Only memoize const fn calls during const eval
Miri and other engines may want to execute the function in order to detect UB inside of them.
r? @RalfJung
add reusable MachineStop variant to Miri engine error enum
Replace the Miri-tool-specific `Exit` error variant with something dynamically typed that all clients of the Miri engine can use.
r? @oli-obk
Cc https://github.com/rust-lang/rust/issues/66902
rustc: move mir::SourceScopeLocalData to a field of SourceScopeData.
By having one `ClearCrossCrate<SourceScopeLocalData>` for each scope, as opposed to a single `ClearCrossCrate` for all the `SourceScopeLocalData`s, we can represent the fact that some scopes have `SourceScopeLocalData` associated with them, and some don't.
This is useful when doing MIR inlining across crates, because the `ClearCrossCrate` will be `Clear` for the cross-crate MIR scopes and `Set` for the local ones.
Also see https://github.com/rust-lang/rust/pull/66203#issuecomment-555589574 for some context around this approach.
Fixes#51314.
[mir-opt] Turn on the `ConstProp` pass by default
perf.rlo shows that running the `ConstProp` pass results in
across-the-board wins regardless of debug or opt complilation mode. As a
result, we're turning it on to get the compile time benefits.
perf.rlo shows that running the `ConstProp` pass results in
across-the-board wins regardless of debug or opt complilation mode. As a
result, we're turning it on to get the compile time benefits.
`ConstProp` doesn't currently intern the memory used by its `Machine` so
we can't yet propagate allocations which is why
`ConstProp::should_const_prop()` checks if the value being propagated is
a scalar or not.
This prepares the code base for when projection is interned. Place's
projection field is going to be `&List<PlaceElem<'tcx>>` so we won't be
able to pattern match against it.
The `ConstProp` can cause many locals to be initialized to a constant
value and then never read from. `ConstProp` can also evaluate ZSTs into
constant values. Previously, many of these would be removed by other
parts of the MIR optimization pipeline. However, evaluating ZSTs
(especially `()`) into constant values defeated those parts of the
optimizer and so in a2e3ed5c05, I added a
hack to `ConstProp` that skips evaluating ZSTs to avoid that regression.
This commit changes `SimplifyLocals` so that it doesn't consider writes
of const values to a local to be a use of that local. In doing so,
`SimplifyLocals` is able to remove otherwise unused locals left behind
by other optimization passes (`ConstProp` in particular).
`const_prop()` now handles writing the Rvalue into the Place in the
stack frame for us. So if we're not supported to propagate that value,
we need to clear it.
