gcc/stack-ptr-mod.c

   1 /* Discover if the stack pointer is modified in a function.
   2    Copyright (C) 2007-2015 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 "tm.h"
  24 #include "input.h"
  25 #include "alias.h"
  26 #include "symtab.h"
  27 #include "tree.h"
  28 #include "rtl.h"
  29 #include "regs.h"
  30 #include "hard-reg-set.h"
  31 #include "function.h"
  32 #include "flags.h"
  33 #include "insn-config.h"
  34 #include "expmed.h"
  35 #include "dojump.h"
  36 #include "explow.h"
  37 #include "calls.h"
  38 #include "emit-rtl.h"
  39 #include "varasm.h"
  40 #include "stmt.h"
  41 #include "expr.h"
  42 #include "tree-pass.h"
  43 #include "predict.h"
  44 #include "dominance.h"
  45 #include "cfg.h"
  46 #include "basic-block.h"
  47 #include "output.h"
  48 #include "df.h"
  49
  50 /* Determine if the stack pointer is constant over the life of the function.
  51    Only useful before prologues have been emitted.  */
  52
  53 static void
  54 notice_stack_pointer_modification_1 (rtx x, const_rtx pat ATTRIBUTE_UNUSED,
  55                                      void *data ATTRIBUTE_UNUSED)
  56 {
  57   if (x == stack_pointer_rtx
  58       /* The stack pointer is only modified indirectly as the result
  59          of a push until later.  See the comments in rtl.texi
  60          regarding Embedded Side-Effects on Addresses.  */
  61       || (MEM_P (x)
  62           && GET_RTX_CLASS (GET_CODE (XEXP (x, 0))) == RTX_AUTOINC
  63           && XEXP (XEXP (x, 0), 0) == stack_pointer_rtx))
  64     crtl->sp_is_unchanging = 0;
  65 }
  66
  67   /* Some targets can emit simpler epilogues if they know that sp was
  68      not ever modified during the function.  After reload, of course,
  69      we've already emitted the epilogue so there's no sense searching.  */
  70
  71 namespace {
  72
  73 const pass_data pass_data_stack_ptr_mod =
  74 {
  75   RTL_PASS, /* type */
  76   "*stack_ptr_mod", /* name */
  77   OPTGROUP_NONE, /* optinfo_flags */
  78   TV_NONE, /* tv_id */
  79   0, /* properties_required */
  80   0, /* properties_provided */
  81   0, /* properties_destroyed */
  82   0, /* todo_flags_start */
  83   0, /* todo_flags_finish */
  84 };
  85
  86 class pass_stack_ptr_mod : public rtl_opt_pass
  87 {
  88 public:
  89   pass_stack_ptr_mod (gcc::context *ctxt)
  90     : rtl_opt_pass (pass_data_stack_ptr_mod, ctxt)
  91   {}
  92
  93   /* opt_pass methods: */
  94   virtual unsigned int execute (function *);
  95
  96 }; // class pass_stack_ptr_mod
  97
  98 unsigned int
  99 pass_stack_ptr_mod::execute (function *fun)
 100 {
 101   basic_block bb;
 102   rtx_insn *insn;
 103
 104   /* Assume that the stack pointer is unchanging if alloca hasn't
 105      been used.  */
 106   crtl->sp_is_unchanging = !fun->calls_alloca;
 107   if (crtl->sp_is_unchanging)
 108     FOR_EACH_BB_FN (bb, fun)
 109       FOR_BB_INSNS (bb, insn)
 110         {
 111           if (INSN_P (insn))
 112             {
 113               /* Check if insn modifies the stack pointer.  */
 114               note_stores (PATTERN (insn),
 115                            notice_stack_pointer_modification_1,
 116                            NULL);
 117               if (! crtl->sp_is_unchanging)
 118                 return 0;
 119             }
 120         }
 121
 122   /* The value coming into this pass was 0, and the exit block uses
 123      are based on this.  If the value is now 1, we need to redo the
 124      exit block uses.  */
 125   if (df && crtl->sp_is_unchanging)
 126     df_update_exit_block_uses ();
 127
 128   return 0;
 129 }
 130
 131 } // anon namespace
 132
 133 rtl_opt_pass *
 134 make_pass_stack_ptr_mod (gcc::context *ctxt)
 135 {
 136   return new pass_stack_ptr_mod (ctxt);
 137 }