Pascal not considered harmful - was Re: Rich kids are into COBOL

[Chuck Guzis]

On 02/20/2015 02:32 PM, Ali wrote:

> Excuse my ignorance but then how is a compiler written? I always thought
> that you would need to know op codes and assembler to write a compiler. I.E.
> you can't write and efficient compiler by using a high level language.

You have a front-end, which does the lexical work and translates the 
program into some intermediate form, such as a tree.  In the middle, you 
have optimization and checking--and finally, you have the back end which 
essentially emits code--but that doesn't necessarily imply that the 
compiler author knows the numeric opcodes or the  precise instruction 
format.  Many compiler backends feed into an existing assembler, which 
puts it all together.

Knowing the numeric opcodes and instruction format isn't all that it 
would seem to be.  I never had much more than a passing familiarity with 
the numeric opcodes of the CDC STAR--given that there was 8 bits for the 
opcode and 8 more "modifier" bits, you arguably had a machine with 
thousands of opcodes.  What was hardest and very important was 
committing to memory the *timings* of those instructions, within a 
superscalar, segmented, pipelined vector architecture.

--Chuck