gcc/c-semantics.c

/* This file contains the definitions and documentation for the common
   tree codes used in the GNU C and C++ compilers (see c-common.def
   for the standard codes).  
   Copyright (C) 2000, 2001 Free Software Foundation, Inc.
   Written by Benjamin Chelf (chelf@codesourcery.com).

This file is part of GNU CC.

GNU CC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU CC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

#include "config.h"
#include "system.h"
#include "tree.h"
#include "function.h"
#include "splay-tree.h"
#include "varray.h"
#include "c-common.h"
#include "except.h"
#include "toplev.h"
#include "flags.h"
#include "ggc.h"
#include "rtl.h"
#include "output.h"
#include "timevar.h"

/* If non-NULL, the address of a language-specific function for
   expanding statements.  */
void (*lang_expand_stmt) PARAMS ((tree));

/* If non-NULL, the address of a language-specific function for
   expanding a DECL_STMT.  After the language-independent cases are
   handled, this function will be called.  If this function is not
   defined, it is assumed that declarations other than those for
   variables and labels do not require any RTL generation.  */
void (*lang_expand_decl_stmt) PARAMS ((tree));

static tree prune_unused_decls PARAMS ((tree *, int *, void *));

/* Create an empty statement tree rooted at T.  */

void
begin_stmt_tree (t)
     tree *t;
{
  /* We create a trivial EXPR_STMT so that last_tree is never NULL in
     what follows.  We remove the extraneous statement in
     finish_stmt_tree.  */
  *t = build_nt (EXPR_STMT, void_zero_node);
  last_tree = *t;
  last_expr_type = NULL_TREE;
}

/* T is a statement.  Add it to the statement-tree.  */

tree
add_stmt (t)
     tree t;
{
  /* Add T to the statement-tree.  */
  TREE_CHAIN (last_tree) = t;
  last_tree = t;
  /* When we expand a statement-tree, we must know whether or not the
     statements are full-expresions.  We record that fact here.  */
  STMT_IS_FULL_EXPR_P (last_tree) = stmts_are_full_exprs_p ();

  /* Keep track of the number of statements in this function.  */
  if (current_function_decl)
    ++DECL_NUM_STMTS (current_function_decl);

  return t;
}

/* Create a declaration statement for the declaration given by the
   DECL.  */

void
add_decl_stmt (decl)
     tree decl;
{
  tree decl_stmt;

  /* We need the type to last until instantiation time.  */
  decl_stmt = build_stmt (DECL_STMT, decl);
  add_stmt (decl_stmt); 
}

/* Add a scope-statement to the statement-tree.  BEGIN_P indicates
   whether this statements opens or closes a scope.  PARTIAL_P is true
   for a partial scope, i.e, the scope that begins after a label when
   an object that needs a cleanup is created.  If BEGIN_P is nonzero,
   returns a new TREE_LIST representing the top of the SCOPE_STMT
   stack.  The TREE_PURPOSE is the new SCOPE_STMT.  If BEGIN_P is
   zero, returns a TREE_LIST whose TREE_VALUE is the new SCOPE_STMT,
   and whose TREE_PURPOSE is the matching SCOPE_STMT iwth
   SCOPE_BEGIN_P set.  */

tree
add_scope_stmt (begin_p, partial_p)
     int begin_p;
     int partial_p;
{
  tree ss;
  tree top;

  /* Build the statement.  */
  ss = build_stmt (SCOPE_STMT, NULL_TREE);
  SCOPE_BEGIN_P (ss) = begin_p;
  SCOPE_PARTIAL_P (ss) = partial_p;

  /* Keep the scope stack up to date.  */
  if (begin_p)
    {
      *current_scope_stmt_stack () 
	= tree_cons (ss, NULL_TREE, *current_scope_stmt_stack ());
      top = *current_scope_stmt_stack ();
    }
  else
    {
      top = *current_scope_stmt_stack ();
      TREE_VALUE (top) = ss;
      *current_scope_stmt_stack () = TREE_CHAIN (top);
    }

  /* Add the new statement to the statement-tree.  */
  add_stmt (ss);

  return top;
}

/* Remove declarations of internal variables that are not used from a
   stmt tree.  To qualify, the variable must have a name and must have
   a zero DECL_SOURCE_LINE.  We tried to remove all variables for
   which TREE_USED was false, but it turns out that there's tons of
   variables for which TREE_USED is false but that are still in fact
   used.  */

static tree
prune_unused_decls (tp, walk_subtrees, data)
     tree *tp;
     int *walk_subtrees ATTRIBUTE_UNUSED;
     void *data ATTRIBUTE_UNUSED;
{
  tree t = *tp;

  if (t == NULL_TREE)
    return error_mark_node;

  if (TREE_CODE (t) == DECL_STMT)
    {
      tree d = DECL_STMT_DECL (t);
      if (!TREE_USED (d) && DECL_NAME (d) && DECL_SOURCE_LINE (d) == 0)
	{
	  *tp = TREE_CHAIN (t);
	  /* Recurse on the new value of tp, otherwise we will skip
	     the next statement.  */
	  return prune_unused_decls (tp, walk_subtrees, data);
	}
    }
  else if (TREE_CODE (t) == SCOPE_STMT)
    {
      /* Remove all unused decls from the BLOCK of this SCOPE_STMT.  */
      tree block = SCOPE_STMT_BLOCK (t);

      if (block)
	{
	  tree *vp;

	  for (vp = &BLOCK_VARS (block); *vp; )
	    {
	      tree v = *vp;
	      if (! TREE_USED (v) && DECL_NAME (v) && DECL_SOURCE_LINE (v) == 0)
		*vp = TREE_CHAIN (v);  /* drop */
	      else
		vp = &TREE_CHAIN (v);  /* advance */
	    }
	  /* If there are now no variables, the entire BLOCK can be dropped.
	     (This causes SCOPE_NULLIFIED_P (t) to be true.)  */
	  if (BLOCK_VARS (block) == NULL_TREE)
	    SCOPE_STMT_BLOCK (t) = NULL_TREE;
	}
    }
  return NULL_TREE;
}

/* Finish the statement tree rooted at T.  */

void
finish_stmt_tree (t)
     tree *t;
{
  tree stmt;
  
  /* Remove the fake extra statement added in begin_stmt_tree.  */
  stmt = TREE_CHAIN (*t);
  *t = stmt;
  last_tree = NULL_TREE;

  /* Remove unused decls from the stmt tree.  */
  walk_stmt_tree (t, prune_unused_decls, NULL);

  if (cfun && stmt)
    {
      /* The line-number recorded in the outermost statement in a function
	 is the line number of the end of the function.  */
      STMT_LINENO (stmt) = lineno;
      STMT_LINENO_FOR_FN_P (stmt) = 1;
    }
}

/* Build a generic statement based on the given type of node and
   arguments. Similar to `build_nt', except that we set
   STMT_LINENO to be the current line number.  */
/* ??? This should be obsolete with the lineno_stmt productions
   in the grammar.  */

tree
build_stmt VPARAMS ((enum tree_code code, ...))
{
#ifndef ANSI_PROTOTYPES
  enum tree_code code;
#endif
  va_list p;
  register tree t;
  register int length;
  register int i;

  VA_START (p, code);

#ifndef ANSI_PROTOTYPES
  code = va_arg (p, enum tree_code);
#endif

  t = make_node (code);
  length = TREE_CODE_LENGTH (code);
  STMT_LINENO (t) = lineno;

  for (i = 0; i < length; i++)
    TREE_OPERAND (t, i) = va_arg (p, tree);

  va_end (p);
  return t;
}

/* Some statements, like for-statements or if-statements, require a
   condition.  This condition can be a declaration.  If T is such a
   declaration it is processed, and an expression appropriate to use
   as the condition is returned.  Otherwise, T itself is returned.  */

tree
expand_cond (t)
     tree t;
{
  if (t && TREE_CODE (t) == TREE_LIST)
    {
      expand_stmt (TREE_PURPOSE (t));
      return TREE_VALUE (t);
    }
  else 
    return t;
}

/* Create RTL for the local static variable DECL.  */

void
make_rtl_for_local_static (decl)
     tree decl;
{
  const char *asmspec = NULL;

  /* If we inlined this variable, we could see it's declaration
     again.  */
  if (TREE_ASM_WRITTEN (decl))
    return;

  /* If the DECL_ASSEMBLER_NAME is not the same as the DECL_NAME, then
     either we already created RTL for this DECL (and since it was a
     local variable, its DECL_ASSEMBLER_NAME got hacked up to prevent
     clashes with other local statics with the same name by a previous
     call to make_decl_rtl), or the user explicitly requested a
     particular assembly name for this variable, using the GNU
     extension for this purpose:

       int i asm ("j");

     There's no way to know which case we're in, here.  But, it turns
     out we're safe.  If there's already RTL, then
     rest_of_decl_compilation ignores the ASMSPEC parameter, so we
     may as well not pass it in.  If there isn't RTL, then we didn't
     already create RTL, which means that the modification to
     DECL_ASSEMBLER_NAME came only via the explicit extension.  */
  if (DECL_ASSEMBLER_NAME (decl) != DECL_NAME (decl)
      && !DECL_RTL (decl))
    asmspec = IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl));

  rest_of_decl_compilation (decl, asmspec, /*top_level=*/0, /*at_end=*/0);
}

/* Let the back-end know about DECL.  */

void
emit_local_var (decl)
     tree decl;
{
  /* Create RTL for this variable.  */
  if (!DECL_RTL_SET_P (decl))
    {
      if (DECL_C_HARD_REGISTER (decl))
	/* The user specified an assembler name for this variable.
	   Set that up now.  */
	rest_of_decl_compilation
	  (decl, IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl)),
	   /*top_level=*/0, /*at_end=*/0);
      else
	expand_decl (decl);
    }

  /* Actually do the initialization.  */
  if (stmts_are_full_exprs_p ())
    expand_start_target_temps ();

  expand_decl_init (decl);

  if (stmts_are_full_exprs_p ())
    expand_end_target_temps ();
}

/* Helper for generating the RTL at the beginning of a scope. */

void
genrtl_do_pushlevel ()
{
  emit_line_note (input_filename, lineno);
  clear_last_expr ();
}

/* Generate the RTL for DESTINATION, which is a GOTO_STMT. */

void
genrtl_goto_stmt (destination)
     tree destination;
{
  if (TREE_CODE (destination) == IDENTIFIER_NODE)
    abort ();
  
  /* We warn about unused labels with -Wunused.  That means we have to
     mark the used labels as used.  */
  if (TREE_CODE (destination) == LABEL_DECL)
    TREE_USED (destination) = 1;
  
  emit_line_note (input_filename, lineno);
  
  if (TREE_CODE (destination) == LABEL_DECL)
    {
      label_rtx (destination);
      expand_goto (destination); 
    }
  else
    expand_computed_goto (destination);
}

/* Generate the RTL for EXPR, which is an EXPR_STMT. */

void 
genrtl_expr_stmt (expr)
     tree expr;
{
  if (expr != NULL_TREE)
    {
      emit_line_note (input_filename, lineno);
      
      if (stmts_are_full_exprs_p ())
	expand_start_target_temps ();
      
      if (expr != error_mark_node)
	expand_expr_stmt (expr);
      
      if (stmts_are_full_exprs_p ())
	expand_end_target_temps ();
    }
}

/* Generate the RTL for T, which is a DECL_STMT. */

void
genrtl_decl_stmt (t)
     tree t;
{
  tree decl;
  emit_line_note (input_filename, lineno);
  decl = DECL_STMT_DECL (t);
  /* If this is a declaration for an automatic local
     variable, initialize it.  Note that we might also see a
     declaration for a namespace-scope object (declared with
     `extern').  We don't have to handle the initialization
     of those objects here; they can only be declarations,
     rather than definitions.  */
  if (TREE_CODE (decl) == VAR_DECL 
      && !TREE_STATIC (decl)
      && !DECL_EXTERNAL (decl))
    {
      /* Let the back-end know about this variable.  */
      if (!anon_aggr_type_p (TREE_TYPE (decl)))
	emit_local_var (decl);
      else
	expand_anon_union_decl (decl, NULL_TREE, 
				DECL_ANON_UNION_ELEMS (decl));
    }
  else if (TREE_CODE (decl) == VAR_DECL && TREE_STATIC (decl))
    {
      if (DECL_ARTIFICIAL (decl) && ! TREE_USED (decl))
	/* Do not emit unused decls. This is not just an
	   optimization. We really do not want to emit
	   __PRETTY_FUNCTION__ etc, if they're never used.  */
	DECL_IGNORED_P (decl) = 1;
      else
	make_rtl_for_local_static (decl);
    }
  else if (TREE_CODE (decl) == LABEL_DECL 
	   && C_DECLARED_LABEL_FLAG (decl))
    declare_nonlocal_label (decl);
  else if (lang_expand_decl_stmt)
    (*lang_expand_decl_stmt) (t);
}

/* Generate the RTL for T, which is an IF_STMT. */

void
genrtl_if_stmt (t)
     tree t;
{
  tree cond;
  genrtl_do_pushlevel ();
  cond = expand_cond (IF_COND (t));
  emit_line_note (input_filename, lineno);
  expand_start_cond (cond, 0);
  if (THEN_CLAUSE (t))
    expand_stmt (THEN_CLAUSE (t));
  if (ELSE_CLAUSE (t))
    {
      expand_start_else ();
      expand_stmt (ELSE_CLAUSE (t));
    }
  expand_end_cond ();
}

/* Generate the RTL for T, which is a WHILE_STMT. */

void
genrtl_while_stmt (t)
     tree t;
{
  tree cond;
  emit_nop ();
  emit_line_note (input_filename, lineno);
  expand_start_loop (1); 
  genrtl_do_pushlevel ();

  cond = expand_cond (WHILE_COND (t));
  emit_line_note (input_filename, lineno);
  expand_exit_loop_if_false (0, cond);
  genrtl_do_pushlevel ();
  
  expand_stmt (WHILE_BODY (t));

  expand_end_loop ();
}

/* Generate the RTL for T, which is a DO_STMT. */

void
genrtl_do_stmt (t)
     tree t;
{
  tree cond = DO_COND (t);

  /* Recognize the common special-case of do { ... } while (0) and do
     not emit the loop widgetry in this case.  In particular this
     avoids cluttering the rtl with dummy loop notes, which can affect
     alignment of adjacent labels.  */
  if (integer_zerop (cond))
    {
      expand_start_null_loop ();
      expand_stmt (DO_BODY (t));
      expand_end_null_loop ();
    }
  else
    {
      emit_nop ();
      emit_line_note (input_filename, lineno);
      expand_start_loop_continue_elsewhere (1);

      expand_stmt (DO_BODY (t));

      expand_loop_continue_here ();
      cond = expand_cond (cond);
      emit_line_note (input_filename, lineno);
      expand_exit_loop_if_false (0, cond);
      expand_end_loop ();
    }
}

/* Build the node for a return statement and return it. */

tree
build_return_stmt (expr)
     tree expr;
{
  return (build_stmt (RETURN_STMT, expr));
}

/* Generate the RTL for STMT, which is a RETURN_STMT. */

void
genrtl_return_stmt (stmt)
     tree stmt;
{
  tree expr = RETURN_EXPR (stmt);

  emit_line_note (input_filename, lineno);
  if (!expr)
    expand_null_return ();
  else
    {
      expand_start_target_temps ();
      expand_return (expr);
      expand_end_target_temps ();
    }
}

/* Generate the RTL for T, which is a FOR_STMT. */

void
genrtl_for_stmt (t)
     tree t;
{
  tree cond;
  const char *saved_filename;
  int saved_lineno;

  if (NEW_FOR_SCOPE_P (t))
    genrtl_do_pushlevel ();

  expand_stmt (FOR_INIT_STMT (t));

  /* Expand the initialization.  */
  emit_nop ();
  emit_line_note (input_filename, lineno);
  expand_start_loop_continue_elsewhere (1); 
  genrtl_do_pushlevel ();
  cond = expand_cond (FOR_COND (t));

  /* Save the filename and line number so that we expand the FOR_EXPR
     we can reset them back to the saved values.  */
  saved_filename = input_filename;
  saved_lineno = lineno;

  /* Expand the condition.  */
  emit_line_note (input_filename, lineno);
  if (cond)
    expand_exit_loop_if_false (0, cond);

  /* Expand the body.  */
  genrtl_do_pushlevel ();
  expand_stmt (FOR_BODY (t));

  /* Expand the increment expression.  */
  input_filename = saved_filename;
  lineno = saved_lineno;
  emit_line_note (input_filename, lineno);
  expand_loop_continue_here ();
  if (FOR_EXPR (t))
    genrtl_expr_stmt (FOR_EXPR (t));
  expand_end_loop ();
}

/* Build a break statement node and return it. */

tree
build_break_stmt ()
{
  return (build_stmt (BREAK_STMT));
}

/* Generate the RTL for a BREAK_STMT. */

void
genrtl_break_stmt ()
{
  emit_line_note (input_filename, lineno);
  if ( ! expand_exit_something ())
    error ("break statement not within loop or switch");
}

/* Build a continue statement node and return it. */

tree
build_continue_stmt ()
{
  return (build_stmt (CONTINUE_STMT));
}

/* Generate the RTL for a CONTINUE_STMT. */

void
genrtl_continue_stmt ()
{
  emit_line_note (input_filename, lineno);
  if (! expand_continue_loop (0))
    error ("continue statement not within a loop");   
}

/* Generate the RTL for T, which is a SCOPE_STMT. */

void
genrtl_scope_stmt (t)
     tree t;
{
  if (!SCOPE_NO_CLEANUPS_P (t))
    {
      if (SCOPE_BEGIN_P (t))
	expand_start_bindings_and_block (2 * SCOPE_NULLIFIED_P (t),
					 SCOPE_STMT_BLOCK (t));
      else if (SCOPE_END_P (t))
	expand_end_bindings (NULL_TREE, !SCOPE_NULLIFIED_P (t), 0);
    }
  else if (!SCOPE_NULLIFIED_P (t))
    {
      rtx note = emit_note (NULL,
			    (SCOPE_BEGIN_P (t) 
			     ? NOTE_INSN_BLOCK_BEG
			     : NOTE_INSN_BLOCK_END));
      NOTE_BLOCK (note) = SCOPE_STMT_BLOCK (t);
    }
}

/* Generate the RTL for T, which is a SWITCH_STMT. */

void
genrtl_switch_stmt (t)
     tree t;
{
  tree cond;
  genrtl_do_pushlevel ();
 
  cond = expand_cond (SWITCH_COND (t));
  if (cond == error_mark_node)
    /* The code is in error, but we don't want expand_end_case to
       crash. */
    cond = boolean_false_node;

  emit_line_note (input_filename, lineno);
  expand_start_case (1, cond, TREE_TYPE (cond), "switch statement");
  expand_stmt (SWITCH_BODY (t));
  expand_end_case (cond);
}

/* Create a CASE_LABEL tree node and return it. */

tree
build_case_label (low_value, high_value, label_decl)
     tree low_value;
     tree high_value;
     tree label_decl;
{
  return build_stmt (CASE_LABEL, low_value, high_value, label_decl);
}


/* Generate the RTL for a CASE_LABEL. */

void 
genrtl_case_label (case_label)
     tree case_label;
{
  tree duplicate;
  tree cleanup;

  cleanup = last_cleanup_this_contour ();
  if (cleanup)
    {
      static int explained = 0;
      warning_with_decl (TREE_PURPOSE (cleanup), 
			 "destructor needed for `%#D'");
      warning ("where case label appears here");
      if (!explained)
	{
	  warning ("(enclose actions of previous case statements requiring destructors in their own scope.)");
	  explained = 1;
	}
    }

  add_case_node (CASE_LOW (case_label), CASE_HIGH (case_label), 
		 CASE_LABEL_DECL (case_label), &duplicate);
}

/* Generate the RTL for T, which is a COMPOUND_STMT. */

void
genrtl_compound_stmt (t)
    tree t;
{
  expand_stmt (COMPOUND_BODY (t));
}

/* Generate the RTL for an ASM_STMT. */

void
genrtl_asm_stmt (cv_qualifier, string, output_operands,
		 input_operands, clobbers, asm_input_p)
     tree cv_qualifier;
     tree string;
     tree output_operands;
     tree input_operands;
     tree clobbers;
     int asm_input_p;
{
  if (cv_qualifier != NULL_TREE
      && cv_qualifier != ridpointers[(int) RID_VOLATILE])
    {
      warning ("%s qualifier ignored on asm",
	       IDENTIFIER_POINTER (cv_qualifier));
      cv_qualifier = NULL_TREE;
    }

  emit_line_note (input_filename, lineno);
  if (asm_input_p)
    expand_asm (string);
  else
    c_expand_asm_operands (string, output_operands, input_operands, 
			   clobbers, cv_qualifier != NULL_TREE,
			   input_filename, lineno);
}

/* Generate the RTL for a DECL_CLEANUP. */

void 
genrtl_decl_cleanup (decl, cleanup)
     tree decl;
     tree cleanup;
{
  if (!decl || (DECL_SIZE (decl) && TREE_TYPE (decl) != error_mark_node))
    expand_decl_cleanup (decl, cleanup);
}

/* We're about to expand T, a statement.  Set up appropriate context
   for the substitution.  */

void
prep_stmt (t)
     tree t;
{
  if (!STMT_LINENO_FOR_FN_P (t))
    lineno = STMT_LINENO (t);
  current_stmt_tree ()->stmts_are_full_exprs_p = STMT_IS_FULL_EXPR_P (t);
}

/* Generate the RTL for the statement T, its substatements, and any
   other statements at its nesting level. */

void
expand_stmt (t)
     tree t;
{
  while (t && t != error_mark_node)
    {
      int saved_stmts_are_full_exprs_p;

      /* Set up context appropriately for handling this statement.  */
      saved_stmts_are_full_exprs_p = stmts_are_full_exprs_p ();
      prep_stmt (t);

      switch (TREE_CODE (t))
	{
	case RETURN_STMT:
	  genrtl_return_stmt (t);
	  break;

	case EXPR_STMT:
	  genrtl_expr_stmt (EXPR_STMT_EXPR (t));
	  break;

	case DECL_STMT:
	  genrtl_decl_stmt (t);
	  break;

	case FOR_STMT:
	  genrtl_for_stmt (t);
	  break;

	case WHILE_STMT:
	  genrtl_while_stmt (t);
	  break;

	case DO_STMT:
	  genrtl_do_stmt (t);
	  break;

	case IF_STMT:
	  genrtl_if_stmt (t);
	  break;

	case COMPOUND_STMT:
	  genrtl_compound_stmt (t);
	  break;

	case BREAK_STMT:
	  genrtl_break_stmt ();
	  break;

	case CONTINUE_STMT:
	  genrtl_continue_stmt ();
	  break;

	case SWITCH_STMT:
	  genrtl_switch_stmt (t);
	  break;

	case CASE_LABEL:
	  genrtl_case_label (t);
	  break;

	case LABEL_STMT:
	  expand_label (LABEL_STMT_LABEL (t));
	  break;

	case GOTO_STMT:
	  genrtl_goto_stmt (GOTO_DESTINATION (t));
	  break;

	case ASM_STMT:
	  genrtl_asm_stmt (ASM_CV_QUAL (t), ASM_STRING (t),
			   ASM_OUTPUTS (t), ASM_INPUTS (t),
			   ASM_CLOBBERS (t), ASM_INPUT_P (t));
	  break;

	case SCOPE_STMT:
	  genrtl_scope_stmt (t);
	  break;

	default:
	  if (lang_expand_stmt)
	    (*lang_expand_stmt) (t);
	  else 
	    abort ();
	  break;
	}

      /* Restore saved state.  */
      current_stmt_tree ()->stmts_are_full_exprs_p
	= saved_stmts_are_full_exprs_p;

      /* Go on to the next statement in this scope.  */
      t = TREE_CHAIN (t);
    }
}