Repository: rust
Issue: Extremely slow optimizer performance when including large array of strings
Labels: A-LLVM,C-enhancement,A-codegen,I-compiletime,T-compiler,C-optimization

Consider the following test program:

```rust
fn main() {
    let words = include!("num_array.rs");
    let mut l = 0;
    for word in words.into_iter() {
        l += word.len();
    }
    println!("{}", l);
}
```

`num_array.rs` contains an array of 250k strings:

```
$ (echo '['; seq 1 250000 | sed 's/.*/"&",/' ; echo ']') > num_array.rs
$ head -n 5 num_array.rs 
[
"1",
"2",
"3",
"4",
$ tail -n 5 num_array.rs 
"249997",
"249998",
"249999",
"250000",
]
```

Compiling this in debug mode took about 45 seconds; long, and potentially a good test case for compiler profiling, but not completely ridiculous.

Compiling this in release mode showed no signs of finishing after 45 minutes.  stracing rustc showed two threads, one blocked in a futex and the other repeatedly allocating and freeing a memory buffer:

```
mmap(0x7fb665a00000, 2097152, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb637400000
munmap(0x7fb637400000, 2097152)         = 0
mmap(0x7fb665a00000, 2097152, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb637400000
munmap(0x7fb637400000, 2097152)         = 0
madvise(0x7fb66531a000, 659456, MADV_DONTNEED) = 0
madvise(0x7fb6653da000, 139264, MADV_DONTNEED) = 0
madvise(0x7fb66540c000, 1576960, MADV_DONTNEED) = 0
madvise(0x7fb665a0c000, 2043904, MADV_DONTNEED) = 0
madvise(0x7fb665600000, 4194304, MADV_DONTNEED) = 0
madvise(0x7fb63e600000, 12582912, MADV_DONTNEED) = 0
madvise(0x7fb661000000, 25165824, MADV_DONTNEED) = 0
madvise(0x7fb66531a000, 659456, MADV_DONTNEED) = 0
madvise(0x7fb6653da000, 139264, MADV_DONTNEED) = 0
madvise(0x7fb66540c000, 1576960, MADV_DONTNEED) = 0
madvise(0x7fb665a0c000, 2043904, MADV_DONTNEED) = 0
madvise(0x7fb667a00000, 10485760, MADV_DONTNEED) = 0
madvise(0x7fb646000000, 100663296, MADV_DONTNEED) = 0
mmap(0x7fb665a00000, 2097152, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb637400000
munmap(0x7fb637400000, 2097152)         = 0
mmap(0x7fb665a00000, 2097152, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb637400000
munmap(0x7fb637400000, 2097152)         = 0
madvise(0x7fb66531a000, 659456, MADV_DONTNEED) = 0
madvise(0x7fb6653da000, 139264, MADV_DONTNEED) = 0
madvise(0x7fb66540c000, 1576960, MADV_DONTNEED) = 0
madvise(0x7fb665a0c000, 2043904, MADV_DONTNEED) = 0
madvise(0x7fb665600000, 4194304, MADV_DONTNEED) = 0
madvise(0x7fb63e600000, 12582912, MADV_DONTNEED) = 0
madvise(0x7fb661000000, 25165824, MADV_DONTNEED) = 0
madvise(0x7fb66531a000, 659456, MADV_DONTNEED) = 0
madvise(0x7fb6653da000, 139264, MADV_DONTNEED) = 0
madvise(0x7fb66540c000, 1576960, MADV_DONTNEED) = 0
madvise(0x7fb665a0c000, 2043904, MADV_DONTNEED) = 0
madvise(0x7fb667a00000, 10485760, MADV_DONTNEED) = 0
madvise(0x7fb646000000, 100663296, MADV_DONTNEED) = 0
```

By way of comparison, an analogous C program compiled with GCC takes 4.6s to compile without optimization, or 5.6s with optimization.  Python parses and runs an analogous program in 1.2s.  So, 45s seems excessive for an unoptimized compile, and 45m+ seems wildly excessive for an optimized compile.

Complete test case (ready to `cargo run` or `cargo run --release`): [testcase.tar.gz](https://github.com/rust-lang/rust/files/736409/testcase.tar.gz)