https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105883
Bug ID: 105883
Summary: Memcmp folded only when size is a power of two
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: denis.campredon at gmail dot com
Target Milestone: ---
Compiled with trunk and -O2, on x86-64, the testcase bellow shows, the calls to
memcmp are folded just when the size is a power of two. Other archs seems to
produce unoptimal code too.
If the arrays are declared const, everything is optimized as expected.
-------
template <int I, typename T>
bool equals() {
T a[16] = {1,2,3,4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16};
T b[16] = {1,2,3,4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16};
static_assert(I <= sizeof a);
return !__builtin_memcmp(a, b, I);
}
template <int I, typename T>
bool not_equals() {
T a[16] = {1,2,3,4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16};
T b[16] = {0,2,3,4,5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16};
static_assert(I <= sizeof a);
return !__builtin_memcmp(a, b, I);
}
#define TEST \
template bool equals<1, char>(); \
template bool equals<2, char>(); \
template bool equals<3, char>(); \
template bool equals<4, char>(); \
template bool equals<5, char>(); \
template bool equals<7, char>(); \
template bool equals<8, char>(); \
template bool equals<15, char>(); \
template bool equals<16, char>(); \
template bool equals<1, long long>(); \
template bool equals<2, long long>(); \
template bool equals<3, long long>(); \
template bool equals<4, long long>(); \
template bool equals<5, long long>(); \
template bool equals<7, long long>(); \
template bool equals<8, long long>(); \
template bool equals<16, long long>(); \
template bool equals<17, long long>(); \
template bool equals<31, long long>(); \
template bool equals<32, long long>(); \
template bool equals<63, long long>(); \
template bool equals<64, long long>(); \
template bool equals<127, long long>(); \
template bool equals<128, long long>();
TEST
#define equals not_equals
TEST
