Am Montag, dem 02.12.2024 um 16:31 +0000 schrieb Qing Zhao:
>
> > On Nov 30, 2024, at 07:10, Martin Uecker <[email protected]> wrote:
> >
> > Am Dienstag, dem 26.11.2024 um 15:15 +0000 schrieb Qing Zhao:
> > >
> > > > On Nov 25, 2024, at 16:46, Martin Uecker <[email protected]> wrote:
> > > >
> > > >
> > > > Hi Qing,
> > > >
> > > > Am Montag, dem 25.11.2024 um 17:40 +0000 schrieb Qing Zhao:
> > > > > Hi, Martin,
> > > > >
> > > > > I didn’t go through all the details of your patch.
> > > > >
> > > > > But I have one question:
> > > > >
> > > > > Did you consider the effect of the option -fstrict-flex-array
> > > > > (https://gcc.gnu.org/onlinedocs/gcc-14.2.0/gcc/C-Dialect-Options.html#index-fstrict-flex-arrays)
> > > > > on how gcc treats the zero size trailing array, 1-element trailing
> > > > > array as flexible array member in the patch?
> > > >
> > > > I used the function which was already there which
> > > > does not take this into account. For the new version
> > > > of the patch this should not matter anymore.
> > >
> > > Why it’s not matter anymore?
> > >
> > > For the following testing case:
> > >
> > > struct S{int x,y[1];}*a;
> > > int main(void){
> > > struct S{int x,y[];};
> > > }
> > >
> > > With your latest patch, the two structures are considered as compatible
> > > with -g;
> > > However, if we add -fstrict-flex-array=2 or -fstrict-flex-array=3, the
> > > trailing array y[1] is NOT treated
> > > as FAM anymore, as a result, these two structure are NOT compatible too.
> > >
> > > Do I miss anything obvious?
> >
> > It is not about compatibility from a language semantic point of you
> > but for TBAA-compatibility which needs to be consistent with it but
> > can (and must be) more general.
> >
> > For TBAA, I think we want
> >
> > struct foo { int x; int y[]; };
> >
> > to be TBAA-compatible to
> >
> > struct foo { int x; int y[3]; };
>
> Okay, I see now. Thank you for the explanation.
> (Now I also see this from the comments of the routine
> gimple_canonical_types_compatible_p -:)
>
>
> Though, what confused me is the testing case in your patch:
>
> diff --git a/gcc/testsuite/gcc.dg/pr114014.c b/gcc/testsuite/gcc.dg/pr114014.c
> new file mode 100644
> index 00000000000..ab783f4f85d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr114014.c
> @@ -0,0 +1,14 @@
> +/* PR c/114014
> + * { dg-do compile }
> + * { dg-options "-std=c23 -g" } */
> +
> +struct r {
> + int a;
> + char b[];
> +};
> +struct r {
> + int a;
> + char b[0];
> +}; /* { dg-error "redefinition" } */
> +
> +
>
> Is the above testing case claiming that b[] and b[0] are compatible from a
> language semantic point of view?
It would test that we do not crash with checking.
Semantically, in c23 if you redeclare a type in the same scope then
it must not only be compatible but is also not allowed to differ.
So a redeclaration in the same scope has stricter requirements than
compatibility (this also true for typedefs for example).
Whether we allow
struct r {
int a;
char b[];
};
struct r {
int a;
char b[0];
};
depends on us because the [0] is an extension. I would make it
compatible but not allow redefinition as the types are different.
Martin
>
> thanks.
>
> Qing
> > even when we do not treat the later as FAM (i.e. still forbid
> > out-of-bounds accesses).
> >
> > E.g. see Richard's comment:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114713#c2
> >
> >
> > Martin
> >
> > > Thanks.
> > >
> > > Qing
> > > >
> > > > Martin
> > > >
> > > >
> > > > >
> > > > > thanks.
> > > > >
> > > > > Qing
> > > > > > On Nov 23, 2024, at 14:45, Martin Uecker <[email protected]> wrote:
> > > > > >
> > > > > >
> > > > > > This patch tries fixes the errors we have because of
> > > > > > flexible array members. I am bit unsure about the exception
> > > > > > for the mode.
> > > > > >
> > > > > > Bootstrapped and regression tested on x86_64.
> > > > > >
> > > > > >
> > > > > >
> > > > > > Fix type compatibility for types with flexible array member
> > > > > > [PR113688,PR114014,PR117724]
> > > > > >
> > > > > > verify_type checks the compatibility of TYPE_CANONICAL using
> > > > > > gimple_canonical_types_compatible_p. But it is stricter than
> > > > > > what the
> > > > > > C standard requires and therefor inconsistent with how
> > > > > > TYPE_CANONICAL is set
> > > > > > in the C FE. Here, the logic is changed to ignore array size when
> > > > > > one of the
> > > > > > types is a flexible array member. To not get errors because of
> > > > > > inconsistent
> > > > > > number of members, zero-sized arrays are not ignored anymore when
> > > > > > checking
> > > > > > fields of a struct (which is stricter than what was done before).
> > > > > > Finally, a exception is added that allows the TYPE_MODE of a type
> > > > > > with
> > > > > > flexible array member to differ from another compatible type.
> > > > > >
> > > > > > PR c/113688
> > > > > > PR c/114014
> > > > > > PR c/117724
> > > > > >
> > > > > > gcc/ChangeLog:
> > > > > > * tree.cc (gimple_canonical_types_compatible_p): Revise
> > > > > > logic for types with FAM.
> > > > > > (verify_type): Add exception for mode for types with FAM.
> > > > > >
> > > > > > gcc/testsuite/ChangeLog:
> > > > > > * gcc.dg/pr113688.c: New test.
> > > > > > * gcc.dg/pr114014.c: New test.
> > > > > > * gcc.dg/pr117724.c: New test.
> > > > > >
> > > > > > diff --git a/gcc/testsuite/gcc.dg/pr113688.c
> > > > > > b/gcc/testsuite/gcc.dg/pr113688.c
> > > > > > new file mode 100644
> > > > > > index 00000000000..8dee8c86f1b
> > > > > > --- /dev/null
> > > > > > +++ b/gcc/testsuite/gcc.dg/pr113688.c
> > > > > > @@ -0,0 +1,8 @@
> > > > > > +/* { dg-do compile } */
> > > > > > +/* { dg-options "-g" } */
> > > > > > +
> > > > > > +struct S{int x,y[1];}*a;
> > > > > > +int main(void){
> > > > > > + struct S{int x,y[];};
> > > > > > +}
> > > > > > +
> > > > > > diff --git a/gcc/testsuite/gcc.dg/pr114014.c
> > > > > > b/gcc/testsuite/gcc.dg/pr114014.c
> > > > > > new file mode 100644
> > > > > > index 00000000000..ab783f4f85d
> > > > > > --- /dev/null
> > > > > > +++ b/gcc/testsuite/gcc.dg/pr114014.c
> > > > > > @@ -0,0 +1,14 @@
> > > > > > +/* PR c/114014
> > > > > > + * { dg-do compile }
> > > > > > + * { dg-options "-std=c23 -g" } */
> > > > > > +
> > > > > > +struct r {
> > > > > > + int a;
> > > > > > + char b[];
> > > > > > +};
> > > > > > +struct r {
> > > > > > + int a;
> > > > > > + char b[0];
> > > > > > +}; /* { dg-error "redefinition" } */
> > > > > > +
> > > > > > +
> > > > > > diff --git a/gcc/testsuite/gcc.dg/pr117724.c
> > > > > > b/gcc/testsuite/gcc.dg/pr117724.c
> > > > > > new file mode 100644
> > > > > > index 00000000000..d631daeb644
> > > > > > --- /dev/null
> > > > > > +++ b/gcc/testsuite/gcc.dg/pr117724.c
> > > > > > @@ -0,0 +1,16 @@
> > > > > > +/* { dg-do compile } */
> > > > > > +/* { dg-options "-g" } */
> > > > > > +
> > > > > > +struct {
> > > > > > + unsigned long len;
> > > > > > + unsigned long size;
> > > > > > + char data[];
> > > > > > +}; /* { dg-warning "unnamed struct" } */
> > > > > > +struct {
> > > > > > + struct {
> > > > > > + unsigned long len;
> > > > > > + unsigned long size;
> > > > > > + char data[6];
> > > > > > + };
> > > > > > +}; /* { dg-warning "unnamed struct" } */
> > > > > > +
> > > > > > diff --git a/gcc/tree.cc b/gcc/tree.cc
> > > > > > index 1da06c7d4e9..dbf6b180496 100644
> > > > > > --- a/gcc/tree.cc
> > > > > > +++ b/gcc/tree.cc
> > > > > > @@ -13900,8 +13900,11 @@ gimple_canonical_types_compatible_p
> > > > > > (const_tree t1, const_tree t2,
> > > > > > || TREE_CODE (t1) == NULLPTR_TYPE)
> > > > > > return true;
> > > > > >
> > > > > > - /* Can't be the same type if they have different mode. */
> > > > > > - if (TYPE_MODE (t1) != TYPE_MODE (t2))
> > > > > > + /* Can't be compatible types if they have different mode. We
> > > > > > allow
> > > > > > + mismatching modes for types with flexible array member. */
> > > > > > + if (!flexible_array_type_p (t1)
> > > > > > + && !flexible_array_type_p (t2)
> > > > > > + && (TYPE_MODE (t1) != TYPE_MODE (t2)))
> > > > > > return false;
> > > > > >
> > > > > > /* Non-aggregate types can be handled cheaply. */
> > > > > > @@ -13952,7 +13955,7 @@ gimple_canonical_types_compatible_p
> > > > > > (const_tree t1, const_tree t2,
> > > > > > {
> > > > > > case ARRAY_TYPE:
> > > > > > /* Array types are the same if the element types are the same
> > > > > > and
> > > > > > - the number of elements are the same. */
> > > > > > + minimum and maximum index are the same. */
> > > > > > if (!gimple_canonical_types_compatible_p (TREE_TYPE (t1),
> > > > > > TREE_TYPE (t2),
> > > > > > trust_type_canonical)
> > > > > > > > TYPE_STRING_FLAG (t1) != TYPE_STRING_FLAG (t2)
> > > > > > @@ -14046,23 +14049,35 @@ gimple_canonical_types_compatible_p
> > > > > > (const_tree t1, const_tree t2,
> > > > > > f1 || f2;
> > > > > > f1 = TREE_CHAIN (f1), f2 = TREE_CHAIN (f2))
> > > > > > {
> > > > > > - /* Skip non-fields and zero-sized fields. */
> > > > > > - while (f1 && (TREE_CODE (f1) != FIELD_DECL
> > > > > > - || (DECL_SIZE (f1)
> > > > > > - && integer_zerop (DECL_SIZE (f1)))))
> > > > > > + /* Skip non-fields. */
> > > > > > + while (f1 && (TREE_CODE (f1) != FIELD_DECL))
> > > > > > f1 = TREE_CHAIN (f1);
> > > > > > - while (f2 && (TREE_CODE (f2) != FIELD_DECL
> > > > > > - || (DECL_SIZE (f2)
> > > > > > - && integer_zerop (DECL_SIZE (f2)))))
> > > > > > + while (f2 && (TREE_CODE (f2) != FIELD_DECL))
> > > > > > f2 = TREE_CHAIN (f2);
> > > > > > if (!f1 || !f2)
> > > > > > break;
> > > > > > +
> > > > > > + tree t1 = TREE_TYPE (f1);
> > > > > > + tree t2 = TREE_TYPE (f2);
> > > > > > +
> > > > > > + /* Special case for flexible array members. */
> > > > > > + if (TREE_CHAIN (f1) == NULL_TREE
> > > > > > + && TREE_CHAIN (f2) == NULL_TREE
> > > > > > + && TREE_CODE (t1) == ARRAY_TYPE
> > > > > > + && TREE_CODE (t2) == ARRAY_TYPE
> > > > > > + && (!DECL_NOT_FLEXARRAY (f1)
> > > > > > + || !DECL_NOT_FLEXARRAY (f2))
> > > > > > + && TYPE_REVERSE_STORAGE_ORDER (t1) == TYPE_REVERSE_STORAGE_ORDER
> > > > > > (t2)
> > > > > > + && TYPE_NONALIASED_COMPONENT (t1) == TYPE_NONALIASED_COMPONENT
> > > > > > (t2)
> > > > > > + && gimple_canonical_types_compatible_p
> > > > > > + (TREE_TYPE (t1), TREE_TYPE (t2),
> > > > > > + trust_type_canonical))
> > > > > > + ;
> > > > > > /* The fields must have the same name, offset and type. */
> > > > > > - if (DECL_NONADDRESSABLE_P (f1) != DECL_NONADDRESSABLE_P (f2)
> > > > > > + else if (DECL_NONADDRESSABLE_P (f1) != DECL_NONADDRESSABLE_P
> > > > > > (f2)
> > > > > > > > !gimple_compare_field_offset (f1, f2)
> > > > > > > > !gimple_canonical_types_compatible_p
> > > > > > - (TREE_TYPE (f1), TREE_TYPE (f2),
> > > > > > - trust_type_canonical))
> > > > > > + (t1, t2, trust_type_canonical))
> > > > > > return false;
> > > > > > }
> > > > > >
> > > > > > @@ -14206,6 +14221,9 @@ verify_type (const_tree t)
> > > > > > }
> > > > > >
> > > > > > if (COMPLETE_TYPE_P (t) && TYPE_CANONICAL (t)
> > > > > > + /* We allow a mismatch for flexible array members. */
> > > > > > + && !flexible_array_type_p (t)
> > > > > > + && !flexible_array_type_p (TYPE_CANONICAL (t))
> > > > > > && TYPE_MODE (t) != TYPE_MODE (TYPE_CANONICAL (t)))
> > > > > > {
> > > > > > error ("%<TYPE_MODE%> of %<TYPE_CANONICAL%> is not compatible");
>
>
