fix(folding): correct unique object rep checks []

src/Changes

@@ -1,5 +1,46 @@
 Version 7.1
 
+10/16/26 [GH #327]
+__has_unique_object_representations fixes
+
+A base class that declares no nonstatic data members of its own but inherits
+some (and is therefore not empty) was treated as an empty base class.  Its
+size was then counted as tail padding, so the trait was incorrectly FALSE for
+classes derived from it.  For example, with --c++11:
+
+  struct A { char i; };
+  struct B : A {};
+  struct C : B {};
+  static_assert(__has_unique_object_representations(C), "");  // Previously
+                                                              // failed.
+
+This is now fixed.  In addition:
+
+  - An unnamed bit-field of nonzero width is now treated as padding (making
+    the result FALSE), as the standard requires.  For example:
+
+      struct S { char a; char : 8; char b; };
+      // __has_unique_object_representations(S) is now FALSE.
+
+    The previous behavior (TRUE) is retained in g++ modes before 13.1
+    (except 10.5, 11.4, and 12.3) and in Clang modes before 17.
+
+  - In a union, an unnamed bit-field overlaps the other members, so the
+    rule above does not apply; as before, a bit-field narrower than the
+    union is treated as padding, except in Clang modes.  Microsoft mode now
+    also does not treat it as padding, matching MSVC.  For example:
+
+      union U { int x : 3; };
+      // __has_unique_object_representations(U) is now TRUE with
+      // --microsoft.
+
+  - Volatile-qualified non-class types (e.g., "volatile int") are treated as
+    not having unique object representations only in g++ modes before
+    version 10 (previously this was done for all g++ versions, including
+    Clang modes).  In other modes the result is the same as for the
+    unqualified type, as the standard requires.
+
+
 10/15/26  [GH #309]
 Position of (lowered) cleanups at the end of a function body
 

src/folding.c

@@ -8939,6 +8939,27 @@ with cssp are trivial.
 }  /* all_copy_constructors_trivial */
 
 
+static a_boolean unnamed_bit_field_is_padding(void)
+/*
+Return TRUE if an unnamed bit-field of non-zero width is considered padding
+by type_has_unique_object_representations.  That is the standard behavior;
+it is not done by Clang before version 17 or by g++ before 13.1 (except for
+the backports to g++ 10.5, 11.4, and 12.3).
+*/
+{
+  a_boolean result = TRUE;
+
+  if (clang_mode) {
+    result = clang_version >= 170000;
+  } else if (gpp_mode) {
+    result = gnu_version >= 120300 ||
+             (gnu_version >= 110400 && gnu_version < 120000) ||
+             (gnu_version >= 100500 && gnu_version < 110000);
+  }  /* if */
+  return result;
+}  /* unnamed_bit_field_is_padding */
+
+
 static a_boolean type_has_unique_object_representations(
                                    a_type_ptr     type,
                                    a_targ_size_t  *after_base_members,
@@ -8999,8 +9020,7 @@ architectures for which these assumptions are not valid.
           if (bcp->offset != end_of_last_subobject) {
             /* There's padding between base class subobjects. */
             result = FALSE;
-          } else if (bcp->type->variant.class_struct_union.field_list ==
-                                                                        NULL) {
+          } else if (is_empty_class_type(bcp->type)) {
             /* An empty base class: treat it as having size 0 and do not
                check type_has_unique_object_representation, since an empty
                class will consist of nothing but padding.  If it was not
@@ -9029,11 +9049,20 @@ architectures for which these assumptions are not valid.
         a_type_ptr field_type = skip_typerefs(field->type);
         if (type->kind == (a_type_kind)tk_union &&
             ((prev_field != NULL && field_type->size != prev_field_size) ||
-             (field->is_bit_field && !clang_mode &&
+             (field->is_bit_field && !clang_mode && !microsoft_mode &&
               field->bit_size < type->size * targ_char_bit))) {
           /* There will be padding in a union if not all fields are the
-             same size or (for g++, not clang) if a bit-field is shorter
-             than the size of the union. */
+             same size or (except for Clang and Microsoft) if a bit-field
+             is shorter than the size of the union. */
+          result = FALSE;
+        } else if (type->kind != tk_union &&
+                   field->is_bit_field && field->bit_size != 0 &&
+                   unnamed_bit_field_is_padding() &&
+                   field->source_corresp.assoc_info ==
+                                     (char*)get_unnamed_field_symbol()) {
+          /* An unnamed bit-field of non-zero width is padding.  (In a
+             union, an unnamed bit-field overlaps the other members, so
+             it is handled by the size test above instead.) */
           result = FALSE;
         } else if (field->offset != end_of_last_subobject ||
             field->offset_bit_remainder != bit_offset_of_end) {
@@ -9078,9 +9107,10 @@ architectures for which these assumptions are not valid.
         }  /* if */
       }  /* if */
     }  /* if */
-  } else if (gpp_mode && is_volatile_qualified_type(orig_type)) {
-    /* g++ treats volatile-qualified types as not having unique object
-       representations. */
+  } else if (gpp_version_is(< 100000) &&
+             is_volatile_qualified_type(orig_type)) {
+    /* g++ before version 10 treats volatile-qualified non-class types as
+       not having unique object representations. */
     result = FALSE;
   } else {
     /* A non-class type. */

tests/expectations/edg_x86_64/imported.log

@@ -6872,7 +6872,6 @@ gnu/cpp/cpp1z/fold1/test.mft.cpp:fn:-DTEST_NUMBER=1 --c++17:FAIL:
 gnu/cpp/cpp1z/fold5.sft.cpp:fn:-DTEST_NUMBER=1 --c++11:FAIL:
 gnu/cpp/cpp1z/fold6.sft.cpp:fn:-DTEST_NUMBER=1 --c++17:FAIL:
 gnu/cpp/cpp1z/has-unique-obj-representations1.sft.cpp:fp:-DTEST_NUMBER=1 --c++11:FAIL:
-gnu/cpp/cpp1z/has-unique-obj-representations3.sft.cpp:fp:-DTEST_NUMBER=1 --c++11:FAIL:
 gnu/cpp/cpp1z/inh-ctor1.sft.cpp:fn:-DTEST_NUMBER=1 --c++11:FAIL:
 gnu/cpp/cpp1z/inh-ctor33.sft.cpp:lp:-DTEST_NUMBER=1 --c++11:FAIL:
 gnu/cpp/cpp1z/inh-ctor38.sft.cpp:rp:-DTEST_NUMBER=1 --c++11:FAIL:

tests/tests/imported/clang/cpp/SemaCXX/.type-traits.rto/default.1.1.txt

@@ -375,38 +375,6 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     static_assert(!__is_trivially_destructible(AnIncompleteType[1])); // expected-error {{incomplete type}}
                                                ^
 
-"Test_name.c", line 3482: error: static assertion failed with "integrals are"
-  static_assert(__has_unique_object_representations(volatile int), "integrals are");
-  ^
-
-"Test_name.c", line 3483: error: static assertion failed with "integrals are"
-  static_assert(__has_unique_object_representations(const volatile int), "integrals are");
-  ^
-
-"Test_name.c", line 3502: error: static assertion failed with "even function pointers"
-  static_assert(__has_unique_object_representations(volatile FP), "even function pointers");
-  ^
-
-"Test_name.c", line 3503: error: static assertion failed with "even function pointers"
-  static_assert(__has_unique_object_representations(const volatile FP), "even function pointers");
-  ^
-
-"Test_name.c", line 3507: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(volatile PMF), "and pointer to members");
-  ^
-
-"Test_name.c", line 3508: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(const volatile PMF), "and pointer to members");
-  ^
-
-"Test_name.c", line 3512: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(volatile PMD), "and pointer to members");
-  ^
-
-"Test_name.c", line 3513: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(const volatile PMD), "and pointer to members");
-  ^
-
 "Test_name.c", line 3544: error: an incomplete class type is not allowed
   static_assert(!__has_unique_object_representations(AnIncompleteType));
                  ^
@@ -431,14 +399,6 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     char d : 1;
          ^
 
-"Test_name.c", line 3777: error: static assertion failed with "Bitfield padding"
-  static_assert(!__has_unique_object_representations(UnnamedBitfield), "Bitfield padding");
-  ^
-
-"Test_name.c", line 3778: error: static assertion failed with "Bitfield padding"
-  static_assert(!__has_unique_object_representations(UnnamedBitfieldPacked), "Bitfield padding");
-  ^
-
 "Test_name.c", line 3790: warning: declared size for bit field is larger than the size of the bit field type; truncated to 8 bits
     bool b : 16;
              ^
@@ -695,5 +655,5 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
   #error Programming model currently unsupported; please add a new entry.
    ^
 
-124 errors and 1 catastrophic error detected in the compilation of "Test_name.c".
+114 errors and 1 catastrophic error detected in the compilation of "Test_name.c".
 Compilation terminated.

tests/tests/imported/clang/cpp/SemaCXX/.type-traits.rto/edg_x86_32.1.1.txt

@@ -379,38 +379,6 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     static_assert(!__is_trivially_destructible(AnIncompleteType[1])); // expected-error {{incomplete type}}
                                                ^
 
-"Test_name.c", line 3482: error: static assertion failed with "integrals are"
-  static_assert(__has_unique_object_representations(volatile int), "integrals are");
-  ^
-
-"Test_name.c", line 3483: error: static assertion failed with "integrals are"
-  static_assert(__has_unique_object_representations(const volatile int), "integrals are");
-  ^
-
-"Test_name.c", line 3502: error: static assertion failed with "even function pointers"
-  static_assert(__has_unique_object_representations(volatile FP), "even function pointers");
-  ^
-
-"Test_name.c", line 3503: error: static assertion failed with "even function pointers"
-  static_assert(__has_unique_object_representations(const volatile FP), "even function pointers");
-  ^
-
-"Test_name.c", line 3507: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(volatile PMF), "and pointer to members");
-  ^
-
-"Test_name.c", line 3508: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(const volatile PMF), "and pointer to members");
-  ^
-
-"Test_name.c", line 3512: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(volatile PMD), "and pointer to members");
-  ^
-
-"Test_name.c", line 3513: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(const volatile PMD), "and pointer to members");
-  ^
-
 "Test_name.c", line 3544: error: an incomplete class type is not allowed
   static_assert(!__has_unique_object_representations(AnIncompleteType));
                  ^
@@ -435,14 +403,6 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     char d : 1;
          ^
 
-"Test_name.c", line 3777: error: static assertion failed with "Bitfield padding"
-  static_assert(!__has_unique_object_representations(UnnamedBitfield), "Bitfield padding");
-  ^
-
-"Test_name.c", line 3778: error: static assertion failed with "Bitfield padding"
-  static_assert(!__has_unique_object_representations(UnnamedBitfieldPacked), "Bitfield padding");
-  ^
-
 "Test_name.c", line 3790: warning: declared size for bit field is larger than the size of the bit field type; truncated to 8 bits
     bool b : 16;
              ^
@@ -695,5 +655,5 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
   #error Programming model currently unsupported; please add a new entry.
    ^
 
-124 errors and 1 catastrophic error detected in the compilation of "Test_name.c".
+114 errors and 1 catastrophic error detected in the compilation of "Test_name.c".
 Compilation terminated.

tests/tests/imported/clang/cpp/SemaCXX/.type-traits.rto/edg_x86_32_cp.1.1.txt

@@ -363,38 +363,6 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     static_assert(!__is_trivially_destructible(AnIncompleteType[1])); // expected-error {{incomplete type}}
                                                ^
 
-"Test_name.c", line 3482: error: static assertion failed with "integrals are"
-  static_assert(__has_unique_object_representations(volatile int), "integrals are");
-  ^
-
-"Test_name.c", line 3483: error: static assertion failed with "integrals are"
-  static_assert(__has_unique_object_representations(const volatile int), "integrals are");
-  ^
-
-"Test_name.c", line 3502: error: static assertion failed with "even function pointers"
-  static_assert(__has_unique_object_representations(volatile FP), "even function pointers");
-  ^
-
-"Test_name.c", line 3503: error: static assertion failed with "even function pointers"
-  static_assert(__has_unique_object_representations(const volatile FP), "even function pointers");
-  ^
-
-"Test_name.c", line 3507: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(volatile PMF), "and pointer to members");
-  ^
-
-"Test_name.c", line 3508: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(const volatile PMF), "and pointer to members");
-  ^
-
-"Test_name.c", line 3512: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(volatile PMD), "and pointer to members");
-  ^
-
-"Test_name.c", line 3513: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(const volatile PMD), "and pointer to members");
-  ^
-
 "Test_name.c", line 3544: error: an incomplete class type is not allowed
   static_assert(!__has_unique_object_representations(AnIncompleteType));
                  ^
@@ -419,14 +387,6 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     char d : 1;
          ^
 
-"Test_name.c", line 3777: error: static assertion failed with "Bitfield padding"
-  static_assert(!__has_unique_object_representations(UnnamedBitfield), "Bitfield padding");
-  ^
-
-"Test_name.c", line 3778: error: static assertion failed with "Bitfield padding"
-  static_assert(!__has_unique_object_representations(UnnamedBitfieldPacked), "Bitfield padding");
-  ^
-
 "Test_name.c", line 3790: warning: declared size for bit field is larger than the size of the bit field type; truncated to 8 bits
     bool b : 16;
              ^
@@ -635,5 +595,5 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
   #error Programming model currently unsupported; please add a new entry.
    ^
 
-124 errors and 1 catastrophic error detected in the compilation of "Test_name.c".
+114 errors and 1 catastrophic error detected in the compilation of "Test_name.c".
 Compilation terminated.

tests/tests/imported/clang/cpp/SemaCXX/.type-traits.rto/edg_x86_64_cp.1.1.txt

@@ -359,38 +359,6 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     static_assert(!__is_trivially_destructible(AnIncompleteType[1])); // expected-error {{incomplete type}}
                                                ^
 
-"Test_name.c", line 3482: error: static assertion failed with "integrals are"
-  static_assert(__has_unique_object_representations(volatile int), "integrals are");
-  ^
-
-"Test_name.c", line 3483: error: static assertion failed with "integrals are"
-  static_assert(__has_unique_object_representations(const volatile int), "integrals are");
-  ^
-
-"Test_name.c", line 3502: error: static assertion failed with "even function pointers"
-  static_assert(__has_unique_object_representations(volatile FP), "even function pointers");
-  ^
-
-"Test_name.c", line 3503: error: static assertion failed with "even function pointers"
-  static_assert(__has_unique_object_representations(const volatile FP), "even function pointers");
-  ^
-
-"Test_name.c", line 3507: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(volatile PMF), "and pointer to members");
-  ^
-
-"Test_name.c", line 3508: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(const volatile PMF), "and pointer to members");
-  ^
-
-"Test_name.c", line 3512: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(volatile PMD), "and pointer to members");
-  ^
-
-"Test_name.c", line 3513: error: static assertion failed with "and pointer to members"
-  static_assert(__has_unique_object_representations(const volatile PMD), "and pointer to members");
-  ^
-
 "Test_name.c", line 3544: error: an incomplete class type is not allowed
   static_assert(!__has_unique_object_representations(AnIncompleteType));
                  ^
@@ -415,14 +383,6 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     char d : 1;
          ^
 
-"Test_name.c", line 3777: error: static assertion failed with "Bitfield padding"
-  static_assert(!__has_unique_object_representations(UnnamedBitfield), "Bitfield padding");
-  ^
-
-"Test_name.c", line 3778: error: static assertion failed with "Bitfield padding"
-  static_assert(!__has_unique_object_representations(UnnamedBitfieldPacked), "Bitfield padding");
-  ^
-
 "Test_name.c", line 3790: warning: declared size for bit field is larger than the size of the bit field type; truncated to 8 bits
     bool b : 16;
              ^
@@ -635,5 +595,5 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
   #error Programming model currently unsupported; please add a new entry.
    ^
 
-124 errors and 1 catastrophic error detected in the compilation of "Test_name.c".
+114 errors and 1 catastrophic error detected in the compilation of "Test_name.c".
 Compilation terminated.

tests/tests/imported/gnu/cpp/cpp1z/.has-unique-obj-representations3.rto/default.1.1.txt

@@ -1,16 +1 @@
 fe_only -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics --c++11 Test_name.c
-"Test_name.c", line 10: error: static assertion failed with ""
-  static_assert (__has_unique_object_representations (U) == false, "");
-  ^
-"Test_name.c", line 10: note: the final comparison was 1 == 0
-  static_assert (__has_unique_object_representations (U) == false, "");
-                                                         ^
-
-"Test_name.c", line 11: error: static assertion failed with ""
-  static_assert (__has_unique_object_representations (V) == false, "");
-  ^
-"Test_name.c", line 11: note: the final comparison was 1 == 0
-  static_assert (__has_unique_object_representations (V) == false, "");
-                                                         ^
-
-2 errors detected in the compilation of "Test_name.c".

tests/tests/regressions/.has-unique-object-rep-bit-field.rto/default.1.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=1 --c++11 -DSTD_MODE Test_name.c

tests/tests/regressions/.has-unique-object-rep-bit-field.rto/default.10.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=10 --c++11 --microsoft Test_name.c

tests/tests/regressions/.has-unique-object-rep-bit-field.rto/default.2.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=2 --c++11 --g++ --gnu_version=90400 -DOLD_PAD Test_name.c

tests/tests/regressions/.has-unique-object-rep-bit-field.rto/default.3.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=3 --c++11 --g++ --gnu_version=100400 -DOLD_PAD Test_name.c