xref: /dragonfly/contrib/gcc-8.0/gcc/init-regs.c (revision 38fd1498)
1 /* Initialization of uninitialized regs.
2    Copyright (C) 2007-2018 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 "tree.h"
26 #include "df.h"
27 #include "memmodel.h"
28 #include "emit-rtl.h"
29 #include "expr.h"
30 #include "tree-pass.h"
31 
32 /* Check all of the uses of pseudo variables.  If any use that is MUST
33    uninitialized, add a store of 0 immediately before it.  For
34    subregs, this makes combine happy.  For full word regs, this makes
35    other optimizations, like the register allocator and the reg-stack
36    happy as well as papers over some problems on the arm and other
37    processors where certain isa constraints cannot be handled by gcc.
38    These are of the form where two operands to an insn my not be the
39    same.  The ra will only make them the same if they do not
40    interfere, and this can only happen if one is not initialized.
41 
42    There is also the unfortunate consequence that this may mask some
43    buggy programs where people forget to initialize stack variable.
44    Any programmer with half a brain would look at the uninitialized
45    variable warnings.  */
46 
47 static void
initialize_uninitialized_regs(void)48 initialize_uninitialized_regs (void)
49 {
50   basic_block bb;
51   auto_bitmap already_genned;
52 
53   if (optimize == 1)
54     {
55       df_live_add_problem ();
56       df_live_set_all_dirty ();
57     }
58 
59   df_analyze ();
60 
61   FOR_EACH_BB_FN (bb, cfun)
62     {
63       rtx_insn *insn;
64       bitmap lr = DF_LR_IN (bb);
65       bitmap ur = DF_LIVE_IN (bb);
66       bitmap_clear (already_genned);
67 
68       FOR_BB_INSNS (bb, insn)
69 	{
70 	  df_ref use;
71 	  if (!NONDEBUG_INSN_P (insn))
72 	    continue;
73 
74 	  FOR_EACH_INSN_USE (use, insn)
75 	    {
76 	      unsigned int regno = DF_REF_REGNO (use);
77 
78 	      /* Only do this for the pseudos.  */
79 	      if (regno < FIRST_PSEUDO_REGISTER)
80 		continue;
81 
82 	      /* Ignore pseudo PIC register.  */
83 	      if (pic_offset_table_rtx
84 		  && regno == REGNO (pic_offset_table_rtx))
85 		continue;
86 
87 	      /* Do not generate multiple moves for the same regno.
88 		 This is common for sequences of subreg operations.
89 		 They would be deleted during combine but there is no
90 		 reason to churn the system.  */
91 	      if (bitmap_bit_p (already_genned, regno))
92 		continue;
93 
94 	      /* A use is MUST uninitialized if it reaches the top of
95 		 the block from the inside of the block (the lr test)
96 		 and no def for it reaches the top of the block from
97 		 outside of the block (the ur test).  */
98 	      if (bitmap_bit_p (lr, regno)
99 		  && (!bitmap_bit_p (ur, regno)))
100 		{
101 		  rtx_insn *move_insn;
102 		  rtx reg = DF_REF_REAL_REG (use);
103 
104 		  bitmap_set_bit (already_genned, regno);
105 
106 		  start_sequence ();
107 		  emit_clobber (reg);
108 		  emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
109 		  move_insn = get_insns ();
110 		  end_sequence ();
111 		  emit_insn_before (move_insn, insn);
112 		  if (dump_file)
113 		    fprintf (dump_file,
114 			     "adding initialization in %s of reg %d at in block %d for insn %d.\n",
115 			     current_function_name (), regno, bb->index,
116 			     INSN_UID (insn));
117 		}
118 	    }
119 	}
120     }
121 
122   if (optimize == 1)
123     {
124       if (dump_file)
125 	df_dump (dump_file);
126       df_remove_problem (df_live);
127     }
128 }
129 
130 namespace {
131 
132 const pass_data pass_data_initialize_regs =
133 {
134   RTL_PASS, /* type */
135   "init-regs", /* name */
136   OPTGROUP_NONE, /* optinfo_flags */
137   TV_NONE, /* tv_id */
138   0, /* properties_required */
139   0, /* properties_provided */
140   0, /* properties_destroyed */
141   0, /* todo_flags_start */
142   TODO_df_finish, /* todo_flags_finish */
143 };
144 
145 class pass_initialize_regs : public rtl_opt_pass
146 {
147 public:
pass_initialize_regs(gcc::context * ctxt)148   pass_initialize_regs (gcc::context *ctxt)
149     : rtl_opt_pass (pass_data_initialize_regs, ctxt)
150   {}
151 
152   /* opt_pass methods: */
gate(function *)153   virtual bool gate (function *) { return optimize > 0; }
execute(function *)154   virtual unsigned int execute (function *)
155     {
156       initialize_uninitialized_regs ();
157       return 0;
158     }
159 
160 }; // class pass_initialize_regs
161 
162 } // anon namespace
163 
164 rtl_opt_pass *
make_pass_initialize_regs(gcc::context * ctxt)165 make_pass_initialize_regs (gcc::context *ctxt)
166 {
167   return new pass_initialize_regs (ctxt);
168 }
169