\"while (1) vs. for (;;): Does Compiler Optimization Eliminate Performance Differences?\"

while (1) vs. for (;;): Is There a Speed Difference?

Question:

Does using while (1) instead of for (;;) result in a performance difference in infinite loops?

Answer:

In most modern compilers, there is no performance difference between while (1) and for (;;).

Explanation:

Here's a technical analysis of how these loops are implemented in compilers:

Perl:

Both while (1) and for (;;) result in the same opcodes, as demonstrated by the perl -MO=Concise output:

<code class="shell">a  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 2 -e:1) v ->3
9     <2> leaveloop vK/2 ->a
3        <{> enterloop(next->8 last->9 redo->4) v ->4
-        <@> lineseq vK ->9
4           <;> nextstate(main 1 -e:1) v ->5
7           <@> print vK ->8
5              <0> pushmark s ->6
6              <$> const[PV "foo\n"] s ->7
8           <0> unstack v ->4
-e syntax OK</code>

GCC:

In GCC, both loops compile to the same assembly code, as shown below:

<code class="assembly">.globl t_while
t_while:
.L2:
    movl    $.LC0, %edi
    call    puts
    jmp .L2
.globl t_for
t_for:
.L5:
    movl    $.LC0, %edi
    call    puts
    jmp .L5</code>

Therefore, in most cases, there is no need to prefer one over the other based on performance concerns. The choice can be based on code readability or other factors.

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