You want to avoid branches in hot paths. If you branch inside the loop, lots of branches. If you branch outside the loop (into different specialized loops), few branches. Big fucking deal.
bool w;
int x[1000];
int y[1000];
for(int i=0;i<1000;i++){
x[i] += y[i];
}
if(w){
for(int i=0;i<1000;i++){
y[i] = 0;
}
}
Easier for humans to reason about the branch, when they know that it happens without input from i or y[i].
This is helpful when the `if` statement is complex, or there are multiple if statements, some of which do take y[i] as input.
A loop contains a branch - keep looping or break. At least according to structured programming -- https://en.wikipedia.org/wiki/Structured_program_theorem.
interesting question...
> A loop is a chunk of code that will be run N times depending
oh! turns out you do!
for (fn, n) = {
stop = void (i) {}
run = void (i) { fn(i); go(i + 1) }
go = void (i) { *((i < n) * &run + (i >= n) * &stop)(i) }
go(0)
}
The machine?
The CPU.
Just a simple example, but the conditional branch occurs on line 14 of the generated assembly. It does a comparison (line 13) and then a conditional jump (jl, line 14).
Anyone who started out programming in assembly languages