Some implementations can use the std::nullopt_t constructor of
std::optional to avoid needing to completely zero out the internal
buffer of the optional and instead only set the validity byte within it.
e.g. Consider the following function:
std::optional<std::vector<ShaderDiskCacheRaw>> fn() {
return {};
}
With libc++ this will result in the following code generation on x86-64:
Fn():
mov rax, rdi
vxorps xmm0, xmm0, xmm0
vmovups ymmword ptr [rdi], ymm0
vzeroupper
ret
With libstdc++, we also get the similar equivalent:
Fn():
vpxor xmm0, xmm0, xmm0
mov rax, rdi
vmovdqu XMMWORD PTR [rdi], xmm0
vmovdqu XMMWORD PTR [rdi+16], xmm0
ret
If we change this function to return std::nullopt instead, then this
simplifies both the code gen from libc++ and libstdc++ down to:
Fn():
mov BYTE PTR [rdi+24], 0
mov rax, rdi
ret
Given how little of a change is necessary to result in better code
generation, this is essentially a "free" very minor optimization.
Previously, we were returning a value that was way too big, causing an integer overflow in Fractured Souls.
According to wwylele, the biggest oberserved save size for 3DS is 1MB, so this new value should leave plenty of room, even if games use a bigger size.
Many of these functions are capable of being used within const contexts,
so we can apply the const qualifier in some cases and add const based
overloads for others, which makes the interface a little bit more
flexible and const-correct.
* core/memory: Amend unusual return value of operator=
operator= usually returns a reference to this. Given there's no comment
explaining why void was used, this can be assumed to be an oversight.
* core/memory: Make use of std::move in Entry::operator=
Same behavior, minus the need for an atomic reference count increment
and decrement (since MemoryRef contains a std::shared_ptr).
* ArmInterface: return ref instead of copy for GetTimer
* ArmInterface: add const ref GetTimer
* ArmInterface: return raw pointer instead of shared_ptr in GetTimer
* remove more unnecessary shared_ptr usage
* Fix save states
* fix unit tests
* video_core: reduce string allocations in shader decompiler
* use append for indentation instead of resize
Co-authored-by: Mat M. <mathew1800@gmail.com>
* am/am: Avoid redundant copy in GetProgramInfoFromCia()
We can just use a reference to the title metadata. Avoids copying
several data entries and std::vector instances that don't need to be
copied.
* hle/service: Avoid redundant copying of std::string
GetUserPath() returns the path as a reference, so we can make use of
said reference to avoid making copies.
By using a reference here, we avoid copying every single element in the
map, each of which contains a std::share_ptr and std::deque containing
std::vectors.
Same behavior, but doesn't result in an allocating copy of the passed in
string. Particularly given the string is only compared against other
existing strings.
Several standard constructors generally check if objects can be moved in
a non-throwing manner (usually via std::move_if_noexcept) to preserve
its exception guarantees. This means that if these were used with
certain containers any reallocations internally would cause resource
churn, as copies would be necessary instead of moves.
This way, if they're every used in that manner, the right behavior is
always performed.
