On Tue, Oct 31, 2023 at 8:05 PM Martin Uecker <uec...@tugraz.at> wrote:
>
>
> This is a revised part of previously posted patch which
> I split up. C FE changes which another false positive
> were already merged, but I still need approval for this
> middle-end change. It would be nice to get this in,
> because it fixes some rather annoying (for me atleast)
> false positive warnings with no easy workaround.
>
> In the following example,
>
> int foo(int n, float matrix[n], float opt[n]);
> foo(n, matrix, NULL);
>
> GCC warns about NULL iff n > 0. This is problematic for
> several reasons:
> 1. It causes false positives (and I turn off -Wnonnull
> in one of my projects for this reason)
> 2. It is inconsistent with regular arrays where there is no
> warning in this case.
> 3. The size parameter is sometimes shared (as in this example)
> so passing zero to avoid the warning is only possible by
> making the code more complex.
> 4. Passing zero as a workaround is technically UB.
>
>
> (The original author of the warning code, Martin S seemed to
> agree with this change according to this discussion in Bugzilla.)
OK.
>
>
> Reduce false positives for -Wnonnull for VLA parameters [PR98541]
>
> This patch limits the warning about NULL arguments to VLA
> parameters declared [static n].
>
> PR c/98541
>
> gcc/
> * gimple-ssa-warn-access.cc
> (pass_waccess::maybe_check_access_sizes): For VLA bounds
> in parameters, only warn about null pointers with 'static'.
>
> gcc/testsuite:
> * gcc.dg/Wnonnull-4: Adapt test.
> * gcc.dg/Wstringop-overflow-40.c: Adapt test.
>
> diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
> index e439d1b9b68..8b734295f09 100644
> --- a/gcc/gimple-ssa-warn-access.cc
> +++ b/gcc/gimple-ssa-warn-access.cc
> @@ -3477,27 +3477,14 @@ pass_waccess::maybe_check_access_sizes (rdwr_map
> *rwm, tree fndecl, tree fntype,
>
> if (integer_zerop (ptr))
> {
> - if (sizidx >= 0 && tree_int_cst_sgn (sizrng[0]) > 0)
> + if (!access.second.internal_p
> + && sizidx >= 0 && tree_int_cst_sgn (sizrng[0]) > 0)
> {
> /* Warn about null pointers with positive sizes. This is
> different from also declaring the pointer argument with
> attribute nonnull when the function accepts null pointers
> only when the corresponding size is zero. */
> - if (access.second.internal_p)
> - {
> - const std::string argtypestr
> - = access.second.array_as_string (ptrtype);
> -
> - if (warning_at (loc, OPT_Wnonnull,
> - "argument %i of variable length "
> - "array %s is null but "
> - "the corresponding bound argument "
> - "%i value is %s",
> - ptridx + 1, argtypestr.c_str (),
> - sizidx + 1, sizstr))
> - arg_warned = OPT_Wnonnull;
> - }
> - else if (warning_at (loc, OPT_Wnonnull,
> + if (warning_at (loc, OPT_Wnonnull,
> "argument %i is null but "
> "the corresponding size argument "
> "%i value is %s",
> diff --git a/gcc/testsuite/gcc.dg/Wnonnull-4.c
> b/gcc/testsuite/gcc.dg/Wnonnull-4.c
> index 2c1c45a9856..1f14fbba45d 100644
> --- a/gcc/testsuite/gcc.dg/Wnonnull-4.c
> +++ b/gcc/testsuite/gcc.dg/Wnonnull-4.c
> @@ -27,9 +27,9 @@ void test_fca_n (int r_m1)
> T ( 0);
>
> // Verify positive bounds.
> - T ( 1); // { dg-warning "argument 2 of variable length array
> 'char\\\[n]' is null but the corresponding bound argument 1 value is 1" }
> - T ( 9); // { dg-warning "argument 2 of variable length array
> 'char\\\[n]' is null but the corresponding bound argument 1 value is 9" }
> - T (max); // { dg-warning "argument 2 of variable length array
> 'char\\\[n]' is null but the corresponding bound argument 1 value is \\d+" }
> + T ( 1); // { dg-bogus "argument 2 of variable length array
> 'char\\\[n]' is null but the corresponding bound argument 1 value is 1" }
> + T ( 9); // { dg-bogus "argument 2 of variable length array
> 'char\\\[n]' is null but the corresponding bound argument 1 value is 9" }
> + T (max); // { dg-bogus "argument 2 of variable length array
> 'char\\\[n]' is null but the corresponding bound argument 1 value is \\d+" }
> }
>
>
> @@ -55,9 +55,9 @@ void test_fsa_x_n (int r_m1)
> T ( 0);
>
> // Verify positive bounds.
> - T ( 1); // { dg-warning "argument 2 of variable length array
> 'short int\\\[]\\\[n]' is null but the corresponding bound argument 1 value
> is 1" }
> - T ( 9); // { dg-warning "argument 2 of variable length array
> 'short int\\\[]\\\[n]' is null but the corresponding bound argument 1 value
> is 9" }
> - T (max); // { dg-warning "argument 2 of variable length array
> 'short int\\\[]\\\[n]' is null but the corresponding bound argument 1 value
> is \\d+" }
> + T ( 1); // { dg-bogus "argument 2 of variable length array
> 'short int\\\[]\\\[n]' is null but the corresponding bound argument 1 value
> is 1" }
> + T ( 9); // { dg-bogus "argument 2 of variable length array
> 'short int\\\[]\\\[n]' is null but the corresponding bound argument 1 value
> is 9" }
> + T (max); // { dg-bogus "argument 2 of variable length array
> 'short int\\\[]\\\[n]' is null but the corresponding bound argument 1 value
> is \\d+" }
> }
>
>
> @@ -83,9 +83,9 @@ void test_fia_1_n (int r_m1)
> T ( 0);
>
> // Verify positive bounds.
> - T ( 1); // { dg-warning "argument 2 of variable length array
> 'int\\\[1]\\\[n]' is null but the corresponding bound argument 1 value is 1" }
> - T ( 9); // { dg-warning "argument 2 of variable length array
> 'int\\\[1]\\\[n]' is null but the corresponding bound argument 1 value is 9" }
> - T (max); // { dg-warning "argument 2 of variable length array
> 'int\\\[1]\\\[n]' is null but the corresponding bound argument 1 value is
> \\d+" }
> + T ( 1); // { dg-bogus "argument 2 of variable length array
> 'int\\\[1]\\\[n]' is null but the corresponding bound argument 1 value is 1" }
> + T ( 9); // { dg-bogus "argument 2 of variable length array
> 'int\\\[1]\\\[n]' is null but the corresponding bound argument 1 value is 9" }
> + T (max); // { dg-bogus "argument 2 of variable length array
> 'int\\\[1]\\\[n]' is null but the corresponding bound argument 1 value is
> \\d+" }
> }
>
>
> @@ -111,9 +111,9 @@ void test_fla_3_n (int r_m1)
> T ( 0);
>
> // Verify positive bounds.
> - T ( 1); // { dg-warning "argument 2 of variable length array
> 'long int\\\[3]\\\[n]' is null but the corresponding bound argument 1 value
> is 1" }
> - T ( 9); // { dg-warning "argument 2 of variable length array
> 'long int\\\[3]\\\[n]' is null but the corresponding bound argument 1 value
> is 9" }
> - T (max); // { dg-warning "argument 2 of variable length array
> 'long int\\\[3]\\\[n]' is null but the corresponding bound argument 1 value
> is \\d+" }
> + T ( 1); // { dg-bogus "argument 2 of variable length array 'long
> int\\\[3]\\\[n]' is null but the corresponding bound argument 1 value is 1" }
> + T ( 9); // { dg-bogus "argument 2 of variable length array 'long
> int\\\[3]\\\[n]' is null but the corresponding bound argument 1 value is 9" }
> + T (max); // { dg-bogus "argument 2 of variable length array 'long
> int\\\[3]\\\[n]' is null but the corresponding bound argument 1 value is
> \\d+" }
> }
>
>
> @@ -139,9 +139,9 @@ void test_fda_n_5 (int r_m1)
> T ( 0);
>
> // Verify positive bounds.
> - T ( 1); // { dg-warning "argument 2 of variable length array
> 'double\\\[n]\\\[5]' is null but the corresponding bound argument 1 value is
> 1" }
> - T ( 9); // { dg-warning "argument 2 of variable length array
> 'double\\\[n]\\\[5]' is null but the corresponding bound argument 1 value is
> 9" }
> - T (max); // { dg-warning "argument 2 of variable length array
> 'double\\\[n]\\\[5]' is null but the corresponding bound argument 1 value is
> \\d+" }
> + T ( 1); // { dg-bogus "argument 2 of variable length array
> 'double\\\[n]\\\[5]' is null but the corresponding bound argument 1 value is
> 1" }
> + T ( 9); // { dg-bogus "argument 2 of variable length array
> 'double\\\[n]\\\[5]' is null but the corresponding bound argument 1 value is
> 9" }
> + T (max); // { dg-bogus "argument 2 of variable length array
> 'double\\\[n]\\\[5]' is null but the corresponding bound argument 1 value is
> \\d+" }
> }
>
>
> @@ -167,7 +167,7 @@ void test_fca_n_n (int r_m1)
> T ( 0);
>
> // Verify positive bounds.
> - T ( 1); // { dg-warning "argument 2 of variable length array
> 'char\\\[n]\\\[n]' is null but the corresponding bound argument 1 value is 1"
> }
> - T ( 9); // { dg-warning "argument 2 of variable length array
> 'char\\\[n]\\\[n]' is null but the corresponding bound argument 1 value is 9"
> }
> - T (max); // { dg-warning "argument 2 of variable length array
> 'char\\\[n]\\\[n]' is null but the corresponding bound argument 1 value is
> \\d+" }
> + T ( 1); // { dg-bogus "argument 2 of variable length array
> 'char\\\[n]\\\[n]' is null but the corresponding bound argument 1 value is 1"
> }
> + T ( 9); // { dg-bogus "argument 2 of variable length array
> 'char\\\[n]\\\[n]' is null but the corresponding bound argument 1 value is 9"
> }
> + T (max); // { dg-bogus "argument 2 of variable length array
> 'char\\\[n]\\\[n]' is null but the corresponding bound argument 1 value is
> \\d+" }
> }
> diff --git a/gcc/testsuite/gcc.dg/Wstringop-overflow-40.c
> b/gcc/testsuite/gcc.dg/Wstringop-overflow-40.c
> index 386c92dc7a8..9e0ad1f3aff 100644
> --- a/gcc/testsuite/gcc.dg/Wstringop-overflow-40.c
> +++ b/gcc/testsuite/gcc.dg/Wstringop-overflow-40.c
> @@ -11,6 +11,7 @@ void fxa2 (int16_t[2]) __attribute__ ((nonnull));
> void fas2 (int16_t[static 2]);
>
> void fvla (unsigned n, int16_t[n]);
> +void fvlaS (unsigned n, int16_t[static n]);
>
> void test_array_1_dim (void)
> {
> @@ -33,7 +34,8 @@ void test_array_1_dim (void)
> fas2 (a1); // { dg-warning "'fas2' accessing 4 bytes in a
> region of size 2 " }
> fas2 (&i); // { dg-warning "'fas2' accessing 4 bytes in a
> region of size 2 " }
>
> - fvla (1, 0); // { dg-warning "\\\[-Wnonnull" }
> + fvla (1, 0);
> + fvlaS (1, 0); // { dg-warning "\\\[-Wnonnull" }
> fvla (1, &i);
> fvla (2, a2);
> fvla (2, a1); // { dg-warning "'fvla' accessing 4 bytes in a
> region of size 2 " }
> @@ -47,6 +49,7 @@ void fxac2 (const int16_t[2]) __attribute__ ((nonnull));
> void facs2 (const int16_t[static 2]);
>
> void fvlac (unsigned n, const int16_t[n]);
> +void fvlacS (unsigned n, const int16_t[static n]);
>
> void test_const_array_1_dim (void)
> {
> @@ -69,7 +72,8 @@ void test_const_array_1_dim (void)
> facs2 (a1); // { dg-warning "'facs2' reading 4 bytes from
> a region of size 2 " }
> facs2 (&i); // { dg-warning "'facs2' reading 4 bytes from
> a region of size 2 " }
>
> - fvlac (1, 0); // { dg-warning "\\\[-Wnonnull" }
> + fvlac (1, 0);
> + fvlacS (1, 0); // { dg-warning "\\\[-Wnonnull" }
> fvlac (1, &i);
> fvlac (2, a2);
> fvlac (2, a1); // { dg-warning "'fvlac' reading 4 bytes from
> a region of size 2 " }
>
