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  99    equivalences that are no longer valid.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