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Sneak peek to C generated code

Next major PureBasic version will feature a brand new C backend,
which will allow to support virtually any CPU, current and future.
The generated file is a big flat file, with no include directive to
allow the fastest compilation speed as possible. In the meantime, we
decided to create a C output as clean as possible to allow easy
modification or even direct reuse into a C project. Let's take a look
to it by comparing a PureBasic snippet and its generated C code
counterpart:

Procedure Test()
  Counter = Counter + 5

  If Counter = 5
    MessageRequester("Hello world", "Hello")
  EndIf

  ProcedureReturn 6
EndProcedure

Test()

And the generated C code (omitting all boilerplate) :

static unsigned short _S1[]={72,101,108,108,111,32,119,111,114,108,100,0};
static unsigned short _S2[]={72,101,108,108,111,0};

static integer f_test()
{
  integer r=0;
  integer v_counter=0;

  v_counter=(v_counter+5);

  if (v_counter==5)
  {
    integer rr0=PB_MessageRequester(_S1,_S2);
  }

  r=6;
  goto end;
  end:
  return r;
}

int __stdcall WinMain(void *instance, void *prevInstance, void *cmdLine, int cmdShow)
{
  PB_Instance = GetModuleHandleW(0);
  PB_MemoryBase = HeapCreate(0,4096,0);
  SYS_InitString();
  PB_InitDesktop();
  PB_InitRequester();

  integer rr1=f_test();

  SYS_Quit();
}

As we can see, the code is pretty close to PureBasic one, and easy to
read. Inline C will be supported, and all the objects like variables,
arrays, lists etc. could be accessed by following the generated token
name pattern (example: 'v_' prefix for variables followed with the
PureBasic name in lowercase).

What about compilation speed ? We are using GCC 8.1.0 with no
optimization (-O0) on Windows 10 x64 on a first gen Core i7 to
perform the tests. We compile a 13.000 lines program, DocMaker, with
debugger ON:

  * GCC backend: about 3 seconds to create the executable
  * FASM backend: about 1 second to create the executable

So that's about 3 times slower but still an OK time to develop. Next
test is a big program, the PureBasic IDE, with about 125.000 lines of
codes with debugger ON. We also includes Microsoft VisualC++ 2015 in
the tests:

  * GCC backend: about 24 seconds to create the executable
  * VC++ backend: about 9 seconds to create the executable
  * FASM backend: about 4 seconds to create the executable

GCC is a lot slower, about 6 times, than the current FASM backend.
The VC++ backend is about 2 times slower, which is much better but
not that great. All in all, the FASM backend will still be better to
use for quick development cycle. Keep in mind than it is very early
tests and as we just seen, just switching the C compiler could
dramatically increase compile time. That's it for now, next time we
will focus about runtime performance between C and FASM backends !

This entry was posted in Compiler on April 22, 2021 by Fred.

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