[PPC] Make assembler.cpp compile over 30 times faster#7120
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Approved to push after we've released 5.1 stable
Clang was taking around 30 seconds to compile assembler.cpp on my machine, with most of its time spent in code generation for the global initializer for `lookup`. Changing the map key from `std::string` to `std::string_view` drops compile time to under a second. This is because the compiler no longer has to code gen the allocation, initialization, and moves of 2,100 `std::string`s. `std::string_view` is effectively free to initialize in comparison. While I was here I made the map `static const`. It's not required for the build time improvement, but it is more correct and helped me check that no-one is mutating the map.
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Clang was taking around 30 seconds to compile assembler.cpp on my machine, with most of its time spent in code generation for the global initializer for
lookup.Changing the map key from
std::stringtostd::string_viewdrops compile time to under a second. This is because the compiler no longer has to code gen the allocation, initialization, and moves of 2,100std::strings.std::string_viewis effectively free to initialize in comparison.While I was here I made the map
static const. It's not required for the build time improvement, but it is more correct and helped me check that no-one is mutating the map.