fix(coroutine): split overlapping state assignments

[MilkBlock]

r? @cijiugechu

Fix #149748

coroutine.rs generated self-assign stmt when crossing yield stmt, which confused the linter.

This PR inserts additional temporary variable to make linter happy.

Before Patch

  bb1: {
      StorageLive(_3);
      _3 = copy ((*_1).0: &i32);
      StorageLive(_4);
      _4 = copy ((*_1).1: &i32);
      nop;
      (((*_1) as variant#3).0: &i32) = copy ((*_1).2: &i32);
      StorageLive(_6);
      StorageLive(_7);
      _7 = copy _4;
      _0 = Option::<&i32>::Some(move _7);
  }
  

After Patch

  bb1: {
      StorageLive(_3);
      _3 = copy ((*_1).0: &i32);
      StorageLive(_4);
      _4 = copy ((*_1).1: &i32);
      nop;
      _10 = copy ((*_1).2: &i32);
      (((*_1) as variant#3).0: &i32) = move _10;
      StorageLive(_6);
      StorageLive(_7);
      _7 = copy _4;
      _0 = Option::<&i32>::Some(move _7);
  }

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[saethlin]

r? saethlin (the person you selected is not a compiler reviewer)

Did you check that the ICE reported still happens? I can't make the compiler hit it.

[MilkBlock]

r? saethlin (the person you selected is not a compiler reviewer)

Did you check that the ICE reported still happens? I can't make the compiler hit it.

This can be reproduced by

rustc +nightly --edition=2024 \
    -Zmir-enable-passes=+Inline,+ReferencePropagation \
    -Zlint-mir \
    ./tests/ui/coroutine/issue-149748.rs
rustc +nightly --version
rustc 1.97.0-nightly (ca9a134e0 2026-04-26)

given code in issue-149748.rs

//@ edition:2024
//@ compile-flags: -Zmir-enable-passes=+Inline,+ReferencePropagation -Zlint-mir
//@ check-pass

#![feature(gen_blocks)]
#![allow(unused_variables, path_statements)]

struct NonCopy(i32);

gen fn refs<'a, 'b>(x: &'a i32, y: &'b i32, z: &'b i32) -> &'b i32 {
    yield y;
    z;
}

gen fn moves(x: NonCopy, y: NonCopy, z: NonCopy) -> NonCopy {
    yield y;
    z;
}

fn main() {
    let z = 3;
    let mut refs_iter = refs(&1, &2, &z);
    assert_eq!(refs_iter.next(), Some(&3));

    let mut moves_iter = moves(NonCopy(1), NonCopy(2), NonCopy(3));
    assert!(matches!(moves_iter.next(), Some(_)));
}