gcc/tree-ssa-scopedtables.c

   1 /* Header file for SSA dominator optimizations.
   2    Copyright (C) 2013-2015 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 "alias.h"
  25 #include "symtab.h"
  26 #include "tree.h"
  27 #include "tree-pretty-print.h"
  28 #include "tree-pass.h"
  29 #include "tree-ssa-scopedtables.h"
  30 #include "tree-ssa-threadedge.h"
  31
  32 const_and_copies::const_and_copies (FILE *file, int flags)
  33 {
  34   stack.create (20);
  35   dump_file = file;
  36   dump_flags = flags;
  37 }
  38
  39 /* Pop entries off the stack until we hit the NULL marker.
  40    For each entry popped, use the SRC/DEST pair to restore
  41    SRC to its prior value.  */
  42
  43 void
  44 const_and_copies::pop_to_marker (void)
  45 {
  46   while (stack.length () > 0)
  47     {
  48       tree prev_value, dest;
  49
  50       dest = stack.pop ();
  51
  52       /* A NULL value indicates we should stop unwinding, otherwise
  53          pop off the next entry as they're recorded in pairs.  */
  54       if (dest == NULL)
  55         break;
  56
  57       if (dump_file && (dump_flags & TDF_DETAILS))
  58         {
  59           fprintf (dump_file, "<<<< COPY ");
  60           print_generic_expr (dump_file, dest, 0);
  61           fprintf (dump_file, " = ");
  62           print_generic_expr (dump_file, SSA_NAME_VALUE (dest), 0);
  63           fprintf (dump_file, "\n");
  64         }
  65
  66       prev_value = stack.pop ();
  67       set_ssa_name_value (dest, prev_value);
  68     }
  69 }
  70
  71 /* Record that X has the value Y.  */
  72
  73 void
  74 const_and_copies::record_const_or_copy (tree x, tree y)
  75 {
  76   record_const_or_copy (x, y, SSA_NAME_VALUE (x));
  77 }
  78
  79 /* Record that X has the value Y and that X's previous value is PREV_X.  */
  80
  81 void
  82 const_and_copies::record_const_or_copy (tree x, tree y, tree prev_x)
  83 {
  84   /* Y may be NULL if we are invalidating entries in the table.  */
  85   if (y && TREE_CODE (y) == SSA_NAME)
  86     {
  87       tree tmp = SSA_NAME_VALUE (y);
  88       y = tmp ? tmp : y;
  89     }
  90
  91   if (dump_file && (dump_flags & TDF_DETAILS))
  92     {
  93       fprintf (dump_file, "0>>> COPY ");
  94       print_generic_expr (dump_file, x, 0);
  95       fprintf (dump_file, " = ");
  96       print_generic_expr (dump_file, y, 0);
  97       fprintf (dump_file, "\n");
  98     }
  99
 100   set_ssa_name_value (x, y);
 101   stack.reserve (2);
 102   stack.quick_push (prev_x);
 103   stack.quick_push (x);
 104 }
 105
 106 /* A new value has been assigned to LHS.  If necessary, invalidate any
 107    equivalences that are no longer valid.   This includes invaliding
 108    LHS and any objects that are currently equivalent to LHS.
 109
 110    Finding the objects that are currently marked as equivalent to LHS
 111    is a bit tricky.  We could walk the ssa names and see if any have
 112    SSA_NAME_VALUE that is the same as LHS.  That's expensive.
 113
 114    However, it's far more efficient to look at the unwinding stack as
 115    that will have all context sensitive equivalences which are the only
 116    ones that we really have to worry about here.   */
 117 void
 118 const_and_copies::invalidate (tree lhs)
 119 {
 120
 121   /* The stack is an unwinding stack.  If the current element is NULL
 122      then it's a "stop unwinding" marker.  Else the current marker is
 123      the SSA_NAME with an equivalence and the prior entry in the stack
 124      is what the current element is equivalent to.  */
 125   for (int i = stack.length() - 1; i >= 0; i--)
 126     {
 127       /* Ignore the stop unwinding markers.  */
 128       if ((stack)[i] == NULL)
 129         continue;
 130
 131       /* We want to check the current value of stack[i] to see if
 132          it matches LHS.  If so, then invalidate.  */
 133       if (SSA_NAME_VALUE ((stack)[i]) == lhs)
 134         record_const_or_copy ((stack)[i], NULL_TREE);
 135
 136       /* Remember, we're dealing with two elements in this case.  */
 137       i--;
 138     }
 139
 140   /* And invalidate any known value for LHS itself.  */
 141   if (SSA_NAME_VALUE (lhs))
 142     record_const_or_copy (lhs, NULL_TREE);
 143 }