while (1) Vs. for (;;) Is there a speed difference?

Question

In perl, they result in the same opcodes:

$ perl -MO=Concise -e 'for(;;) { print "foo\n" }'
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

$ perl -MO=Concise -e 'while(1) { print "foo\n" }'
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

Likewise in GCC:

#include <stdio.h>

void t_while() {
    while(1)
        printf("foo\n");
}

void t_for() {
    for(;;)
        printf("foo\n");
}

    .file   "test.c"
    .section    .rodata
.LC0:
    .string "foo"
    .text
.globl t_while
    .type   t_while, @function
t_while:
.LFB2:
    pushq   %rbp
.LCFI0:
    movq    %rsp, %rbp
.LCFI1:
.L2:
    movl    $.LC0, %edi
    call    puts
    jmp .L2
.LFE2:
    .size   t_while, .-t_while
.globl t_for
    .type   t_for, @function
t_for:
.LFB3:
    pushq   %rbp
.LCFI2:
    movq    %rsp, %rbp
.LCFI3:
.L5:
    movl    $.LC0, %edi
    call    puts
    jmp .L5
.LFE3:
    .size   t_for, .-t_for
    .section    .eh_frame,"a",@progbits
.Lframe1:
    .long   .LECIE1-.LSCIE1
.LSCIE1:
    .long   0x0
    .byte   0x1
    .string "zR"
    .uleb128 0x1
    .sleb128 -8
    .byte   0x10
    .uleb128 0x1
    .byte   0x3
    .byte   0xc
    .uleb128 0x7
    .uleb128 0x8
    .byte   0x90
    .uleb128 0x1
    .align 8
.LECIE1:
.LSFDE1:
    .long   .LEFDE1-.LASFDE1
.LASFDE1:
    .long   .LASFDE1-.Lframe1
    .long   .LFB2
    .long   .LFE2-.LFB2
    .uleb128 0x0
    .byte   0x4
    .long   .LCFI0-.LFB2
    .byte   0xe
    .uleb128 0x10
    .byte   0x86
    .uleb128 0x2
    .byte   0x4
    .long   .LCFI1-.LCFI0
    .byte   0xd
    .uleb128 0x6
    .align 8
.LEFDE1:
.LSFDE3:
    .long   .LEFDE3-.LASFDE3
.LASFDE3:
    .long   .LASFDE3-.Lframe1
    .long   .LFB3
    .long   .LFE3-.LFB3
    .uleb128 0x0
    .byte   0x4
    .long   .LCFI2-.LFB3
    .byte   0xe
    .uleb128 0x10
    .byte   0x86
    .uleb128 0x2
    .byte   0x4
    .long   .LCFI3-.LCFI2
    .byte   0xd
    .uleb128 0x6
    .align 8
.LEFDE3:
    .ident  "GCC: (Ubuntu 4.3.3-5ubuntu4) 4.3.3"
    .section    .note.GNU-stack,"",@progbits

So I guess the answer is, they're the same in many compilers. Of course, for some other compilers this may not necessarily be the case, but chances are the code inside of the loop is going to be a few thousand times more expensive than the loop itself anyway, so who cares?

There's not much reason to prefer one over the other. I do think that while(1) and particularly while(true) are more readable than for(;;), but that's just my preference.

Using GCC, they both seem to compile to the same assembly language:

L2:
        jmp     L2

There is no difference according to the standard. 6.5.3/1 has:

The for statement

for ( for-init-statement ; conditionopt ; expressionopt ) statement

is equivalent to

{
  for-init-statement
  while ( condition ) {
    statement
    expression ;
  }
}

And 6.5.3/2 has:

Either or both of the condition and the expression can be omitted. A missing condition makes the implied while clause equivalent to while(true).

So according to the C++ standard the code:

for (;;);

is exactly the same as:

{
  while (true) {
    ;
    ;
  }
}

for(;;) is one less character to type if you want to go in that direction to optimize things.

The Visual C++ compiler used to emit a warning for

while (1) 

(constant expression) but not for

for (;;)

I've continued the practice of preferring for (;;) for that reason, but I don't know if the compiler still does that these days.

Turbo C with this old compilers for(;;) results in faster code then while(1).

Today gcc, Visual C (I think almost all) compilers optimize well, and CPUs with 4.7 MHz are rarely used.

In those days a for( i=10; i; i-- ) was faster than for( i=1; i <=10; i++ ), because compare i is 0, results in a CPU-Zero-Flag conditional Jump. And the Zero-Flag was modified with the last decrement operation ( i-- ), no extra cmp-operation is needed.

    call    __printf_chk
    decl    %ebx          %ebx=iterator i 
    jnz     .L2
    movl    -4(%ebp), %ebx
    leave

and here with for(i=1; i<=10; i++) with extra cmpl:

    call    __printf_chk
    incl    %ebx
    cmpl    $11, %ebx
    jne     .L2
    movl    -4(%ebp), %ebx
    leave