gcc/function-abi.cc

   1 /* Information about fuunction binary interfaces.
   2    Copyright (C) 2019-2021 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 "target.h"
  25 #include "rtl.h"
  26 #include "tree.h"
  27 #include "regs.h"
  28 #include "function-abi.h"
  29 #include "varasm.h"
  30 #include "cgraph.h"
  31
  32 target_function_abi_info default_target_function_abi_info;
  33 #if SWITCHABLE_TARGET
  34 target_function_abi_info *this_target_function_abi_info
  35   = &default_target_function_abi_info;
  36 #endif
  37
  38 /* Initialize a predefined function ABI with the given values of
  39    ID and FULL_REG_CLOBBERS.  */
  40
  41 void
  42 predefined_function_abi::initialize (unsigned int id,
  43                                      const_hard_reg_set full_reg_clobbers)
  44 {
  45   m_id = id;
  46   m_initialized = true;
  47   m_full_reg_clobbers = full_reg_clobbers;
  48
  49   /* Set up the value of m_full_and_partial_reg_clobbers.
  50
  51      If the ABI specifies that part of a hard register R is call-clobbered,
  52      we should be able to find a single-register mode M for which
  53      targetm.hard_regno_call_part_clobbered (m_id, R, M) is true.
  54      In other words, it shouldn't be the case that R can hold all
  55      single-register modes across a call, but can't hold part of
  56      a multi-register mode.
  57
  58      If that assumption doesn't hold for a future target, we would need
  59      to change the interface of TARGET_HARD_REGNO_CALL_PART_CLOBBERED so
  60      that it tells us which registers in a multi-register value are
  61      actually clobbered.  */
  62   m_full_and_partial_reg_clobbers = full_reg_clobbers;
  63   for (unsigned int i = 0; i < NUM_MACHINE_MODES; ++i)
  64     {
  65       machine_mode mode = (machine_mode) i;
  66       for (unsigned int regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno)
  67         if (targetm.hard_regno_mode_ok (regno, mode)
  68             && hard_regno_nregs (regno, mode) == 1
  69             && targetm.hard_regno_call_part_clobbered (m_id, regno, mode))
  70           SET_HARD_REG_BIT (m_full_and_partial_reg_clobbers, regno);
  71     }
  72
  73   /* For each mode MODE, work out which registers are unable to hold
  74      any part of a MODE value across a call, i.e. those for which no
  75      overlapping call-preserved (reg:MODE REGNO) exists.
  76
  77      We assume that this can be flipped around to say that a call
  78      preserves (reg:MODE REGNO) unless the register overlaps this set.
  79      The usual reason for this being true is that if (reg:MODE REGNO)
  80      contains a part-clobbered register, that register would be
  81      part-clobbered regardless of which part of MODE it holds.
  82      For example, if (reg:M 2) occupies two registers and if the
  83      register 3 portion of it is part-clobbered, (reg:M 3) is usually
  84      either invalid or also part-clobbered.  */
  85   for (unsigned int i = 0; i < NUM_MACHINE_MODES; ++i)
  86     {
  87       machine_mode mode = (machine_mode) i;
  88       m_mode_clobbers[i] = m_full_and_partial_reg_clobbers;
  89       for (unsigned int regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno)
  90         if (targetm.hard_regno_mode_ok (regno, mode)
  91             && !overlaps_hard_reg_set_p (m_full_reg_clobbers, mode, regno)
  92             && !targetm.hard_regno_call_part_clobbered (m_id, regno, mode))
  93           remove_from_hard_reg_set (&m_mode_clobbers[i], mode, regno);
  94     }
  95
  96   /* Check that the assumptions above actually hold, i.e. that testing
  97      for single-register modes makes sense, and that overlap tests for
  98      mode_clobbers work as expected.  */
  99   if (flag_checking)
 100     for (unsigned int i = 0; i < NUM_MACHINE_MODES; ++i)
 101       {
 102         machine_mode mode = (machine_mode) i;
 103         const_hard_reg_set all_clobbers = m_full_and_partial_reg_clobbers;
 104         for (unsigned int regno = 0; regno < FIRST_PSEUDO_REGISTER; ++regno)
 105           if (targetm.hard_regno_mode_ok (regno, mode)
 106               && !overlaps_hard_reg_set_p (m_full_reg_clobbers, mode, regno)
 107               && targetm.hard_regno_call_part_clobbered (m_id, regno, mode))
 108             gcc_assert (overlaps_hard_reg_set_p (all_clobbers, mode, regno)
 109                         && overlaps_hard_reg_set_p (m_mode_clobbers[i],
 110                                                     mode, regno));
 111       }
 112 }
 113
 114 /* If the ABI has been initialized, add REGNO to the set of registers
 115    that can be completely altered by a call.  */
 116
 117 void
 118 predefined_function_abi::add_full_reg_clobber (unsigned int regno)
 119 {
 120   if (!m_initialized)
 121     return;
 122
 123   SET_HARD_REG_BIT (m_full_reg_clobbers, regno);
 124   SET_HARD_REG_BIT (m_full_and_partial_reg_clobbers, regno);
 125   for (unsigned int i = 0; i < NUM_MACHINE_MODES; ++i)
 126     SET_HARD_REG_BIT (m_mode_clobbers[i], regno);
 127 }
 128
 129 /* Return the set of registers that the caller of the recorded functions must
 130    save in order to honor the requirements of CALLER_ABI.  */
 131
 132 HARD_REG_SET
 133 function_abi_aggregator::
 134 caller_save_regs (const function_abi &caller_abi) const
 135 {
 136   HARD_REG_SET result;
 137   CLEAR_HARD_REG_SET (result);
 138   for (unsigned int abi_id = 0; abi_id < NUM_ABI_IDS; ++abi_id)
 139     {
 140       const predefined_function_abi &callee_abi = function_abis[abi_id];
 141
 142       /* Skip cases that clearly aren't problematic.  */
 143       if (abi_id == caller_abi.id ()
 144           || hard_reg_set_empty_p (m_abi_clobbers[abi_id]))
 145         continue;
 146
 147       /* Collect the set of registers that can be "more clobbered" by
 148          CALLEE_ABI than by CALLER_ABI.  */
 149       HARD_REG_SET extra_clobbers;
 150       CLEAR_HARD_REG_SET (extra_clobbers);
 151       for (unsigned int i = 0; i < NUM_MACHINE_MODES; ++i)
 152         {
 153           machine_mode mode = (machine_mode) i;
 154           extra_clobbers |= (callee_abi.mode_clobbers (mode)
 155                              & ~caller_abi.mode_clobbers (mode));
 156         }
 157
 158       /* Restrict it to the set of registers that we actually saw
 159          clobbers for (e.g. taking -fipa-ra into account).  */
 160       result |= (extra_clobbers & m_abi_clobbers[abi_id]);
 161     }
 162   return result;
 163 }
 164
 165 /* Return the set of registers that cannot be used to hold a value of
 166    mode MODE across the calls in a region described by ABIS and MASK, where:
 167
 168    * Bit ID of ABIS is set if the region contains a call with
 169      function_abi identifier ID.
 170
 171    * MASK contains all the registers that are fully or partially
 172      clobbered by calls in the region.
 173
 174    This is not quite as accurate as testing each individual call,
 175    but it's a close and conservatively-correct approximation.
 176    It's much better for some targets than just using MASK.  */
 177
 178 HARD_REG_SET
 179 call_clobbers_in_region (unsigned int abis, const_hard_reg_set mask,
 180                          machine_mode mode)
 181 {
 182   HARD_REG_SET result;
 183   CLEAR_HARD_REG_SET (result);
 184   for (unsigned int id = 0; abis; abis >>= 1, ++id)
 185     if (abis & 1)
 186       result |= function_abis[id].mode_clobbers (mode);
 187   return result & mask;
 188 }
 189
 190 /* Return the predefined ABI used by functions with type TYPE.  */
 191
 192 const predefined_function_abi &
 193 fntype_abi (const_tree type)
 194 {
 195   gcc_assert (FUNC_OR_METHOD_TYPE_P (type));
 196   if (targetm.calls.fntype_abi)
 197     return targetm.calls.fntype_abi (type);
 198   return default_function_abi;
 199 }
 200
 201 /* Return the ABI of function decl FNDECL.  */
 202
 203 function_abi
 204 fndecl_abi (const_tree fndecl)
 205 {
 206   gcc_assert (TREE_CODE (fndecl) == FUNCTION_DECL);
 207   const predefined_function_abi &base_abi = fntype_abi (TREE_TYPE (fndecl));
 208
 209   if (flag_ipa_ra && decl_binds_to_current_def_p (fndecl))
 210     if (cgraph_rtl_info *info = cgraph_node::rtl_info (fndecl))
 211       return function_abi (base_abi, info->function_used_regs);
 212
 213   return base_abi;
 214 }
 215
 216 /* Return the ABI of the function called by INSN.  */
 217
 218 function_abi
 219 insn_callee_abi (const rtx_insn *insn)
 220 {
 221   gcc_assert (insn && CALL_P (insn));
 222
 223   if (flag_ipa_ra)
 224     if (tree fndecl = get_call_fndecl (insn))
 225       return fndecl_abi (fndecl);
 226
 227   if (targetm.calls.insn_callee_abi)
 228     return targetm.calls.insn_callee_abi (insn);
 229
 230   return default_function_abi;
 231 }
 232
 233 /* Return the ABI of the function called by CALL_EXPR EXP.  Return the
 234    default ABI for erroneous calls.  */
 235
 236 function_abi
 237 expr_callee_abi (const_tree exp)
 238 {
 239   gcc_assert (TREE_CODE (exp) == CALL_EXPR);
 240
 241   if (tree fndecl = get_callee_fndecl (exp))
 242     return fndecl_abi (fndecl);
 243
 244   tree callee = CALL_EXPR_FN (exp);
 245   if (callee == error_mark_node)
 246     return default_function_abi;
 247
 248   tree type = TREE_TYPE (callee);
 249   if (type == error_mark_node)
 250     return default_function_abi;
 251
 252   gcc_assert (POINTER_TYPE_P (type));
 253   return fntype_abi (TREE_TYPE (type));
 254 }