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A. add the following to clarify the relationship between -Warray-bounds
and the LEVEL of -fstrict-flex-array:
By default, the trailing array of a structure will be treated as a
flexible array member by '-Warray-bounds' or '-Warray-bounds=N' if
it is declared as either a flexible array member per C99 standard
onwards ('[]'), a GCC zero-length array extension ('[0]'), or an
one-element array ('[1]'). As a result, out of bounds subscripts
or offsets into zero-length arrays or one-element arrays are not
warned by default.
You can add the option '-fstrict-flex-arrays' or
'-fstrict-flex-arrays=LEVEL' to control how this option treat
trailing array of a structure as a flexible array member.
when LEVEL<=1, no change to the default behavior.
when LEVEL=2, additional warnings will be issued for out of bounds
subscripts or offsets into one-element arrays;
when LEVEL=3, in addition to LEVEL=2, additional warnings will be
issued for out of bounds subscripts or offsets into zero-length
arrays.
B. change -Warray-bounds=2 to exclude its control on how to treat
trailing arrays as flexible array members:
'-Warray-bounds=2'
This warning level also warns about the intermediate results
of pointer arithmetic that may yield out of bounds values.
This warning level may give a larger number of false positives
and is deactivated by default.
gcc/ChangeLog:
* attribs.cc (strict_flex_array_level_of): New function.
* attribs.h (strict_flex_array_level_of): Prototype for new function.
* doc/invoke.texi: Update -Warray-bounds by specifying the impact from
-fstrict-flex-arrays. Also update -Warray-bounds=2 by eliminating its
impact on treating trailing arrays as flexible array members.
* gimple-array-bounds.cc (get_up_bounds_for_array_ref): New function.
(check_out_of_bounds_and_warn): New function.
(array_bounds_checker::check_array_ref): Update with call to the above
new functions.
* tree.cc (array_ref_flexible_size_p): Add one new argument.
(component_ref_sam_type): New function.
(component_ref_size): Control with level of strict-flex-array.
* tree.h (array_ref_flexible_size_p): Update prototype.
(enum struct special_array_member): Add two new enum values.
(component_ref_sam_type): New prototype.
gcc/c/ChangeLog:
* c-decl.cc (is_flexible_array_member_p): Call new function
strict_flex_array_level_of.
gcc/testsuite/ChangeLog:
* gcc.dg/Warray-bounds-11.c: Update warnings for -Warray-bounds=2.
* gcc.dg/Warray-bounds-flex-arrays-1.c: New test.
* gcc.dg/Warray-bounds-flex-arrays-2.c: New test.
* gcc.dg/Warray-bounds-flex-arrays-3.c: New test.
* gcc.dg/Warray-bounds-flex-arrays-4.c: New test.
* gcc.dg/Warray-bounds-flex-arrays-5.c: New test.
* gcc.dg/Warray-bounds-flex-arrays-6.c: New test.
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