gcc/stack-ptr-mod.cc

   1 /* Discover if the stack pointer is modified in a function.
   2    Copyright (C) 2007-2023 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   unsigned int execute (function *) final override;
  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 (insn, notice_stack_pointer_modification_1, NULL);
  95               if (! crtl->sp_is_unchanging)
  96                 return 0;
  97             }
  98         }
  99
 100   /* The value coming into this pass was 0, and the exit block uses
 101      are based on this.  If the value is now 1, we need to redo the
 102      exit block uses.  */
 103   if (df && crtl->sp_is_unchanging)
 104     df_update_exit_block_uses ();
 105
 106   return 0;
 107 }
 108
 109 } // anon namespace
 110
 111 rtl_opt_pass *
 112 make_pass_stack_ptr_mod (gcc::context *ctxt)
 113 {
 114   return new pass_stack_ptr_mod (ctxt);
 115 }