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? thanks. Qing > On Nov 23, 2024, at 14:45, Martin Uecker <uec...@tugraz.at> 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"); > >
