Re: transpiling to low level C

On 12/16/2024 7:19 PM, Keith Thompson wrote:

bart <bc@freeuk.com> writes:
[SNIP]

In that case I've no idea what you were trying to say.
>
When somebody says that 'goto' can emulate any control structure, then
clearly some of them need to be conditional; that is implied.
>
Your reply suggested they you can do away with 'goto', and use
recursive functions, in a scenario where no other control structures
need exist.
>
OK, if this is not for an IL, then it's not a language I would care
for either. Why tie one hand behind your back for no good reason?

 I read Janis's post.  I saw a suggestion that certain constructs are
*theoretically* unnecessary.  I saw no suggestion of any advocacy for
such an approach.
 """
A 'goto' may be used but it isn't strictly *necessary*. What *is*
necessary, though, that is an 'if' (some conditional branch), and
either 'goto' or recursive functions.
"""
 

While if-call is technically possible, it is likely to result in a significantly higher performance overhead if compared with if-goto.
Say:
   if-goto:
     can be a single CPU instruction on some targets.
     Both RISC-V and BJX2 can do single-instruction compare-and-branch.
   if-call:
     A whole lot more than 1 instruction...
     One may have call/return, stack frame creation, ...
       Or, a backend that is very clever about inlining.
Also: if-goto can readily express pretty much every other intra-function control flow construct:
   for, while, switch, break, continue, ...
And, is less awkward for a compiler than trying to map control flow to any of the other constructs. Also it is generally the fastest construct for implementing these higher level constructs.
Meanwhile, if-call, good luck... You are also going to need something beyond normal C style variable scoping to make this work acceptably. At best, it is likely to be very awkward and likely to perform poorly.
Though, it is possible that one could make a case for a 3-way branch operator in the IR, say:
   if3(x,y) A, B, C
Which does the equivalent of, say:
   if(x<y)goto A;
   else if(x>y)goto B;
   else goto C;
This would be a bit niche, but could be useful for things like implementing "switch()" via binary subdivision.
Though, functionally could decay into normal if-goto in various cases.
...

[...]
 

So what was your proposal about?

 I saw no proposal.