[ER] A missed removal of division by zero test #86109
Description
This function foo:
type T = i16; pub fn foo(start: T) -> T { if start <= 0 { return 0; } let mut count = 0; for i in start .. 10_000 { if 752 % i != 0 { count += 1; } } count } fn main() { println!("{}", (T::MIN ..= T::MAX) .map(foo) .sum::<T>()); }Compiled with optimizations by rustc (1.54.0-nightly 4de7572 2021-05-01) gives:
foo: lea eax, [rdi - 1] movzx eax, ax cmp eax, 9998 ja .LBB0_1 mov r8d, 9999 sub r8d, edi mov esi, edi neg esi xor ecx, ecx .LBB0_4: cmp r8w, si jae .LBB0_6 mov ax, 752 xor edx, edx idiv di lea eax, [rdi + 1] cmp dx, 1 sbb cx, -1 movzx edx, ax mov edi, eax cmp edx, 10000 jne .LBB0_4 mov eax, ecx ret .LBB0_1: xor ecx, ecx mov eax, ecx ret .LBB0_6: push rax lea rdi, [rip + str.0] lea rdx, [rip + .L__unnamed_1] mov esi, 57 call qword ptr [rip + core::panicking::panic@GOTPCREL] ud2 str.0: .ascii "attempt to calculate the remainder with a divisor of zero"Running the code you confirm that the divisor can't be zero.
I think Rustc should be able to remove this test.
(The same code with T=u16 contains no division by zero test).