85d37c9994
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.
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|---|---|---|
| .. | ||
| texture_filters | ||
| frame_dumper_opengl.cpp | ||
| frame_dumper_opengl.h | ||
| gl_format_reinterpreter.cpp | ||
| gl_format_reinterpreter.h | ||
| gl_rasterizer_cache.cpp | ||
| gl_rasterizer_cache.h | ||
| gl_rasterizer.cpp | ||
| gl_rasterizer.h | ||
| gl_resource_manager.cpp | ||
| gl_resource_manager.h | ||
| gl_shader_decompiler.cpp | ||
| gl_shader_decompiler.h | ||
| gl_shader_disk_cache.cpp | ||
| gl_shader_disk_cache.h | ||
| gl_shader_gen.cpp | ||
| gl_shader_gen.h | ||
| gl_shader_manager.cpp | ||
| gl_shader_manager.h | ||
| gl_shader_util.cpp | ||
| gl_shader_util.h | ||
| gl_state.cpp | ||
| gl_state.h | ||
| gl_stream_buffer.cpp | ||
| gl_stream_buffer.h | ||
| gl_surface_params.cpp | ||
| gl_surface_params.h | ||
| gl_vars.cpp | ||
| gl_vars.h | ||
| pica_to_gl.h | ||
| post_processing_opengl.cpp | ||
| post_processing_opengl.h | ||
| renderer_opengl.cpp | ||
| renderer_opengl.h | ||