Trait rustc_mir_transform::MirPass[−][src]

pub trait MirPass<'tcx> {
    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>);

    fn name(&self) -> Cow<'_, str> { ... }
}
Expand description

A streamlined trait that you can implement to create a pass; the pass will be named after the type, and it will consist of a main loop that goes over each available MIR and applies run_pass.

Required methods

Provided methods

Implementors

Breaks outgoing critical edges for call terminators in the MIR.

Critical edges are edges that are neither the only edge leaving a block, nor the only edge entering one.

When you want something to happen “along” an edge, you can either do at the end of the predecessor block, or at the start of the successor block. Critical edges have to be broken in order to prevent “edge actions” from affecting other edges. We need this for calls that are codegened to LLVM invoke instructions, because invoke is a block terminator in LLVM so we can’t insert any code to handle the call’s result into the block that performs the call.

This function will break those edges by inserting new blocks along them.

NOTE: Simplify CFG will happily undo most of the work this pass does.

If a source block is found that switches between two blocks that are exactly the same modulo const bool assignments (e.g., one assigns true another false to the same place), merge a target block statements into the source block, using Eq / Ne comparison with switch value where const bools value differ.

For example:

bb0: {
    switchInt(move _3) -> [42_isize: bb1, otherwise: bb2];
}

bb1: {
    _2 = const true;
    goto -> bb3;
}

bb2: {
    _2 = const false;
    goto -> bb3;
}

into:

bb0: {
   _2 = Eq(move _3, const 42_isize);
   goto -> bb3;
}