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 "hash-set.h"
  25 #include "machmode.h"
  26 #include "vec.h"
  27 #include "double-int.h"
  28 #include "input.h"
  29 #include "alias.h"
  30 #include "symtab.h"
  31 #include "wide-int.h"
  32 #include "inchash.h"
  33 #include "tree.h"
  34 #include "rtl.h"
  35 #include "regs.h"
  36 #include "hashtab.h"
  37 #include "hard-reg-set.h"
  38 #include "function.h"
  39 #include "flags.h"
  40 #include "statistics.h"
  41 #include "real.h"
  42 #include "fixed-value.h"
  43 #include "insn-config.h"
  44 #include "expmed.h"
  45 #include "dojump.h"
  46 #include "explow.h"
  47 #include "calls.h"
  48 #include "emit-rtl.h"
  49 #include "varasm.h"
  50 #include "stmt.h"
  51 #include "expr.h"
  52 #include "tree-pass.h"
  53 #include "predict.h"
  54 #include "dominance.h"
  55 #include "cfg.h"
  56 #include "basic-block.h"
  57 #include "output.h"
  58 #include "df.h"
  59
  60 /* Determine if the stack pointer is constant over the life of the function.
  61    Only useful before prologues have been emitted.  */
  62
  63 static void
  64 notice_stack_pointer_modification_1 (rtx x, const_rtx pat ATTRIBUTE_UNUSED,
  65                                      void *data ATTRIBUTE_UNUSED)
  66 {
  67   if (x == stack_pointer_rtx
  68       /* The stack pointer is only modified indirectly as the result
  69          of a push until later.  See the comments in rtl.texi
  70          regarding Embedded Side-Effects on Addresses.  */
  71       || (MEM_P (x)
  72           && GET_RTX_CLASS (GET_CODE (XEXP (x, 0))) == RTX_AUTOINC
  73           && XEXP (XEXP (x, 0), 0) == stack_pointer_rtx))
  74     crtl->sp_is_unchanging = 0;
  75 }
  76
  77   /* Some targets can emit simpler epilogues if they know that sp was
  78      not ever modified during the function.  After reload, of course,
  79      we've already emitted the epilogue so there's no sense searching.  */
  80
  81 namespace {
  82
  83 const pass_data pass_data_stack_ptr_mod =
  84 {
  85   RTL_PASS, /* type */
  86   "*stack_ptr_mod", /* name */
  87   OPTGROUP_NONE, /* optinfo_flags */
  88   TV_NONE, /* tv_id */
  89   0, /* properties_required */
  90   0, /* properties_provided */
  91   0, /* properties_destroyed */
  92   0, /* todo_flags_start */
  93   0, /* todo_flags_finish */
  94 };
  95
  96 class pass_stack_ptr_mod : public rtl_opt_pass
  97 {
  98 public:
  99   pass_stack_ptr_mod (gcc::context *ctxt)
 100     : rtl_opt_pass (pass_data_stack_ptr_mod, ctxt)
 101   {}
 102
 103   /* opt_pass methods: */
 104   virtual unsigned int execute (function *);
 105
 106 }; // class pass_stack_ptr_mod
 107
 108 unsigned int
 109 pass_stack_ptr_mod::execute (function *fun)
 110 {
 111   basic_block bb;
 112   rtx_insn *insn;
 113
 114   /* Assume that the stack pointer is unchanging if alloca hasn't
 115      been used.  */
 116   crtl->sp_is_unchanging = !fun->calls_alloca;
 117   if (crtl->sp_is_unchanging)
 118     FOR_EACH_BB_FN (bb, fun)
 119       FOR_BB_INSNS (bb, insn)
 120         {
 121           if (INSN_P (insn))
 122             {
 123               /* Check if insn modifies the stack pointer.  */
 124               note_stores (PATTERN (insn),
 125                            notice_stack_pointer_modification_1,
 126                            NULL);
 127               if (! crtl->sp_is_unchanging)
 128                 return 0;
 129             }
 130         }
 131
 132   /* The value coming into this pass was 0, and the exit block uses
 133      are based on this.  If the value is now 1, we need to redo the
 134      exit block uses.  */
 135   if (df && crtl->sp_is_unchanging)
 136     df_update_exit_block_uses ();
 137
 138   return 0;
 139 }
 140
 141 } // anon namespace
 142
 143 rtl_opt_pass *
 144 make_pass_stack_ptr_mod (gcc::context *ctxt)
 145 {
 146   return new pass_stack_ptr_mod (ctxt);
 147 }