csa (insn);
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362 if (set)
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363 {
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364 rtx dest = SET_DEST (set);
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365 rtx src = SET_SRC (set);
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366
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367 /* Find constant additions to the stack pointer. */
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368 if (dest == stack_pointer_rtx
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369 && GET_CODE (src) == PLUS
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370 && XEXP (src, 0) == stack_pointer_rtx
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371 && GET_CODE (XEXP (src, 1)) == CONST_INT)
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372 {
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373 HOST_WIDE_INT this_adjust = INTVAL (XEXP (src, 1));
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374
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375 /* If we've not seen an adjustment previously, record
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376 it now and continue. */
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377 if (! last_sp_set)
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378 {
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379 last_sp_set = insn;
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380 last_sp_adjust = this_adjust;
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381 continue;
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382 }
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383
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384 /* If not all recorded memrefs can be adjusted, or the
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385 adjustment is now too large for a constant addition,
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386 we cannot merge the two stack adjustments.
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387
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388 Also we need to be careful to not move stack pointer
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389 such that we create stack accesses outside the allocated
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390 area. We can combine an allocation into the first insn,
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391 or a deallocation into the second insn. We can not
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392 combine an allocation followed by a deallocation.
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393
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394 The only somewhat frequent occurrence of the later is when
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395 a function allocates a stack frame but does not use it.
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396 For this case, we would need to analyze rtl stream to be
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397 sure that allocated area is really unused. This means not
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398 only checking the memory references, but also all registers
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399 or global memory references possibly containing a stack
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400 frame address.
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401
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402 Perhaps the best way to address this problem is to teach
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403 gcc not to allocate stack for objects never used. */
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404
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405 /* Combine an allocation into the first instruction. */
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406 if (STACK_GROWS_DOWNWARD ? this_adjust <= 0 : this_adjust >= 0)
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407 {
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408 if (try_apply_stack_adjustment (last_sp_set, memlist,
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409 last_sp_adjust + this_adjust,
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410 this_adjust))
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411 {
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412 if (RTX_FRAME_RELATED_P (last_sp_set))
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413 adjust_frame_related_expr (last_sp_set, insn,
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414 this_adjust);
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415 /* It worked! */
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416 delete_insn (insn);
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417 last_sp_adjust += this_adjust;
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418 continue;
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419 }
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420 }
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421
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422 /* Otherwise we have a deallocation. Do not combine with
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423 a previous allocation. Combine into the second insn. */
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424 else if (STACK_GROWS_DOWNWARD
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425 ? last_sp_adjust >= 0 : last_sp_adjust <= 0)
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426 {
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427 if (try_apply_stack_adjustment (insn, memlist,
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428 last_sp_adjust + this_adjust,
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429 -last_sp_adjust))
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430 {
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431 /* It worked! */
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432 delete_insn (last_sp_set);
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433 last_sp_set = insn;
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434 last_sp_adjust += this_adjust;
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435 free_csa_memlist (memlist);
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436 memlist = NULL;
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437 continue;
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438 }
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439 }
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440
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441 /* Combination failed. Restart processing from here. If
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442 deallocation+allocation conspired to cancel, we can
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443 delete the old deallocation insn. */
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444 if (last_sp_set && last_sp_adjust == 0)
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445 delete_insn (last_sp_set);
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446 free_csa_memlist (memlist);
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447 memlist = NULL;
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448 last_sp_set = insn;
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449 last_sp_adjust = this_adjust;
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450 continue;
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451 }
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452
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453 /* Find a predecrement of exactly the previous adjustment and
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454 turn it into a direct store. Obviously we can't do this if
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455 there were any intervening uses of the stack pointer. */
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456 if (memlist == NULL
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457 && MEM_P (dest)
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|
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458 && ((GET_CODE (XEXP (dest, 0)) == PRE_DEC
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459 && (last_sp_adjust
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|
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460 == (HOST_WIDE_INT) GET_MODE_SIZE (GET_MODE (dest))))
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461 || (GET_CODE (XEXP (dest, 0)) == PRE_MODIFY
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462 && GET_CODE (XEXP (XEXP (dest, 0), 1)) == PLUS
|
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463 && XEXP (XEXP (XEXP (dest, 0), 1), 0) == stack_pointer_rtx
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|
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464 && (GET_CODE (XEXP (XEXP (XEXP (dest, 0), 1), 1))
|
|
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465 == CONST_INT)
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|
|
466 && (INTVAL (XEXP (XEXP (XEXP (dest, 0), 1), 1))
|
|
|
467 == -last_sp_adjust)))
|
|
|
468 && XEXP (XEXP (dest, 0), 0) == stack_pointer_rtx
|
|
|
469 && ! reg_mentioned_p (stack_pointer_rtx, src)
|
|
|
470 && memory_address_p (GET_MODE (dest), stack_pointer_rtx)
|
|
|
471 && validate_change (insn, &SET_DEST (set),
|
|
|
472 replace_equiv_address (dest,
|
|
|
473 stack_pointer_rtx),
|
|
|
474 0))
|
|
|
475 {
|
|
|
476 delete_insn (last_sp_set);
|
|
|
477 free_csa_memlist (memlist);
|
|
|
478 memlist = NULL;
|
|
|
479 last_sp_set = NULL_RTX;
|
|
|
480 last_sp_adjust = 0;
|
|
|
481 continue;
|
|
|
482 }
|
|
|
483 }
|
|
|
484
|
|
|
485 data.insn = insn;
|
|
|
486 data.memlist = memlist;
|
|
|
487 if (!CALL_P (insn) && last_sp_set
|
|
|
488 && !for_each_rtx (&PATTERN (insn), record_stack_memrefs, &data))
|
|
|
489 {
|
|
|
490 memlist = data.memlist;
|
|
|
491 continue;
|
|
|
492 }
|
|
|
493 memlist = data.memlist;
|
|
|
494
|
|
|
495 /* Otherwise, we were not able to process the instruction.
|
|
|
496 Do not continue collecting data across such a one. */
|
|
|
497 if (last_sp_set
|
|
|
498 && (CALL_P (insn)
|
|
|
499 || reg_mentioned_p (stack_pointer_rtx, PATTERN (insn))))
|
|
|
500 {
|
|
|
501 if (last_sp_set && last_sp_adjust == 0)
|
|
|
502 delete_insn (last_sp_set);
|
|
|
503 free_csa_memlist (memlist);
|
|
|
504 memlist = NULL;
|
|
|
505 last_sp_set = NULL_RTX;
|
|
|
506 last_sp_adjust = 0;
|
|
|
507 }
|
|
|
508 }
|
|
|
509
|
|
|
510 if (last_sp_set && last_sp_adjust == 0)
|
|
|
511 delete_insn (last_sp_set);
|
|
|
512
|
|
|
513 if (memlist)
|
|
|
514 free_csa_memlist (memlist);
|
|
|
515 }
|
|
|
516
|
|
|
517
|
|
|
518 static bool
|
|
|
519 gate_handle_stack_adjustments (void)
|
|
|
520 {
|
|
|
521 return (optimize > 0);
|
|
|
522 }
|
|
|
523
|
|
|
524 static unsigned int
|
|
|
525 rest_of_handle_stack_adjustments (void)
|
|
|
526 {
|
|
|
527 cleanup_cfg (flag_crossjumping ? CLEANUP_CROSSJUMP : 0);
|
|
|
528
|
|
|
529 /* This is kind of a heuristic. We need to run combine_stack_adjustments
|
|
|
530 even for machines with possibly nonzero RETURN_POPS_ARGS
|
|
|
531 and ACCUMULATE_OUTGOING_ARGS. We expect that only ports having
|
|
|
532 push instructions will have popping returns. */
|
|
|
533 #ifndef PUSH_ROUNDING
|
|
|
534 if (!ACCUMULATE_OUTGOING_ARGS)
|
|
|
535 #endif
|
|
|
536 {
|
|
|
537 df_note_add_problem ();
|
|
|
538 df_analyze ();
|
|
|
539 combine_stack_adjustments ();
|
|
|
540 }
|
|
|
541 return 0;
|
|
|
542 }
|
|
|
543
|
|
|
544 struct rtl_opt_pass pass_stack_adjustments =
|
|
|
545 {
|
|
|
546 {
|
|
|
547 RTL_PASS,
|
|
|
548 "csa", /* name */
|
|
|
549 gate_handle_stack_adjustments, /* gate */
|
|
|
550 rest_of_handle_stack_adjustments, /* execute */
|
|
|
551 NULL, /* sub */
|
|
|
552 NULL, /* next */
|
|
|
553 0, /* static_pass_number */
|
|
|
554 0, /* tv_id */
|
|
|
555 0, /* properties_required */
|
|
|
556 0, /* properties_provided */
|
|
|
557 0, /* properties_destroyed */
|
|
|
558 0, /* todo_flags_start */
|
|
|
559 TODO_df_finish | TODO_verify_rtl_sharing |
|
|
|
560 TODO_dump_func |
|
|
|
561 TODO_ggc_collect, /* todo_flags_finish */
|
|
|
562 }
|
|
|
563 };
|
|
|
564
|
