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gcc 7

author | kono |
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date | Fri, 27 Oct 2017 22:46:09 +0900 |

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/* Profile counter container type. Copyright (C) 2017 Free Software Foundation, Inc. Contributed by Jan Hubicka This file is part of GCC. GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GCC; see the file COPYING3. If not see <http://www.gnu.org/licenses/>. */ #ifndef GCC_PROFILE_COUNT_H #define GCC_PROFILE_COUNT_H /* Quality of the profile count. Because gengtype does not support enums inside of classes, this is in global namespace. */ enum profile_quality { /* Profile is based on static branch prediction heuristics. It may or may not reflect the reality. */ profile_guessed = 0, /* Profile was determined by autofdo. */ profile_afdo = 1, /* Profile was originally based on feedback but it was adjusted by code duplicating optimization. It may not precisely reflect the particular code path. */ profile_adjusted = 2, /* Profile was read from profile feedback or determined by accurate static method. */ profile_precise = 3 }; /* The base value for branch probability notes and edge probabilities. */ #define REG_BR_PROB_BASE 10000 #define RDIV(X,Y) (((X) + (Y) / 2) / (Y)) bool slow_safe_scale_64bit (uint64_t a, uint64_t b, uint64_t c, uint64_t *res); /* Compute RES=(a*b + c/2)/c capping and return false if overflow happened. */ inline bool safe_scale_64bit (uint64_t a, uint64_t b, uint64_t c, uint64_t *res) { #if (GCC_VERSION >= 5000) uint64_t tmp; if (!__builtin_mul_overflow (a, b, &tmp) && !__builtin_add_overflow (tmp, c/2, &tmp)) { *res = tmp / c; return true; } if (c == 1) { *res = (uint64_t) -1; return false; } #else if (a < ((uint64_t)1 << 31) && b < ((uint64_t)1 << 31) && c < ((uint64_t)1 << 31)) { *res = (a * b + (c / 2)) / c; return true; } #endif return slow_safe_scale_64bit (a, b, c, res); } /* Data type to hold probabilities. It implements fixed point arithmetics with capping so probability is always in range [0,1] and scaling requiring values greater than 1 needs to be represented otherwise. In addition to actual value the quality of profile is tracked and propagated through all operations. Special value UNINITIALIZED is used for probabilities that has not been determined yet (for example bacause of -fno-guess-branch-probability) Typically probabilities are derived from profile feedback (via probability_in_gcov_type), autoFDO or guessed statically and then propagated thorough the compilation. Named probabilities are available: - never (0 probability) - guessed_never - very_unlikely (1/2000 probability) - unlikely (1/5 probablity) - even (1/2 probability) - likely (4/5 probability) - very_likely (1999/2000 probability) - guessed_always - always Named probabilities except for never/always are assumed to be statically guessed and thus not necessarily accurate. The difference between never and guessed_never is that the first one should be used only in case that well behaving program will very likely not execute the "never" path. For example if the path is going to abort () call or it exception handling. Always and guessed_always probabilities are symmetric. For legacy code we support conversion to/from REG_BR_PROB_BASE based fixpoint integer arithmetics. Once the code is converted to branch probabilities, these conversions will probably go away because they are lossy. */ class GTY((user)) profile_probability { static const int n_bits = 30; /* We can technically use ((uint32_t) 1 << (n_bits - 1)) - 2 but that will lead to harder multiplication sequences. */ static const uint32_t max_probability = (uint32_t) 1 << (n_bits - 2); static const uint32_t uninitialized_probability = ((uint32_t) 1 << (n_bits - 1)) - 1; uint32_t m_val : 30; enum profile_quality m_quality : 2; friend class profile_count; public: /* Named probabilities. */ static profile_probability never () { profile_probability ret; ret.m_val = 0; ret.m_quality = profile_precise; return ret; } static profile_probability guessed_never () { profile_probability ret; ret.m_val = 0; ret.m_quality = profile_guessed; return ret; } static profile_probability very_unlikely () { /* Be consistent with PROB_VERY_UNLIKELY in predict.h. */ profile_probability r = profile_probability::always ().apply_scale (1, 2000); r.m_val--; return r; } static profile_probability unlikely () { /* Be consistent with PROB_VERY_LIKELY in predict.h. */ profile_probability r = profile_probability::always ().apply_scale (1, 5); r.m_val--; return r; } static profile_probability even () { return profile_probability::always ().apply_scale (1, 2); } static profile_probability very_likely () { return profile_probability::always () - very_unlikely (); } static profile_probability likely () { return profile_probability::always () - unlikely (); } static profile_probability guessed_always () { profile_probability ret; ret.m_val = max_probability; ret.m_quality = profile_guessed; return ret; } static profile_probability always () { profile_probability ret; ret.m_val = max_probability; ret.m_quality = profile_precise; return ret; } /* Probabilities which has not been initialized. Either because initialization did not happen yet or because profile is unknown. */ static profile_probability uninitialized () { profile_probability c; c.m_val = uninitialized_probability; c.m_quality = profile_guessed; return c; } /* Return true if value has been initialized. */ bool initialized_p () const { return m_val != uninitialized_probability; } /* Return true if value can be trusted. */ bool reliable_p () const { return m_quality >= profile_adjusted; } /* Conversion from and to REG_BR_PROB_BASE integer fixpoint arithmetics. this is mostly to support legacy code and should go away. */ static profile_probability from_reg_br_prob_base (int v) { profile_probability ret; gcc_checking_assert (v >= 0 && v <= REG_BR_PROB_BASE); ret.m_val = RDIV (v * (uint64_t) max_probability, REG_BR_PROB_BASE); ret.m_quality = profile_guessed; return ret; } int to_reg_br_prob_base () const { gcc_checking_assert (initialized_p ()); return RDIV (m_val * (uint64_t) REG_BR_PROB_BASE, max_probability); } /* Conversion to and from RTL representation of profile probabilities. */ static profile_probability from_reg_br_prob_note (int v) { profile_probability ret; ret.m_val = ((unsigned int)v) / 4; ret.m_quality = (enum profile_quality)(v & 3); return ret; } int to_reg_br_prob_note () const { gcc_checking_assert (initialized_p ()); int ret = m_val * 4 + m_quality; gcc_checking_assert (profile_probability::from_reg_br_prob_note (ret) == *this); return ret; } /* Return VAL1/VAL2. */ static profile_probability probability_in_gcov_type (gcov_type val1, gcov_type val2) { profile_probability ret; gcc_checking_assert (val1 >= 0 && val2 > 0); if (val1 > val2) ret.m_val = max_probability; else { uint64_t tmp; safe_scale_64bit (val1, max_probability, val2, &tmp); gcc_checking_assert (tmp <= max_probability); ret.m_val = tmp; } ret.m_quality = profile_precise; return ret; } /* Basic operations. */ bool operator== (const profile_probability &other) const { return m_val == other.m_val && m_quality == other.m_quality; } profile_probability operator+ (const profile_probability &other) const { if (other == profile_probability::never ()) return *this; if (*this == profile_probability::never ()) return other; if (!initialized_p () || !other.initialized_p ()) return profile_probability::uninitialized (); profile_probability ret; ret.m_val = MIN ((uint32_t)(m_val + other.m_val), max_probability); ret.m_quality = MIN (m_quality, other.m_quality); return ret; } profile_probability &operator+= (const profile_probability &other) { if (other == profile_probability::never ()) return *this; if (*this == profile_probability::never ()) { *this = other; return *this; } if (!initialized_p () || !other.initialized_p ()) return *this = profile_probability::uninitialized (); else { m_val = MIN ((uint32_t)(m_val + other.m_val), max_probability); m_quality = MIN (m_quality, other.m_quality); } return *this; } profile_probability operator- (const profile_probability &other) const { if (*this == profile_probability::never () || other == profile_probability::never ()) return *this; if (!initialized_p () || !other.initialized_p ()) return profile_probability::uninitialized (); profile_probability ret; ret.m_val = m_val >= other.m_val ? m_val - other.m_val : 0; ret.m_quality = MIN (m_quality, other.m_quality); return ret; } profile_probability &operator-= (const profile_probability &other) { if (*this == profile_probability::never () || other == profile_probability::never ()) return *this; if (!initialized_p () || !other.initialized_p ()) return *this = profile_probability::uninitialized (); else { m_val = m_val >= other.m_val ? m_val - other.m_val : 0; m_quality = MIN (m_quality, other.m_quality); } return *this; } profile_probability operator* (const profile_probability &other) const { if (*this == profile_probability::never () || other == profile_probability::never ()) return profile_probability::never (); if (!initialized_p () || !other.initialized_p ()) return profile_probability::uninitialized (); profile_probability ret; ret.m_val = RDIV ((uint64_t)m_val * other.m_val, max_probability); ret.m_quality = MIN (m_quality, other.m_quality); return ret; } profile_probability &operator*= (const profile_probability &other) { if (*this == profile_probability::never () || other == profile_probability::never ()) return *this = profile_probability::never (); if (!initialized_p () || !other.initialized_p ()) return *this = profile_probability::uninitialized (); else { m_val = RDIV ((uint64_t)m_val * other.m_val, max_probability); m_quality = MIN (m_quality, other.m_quality); } return *this; } profile_probability operator/ (const profile_probability &other) const { if (*this == profile_probability::never ()) return profile_probability::never (); if (!initialized_p () || !other.initialized_p ()) return profile_probability::uninitialized (); profile_probability ret; if (m_val >= other.m_val) ret.m_val = max_probability; else if (!m_val) ret.m_val = 0; else { gcc_checking_assert (other.m_val); ret.m_val = MIN (RDIV ((uint64_t)m_val * max_probability, other.m_val), max_probability); } ret.m_quality = MIN (m_quality, other.m_quality); return ret; } profile_probability &operator/= (const profile_probability &other) { if (*this == profile_probability::never ()) return *this = profile_probability::never (); if (!initialized_p () || !other.initialized_p ()) return *this = profile_probability::uninitialized (); else { if (m_val > other.m_val) m_val = max_probability; else if (!m_val) ; else { gcc_checking_assert (other.m_val); m_val = MIN (RDIV ((uint64_t)m_val * max_probability, other.m_val), max_probability); } m_quality = MIN (m_quality, other.m_quality); } return *this; } gcov_type apply (gcov_type val) const { if (*this == profile_probability::uninitialized ()) return val / 2; return RDIV (val * m_val, max_probability); } /* Return 1-*THIS. */ profile_probability invert () const { return profile_probability::always() - *this; } /* Return THIS with quality dropped to GUESSED. */ profile_probability guessed () const { profile_probability ret = *this; ret.m_quality = profile_guessed; return ret; } /* Return THIS with quality dropped to AFDO. */ profile_probability afdo () const { profile_probability ret = *this; ret.m_quality = profile_afdo; return ret; } profile_probability combine_with_freq (int freq1, profile_probability other, int freq2) const { profile_probability ret; if (*this == profile_probability::uninitialized () || other == profile_probability::uninitialized ()) return profile_probability::uninitialized (); gcc_checking_assert (freq1 >= 0 && freq2 >= 0); if (!freq1 && !freq2) { ret.m_val = (m_val + other.m_val) / 2; } else ret.m_val = RDIV (m_val * (uint64_t) freq1 + other.m_val * (uint64_t) freq2, freq1 + freq2); ret.m_quality = MIN (m_quality, other.m_quality); return ret; } /* Return *THIS * NUM / DEN. */ profile_probability apply_scale (int64_t num, int64_t den) const { if (*this == profile_probability::never ()) return *this; if (!initialized_p ()) return profile_probability::uninitialized (); profile_probability ret; uint64_t tmp; safe_scale_64bit (m_val, num, den, &tmp); ret.m_val = MIN (tmp, max_probability); ret.m_quality = MIN (m_quality, profile_adjusted); return ret; } /* Return true when the probability of edge is reliable. The profile guessing code is good at predicting branch outcome (ie. taken/not taken), that is predicted right slightly over 75% of time. It is however notoriously poor on predicting the probability itself. In general the profile appear a lot flatter (with probabilities closer to 50%) than the reality so it is bad idea to use it to drive optimization such as those disabling dynamic branch prediction for well predictable branches. There are two exceptions - edges leading to noreturn edges and edges predicted by number of iterations heuristics are predicted well. This macro should be able to distinguish those, but at the moment it simply check for noreturn heuristic that is only one giving probability over 99% or bellow 1%. In future we might want to propagate reliability information across the CFG if we find this information useful on multiple places. */ bool probably_reliable_p () const { if (m_quality >= profile_adjusted) return true; if (!initialized_p ()) return false; return m_val < max_probability / 100 || m_val > max_probability - max_probability / 100; } /* Return false if profile_probability is bogus. */ bool verify () const { if (m_val == uninitialized_probability) return m_quality == profile_guessed; else return m_val <= max_probability; } /* Comparsions are three-state and conservative. False is returned if the inequality can not be decided. */ bool operator< (const profile_probability &other) const { return initialized_p () && other.initialized_p () && m_val < other.m_val; } bool operator> (const profile_probability &other) const { return initialized_p () && other.initialized_p () && m_val > other.m_val; } bool operator<= (const profile_probability &other) const { return initialized_p () && other.initialized_p () && m_val <= other.m_val; } bool operator>= (const profile_probability &other) const { return initialized_p () && other.initialized_p () && m_val >= other.m_val; } /* Output THIS to F. */ void dump (FILE *f) const; /* Print THIS to stderr. */ void debug () const; /* Return true if THIS is known to differ significantly from OTHER. */ bool differs_from_p (profile_probability other) const; /* Return if difference is greater than 50%. */ bool differs_lot_from_p (profile_probability other) const; /* LTO streaming support. */ static profile_probability stream_in (struct lto_input_block *); void stream_out (struct output_block *); void stream_out (struct lto_output_stream *); }; /* Main data type to hold profile counters in GCC. In most cases profile counts originate from profile feedback. They are 64bit integers representing number of executions during the train run. As the profile is maintained during the compilation, many adjustments are made. Not all transformations can be made precisely, most importantly when code is being duplicated. It also may happen that part of CFG has profile counts known while other do not - for example when LTO optimizing partly profiled program or when profile was lost due to COMDAT merging. For this reason profile_count tracks more information than just unsigned integer and it is also ready for profile mismatches. The API of this data type represent operations that are natural on profile counts - sum, difference and operation with scales and probabilities. All operations are safe by never getting negative counts and they do end up in uninitialized scale if any of the parameters is uninitialized. All comparsions that are three state and handling of probabilities. Thus a < b is not equal to !(a >= b). The following pre-defined counts are available: profile_count::zero () for code that is known to execute zero times at runtime (this can be detected statically i.e. for paths leading to abort (); profile_count::one () for code that is known to execute once (such as main () function profile_count::uninitialized () for unknown execution count. */ class GTY(()) profile_count { /* Use 62bit to hold basic block counters. Should be at least 64bit. Although a counter cannot be negative, we use a signed type to hold various extra stages. */ static const int n_bits = 62; static const uint64_t max_count = ((uint64_t) 1 << n_bits) - 2; static const uint64_t uninitialized_count = ((uint64_t) 1 << n_bits) - 1; uint64_t m_val : n_bits; enum profile_quality m_quality : 2; public: /* Used for counters which are expected to be never executed. */ static profile_count zero () { return from_gcov_type (0); } static profile_count guessed_zero () { profile_count c; c.m_val = 0; c.m_quality = profile_guessed; return c; } static profile_count one () { return from_gcov_type (1); } /* Value of counters which has not been initialized. Either because initialization did not happen yet or because profile is unknown. */ static profile_count uninitialized () { profile_count c; c.m_val = uninitialized_count; c.m_quality = profile_guessed; return c; } /* The profiling runtime uses gcov_type, which is usually 64bit integer. Conversions back and forth are used to read the coverage and get it into internal representation. */ static profile_count from_gcov_type (gcov_type v) { profile_count ret; gcc_checking_assert (v >= 0 && (uint64_t) v <= max_count); ret.m_val = v; ret.m_quality = profile_precise; return ret; } /* Conversion to gcov_type is lossy. */ gcov_type to_gcov_type () const { gcc_checking_assert (initialized_p ()); return m_val; } /* Return true if value has been initialized. */ bool initialized_p () const { return m_val != uninitialized_count; } /* Return true if value can be trusted. */ bool reliable_p () const { return m_quality >= profile_adjusted; } /* When merging basic blocks, the two different profile counts are unified. Return true if this can be done without losing info about profile. The only case we care about here is when first BB contains something that makes it terminate in a way not visible in CFG. */ bool ok_for_merging (profile_count other) const { if (m_quality < profile_adjusted || other.m_quality < profile_adjusted) return true; return !(other < *this); } /* When merging two BBs with different counts, pick common count that looks most representative. */ profile_count merge (profile_count other) const { if (*this == other || !other.initialized_p () || m_quality > other.m_quality) return *this; if (other.m_quality > m_quality || other > *this) return other; return *this; } /* Basic operations. */ bool operator== (const profile_count &other) const { return m_val == other.m_val && m_quality == other.m_quality; } profile_count operator+ (const profile_count &other) const { if (other == profile_count::zero ()) return *this; if (*this == profile_count::zero ()) return other; if (!initialized_p () || !other.initialized_p ()) return profile_count::uninitialized (); profile_count ret; ret.m_val = m_val + other.m_val; ret.m_quality = MIN (m_quality, other.m_quality); return ret; } profile_count &operator+= (const profile_count &other) { if (other == profile_count::zero ()) return *this; if (*this == profile_count::zero ()) { *this = other; return *this; } if (!initialized_p () || !other.initialized_p ()) return *this = profile_count::uninitialized (); else { m_val += other.m_val; m_quality = MIN (m_quality, other.m_quality); } return *this; } profile_count operator- (const profile_count &other) const { if (*this == profile_count::zero () || other == profile_count::zero ()) return *this; if (!initialized_p () || !other.initialized_p ()) return profile_count::uninitialized (); profile_count ret; ret.m_val = m_val >= other.m_val ? m_val - other.m_val : 0; ret.m_quality = MIN (m_quality, other.m_quality); return ret; } profile_count &operator-= (const profile_count &other) { if (*this == profile_count::zero () || other == profile_count::zero ()) return *this; if (!initialized_p () || !other.initialized_p ()) return *this = profile_count::uninitialized (); else { m_val = m_val >= other.m_val ? m_val - other.m_val: 0; m_quality = MIN (m_quality, other.m_quality); } return *this; } /* Return false if profile_count is bogus. */ bool verify () const { return m_val != uninitialized_count || m_quality == profile_guessed; } /* Comparsions are three-state and conservative. False is returned if the inequality can not be decided. */ bool operator< (const profile_count &other) const { return initialized_p () && other.initialized_p () && m_val < other.m_val; } bool operator> (const profile_count &other) const { return initialized_p () && other.initialized_p () && m_val > other.m_val; } bool operator< (const gcov_type other) const { gcc_checking_assert (other >= 0); return initialized_p () && m_val < (uint64_t) other; } bool operator> (const gcov_type other) const { gcc_checking_assert (other >= 0); return initialized_p () && m_val > (uint64_t) other; } bool operator<= (const profile_count &other) const { return initialized_p () && other.initialized_p () && m_val <= other.m_val; } bool operator>= (const profile_count &other) const { return initialized_p () && other.initialized_p () && m_val >= other.m_val; } bool operator<= (const gcov_type other) const { gcc_checking_assert (other >= 0); return initialized_p () && m_val <= (uint64_t) other; } bool operator>= (const gcov_type other) const { gcc_checking_assert (other >= 0); return initialized_p () && m_val >= (uint64_t) other; } /* PROB is a probability in scale 0...REG_BR_PROB_BASE. Scale counter accordingly. */ profile_count apply_probability (int prob) const { gcc_checking_assert (prob >= 0 && prob <= REG_BR_PROB_BASE); if (m_val == 0) return *this; if (!initialized_p ()) return profile_count::uninitialized (); profile_count ret; ret.m_val = RDIV (m_val * prob, REG_BR_PROB_BASE); ret.m_quality = MIN (m_quality, profile_adjusted); return ret; } /* Scale counter according to PROB. */ profile_count apply_probability (profile_probability prob) const { if (*this == profile_count::zero ()) return *this; if (prob == profile_probability::never ()) return profile_count::zero (); if (!initialized_p ()) return profile_count::uninitialized (); profile_count ret; uint64_t tmp; safe_scale_64bit (m_val, prob.m_val, profile_probability::max_probability, &tmp); ret.m_val = tmp; ret.m_quality = MIN (m_quality, prob.m_quality); return ret; } /* Return *THIS * NUM / DEN. */ profile_count apply_scale (int64_t num, int64_t den) const { if (m_val == 0) return *this; if (!initialized_p ()) return profile_count::uninitialized (); profile_count ret; uint64_t tmp; gcc_checking_assert (num >= 0 && den > 0); safe_scale_64bit (m_val, num, den, &tmp); ret.m_val = MIN (tmp, max_count); ret.m_quality = MIN (m_quality, profile_adjusted); return ret; } profile_count apply_scale (profile_count num, profile_count den) const { if (m_val == 0) return *this; if (num.m_val == 0) return num; if (!initialized_p () || !num.initialized_p () || !den.initialized_p ()) return profile_count::uninitialized (); gcc_checking_assert (den > 0); if (num == den) return *this; profile_count ret; uint64_t val; safe_scale_64bit (m_val, num.m_val, den.m_val, &val); ret.m_val = MIN (val, max_count); ret.m_quality = MIN (m_quality, profile_adjusted); return ret; } /* Return THIS with quality dropped to GUESSED. */ profile_count guessed () const { profile_count ret = *this; ret.m_quality = profile_guessed; return ret; } /* Return THIS with quality dropped to AFDO. */ profile_count afdo () const { profile_count ret = *this; ret.m_quality = profile_afdo; return ret; } /* Return probability of event with counter THIS within event with counter OVERALL. */ profile_probability probability_in (const profile_count overall) const { if (!m_val) return profile_probability::never (); if (!initialized_p () || !overall.initialized_p () || !overall.m_val) return profile_probability::uninitialized (); profile_probability ret; if (overall < m_val) ret.m_val = profile_probability::max_probability; else ret.m_val = RDIV (m_val * profile_probability::max_probability, overall.m_val); ret.m_quality = MIN (m_quality, overall.m_quality); return ret; } /* Output THIS to F. */ void dump (FILE *f) const; /* Print THIS to stderr. */ void debug () const; /* Return true if THIS is known to differ significantly from OTHER. */ bool differs_from_p (profile_count other) const; /* LTO streaming support. */ static profile_count stream_in (struct lto_input_block *); void stream_out (struct output_block *); void stream_out (struct lto_output_stream *); }; #endif