https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115719
Bug ID: 115719
Summary: __builtin_memcmp missed if it compare length of 3
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: kese111 at gmail dot com
Target Milestone: ---
here is example code:
bool test_even_3(const char* input) {
return (
__builtin_memcmp(input, "ab", 2) == 0 ||
__builtin_memcmp(input, "abc", 3) == 0
);
}
bool test_even_4(const char* input) {
return (
__builtin_memcmp(input, "ab", 2) == 0 ||
__builtin_memcmp(input, "abc", 3) == 0 ||
__builtin_memcmp(input, "abcd", 4) == 0
);
}
and its results for x86-gcc-trunk(Compiler explorer)
test_even_3(char const*):
cmp WORD PTR [rdi], 25185
mov eax, 1
je .L12
mov eax, 1
test eax, eax
sete al
.L12:
ret
test_even_4(char const*):
cmp WORD PTR [rdi], 25185
mov eax, 1
je .L17
cmp DWORD PTR [rdi], 1684234849
sete al
.L17:
ret
used O2 optimizing.
what am I missing?
