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

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

> 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?

Yes.

> 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

This is good too.
My only concern with doing this is, the default warning messages of -Warray-bounds would be different than
the current ones, will this have any impact on the current users?

> 
> ?  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?

-Wstrict-flex-arrays does NOT have the argument “N”.  Its level will be consistent with the level “N” of the corresponding
-fstrict-flex-array=N.  
-Wstrict-flex-arrays option is only valid when -fstrict-flex-arrays is present, it will report any misuse of treating trailing array 
as flexible array at the LEVEL of -fstrict-flex-arrays. 

Let me know if it is still not very clear.

thanks.

Qing
> 
> 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)