https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62032
--- Comment #3 from bin.cheng <amker.cheng at gmail dot com> --- I did some investigation and think it's a latent bug of lto which reveaded by r213585. Before the revision, pass_fold_builtins::execute calls gimple_fold_builtins directly to fold __builtin___vsnprintf_chk (_26, _25, 0, 4294967295, "%d - %c", ap);. It works fine by simplifying the builtin into __builtin_vsnprintf (_26, _25, "%d - %c", ap);. After the revision, it calls to fold_stmt->gimple_fold_call->gimple_fold_builtin to do the job. But before that, it calls gimple_call_builtin_p to verify that it IS a valid builtin call, which in turn calls gimple_builtin_call_types_compatible_p to check that types between parameter and argument match each other. Well, the check fails on the last parameter/argument, as dumped below: TREE_TYPE of ARGUMENT: <record_type 0x7fc34cc9fc78 va_list SI size <integer_cst 0x7fc34ce71dc8 type <integer_type 0x7fc34ce7c0a8 bitsizetype> constant 32> unit size <integer_cst 0x7fc34ce71de0 type <integer_type 0x7fc34ce7c000 sizetype> constant 4> align 32 symtab 0 alias set -1 canonical type 0x7fc34ce899d8 fields <field_decl 0x7fc34ce87130 __ap type <pointer_type 0x7fc34ce84000 type <void_type 0x7fc34ce7cf18 void> public unsigned SI size <integer_cst 0x7fc34ce71dc8 32> unit size <integer_cst 0x7fc34ce71de0 4> align 32 symtab 0 alias set 3 canonical type 0x7fc34ce84000 pointer_to_this <pointer_type 0x7fc34ce8a348>> unsigned SI file <built-in> line 0 col 0 size <integer_cst 0x7fc34ce71dc8 32> unit size <integer_cst 0x7fc34ce71de0 4> align 32 offset_align 64 offset <integer_cst 0x7fc34ce71df8 constant 0> bit offset <integer_cst 0x7fc34ce71e58 constant 0> context <record_type 0x7fc34ce899d8 __va_list>> context <translation_unit_decl 0x7fc34df310f0 D.4035> pointer_to_this <pointer_type 0x7fc34ccaa2a0> chain <type_decl 0x7fc34ce87da8 __va_list>> TREE_TYPE of PARAMETER of function BUILT_IN_VSNPRINTF_CHK: <reference_type 0x7fc34ce89c78 type <record_type 0x7fc34ce899d8 __va_list SI size <integer_cst 0x7fc34ce71dc8 constant 32> unit size <integer_cst 0x7fc34ce71de0 constant 4> align 32 symtab 0 alias set 7 canonical type 0x7fc34ce899d8 fields <field_decl 0x7fc34ce87130 __ap type <pointer_type 0x7fc34ce84000> unsigned SI file <built-in> line 0 col 0 size <integer_cst 0x7fc34ce71dc8 32> unit size <integer_cst 0x7fc34ce71de0 4> align 32 offset_align 64 offset <integer_cst 0x7fc34ce71df8 constant 0> bit offset <integer_cst 0x7fc34ce71e58 constant 0> context <record_type 0x7fc34ce899d8 __va_list>> pointer_to_this <pointer_type 0x7fc34ccc4888> reference_to_this <reference_type 0x7fc34ccaa0a8> chain <type_decl 0x7fc34ce87098 __va_list>> unsigned SI size <integer_cst 0x7fc34ce71dc8 32> unit size <integer_cst 0x7fc34ce71de0 4> align 32 symtab 0 alias set -1 canonical type 0x7fc34ce89c78> The root cause lies in gcc/lto/lto-lang.c:lto_init, there is below code snippet: if (TREE_CODE (va_list_type_node) == ARRAY_TYPE) { tree x = build_pointer_type (TREE_TYPE (va_list_type_node)); lto_define_builtins (x, x); } else { lto_define_builtins (va_list_type_node, build_reference_type (va_list_type_node)); } While prototype of lto_define_builtins is like below. static void lto_define_builtins (tree va_list_ref_type_node ATTRIBUTE_UNUSED, tree va_list_arg_type_node ATTRIBUTE_UNUSED); Apparently, the arguments passed to lto_define_builtins are mis-matched. In fact, I think it should be consistent with function calls to c_define_builtins in c front-end. I think above analysis also explains why it happens only with lto. I will send a patch fixing this soon. Thanks, bin