Ping * 2: [PATCH v2] Provide more contexts for -Warray-bounds warning messages

[Qing Zhao <qing.zhao@oracle.com>]

The 2nd ping for the following patch:

https://gcc.gnu.org/pipermail/gcc-patches/2024-July/657150.html

thanks.

Qing

> On Jul 22, 2024, at 09:01, Qing Zhao <qing.zhao@oracle.com> wrote:
> 
> Hi, Richard,
> 
> Could you please take a look at the patch and let me know any comment you have (especially on the middle-end part)?
> 
> David, let me know if you have further comment and suggestions. 
> 
> Thanks a lot.
> 
> Qing
> 
>> On Jul 12, 2024, at 10:03, Qing Zhao <qing.zhao@oracle.com> wrote:
>> 
>> due to code duplication from jump threading [PR109071]
>> Control this with a new option -fdiagnostic-explain-harder.
>> 
>> Compared to V1, the major difference are: (address David's comments)
>> 
>> 1. Change the name of the option from:
>> 
>> -fdiagnostic-try-to-explain-harder 
>> To
>> -fdiagnostic-explain-harder 
>> 
>> 2. Sync the commit comments with the real output of the compilation message.
>> 
>> 3. Add one more event in the end of the path to repeat the out-of-bound
>>  issue.
>> 
>> 4. Fixed the unnecessary changes in Makefile.in.
>> 
>> 5. Add new copy_history_diagnostic_path.[cc|h] to implement a new
>> class copy_history_diagnostic_path : public diagnostic_path
>> 
>> for copy_history_t. 
>> 
>> 6. Only building the rich locaiton and populating the path when warning_at
>> is called.
>> 
>> There are two comments from David that I didn't addressed in this version:
>> 
>> 1. Make regenerate-opt-urls.
>> will do this in a later version. 
>> 
>> 2. Add a ⚠️  emoji for the last event. 
>> I didn't add this yet since I think the current message is clear enough.
>> might not worth the effort to add this emoji (it's not that straightforward
>> to add on). 
>> 
>> With this new version, the message emitted by GCC:
>> 
>> $gcc -O2 -Wall -fdiagnostics-explain-harder -c -o t.o t.c
>> t.c: In function ‘sparx5_set’:
>> t.c:12:23: warning: array subscript 4 is above array bounds of ‘int[4]’ [-Warray-bounds=]
>>  12 |   int *val = &sg->vals[index];
>>     |               ~~~~~~~~^~~~~~~
>> ‘sparx5_set’: events 1-2
>>   4 |   if (*index >= 4)
>>     |      ^
>>     |      |
>>     |      (1) when the condition is evaluated to true
>> ......
>>  12 |   int *val = &sg->vals[index];
>>     |               ~~~~~~~~~~~~~~~
>>     |                       |
>>     |                       (2) out of array bounds here
>> t.c:8:18: note: while referencing ‘vals’
>>   8 | struct nums {int vals[4];};
>>     |                  ^~~~
>> 
>> Bootstrapped and regression tested on both aarch64 and x86. no issues.
>> 
>> Let me know any further comments and suggestions.
>> 
>> thanks.
>> 
>> Qing
>> 
>> ==================================================
>> $ cat t.c
>> extern void warn(void);
>> static inline void assign(int val, int *regs, int *index)
>> {
>> if (*index >= 4)
>>   warn();
>> *regs = val;
>> }
>> struct nums {int vals[4];};
>> 
>> void sparx5_set (int *ptr, struct nums *sg, int index)
>> {
>> int *val = &sg->vals[index];
>> 
>> assign(0,    ptr, &index);
>> assign(*val, ptr, &index);
>> }
>> 
>> $ gcc -Wall -O2  -c -o t.o t.c
>> t.c: In function ‘sparx5_set’:
>> t.c:12:23: warning: array subscript 4 is above array bounds of ‘int[4]’ [-Warray-bounds=]
>>  12 |   int *val = &sg->vals[index];
>>     |               ~~~~~~~~^~~~~~~
>> t.c:8:18: note: while referencing ‘vals’
>>   8 | struct nums {int vals[4];};
>>     |                  ^~~~
>> 
>> In the above, Although the warning is correct in theory, the warning message
>> itself is confusing to the end-user since there is information that cannot
>> be connected to the source code directly.
>> 
>> It will be a nice improvement to add more information in the warning message
>> to report where such index value come from.
>> 
>> In order to achieve this, we add a new data structure copy_history to record
>> the condition and the transformation that triggered the code duplication.
>> Whenever there is a code duplication due to some specific transformations,
>> such as jump threading, loop switching, etc, a copy_history structure is
>> created and attached to the duplicated gimple statement.
>> 
>> During array out-of-bound checking or other warning checking, the copy_history
>> that was attached to the gimple statement is used to form a sequence of
>> diagnostic events that are added to the corresponding rich location to be used
>> to report the warning message.
>> 
>> This behavior is controled by the new option -fdiagnostic-explain-harder
>> which is off by default.
>> 
>> With this change, by adding -fdiagnostic-explain-harder,
>> the warning message for the above testing case is now:
>> 
>> $ gcc -Wall -O2 -fdiagnostics-explain-harder -c -o t.o t.c
>> t.c: In function ‘sparx5_set’:
>> t.c:12:23: warning: array subscript 4 is above array bounds of ‘int[4]’ [-Warray-bounds=]
>>  12 |   int *val = &sg->vals[index];
>>     |               ~~~~~~~~^~~~~~~
>> ‘sparx5_set’: events 1-2
>>   4 |   if (*index >= 4)
>>     |      ^
>>     |      |
>>     |      (1) when the condition is evaluated to true
>> ......
>>  12 |   int *val = &sg->vals[index];
>>     |               ~~~~~~~~~~~~~~~
>>     |                       |
>>     |                       (2) out of array bounds here
>> t.c:8:18: note: while referencing ‘vals’
>>   8 | struct nums {int vals[4];};
>>     |                  ^~~~
>> 
>> gcc/ChangeLog:
>> 
>> PR tree-optimization/109071
>> 
>> * Makefile.in (OBJS): Add diagnostic-copy-history.o
>> and copy-history-diagnostic-path.o.
>> * gcc/common.opt (fdiagnostics-explain-harder): New option.
>> * gcc/doc/invoke.texi (fdiagnostics-explain-harder): Add
>> documentation for the new option.
>> * gimple-array-bounds.cc (build_rich_location_with_diagnostic_path):
>> New function.
>> (check_out_of_bounds_and_warn): Add one new parameter. Use rich
>> location with copy_history_diagnostic_path for warning_at.
>> (array_bounds_checker::check_array_ref): Use rich location with
>> copy_history_diagnostic_path for warning_at.
>> (array_bounds_checker::check_mem_ref): Add one new parameter.
>> Use rich location with copy_history_diagnostic_path for warning_at.
>> (array_bounds_checker::check_addr_expr): Use rich location with
>> copy_history_diagnostic_path for warning_at.
>> (array_bounds_checker::check_array_bounds): Call check_mem_ref with
>> one more parameter.
>> * gimple-array-bounds.h: Update prototype for check_mem_ref.
>> * gimple-iterator.cc (gsi_remove): (gsi_remove): Remove the copy
>> history when removing the gimple.
>> * toplev.cc (toplev::finalize):  Call copy_history_finalize.
>> * tree-ssa-threadupdate.cc (set_copy_history_to_stmts_in_bb): New
>> function.
>> (back_jt_path_registry::duplicate_thread_path): Call the new function
>> to set copy history for every duplicated gimple.
>> * copy-history-diagnostic-path.cc: New file.
>> * copy-history-diagnostic-path.h: New file.
>> * diagnostic-copy-history.cc: New file.
>> * diagnostic-copy-history.h: New file.
>> 
>> gcc/testsuite/ChangeLog:
>> 
>> PR tree-optimization/109071
>> 
>> * gcc.dg/pr109071.c: New test.
>> ---
>> gcc/Makefile.in                     |   2 +
>> gcc/common.opt                      |   4 +
>> gcc/copy-history-diagnostic-path.cc |  86 +++++++++++++++
>> gcc/copy-history-diagnostic-path.h  |  87 +++++++++++++++
>> gcc/diagnostic-copy-history.cc      | 163 ++++++++++++++++++++++++++++
>> gcc/diagnostic-copy-history.h       |  80 ++++++++++++++
>> gcc/doc/invoke.texi                 |   7 ++
>> gcc/gimple-array-bounds.cc          |  94 +++++++++++++---
>> gcc/gimple-array-bounds.h           |   2 +-
>> gcc/gimple-iterator.cc              |   3 +
>> gcc/testsuite/gcc.dg/pr109071.c     |  43 ++++++++
>> gcc/toplev.cc                       |   3 +
>> gcc/tree-ssa-threadupdate.cc        |  42 +++++++
>> 13 files changed, 598 insertions(+), 18 deletions(-)
>> create mode 100644 gcc/copy-history-diagnostic-path.cc
>> create mode 100644 gcc/copy-history-diagnostic-path.h
>> create mode 100644 gcc/diagnostic-copy-history.cc
>> create mode 100644 gcc/diagnostic-copy-history.h
>> create mode 100644 gcc/testsuite/gcc.dg/pr109071.c
>> 
>> diff --git a/gcc/Makefile.in b/gcc/Makefile.in
>> index 7d3ea27a6ab..f8bbfda845f 100644
>> --- a/gcc/Makefile.in
>> +++ b/gcc/Makefile.in
>> @@ -1436,6 +1436,8 @@ OBJS = \
>> df-problems.o \
>> df-scan.o \
>> dfp.o \
>> + diagnostic-copy-history.o \
>> + copy-history-diagnostic-path.o \
>> digraph.o \
>> dojump.o \
>> dominance.o \
>> diff --git a/gcc/common.opt b/gcc/common.opt
>> index a300470bbc5..714280390d9 100644
>> --- a/gcc/common.opt
>> +++ b/gcc/common.opt
>> @@ -1558,6 +1558,10 @@ fdiagnostics-minimum-margin-width=
>> Common Joined UInteger Var(diagnostics_minimum_margin_width) Init(6)
>> Set minimum width of left margin of source code when showing source.
>> 
>> +fdiagnostics-explain-harder
>> +Common Var(flag_diagnostics_explain_harder)
>> +Collect and print more context information for diagnostics.
>> +
>> fdisable-
>> Common Joined RejectNegative Var(common_deferred_options) Defer
>> -fdisable-[tree|rtl|ipa]-<pass>=range1+range2 Disable an optimization pass.
>> diff --git a/gcc/copy-history-diagnostic-path.cc b/gcc/copy-history-diagnostic-path.cc
>> new file mode 100644
>> index 00000000000..65e5c056165
>> --- /dev/null
>> +++ b/gcc/copy-history-diagnostic-path.cc
>> @@ -0,0 +1,86 @@
>> +/* Classes for implementing diagnostic paths for copy_history_t.
>> +   Copyright (C) 2024-2024 Free Software Foundation, Inc.
>> +   Contributed by Qing Zhao<qing.zhao@oracle.com>
>> +
>> +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/>.  */
>> +
>> +#include "config.h"
>> +#include "system.h"
>> +#include "coretypes.h"
>> +#include "function.h"
>> +#include "copy-history-diagnostic-path.h"
>> +
>> +bool
>> +copy_history_diagnostic_path::same_function_p (int event_idx_a,
>> +       int event_idx_b) const
>> +{
>> +  return (m_events[event_idx_a]->get_fndecl ()
>> +  == m_events[event_idx_b]->get_fndecl ());
>> +}
>> +
>> +/* Add an event to this path at LOC within function FNDECL at
>> +   stack depth DEPTH.
>> +
>> +   Use m_context's printer to format FMT, as the text of the new
>> +   event.  */
>> +
>> +void
>> +copy_history_diagnostic_path::add_event (location_t loc, tree fndecl, int depth,
>> + const char *fmt, ...)
>> +{
>> +  pretty_printer *pp = m_event_pp;
>> +  pp_clear_output_area (pp);
>> +
>> +  rich_location rich_loc (line_table, UNKNOWN_LOCATION);
>> +
>> +  va_list ap;
>> +
>> +  va_start (ap, fmt);
>> +
>> +  text_info ti (fmt, &ap, 0, nullptr, &rich_loc);
>> +  pp_format (pp, &ti);
>> +  pp_output_formatted_text (pp);
>> +
>> +  va_end (ap);
>> +
>> +  simple_diagnostic_event *new_event
>> +    = new simple_diagnostic_event (loc, fndecl, depth, pp_formatted_text (pp));
>> +  m_events.safe_push (new_event);
>> +
>> +  pp_clear_output_area (pp);
>> +
>> +  return;
>> +}
>> +
>> +/* Populate the diagnostic_path from the copy_history.  */
>> +void
>> +copy_history_diagnostic_path::populate_path_from_copy_history ()
>> +{
>> +  if (!m_copy_history)
>> +    return;
>> +
>> +  for (copy_history_t cur_ch = m_copy_history; cur_ch;
>> +       cur_ch = cur_ch->prev_copy)
>> +    add_event (cur_ch->condition, cfun->decl, 1,
>> +       "when the condition is evaluated to %s",
>> +       cur_ch->is_true_path ? "true" : "false");
>> +
>> +  /* Add an end of path warning event in the end of the path.  */
>> +  add_event (m_location, cfun->decl, 1,
>> +     "out of array bounds here");
>> +  return;
>> +}
>> diff --git a/gcc/copy-history-diagnostic-path.h b/gcc/copy-history-diagnostic-path.h
>> new file mode 100644
>> index 00000000000..377e9136070
>> --- /dev/null
>> +++ b/gcc/copy-history-diagnostic-path.h
>> @@ -0,0 +1,87 @@
>> +/* Classes for implementing diagnostic paths for copy_history_t.
>> +   Copyright (C) 2024-2024 Free Software Foundation, Inc.
>> +   Contributed by Qing Zhao<qing.zhao@oracle.com>
>> +
>> +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_COPY_HISTORY_DIAGNOSTIC_PATH_H
>> +#define GCC_COPY_HISTORY_DIAGNOSTIC_PATH_H
>> +
>> +#include "diagnostic-path.h"
>> +#include "simple-diagnostic-path.h"
>> +#include "diagnostic-copy-history.h"
>> +
>> +/* An implementation of diagnostic_path for copy_history_t, as a
>> +   vector of simple_diagnostic_event instances.  */
>> +
>> +class copy_history_diagnostic_path : public diagnostic_path
>> +{
>> + public:
>> +  copy_history_diagnostic_path (pretty_printer *event_pp,
>> + copy_history_t cp_history,
>> + location_t loc)
>> +  : diagnostic_path (),
>> +    m_thread ("main"),
>> +    m_event_pp (event_pp),
>> +    m_copy_history (cp_history),
>> +    m_location (loc)
>> +  {}
>> +
>> +  unsigned num_events () const final override
>> +  {
>> +    return m_events.length ();
>> +  }
>> +  const diagnostic_event & get_event (int idx) const final override
>> +  {
>> +    return *m_events[idx];
>> +  }
>> +  unsigned num_threads () const final override
>> +  {
>> +    return 1;
>> +  }
>> +  const diagnostic_thread &
>> +  get_thread (diagnostic_thread_id_t) const final override
>> +  {
>> +    return m_thread;
>> +  }
>> +  bool
>> +  same_function_p (int event_idx_a,
>> +   int event_idx_b) const final override;
>> +
>> +  void add_event (location_t loc, tree fndecl, int depth,
>> +  const char *fmt, ...);
>> +
>> +  void populate_path_from_copy_history ();
>> +
>> + private:
>> +  simple_diagnostic_thread m_thread;
>> +
>> +  /* The events that have occurred along this path.  */
>> +  auto_delete_vec<simple_diagnostic_event> m_events;
>> +
>> +  pretty_printer *m_event_pp;
>> +
>> +  /* The copy_history associated with this path.  */
>> +  copy_history_t m_copy_history;
>> +
>> +  /* The location for the gimple statement where the
>> +     diagnostic message emitted.  */
>> +  location_t m_location;
>> +
>> +};
>> +
>> +#endif /* ! GCC_COPY_HISTORY_DIAGNOSTIC_PATH_H */
>> diff --git a/gcc/diagnostic-copy-history.cc b/gcc/diagnostic-copy-history.cc
>> new file mode 100644
>> index 00000000000..2733d137622
>> --- /dev/null
>> +++ b/gcc/diagnostic-copy-history.cc
>> @@ -0,0 +1,163 @@
>> +/* Functions to handle copy history.
>> +   Copyright (C) 2024-2024 Free Software Foundation, Inc.
>> +   Contributed by Qing Zhao <qing.zhao@oracle.com>
>> +
>> +   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/>.  */
>> +
>> +#include "config.h"
>> +#include "system.h"
>> +#include "coretypes.h"
>> +#include "backend.h"
>> +#include "tree.h"
>> +#include "diagnostic-copy-history.h"
>> +
>> +/* A mapping from a gimple to a pointer to the copy history of it.  */
>> +static copy_history_map_t *copy_history_map;
>> +
>> +/* Obstack for copy history.  */
>> +static struct obstack copy_history_obstack;
>> +
>> +/* Create a new copy history.  */
>> +
>> +copy_history_t
>> +create_copy_history (location_t condition,
>> +     bool is_true_path,
>> +     enum copy_reason reason,
>> +     copy_history_t prev_copy)
>> +{
>> +  static bool initialized = false;
>> +
>> +  if (!initialized)
>> +    {
>> +      gcc_obstack_init (&copy_history_obstack);
>> +      initialized = true;
>> +    }
>> +
>> +  copy_history_t copy_history
>> +    = (copy_history_t) obstack_alloc (&copy_history_obstack,
>> +      sizeof (struct copy_history));
>> +  copy_history->condition = condition;
>> +  copy_history->is_true_path = is_true_path;
>> +  copy_history->reason = reason;
>> +  copy_history->prev_copy = prev_copy;
>> +  return copy_history;
>> +}
>> +
>> +/* Insert the copy history for the gimple STMT assuming the linked list
>> +   of CP_HISTORY does not have duplications.  It's the caller's
>> +   responsibility to make sure that the linked list of CP_HISTORY does
>> +   not have duplications.  */
>> +
>> +void
>> +insert_copy_history (gimple *stmt, copy_history_t cp_history)
>> +{
>> +  if (!copy_history_map)
>> +    copy_history_map = new copy_history_map_t;
>> +
>> +  copy_history_map->put (stmt, cp_history);
>> +  return;
>> +}
>> +
>> +/* Get the copy history for the gimple STMT, return NULL when there is
>> +   no associated copy history.  */
>> +
>> +copy_history_t
>> +get_copy_history (gimple *stmt)
>> +{
>> +  if (!copy_history_map)
>> +    return NULL;
>> +
>> +  if (const copy_history_t *cp_history_p = copy_history_map->get (stmt))
>> +    return *cp_history_p;
>> +
>> +  return NULL;
>> +}
>> +
>> +/* Remove the copy history for STMT.  */
>> +
>> +void
>> +remove_copy_history (gimple *stmt)
>> +{
>> +  if (!copy_history_map)
>> +    return;
>> +  copy_history_map->remove (stmt);
>> +  return;
>> +}
>> +
>> +/* Check whether the cond_location, is_true_path and reason existed
>> + * in the OLD_COPY_HISTORY.  */
>> +
>> +static bool
>> +is_copy_history_existed (location_t cond_location, bool is_true_path,
>> + enum copy_reason reason,
>> + copy_history_t old_copy_history)
>> +{
>> +  for (copy_history_t cur_ch = old_copy_history; cur_ch;
>> +       cur_ch = cur_ch->prev_copy)
>> +    if ((cur_ch->condition == cond_location)
>> + && (cur_ch->is_true_path == is_true_path)
>> + && (cur_ch->reason == reason))
>> +      return true;
>> +
>> +  return false;
>> +}
>> +
>> +/* Set copy history for the gimple STMT.  Return TRUE when a new copy
>> + * history is created and inserted.  Otherwise return FALSE.  */
>> +
>> +bool
>> +set_copy_history (gimple *stmt, location_t cond_location,
>> +  bool is_true_path, enum copy_reason reason)
>> +{
>> +
>> +  /* First, get the old copy history associated with this STMT.  */
>> +  copy_history_t old_cp_history = get_copy_history (stmt);
>> +
>> +  /* If the current copy history is not in the STMT's copy history linked
>> +     list yet, create the new copy history, put the old_copy_history as the
>> +     prev_copy of it.  */
>> +  copy_history_t new_cp_history = NULL;
>> +  if (!is_copy_history_existed (cond_location, is_true_path,
>> + reason, old_cp_history))
>> +    new_cp_history
>> +      = create_copy_history (cond_location, is_true_path,
>> +     reason, old_cp_history);
>> +
>> +  /* Insert the copy history into the hash map.  */
>> +  if (new_cp_history)
>> +    {
>> +      insert_copy_history (stmt, new_cp_history);
>> +      return true;
>> +    }
>> +
>> +  return false;
>> +}
>> +
>> +/* Reset all state for diagnostic-copy-history.cc so that we can rerun the
>> +   compiler within the same process.  For use by toplev::finalize.  */
>> +
>> +void
>> +copy_history_finalize (void)
>> +{
>> +  if (copy_history_map)
>> +    {
>> +      delete copy_history_map;
>> +      copy_history_map = NULL;
>> +    }
>> +  obstack_free (&copy_history_obstack, NULL);
>> +  return;
>> +}
>> diff --git a/gcc/diagnostic-copy-history.h b/gcc/diagnostic-copy-history.h
>> new file mode 100644
>> index 00000000000..0c2c55a2a81
>> --- /dev/null
>> +++ b/gcc/diagnostic-copy-history.h
>> @@ -0,0 +1,80 @@
>> +/* Copy history associated with a gimple statement to record its history
>> +   of duplications due to different transformations.
>> +   The copy history will be used to construct events for later diagnostic.
>> +
>> +   Copyright (C) 2024-2024 Free Software Foundation, Inc.
>> +   Contributed by Qing Zhao <qing.zhao@oracle.com>
>> +
>> +   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 DIAGNOSTIC_COPY_HISTORY_H_INCLUDED
>> +#define DIAGNOSTIC_COPY_HISTORY_H_INCLUDED
>> +
>> +#include "hash-map.h"
>> +#include "line-map.h"
>> +
>> +/* An enum for the reason why this copy is made.  Right now, there are
>> +   three reasons, we can add more if needed.  */
>> +enum copy_reason {
>> +  COPY_BY_THREAD_JUMP,
>> +  COPY_BY_LOOP_UNSWITCH,
>> +  COPY_BY_LOOP_UNROLL
>> +};
>> +
>> +/* This data structure records the information when a statement is
>> +   duplicated during different transformations.  Such information
>> +   will be used by the later diagnostic messages to report more
>> +   contexts of the warnings or errors.  */
>> +struct copy_history {
>> +  /* The location of the condition statement that triggered the code
>> +     duplication.  */
>> +  location_t condition;
>> +
>> +  /* Whether this copy is on the TRUE path of the condition.  */
>> +  bool is_true_path;
>> +
>> +  /* The reason for the code duplication.  */
>> +  enum copy_reason reason;
>> +
>> +  /* This statement itself might be a previous code duplication.  */
>> +  struct copy_history *prev_copy;
>> +};
>> +
>> +typedef struct copy_history *copy_history_t;
>> +
>> +/* Create a new copy history.  */
>> +extern copy_history_t create_copy_history (location_t, bool,
>> +   enum copy_reason, copy_history_t);
>> +
>> +typedef hash_map<gimple *, copy_history_t> copy_history_map_t;
>> +
>> +/* Get the copy history for the gimple STMT, return NULL when there is
>> +   no associated copy history.  */
>> +extern copy_history_t get_copy_history (gimple *);
>> +
>> +/* Remove the copy history for STMT from the copy_history_map.  */
>> +extern void remove_copy_history (gimple *);
>> +
>> +/* Set copy history for the gimple STMT.  */
>> +extern bool set_copy_history (gimple *, location_t,
>> +      bool, enum copy_reason);
>> +
>> +/* Reset all state for diagnostic-copy-history.cc so that we can rerun the
>> +   compiler within the same process.  For use by toplev::finalize.  */
>> +extern void copy_history_finalize (void);
>> +
>> +#endif // DIAGNOSTIC_COPY_HISTORY_H_INCLUDED
>> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
>> index b37c7af7a39..bb0c6a87523 100644
>> --- a/gcc/doc/invoke.texi
>> +++ b/gcc/doc/invoke.texi
>> @@ -321,6 +321,7 @@ Objective-C and Objective-C++ Dialects}.
>> -fdiagnostics-column-origin=@var{origin}
>> -fdiagnostics-escape-format=@r{[}unicode@r{|}bytes@r{]}
>> -fdiagnostics-text-art-charset=@r{[}none@r{|}ascii@r{|}unicode@r{|}emoji@r{]}}
>> +-fdiagnostics-explain-harder
>> 
>> @item Warning Options
>> @xref{Warning Options,,Options to Request or Suppress Warnings}.
>> @@ -5518,6 +5519,12 @@ left margin.
>> This option controls the minimum width of the left margin printed by
>> @option{-fdiagnostics-show-line-numbers}.  It defaults to 6.
>> 
>> +@opindex fdiagnostics-explain-harder
>> +@item -fdiagnostics-explain-harder
>> +With this option, the compiler collects more context information for
>> +diagnostics and emits them to the users to provide more hints on how
>> +the diagnostics come from.
>> +
>> @opindex fdiagnostics-parseable-fixits
>> @item -fdiagnostics-parseable-fixits
>> Emit fix-it hints in a machine-parseable format, suitable for consumption
>> diff --git a/gcc/gimple-array-bounds.cc b/gcc/gimple-array-bounds.cc
>> index 1637a2fc4f4..ba98ab3b413 100644
>> --- a/gcc/gimple-array-bounds.cc
>> +++ b/gcc/gimple-array-bounds.cc
>> @@ -31,6 +31,9 @@ along with GCC; see the file COPYING3.  If not see
>> #include "tree-dfa.h"
>> #include "fold-const.h"
>> #include "diagnostic-core.h"
>> +#include "simple-diagnostic-path.h"
>> +#include "diagnostic-copy-history.h"
>> +#include "copy-history-diagnostic-path.h"
>> #include "intl.h"
>> #include "tree-vrp.h"
>> #include "alloc-pool.h"
>> @@ -254,6 +257,25 @@ get_up_bounds_for_array_ref (tree ref, tree *decl,
>>  return;
>> }
>> 
>> +/* Build a rich location for LOCATION, and populate the diagonistic path
>> +   for it.  */
>> +
>> +static rich_location *
>> +build_rich_location_with_diagnostic_path (location_t location, gimple *stmt)
>> +{
>> +  /* Generate a rich location for this location.  */
>> +  rich_location *richloc = new rich_location (line_table, location);
>> +
>> +  copy_history_t cp_history = stmt ? get_copy_history (stmt) : NULL;
>> +  copy_history_diagnostic_path *path
>> +    = new copy_history_diagnostic_path (global_dc->printer,
>> + cp_history, location);
>> +  path->populate_path_from_copy_history ();
>> +
>> +  richloc->set_path (path);
>> +  return richloc;
>> +}
>> +
>> /* Given the LOW_SUB_ORG, LOW_SUB and UP_SUB, and the computed UP_BOUND
>>   and UP_BOUND_P1, check whether the array reference REF is out of bound.
>>   When out of bounds, set OUT_OF_BOUND to true.
>> @@ -262,6 +284,7 @@ get_up_bounds_for_array_ref (tree ref, tree *decl,
>> 
>> static bool
>> check_out_of_bounds_and_warn (location_t location, tree ref,
>> +      gimple *stmt,
>>     tree low_sub_org, tree low_sub, tree up_sub,
>>     tree up_bound, tree up_bound_p1,
>>     const irange *vr,
>> @@ -280,9 +303,13 @@ check_out_of_bounds_and_warn (location_t location, tree ref,
>>    {
>>      *out_of_bound = true;
>>      if (for_array_bound)
>> - warned = warning_at (location, OPT_Warray_bounds_,
>> + {
>> +  rich_location *richloc
>> +    = build_rich_location_with_diagnostic_path (location, stmt);
>> +  warned = warning_at (richloc, OPT_Warray_bounds_,
>>    "array subscript %E is outside array"
>>    " bounds of %qT", low_sub_org, artype);
>> + }
>>    }
>> 
>>  if (warned)
>> @@ -299,10 +326,14 @@ check_out_of_bounds_and_warn (location_t location, tree ref,
>> {
>> *out_of_bound = true;
>> if (for_array_bound)
>> -    warned = warning_at (location, OPT_Warray_bounds_,
>> +    {
>> +      rich_location *richloc
>> + = build_rich_location_with_diagnostic_path (location, stmt);
>> +      warned = warning_at (richloc, OPT_Warray_bounds_,
>> "array subscript [%E, %E] is outside "
>> "array bounds of %qT",
>> low_sub, up_sub, artype);
>> +    }
>> }
>>    }
>>  else if (up_bound
>> @@ -313,18 +344,26 @@ check_out_of_bounds_and_warn (location_t location, tree ref,
>>    {
>>      *out_of_bound = true;
>>      if (for_array_bound)
>> - warned = warning_at (location, OPT_Warray_bounds_,
>> + {
>> +  rich_location *richloc
>> +    = build_rich_location_with_diagnostic_path (location, stmt);
>> +  warned = warning_at (richloc, OPT_Warray_bounds_,
>>    "array subscript %E is above array bounds of %qT",
>>    up_sub, artype);
>> + }
>>    }
>>  else if (TREE_CODE (low_sub) == INTEGER_CST
>>  && tree_int_cst_lt (low_sub, low_bound))
>>    {
>>      *out_of_bound = true;
>>      if (for_array_bound)
>> - warned = warning_at (location, OPT_Warray_bounds_,
>> + {
>> +  rich_location *richloc
>> +    = build_rich_location_with_diagnostic_path (location, stmt);
>> +  warned = warning_at (richloc, OPT_Warray_bounds_,
>>    "array subscript %E is below array bounds of %qT",
>>    low_sub, artype);
>> + }
>>    }
>>  return warned;
>> }
>> @@ -388,21 +427,24 @@ array_bounds_checker::check_array_ref (location_t location, tree ref,
>> }
>>    }
>> 
>> -  warned = check_out_of_bounds_and_warn (location, ref,
>> +  warned = check_out_of_bounds_and_warn (location, ref, stmt,
>> low_sub_org, low_sub, up_sub,
>> up_bound, up_bound_p1, &vr,
>> ignore_off_by_one, warn_array_bounds,
>> &out_of_bound);
>> 
>> -
>>  if (!warned && sam == special_array_member::int_0)
>> -    warned = warning_at (location, OPT_Wzero_length_bounds,
>> +    {
>> +      rich_location *richloc
>> + = build_rich_location_with_diagnostic_path (location, stmt);
>> +      warned = warning_at (richloc, OPT_Wzero_length_bounds,
>> (TREE_CODE (low_sub) == INTEGER_CST
>> ? G_("array subscript %E is outside the bounds "
>>      "of an interior zero-length array %qT")
>> : G_("array subscript %qE is outside the bounds "
>>      "of an interior zero-length array %qT")),
>> low_sub, artype);
>> +    }
>> 
>>  if (warned && dump_file && (dump_flags & TDF_DETAILS))
>>    {
>> @@ -419,8 +461,10 @@ array_bounds_checker::check_array_ref (location_t location, tree ref,
>> || sam == special_array_member::trail_n)
>>      && DECL_NOT_FLEXARRAY (afield_decl))
>>    {
>> +      rich_location *richloc
>> + = build_rich_location_with_diagnostic_path (location, stmt);
>>      bool warned1
>> - = warning_at (location, OPT_Wstrict_flex_arrays,
>> + = warning_at (richloc, OPT_Wstrict_flex_arrays,
>>     "trailing array %qT should not be used as "
>>     "a flexible array member",
>>     artype);
>> @@ -478,6 +522,7 @@ array_bounds_checker::check_array_ref (location_t location, tree ref,
>> 
>> bool
>> array_bounds_checker::check_mem_ref (location_t location, tree ref,
>> +     gimple *stmt,
>>    bool ignore_off_by_one)
>> {
>>  if (warning_suppressed_p (ref, OPT_Warray_bounds_))
>> @@ -580,16 +625,24 @@ array_bounds_checker::check_mem_ref (location_t location, tree ref,
>>  if (lboob)
>>    {
>>      if (offrange[0] == offrange[1])
>> - warned = warning_at (location, OPT_Warray_bounds_,
>> + {
>> +  rich_location *richloc
>> +    = build_rich_location_with_diagnostic_path (location, stmt);
>> +  warned = warning_at (richloc, OPT_Warray_bounds_,
>>    "array subscript %wi is outside array bounds "
>>    "of %qT",
>>    offrange[0].to_shwi (), reftype);
>> + }
>>      else
>> - warned = warning_at (location, OPT_Warray_bounds_,
>> + {
>> +  rich_location *richloc
>> +    = build_rich_location_with_diagnostic_path (location, stmt);
>> +  warned = warning_at (richloc, OPT_Warray_bounds_,
>>    "array subscript [%wi, %wi] is outside "
>>    "array bounds of %qT",
>>    offrange[0].to_shwi (),
>>    offrange[1].to_shwi (), reftype);
>> + }
>>    }
>>  else if (uboob && !ignore_off_by_one)
>>    {
>> @@ -599,8 +652,9 @@ array_bounds_checker::check_mem_ref (location_t location, tree ref,
>>  it were an untyped array of bytes.  */
>> backtype = build_array_type_nelts (unsigned_char_type_node,
>>  aref.sizrng[1].to_uhwi ());
>> -
>> -      warned = warning_at (location, OPT_Warray_bounds_,
>> +      rich_location *richloc
>> + = build_rich_location_with_diagnostic_path (location, stmt);
>> +      warned = warning_at (richloc, OPT_Warray_bounds_,
>>  "array subscript %<%T[%wi]%> is partly "
>>  "outside array bounds of %qT",
>>  axstype, offrange[0].to_shwi (), backtype);
>> @@ -623,7 +677,9 @@ array_bounds_checker::check_mem_ref (location_t location, tree ref,
>>    {
>>      HOST_WIDE_INT tmpidx = (aref.offmax[i] / eltsize).to_shwi ();
>> 
>> -      if (warning_at (location, OPT_Warray_bounds_,
>> +      rich_location *richloc
>> + = build_rich_location_with_diagnostic_path (location, stmt);
>> +      if (warning_at (richloc, OPT_Warray_bounds_,
>>     "intermediate array offset %wi is outside array bounds "
>>     "of %qT", tmpidx, reftype))
>> {
>> @@ -656,7 +712,7 @@ array_bounds_checker::check_addr_expr (location_t location, tree t,
>> ignore_off_by_one = false;
>> }
>>      else if (TREE_CODE (t) == MEM_REF)
>> - warned = check_mem_ref (location, t, ignore_off_by_one);
>> + warned = check_mem_ref (location, t, stmt, ignore_off_by_one);
>> 
>>      if (warned)
>> suppress_warning (t, OPT_Warray_bounds_);
>> @@ -702,7 +758,9 @@ array_bounds_checker::check_addr_expr (location_t location, tree t,
>> dump_generic_expr (MSG_NOTE, TDF_SLIM, t);
>> fprintf (dump_file, "\n");
>> }
>> -      warned = warning_at (location, OPT_Warray_bounds_,
>> +      rich_location *richloc
>> + = build_rich_location_with_diagnostic_path (location, stmt);
>> +      warned = warning_at (richloc, OPT_Warray_bounds_,
>>  "array subscript %wi is below "
>>  "array bounds of %qT",
>>  idx.to_shwi (), TREE_TYPE (tem));
>> @@ -716,7 +774,9 @@ array_bounds_checker::check_addr_expr (location_t location, tree t,
>> dump_generic_expr (MSG_NOTE, TDF_SLIM, t);
>> fprintf (dump_file, "\n");
>> }
>> -      warned = warning_at (location, OPT_Warray_bounds_,
>> +      rich_location *richloc
>> + = build_rich_location_with_diagnostic_path (location, stmt);
>> +      warned = warning_at (richloc, OPT_Warray_bounds_,
>>  "array subscript %wu is above "
>>  "array bounds of %qT",
>>  idx.to_uhwi (), TREE_TYPE (tem));
>> @@ -811,7 +871,7 @@ array_bounds_checker::check_array_bounds (tree *tp, int *walk_subtree,
>>    warned = checker->check_array_ref (location, t, wi->stmt,
>>      false/*ignore_off_by_one*/);
>>  else if (TREE_CODE (t) == MEM_REF)
>> -    warned = checker->check_mem_ref (location, t,
>> +    warned = checker->check_mem_ref (location, t, wi->stmt,
>>    false /*ignore_off_by_one*/);
>>  else if (TREE_CODE (t) == ADDR_EXPR)
>>    {
>> diff --git a/gcc/gimple-array-bounds.h b/gcc/gimple-array-bounds.h
>> index aa7ca8e9730..2d1d48d1e94 100644
>> --- a/gcc/gimple-array-bounds.h
>> +++ b/gcc/gimple-array-bounds.h
>> @@ -33,7 +33,7 @@ public:
>> private:
>>  static tree check_array_bounds (tree *tp, int *walk_subtree, void *data);
>>  bool check_array_ref (location_t, tree, gimple *, bool ignore_off_by_one);
>> -  bool check_mem_ref (location_t, tree, bool ignore_off_by_one);
>> +  bool check_mem_ref (location_t, tree, gimple *, bool ignore_off_by_one);
>>  void check_addr_expr (location_t, tree, gimple *);
>>  void get_value_range (irange &r, const_tree op, gimple *);
>> 
>> diff --git a/gcc/gimple-iterator.cc b/gcc/gimple-iterator.cc
>> index 93646262eac..472a79360d7 100644
>> --- a/gcc/gimple-iterator.cc
>> +++ b/gcc/gimple-iterator.cc
>> @@ -33,6 +33,7 @@ along with GCC; see the file COPYING3.  If not see
>> #include "tree-ssa.h"
>> #include "value-prof.h"
>> #include "gimplify.h"
>> +#include "diagnostic-copy-history.h"
>> 
>> 
>> /* Mark the statement STMT as modified, and update it.  */
>> @@ -581,6 +582,8 @@ gsi_remove (gimple_stmt_iterator *i, bool remove_permanently)
>> cfun->debug_marker_count--;
>>      require_eh_edge_purge = remove_stmt_from_eh_lp (stmt);
>>      gimple_remove_stmt_histograms (cfun, stmt);
>> +      if (get_copy_history (stmt) != NULL)
>> + remove_copy_history (stmt);
>>    }
>> 
>>  /* Update the iterator and re-wire the links in I->SEQ.  */
>> diff --git a/gcc/testsuite/gcc.dg/pr109071.c b/gcc/testsuite/gcc.dg/pr109071.c
>> new file mode 100644
>> index 00000000000..95ae576451e
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/pr109071.c
>> @@ -0,0 +1,43 @@
>> +/* PR tree-optimization/109071 need more context for -Warray-bounds warnings
>> +   due to code duplication from jump threading.  */  
>> +/* { dg-options "-O2 -Wall -fdiagnostics-explain-harder" } */
>> +/* { dg-additional-options "-fdiagnostics-show-line-numbers -fdiagnostics-path-format=inline-events -fdiagnostics-show-caret" } */
>> +/* { dg-enable-nn-line-numbers "" } */
>> +
>> +extern void warn(void);
>> +static inline void assign(int val, int *regs, int index)
>> +{
>> +  if (index >= 4)
>> +    warn();
>> +  *regs = val;
>> +}
>> +struct nums {int vals[4];};
>> +
>> +void sparx5_set (int *ptr, struct nums *sg, int index)
>> +{
>> +  int *val = &sg->vals[index]; /* { dg-warning "is above array bounds" } */
>> +
>> +  assign(0,    ptr, index);
>> +  assign(*val, ptr, index);
>> +}
>> +/* { dg-begin-multiline-output "" }
>> +   NN |   int *val = &sg->vals[index];
>> +      |               ~~~~~~~~^~~~~~~
>> +  'sparx5_set': events 1-2
>> +   NN |   if (index >= 4)
>> +      |      ^
>> +      |      |
>> +      |      (1) when the condition is evaluated to true
>> +......
>> +   { dg-end-multiline-output "" } */
>> +
>> +/* { dg-begin-multiline-output "" }
>> +      |               ~~~~~~~~~~~~~~~
>> +      |                       |
>> +      |                       (2) out of array bounds here
>> +   { dg-end-multiline-output "" } */
>> +
>> +/* { dg-begin-multiline-output "" }
>> +   NN | struct nums {int vals[4];};
>> +      |                  ^~~~
>> +   { dg-end-multiline-output "" } */
>> diff --git a/gcc/toplev.cc b/gcc/toplev.cc
>> index f715f977b72..e9ae55f64be 100644
>> --- a/gcc/toplev.cc
>> +++ b/gcc/toplev.cc
>> @@ -41,6 +41,7 @@ along with GCC; see the file COPYING3.  If not see
>> #include "cgraph.h"
>> #include "coverage.h"
>> #include "diagnostic.h"
>> +#include "diagnostic-copy-history.h"
>> #include "varasm.h"
>> #include "tree-inline.h"
>> #include "realmpfr.h" /* For GMP/MPFR/MPC versions, in print_version.  */
>> @@ -2381,6 +2382,8 @@ toplev::finalize (void)
>>  tree_cc_finalize ();
>>  reginfo_cc_finalize ();
>> 
>> +  copy_history_finalize ();
>> +
>>  /* save_decoded_options uses opts_obstack, so these must
>>     be cleaned up together.  */
>>  obstack_free (&opts_obstack, NULL);
>> diff --git a/gcc/tree-ssa-threadupdate.cc b/gcc/tree-ssa-threadupdate.cc
>> index fa61ba9512b..9292f0c2aa1 100644
>> --- a/gcc/tree-ssa-threadupdate.cc
>> +++ b/gcc/tree-ssa-threadupdate.cc
>> @@ -36,6 +36,7 @@ along with GCC; see the file COPYING3.  If not see
>> #include "tree-cfg.h"
>> #include "tree-vectorizer.h"
>> #include "tree-pass.h"
>> +#include "diagnostic-copy-history.h"
>> 
>> /* Given a block B, update the CFG and SSA graph to reflect redirecting
>>   one or more in-edges to B to instead reach the destination of an
>> @@ -2371,6 +2372,37 @@ back_jt_path_registry::adjust_paths_after_duplication (unsigned curr_path_num)
>>    }
>> }
>> 
>> +/* Set copy history to all the stmts in the basic block BB based on
>> +   the entry edge ENTRY and whether this basic block is on the true
>> +   path of the condition in the destination of the edge ENTRY.
>> +   Return TRUE when copy history are set, otherwise return FALSE.  */
>> +
>> +static bool
>> +set_copy_history_to_stmts_in_bb (basic_block bb, edge entry, bool is_true_path)
>> +{
>> +  /* First, get the condition statement in the destination of the
>> +     edge ENTRY.  */
>> +  basic_block cond_block = entry->dest;
>> +  gimple *cond_stmt = NULL;
>> +  gimple_stmt_iterator gsi;
>> +  gsi = gsi_last_bb (cond_block);
>> +  /* if the cond_block ends with a conditional statement, get it.  */
>> +  if (!gsi_end_p (gsi)
>> +      && gsi_stmt (gsi)
>> +      && (gimple_code (gsi_stmt (gsi)) == GIMPLE_COND))
>> +    cond_stmt = gsi_stmt (gsi);
>> +
>> +  if (!cond_stmt)
>> +    return false;
>> +
>> +  for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
>> +    set_copy_history (gsi_stmt (gsi),
>> +      gimple_location (cond_stmt),
>> +      is_true_path,
>> +      COPY_BY_THREAD_JUMP);
>> +  return true;
>> +}
>> +
>> /* Duplicates a jump-thread path of N_REGION basic blocks.
>>   The ENTRY edge is redirected to the duplicate of the region.
>> 
>> @@ -2419,6 +2451,16 @@ back_jt_path_registry::duplicate_thread_path (edge entry,
>>  copy_bbs (region, n_region, region_copy, &exit, 1, &exit_copy, loop,
>>   split_edge_bb_loc (entry), false);
>> 
>> +  /* Set the copy history for all the stmts in both original and copied
>> +     basic blocks.  The copied regions are in the true path.  */
>> +  if (flag_diagnostics_explain_harder)
>> +    for (i = 0; i < n_region; i++)
>> +      {
>> + set_copy_history_to_stmts_in_bb (region[i], entry, false);
>> + set_copy_history_to_stmts_in_bb (region_copy[i], entry, true);
>> +      }
>> +
>> +
>>  /* Fix up: copy_bbs redirects all edges pointing to copied blocks.  The
>>     following code ensures that all the edges exiting the jump-thread path are
>>     redirected back to the original code: these edges are exceptions
>> -- 
>> 2.31.1
>> 
>