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1 /* Discover if the stack pointer is modified in a function.
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2 Copyright (C) 2007, 2008
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3 Free Software Foundation, Inc.
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4
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5 This file is part of GCC.
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6
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7 GCC is free software; you can redistribute it and/or modify it under
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8 the terms of the GNU General Public License as published by the Free
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9 Software Foundation; either version 3, or (at your option) any later
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10 version.
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11
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12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
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14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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15 for more details.
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16
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17 You should have received a copy of the GNU General Public License
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18 along with GCC; see the file COPYING3. If not see
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19 <http://www.gnu.org/licenses/>. */
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20
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21 #include "config.h"
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22 #include "system.h"
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23 #include "coretypes.h"
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24 #include "tm.h"
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25 #include "tree.h"
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26 #include "rtl.h"
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27 #include "regs.h"
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28 #include "expr.h"
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29 #include "tree-pass.h"
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30 #include "basic-block.h"
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31 #include "flags.h"
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32 #include "output.h"
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33 #include "df.h"
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34
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35 /* Determine if the stack pointer is constant over the life of the function.
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36 Only useful before prologues have been emitted. */
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37
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38 static void
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39 notice_stack_pointer_modification_1 (rtx x, const_rtx pat ATTRIBUTE_UNUSED,
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40 void *data ATTRIBUTE_UNUSED)
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41 {
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42 if (x == stack_pointer_rtx
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43 /* The stack pointer is only modified indirectly as the result
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44 of a push until later. See the comments in rtl.texi
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45 regarding Embedded Side-Effects on Addresses. */
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46 || (MEM_P (x)
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47 && GET_RTX_CLASS (GET_CODE (XEXP (x, 0))) == RTX_AUTOINC
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48 && XEXP (XEXP (x, 0), 0) == stack_pointer_rtx))
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49 current_function_sp_is_unchanging = 0;
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50 }
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51
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52 static void
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53 notice_stack_pointer_modification (void)
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54 {
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55 basic_block bb;
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56 rtx insn;
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57
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58 /* Assume that the stack pointer is unchanging if alloca hasn't
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59 been used. */
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60 current_function_sp_is_unchanging = !cfun->calls_alloca;
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61 if (current_function_sp_is_unchanging)
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62 FOR_EACH_BB (bb)
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63 FOR_BB_INSNS (bb, insn)
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64 {
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65 if (INSN_P (insn))
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66 {
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67 /* Check if insn modifies the stack pointer. */
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68 note_stores (PATTERN (insn),
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69 notice_stack_pointer_modification_1,
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70 NULL);
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71 if (! current_function_sp_is_unchanging)
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72 return;
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73 }
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74 }
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75
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76 /* The value coming into this pass was 0, and the exit block uses
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77 are based on this. If the value is now 1, we need to redo the
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78 exit block uses. */
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79 if (df && current_function_sp_is_unchanging)
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80 df_update_exit_block_uses ();
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81 }
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82
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83 /* Some targets can emit simpler epilogues if they know that sp was
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84 not ever modified during the function. After reload, of course,
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85 we've already emitted the epilogue so there's no sense searching. */
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86
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87 static unsigned int
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88 rest_of_handle_stack_ptr_mod (void)
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89 {
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90 notice_stack_pointer_modification ();
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91 return 0;
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92 }
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93
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94 struct rtl_opt_pass pass_stack_ptr_mod =
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95 {
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96 {
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97 RTL_PASS,
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98 NULL, /* name */
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99 NULL, /* gate */
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100 rest_of_handle_stack_ptr_mod, /* execute */
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101 NULL, /* sub */
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102 NULL, /* next */
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103 0, /* static_pass_number */
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104 0, /* tv_id */
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105 0, /* properties_required */
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106 0, /* properties_provided */
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107 0, /* properties_destroyed */
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108 0, /* todo_flags_start */
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109 0 /* todo_flags_finish */
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110 }
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111 };
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