CopyProp miscompilation when src is moved more than once #137936
Description
#![feature(custom_mir, core_intrinsics, freeze)] #![allow(internal_features, unused_assignments)] extern crate core; use core::intrinsics::mir::*; use core::mem::MaybeUninit; use core::marker::Freeze; #[custom_mir(dialect = "analysis", phase = "post-cleanup")] fn f<T: Copy + Freeze>(a: MaybeUninit<T>) { mir! { { let b = Move(a); let c = Move(a); Call(RET = g(Move(b), Move(c)), ReturnTo(ret), UnwindContinue()) } ret = { Return() } } } fn g<T: Copy + Freeze>(mut a: T, mut b: T) { assert_ne!(&mut a as *mut _ as usize, &mut b as *mut _ as usize); } fn main() { f(MaybeUninit::<[u8; 64]>::uninit()); }The CopyProp introduces following changes:
--- a.f.005-021.CopyProp.before.mir 2025-03-03 13:42:20.628850669 +0100 +++ a.f.005-021.CopyProp.after.mir 2025-03-03 13:42:20.628850669 +0100 @@ -1,17 +1,15 @@ -// MIR for `f` before CopyProp +// MIR for `f` after CopyProp fn f(_1: MaybeUninit<T>) -> () { let mut _0: (); let mut _2: std::mem::MaybeUninit<T>; let mut _3: std::mem::MaybeUninit<T>; bb0: { - _2 = move _1; - _3 = move _1; - _0 = g::<MaybeUninit<T>>(move _2, move _3) -> [return: bb1, unwind continue]; + _0 = g::<MaybeUninit<T>>(move _1, move _1) -> [return: bb1, unwind continue]; } bb1: { return; } }$ rustc a.rs -Zmir-opt-level=0 && ./a $ rustc a.rs -Zmir-opt-level=1 && ./a thread 'main' panicked at a.rs:23:5: assertion `left != right` failed left: 140729201385720 right: 140729201385720 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace