Incremental compilation breaks sanitizers

[japaric]

STR

examples/uninitialized-read.rs

use std::mem;

fn main() {
    let xs: [u8; 4] = unsafe { mem::uninitialized() };
    let y = xs[0] + xs[1];
}

$ export CARGO_INCREMENTAL=1

$ cargo run --target x86_64-unknown-linux-gnu --example uninitialized-read
   Compiling msan v0.1.0 (file:///home/japaric/rust/san/msan)
    Finished dev [unoptimized + debuginfo] target(s) in 0.38 secs
     Running `target/x86_64-unknown-linux-gnu/debug/examples/uninitialized-read`

# sanitizer doesn't kick in
$ RUSTFLAGS="-Z sanitizer=memory" cargo run --target x86_64-unknown-linux-gnu --example uninitialized-read
   Compiling msan v0.1.0 (file:///home/japaric/rust/san/msan)
    Finished dev [unoptimized + debuginfo] target(s) in 0.38 secs
     Running `target/x86_64-unknown-linux-gnu/debug/examples/uninitialized-read`

$ unset CARGO_INCREMENTAL

$ cargo clean

$ cargo run --target x86_64-unknown-linux-gnu --example uninitialized-read
   Compiling msan v0.1.0 (file:///home/japaric/rust/san/msan)
    Finished dev [unoptimized + debuginfo] target(s) in 0.37 secs
     Running `target/x86_64-unknown-linux-gnu/debug/examples/uninitialized-read`

# sanitizer works this time
$ RUSTFLAGS="-Z sanitizer=memory" cargo run --target x86_64-unknown-linux-gnu --example uninitialized-read
   Compiling msan v0.1.0 (file://PWD)
    Finished dev [unoptimized + debuginfo] target(s) in 0.37 secs
     Running `target/x86_64-unknown-linux-gnu/debug/examples/uninitialized-read`
==2346==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x564db789c7da in uninitialized_read::main::h0c073cea3836efc1 $PWD/examples/uninitialized-read.rs:5
    #1 0x564db7919446 in __rust_maybe_catch_panic ($PWD/target/x86_64-unknown-linux-gnu/debug/examples/uninitialized-read+0x87446)
    #2 0x564db7911df9 in std::rt::lang_start::h6954771f55df116b ($PWD/target/x86_64-unknown-linux-gnu/debug/examples/uninitialized-read+0x7fdf9)
    #3 0x564db789c8a9 in main ($PWD/target/x86_64-unknown-linux-gnu/debug/examples/uninitialized-read+0xa8a9)
    #4 0x7f80c46ab290 in __libc_start_main (/usr/lib/libc.so.6+0x20290)
    #5 0x564db789c4f9 in _start ($PWD/target/x86_64-unknown-linux-gnu/debug/examples/uninitialized-read+0xa4f9)

SUMMARY: MemorySanitizer: use-of-uninitialized-value $PWD/examples/uninitialized-read.rs:5 in uninitialized_read::main::h0c073cea3836efc1
Exiting

Meta

TODO Sanitizers are not yet in tree. (cf. #38699)

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cc @michaelwoerister