bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Rollup merge of #127168 - DianQK:cast-size, r=workingjubilee

Browse source 
Use the aligned size for alloca at args/ret when the pass mode is cast

Fixes #75839. Fixes #121028.

The `load` and `store` instructions in LLVM access the aligned size. For example, `load { i64, i32 }` accesses 16 bytes on x86_64: https://alive2.llvm.org/ce/z/n8CHAp.

BTW, this example is expected to be optimized to immediate UB by Alive2: https://rust.godbolt.org/z/b7xK7hv1c and https://alive2.llvm.org/ce/z/vZDtZH.

r? compiler
This commit is contained in:
Matthias Krüger 2024-07-02 17:47:48 +02:00 • committed by GitHub
commit 33b0238586
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
7 changed files with 381 additions and 39 deletions
Download patch file Download diff file Expand all files Collapse all files

2
compiler/rustc_codegen_ssa/src/mir/block.rs
View file

@ -1521,7 +1521,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
// when passed by value, making it smaller.
// - On some ABIs, the Rust layout { u16, u16, u16 } may be padded up to 8 bytes
// when passed by value, making it larger.
let copy_bytes = cmp::min(scratch_size.bytes(), arg.layout.size.bytes());
let copy_bytes = cmp::min(cast.unaligned_size(bx).bytes(), arg.layout.size.bytes());
// Allocate some scratch space...
let llscratch = bx.alloca(scratch_size, scratch_align);
bx.lifetime_start(llscratch, scratch_size);

18
compiler/rustc_codegen_ssa/src/mir/mod.rs
View file

@ -230,10 +230,20 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
let layout = start_bx.layout_of(fx.monomorphize(decl.ty));
assert!(!layout.ty.has_erasable_regions());
if local == mir::RETURN_PLACE && fx.fn_abi.ret.is_indirect() {
debug!("alloc: {:?} (return place) -> place", local);
let llretptr = start_bx.get_param(0);
return LocalRef::Place(PlaceRef::new_sized(llretptr, layout));
if local == mir::RETURN_PLACE {
match fx.fn_abi.ret.mode {
PassMode::Indirect { .. } => {
debug!("alloc: {:?} (return place) -> place", local);
let llretptr = start_bx.get_param(0);
return LocalRef::Place(PlaceRef::new_sized(llretptr, layout));
}
PassMode::Cast { ref cast, .. } => {
debug!("alloc: {:?} (return place) -> place", local);
let size = cast.size(&start_bx);
return LocalRef::Place(PlaceRef::alloca_size(&mut start_bx, size, layout));
}
_ => {}
};
}
if memory_locals.contains(local) {

10
compiler/rustc_codegen_ssa/src/mir/place.rs
View file

@ -108,9 +108,17 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
pub fn alloca<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
bx: &mut Bx,
layout: TyAndLayout<'tcx>,
) -> Self {
Self::alloca_size(bx, layout.size, layout)
}
pub fn alloca_size<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
bx: &mut Bx,
size: Size,
layout: TyAndLayout<'tcx>,
) -> Self {
assert!(layout.is_sized(), "tried to statically allocate unsized place");
PlaceValue::alloca(bx, layout.size, layout.align.abi).with_type(layout)
PlaceValue::alloca(bx, size, layout.align.abi).with_type(layout)
}
/// Returns a place for an indirect reference to an unsized place.