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Auto merge of #127638 - adwinwhite:cache_string, r=oli-obk

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Add cache for `allocate_str`

Best effort cache for string allocation in const eval.

Fixes [rust-lang/miri#3470](https://github.com/rust-lang/miri/issues/3470).
This commit is contained in:
bors 2024-07-16 02:41:07 +00:00
commit 5c84886056
4 changed files with 28 additions and 10 deletions
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14
compiler/rustc_const_eval/src/interpret/place.rs
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@ -995,13 +995,25 @@ where
}
/// Returns a wide MPlace of type `str` to a new 1-aligned allocation.
/// Immutable strings are deduplicated and stored in global memory.
pub fn allocate_str(
&mut self,
str: &str,
kind: MemoryKind<M::MemoryKind>,
mutbl: Mutability,
) -> InterpResult<'tcx, MPlaceTy<'tcx, M::Provenance>> {
let ptr = self.allocate_bytes_ptr(str.as_bytes(), Align::ONE, kind, mutbl)?;
let tcx = self.tcx.tcx;
// Use cache for immutable strings.
let ptr = if mutbl.is_not() {
// Use dedup'd allocation function.
let id = tcx.allocate_bytes_dedup(str.as_bytes());
// Turn untagged "global" pointers (obtained via `tcx`) into the machine pointer to the allocation.
M::adjust_alloc_root_pointer(&self, Pointer::from(id), Some(kind))?
} else {
self.allocate_bytes_ptr(str.as_bytes(), Align::ONE, kind, mutbl)?
};
let meta = Scalar::from_target_usize(u64::try_from(str.len()).unwrap(), self);
let layout = self.layout_of(self.tcx.types.str_).unwrap();
Ok(self.ptr_with_meta_to_mplace(ptr.into(), MemPlaceMeta::Meta(meta), layout))