Trait naga::back::spv::selection::MergeTuple

pub(super) trait MergeTuple: Sized {
    // Required method
    fn write_phis(
        self,
        ctx: &mut BlockContext<'_>,
        block: &mut Block,
        predecessors: &[(Self, Word)],
    ) -> Self;
}

A trait to help Selection manage any number of merged values.

Some selection constructs, like a ReadZeroSkipWrite bounds check on a Load expression, produce a single merged value. Others produce no merged value, like a bounds check on a Store statement.

To let Selection work nicely with both cases, we let the merge type argument passed to Selection::start be any type that implements this MergeTuple trait. MergeTuple is then implemented for (), Word, (Word, Word), and so on.

A MergeTuple type can represent either a bunch of SPIR-V types or values; the merge_types argument to Selection::start are type ids, whereas the values arguments to the if_true and finish methods are value ids. The set of merged value returned by finish is a tuple of value ids.

In fact, since Naga only uses zero- and single-valued selection constructs at present, we only implement MergeTuple for () and Word. But if you add more cases, feel free to add more implementations. Once const generics are available, we could have a single implementation of MergeTuple for all lengths of arrays, and be done with it.

Required Methods

fn write_phis( self, ctx: &mut BlockContext<'_>, block: &mut Block, predecessors: &[(Self, Word)], ) -> Self

Write OpPhi instructions for the given set of predecessors.

The predecessors vector should be a vector of (LABEL, VALUES) pairs, where each VALUES holds the values contributed by the branch from LABEL, which should be one of the current block’s predecessors.

Object Safety

This trait is not object safe.

Implementations on Foreign Types

impl MergeTuple for ()

Selections that produce no merged values.

For example, ImageStore under BoundsCheckPolicy::ReadZeroSkipWrite either does the store or skips it, but in neither case does it produce a value.

fn write_phis(self, _: &mut BlockContext<'_>, _: &mut Block, _: &[((), Word)])

No phis need to be generated.

impl MergeTuple for Word

Selections that produce a single merged value.

For example, ImageLoad with BoundsCheckPolicy::ReadZeroSkipWrite either returns a texel value or zeros.

fn write_phis( self, ctx: &mut BlockContext<'_>, block: &mut Block, predecessors: &[(Word, Word)], ) -> Word

Implementors