gcc/params.def

   1 /* params.def - Run-time parameters.
   2    Copyright (C) 2001, 2002, 2004, 2005 Free Software Foundation, Inc.
   3    Written by Mark Mitchell <mark@codesourcery.com>.
   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 2, 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 COPYING.  If not, write to the Free
  19 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
  20 02110-1301, USA.
  21
  22 */
  23
  24 /* This file contains definitions for language-independent
  25    parameters.  The DEFPARAM macro takes 6 arguments:
  26
  27      - The enumeral corresponding to this parameter.
  28
  29      - The name that can be used to set this parameter using the
  30        command-line option `--param <name>=<value>'.
  31
  32      - A help string explaining how the parameter is used.
  33
  34      - A default value for the parameter.
  35
  36      - The minimum acceptable value for the parameter.
  37
  38      - The maximum acceptable value for the parameter (if greater than
  39      the minimum).
  40
  41    Be sure to add an entry to invoke.texi summarizing the parameter.  */
  42
  43 /* The maximum number of fields in a variable with only implicit uses
  44    for which structure aliasing will consider trying to track each
  45    field.  The default is 5.  */
  46 DEFPARAM (PARAM_SALIAS_MAX_IMPLICIT_FIELDS,
  47           "salias-max-implicit-fields",
  48           "The maximum number of fields in a structure variable without direct structure accesses that GCC will attempt to track separately",
  49           5, 0, 0)
  50
  51 /* The maximum structure size at which the scalar replacement of
  52    aggregates (SRA) pass will perform block copies.  The default
  53    value, 0, implies that GCC will select the most appropriate size
  54    itself.  */
  55 DEFPARAM (PARAM_SRA_MAX_STRUCTURE_SIZE,
  56           "sra-max-structure-size",
  57           "The maximum structure size (in bytes) for which GCC will "
  58           "use by-element copies",
  59           0, 0, 0)
  60
  61 /* The maximum number of structure fields which the SRA pass will
  62    instantiate to avoid block copies.  The default value, 0, implies
  63    that GCC will select the appropriate value itself.  */
  64 DEFPARAM (PARAM_SRA_MAX_STRUCTURE_COUNT,
  65           "sra-max-structure-count",
  66           "The maximum number of structure fields for which GCC will "
  67           "use by-element copies",
  68           0, 0, 0)
  69
  70 /* The ratio between instantiated fields and the complete structure
  71    size.  We say that if the ratio of the number of bytes in
  72    instantiated fields to the number of bytes in the complete
  73    structure exceeds this parameter, or if the number of instantiated
  74    fields to the total number of fields exceeds this parameter, then
  75    block copies are not used.  The default is 75%.  */
  76 DEFPARAM (PARAM_SRA_FIELD_STRUCTURE_RATIO,
  77           "sra-field-structure-ratio",
  78           "The threshold ratio between instantiated fields and the total structure size",
  79           75, 0, 100)
  80
  81 /* The single function inlining limit. This is the maximum size
  82    of a function counted in internal gcc instructions (not in
  83    real machine instructions) that is eligible for inlining
  84    by the tree inliner.
  85    The default value is 450.
  86    Only functions marked inline (or methods defined in the class
  87    definition for C++) are affected by this.
  88    There are more restrictions to inlining: If inlined functions
  89    call other functions, the already inlined instructions are
  90    counted and once the recursive inline limit (see
  91    "max-inline-insns" parameter) is exceeded, the acceptable size
  92    gets decreased.  */
  93 DEFPARAM (PARAM_MAX_INLINE_INSNS_SINGLE,
  94           "max-inline-insns-single",
  95           "The maximum number of instructions in a single function eligible for inlining",
  96           450, 0, 0)
  97
  98 /* The single function inlining limit for functions that are
  99    inlined by virtue of -finline-functions (-O3).
 100    This limit should be chosen to be below or equal to the limit
 101    that is applied to functions marked inlined (or defined in the
 102    class declaration in C++) given by the "max-inline-insns-single"
 103    parameter.
 104    The default value is 90.  */
 105 DEFPARAM (PARAM_MAX_INLINE_INSNS_AUTO,
 106           "max-inline-insns-auto",
 107           "The maximum number of instructions when automatically inlining",
 108           90, 0, 0)
 109
 110 DEFPARAM (PARAM_MAX_INLINE_INSNS_RECURSIVE,
 111           "max-inline-insns-recursive",
 112           "The maximum number of instructions inline function can grow to via recursive inlining",
 113           450, 0, 0)
 114
 115 DEFPARAM (PARAM_MAX_INLINE_INSNS_RECURSIVE_AUTO,
 116           "max-inline-insns-recursive-auto",
 117           "The maximum number of instructions non-inline function can grow to via recursive inlining",
 118           450, 0, 0)
 119
 120 DEFPARAM (PARAM_MAX_INLINE_RECURSIVE_DEPTH,
 121           "max-inline-recursive-depth",
 122           "The maximum depth of recursive inlining for inline functions",
 123           8, 0, 0)
 124
 125 DEFPARAM (PARAM_MAX_INLINE_RECURSIVE_DEPTH_AUTO,
 126           "max-inline-recursive-depth-auto",
 127           "The maximum depth of recursive inlining for non-inline functions",
 128           8, 0, 0)
 129
 130 DEFPARAM (PARAM_MIN_INLINE_RECURSIVE_PROBABILITY,
 131           "min-inline-recursive-probability",
 132           "Inline recursively only when the probability of call being executed exceeds the parameter",
 133           10, 0, 0)
 134
 135 /* Limit the number of expansions created by the variable expansion
 136    optimization to avoid register pressure.  */
 137 DEFPARAM (PARAM_MAX_VARIABLE_EXPANSIONS,
 138           "max-variable-expansions-in-unroller",
 139           "If -fvariable-expansion-in-unroller is used, the maximum number of times that an individual variable will be expanded during loop unrolling",
 140           1, 0, 0)
 141
 142 /* The maximum number of instructions to consider when looking for an
 143    instruction to fill a delay slot.  If more than this arbitrary
 144    number of instructions is searched, the time savings from filling
 145    the delay slot will be minimal so stop searching.  Increasing
 146    values mean more aggressive optimization, making the compile time
 147    increase with probably small improvement in executable run time.  */
 148 DEFPARAM (PARAM_MAX_DELAY_SLOT_INSN_SEARCH,
 149           "max-delay-slot-insn-search",
 150           "The maximum number of instructions to consider to fill a delay slot",
 151           100, 0, 0)
 152
 153 /* When trying to fill delay slots, the maximum number of instructions
 154    to consider when searching for a block with valid live register
 155    information.  Increasing this arbitrarily chosen value means more
 156    aggressive optimization, increasing the compile time.  This
 157    parameter should be removed when the delay slot code is rewritten
 158    to maintain the control-flow graph.  */
 159 DEFPARAM(PARAM_MAX_DELAY_SLOT_LIVE_SEARCH,
 160          "max-delay-slot-live-search",
 161          "The maximum number of instructions to consider to find accurate live register information",
 162          333, 0, 0)
 163
 164 /* This parameter limits the number of branch elements that the
 165    scheduler will track anti-dependencies through without resetting
 166    the tracking mechanism.  Large functions with few calls or barriers
 167    can generate lists containing many 1000's of dependencies.  Generally
 168    the compiler either uses all available memory, or runs for far too long.  */
 169 DEFPARAM(PARAM_MAX_PENDING_LIST_LENGTH,
 170          "max-pending-list-length",
 171          "The maximum length of scheduling's pending operations list",
 172          32, 0, 0)
 173
 174 DEFPARAM(PARAM_LARGE_FUNCTION_INSNS,
 175          "large-function-insns",
 176          "The size of function body to be considered large",
 177          2700, 0, 0)
 178 DEFPARAM(PARAM_LARGE_FUNCTION_GROWTH,
 179          "large-function-growth",
 180          "Maximal growth due to inlining of large function (in percent)",
 181          100, 0, 0)
 182 DEFPARAM(PARAM_LARGE_UNIT_INSNS,
 183          "large-unit-insns",
 184          "The size of translation unit to be considered large",
 185          10000, 0, 0)
 186 DEFPARAM(PARAM_INLINE_UNIT_GROWTH,
 187          "inline-unit-growth",
 188          "how much can given compilation unit grow because of the inlining (in percent)",
 189          50, 0, 0)
 190 DEFPARAM(PARAM_INLINE_CALL_COST,
 191          "inline-call-cost",
 192          "expense of call operation relative to ordinary arithmetic operations",
 193          16, 0, 0)
 194
 195 /* The GCSE optimization will be disabled if it would require
 196    significantly more memory than this value.  */
 197 DEFPARAM(PARAM_MAX_GCSE_MEMORY,
 198          "max-gcse-memory",
 199          "The maximum amount of memory to be allocated by GCSE",
 200          50 * 1024 * 1024, 0, 0)
 201 /* The number of repetitions of copy/const prop and PRE to run.  */
 202 DEFPARAM(PARAM_MAX_GCSE_PASSES,
 203         "max-gcse-passes",
 204         "The maximum number of passes to make when doing GCSE",
 205         1, 1, 0)
 206 /* This is the threshold ratio when to perform partial redundancy
 207    elimination after reload. We perform partial redundancy elimination
 208    when the following holds:
 209    (Redundant load execution count)
 210    ------------------------------- >= GCSE_AFTER_RELOAD_PARTIAL_FRACTION
 211    (Added loads execution count)                                          */
 212 DEFPARAM(PARAM_GCSE_AFTER_RELOAD_PARTIAL_FRACTION,
 213         "gcse-after-reload-partial-fraction",
 214         "The threshold ratio for performing partial redundancy elimination after reload",
 215         3, 0, 0)
 216 /* This is the threshold ratio of the critical edges execution count compared to
 217    the redundant loads execution count that permits performing the load
 218    redundancy elimination in gcse after reload.  */
 219 DEFPARAM(PARAM_GCSE_AFTER_RELOAD_CRITICAL_FRACTION,
 220         "gcse-after-reload-critical-fraction",
 221         "The threshold ratio of critical edges execution count that permit performing redundancy elimination after reload",
 222         10, 0, 0)
 223 /* This parameter limits the number of insns in a loop that will be unrolled,
 224    and by how much the loop is unrolled.
 225
 226    This limit should be at most half of the peeling limits:  loop unroller
 227    decides to not unroll loops that iterate fewer than 2*number of allowed
 228    unrollings and thus we would have loops that are neither peeled or unrolled
 229    otherwise.  */
 230 DEFPARAM(PARAM_MAX_UNROLLED_INSNS,
 231          "max-unrolled-insns",
 232          "The maximum number of instructions to consider to unroll in a loop",
 233          200, 0, 0)
 234 /* This parameter limits how many times the loop is unrolled depending
 235    on number of insns really executed in each iteration.  */
 236 DEFPARAM(PARAM_MAX_AVERAGE_UNROLLED_INSNS,
 237          "max-average-unrolled-insns",
 238          "The maximum number of instructions to consider to unroll in a loop on average",
 239          80, 0, 0)
 240 /* The maximum number of unrollings of a single loop.  */
 241 DEFPARAM(PARAM_MAX_UNROLL_TIMES,
 242         "max-unroll-times",
 243         "The maximum number of unrollings of a single loop",
 244         8, 0, 0)
 245 /* The maximum number of insns of a peeled loop.  */
 246 DEFPARAM(PARAM_MAX_PEELED_INSNS,
 247         "max-peeled-insns",
 248         "The maximum number of insns of a peeled loop",
 249         400, 0, 0)
 250 /* The maximum number of peelings of a single loop.  */
 251 DEFPARAM(PARAM_MAX_PEEL_TIMES,
 252         "max-peel-times",
 253         "The maximum number of peelings of a single loop",
 254         16, 0, 0)
 255 /* The maximum number of insns of a peeled loop.  */
 256 DEFPARAM(PARAM_MAX_COMPLETELY_PEELED_INSNS,
 257         "max-completely-peeled-insns",
 258         "The maximum number of insns of a completely peeled loop",
 259         400, 0, 0)
 260 /* The maximum number of peelings of a single loop that is peeled completely.  */
 261 DEFPARAM(PARAM_MAX_COMPLETELY_PEEL_TIMES,
 262         "max-completely-peel-times",
 263         "The maximum number of peelings of a single loop that is peeled completely",
 264         16, 0, 0)
 265 /* The maximum number of insns of a peeled loop that rolls only once.  */
 266 DEFPARAM(PARAM_MAX_ONCE_PEELED_INSNS,
 267         "max-once-peeled-insns",
 268         "The maximum number of insns of a peeled loop that rolls only once",
 269         400, 0, 0)
 270
 271 /* The maximum number of insns of an unswitched loop.  */
 272 DEFPARAM(PARAM_MAX_UNSWITCH_INSNS,
 273         "max-unswitch-insns",
 274         "The maximum number of insns of an unswitched loop",
 275         50, 0, 0)
 276 /* The maximum level of recursion in unswitch_single_loop.  */
 277 DEFPARAM(PARAM_MAX_UNSWITCH_LEVEL,
 278         "max-unswitch-level",
 279         "The maximum number of unswitchings in a single loop",
 280         3, 0, 0)
 281
 282 /* The maximum number of iterations of a loop the brute force algorithm
 283    for analysis of # of iterations of the loop tries to evaluate.  */
 284 DEFPARAM(PARAM_MAX_ITERATIONS_TO_TRACK,
 285         "max-iterations-to-track",
 286         "Bound on the number of iterations the brute force # of iterations analysis algorithm evaluates",
 287         1000, 0, 0)
 288
 289 DEFPARAM(PARAM_MAX_SMS_LOOP_NUMBER,
 290          "max-sms-loop-number",
 291          "Maximum number of loops to perform swing modulo scheduling on (mainly for debugging)",
 292          -1, -1, -1)
 293
 294 /* This parameter is used to tune SMS MAX II calculations.  */
 295 DEFPARAM(PARAM_SMS_MAX_II_FACTOR,
 296          "sms-max-ii-factor",
 297          "A factor for tuning the upper bound that swing modulo scheduler uses for scheduling a loop",
 298          100, 0, 0)
 299 DEFPARAM(PARAM_SMS_DFA_HISTORY,
 300          "sms-dfa-history",
 301          "The number of cycles the swing modulo scheduler considers when checking conflicts using DFA",
 302          0, 0, 0)
 303 DEFPARAM(PARAM_SMS_LOOP_AVERAGE_COUNT_THRESHOLD,
 304          "sms-loop-average-count-threshold",
 305          "A threshold on the average loop count considered by the swing modulo scheduler",
 306          0, 0, 0)
 307
 308 DEFPARAM(HOT_BB_COUNT_FRACTION,
 309          "hot-bb-count-fraction",
 310          "Select fraction of the maximal count of repetitions of basic block in program given basic block needs to have to be considered hot",
 311          10000, 0, 0)
 312 DEFPARAM(HOT_BB_FREQUENCY_FRACTION,
 313          "hot-bb-frequency-fraction",
 314          "Select fraction of the maximal frequency of executions of basic block in function given basic block needs to have to be considered hot",
 315          1000, 0, 0)
 316
 317 /* For guessed profiles, the loops having unknown number of iterations
 318    are predicted to iterate relatively few (10) times at average.
 319    For functions containing one loop with large known number of iterations
 320    and other loops having unbounded loops we would end up predicting all
 321    the other loops cold that is not usually the case.  So we need to artificially
 322    flatten the profile.
 323
 324    We need to cut the maximal predicted iterations to large enough iterations
 325    so the loop appears important, but safely within HOT_BB_COUNT_FRACTION
 326    range.  */
 327
 328 DEFPARAM(PARAM_MAX_PREDICTED_ITERATIONS,
 329          "max-predicted-iterations",
 330          "The maximum number of loop iterations we predict statically",
 331          100, 0, 0)
 332 DEFPARAM(TRACER_DYNAMIC_COVERAGE_FEEDBACK,
 333          "tracer-dynamic-coverage-feedback",
 334          "The percentage of function, weighted by execution frequency, that must be covered by trace formation. Used when profile feedback is available",
 335          95, 0, 100)
 336 DEFPARAM(TRACER_DYNAMIC_COVERAGE,
 337          "tracer-dynamic-coverage",
 338          "The percentage of function, weighted by execution frequency, that must be covered by trace formation. Used when profile feedback is not available",
 339          75, 0, 100)
 340 DEFPARAM(TRACER_MAX_CODE_GROWTH,
 341          "tracer-max-code-growth",
 342          "Maximal code growth caused by tail duplication (in percent)",
 343          100, 0, 0)
 344 DEFPARAM(TRACER_MIN_BRANCH_RATIO,
 345          "tracer-min-branch-ratio",
 346          "Stop reverse growth if the reverse probability of best edge is less than this threshold (in percent)",
 347          10, 0, 100)
 348 DEFPARAM(TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK,
 349          "tracer-min-branch-probability-feedback",
 350          "Stop forward growth if the probability of best edge is less than this threshold (in percent). Used when profile feedback is available",
 351          80, 0, 100)
 352 DEFPARAM(TRACER_MIN_BRANCH_PROBABILITY,
 353          "tracer-min-branch-probability",
 354          "Stop forward growth if the probability of best edge is less than this threshold (in percent). Used when profile feedback is not available",
 355          50, 0, 100)
 356
 357 /* The maximum number of incoming edges to consider for crossjumping.  */
 358 DEFPARAM(PARAM_MAX_CROSSJUMP_EDGES,
 359          "max-crossjump-edges",
 360          "The maximum number of incoming edges to consider for crossjumping",
 361          100, 0, 0)
 362
 363 /* The minimum number of matching instructions to consider for crossjumping.  */
 364 DEFPARAM(PARAM_MIN_CROSSJUMP_INSNS,
 365      "min-crossjump-insns",
 366      "The minimum number of matching instructions to consider for crossjumping",
 367      5, 0, 0)
 368
 369 /* The maximum number expansion factor when copying basic blocks.  */
 370 DEFPARAM(PARAM_MAX_GROW_COPY_BB_INSNS,
 371      "max-grow-copy-bb-insns",
 372      "The maximum expansion factor when copying basic blocks",
 373      8, 0, 0)
 374
 375 /* The maximum number of insns to duplicate when unfactoring computed gotos.  */
 376 DEFPARAM(PARAM_MAX_GOTO_DUPLICATION_INSNS,
 377      "max-goto-duplication-insns",
 378      "The maximum number of insns to duplicate when unfactoring computed gotos",
 379      8, 0, 0)
 380
 381 /* The maximum length of path considered in cse.  */
 382 DEFPARAM(PARAM_MAX_CSE_PATH_LENGTH,
 383          "max-cse-path-length",
 384          "The maximum length of path considered in cse",
 385          10, 0, 0)
 386 DEFPARAM(PARAM_MAX_CSE_INSNS,
 387          "max-flow-memory-locations",
 388          "The maximum instructions CSE process before flushing",
 389          1000, 0, 0)
 390
 391 /* The cost of expression in loop invariant motion that is considered
 392    expensive.  */
 393 DEFPARAM(PARAM_LIM_EXPENSIVE,
 394          "lim-expensive",
 395          "The minimum cost of an expensive expression in the loop invariant motion",
 396          20, 0, 0)
 397
 398 /* Bound on number of candidates for induction variables below that
 399    all candidates are considered for each use in induction variable
 400    optimizations.  */
 401
 402 DEFPARAM(PARAM_IV_CONSIDER_ALL_CANDIDATES_BOUND,
 403          "iv-consider-all-candidates-bound",
 404          "Bound on number of candidates below that all candidates are considered in iv optimizations",
 405          30, 0, 0)
 406
 407 /* The induction variable optimizations give up on loops that contain more
 408    induction variable uses.  */
 409
 410 DEFPARAM(PARAM_IV_MAX_CONSIDERED_USES,
 411          "iv-max-considered-uses",
 412          "Bound on number of iv uses in loop optimized in iv optimizations",
 413          250, 0, 0)
 414
 415 /* If there are at most this number of ivs in the set, try removing unnecessary
 416    ivs from the set always.  */
 417
 418 DEFPARAM(PARAM_IV_ALWAYS_PRUNE_CAND_SET_BOUND,
 419          "iv-always-prune-cand-set-bound",
 420          "If number of candidates in the set is smaller, we always try to remove unused ivs during its optimization",
 421          10, 0, 0)
 422
 423 DEFPARAM(PARAM_SCEV_MAX_EXPR_SIZE,
 424          "scev-max-expr-size",
 425          "Bound on size of expressions used in the scalar evolutions analyzer",
 426          20, 0, 0)
 427
 428 DEFPARAM(PARAM_VECT_MAX_VERSION_CHECKS,
 429          "vect-max-version-checks",
 430          "Bound on number of runtime checks inserted by the vectorizer's loop versioning",
 431          6, 0, 0)
 432
 433 /* The product of the next two is used to decide whether or not to
 434    use .GLOBAL_VAR.  See tree-dfa.c.  */
 435 DEFPARAM(PARAM_GLOBAL_VAR_THRESHOLD,
 436         "global-var-threshold",
 437         "Given N calls and V call-clobbered vars in a function.  Use .GLOBAL_VAR if NxV is larger than this limit",
 438         500000, 0, 0)
 439
 440 DEFPARAM(PARAM_MAX_CSELIB_MEMORY_LOCATIONS,
 441          "max-cselib-memory-locations",
 442          "The maximum memory locations recorded by cselib",
 443          500, 0, 0)
 444 DEFPARAM(PARAM_MAX_FLOW_MEMORY_LOCATIONS,
 445          "max-flow-memory-locations",
 446          "The maximum memory locations recorded by flow",
 447          100, 0, 0)
 448
 449 #ifdef ENABLE_GC_ALWAYS_COLLECT
 450 # define GGC_MIN_EXPAND_DEFAULT 0
 451 # define GGC_MIN_HEAPSIZE_DEFAULT 0
 452 #else
 453 # define GGC_MIN_EXPAND_DEFAULT 30
 454 # define GGC_MIN_HEAPSIZE_DEFAULT 4096
 455 #endif
 456
 457 DEFPARAM(GGC_MIN_EXPAND,
 458          "ggc-min-expand",
 459          "Minimum heap expansion to trigger garbage collection, as a percentage of the total size of the heap",
 460          GGC_MIN_EXPAND_DEFAULT, 0, 0)
 461
 462 DEFPARAM(GGC_MIN_HEAPSIZE,
 463          "ggc-min-heapsize",
 464          "Minimum heap size before we start collecting garbage, in kilobytes",
 465          GGC_MIN_HEAPSIZE_DEFAULT, 0, 0)
 466
 467 #undef GGC_MIN_EXPAND_DEFAULT
 468 #undef GGC_MIN_HEAPSIZE_DEFAULT
 469
 470 DEFPARAM(PARAM_MAX_RELOAD_SEARCH_INSNS,
 471          "max-reload-search-insns",
 472          "The maximum number of instructions to search backward when looking for equivalent reload",
 473          100, 0, 0)
 474
 475 DEFPARAM(PARAM_MAX_ALIASED_VOPS,
 476          "max-aliased-vops",
 477          "The maximum number of virtual operands allowed to represent aliases before triggering alias grouping",
 478          500, 0, 0)
 479
 480 DEFPARAM(PARAM_MAX_SCHED_REGION_BLOCKS,
 481          "max-sched-region-blocks",
 482          "The maximum number of blocks in a region to be considered for interblock scheduling",
 483          10, 0, 0)
 484
 485 DEFPARAM(PARAM_MAX_SCHED_REGION_INSNS,
 486          "max-sched-region-insns",
 487          "The maximum number of insns in a region to be considered for interblock scheduling",
 488          100, 0, 0)
 489
 490 DEFPARAM(PARAM_MIN_SPEC_PROB,
 491          "min-spec-prob",
 492          "The minimum probability of reaching a source block for interblock speculative scheduling",
 493          40, 0, 0)
 494
 495 DEFPARAM(PARAM_MAX_LAST_VALUE_RTL,
 496          "max-last-value-rtl",
 497          "The maximum number of RTL nodes that can be recorded as combiner's last value",
 498          10000, 0, 0)
 499
 500 /* INTEGER_CST nodes are shared for values [{-1,0} .. N) for
 501    {signed,unsigned} integral types.  This determines N.
 502    Experimentation shows 256 to be a good value.  */
 503 DEFPARAM (PARAM_INTEGER_SHARE_LIMIT,
 504           "integer-share-limit",
 505           "The upper bound for sharing integer constants",
 506           256, 2, 2)
 507
 508 /* Incremental SSA updates for virtual operands may be very slow if
 509    there is a large number of mappings to process.  In those cases, it
 510    is faster to rewrite the virtual symbols from scratch as if they
 511    had been recently introduced.  This heuristic cannot be applied to
 512    SSA mappings for real SSA names, only symbols kept in FUD chains.
 513
 514    PARAM_MIN_VIRTUAL_MAPPINGS specifies the minimum number of virtual
 515    mappings that should be registered to trigger the heuristic.
 516
 517    PARAM_VIRTUAL_MAPPINGS_TO_SYMS_RATIO specifies the ratio between
 518    mappings and symbols.  If the number of virtual mappings is
 519    PARAM_VIRTUAL_MAPPINGS_TO_SYMS_RATIO bigger than the number of
 520    virtual symbols to be updated, then the updater switches to a full
 521    update for those symbols.  */
 522 DEFPARAM (PARAM_MIN_VIRTUAL_MAPPINGS,
 523           "min-virtual-mappings",
 524           "Minimum number of virtual mappings to consider switching to full virtual renames",
 525           100, 0, 0)
 526
 527 DEFPARAM (PARAM_VIRTUAL_MAPPINGS_TO_SYMS_RATIO,
 528           "virtual-mappings-ratio",
 529           "Ratio between virtual mappings and virtual symbols to do full virtual renames",
 530           3, 0, 0)
 531
 532 DEFPARAM (PARAM_SSP_BUFFER_SIZE,
 533           "ssp-buffer-size",
 534           "The lower bound for a buffer to be considered for stack smashing protection",
 535           8, 1, 0)
 536
 537 /* When we thread through a block we have to make copies of the
 538    statements within the block.  Clearly for large blocks the code
 539    duplication is bad.
 540
 541    PARAM_MAX_JUMP_THREAD_DUPLICATION_STMTS specifies the maximum number
 542    of statements and PHI nodes allowed in a block which is going to
 543    be duplicated for thread jumping purposes.
 544
 545    Some simple analysis showed that more than 99% of the jump
 546    threading opportunities are for blocks with less than 15
 547    statements.  So we can get the benefits of jump threading
 548    without excessive code bloat for pathological cases with the
 549    throttle set at 15 statements.  */
 550 DEFPARAM (PARAM_MAX_JUMP_THREAD_DUPLICATION_STMTS,
 551           "max-jump-thread-duplication-stmts",
 552           "Maximum number of statements allowed in a block that needs to be duplicated when threading jumps",
 553           15, 0, 0)
 554
 555 /*
 556 Local variables:
 557 mode:c
 558 End: */