If python compiles to assembly and an OS is written in it, will it compete favorably with C in benchmarks?

Question

Ok, I have used the word python in the question, but it well could be language agnostic in that: If a language X has a well optimised compiler targeting assembly and an OS is written in that language, then will it compete favorably with C in benchmarks?

This comes from two conceptions I have (could be wrong):

• Languages are defined by grammar rules (syntax-semantics); they themselves are independent of performance. Performance is a function of implementation.
• C is often efficient because the most popular OS(es) are written in it - so limited wrapping and unwrapping - and it compiles to (these days) well optimized assembly code.

And, yes, before some of us pull out guns, I understand and appreciate that in certain situations some languages may outperform C, but by and large C does better than most languages in most situations.

Answer 1

Theoretically speaking, for any idealized program there will be some set of assembly instructions that is the most efficient way to enact that program. In theory, any language could potentially be compiled to these ideal machine instructions, given a smart enough compiler.

Practically speaking, no, there is no compiler that would turn python into machine code that is as fast as an optimized C program doing the same thing. What's more, it's unlikely that such a compiler can be written, because python doesn't have primitives for low level things like pointers. In order to make the code optimally fast, the compiler would have to figure out the intentions of the code before it could translate it into low level commands, which is a ridiculously hard problem.

That's not to say it can't come close. Maybe.

Answer 2

In general, most block-structured statically-typed languages will compile into very similar machine code (most machine architectures provide support for HLL concepts like for loops and switch statements). The problem with Python, as others have noted, is its dynamic nature. This means more run-time checks and a bigger run-time library, which means slower execution, there's just no way around that. The doesn't mean it's not possible to write an OS in it, but you're never going to get the raw performance that simpler languages like C or FORTRAN can provide.

What would be interesting to see would be "systems Python", with support for pointers and possibly with some restrictions on the language's dynamic features to permit more efficient compiled forms. I'm not familiar enough with Python to know how feasible that is, but there have been similar things done before.

Answer 3

Instead of compiling to assembly, lets take a more practical approach (that do exist).

There are programs such as f2c and p2c that compile fortran and pascal to c. The question is then "can these compilers write better code than you can?" In p2c (for example), it is necessary to write additional code in C to handle string processing.

This translates to assembly too. Any time there is something that the language is doing for you, under the covers, there is the likely hood that a programmer with understanding of the structures and algorithms necessary for that would write more compact (and faster) code in C.

---

(edit)

Lets consider a dynamic typed language that has strings and ints, a "+" operator that is thoroughly overloaded and a print command.

var foo = 3;
var bar = "a";
var qux = bar + foo;
print qux;

The C version of this program would be:

#include <stdio.h>
#include <string.h>

int main(int argc, char **argv) {
    int foo = 3;
    char *bar = "a";
    char qux[3];
    sprintf(qux,"%s%d",bar,foo);
    printf("%s",qux);
}

(Yes, I know that isn't optimal and is a contrived example) Which compiles to the following assembly on my machine (gcc -S -O9 foo.c)

    .file   "foo.c"
    .section    .rodata.str1.1,"aMS",@progbits,1
.LC0:
    .string "a"
.LC1:
    .string "%s%d"
.LC2:
    .string "%s"
    .text
    .p2align 4,,15
.globl main
    .type   main, @function
main:
.LFB23:
    .cfi_startproc
    pushq   %rbx
    .cfi_def_cfa_offset 16
    movl    $3, %ecx
    movl    $.LC0, %edx
    movl    $.LC1, %esi
    xorl    %eax, %eax
    subq    $16, %rsp
    .cfi_def_cfa_offset 32
    movq    %rsp, %rdi
    .cfi_offset 3, -16
    call    sprintf
    movq    %rsp, %rsi
    movl    $.LC2, %edi
    xorl    %eax, %eax
    call    printf
    addq    $16, %rsp
    .cfi_def_cfa_offset 16
    popq    %rbx
    .cfi_def_cfa_offset 8
    ret
    .cfi_endproc
.LFE23:
    .size   main, .-main
    .ident  "GCC: (SUSE Linux) 4.5.1 20101208 [gcc-4_5-branch revision 167585]"
    .section    .comment.SUSE.OPTs,"MS",@progbits,1
    .string "Ospwg"
    .section    .note.GNU-stack,"",@progbits

At this point, the question is what would it take to write a compiler that would be able to analyze the dynamic code and generate that assembly. While it might be possible with that extremely limited language, once you start adding more complexity to the language, a translation into something closer to the machine requires more and more code to handle the dynamic typing, or its own runtime (objective C takes this approach) - in either case, it will be slower than something written in C that doesn't need to have that overhead.

Or, the compiler has analyzed all the execution paths of the code (for the dynamic language) which I believe is equivalent to solving the halting problem.

Answer 4

No, it's never going to happen. Even if you performed a perfect reduction from Python to machine code, there are still things like Python creates all objects on the heap and such which must be translated for the program to execute correctly which are slower than a C program placing some or many objects on the stack. In addition, there will be dynamic types and lookups which cannot be statically inferred, for example.

It's quite impossible.

Answer 5

When you use Python as an example, are you considering both the language and its compiler/interpreter to produce an operating system? Or you are writing a compiler to convert your high level language into bare metal opcode?

Such high level languages are usually managed in a sense that you never handle garbage collection, pointers, physical addresses, etc. Which make it hard (for me at least) to imagine how to produce an operating system directly communicating with the machine.

Unless you are writing some high level operating system consuming services produced by some underlying hardware abstraction layer, and a physical address manager, which sounds like a smart idea; having some modular operating system partially written in C, partially in R, and the rest in Python

Answer 6

Generally I don't think a compiled Python program will outperform an equivalent C program (although there might be some exceptional situations). But the reasoning might not be what you expect.

Summary

• Not all compiled languages are equal regarding performance.

• Mixed language between OS and application doesn't matter much.

Reasoning

You write:

This comes from two conceptions I have (could be wrong):

• Languages are defined by grammar rules (syntax-semantics); they themselves are independent of performance. Performance is a function of implementation.

• C is often efficient because the most popular OS(es) are written in it - so limited wrapping and unwrapping - and it compiles to (these days) well optimized assembly code.

You're not completely right.

As others already pointed out, Python's dynamic nature implies some overhead in the resulting assembly / machine instructions.

So, for some languages (e.g. Python or Java), to fulfill their semantics the resulting machine code must include additional overhead instructions that a lower-level language like C doesn't need. So languages are not "independent of performance".

You mention the relationship of application language to OS language. This matters only at the interface between application code and OS calls when it's necessary to pass parameters and data structures between application and OS. If they a really conceptually different, you might experience a slow-down of system calls because of necessary data conversions.

But as long as your program is computing and not doing I/O, it doesn't call the OS, so there's no need to convert anything, and for your application, the OS is just a library that you might call when you feel the need to do so. The rest of the time, it just occupies memory, but no CPU resources.

So why is C a good language for an OS and Python not?

The reason for C-based OSes is not to best support C-written applications, but because an OS must interact with the machine hardware on a low level, and here C can do almost everything that assembly can do (e.g. using pointers representing absolute addresses). Python's concepts don't support this low-level view of your machine that an OS must deal with.

So, for every layer of the overall software, you should choose the appropriate language (and make sure they can interact without too much pain). For an OS, C is a good choice, and for applications you can choose whatever best fits the application's needs.

And one last statement on performance: 90% of wasted-performance cases exist because of poor algorithms or poor programmer's skills, easily losing factors of 10 or 100 when compared to a proper solution, whereas a compiled language might lose a factor of maybe 3 against C.

Answer 7

Python is intrinsically slower than C. For example, addition in C can compile into a single machine instruction, while Python needs to perform a runtime lookup to check if any of the operand types has overloaded addition.

Even the theoretical "sufficently smart compiler" would not be able to compile this overhead away in all cases, since overloads can be can be added and altered at runtime triggered by non-deterministic factors like user input.

So even with a super-optimized compiler, Python would never be as fast.

So while you are theoretically correct that performance is a function of implementation rather than the language itself, the semantics of a language may make it more or less amenable to fast code. C was deliberately designed to avoid unnecessary overhead while Python prioritize flexibility and ease of use above raw speed.

Answer 8

This may be possible if you write in a restricted version of Python that can be easily compiled/optimised to machine code.

Python as it's commonly used are very dynamic, and it contains a number of constructs that are hard to optimise for a compiler.

For example, iterators are very hard to optimise as there need to be code generator for every type of iterable data types. But if you restrict your constructs to just using for-range iteration and list iteration, that can be much more easily optimised.

Once you've defined a subset of Python and wrote an optimising compiler for that subset, then you'll likely end up with something that looks very similar to RPython that's used by PyPy project. It's basically a language that feels just like writing C but with a superficially Python-like syntax.

Answer 9

There are JavaScript implementations using JIT compilers that come pretty close to C efficiency. Enough to run a word processor or spreadsheet in a browser. (Apple does this by switching from interpreted code to quickly compiled code to optimised code to code compiled with clang at highest optimisation).

That can be done because things that could be in principle dynamic are not in practice. Say x could have any type, but the last million times you checked it was an integer. So you compile code that checks once that it is an integer and then runs optimised code for this - if it’s a string at the billionth check then you recompile the code.

Same thing could be done for python.

PS. It doesn't matter one bit what language the OS is written in. That would affect all code running on that OS in exactly the same way.

Answer 10

I just read an article saying that llvm is designed to have a front-end for any language (ie Python) and has a common optimizer/generator. So you could write a front-end... So it could be as fast. (even faster if you believe HotSpot numbers you can get even faster)

Java is actually a pretty good example. It's normally byte-code, but there are several ways to compile it to native code.

What you might run into is the problems with accessing devices, memory management, interupts, and such without adding some system specific additions.

I think you could take Linux as an example. There is a bunch of code that is common across platforms. That could probably be written in anything. But there is also system/device specific code. That would need a more system level language. And yes, you could probably find a way in Python to handle that.

Answer 11

C compiles to machine, not assembly. If python, or any other language, also compiled to the machine codes, then it would be just as fast (this also depends on how well the compiler optimizes, though).