Module rustc_mir::transform::remove_dead_blocks

Unstable (rustc_private)

A pass that erases the contents of dead blocks. This pass must run before any analysis passes because some of the dead blocks can be ill-typed.

The main problem is that typeck lets most blocks whose end is not reachable have an arbitrary return type, rather than having the usual () return type (as a note, typeck's notion of reachability is in fact slightly weaker than MIR CFG reachability - see #31617).

A standard example of the situation is: rust fn example() { let _a: char = { return; }; }

Here the block ({ return; }) has the return type char, rather than (), but the MIR we naively generate still contains the _a = () write in the unreachable block "after" the return.

As we have to run this pass even when we want to debug the MIR, this pass just replaces the blocks with empty "return" blocks and does not renumber anything.

Structs

RemoveDeadBlocks

[Unstable]