#![feature(iterator_step_by)] #[inline(never)] pub fn first_foo(mut a: i32, b: i32) -> i32 { let mut tot = 0; while a < b { tot += a; a += 3; } tot } #[inline(never)] pub fn second_foo(x: std::ops::Range<i32>) -> i32 { let mut tot = 0; #[allow(deprecated)] for a in x.step_by(3) { tot += a; } tot } fn main() { println!("{}", first_foo(0, 1000)); println!("{}", first_foo(0, 100000)); println!("{}", second_foo(0 .. 1000)); println!("{}", second_foo(0 .. 100000)); } 

_ZN4test9first_foo17he3a0bddb42457919E: testl %ecx, %ecx jle .LBB0_1 xorl %edx, %edx xorl %eax, %eax .p2align 4, 0x90 .LBB0_4: addl %edx, %eax addl $3, %edx cmpl %ecx, %edx jl .LBB0_4 jmp .LBB0_2 .LBB0_1: xorl %eax, %eax .LBB0_2: retq _ZN4test10second_foo17hd5d21559ba84e6d1E: movq %rcx, %r9 shrq $32, %r9 xorl %r8d, %r8d xorl %r10d, %r10d xorl %eax, %eax testb $1, %r10b je .LBB1_11 jmp .LBB1_2 .p2align 4, 0x90 .LBB1_7: shrq $32, %rdx addl %eax, %edx movb $1, %r10b movl %edx, %eax testb $1, %r10b je .LBB1_11 .LBB1_2: cmpl %r9d, %ecx jge .LBB1_5 leal 1(%rcx), %edx cmpl %r9d, %edx jge .LBB1_4 leal 2(%rcx), %edx cmpl %r9d, %edx jge .LBB1_9 addl $3, %ecx shlq $32, %rdx movl $1, %r10d jmp .LBB1_6 .p2align 4, 0x90 .LBB1_11: movq %rcx, %r10 shlq $32, %r10 xorl %edx, %edx cmpl %r9d, %ecx setl %dl cmovgeq %r8, %r10 addl %edx, %ecx jmp .LBB1_6 .p2align 4, 0x90 .LBB1_4: movl %edx, %ecx jmp .LBB1_5 .LBB1_9: movl %edx, %ecx .p2align 4, 0x90 .LBB1_5: xorl %edx, %edx xorl %r10d, %r10d .LBB1_6: orq %r10, %rdx testl %edx, %edx jne .LBB1_7 retq 

_ZN5test210second_foo17h5b0eb3168418bdd1E: movq %rcx, %rdx shrq $32, %rdx xorl %eax, %eax cmpl %edx, %ecx jge .LBB1_3 xorl %eax, %eax .p2align 4, 0x90 .LBB1_2: addl %ecx, %eax addl $3, %ecx cmovol %edx, %ecx ; what is this for? cmpl %edx, %ecx jl .LBB1_2 .LBB1_3: retq