Re: Thompson's 2c vs. gcc

>>>[Comparison of output code from GCC, lcc, and Plan 9 C compilers.]


Preston Briggs writes:
>>[GCC 1.35 didn't generate very good MIPS code. It's better now.]


jbuck@forney.berkeley.edu (Joe Buck):
>[Gcc did not have an instruction scheduler and did not fill delayed
> branch slots. Adding them makes about a 30% difference on SPARCs.]


I believe that GCC ports rely on the MIPS assembler. The MIPS assembler
by default provides a virtual machine without delay slots then rearranges
instructions to fill the real delay slots. The assembler can be told to
reveal the underlying machine to allow explicit delay slot filling.


The current GCC produces code both ways. It is thus better able to take
advantage of delay slot filling. But even the older ports did some just
by virtue of the assembler.


I do agree that GCC produces better quality MIPS code than it did a few
years ago.


;-D on ( Quality time with your compiler ) Pardo
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