GVN: Only propagate borrows from SSA locals
Fixes https://github.com/rust-lang/rust/issues/141313. This is a more principled fix than https://github.com/rust-lang/rust/pull/147886.
Using a reference that is not a borrowing of an SSA local at a new location may be UB.
The PR has two major changes.
The first one, when introducing a new dereference at a new location, is that the reference must point to an SSA local or be an immutable argument. `dereference_address` has handled SSA locals.
The second one, if we cannot guard to the reference point to an SSA local in `visit_assign`, we have to rewrite the value to opaque. This avoids unifying the following dereferences that also are references:
```rust
let b: &T = *a;
// ... `a` is allowed to be modified. `c` and `b` have different borrowing lifetime.
// Unifying them will extend the lifetime of `b`.
let c: &T = *a;
```
See also https://github.com/rust-lang/rust/issues/130853.
This still allows unifying non-reference dereferences:
```rust
let a: &T = ...;
let b: T = *a;
// ... a is NOT allowed to be modified.
let c: T = *a;
```
r? @cjgillot
GVN: Elide more intermediate transmutes
We already skipped intermediate steps like `u32` or `i32` that support any (initialized) value.
This extends that to also allow skipping intermediate steps whose values are a superset of either the source or destination type. Most importantly, that means that `usize` → `NonZeroUsize` → `ptr::Alignment` and `ptr::Alignment` → `NonZeroUsize` → `usize` can skip the middle because `NonZeroUsize` is a superset of `Alignment`.
Then `Alignment::as_usize` is updated to take advantage of that and let us remove some more locals in a few places.
r? cjgillot
Fix suppression of `unused_assignment` in binding of `unused_variable`
Unused assignments to an unused variable should trigger only the `unused_variables` lint and not also the `unused_assignments` lint. This was previously implemented by checking whether the span of the assignee was within the span of the binding pattern, however that failed to capture situations was imported from elsewhere (eg from the input tokenstream of a proc-macro that generates the binding pattern).
By comparing the span of the assignee to those of the variable introductions instead, a reported stable-to-stable regression is resolved.
This fix also impacted some other preexisting tests, which had (undesirably) been triggering both the `unused_variables` and `unused_assignments` lints on the same initializing assignment; those tests have therefore now been updated to expect only the former lint.
Fixesrust-lang/rust#151514
r? cjgillot (as author of reworked liveness testing in rust-lang/rust#142390)
Unused assignments to an unused variable should trigger only the
`unused_variables` lint and not also the `unused_assignments` lint.
This was previously implemented by checking whether the span of the
assignee was within the span of the binding pattern, however that failed
to capture situations was imported from elsewhere (eg from the input
tokenstream of a proc-macro that generates the binding pattern).
By comparing the span of the assignee to those of the variable
introductions instead, a reported stable-to-stable regression is
resolved.
This fix also impacted some other preexisting tests, which had
(undesirably) been triggering both the `unused_variables` and
`unused_assignments` lints on the same initializing assignment; those
tests have therefore now been updated to expect only the former lint.
compiler: upgrade to hashbrown 0.16.1
See also rust-lang/rust#135634, rust-lang/rust#149159, and rust-lang/hashbrown#662.
This includes an in-tree upgrade of `indexmap` as well, which uses the
new `HashTable` buckets API internally, hopefully impacting performance
for the better.
And finally, we can remove `#[rustc_unsafe_specialization_marker]` on `Copy`!
cc @joboet
r? @Amanieu
New MIR Pass: SsaRangePropagation
As an alternative to https://github.com/rust-lang/rust/pull/150192.
Introduces a new pass that propagates the known ranges of SSA locals.
We can know the ranges of SSA locals at some locations for the following code:
```rust
fn foo(a: u32) {
let b = a < 9;
if b {
let c = b; // c is true since b is whitin the range [1, 2)
let d = a < 8; // d is true since b whitin the range [0, 9)
}
}
```
This PR only implements a trivial range: we know one value on switch, assert, and assume.
Only use SSA locals in SimplifyComparisonIntegral
Fixes https://github.com/rust-lang/rust/issues/150904.
The place may be modified from the comparison statement to the switchInt terminator.
Best reviewed commit by commit.
Remove `Deref`/`DerefMut` impl for `Providers`.
It's described as a "backwards compatibility hack to keep the diff small". Removing it requires only a modest amount of churn, and the resulting code is clearer without the invisible derefs.
r? @oli-obk
It's described as a "backwards compatibility hack to keep the diff
small". Removing it requires only a modest amount of churn, and the
resulting code is clearer without the invisible derefs.
See also #135634, #149159, and rust-lang/hashbrown#662.
This includes an in-tree upgrade of `indexmap` as well, which uses the
new `HashTable` buckets API internally, hopefully impacting performance
for the better!
Move can be used only when both the compared operand and the operand on switch are move operands.
This commit directly changes to Copy, because I don't know if Move has beneficial.
Jonathan Brouwer