The resulting C code for the following code example code produces an expensive,
unnecessary copy of a `Position` in the function `inCheck` when compiled with
`nim c -d:danger -d:lto --panics:on --gc:arc --run main.nim`
type Position* = object
pieces: array[6, uint64]
colors: array[2, uint64]
func isAttacked*(position: Position, target: int8): bool =
false
func kingSquare*(position: Position): int8 =
12
func inCheck*(position: Position): bool =
position.isAttacked(position.kingSquare)
var p: Position
echo p.inCheck()
Run
Resulting C code:
N_LIB_PRIVATE N_NIMCALL(NIM_BOOL,
isAttacked_main_4)(tyObject_Position__XJEOqi2mMysguMih68T9bQg* position, NI8
target) {
NIM_BOOL result;
result = (NIM_BOOL)0;
result = NIM_FALSE;
return result;
}
N_LIB_PRIVATE N_NIMCALL(NI8,
kingSquare_main_8)(tyObject_Position__XJEOqi2mMysguMih68T9bQg* position) {
NI8 result;
result = (NI8)0;
result = ((NI8) 12);
return result;
}
N_LIB_PRIVATE N_NIMCALL(NIM_BOOL,
inCheck_main_11)(tyObject_Position__XJEOqi2mMysguMih68T9bQg* position) {
NIM_BOOL result;
tyObject_Position__XJEOqi2mMysguMih68T9bQg T1_;
NI8 T2_;
result = (NIM_BOOL)0;
T1_ = (*position); // I believe this is the expensive copy
T2_ = (NI8)0;
T2_ = kingSquare_main_8(position);
result = isAttacked_main_4((&T1_), T2_);
return result;
}
Run
The expensive copy is omitted when compiling with `nim c -d:danger -d:lto
--gc:refc --run main.nim`:
N_LIB_PRIVATE N_NIMCALL(NIM_BOOL,
isAttacked_main_4)(tyObject_Position__XJEOqi2mMysguMih68T9bQg* position, NI8
target) {
NIM_BOOL result;
result = (NIM_BOOL)0;
result = NIM_FALSE;
return result;
}
N_LIB_PRIVATE N_NIMCALL(NI8,
kingSquare_main_8)(tyObject_Position__XJEOqi2mMysguMih68T9bQg* position) {
NI8 result;
result = (NI8)0;
result = ((NI8) 12);
return result;
}
N_LIB_PRIVATE N_NIMCALL(NIM_BOOL,
inCheck_main_11)(tyObject_Position__XJEOqi2mMysguMih68T9bQg* position) {
NIM_BOOL result;
NI8 T1_;
result = (NIM_BOOL)0;
T1_ = (NI8)0;
T1_ = kingSquare_main_8(position);
result = isAttacked_main_4(position, T1_);
return result;
}
Run
Is this a bug that can be fixed (because I suspect that this issue is the
reason why my program is slower with `--gc:arc` than with the default GC), or
is this inherent to the design of ARC?
