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