gcc/function-abi.h

   1 /* Information about fuunction binary interfaces.
   2    Copyright (C) 2019-2020 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 #ifndef GCC_FUNCTION_ABI_H
  21 #define GCC_FUNCTION_ABI_H
  22
  23 /* Most targets use the same ABI for all functions in a translation
  24    unit, but some targets support interoperability between several ABIs.
  25    Each such ABI has a unique 0-based identifier, with 0 always being
  26    the default choice of ABI.
  27
  28    NUM_ABI_IDS is the maximum number of such ABIs that GCC can handle at once.
  29    A bitfield with this number of bits can represent any combinaion of the
  30    supported ABIs.  */
  31 const size_t NUM_ABI_IDS = 8;
  32
  33 /* Information about one of the target's predefined ABIs.  */
  34 class predefined_function_abi
  35 {
  36 public:
  37   /* A target-specific identifier for this ABI.  The value must be in
  38      the range [0, NUM_ABI_IDS - 1].  */
  39   unsigned int id () const { return m_id; }
  40
  41   /* True if this ABI has been initialized.  */
  42   bool initialized_p () const { return m_initialized; }
  43
  44   /* Return true if a function call is allowed to alter every bit of
  45      register REGNO, so that the register contains an arbitrary value
  46      on return.  If so, the register cannot hold any part of a value
  47      that is live across a call.  */
  48   bool
  49   clobbers_full_reg_p (unsigned int regno) const
  50   {
  51     return TEST_HARD_REG_BIT (m_full_reg_clobbers, regno);
  52   }
  53
  54   /* Return true if a function call is allowed to alter some or all bits
  55      of register REGNO.
  56
  57      This is true whenever clobbers_full_reg_p (REGNO) is true.  It is
  58      also true if, for example, the ABI says that a call must preserve the
  59      low 32 or 64 bits of REGNO, but can clobber the upper bits of REGNO.
  60      In the latter case, it is possible for REGNO to hold values that
  61      are live across a call, provided that the value occupies only the
  62      call-preserved part of the register.  */
  63   bool
  64   clobbers_at_least_part_of_reg_p (unsigned int regno) const
  65   {
  66     return TEST_HARD_REG_BIT (m_full_and_partial_reg_clobbers, regno);
  67   }
  68
  69   /* Return true if a function call is allowed to clobber at least part
  70      of (reg:MODE REGNO).  If so, it is not possible for the register
  71      as a whole to be live across a call.  */
  72   bool
  73   clobbers_reg_p (machine_mode mode, unsigned int regno) const
  74   {
  75     return overlaps_hard_reg_set_p (m_mode_clobbers[mode], mode, regno);
  76   }
  77
  78   /* Return the set of registers that a function call is allowed to
  79      alter completely, so that the registers contain arbitrary values
  80      on return.  This doesn't include registers that a call can only
  81      partly clobber (as per TARGET_HARD_REGNO_CALL_PART_CLOBBERED).
  82
  83      These registers cannot hold any part of a value that is live across
  84      a call.  */
  85   HARD_REG_SET full_reg_clobbers () const { return m_full_reg_clobbers; }
  86
  87   /* Return the set of registers that a function call is allowed to alter
  88      to some degree.  For example, if an ABI says that a call must preserve
  89      the low 32 or 64 bits of a register R, but can clobber the upper bits
  90      of R, R would be in this set but not in full_reg_clobbers ().
  91
  92      This set is a superset of full_reg_clobbers ().  It is possible for a
  93      register in full_and_partial_reg_clobbers () & ~full_reg_clobbers ()
  94      to contain values that are live across a call, provided that the live
  95      value only occupies the call-preserved part of the register.  */
  96   HARD_REG_SET
  97   full_and_partial_reg_clobbers () const
  98   {
  99     return m_full_and_partial_reg_clobbers;
 100   }
 101
 102   /* Return the set of registers that cannot be used to hold a value of
 103      mode MODE across a function call.  That is:
 104
 105        (reg:REGNO MODE)
 106
 107      might be clobbered by a call whenever:
 108
 109        overlaps_hard_reg_set (mode_clobbers (MODE), MODE, REGNO)
 110
 111      In allocation terms, the registers in the returned set conflict
 112      with any value of mode MODE that is live across a call.  */
 113   HARD_REG_SET
 114   mode_clobbers (machine_mode mode) const
 115   {
 116     return m_mode_clobbers[mode];
 117   }
 118
 119   void initialize (unsigned int, const_hard_reg_set);
 120   void add_full_reg_clobber (unsigned int);
 121
 122 private:
 123   unsigned int m_id : NUM_ABI_IDS;
 124   unsigned int m_initialized : 1;
 125   HARD_REG_SET m_full_reg_clobbers;
 126   HARD_REG_SET m_full_and_partial_reg_clobbers;
 127   HARD_REG_SET m_mode_clobbers[NUM_MACHINE_MODES];
 128 };
 129
 130 /* Describes either a predefined ABI or the ABI of a particular function.
 131    In the latter case, the ABI might make use of extra function-specific
 132    information, such as for -fipa-ra.  */
 133 class function_abi
 134 {
 135 public:
 136   /* Initialize the structure for a general function with the given ABI.  */
 137   function_abi (const predefined_function_abi &base_abi)
 138     : m_base_abi (&base_abi),
 139       m_mask (base_abi.full_and_partial_reg_clobbers ()) {}
 140
 141   /* Initialize the structure for a function that has the given ABI and
 142      that is known not to clobber registers outside MASK.  */
 143   function_abi (const predefined_function_abi &base_abi,
 144                 const_hard_reg_set mask)
 145     : m_base_abi (&base_abi), m_mask (mask) {}
 146
 147   /* The predefined ABI from which this ABI is derived.  */
 148   const predefined_function_abi &base_abi () const { return *m_base_abi; }
 149
 150   /* The target-specific identifier of the predefined ABI.  */
 151   unsigned int id () const { return m_base_abi->id (); }
 152
 153   /* See the corresponding predefined_function_abi functions for
 154      details about the following functions.  */
 155
 156   HARD_REG_SET
 157   full_reg_clobbers () const
 158   {
 159     return m_mask & m_base_abi->full_reg_clobbers ();
 160   }
 161
 162   HARD_REG_SET
 163   full_and_partial_reg_clobbers () const
 164   {
 165     return m_mask & m_base_abi->full_and_partial_reg_clobbers ();
 166   }
 167
 168   HARD_REG_SET
 169   mode_clobbers (machine_mode mode) const
 170   {
 171     return m_mask & m_base_abi->mode_clobbers (mode);
 172   }
 173
 174   bool
 175   clobbers_full_reg_p (unsigned int regno) const
 176   {
 177     return (TEST_HARD_REG_BIT (m_mask, regno)
 178             & m_base_abi->clobbers_full_reg_p (regno));
 179   }
 180
 181   bool
 182   clobbers_at_least_part_of_reg_p (unsigned int regno) const
 183   {
 184     return (TEST_HARD_REG_BIT (m_mask, regno)
 185             & m_base_abi->clobbers_at_least_part_of_reg_p (regno));
 186   }
 187
 188   bool
 189   clobbers_reg_p (machine_mode mode, unsigned int regno) const
 190   {
 191     return overlaps_hard_reg_set_p (mode_clobbers (mode), mode, regno);
 192   }
 193
 194   bool
 195   operator== (const function_abi &other) const
 196   {
 197     return m_base_abi == other.m_base_abi && m_mask == other.m_mask;
 198   }
 199
 200   bool
 201   operator!= (const function_abi &other) const
 202   {
 203     return !operator== (other);
 204   }
 205
 206 protected:
 207   const predefined_function_abi *m_base_abi;
 208   HARD_REG_SET m_mask;
 209 };
 210
 211 /* This class collects information about the ABIs of functions that are
 212    called in a particular region of code.  It is mostly intended to be
 213    used as a local variable during an IR walk.  */
 214 class function_abi_aggregator
 215 {
 216 public:
 217   function_abi_aggregator () : m_abi_clobbers () {}
 218
 219   /* Record that the code region calls a function with the given ABI.  */
 220   void
 221   note_callee_abi (const function_abi &abi)
 222   {
 223     m_abi_clobbers[abi.id ()] |= abi.full_and_partial_reg_clobbers ();
 224   }
 225
 226   HARD_REG_SET caller_save_regs (const function_abi &) const;
 227
 228 private:
 229   HARD_REG_SET m_abi_clobbers[NUM_ABI_IDS];
 230 };
 231
 232 struct target_function_abi_info
 233 {
 234   /* An array of all the target ABIs that are available in this
 235      translation unit.  Not all entries are used for all targets,
 236      but the structures are relatively small, and using a fixed-size
 237      array avoids extra indirection.
 238
 239      There are various ways of getting an ABI descriptor:
 240
 241      * fndecl_abi (FNDECL) is the ABI of function FNDECL.
 242
 243      * fntype_abi (FNTYPE) is the ABI of a function with type FNTYPE.
 244
 245      * crtl->abi is the ABI of the function that we are currently
 246        compiling to rtl.
 247
 248      * insn_callee_abi (INSN) is the ABI used by the target of call insn INSN.
 249
 250      * eh_edge_abi is the "ABI" used when taking an EH edge from an
 251        exception-throwing statement to an exception handler.  Catching
 252        exceptions from calls can be treated as an abnormal return from
 253        those calls, and this ABI therefore describes the ABI of functions
 254        on such an abnormal return.  Statements that throw non-call
 255        exceptions can be treated as being implicitly wrapped in a call
 256        that has such an abnormal return.
 257
 258        At present, no target needs to support more than one EH ABI.
 259
 260      * function_abis[N] is the ABI with identifier N.  This can be useful
 261        when referring back to ABIs that have been collected by number in
 262        a bitmask, such as after walking function calls in a particular
 263        region of code.
 264
 265      * default_function_abi refers specifically to the target's default
 266        choice of ABI, regardless of which (if any) functions actually
 267        use it.  This ABI and data derived from it do *not* provide
 268        globally conservatively-correct information, so it is only
 269        useful in very specific circumstances.  */
 270   predefined_function_abi x_function_abis[NUM_ABI_IDS];
 271 };
 272
 273 extern target_function_abi_info default_target_function_abi_info;
 274 #if SWITCHABLE_TARGET
 275 extern target_function_abi_info *this_target_function_abi_info;
 276 #else
 277 #define this_target_function_abi_info (&default_target_function_abi_info)
 278 #endif
 279
 280 /* See the comment above x_function_abis for when these macros should be used.
 281    At present, eh_edge_abi is always the default ABI, but that could change
 282    in future if a target needs it to.  */
 283 #define function_abis \
 284   (this_target_function_abi_info->x_function_abis)
 285 #define default_function_abi \
 286   (this_target_function_abi_info->x_function_abis[0])
 287 #define eh_edge_abi default_function_abi
 288
 289 extern HARD_REG_SET call_clobbers_in_region (unsigned int, const_hard_reg_set,
 290                                              machine_mode mode);
 291
 292 /* Return true if (reg:MODE REGNO) might be clobbered by one of the
 293    calls in a region described by ABIS and MASK, where:
 294
 295    * Bit ID of ABIS is set if the region contains a call with
 296      function_abi identifier ID.
 297
 298    * MASK contains all the registers that are fully or partially
 299      clobbered by calls in the region.
 300
 301    This is not quite as accurate as testing each individual call,
 302    but it's a close and conservatively-correct approximation.
 303    It's much better for some targets than:
 304
 305      overlaps_hard_reg_set_p (MASK, MODE, REGNO).  */
 306
 307 inline bool
 308 call_clobbered_in_region_p (unsigned int abis, const_hard_reg_set mask,
 309                             machine_mode mode, unsigned int regno)
 310 {
 311   HARD_REG_SET clobbers = call_clobbers_in_region (abis, mask, mode);
 312   return overlaps_hard_reg_set_p (clobbers, mode, regno);
 313 }
 314
 315 extern const predefined_function_abi &fntype_abi (const_tree);
 316 extern function_abi fndecl_abi (const_tree);
 317 extern function_abi insn_callee_abi (const rtx_insn *);
 318 extern function_abi expr_callee_abi (const_tree);
 319
 320 #endif