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codegen: use new {re,de,}allocator annotations in llvm

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This obviates the patch that teaches LLVM internals about
_rust_{re,de}alloc functions by putting annotations directly in the IR
for the optimizer.

The sole test change is required to anchor FileCheck to the body of the
`box_uninitialized` method, so it doesn't see the `allocalign` on
`__rust_alloc` and get mad about the string `alloca` showing up. Since I
was there anyway, I added some checks on the attributes to prove the
right attributes got set.

While we're here, we also emit allocator attributes on
__rust_alloc_zeroed. This should allow LLVM to perform more
optimizations for zeroed blocks, and probably fixes #90032. [This
comment](https://github.com/rust-lang/rust/issues/24194#issuecomment-308791157)
mentions "weird UB-like behaviour with bitvec iterators in
rustc_data_structures" so we may need to back this change out if things
go wrong.

The new test cases require LLVM 15, so we copy them into LLVM
14-supporting versions, which we can delete when we drop LLVM 14.
This commit is contained in:
Augie Fackler 2022-03-21 15:30:54 -04:00
parent 2fdbf075cf
commit 130a1df71e
14 changed files with 356 additions and 4 deletions
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8
compiler/rustc_middle/src/middle/codegen_fn_attrs.rs
View file

@ -50,7 +50,7 @@ bitflags! {
/// the hot path.
const COLD = 1 << 0;
/// `#[rustc_allocator]`: a hint to LLVM that the pointer returned from this
/// function is never null.
/// function is never null and the function has no side effects other than allocating.
const ALLOCATOR = 1 << 1;
/// An indicator that function will never unwind. Will become obsolete
/// once C-unwind is fully stabilized.
@ -91,6 +91,12 @@ bitflags! {
const NO_COVERAGE = 1 << 15;
/// `#[used(linker)]`: indicates that LLVM nor the linker can eliminate this function.
const USED_LINKER = 1 << 16;
/// `#[rustc_deallocator]`: a hint to LLVM that the function only deallocates memory.
const DEALLOCATOR = 1 << 17;
/// `#[rustc_reallocator]`: a hint to LLVM that the function only reallocates memory.
const REALLOCATOR = 1 << 18;
/// `#[rustc_allocator_zeroed]`: a hint to LLVM that the function only allocates zeroed memory.
const ALLOCATOR_ZEROED = 1 << 19;
}
}