gcc/tree-optimize.c

   1 /* Control and data flow functions for trees.
   2    Copyright 2001, 2002, 2003 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
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GCC is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING.  If not, write to
  18 the Free Software Foundation, 59 Temple Place - Suite 330,
  19 Boston, MA 02111-1307, USA.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "toplev.h"
  25 #include "tree.h"
  26 #include "tree-inline.h"
  27 #include "flags.h"
  28 #include "langhooks.h"
  29 #include "cgraph.h"
  30 #include "timevar.h"
  31 #include "tm.h"
  32 #include "function.h"
  33 #include "ggc.h"
  34
  35
  36 /* Called to move the SAVE_EXPRs for parameter declarations in a
  37    nested function into the nested function.  DATA is really the
  38    nested FUNCTION_DECL.  */
  39
  40 static tree
  41 set_save_expr_context (tree *tp,
  42                        int *walk_subtrees,
  43                        void *data)
  44 {
  45   if (TREE_CODE (*tp) == SAVE_EXPR && !SAVE_EXPR_CONTEXT (*tp))
  46     SAVE_EXPR_CONTEXT (*tp) = (tree) data;
  47   /* Do not walk back into the SAVE_EXPR_CONTEXT; that will cause
  48      circularity.  */
  49   else if (DECL_P (*tp))
  50     *walk_subtrees = 0;
  51
  52   return NULL;
  53 }
  54
  55 /* Clear out the DECL_RTL for the non-static local variables in BLOCK and
  56    its sub-blocks.  DATA is the decl of the function being processed.  */
  57
  58 static tree
  59 clear_decl_rtl (tree *tp, int *walk_subtrees ATTRIBUTE_UNUSED, void *data)
  60 {
  61   bool nonstatic_p, local_p;
  62   tree t = *tp;
  63
  64   switch (TREE_CODE (t))
  65     {
  66     case VAR_DECL:
  67       nonstatic_p = !TREE_STATIC (t) && !DECL_EXTERNAL (t);
  68       local_p = DECL_CONTEXT (t) == data;
  69       break;
  70
  71     case PARM_DECL:
  72     case LABEL_DECL:
  73       nonstatic_p = true;
  74       local_p = DECL_CONTEXT (t) == data;
  75       break;
  76
  77     case RESULT_DECL:
  78       nonstatic_p = local_p = true;
  79       break;
  80
  81     default:
  82       nonstatic_p = local_p = false;
  83       break;
  84     }
  85
  86   if (nonstatic_p && local_p)
  87     SET_DECL_RTL (t, NULL);
  88
  89   return NULL;
  90 }
  91
  92 /* For functions-as-trees languages, this performs all optimization and
  93    compilation for FNDECL.  */
  94
  95 void
  96 tree_rest_of_compilation (tree fndecl)
  97 {
  98   static int nesting = -1;
  99
 100   timevar_push (TV_EXPAND);
 101
 102   ++nesting;
 103
 104   if (flag_unit_at_a_time && !cgraph_global_info_ready)
 105     abort ();
 106
 107   if (nesting > 0)
 108     /* Squirrel away our current state.  */
 109     push_function_context ();
 110
 111   /* Initialize the RTL code for the function.  */
 112   current_function_decl = fndecl;
 113   input_location = DECL_SOURCE_LOCATION (fndecl);
 114   init_function_start (fndecl);
 115
 116   /* This function is being processed in whole-function mode.  */
 117   cfun->x_whole_function_mode_p = 1;
 118
 119   /* Even though we're inside a function body, we still don't want to
 120      call expand_expr to calculate the size of a variable-sized array.
 121      We haven't necessarily assigned RTL to all variables yet, so it's
 122      not safe to try to expand expressions involving them.  */
 123   immediate_size_expand = 0;
 124   cfun->x_dont_save_pending_sizes_p = 1;
 125
 126   /* If the function has a variably modified type, there may be
 127      SAVE_EXPRs in the parameter types.  Their context must be set to
 128      refer to this function; they cannot be expanded in the containing
 129      function.  */
 130   if (decl_function_context (fndecl)
 131       && variably_modified_type_p (TREE_TYPE (fndecl)))
 132     walk_tree (&TREE_TYPE (fndecl), set_save_expr_context, fndecl,
 133                NULL);
 134
 135   /* Set up parameters and prepare for return, for the function.  */
 136   expand_function_start (fndecl, 0);
 137
 138   /* Allow language dialects to perform special processing.  */
 139   (*lang_hooks.rtl_expand.start) ();
 140
 141   /* If this function is `main', emit a call to `__main'
 142      to run global initializers, etc.  */
 143   if (DECL_NAME (fndecl)
 144       && MAIN_NAME_P (DECL_NAME (fndecl))
 145       && DECL_FILE_SCOPE_P (fndecl))
 146     expand_main_function ();
 147
 148   /* Generate the RTL for this function.  */
 149   (*lang_hooks.rtl_expand.stmt) (DECL_SAVED_TREE (fndecl));
 150
 151   /* We hard-wired immediate_size_expand to zero above.
 152      expand_function_end will decrement this variable.  So, we set the
 153      variable to one here, so that after the decrement it will remain
 154      zero.  */
 155   immediate_size_expand = 1;
 156
 157   /* Allow language dialects to perform special processing.  */
 158   (*lang_hooks.rtl_expand.end) ();
 159
 160   /* Generate rtl for function exit.  */
 161   expand_function_end ();
 162
 163   /* If this is a nested function, protect the local variables in the stack
 164      above us from being collected while we're compiling this function.  */
 165   if (nesting > 0)
 166     ggc_push_context ();
 167
 168   /* There's no need to defer outputting this function any more; we
 169      know we want to output it.  */
 170   DECL_DEFER_OUTPUT (fndecl) = 0;
 171
 172   /* Run the optimizers and output the assembler code for this function.  */
 173   rest_of_compilation (fndecl);
 174
 175   /* Undo the GC context switch.  */
 176   if (nesting > 0)
 177     ggc_pop_context ();
 178
 179   /* If requested, warn about function definitions where the function will
 180      return a value (usually of some struct or union type) which itself will
 181      take up a lot of stack space.  */
 182   if (warn_larger_than && !DECL_EXTERNAL (fndecl) && TREE_TYPE (fndecl))
 183     {
 184       tree ret_type = TREE_TYPE (TREE_TYPE (fndecl));
 185
 186       if (ret_type && TYPE_SIZE_UNIT (ret_type)
 187           && TREE_CODE (TYPE_SIZE_UNIT (ret_type)) == INTEGER_CST
 188           && 0 < compare_tree_int (TYPE_SIZE_UNIT (ret_type),
 189                                    larger_than_size))
 190         {
 191           const location_t *locus = &DECL_SOURCE_LOCATION (fndecl);
 192           unsigned int size_as_int
 193             = TREE_INT_CST_LOW (TYPE_SIZE_UNIT (ret_type));
 194
 195           if (compare_tree_int (TYPE_SIZE_UNIT (ret_type), size_as_int) == 0)
 196             warning ("%Hsize of return value of '%D' is %u bytes",
 197                      locus, fndecl, size_as_int);
 198           else
 199             warning ("%Hsize of return value of '%D' is larger than %wd bytes",
 200                      locus, fndecl, larger_than_size);
 201         }
 202     }
 203
 204   /* ??? Looks like some of this could be combined.  */
 205
 206   /* If possible, obliterate the body of the function so that it can
 207      be garbage collected.  */
 208   if (dump_enabled_p (TDI_all))
 209     /* Keep the body; we're going to dump it.  */
 210     ;
 211   else if (DECL_INLINE (fndecl) && flag_inline_trees)
 212     /* We might need the body of this function so that we can expand
 213        it inline somewhere else.  */
 214     ;
 215   else
 216     /* We don't need the body; blow it away.  */
 217     DECL_SAVED_TREE (fndecl) = NULL;
 218
 219   /* Since we don't need the RTL for this function anymore, stop pointing to
 220      it.  That's especially important for LABEL_DECLs, since you can reach all
 221      the instructions in the function from the CODE_LABEL stored in the
 222      DECL_RTL for the LABEL_DECL.  Walk the BLOCK-tree, clearing DECL_RTL for
 223      LABEL_DECLs and non-static local variables.  Note that we must check the
 224      context of the variables, otherwise processing a nested function can kill
 225      the rtl of a variable from an outer function.  */
 226   walk_tree_without_duplicates (&DECL_SAVED_TREE (fndecl),
 227                                 clear_decl_rtl,
 228                                 fndecl);
 229
 230   if (DECL_SAVED_INSNS (fndecl) == 0 && ! nesting && ! flag_inline_trees)
 231     {
 232       /* Stop pointing to the local nodes about to be freed.
 233          But DECL_INITIAL must remain nonzero so we know this
 234          was an actual function definition.
 235          For a nested function, this is done in c_pop_function_context.
 236          If rest_of_compilation set this to 0, leave it 0.  */
 237       if (DECL_INITIAL (fndecl) != 0)
 238         DECL_INITIAL (fndecl) = error_mark_node;
 239
 240       DECL_ARGUMENTS (fndecl) = 0;
 241     }
 242
 243   if (nesting > 0)
 244     /* Return to the enclosing function.  */
 245     pop_function_context ();
 246
 247   --nesting;
 248
 249   timevar_pop (TV_EXPAND);
 250 }