bjoernager/rust
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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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51
compiler/rustc_codegen_llvm/src/attributes.rs
View file

@ -13,7 +13,7 @@ use smallvec::SmallVec;
use crate::attributes;
use crate::llvm::AttributePlace::Function;
use crate::llvm::{self, Attribute, AttributeKind, AttributePlace};
use crate::llvm::{self, AllocKindFlags, Attribute, AttributeKind, AttributePlace};
use crate::llvm_util;
pub use rustc_attr::{InlineAttr, InstructionSetAttr, OptimizeAttr};
@ -227,6 +227,10 @@ pub(crate) fn default_optimisation_attrs<'ll>(
attrs
}
fn create_alloc_family_attr(llcx: &llvm::Context) -> &llvm::Attribute {
llvm::CreateAttrStringValue(llcx, "alloc-family", "__rust_alloc")
}
/// Composite function which sets LLVM attributes for function depending on its AST (`#[attribute]`)
/// attributes.
pub fn from_fn_attrs<'ll, 'tcx>(
@ -309,11 +313,54 @@ pub fn from_fn_attrs<'ll, 'tcx>(
// Need this for AArch64.
to_add.push(llvm::CreateAttrStringValue(cx.llcx, "branch-target-enforcement", "false"));
}
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR) {
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR)
|| codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR_ZEROED)
{
if llvm_util::get_version() >= (15, 0, 0) {
to_add.push(create_alloc_family_attr(cx.llcx));
// apply to argument place instead of function
let alloc_align = AttributeKind::AllocAlign.create_attr(cx.llcx);
attributes::apply_to_llfn(llfn, AttributePlace::Argument(1), &[alloc_align]);
to_add.push(llvm::CreateAllocSizeAttr(cx.llcx, 0));
let mut flags = AllocKindFlags::Alloc | AllocKindFlags::Aligned;
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR) {
flags |= AllocKindFlags::Uninitialized;
} else {
flags |= AllocKindFlags::Zeroed;
}
to_add.push(llvm::CreateAllocKindAttr(cx.llcx, flags));
}
// apply to return place instead of function (unlike all other attributes applied in this function)
let no_alias = AttributeKind::NoAlias.create_attr(cx.llcx);
attributes::apply_to_llfn(llfn, AttributePlace::ReturnValue, &[no_alias]);
}
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::REALLOCATOR) {
if llvm_util::get_version() >= (15, 0, 0) {
to_add.push(create_alloc_family_attr(cx.llcx));
to_add.push(llvm::CreateAllocKindAttr(
cx.llcx,
AllocKindFlags::Realloc | AllocKindFlags::Aligned,
));
// applies to argument place instead of function place
let allocated_pointer = AttributeKind::AllocatedPointer.create_attr(cx.llcx);
attributes::apply_to_llfn(llfn, AttributePlace::Argument(0), &[allocated_pointer]);
// apply to argument place instead of function
let alloc_align = AttributeKind::AllocAlign.create_attr(cx.llcx);
attributes::apply_to_llfn(llfn, AttributePlace::Argument(2), &[alloc_align]);
to_add.push(llvm::CreateAllocSizeAttr(cx.llcx, 3));
}
let no_alias = AttributeKind::NoAlias.create_attr(cx.llcx);
attributes::apply_to_llfn(llfn, AttributePlace::ReturnValue, &[no_alias]);
}
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::DEALLOCATOR) {
if llvm_util::get_version() >= (15, 0, 0) {
to_add.push(create_alloc_family_attr(cx.llcx));
to_add.push(llvm::CreateAllocKindAttr(cx.llcx, AllocKindFlags::Free));
// applies to argument place instead of function place
let allocated_pointer = AttributeKind::AllocatedPointer.create_attr(cx.llcx);
attributes::apply_to_llfn(llfn, AttributePlace::Argument(0), &[allocated_pointer]);
}
}
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::CMSE_NONSECURE_ENTRY) {
to_add.push(llvm::CreateAttrString(cx.llcx, "cmse_nonsecure_entry"));
}