Benchmarking c compilers

This is a discussion on Benchmarking c compilers within the C Programming forums, part of the General Programming Boards category; What would be an appropriate simple function to compare the relative execution speed of different c compilers. I've used the ...

  1. #1
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    Benchmarking c compilers

    What would be an appropriate simple function to compare the relative execution speed of different c compilers. I've used the following, which shows clear differences between gcc, Pelles C and Borland, for example but doesn't necessarily evaluate all compiler optimizations.

    Code:
    
    #include <stdio.h> 
    #include <math.h>
    #include <time.h>
     
    #define NRUNS 1000
     
    int main()
    {
    	int h=0,i,j,k;
    	double d=0,pi = 4.0*atan(1.0);
    	time_t start,end;
    	printf("Starting now ...");
    	start=clock();
    	for (i=0;i<NRUNS;i++)
    	{	
    		for (j=0;j<NRUNS;j++)
    		{
    			for (k=0;k<NRUNS;k++)
    			{
    				d+=sqrt(pi);
    				h++;
    			}
    		}
    	}
    	end=clock();
    	printf(" done. \n");
    	printf("h: %d \n", h);
    	printf("d: %f \n", d);
    	printf("Time (seconds): %15.3f \n", (double)(end-start)/CLOCKS_PER_SEC);
    	return 0;
    }

  2. #2
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    I sure wouldn't use this.

    All you're really testing is sqrt(). That's a very small part of most programs. I'm sure there are benchmark programs that do a host of tests for this purpose.

    Also, you're not using the high speed timer available for Windows and Linux.

    I like the way you're thinking about testing these different compilers, however!

  3. #3
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    Also, if the compiler is at least a little bit clever, it will move this out of the inner loop, and then collapse the three loops into nothing.
    Code:
    				d+=sqrt(pi);
    				h++;
    After all, just doing h = NRUNS * NRUNS * NRUNS after the loop, and d = (NRUNS * NRUNS * NRUNS) * sqrt(pi) will provide the d and h values.

    Also, assuming the compiler DIDN'T optimize everything, sqrt() is a fairly long operation in relation to the rest of the code, so it will be "most of the time inside your loop". On top of that, different C libraries and/or compiler switches may produce different code for sqrt() - anything from 26 or 100 clock-cycles on a modern x86 processor. This is of course meaningfull if your code does a lot of sqrt() calculations, but not so useful if your code is doing mostly other calculations.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  4. #4
    Captain Crash brewbuck's Avatar
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    I'd get the source code to some real application and compile that under different compilers. Anything less than a few thousand lines of code isn't going to exercise the compiler nearly enough for good results.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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    Thanks

    Of course I agree with all that was posted but perhaps I should have stated my intentions more clearly. I'm writing a small (< 100 lines) packing simulation program which is cpu intensive and one run takes ~27 hours (compiled using a BASIC compiler). The math it includes is very simple (nearest neighbor algo). The prog can easily be converted to C and I'm in the need for speed. I can't afford Intel so I'm evaluating a number of free alternatives using the code listing provided. A few minutes difference in performance doesn't bother me but if I can shave a few hours off, well ...
    Last edited by freevryheid; 01-23-2009 at 01:59 PM. Reason: just how small?

  6. #6
    CSharpener vart's Avatar
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    Quote Originally Posted by freevryheid View Post
    I can't afford Intel
    linux version of Intel compiler is free for personal use.
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  7. #7
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    Quote Originally Posted by freevryheid View Post
    Thanks

    Of course I agree with all that was posted but perhaps I should have stated my intentions more clearly. I'm writing a small (< 100 lines) packing simulation program which is cpu intensive and one run takes ~27 hours (compiled using a BASIC compiler). The math it includes is very simple (nearest neighbor algo). The prog can easily be converted to C and I'm in the need for speed. I can't afford Intel so I'm evaluating a number of free alternatives using the code listing provided. A few minutes difference in performance doesn't bother me but if I can shave a few hours off, well ...
    A packing simulation? A 27 hour run-time packing simulation?

    You post that baby up here and I'll bet you a dollar to a donut that we can chew that little baby right on down in run time!

    Your OS is Windows or Linux?

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