gcc/ipa-param-manipulation.h

   1 /* Manipulation of formal and actual parameters of functions and function
   2    calls.
   3    Copyright (C) 2017-2021 Free Software Foundation, Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 3, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.
  20
  21
  22
  23 This file defines classes and other data structures that are used to manipulate
  24 the prototype of a function, especially to create, remove or split its formal
  25 parameters, but also to remove its return value, and also its call statements
  26 correspondingly.
  27
  28 The most basic one is a vector of structures ipa_adjusted_param.  It is simply
  29 a description how the new parameters should look like after the transformation
  30 in what way they relate to the previous ones (if in any).  Such relation to an
  31 old parameter can be an outright copy or an IPA-SRA replacement. If an old
  32 parameter is not listed or otherwise mentioned, it is removed as unused or at
  33 least unnecessary.  Note that this most basic structure does not work for
  34 modifying calls of functions with variable number of arguments.
  35
  36 Class ipa_param_adjustments is only a little more than a thin encapsulation of
  37 a vector of ipa_param_adjustments.  Along with this vector it contains an index
  38 of the first potential vararg argument and a boolean flag whether the return
  39 value should be removed or not.  Moreover, the class contains method
  40 modify_call which can transform a call statement so that it correctly calls a
  41 modified function.  These two data structures were designed to have a small
  42 memory footprint because they are allocated for each clone of a call graph node
  43 that has its prototype changed and live until the end of IPA clone
  44 materialization and call redirection phase.
  45
  46 On the other hand, class ipa_param_body_adjustments can afford to allocate more
  47 data because its life span is much smaller, it is allocated and destroyed in
  48 the course of materialization of each single clone that needs it or only when a
  49 particular pass needs to change a function it is operating on.  This class has
  50 various methods required to change function declaration and the body of the
  51 function according to instructions given either by class ipa_param_adjustments
  52 or only a vector of ipa_adjusted_params.
  53
  54 When these classes are used in the context of call graph clone materialization
  55 and subsequent call statement redirection - which is the point at which we
  56 modify arguments in call statements - they need to cooperate with each other in
  57 order to handle what we refer to as transitive (IPA-SRA) splits.  These are
  58 situations when a formal parameter of one function is split into several
  59 smaller ones and some of them are then passed on in a call to another function
  60 because the formal parameter of this callee has also been split.
  61
  62 Consider a simple example:
  63
  64 struct S {int a, b, c;};
  65 struct Z {int x; S s;};
  66
  67 foo (S s)
  68 {
  69   use (s.b);
  70 }
  71
  72 bar (Z z)
  73 {
  74   use (z.s.a);
  75   foo (z.s);
  76 }
  77
  78 baz ()
  79 {
  80   bar (*global);
  81 }
  82
  83 Both bar and foo would have their parameter split.  Foo would receive one
  84 replacement representing s.b.  Function bar would see its parameter split into
  85 one replacement representing z.s.a and another representing z.s.b which would
  86 be passed on to foo.  It would be a so called transitive split IPA-SRA
  87 replacement, one which is passed in a call as an actual argument to another
  88 IPA-SRA replacement in another function.
  89
  90 Note that the call chain the example can be arbitrarily long and recursive and
  91 that any function in it can be cloned by another IPA pass and any number of
  92 adjacent functions in the call chain can be inlined into each other.  Call
  93 redirection takes place only after bodies of the function have been modified by
  94 all of the above.
  95
  96 Call redirection has to be able to find the right decl or SSA_NAME that
  97 corresponds to the transitive split in the caller.  The SSA names are assigned
  98 right after clone materialization/ modification and cannot be "added"
  99 afterwards.  Moreover, if the caller has been inlined the SSA_NAMEs in question
 100 no longer belong to PARM_DECLs but to VAR_DECLs, indistinguishable from any
 101 others.
 102
 103 Therefore, when clone materialization finds a call statement which it knows is
 104 a part of a transitive split, it will modify it into:
 105
 106   foo (DUMMY_Z_VAR.s, repl_for_a, repl_for_b, <rest of original arguments>);
 107
 108 It will also store {DUMMY_S_VAR, 32} and {DUMMY_S_VAR, 64} representing offsets
 109 of z.s.a and z.s.b (assuming a 32-bit int) into foo's cgraph node
 110 clone->performed_splits vector (which is storing structures of type
 111 ipa_param_performed_split also defined in this header file).
 112
 113 Call redirection will identify that expression DUMMY_Z_VAR.s is based on a
 114 variable stored in performed_splits vector and learn that the following
 115 arguments, already in SSA form, represent offsets 32 and 64 in a split original
 116 parameter.  It subtracts offset of DUMMY_Z_VAR.s from 32 and 64 and arrives at
 117 offsets 0 and 32 within callee's original parameter.  At this point it also
 118 knows from the call graph that only the bit with offset 32 is needed and so
 119 changes the call statement into final:
 120
 121 bar (repl_for_b, <rest of original arguments>);  */
 122
 123 #ifndef IPA_PARAM_MANIPULATION_H
 124 #define IPA_PARAM_MANIPULATION_H
 125
 126 /* Indices into ipa_param_prefixes to identify a human-readable prefix for newly
 127    synthesized parameters.  Keep in sync with the array.  */
 128 enum ipa_param_name_prefix_indices
 129   {
 130    IPA_PARAM_PREFIX_SYNTH,
 131    IPA_PARAM_PREFIX_ISRA,
 132    IPA_PARAM_PREFIX_SIMD,
 133    IPA_PARAM_PREFIX_MASK,
 134    IPA_PARAM_PREFIX_COUNT
 135 };
 136
 137 /* We do not support manipulating functions with more than
 138    1<<IPA_PARAM_MAX_INDEX_BITS parameters.  */
 139 #define IPA_PARAM_MAX_INDEX_BITS 16
 140
 141 /* Operation to be performed for the parameter in ipa_parm_adjustment
 142    below.  */
 143
 144 enum ipa_parm_op
 145 {
 146   /* Do not use or you will trigger an assert.  */
 147   IPA_PARAM_OP_UNDEFINED,
 148
 149   /* This new parameter is an unmodified parameter at index base_index. */
 150   IPA_PARAM_OP_COPY,
 151
 152   /* This describes a brand new parameter.  If it somehow relates to any
 153      original parameters, the user needs to manage the transition itself.  */
 154   IPA_PARAM_OP_NEW,
 155
 156     /* Split parameter as indicated by fields base_index, offset and type.  */
 157   IPA_PARAM_OP_SPLIT
 158 };
 159
 160 /* Structure that describes one parameter of a function after transformation.
 161    Omitted parameters will be removed.  */
 162
 163 struct GTY(()) ipa_adjusted_param
 164 {
 165   /* Type of the new parameter.  Required for all operations except
 166      IPA_PARM_OP_COPY when the original type will be preserved.  */
 167   tree type;
 168
 169   /* Alias reference type to be used in MEM_REFs when adjusting caller
 170      arguments.  Required for IPA_PARM_OP_SPLIT operation.  */
 171   tree alias_ptr_type;
 172
 173   /* Offset into the original parameter (for the cases when the new parameter
 174      is a component of an original one).  Required for IPA_PARM_OP_SPLIT
 175      operation.  */
 176   unsigned unit_offset;
 177
 178   /* Zero based index of the original parameter this one is based on.  Required
 179      for IPA_PARAM_OP_COPY and IPA_PARAM_OP_SPLIT, users of IPA_PARAM_OP_NEW
 180      only need to specify it if they use replacement lookup provided by
 181      ipa_param_body_adjustments.  */
 182   unsigned base_index : IPA_PARAM_MAX_INDEX_BITS;
 183
 184   /* Zero based index of the parameter this one is based on in the previous
 185      clone.  If there is no previous clone, it must be equal to base_index.  */
 186   unsigned prev_clone_index : IPA_PARAM_MAX_INDEX_BITS;
 187
 188   /* Specify the operation, if any, to be performed on the parameter.  */
 189   enum ipa_parm_op op : 2;
 190
 191   /* If set, this structure describes a parameter copied over from a previous
 192      IPA clone, any transformations are thus not to be re-done.  */
 193   unsigned prev_clone_adjustment : 1;
 194
 195   /* Index into ipa_param_prefixes specifying a prefix to be used with
 196      DECL_NAMEs of newly synthesized parameters.  */
 197   unsigned param_prefix_index : 2;
 198
 199   /* Storage order of the original parameter (for the cases when the new
 200      parameter is a component of an original one).  */
 201   unsigned reverse : 1;
 202
 203   /* A bit free for the user.  */
 204   unsigned user_flag : 1;
 205 };
 206
 207 void ipa_dump_adjusted_parameters (FILE *f,
 208                                    vec<ipa_adjusted_param, va_gc> *adj_params);
 209
 210 /* Structure to remember the split performed on a node so that edge redirection
 211    (i.e. splitting arguments of call statements) know how split formal
 212    parameters of the caller are represented.  */
 213
 214 struct GTY(()) ipa_param_performed_split
 215 {
 216   /* The dummy VAR_DECL that was created instead of the split parameter that
 217      sits in the call in the meantime between clone materialization and call
 218      redirection.  All entries in a vector of performed splits that correspond
 219      to the same dumy decl must be grouped together.  */
 220   tree dummy_decl;
 221   /* Offset into the original parameter.  */
 222   unsigned unit_offset;
 223 };
 224
 225 /* Class used to record planned modifications to parameters of a function and
 226    also to perform necessary modifications at the caller side at the gimple
 227    level.  Used to describe all cgraph node clones that have their parameters
 228    changed, therefore the class should only have a small memory footprint.  */
 229
 230 class GTY(()) ipa_param_adjustments
 231 {
 232 public:
 233   /* Constructor from NEW_PARAMS showing how new parameters should look like
 234       plus copying any pre-existing actual arguments starting from argument
 235       with index ALWAYS_COPY_START (if non-negative, negative means do not copy
 236       anything beyond what is described in NEW_PARAMS), and SKIP_RETURN, which
 237       indicates that the function should return void after transformation.  */
 238
 239   ipa_param_adjustments (vec<ipa_adjusted_param, va_gc> *new_params,
 240                          int always_copy_start, bool skip_return)
 241     : m_adj_params (new_params), m_always_copy_start (always_copy_start),
 242     m_skip_return (skip_return)
 243     {}
 244
 245   /* Modify a call statement arguments (and possibly remove the return value)
 246      as described in the data fields of this class.  */
 247   gcall *modify_call (gcall *stmt,
 248                       vec<ipa_param_performed_split, va_gc> *performed_splits,
 249                       tree callee_decl, bool update_references);
 250   /* Return if the first parameter is left intact.  */
 251   bool first_param_intact_p ();
 252   /* Build a function type corresponding to the modified call.  */
 253   tree build_new_function_type (tree old_type, bool type_is_original_p);
 254   /* Build a declaration corresponding to the target of the modified call.  */
 255   tree adjust_decl (tree orig_decl);
 256   /* Fill a vector marking which parameters are intact by the described
 257      modifications. */
 258   void get_surviving_params (vec<bool> *surviving_params);
 259   /* Fill a vector with new indices of surviving original parameters.  */
 260   void get_updated_indices (vec<int> *new_indices);
 261   /* Return the original index for the given new parameter index.  Return a
 262      negative number if not available.  */
 263   int get_original_index (int newidx);
 264
 265   void dump (FILE *f);
 266   void debug ();
 267
 268   /* How the known part of arguments should look like.  */
 269   vec<ipa_adjusted_param, va_gc> *m_adj_params;
 270
 271   /* If non-negative, copy any arguments starting at this offset without any
 272      modifications so that functions with variable number of arguments can be
 273      modified. This number should be equal to the number of original forma
 274      parameters.  */
 275   int m_always_copy_start;
 276   /* If true, make the function not return any value.  */
 277   bool m_skip_return;
 278
 279 private:
 280   ipa_param_adjustments () {}
 281
 282   void init (vec<tree> *cur_params);
 283   int get_max_base_index ();
 284   bool method2func_p (tree orig_type);
 285 };
 286
 287 /* Structure used to map expressions accessing split or replaced parameters to
 288    new PARM_DECLs.  */
 289
 290 struct ipa_param_body_replacement
 291 {
 292   /* The old decl of the original parameter.   */
 293   tree base;
 294   /* The new decl it should be replaced with.  */
 295   tree repl;
 296   /* When modifying clones during IPA clone materialization, this is a dummy
 297      decl used to mark calls in which we need to apply transitive splitting,
 298      these dummy delcls are inserted as arguments to such calls and then
 299      followed by all the replacements with offset info stored in
 300      ipa_param_performed_split.
 301
 302      Users of ipa_param_body_adjustments that modify standalone functions
 303      outside of IPA clone materialization can use this field for their internal
 304      purposes.  */
 305   tree dummy;
 306   /* The offset within BASE that REPL represents.  */
 307   unsigned unit_offset;
 308 };
 309
 310 struct ipa_replace_map;
 311
 312 /* Class used when actually performing adjustments to formal parameters of a
 313    function to map accesses that need to be replaced to replacements.  The
 314    class attempts to work in two very different sets of circumstances: as a
 315    part of tree-inine.c's tree_function_versioning machinery to clone functions
 316    (when M_ID is not NULL) and in s standalone fashion, modifying an existing
 317    function in place (when M_ID is NULL).  While a lot of stuff handled in a
 318    unified way in both modes, there are many aspects of the processs that
 319    requires distinct paths.  */
 320
 321 class ipa_param_body_adjustments
 322 {
 323 public:
 324   /* Constructor to use from within tree-inline.  */
 325   ipa_param_body_adjustments (ipa_param_adjustments *adjustments,
 326                               tree fndecl, tree old_fndecl,
 327                               struct copy_body_data *id, tree *vars,
 328                               vec<ipa_replace_map *, va_gc> *tree_map);
 329   /* Constructor to use for modifying a function outside of tree-inline from an
 330      instance of ipa_param_adjustments.  */
 331   ipa_param_body_adjustments (ipa_param_adjustments *adjustments,
 332                               tree fndecl);
 333   /* Constructor to use for modifying a function outside of tree-inline from a
 334      simple vector of desired parameter modification.  */
 335   ipa_param_body_adjustments (vec<ipa_adjusted_param, va_gc> *adj_params,
 336                               tree fndecl);
 337
 338   /* The do-it-all function for modifying a function outside of
 339      tree-inline.  */
 340   bool perform_cfun_body_modifications ();
 341
 342   /* Change the PARM_DECLs.  */
 343   void modify_formal_parameters ();
 344   /* Register a replacement decl for the transformation done in APM.  */
 345   void register_replacement (ipa_adjusted_param *apm, tree replacement,
 346                              tree dummy = NULL_TREE);
 347   /* Lookup a replacement for a given offset within a given parameter.  */
 348   tree lookup_replacement (tree base, unsigned unit_offset);
 349   /* Lookup a replacement for an expression, if there is one.  */
 350   ipa_param_body_replacement *get_expr_replacement (tree expr,
 351                                                     bool ignore_default_def);
 352   /* Lookup the new base for surviving names previously belonging to a
 353      parameter. */
 354   tree get_replacement_ssa_base (tree old_decl);
 355   /* Modify a statement.  */
 356   bool modify_gimple_stmt (gimple **stmt, gimple_seq *extra_stmts);
 357   /* Return the new chain of parameters.  */
 358   tree get_new_param_chain ();
 359
 360   /* Pointers to data structures defining how the function should be
 361      modified.  */
 362   vec<ipa_adjusted_param, va_gc> *m_adj_params;
 363   ipa_param_adjustments *m_adjustments;
 364
 365   /* Vector of old parameter declarations that must have their debug bind
 366      statements re-mapped and debug decls created.  */
 367
 368   auto_vec<tree, 16> m_reset_debug_decls;
 369
 370   /* Set to true if there are any IPA_PARAM_OP_SPLIT adjustments among stored
 371      adjustments.  */
 372   bool m_split_modifications_p;
 373 private:
 374   void common_initialization (tree old_fndecl, tree *vars,
 375                               vec<ipa_replace_map *, va_gc> *tree_map);
 376   tree carry_over_param (tree t);
 377   unsigned get_base_index (ipa_adjusted_param *apm);
 378   ipa_param_body_replacement *lookup_replacement_1 (tree base,
 379                                                     unsigned unit_offset);
 380   tree replace_removed_params_ssa_names (tree old_name, gimple *stmt);
 381   bool modify_expression (tree *expr_p, bool convert);
 382   bool modify_assignment (gimple *stmt, gimple_seq *extra_stmts);
 383   bool modify_call_stmt (gcall **stmt_p);
 384   bool modify_cfun_body ();
 385   void reset_debug_stmts ();
 386
 387   /* Declaration of the function that is being transformed.  */
 388
 389   tree m_fndecl;
 390
 391   /* If non-NULL, the tree-inline master data structure guiding materialization
 392      of the current clone.  */
 393   struct copy_body_data *m_id;
 394
 395   /* Vector of old parameter declarations (before changing them).  */
 396
 397   auto_vec<tree, 16> m_oparms;
 398
 399   /* Vector of parameter declarations the function will have after
 400      transformation.  */
 401
 402   auto_vec<tree, 16> m_new_decls;
 403
 404   /* If the function type has non-NULL TYPE_ARG_TYPES, this is the vector of
 405      these types after transformation, otherwise an empty one.  */
 406
 407   auto_vec<tree, 16> m_new_types;
 408
 409   /* Vector of structures telling how to replace old parameters in the
 410      function body.  TODO: Even though there usually be only few, but should we
 411      use a hash?  */
 412
 413   auto_vec<ipa_param_body_replacement, 16> m_replacements;
 414
 415   /* Vector for remapping SSA_BASES from old parameter declarations that are
 416      being removed as a part of the transformation.  Before a new VAR_DECL is
 417      created, it holds the old PARM_DECL, once the variable is built it is
 418      stored here.  */
 419
 420   auto_vec<tree> m_removed_decls;
 421
 422   /* Hash to quickly lookup the item in m_removed_decls given the old decl.  */
 423
 424   hash_map<tree, unsigned> m_removed_map;
 425
 426   /* True iff the transformed function is a class method that is about to loose
 427      its this pointer and must be converted to a normal function.  */
 428
 429   bool m_method2func;
 430 };
 431
 432 void push_function_arg_decls (vec<tree> *args, tree fndecl);
 433 void push_function_arg_types (vec<tree> *types, tree fntype);
 434
 435 #endif  /* IPA_PARAM_MANIPULATION_H */