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