Performance Evaluation

We implemented the test programs in Pascal first and ported them to C and Oberon, preserving the structure as good as we could. The compilers tested were MPW Pascal, MPW C, MPW Oberon, and MacOberon. MPW Pascal and MPW C are commercial products. The latter two work with intermediate code and supposedly employ elaborate optimizations to reduce code size and execution speed. We measured on a Macintosh Quadra 700 equipped with a 25 MHz MC 68040 and 8 MBytes of RAM. Table 1 shows the time consumed averaged over five executions of the respective programs.

MPW Oberon generates the fastest code on average. The fact that MPW Oberon is even faster than MPW C came as a genuine surprise, after all MPW C is a sophisticated optimizing compiler in its third version. MacOberon, the second Oberon compiler in our test series, produces equally good code as the C compiler, proving that a good programming language can be as efficient as C (against popular belief!). Analysis of the object code revealed that C wins in the first three categories because it uses register variables. The two Oberon compilers are not taking advantage of register variables.

Table 1: Execution times in milliseconds. Best values bold.

	MPW Pascal	MPW C	MPW Oberon	MacOberon
Powers	375	246	411	788
Heuristic	2089	1765	1795	1854
Primes	914	576	1003	991
Integrate	4952	5442	3964	4087
KnightsTour	7826	4705	4248	4867
Marriage	1714	2075	1970	2157
Selection	2313	481	355	421
Bubble	3809	2759	2457	3889
Hanoi	2584	4193	2201	2160
Quicksort	2998	2092	2357	2598
Queens	5489	8046	5380	4743
IMatMult	249	290	181	222
RMatMult	266	312	183	226
Rating	39	34	23	34

In table 2 MPW Oberon wins again, now in the time it needs to translate the sample programs. We believe that our compiler treats the import of modules in a more efficient fashion than the other compilers, for example with a better data structure for identifiers (see above). The effect of differences in import module treatment are somewhat out of proportion since the examples are very short.

Table 2: Compilation time in milliseconds. Best values bold.

	MPW Pascal	MPW C	MPW Oberon	MacOberon
Powers	992	1614	102	590
Heuristic	1042	1800	218	633
Primes	1406	1484	168	636
Integrate	1018	1340	212	640
KnightsTour	1044	1998	214	647
Marriage	1556	2160	188	660
Selection	1022	1236	210	586
Bubble	1422	1400	162	529
Hanoi	938	1432	170	653
Quicksort	1492	1682	198	553
Queens	1088	2234	202	569
IMatMult	1210	1704	200	660
RMatMult	1216	1456	180	633
Rating	40	51	13	26

Finally table 3 lists the size of the generated object code. C takes this category with a wide margin for two reasons:

• C keeps as many variables as possible in registers, resulting in fewer load instructions and shorter opcodes.
• The drastic differences between C and the other languages (KnigthsTour, Marriage, Selection) is mostly due to variable initialization code. MPW C exploits the static initialization of variables of the C language [KerRi]. In the case of MPW Oberon, the dynamic initialization code for Marriage is 774 bytes. Without dynamic initialization, MPW Oberon generates about 10-20% more code than MPW C.