1 /* Discover if the stack pointer is modified in a function. 2 Copyright (C) 2007-2018 Free Software Foundation, Inc. 3 4 This file is part of GCC. 5 6 GCC is free software; you can redistribute it and/or modify it under 7 the terms of the GNU General Public License as published by the Free 8 Software Foundation; either version 3, or (at your option) any later 9 version. 10 11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY 12 WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with GCC; see the file COPYING3. If not see 18 <http://www.gnu.org/licenses/>. */ 19 20 #include "config.h" 21 #include "system.h" 22 #include "coretypes.h" 23 #include "backend.h" 24 #include "rtl.h" 25 #include "df.h" 26 #include "memmodel.h" 27 #include "emit-rtl.h" 28 #include "tree-pass.h" 29 30 /* Determine if the stack pointer is constant over the life of the function. 31 Only useful before prologues have been emitted. */ 32 33 static void 34 notice_stack_pointer_modification_1 (rtx x, const_rtx pat ATTRIBUTE_UNUSED, 35 void *data ATTRIBUTE_UNUSED) 36 { 37 if (x == stack_pointer_rtx 38 /* The stack pointer is only modified indirectly as the result 39 of a push until later. See the comments in rtl.texi 40 regarding Embedded Side-Effects on Addresses. */ 41 || (MEM_P (x) 42 && GET_RTX_CLASS (GET_CODE (XEXP (x, 0))) == RTX_AUTOINC 43 && XEXP (XEXP (x, 0), 0) == stack_pointer_rtx)) 44 crtl->sp_is_unchanging = 0; 45 } 46 47 /* Some targets can emit simpler epilogues if they know that sp was 48 not ever modified during the function. After reload, of course, 49 we've already emitted the epilogue so there's no sense searching. */ 50 51 namespace { 52 53 const pass_data pass_data_stack_ptr_mod = 54 { 55 RTL_PASS, /* type */ 56 "*stack_ptr_mod", /* name */ 57 OPTGROUP_NONE, /* optinfo_flags */ 58 TV_NONE, /* tv_id */ 59 0, /* properties_required */ 60 0, /* properties_provided */ 61 0, /* properties_destroyed */ 62 0, /* todo_flags_start */ 63 0, /* todo_flags_finish */ 64 }; 65 66 class pass_stack_ptr_mod : public rtl_opt_pass 67 { 68 public: 69 pass_stack_ptr_mod (gcc::context *ctxt) 70 : rtl_opt_pass (pass_data_stack_ptr_mod, ctxt) 71 {} 72 73 /* opt_pass methods: */ 74 virtual unsigned int execute (function *); 75 76 }; // class pass_stack_ptr_mod 77 78 unsigned int 79 pass_stack_ptr_mod::execute (function *fun) 80 { 81 basic_block bb; 82 rtx_insn *insn; 83 84 /* Assume that the stack pointer is unchanging if alloca hasn't 85 been used. */ 86 crtl->sp_is_unchanging = !fun->calls_alloca; 87 if (crtl->sp_is_unchanging) 88 FOR_EACH_BB_FN (bb, fun) 89 FOR_BB_INSNS (bb, insn) 90 { 91 if (INSN_P (insn)) 92 { 93 /* Check if insn modifies the stack pointer. */ 94 note_stores (PATTERN (insn), 95 notice_stack_pointer_modification_1, 96 NULL); 97 if (! crtl->sp_is_unchanging) 98 return 0; 99 } 100 } 101 102 /* The value coming into this pass was 0, and the exit block uses 103 are based on this. If the value is now 1, we need to redo the 104 exit block uses. */ 105 if (df && crtl->sp_is_unchanging) 106 df_update_exit_block_uses (); 107 108 return 0; 109 } 110 111 } // anon namespace 112 113 rtl_opt_pass * 114 make_pass_stack_ptr_mod (gcc::context *ctxt) 115 { 116 return new pass_stack_ptr_mod (ctxt); 117 } 118