bearophile wrote:
This is something that I want for D too, it's important:
Jonathan Shapiro (of BitC) makes an excellent argument that, in a systems
language, it is often undesirable to depend on the whims of an
ill-specified optimizer to convert abstract code into efficient machine
code. The BitC specification thus includes the idea of guaranteed
optimizations, to allow code to be written in a high-level style with
predictably low or nonexistent runtime cost (link). [...] Because Clay
seeks to support systems programming with high-level abstraction, certain
patterns should be guaranteed to be optimized in a certain way, instead of
being left to the whims of LLVM or a C compiler.
>> [...]
>> It should be possible to specify
that one or more of these optimizations is required, and have the compiler
raise an error when they cannot be applied for some reason.<
Frankly, this is meaningless. For example, while C does not specify what
optimizations will be done, in practice you'd be very hard pressed to find one
that didn't do:
1. replacing a*4 with a<<2
2. doing decent register allocation, obviating the role of the "register"
keyword
3. dead assignment elimination
4. named return value optimization
5. etc.
Additional optimizations should not be prevented, however.
I.e. the same situation as today.
