Question

Say I have a poor language – that creates lot of redundant assembly code ( like say for something as simple as a+b it creates a 10 liner assembly but does the job )
and another C like language which creates nice optimized assembly code ( 2 lines for a simple code like a + b) .
I create a compiler in both these languages with the same subset
Now I get a compiler for my language and am ready for bootstrapping
Don’t you think the compiler of the former case would be a bad choice though it can do bootstrapping albeit a poort code generation ?
Alternatively isn’t the first language used for defining the subset going to have its influence in all the layers about ? I.e a compiler generated from this compiler ?

Answer 1

A freshly boot strapped compiler won’t beat a C compiler, that’s for sure. But nobody says it has to stay that way (well, you’ll have a very hard time beating even modern C compilers, but let’s assume we’re competing with something else than compilers for portable assembly language refined over thirty years). Depending on your language, it’s very possible that extending the bootstrapped compiler is much easier than extending the one written in C. This can allow many optimization passes that would have been harder to implement in C, gradually increasing the performance of your compiler (as it self-hosts, i.e. compiles itself) and the performance of all other programs you compile.

That distinction brings us to another important point: The compiler’s performance is rarely relevant, as long as it’s not completely unreasonable. The performance of the generated code is usually much more important, and that depends on your compiler’s code generator, not on the code generator of the compiler used to compile your generator.

Third, with projects such as LLVM, generating decent assembly code is no longer as hard as it used to be. If you generate okay LLVM code, even if it contains redundancy, LLVM has many optimization passes that can take care of that and will produce better actual assembly code and allocate registers better than you could do by yourself within a reasonable timespan.