Hi, this patch implements warning when we merge two virtual tables that do not match. It compares the size and also go into fields. I had to implement my own comparsion code, since the vtables may subtly differ - in RTTI and also I need to do so during DECL merging (since we will forget about the decl then)
Here is an example of real ODR violation in bugzilla it finds. ../../dist/include/mozilla/a11y/DocAccessible.h:40:0: warning: type �struct DocAccessible� violates one definition rule [enabled by default] class DocAccessible : public HyperTextAccessibleWrap, ^ /aux/hubicka/firefox/accessible/src/generic/DocAccessible.h:40:0: note: a type with the same name but different virtual table is defined in another translation unit class DocAccessible : public HyperTextAccessibleWrap, ^ /aux/hubicka/firefox/accessible/src/generic/DocAccessible.cpp:1232:0: note: the first different method is �HandleAccEvent� DocAccessible::HandleAccEvent(AccEvent* aEvent) ^ /aux/hubicka/firefox/accessible/src/atk/AccessibleWrap.cpp:956:0: note: a conflicting method is �HandleAccEvent� AccessibleWrap::HandleAccEvent(AccEvent* aEvent) ^ The patch is not terribly pretty, but does the job. I will wait for few days for comments/suggestins and then plan to commit it. PR lto/59468 * lto/lto-symtab.c (lto_symtab_prevailing_decl): Check virtual tables for ODR violations. * ipa-devirt.c (compare_virtual_tables): New function. * ipa-utils.h (compare_virtual_tables): Declare. Index: lto/lto-symtab.c =================================================================== --- lto/lto-symtab.c (revision 207702) +++ lto/lto-symtab.c (working copy) @@ -679,5 +679,13 @@ lto_symtab_prevailing_decl (tree decl) if (!ret) return decl; + /* Check and report ODR violations on virtual tables. */ + if (decl != ret->decl && DECL_VIRTUAL_P (decl)) + { + compare_virtual_tables (ret->decl, decl); + /* We are done with checking and DECL will die after merigng. */ + DECL_VIRTUAL_P (decl) = 0; + } + return ret->decl; } Index: ipa-devirt.c =================================================================== --- ipa-devirt.c (revision 207702) +++ ipa-devirt.c (working copy) @@ -1675,6 +1673,101 @@ update_type_inheritance_graph (void) } +/* Compare two virtual tables, PREVAILING and VTABLE and output ODR + violation warings. */ + +void +compare_virtual_tables (tree prevailing, tree vtable) +{ + tree init1 = DECL_INITIAL (prevailing), init2 = DECL_INITIAL (vtable); + if (init1 == init2) + return; + if (init2 == error_mark_node) + return; + /* Be sure to keep virtual table contents even for external + vtables when they are available. */ + if (init1 == error_mark_node || !init1) + { + DECL_INITIAL (prevailing) = DECL_INITIAL (vtable); + return; + } + if (!init2 && DECL_EXTERNAL (vtable)) + return; + if (DECL_VIRTUAL_P (prevailing) && init1 && init2 + && CONSTRUCTOR_NELTS (init1) == CONSTRUCTOR_NELTS (init2)) + { + unsigned i; + tree field1, field2; + tree val1, val2; + bool matched = true; + + FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (init1), + i, field1, val1) + { + gcc_assert (!field1); + field2 = CONSTRUCTOR_ELT (init2, i)->index; + val2 = CONSTRUCTOR_ELT (init2, i)->value; + gcc_assert (!field2); + if (val2 == val1) + continue; + STRIP_NOPS (val1); + STRIP_NOPS (val2); + /* Unwind + val <addr_expr type <pointer_type> + readonly constant + arg 0 <mem_ref type <pointer_type __vtbl_ptr_type> + readonly + arg 0 <addr_expr type <pointer_type> + arg 0 <var_decl _ZTCSd0_Si>> arg 1 <integer_cst 24>>> */ + + while ((TREE_CODE (val1) == MEM_REF + && TREE_CODE (val2) == MEM_REF + && (TREE_OPERAND (val1, 1) + == TREE_OPERAND (val2, 1))) + || (TREE_CODE (val1) == ADDR_EXPR + && TREE_CODE (val2) == ADDR_EXPR)) + { + val1 = TREE_OPERAND (val1, 0); + val2 = TREE_OPERAND (val2, 0); + } + if (val1 == val2) + continue; + if (TREE_CODE (val2) == ADDR_EXPR) + { + tree tmp = val1; + val1 = val2; + val2 = tmp; + } + /* Allow combining RTTI and non-RTTI is OK. */ + if (TREE_CODE (val1) == ADDR_EXPR + && TREE_CODE (TREE_OPERAND (val1, 0)) == VAR_DECL + && !DECL_VIRTUAL_P (TREE_OPERAND (val1, 0)) + && TREE_CODE (val2) == NOP_EXPR + && integer_zerop (TREE_OPERAND (val2, 0))) + continue; + if (TREE_CODE (val1) == NOP_EXPR + && TREE_CODE (val2) == NOP_EXPR + && integer_zerop (TREE_OPERAND (val1, 0)) + && integer_zerop (TREE_OPERAND (val2, 0))) + continue; + if (DECL_P (val1) && DECL_P (val2) + && DECL_ASSEMBLER_NAME (val1) == DECL_ASSEMBLER_NAME (val2)) + continue; + matched = false; + break; + } + if (matched) + return; + } + odr_violation_reported = true; + if (warning_at (DECL_SOURCE_LOCATION (TYPE_NAME (DECL_CONTEXT (vtable))), 0, + "type %qD violates one definition rule ", + DECL_CONTEXT (vtable))) + inform (DECL_SOURCE_LOCATION (TYPE_NAME (DECL_CONTEXT (prevailing))), + "a type with the same name but different virtual table is " + "defined in another translation unit"); +} + /* Return true if N looks like likely target of a polymorphic call. Rule out cxa_pure_virtual, noreturns, function declared cold and other obvious cases. */ Index: ipa-utils.h =================================================================== --- ipa-utils.h (revision 207702) +++ ipa-utils.h (working copy) @@ -92,6 +92,7 @@ bool get_polymorphic_call_info_from_inva tree, tree, HOST_WIDE_INT); tree vtable_pointer_value_to_binfo (tree t); bool vtable_pointer_value_to_vtable (tree, tree *, unsigned HOST_WIDE_INT *); +void compare_virtual_tables (tree, tree); /* Return vector containing possible targets of polymorphic call E. If FINALP is non-NULL, store true if the list is complette.