src/test/ui/issues/issue-40883.rs

   1 // run-pass
   2 #![allow(dead_code)]
   3 // check that we don't have linear stack usage with multiple calls to `push`
   4
   5 #![feature(test)]
   6
   7 extern crate test;
   8 use std::mem;
   9
  10 fn meal() -> Big {
  11     if test::black_box(false) {
  12         panic!()
  13     }
  14     Big { drop_me: [
  15         None, None, None, None, None, None, None, None,
  16         None, None, None, None, None, None, None, None,
  17         None, None, None, None, None, None, None, None,
  18         None, None, None, None, None, None, None, None,
  19         None, None, None, None, None, None, None, None,
  20         None, None, None, None, None, None, None, None,
  21     ]}
  22 }
  23
  24 pub struct Big {
  25     drop_me: [Option<Box<u8>>; 48],
  26 }
  27
  28 #[inline]
  29 fn push(out: &mut Vec<Big>) {
  30     out.push(meal());
  31 }
  32
  33 #[inline(never)]
  34 pub fn supersize_me(out: &mut Vec<Big>) {
  35     push(out);
  36     push(out);
  37     push(out);
  38     push(out);
  39     push(out);
  40     push(out);
  41     push(out);
  42     push(out);
  43     push(out);
  44     push(out);
  45     push(out);
  46     push(out);
  47     push(out);
  48     push(out);
  49     push(out);
  50     push(out); // 16 calls to `push`
  51
  52     verify_stack_usage(out);
  53
  54     push(out);
  55     push(out);
  56     push(out);
  57     push(out);
  58     push(out);
  59     push(out);
  60     push(out);
  61     push(out);
  62     push(out);
  63     push(out);
  64     push(out);
  65     push(out);
  66     push(out);
  67     push(out);
  68     push(out);
  69     push(out); // 16 calls to `push`
  70 }
  71
  72 #[inline(never)]
  73 fn verify_stack_usage(before_ptr: *mut Vec<Big>) {
  74     // To check stack usage, create locals before and after
  75     // and check the difference in addresses between them.
  76     let mut stack_var: Vec<Big> = vec![];
  77     test::black_box(&mut stack_var);
  78     let stack_usage = isize::abs(
  79         (&mut stack_var as *mut _ as isize) -
  80             (before_ptr as isize)) as usize;
  81     // Give space for 2 copies of `Big` + 272 "misc" bytes
  82     // (value observed on x86_64-pc-windows-gnu).
  83     if stack_usage > mem::size_of::<Big>() * 2 + 272 {
  84         panic!("used {} bytes of stack, but `struct Big` is only {} bytes",
  85                stack_usage, mem::size_of::<Big>());
  86     }
  87
  88 }
  89
  90 pub fn main() {
  91     let mut v = vec![];
  92     test::black_box(&mut v);
  93     supersize_me(&mut v);
  94 }