Re:No sane compiler would optimize atomics (2015)
by UncleMeat on Tuesday July 13, 2021 @08:26AM
(#27820074)
> I want the compiler to take my exact instructions and generate the best machine code it can, that follows those exact instructions.
Two problems.
1. Your definition of "exact" is not exact. It is exact in your mind, but it isn't going to be precisely the same across all developers and compiler authors cannot reasonably develop hard requirements from this. This is especially true when targeting different machines. Operations on a uin64_t aren't going to look the same on a 32 bit machine, for example.
2. Attempting to do this makes your programs slow as hell. You can claim that compiler optimizations don't matter... but you are free to deploy debug builds if you really think this. C and C++ especially aim to provide a sort of ambient performance where everything is fast rather than just providing speed for hot loops. People complain nearly daily about modern applications being slow and then turn around and say we should throw away decades of compiler optimizations.
Two problems.
1. Your definition of "exact" is not exact. It is exact in your mind, but it isn't going to be precisely the same across all developers and compiler authors cannot reasonably develop hard requirements from this. This is especially true when targeting different machines. Operations on a uin64_t aren't going to look the same on a 32 bit machine, for example.
2. Attempting to do this makes your programs slow as hell. You can claim that compiler optimizations don't matter... but you are free to deploy debug builds if you really think this. C and C++ especially aim to provide a sort of ambient performance where everything is fast rather than just providing speed for hot loops. People complain nearly daily about modern applications being slow and then turn around and say we should throw away decades of compiler optimizations.