Re: Ada vs. C performance, was Possible to write compiler to Java VM?

Arch Robison <robison@kai.com> writes:
> >[Do Ada compilers really generate better code than C compilers for similar
> >source code? -John]
> [...] This is of course a single data point, probably obsolete. But I think
> there is a strong reason to suspect that C compilers will generally
> generate better code than Ada compilers. [...]


      Of course the argument doesn't hold with GNAT since the backend is
the same for Ada and C. I'm pretty sure that for every C program, you
can write an Ada program (C-style) that will generate the same code. I
don't know if in some case the reverse is false and if indeed GCC take
advantage of more semantic information (write an Ada program with no C
equivalent for performance).


      I agree that optimization is a commercial issue, so pinpointing
early Ada compilers is not really relevant (except for creating myth
of inefficiency ;-).


      A minor point, it's easy, given a factor k, to write an Ada program
that will outperform the "same" C program, just put a large local
array in a procedure and call it a lot, in C it must be initialized to
zero, and this is not the case in Ada so it will be faster (how
semantic can affect performance ;-). (I don't think there's a way to
have non zero'ed data on the stack in C.)


--
Laurent Guerby <guerby@gnat.com>, Team Ada.
--

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