239 lines
9.9 KiB
Modula-2
239 lines
9.9 KiB
Modula-2
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/* Definitions for the branch prediction routines in the GNU compiler.
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Copyright (C) 2001-2023 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free
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Software Foundation; either version 3, or (at your option) any later
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version.
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GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING3. If not see
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<http://www.gnu.org/licenses/>. */
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/* Before including this file, you should define a macro:
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DEF_PREDICTOR (ENUM, NAME, HITRATE)
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This macro will be called once for each predictor. The ENUM will
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be of type `enum br_predictor', and will enumerate all supported
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predictors. The order of DEF_PREDICTOR calls is important, as
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in the first match combining heuristics, the predictor appearing
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first in this file will win.
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NAME is used in the debugging output to determine predictor type.
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HITRATE is the probability that edge predicted by predictor as taken
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will be really taken (so it should be always above
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REG_BR_PROB_BASE / 2). */
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/* A value used as final outcome of all heuristics. */
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DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0)
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/* An outcome estimated by Dempster-Shaffer theory. */
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DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0)
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/* A combined heuristics using probability determined by first
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matching heuristics from this list. */
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DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0)
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/* Heuristic applying when no heuristic below applies. */
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DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0)
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/* Mark unconditional jump as taken. */
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DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS,
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PRED_FLAG_FIRST_MATCH)
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/* Return value of malloc function is almost always non-null. */
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DEF_PREDICTOR (PRED_MALLOC_NONNULL, "malloc returned non-NULL", \
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PROB_VERY_LIKELY, PRED_FLAG_FIRST_MATCH)
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/* Use number of loop iterations determined by # of iterations
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analysis to set probability. We don't want to use Dempster-Shaffer
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theory here, as the predictions is exact. */
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DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_UNINITIALIZED,
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PRED_FLAG_FIRST_MATCH)
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/* Assume that any given atomic operation has low contention,
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and thus the compare-and-swap operation succeeds. */
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DEF_PREDICTOR (PRED_COMPARE_AND_SWAP, "compare and swap", PROB_VERY_LIKELY,
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PRED_FLAG_FIRST_MATCH)
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/* Hints dropped by user via __builtin_expect feature. Note: the
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probability of PROB_VERY_LIKELY is now overwritten by param
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builtin_expect_probability with a default value of HITRATE(90).
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Refer to param.def for details. */
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DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY,
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PRED_FLAG_FIRST_MATCH)
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/* Hints provided by user via __builtin_expect_with_probability. */
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DEF_PREDICTOR (PRED_BUILTIN_EXPECT_WITH_PROBABILITY,
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"__builtin_expect_with_probability", PROB_UNINITIALIZED,
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PRED_FLAG_FIRST_MATCH)
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/* Branches to hot labels are likely. */
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DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (90),
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PRED_FLAG_FIRST_MATCH)
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/* Branches to cold labels are extremely unlikely. */
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DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", HITRATE (90),
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PRED_FLAG_FIRST_MATCH)
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/* Use number of loop iterations guessed by the contents of the loop. */
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DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations",
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PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH)
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/* Use number of loop iterations guessed by the contents of the loop. */
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DEF_PREDICTOR (PRED_LOOP_ITERATIONS_MAX, "guessed loop iterations",
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PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH)
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/* Branch containing goto is probably not taken. */
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DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (67), 0)
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/* Branch to basic block containing call marked by noreturn attribute. */
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DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY,
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PRED_FLAG_FIRST_MATCH)
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/* Branch to basic block containing call marked by cold function attribute. */
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DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY,
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PRED_FLAG_FIRST_MATCH)
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/* Edge causing loop to terminate is probably not taken. */
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DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (89),
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PRED_FLAG_FIRST_MATCH)
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/* Same as LOOP_EXIT but for loops containing recursive call. */
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DEF_PREDICTOR (PRED_LOOP_EXIT_WITH_RECURSION, "loop exit with recursion",
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HITRATE (78), PRED_FLAG_FIRST_MATCH)
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/* Edge causing loop to terminate by computing value used by later
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conditional. */
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DEF_PREDICTOR (PRED_LOOP_EXTRA_EXIT, "extra loop exit", HITRATE (67),
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PRED_FLAG_FIRST_MATCH)
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/* Pointers are usually not NULL. */
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DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (70), 0)
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DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (70), 0)
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/* NE is probable, EQ not etc... */
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DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (59), 0)
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DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (66), 0)
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DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0)
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DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)",
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HITRATE (59), 0)
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DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)",
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HITRATE (66), 0)
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DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0)
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/* Branch guarding call is probably taken. */
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DEF_PREDICTOR (PRED_CALL, "call", HITRATE (67), 0)
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/* Call predictors are for now ignored, lets leave the predictor
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to measure its benefit. */
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DEF_PREDICTOR (PRED_INDIR_CALL, "indirect call", PROB_EVEN, 0)
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DEF_PREDICTOR (PRED_POLYMORPHIC_CALL, "polymorphic call", PROB_EVEN, 0)
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DEF_PREDICTOR (PRED_RECURSIVE_CALL, "recursive call", PROB_EVEN, 0)
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/* Branch causing function to terminate is probably not taken. */
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DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (66),
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0)
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/* Branch containing goto is probably not taken. */
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DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (66), 0)
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/* Branch ending with return constant is probably not taken. */
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DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (65), 0)
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/* Branch ending with return negative constant is probably not taken. */
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DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (98), 0)
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/* Branch ending with return; is probably not taken */
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DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (71), 0)
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/* Branches to compare induction variable to a loop bound is
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extremely likely. */
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DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare",
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HITRATE (64), 0)
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/* Use number of loop iterations determined by # of iterations analysis
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to set probability of branches that compares IV to loop bound variable. */
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DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_UNINITIALIZED,
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PRED_FLAG_FIRST_MATCH)
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/* In the following code
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for (loop1)
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if (cond)
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for (loop2)
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body;
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guess that cond is unlikely. */
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DEF_PREDICTOR (PRED_LOOP_GUARD, "loop guard", HITRATE (73), 0)
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/* Same but for loops containing recursion. */
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DEF_PREDICTOR (PRED_LOOP_GUARD_WITH_RECURSION, "loop guard with recursion",
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HITRATE (85), 0)
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/* The following predictors are used in Fortran. */
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/* Branch leading to an integer overflow are extremely unlikely. */
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DEF_PREDICTOR (PRED_FORTRAN_OVERFLOW, "Fortran overflow", PROB_ALWAYS,
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PRED_FLAG_FIRST_MATCH)
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/* Branch leading to a failure status are unlikely. This can occur for out
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of memory. This predictor only occurs when the user explicitly asked
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for a return status. By default, the code aborts,
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which is handled via PRED_NORETURN. */
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DEF_PREDICTOR (PRED_FORTRAN_FAIL_ALLOC, "Fortran fail alloc",
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PROB_VERY_LIKELY, 0)
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/* Predictor is used for an allocation of an already allocated memory or
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deallocating an already deallocated allocatable. */
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DEF_PREDICTOR (PRED_FORTRAN_REALLOC, "Fortran repeated allocation/deallocation",
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PROB_LIKELY, 0)
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/* Branch leading to an I/O failure status are unlikely. This predictor is
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used for I/O failures such as for invalid unit numbers. This predictor
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only occurs when the user explicitly asked for a return status. By default,
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the code aborts, which is handled via PRED_NORETURN. */
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DEF_PREDICTOR (PRED_FORTRAN_FAIL_IO, "Fortran fail IO", HITRATE (85), 0)
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/* Branch leading to a run-time warning message which is printed only once
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are unlikely. The print-warning branch itself can be likely or unlikely. */
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DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "Fortran warn once", HITRATE (75), 0)
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/* Branch belonging to a zero-sized array. */
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DEF_PREDICTOR (PRED_FORTRAN_SIZE_ZERO, "Fortran zero-sized array", \
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HITRATE (99), 0)
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/* Branch belonging to an invalid bound index, in a context where it is
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standard conform and well defined but rather pointless and, hence, rather
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unlikely to occur. */
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DEF_PREDICTOR (PRED_FORTRAN_INVALID_BOUND, "Fortran invalid bound", \
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HITRATE (90), 0)
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/* Branch belonging to the handling of absent optional arguments. This
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predictor is used when an optional dummy argument, associated with an
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absent argument, is passed on as actual argument to another procedure,
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which in turn has an optional argument. */
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DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "Fortran absent dummy", \
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HITRATE (60), 0)
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/* Fortran DO statement generates a pre-header guard:
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empty = (step > 0 ? to < from : to > from), which can be predicted
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to be very likely. */
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DEF_PREDICTOR (PRED_FORTRAN_LOOP_PREHEADER, "Fortran loop preheader", \
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HITRATE (99), 0)
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/* Fortran assumed size arrays can be non-contiguous, so they need
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to be repacked. */
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DEF_PREDICTOR (PRED_FORTRAN_CONTIGUOUS, "Fortran contiguous", \
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HITRATE (75), 0)
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