Re: Ping---[V3][PATCH 2/2] Add a new warning option -Wstrict-flex-arrays.

[Richard Biener <rguenther@suse.de>]

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On Thu, 15 Dec 2022, Qing Zhao wrote:

> 
> 
> > On Dec 15, 2022, at 2:47 AM, Richard Biener <rguenther@suse.de> wrote:
> > 
> > On Wed, 14 Dec 2022, Qing Zhao wrote:
> > 
> >> Hi, Richard,
> >> 
> >> I guess that we now agreed on the following:
> >> 
> >> “ the information that we ran into a trailing array but didn't consider 
> >> it a flex array because of -fstrict-flex-arrays is always a useful information”
> >> 
> >> The only thing we didn’t decide is:
> >> 
> >> A. Amend such new information to -Warray-bounds when -fstrict-flex-arrays=N (N>0) specified.
> >> 
> >> OR
> >> 
> >> B. Issue such new information with a new warning option -Wstrict-flex-arrays when -fstrict-flex-arrays=N (N>0) specified.
> >> 
> >> My current patch implemented B. 
> > 
> > Plus it implements it to specify a different flex-array variant for
> > the extra diagnostic.
> Could you clarify a little bit on this? (Don’t quite understand…)
> > 
> >> If you think A is better, I will change the patch as A. 
> > 
> > I would tend to A since, as I said, it's useful information that
> > shouldn't be hidden and not adding an option removes odd combination
> > possibilities such as -Wno-array-bounds -Wstrict-flex-arrays.
> 
> With current implementation, the above combination will ONLY report the 
> misuse of trailing array as flex-array.  No out-of-bounds warnings 
> issued.
> 
> > In particular I find, say, -fstrict-flex-arrays=2 -Wstrict-flex-arrays=1
> > hardly useful.
> 
> The above combination will NOT happen, because there is NO level argument for -Wstrict-flex-arrays.
> 
> The only combination will be:    -fstrict-flex-arrays=N -Wstrict-flex-arrays
> 
> When N > 0, -Wstrict-flex-arrays will report any misuse of trailing arrays as flexible array per the value of N.
> > 
> > But I'm interested in other opinions.
> 
> Adding a separate -Wstrict-flex-arrays will provide users a choice to ONLY look at the mis-use of trailing arrays as flex-arrays.  Without this new option, such information will be buried into tons of out-of-bounds messges. 
> 
> I think this is the major benefit to have one separate new warning -Wstrict-flex-arrays. 
> 
> Do we need to provide the users this choice?

Ah, OK - I can see the value of auditing code this way before
enabling -fstrict-flex-arrays.

> +  if (opts->x_warn_strict_flex_arrays)
> +    if (opts->x_flag_strict_flex_arrays == 0)
> +      {
> +     opts->x_warn_strict_flex_arrays = 0;
> +     warning_at (UNKNOWN_LOCATION, 0,
> +                 "%<-Wstrict-flex-arrays%> is ignored when"
> +                 " %<-fstrict-flex-arrays%> does not present");

"is not present".

The patch is OK with that change.

Thanks and sorry for the slow process ...

Richard.

> Thanks.
> 
> Qing
> > 
> > Thanks,
> > Richard.
> > 
> >> Let me know your opinion.
> >> 
> >> thanks.
> >> 
> >> Qing
> >> 
> >> 
> >>> On Dec 14, 2022, at 4:03 AM, Richard Biener <rguenther@suse.de> wrote:
> >>> 
> >>> On Tue, 13 Dec 2022, Qing Zhao wrote:
> >>> 
> >>>> Richard, 
> >>>> 
> >>>> Do you have any decision on this one? 
> >>>> Do we need this warning option For GCC? 
> >>> 
> >>> Looking at the testcases it seems that the diagnostic amends
> >>> -Warray-bounds diagnostics for trailing but not flexible arrays?
> >>> Wouldn't it be better to generally diagnose this, so have
> >>> -Warray-bounds, with -fstrict-flex-arrays, for
> >>> 
> >>> struct X { int a[1]; };
> >>> int foo (struct X *p)
> >>> {
> >>> return p->a[1];
> >>> }
> >>> 
> >>> emit
> >>> 
> >>> warning: array subscript 1 is above array bounds ...
> >>> note: the trailing array is only a flexible array member with 
> >>> -fno-strict-flex-arrays
> >>> 
> >>> ?  Having -Wstrict-flex-arrays=N and N not agree with the
> >>> -fstrict-flex-arrays level sounds hardly useful to me but the
> >>> information that we ran into a trailing array but didn't consider
> >>> it a flex array because of -fstrict-flex-arrays is always a
> >>> useful information?
> >>> 
> >>> But maybe I misunderstood this new diagnostic?
> >>> 
> >>> Thanks,
> >>> Richard.
> >>> 
> >>> 
> >>>> thanks.
> >>>> 
> >>>> Qing
> >>>> 
> >>>>> On Dec 6, 2022, at 11:18 AM, Qing Zhao <qing.zhao@oracle.com> wrote:
> >>>>> 
> >>>>> '-Wstrict-flex-arrays'
> >>>>>   Warn about inproper usages of flexible array members according to
> >>>>>   the LEVEL of the 'strict_flex_array (LEVEL)' attribute attached to
> >>>>>   the trailing array field of a structure if it's available,
> >>>>>   otherwise according to the LEVEL of the option
> >>>>>   '-fstrict-flex-arrays=LEVEL'.
> >>>>> 
> >>>>>   This option is effective only when LEVEL is bigger than 0.
> >>>>>   Otherwise, it will be ignored with a warning.
> >>>>> 
> >>>>>   when LEVEL=1, warnings will be issued for a trailing array
> >>>>>   reference of a structure that have 2 or more elements if the
> >>>>>   trailing array is referenced as a flexible array member.
> >>>>> 
> >>>>>   when LEVEL=2, in addition to LEVEL=1, additional warnings will be
> >>>>>   issued for a trailing one-element array reference of a structure if
> >>>>>   the array is referenced as a flexible array member.
> >>>>> 
> >>>>>   when LEVEL=3, in addition to LEVEL=2, additional warnings will be
> >>>>>   issued for a trailing zero-length array reference of a structure if
> >>>>>   the array is referenced as a flexible array member.
> >>>>> 
> >>>>> gcc/ChangeLog:
> >>>>> 
> >>>>> 	* doc/invoke.texi: Document -Wstrict-flex-arrays option.
> >>>>> 	* gimple-array-bounds.cc (check_out_of_bounds_and_warn): Add two more
> >>>>> 	arguments.
> >>>>> 	(array_bounds_checker::check_array_ref): Issue warnings for
> >>>>> 	-Wstrict-flex-arrays.
> >>>>> 	* opts.cc (finish_options): Issue warning for unsupported combination
> >>>>> 	of -Wstrict_flex_arrays and -fstrict-flex-array.
> >>>>> 	* tree-vrp.cc (execute_ranger_vrp): Enable the pass when
> >>>>> 	warn_strict_flex_array is true.
> >>>>> 
> >>>>> gcc/c-family/ChangeLog:
> >>>>> 
> >>>>> 	* c.opt (Wstrict-flex-arrays): New option.
> >>>>> 
> >>>>> gcc/testsuite/ChangeLog:
> >>>>> 
> >>>>> 	* gcc.dg/Warray-bounds-flex-arrays-1.c: Update testing case with
> >>>>> 	-Wstrict-flex-arrays.
> >>>>> 	* gcc.dg/Warray-bounds-flex-arrays-2.c: Likewise.
> >>>>> 	* gcc.dg/Warray-bounds-flex-arrays-3.c: Likewise.
> >>>>> 	* gcc.dg/Warray-bounds-flex-arrays-4.c: Likewise.
> >>>>> 	* gcc.dg/Warray-bounds-flex-arrays-5.c: Likewise.
> >>>>> 	* gcc.dg/Warray-bounds-flex-arrays-6.c: Likewise.
> >>>>> 	* c-c++-common/Wstrict-flex-arrays.c: New test.
> >>>>> 	* gcc.dg/Wstrict-flex-arrays-2.c: New test.
> >>>>> 	* gcc.dg/Wstrict-flex-arrays-3.c: New test.
> >>>>> 	* gcc.dg/Wstrict-flex-arrays.c: New test.
> >>>>> ---
> >>>>> gcc/c-family/c.opt                            |   5 +
> >>>>> gcc/doc/invoke.texi                           |  27 ++++-
> >>>>> gcc/gimple-array-bounds.cc                    | 103 ++++++++++++++----
> >>>>> gcc/opts.cc                                   |   8 ++
> >>>>> .../c-c++-common/Wstrict-flex-arrays.c        |   9 ++
> >>>>> .../gcc.dg/Warray-bounds-flex-arrays-1.c      |   5 +-
> >>>>> .../gcc.dg/Warray-bounds-flex-arrays-2.c      |   6 +-
> >>>>> .../gcc.dg/Warray-bounds-flex-arrays-3.c      |   7 +-
> >>>>> .../gcc.dg/Warray-bounds-flex-arrays-4.c      |   5 +-
> >>>>> .../gcc.dg/Warray-bounds-flex-arrays-5.c      |   6 +-
> >>>>> .../gcc.dg/Warray-bounds-flex-arrays-6.c      |   7 +-
> >>>>> gcc/testsuite/gcc.dg/Wstrict-flex-arrays-2.c  |  39 +++++++
> >>>>> gcc/testsuite/gcc.dg/Wstrict-flex-arrays-3.c  |  39 +++++++
> >>>>> gcc/testsuite/gcc.dg/Wstrict-flex-arrays.c    |  39 +++++++
> >>>>> gcc/tree-vrp.cc                               |   2 +-
> >>>>> 15 files changed, 273 insertions(+), 34 deletions(-)
> >>>>> create mode 100644 gcc/testsuite/c-c++-common/Wstrict-flex-arrays.c
> >>>>> create mode 100644 gcc/testsuite/gcc.dg/Wstrict-flex-arrays-2.c
> >>>>> create mode 100644 gcc/testsuite/gcc.dg/Wstrict-flex-arrays-3.c
> >>>>> create mode 100644 gcc/testsuite/gcc.dg/Wstrict-flex-arrays.c
> >>>>> 
> >>>>> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> >>>>> index 0d0ad0a6374..33edeefd285 100644
> >>>>> --- a/gcc/c-family/c.opt
> >>>>> +++ b/gcc/c-family/c.opt
> >>>>> @@ -976,6 +976,11 @@ Wstringop-truncation
> >>>>> C ObjC C++ LTO ObjC++ Var(warn_stringop_truncation) Warning Init (1) LangEnabledBy(C ObjC C++ LTO ObjC++, Wall)
> >>>>> Warn about truncation in string manipulation functions like strncat and strncpy.
> >>>>> 
> >>>>> +Wstrict-flex-arrays
> >>>>> +C C++ Var(warn_strict_flex_arrays) Warning
> >>>>> +Warn about inproper usages of flexible array members
> >>>>> +according to the level of -fstrict-flex-arrays.
> >>>>> +
> >>>>> Wsuggest-attribute=format
> >>>>> C ObjC C++ ObjC++ Var(warn_suggest_attribute_format) Warning
> >>>>> Warn about functions which might be candidates for format attributes.
> >>>>> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> >>>>> index 726392409b6..4402b0427ef 100644
> >>>>> --- a/gcc/doc/invoke.texi
> >>>>> +++ b/gcc/doc/invoke.texi
> >>>>> @@ -398,7 +398,7 @@ Objective-C and Objective-C++ Dialects}.
> >>>>> -Wstrict-aliasing=n  -Wstrict-overflow  -Wstrict-overflow=@var{n} @gol
> >>>>> -Wstring-compare @gol
> >>>>> -Wno-stringop-overflow -Wno-stringop-overread @gol
> >>>>> --Wno-stringop-truncation @gol
> >>>>> +-Wno-stringop-truncation -Wstrict-flex-arrays @gol
> >>>>> -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}malloc@r{]} @gol
> >>>>> -Wswitch  -Wno-switch-bool  -Wswitch-default  -Wswitch-enum @gol
> >>>>> -Wno-switch-outside-range  -Wno-switch-unreachable  -Wsync-nand @gol
> >>>>> @@ -7835,6 +7835,31 @@ however, are not suitable arguments to functions that expect
> >>>>> such arrays GCC issues warnings unless it can prove that the use is
> >>>>> safe.  @xref{Common Variable Attributes}.
> >>>>> 
> >>>>> +@item -Wstrict-flex-arrays
> >>>>> +@opindex Wstrict-flex-arrays
> >>>>> +@opindex Wno-strict-flex-arrays
> >>>>> +Warn about inproper usages of flexible array members
> >>>>> +according to the @var{level} of the @code{strict_flex_array (@var{level})}
> >>>>> +attribute attached to the trailing array field of a structure if it's
> >>>>> +available, otherwise according to the @var{level} of the option
> >>>>> +@option{-fstrict-flex-arrays=@var{level}}.
> >>>>> +
> >>>>> +This option is effective only when @var{level} is bigger than 0.  Otherwise,
> >>>>> +it will be ignored with a warning.
> >>>>> +
> >>>>> +when @var{level}=1, warnings will be issued for a trailing array reference
> >>>>> +of a structure that have 2 or more elements if the trailing array is referenced
> >>>>> +as a flexible array member.
> >>>>> +
> >>>>> +when @var{level}=2, in addition to @var{level}=1, additional warnings will be
> >>>>> +issued for a trailing one-element array reference of a structure
> >>>>> +if the array is referenced as a flexible array member.
> >>>>> +
> >>>>> +when @var{level}=3, in addition to @var{level}=2, additional warnings will be
> >>>>> +issued for a trailing zero-length array reference of a structure
> >>>>> +if the array is referenced as a flexible array member.
> >>>>> +
> >>>>> +
> >>>>> @item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}cold@r{|}malloc@r{]}
> >>>>> @opindex Wsuggest-attribute=
> >>>>> @opindex Wno-suggest-attribute=
> >>>>> diff --git a/gcc/gimple-array-bounds.cc b/gcc/gimple-array-bounds.cc
> >>>>> index db3459af325..825f11331b5 100644
> >>>>> --- a/gcc/gimple-array-bounds.cc
> >>>>> +++ b/gcc/gimple-array-bounds.cc
> >>>>> @@ -252,25 +252,34 @@ get_up_bounds_for_array_ref (tree ref, tree *decl,
> >>>>> 
> >>>>> /* 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.
> >>>>> -   Issue warnings if out of bound, return TRUE if warnings are issued.  */ 
> >>>>> +   When out of bounds, set OUT_OF_BOUND to true.
> >>>>> +   Issue warnings if FOR_ARRAY_BOUND is true.
> >>>>> +   return TRUE if warnings are issued.  */
> >>>>> +
> >>>>> 
> >>>>> static bool
> >>>>> check_out_of_bounds_and_warn (location_t location, tree ref,
> >>>>> 			      tree low_sub_org, tree low_sub, tree up_sub,
> >>>>> 			      tree up_bound, tree up_bound_p1,
> >>>>> 			      const value_range *vr,
> >>>>> -			      bool ignore_off_by_one)
> >>>>> +			      bool ignore_off_by_one, bool for_array_bound,
> >>>>> +			      bool *out_of_bound)
> >>>>> {
> >>>>> tree low_bound = array_ref_low_bound (ref);
> >>>>> tree artype = TREE_TYPE (TREE_OPERAND (ref, 0));
> >>>>> 
> >>>>> bool warned = false;
> >>>>> +  *out_of_bound = false;
> >>>>> 
> >>>>> /* Empty array.  */
> >>>>> if (up_bound && tree_int_cst_equal (low_bound, up_bound_p1))
> >>>>> -    warned = warning_at (location, OPT_Warray_bounds_,
> >>>>> -			 "array subscript %E is outside array bounds of %qT",
> >>>>> -			 low_sub_org, artype);
> >>>>> +    {
> >>>>> +      *out_of_bound = true;
> >>>>> +      if (for_array_bound)
> >>>>> +	warned = warning_at (location, OPT_Warray_bounds_,
> >>>>> +			     "array subscript %E is outside array"
> >>>>> +			     " bounds of %qT", low_sub_org, artype);
> >>>>> +    }
> >>>>> 
> >>>>> if (warned)
> >>>>>   ; /* Do nothing.  */
> >>>>> @@ -283,24 +292,33 @@ check_out_of_bounds_and_warn (location_t location, tree ref,
> >>>>> 	      : tree_int_cst_le (up_bound, up_sub))
> >>>>> 	  && TREE_CODE (low_sub) == INTEGER_CST
> >>>>> 	  && tree_int_cst_le (low_sub, low_bound))
> >>>>> -	warned = warning_at (location, OPT_Warray_bounds_,
> >>>>> -			     "array subscript [%E, %E] is outside "
> >>>>> -			     "array bounds of %qT",
> >>>>> -			     low_sub, up_sub, artype);
> >>>>> +	{
> >>>>> +	  *out_of_bound = true;
> >>>>> +	  warned = warning_at (location, OPT_Warray_bounds_,
> >>>>> +			       "array subscript [%E, %E] is outside "
> >>>>> +			       "array bounds of %qT",
> >>>>> +			       low_sub, up_sub, artype);
> >>>>> +	}
> >>>>>   }
> >>>>> else if (up_bound
> >>>>> 	   && TREE_CODE (up_sub) == INTEGER_CST
> >>>>> 	   && (ignore_off_by_one
> >>>>> 	       ? !tree_int_cst_le (up_sub, up_bound_p1)
> >>>>> 	       : !tree_int_cst_le (up_sub, up_bound)))
> >>>>> -    warned = warning_at (location, OPT_Warray_bounds_,
> >>>>> -			 "array subscript %E is above array bounds of %qT",
> >>>>> -			 up_sub, artype);
> >>>>> +    {
> >>>>> +      *out_of_bound = true;
> >>>>> +      warned = warning_at (location, 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))
> >>>>> -    warned = warning_at (location, OPT_Warray_bounds_,
> >>>>> -			 "array subscript %E is below array bounds of %qT",
> >>>>> -			 low_sub, artype);
> >>>>> +    {
> >>>>> +      *out_of_bound = true;
> >>>>> +      warned = warning_at (location, OPT_Warray_bounds_,
> >>>>> +			   "array subscript %E is below array bounds of %qT",
> >>>>> +			   low_sub, artype);
> >>>>> +    }
> >>>>> return warned;
> >>>>> }
> >>>>> 
> >>>>> @@ -333,14 +351,21 @@ array_bounds_checker::check_array_ref (location_t location, tree ref,
> >>>>> 
> >>>>> tree arg = TREE_OPERAND (ref, 0);
> >>>>> const bool compref = TREE_CODE (arg) == COMPONENT_REF;
> >>>>> +  unsigned int strict_flex_array_level = flag_strict_flex_arrays;
> >>>>> 
> >>>>> if (compref)
> >>>>> -    /* Try to determine special array member type for this COMPONENT_REF.  */
> >>>>> -    sam = component_ref_sam_type (arg);
> >>>>> +    {
> >>>>> +      /* Try to determine special array member type for this COMPONENT_REF.  */
> >>>>> +      sam = component_ref_sam_type (arg);
> >>>>> +      /* Get the level of strict_flex_array for this array field.  */
> >>>>> +      tree afield_decl = TREE_OPERAND (arg, 1);
> >>>>> +      strict_flex_array_level = strict_flex_array_level_of (afield_decl);
> >>>>> +    }
> >>>>> 
> >>>>> get_up_bounds_for_array_ref (ref, &decl, &up_bound, &up_bound_p1);
> >>>>> 
> >>>>> bool warned = false;
> >>>>> +  bool out_of_bound = false;
> >>>>> 
> >>>>> tree artype = TREE_TYPE (TREE_OPERAND (ref, 0));
> >>>>> tree low_sub_org = TREE_OPERAND (ref, 1);
> >>>>> @@ -361,7 +386,8 @@ array_bounds_checker::check_array_ref (location_t location, tree ref,
> >>>>> warned = check_out_of_bounds_and_warn (location, ref,
> >>>>> 					 low_sub_org, low_sub, up_sub,
> >>>>> 					 up_bound, up_bound_p1, vr,
> >>>>> -					 ignore_off_by_one);
> >>>>> +					 ignore_off_by_one, warn_array_bounds,
> >>>>> +					 &out_of_bound);
> >>>>> 
> >>>>> 
> >>>>> if (!warned && sam == special_array_member::int_0)
> >>>>> @@ -373,19 +399,56 @@ array_bounds_checker::check_array_ref (location_t location, tree ref,
> >>>>> 			       "of an interior zero-length array %qT")),
> >>>>> 			 low_sub, artype);
> >>>>> 
> >>>>> -  if (warned)
> >>>>> +  if (warned || out_of_bound)
> >>>>>   {
> >>>>> -      if (dump_file && (dump_flags & TDF_DETAILS))
> >>>>> +      if (warned && dump_file && (dump_flags & TDF_DETAILS))
> >>>>> 	{
> >>>>> 	  fprintf (dump_file, "Array bound warning for ");
> >>>>> 	  dump_generic_expr (MSG_NOTE, TDF_SLIM, ref);
> >>>>> 	  fprintf (dump_file, "\n");
> >>>>> 	}
> >>>>> 
> >>>>> +      /* issue warnings for -Wstrict-flex-arrays according to the level of
> >>>>> +	 flag_strict_flex_arrays.  */
> >>>>> +      if (out_of_bound && warn_strict_flex_arrays)
> >>>>> +      switch (strict_flex_array_level)
> >>>>> +	{
> >>>>> +	  case 3:
> >>>>> +	    /* Issue additional warnings for trailing arrays [0].  */
> >>>>> +	    if (sam == special_array_member::trail_0)
> >>>>> +	      warned = warning_at (location, OPT_Wstrict_flex_arrays,
> >>>>> +				   "trailing array %qT should not be used as "
> >>>>> +				   "a flexible array member for level 3",
> >>>>> +				   artype);
> >>>>> +	    /* FALLTHROUGH.  */
> >>>>> +	  case 2:
> >>>>> +	    /* Issue additional warnings for trailing arrays [1].  */
> >>>>> +	    if (sam == special_array_member::trail_1)
> >>>>> +	      warned = warning_at (location, OPT_Wstrict_flex_arrays,
> >>>>> +				   "trailing array %qT should not be used as "
> >>>>> +				   "a flexible array member for level 2 and "
> >>>>> +				   "above", artype);
> >>>>> +	    /* FALLTHROUGH.  */
> >>>>> +	  case 1:
> >>>>> +	    /* Issue warnings for trailing arrays [n].  */
> >>>>> +	    if (sam == special_array_member::trail_n)
> >>>>> +	      warned = warning_at (location, OPT_Wstrict_flex_arrays,
> >>>>> +				   "trailing array %qT should not be used as "
> >>>>> +				   "a flexible array member for level 1 and "
> >>>>> +				   "above", artype);
> >>>>> +	    break;
> >>>>> +	  case 0:
> >>>>> +	    /* Do nothing.  */
> >>>>> +	    break;
> >>>>> +	  default:
> >>>>> +	    gcc_unreachable ();
> >>>>> +	}
> >>>>> +
> >>>>>     /* Avoid more warnings when checking more significant subscripts
> >>>>> 	 of the same expression.  */
> >>>>>     ref = TREE_OPERAND (ref, 0);
> >>>>>     suppress_warning (ref, OPT_Warray_bounds_);
> >>>>> +      suppress_warning (ref, OPT_Wstrict_flex_arrays);
> >>>>> 
> >>>>>     if (decl)
> >>>>> 	ref = decl;
> >>>>> diff --git a/gcc/opts.cc b/gcc/opts.cc
> >>>>> index 73fc97756e4..8db53ad6c77 100644
> >>>>> --- a/gcc/opts.cc
> >>>>> +++ b/gcc/opts.cc
> >>>>> @@ -1411,6 +1411,14 @@ finish_options (struct gcc_options *opts, struct gcc_options *opts_set,
> >>>>>     opts->x_profile_flag = 0;
> >>>>>   }
> >>>>> 
> >>>>> +  if (opts->x_warn_strict_flex_arrays)
> >>>>> +    if (opts->x_flag_strict_flex_arrays == 0)
> >>>>> +      {
> >>>>> +	opts->x_warn_strict_flex_arrays = 0;
> >>>>> +	warning_at (UNKNOWN_LOCATION, 0,
> >>>>> +		    "%<-Wstrict-flex-arrays%> is ignored when"
> >>>>> +		    " %<-fstrict-flex-arrays%> does not present");
> >>>>> +      }
> >>>>> 
> >>>>> diagnose_options (opts, opts_set, loc);
> >>>>> }
> >>>>> diff --git a/gcc/testsuite/c-c++-common/Wstrict-flex-arrays.c b/gcc/testsuite/c-c++-common/Wstrict-flex-arrays.c
> >>>>> new file mode 100644
> >>>>> index 00000000000..72b4b7c6406
> >>>>> --- /dev/null
> >>>>> +++ b/gcc/testsuite/c-c++-common/Wstrict-flex-arrays.c
> >>>>> @@ -0,0 +1,9 @@
> >>>>> +/* Test the usage of option -Wstrict-flex-arrays.  */
> >>>>> +/* { dg-do compile } */
> >>>>> +/* { dg-options "-O2 -Wstrict-flex-arrays" } */
> >>>>> +
> >>>>> +int main(int argc, char *argv[])
> >>>>> +{
> >>>>> +    return 0;
> >>>>> +}
> >>>>> +/* { dg-warning "is ignored when \'-fstrict-flex-arrays\' does not present" "" { target *-*-* } 0 } */
> >>>>> diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-1.c b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-1.c
> >>>>> index d36ba4d86cb..65c9fec43af 100644
> >>>>> --- a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-1.c
> >>>>> +++ b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-1.c
> >>>>> @@ -1,6 +1,6 @@
> >>>>> -/* Test -fstrict-flex-arrays + -Warray-bounds.  */
> >>>>> +/* Test -fstrict-flex-arrays + -Warray-bounds + -Wstrict-flex-arrays.  */
> >>>>> /* { dg-do compile} */
> >>>>> -/* { dg-options "-O2 -fstrict-flex-arrays=1 -Warray-bounds" } */
> >>>>> +/* { dg-options "-O2 -Wstrict-flex-arrays -fstrict-flex-arrays=1 -Warray-bounds" } */
> >>>>> 
> >>>>> struct trailing_array_1 {
> >>>>>   int a;
> >>>>> @@ -32,6 +32,7 @@ void __attribute__((__noinline__)) stuff(
> >>>>>   struct trailing_array_4 *trailing_flex)
> >>>>> {
> >>>>>   normal->c[5] = 5; 	/*{ dg-warning "array subscript 5 is above array bounds of" } */
> >>>>> +    			/*{ dg-warning "should not be used as a flexible array member for level 1 and above" "" { target *-*-* } .-1 } */
> >>>>>   trailing_1->c[2] = 2; /* { dg-bogus "array subscript " } */
> >>>>>   trailing_0->c[1] = 1; /* { dg-bogus "array subscript " } */
> >>>>>   trailing_flex->c[10] = 10; /* { dg-bogus "array subscript " } */
> >>>>> diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-2.c b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-2.c
> >>>>> index f63206e1948..2b5a895c598 100644
> >>>>> --- a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-2.c
> >>>>> +++ b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-2.c
> >>>>> @@ -1,6 +1,6 @@
> >>>>> -/* Test -fstrict-flex-arrays + -Warray-bounds.  */
> >>>>> +/* Test -fstrict-flex-arrays + -Warray-bounds + -Wstrict-flex-arrays.  */
> >>>>> /* { dg-do compile } */
> >>>>> -/* { dg-options "-O2 -fstrict-flex-arrays=2 -Warray-bounds" } */
> >>>>> +/* { dg-options "-O2 -Wstrict-flex-arrays -fstrict-flex-arrays=2 -Warray-bounds" } */
> >>>>> 
> >>>>> struct trailing_array_1 {
> >>>>>   int a;
> >>>>> @@ -32,7 +32,9 @@ void __attribute__((__noinline__)) stuff(
> >>>>>   struct trailing_array_4 *trailing_flex)
> >>>>> {
> >>>>>   normal->c[5] = 5; 	/*{ dg-warning "array subscript 5 is above array bounds of" } */
> >>>>> +    			/*{ dg-warning "should not be used as a flexible array member for level 1 and above" "" { target *-*-* } .-1 } */
> >>>>>   trailing_1->c[2] = 2; /* { dg-warning "array subscript 2 is above array bounds of"  } */
> >>>>> +    			  /* { dg-warning "should not be used as a flexible array member for level 2 and above" "" { target *-*-* } .-1 } */
> >>>>>   trailing_0->c[1] = 1; /* { dg-bogus "array subscript " } */
> >>>>>   trailing_flex->c[10] = 10; /* { dg-bogus "array subscript " } */
> >>>>> 
> >>>>> diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-3.c b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-3.c
> >>>>> index e3273714e8b..25b903f2615 100644
> >>>>> --- a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-3.c
> >>>>> +++ b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-3.c
> >>>>> @@ -1,6 +1,6 @@
> >>>>> -/* Test -fstrict-flex-arrays + -Warray-bounds.  */
> >>>>> +/* Test -fstrict-flex-arrays + -Warray-bounds + -Wstrict-flex-arrays.  */
> >>>>> /* { dg-do compile } */
> >>>>> -/* { dg-options "-O2 -fstrict-flex-arrays=3 -Warray-bounds" } */
> >>>>> +/* { dg-options "-O2 -Wstrict-flex-arrays -fstrict-flex-arrays=3 -Warray-bounds" } */
> >>>>> 
> >>>>> struct trailing_array_1 {
> >>>>>   int a;
> >>>>> @@ -32,8 +32,11 @@ void __attribute__((__noinline__)) stuff(
> >>>>>   struct trailing_array_4 *trailing_flex)
> >>>>> {
> >>>>>   normal->c[5] = 5; 	/*{ dg-warning "array subscript 5 is above array bounds of" } */ 
> >>>>> +    			/*{ dg-warning "should not be used as a flexible array member for level 1 and above" "" { target *-*-* } .-1 } */
> >>>>>   trailing_1->c[2] = 2; /*{ dg-warning "array subscript 2 is above array bounds of" } */ 
> >>>>> +    			  /* { dg-warning "should not be used as a flexible array member for level 2 and above" "" { target *-*-* } .-1 } */
> >>>>>   trailing_0->c[1] = 1; /*{ dg-warning "array subscript 1 is outside array bounds of" } */ 
> >>>>> +    			  /* { dg-warning "should not be used as a flexible array member for level 3" "" { target *-*-* } .-1 } */
> >>>>>   trailing_flex->c[10] = 10; /* { dg-bogus "array subscript" } */
> >>>>> 
> >>>>> }
> >>>>> diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-4.c b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-4.c
> >>>>> index cabaea77dc2..5fc500a19ca 100644
> >>>>> --- a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-4.c
> >>>>> +++ b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-4.c
> >>>>> @@ -1,6 +1,6 @@
> >>>>> -/* Test -fstrict-flex-arrays + -Warray-bounds=2.  */
> >>>>> +/* Test -fstrict-flex-arrays + -Warray-bounds=2 + -Wstrict-flex-arrays.  */
> >>>>> /* { dg-do compile } */
> >>>>> -/* { dg-options "-O2 -fstrict-flex-arrays=1 -Warray-bounds=2" } */
> >>>>> +/* { dg-options "-O2 -Wstrict-flex-arrays -fstrict-flex-arrays=1 -Warray-bounds=2" } */
> >>>>> 
> >>>>> struct trailing_array_1 {
> >>>>>   int a;
> >>>>> @@ -32,6 +32,7 @@ void __attribute__((__noinline__)) stuff(
> >>>>>   struct trailing_array_4 *trailing_flex)
> >>>>> {
> >>>>>   normal->c[5] = 5; 	/*{ dg-warning "array subscript 5 is above array bounds of" } */
> >>>>> +    			/*{ dg-warning "should not be used as a flexible array member for level 1 and above" "" { target *-*-* } .-1 } */
> >>>>>   trailing_1->c[2] = 2; /* { dg-bogus "array subscript " } */
> >>>>>   trailing_0->c[1] = 1; /* { dg-bogus "array subscript " } */
> >>>>>   trailing_flex->c[10] = 10; /* { dg-bogus "array subscript " } */
> >>>>> diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-5.c b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-5.c
> >>>>> index 8b7db6e4f39..30bb4ca8832 100644
> >>>>> --- a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-5.c
> >>>>> +++ b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-5.c
> >>>>> @@ -1,6 +1,6 @@
> >>>>> -/* Test -fstrict-flex-arrays + -Warray-bounds=2.  */
> >>>>> +/* Test -fstrict-flex-arrays + -Warray-bounds=2 + -Wstrict-flex-arrays.  */
> >>>>> /* { dg-do compile } */
> >>>>> -/* { dg-options "-O2 -fstrict-flex-arrays=2 -Warray-bounds=2" } */
> >>>>> +/* { dg-options "-O2 -Wstrict-flex-arrays -fstrict-flex-arrays=2 -Warray-bounds=2" } */
> >>>>> 
> >>>>> struct trailing_array_1 {
> >>>>>   int a;
> >>>>> @@ -32,7 +32,9 @@ void __attribute__((__noinline__)) stuff(
> >>>>>   struct trailing_array_4 *trailing_flex)
> >>>>> {
> >>>>>   normal->c[5] = 5;   /*{ dg-warning "array subscript 5 is above array bounds of" } */
> >>>>> +    			/*{ dg-warning "should not be used as a flexible array member for level 1 and above" "" { target *-*-* } .-1 } */
> >>>>>   trailing_1->c[2] = 2; /*{ dg-warning "array subscript 2 is above array bounds of" } */
> >>>>> +    			  /* { dg-warning "should not be used as a flexible array member for level 2 and above" "" { target *-*-* } .-1 } */
> >>>>>   trailing_0->c[1] = 1; /* { dg-bogus "array subscript " } */
> >>>>>   trailing_flex->c[10] = 10; /* { dg-bogus "array subscript " } */
> >>>>> 
> >>>>> diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-6.c b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-6.c
> >>>>> index 035bf481396..e847a44516e 100644
> >>>>> --- a/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-6.c
> >>>>> +++ b/gcc/testsuite/gcc.dg/Warray-bounds-flex-arrays-6.c
> >>>>> @@ -1,6 +1,6 @@
> >>>>> -/* Test -fstrict-flex-arrays + -Warray-bounds=2.  */
> >>>>> +/* Test -fstrict-flex-arrays + -Warray-bounds=2 + -Wstrict-flex-arrays.  */
> >>>>> /* { dg-do compile } */
> >>>>> -/* { dg-options "-O2 -fstrict-flex-arrays=3 -Warray-bounds=2" } */
> >>>>> +/* { dg-options "-O2 -Wstrict-flex-arrays -fstrict-flex-arrays=3 -Warray-bounds=2" } */
> >>>>> 
> >>>>> struct trailing_array_1 {
> >>>>>   int a;
> >>>>> @@ -32,8 +32,11 @@ void __attribute__((__noinline__)) stuff(
> >>>>>   struct trailing_array_4 *trailing_flex)
> >>>>> {
> >>>>>   normal->c[5] = 5; 	/*{ dg-warning "array subscript 5 is above array bounds of" } */ 
> >>>>> +    			/*{ dg-warning "should not be used as a flexible array member for level 1 and above" "" { target *-*-* } .-1 } */
> >>>>>   trailing_1->c[2] = 2; /*{ dg-warning "array subscript 2 is above array bounds of" } */
> >>>>> +    			  /* { dg-warning "should not be used as a flexible array member for level 2 and above" "" { target *-*-* } .-1 } */
> >>>>>   trailing_0->c[1] = 1; /*{ dg-warning "array subscript 1 is outside array bounds of" } */
> >>>>> +    			  /* { dg-warning "should not be used as a flexible array member for level 3" "" { target *-*-* } .-1 } */
> >>>>>   trailing_flex->c[10] = 10; /* { dg-bogus "array subscript " } */
> >>>>> 
> >>>>> }
> >>>>> diff --git a/gcc/testsuite/gcc.dg/Wstrict-flex-arrays-2.c b/gcc/testsuite/gcc.dg/Wstrict-flex-arrays-2.c
> >>>>> new file mode 100644
> >>>>> index 00000000000..2e241f96208
> >>>>> --- /dev/null
> >>>>> +++ b/gcc/testsuite/gcc.dg/Wstrict-flex-arrays-2.c
> >>>>> @@ -0,0 +1,39 @@
> >>>>> +/* Test -Wstrict-flex-arrays.  */
> >>>>> +/* { dg-do compile } */
> >>>>> +/* { dg-options "-O2 -Wstrict-flex-arrays -fstrict-flex-arrays=2" } */
> >>>>> +
> >>>>> +struct trailing_array_1 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[4]; 
> >>>>> +};
> >>>>> +
> >>>>> +struct trailing_array_2 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[1]; 
> >>>>> +};
> >>>>> +
> >>>>> +struct trailing_array_3 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[0];
> >>>>> +};
> >>>>> +struct trailing_array_4 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[];
> >>>>> +};
> >>>>> +
> >>>>> +void __attribute__((__noinline__)) stuff(
> >>>>> +    struct trailing_array_1 *normal,
> >>>>> +    struct trailing_array_2 *trailing_1,
> >>>>> +    struct trailing_array_3 *trailing_0,
> >>>>> +    struct trailing_array_4 *trailing_flex)
> >>>>> +{
> >>>>> +    normal->c[5] = 5; 	/*{ dg-warning "should not be used as a flexible array member for level 1 and above" } */
> >>>>> +    trailing_1->c[2] = 2; /* { dg-warning "should not be used as a flexible array member for level 2 and above" } */
> >>>>> +    trailing_0->c[1] = 1; /* { dg-bogus "should not be used as a flexible array member for level 2 and above" } */
> >>>>> +    trailing_flex->c[10] = 10; /* { dg-bogus "should not be used as a flexible array member for level 2 and above" } */
> >>>>> +
> >>>>> +}
> >>>>> diff --git a/gcc/testsuite/gcc.dg/Wstrict-flex-arrays-3.c b/gcc/testsuite/gcc.dg/Wstrict-flex-arrays-3.c
> >>>>> new file mode 100644
> >>>>> index 00000000000..97eb65ba0a9
> >>>>> --- /dev/null
> >>>>> +++ b/gcc/testsuite/gcc.dg/Wstrict-flex-arrays-3.c
> >>>>> @@ -0,0 +1,39 @@
> >>>>> +/* Test -Wstrict-flex-arrays.  */
> >>>>> +/* { dg-do compile } */
> >>>>> +/* { dg-options "-O2 -Wstrict-flex-arrays -fstrict-flex-arrays=3" } */
> >>>>> +
> >>>>> +struct trailing_array_1 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[4]; 
> >>>>> +};
> >>>>> +
> >>>>> +struct trailing_array_2 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[1]; 
> >>>>> +};
> >>>>> +
> >>>>> +struct trailing_array_3 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[0];
> >>>>> +};
> >>>>> +struct trailing_array_4 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[];
> >>>>> +};
> >>>>> +
> >>>>> +void __attribute__((__noinline__)) stuff(
> >>>>> +    struct trailing_array_1 *normal,
> >>>>> +    struct trailing_array_2 *trailing_1,
> >>>>> +    struct trailing_array_3 *trailing_0,
> >>>>> +    struct trailing_array_4 *trailing_flex)
> >>>>> +{
> >>>>> +    normal->c[5] = 5; 	/*{ dg-warning "should not be used as a flexible array member for level 1 and above" } */
> >>>>> +    trailing_1->c[2] = 2; /* { dg-warning "should not be used as a flexible array member for level 2 and above" } */
> >>>>> +    trailing_0->c[1] = 1; /* { dg-warning "should not be used as a flexible array member for level 3" } */
> >>>>> +    trailing_flex->c[10] = 10; /* { dg-bogus "should not be used as a flexible array member for level 3" } */
> >>>>> +
> >>>>> +}
> >>>>> diff --git a/gcc/testsuite/gcc.dg/Wstrict-flex-arrays.c b/gcc/testsuite/gcc.dg/Wstrict-flex-arrays.c
> >>>>> new file mode 100644
> >>>>> index 00000000000..110fdc72778
> >>>>> --- /dev/null
> >>>>> +++ b/gcc/testsuite/gcc.dg/Wstrict-flex-arrays.c
> >>>>> @@ -0,0 +1,39 @@
> >>>>> +/* Test -Wstrict-flex-arrays.  */
> >>>>> +/* { dg-do compile } */
> >>>>> +/* { dg-options "-O2 -Wstrict-flex-arrays -fstrict-flex-arrays=1" } */
> >>>>> +
> >>>>> +struct trailing_array_1 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[4]; 
> >>>>> +};
> >>>>> +
> >>>>> +struct trailing_array_2 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[1]; 
> >>>>> +};
> >>>>> +
> >>>>> +struct trailing_array_3 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[0];
> >>>>> +};
> >>>>> +struct trailing_array_4 {
> >>>>> +    int a;
> >>>>> +    int b;
> >>>>> +    int c[];
> >>>>> +};
> >>>>> +
> >>>>> +void __attribute__((__noinline__)) stuff(
> >>>>> +    struct trailing_array_1 *normal,
> >>>>> +    struct trailing_array_2 *trailing_1,
> >>>>> +    struct trailing_array_3 *trailing_0,
> >>>>> +    struct trailing_array_4 *trailing_flex)
> >>>>> +{
> >>>>> +    normal->c[5] = 5; 	/*{ dg-warning "should not be used as a flexible array member for level 1 and above" } */
> >>>>> +    trailing_1->c[2] = 2; /* { dg-bogus "should not be used as a flexible array member for level 1 and above" } */
> >>>>> +    trailing_0->c[1] = 1; /* { dg-bogus "should not be used as a flexible array member for level 1 and above" } */
> >>>>> +    trailing_flex->c[10] = 10; /* { dg-bogus "should not be used as a flexible array member for level 1 and above" } */
> >>>>> +
> >>>>> +}
> >>>>> diff --git a/gcc/tree-vrp.cc b/gcc/tree-vrp.cc
> >>>>> index 3846dc1d849..e6c6c5a301d 100644
> >>>>> --- a/gcc/tree-vrp.cc
> >>>>> +++ b/gcc/tree-vrp.cc
> >>>>> @@ -1087,7 +1087,7 @@ execute_ranger_vrp (struct function *fun, bool warn_array_bounds_p,
> >>>>> if (dump_file && (dump_flags & TDF_DETAILS))
> >>>>>   ranger->dump (dump_file);
> >>>>> 
> >>>>> -  if (warn_array_bounds && warn_array_bounds_p)
> >>>>> +  if ((warn_array_bounds || warn_strict_flex_arrays) && warn_array_bounds_p)
> >>>>>   {
> >>>>>     // Set all edges as executable, except those ranger says aren't.
> >>>>>     int non_exec_flag = ranger->non_executable_edge_flag;
> >>>>> -- 
> >>>>> 2.31.1
> >>>>> 
> >>>> 
> >>>> 
> >>> 
> >>> -- 
> >>> Richard Biener <rguenther@suse.de>
> >>> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
> >>> Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
> >>> HRB 36809 (AG Nuernberg)
> >> 
> >> 
> > 
> > -- 
> > Richard Biener <rguenther@suse.de>
> > SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
> > Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
> > HRB 36809 (AG Nuernberg)
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)