bjoernager/rust
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Auto merge of #136035 - SpecificProtagonist:miri-zeroed-alloc, r=oli-obk

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miri: optimize zeroed alloc

When allocating zero-initialized memory in MIR interpretation, rustc allocates zeroed memory, marks it as initialized and then re-zeroes it. Remove the last step.

I don't expect this to have much of an effect on performance normally, but in my case in which I'm creating a large allocation via mmap it gets in the way.
This commit is contained in:
bors 2025-01-30 01:27:21 +00:00
commit 5e5567993d
14 changed files with 88 additions and 79 deletions
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12
compiler/rustc_smir/src/rustc_smir/alloc.rs
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@ -1,6 +1,6 @@
use rustc_abi::{Align, Size};
use rustc_middle::mir::ConstValue;
use rustc_middle::mir::interpret::{AllocRange, Pointer, alloc_range};
use rustc_middle::mir::interpret::{AllocInit, AllocRange, Pointer, alloc_range};
use stable_mir::Error;
use stable_mir::mir::Mutability;
use stable_mir::ty::{Allocation, ProvenanceMap};
@ -44,7 +44,8 @@ pub(crate) fn try_new_allocation<'tcx>(
.layout_of(rustc_middle::ty::TypingEnv::fully_monomorphized().as_query_input(ty))
.map_err(|e| e.stable(tables))?
.align;
let mut allocation = rustc_middle::mir::interpret::Allocation::uninit(size, align.abi);
let mut allocation =
rustc_middle::mir::interpret::Allocation::new(size, align.abi, AllocInit::Uninit);
allocation
.write_scalar(&tables.tcx, alloc_range(Size::ZERO, size), scalar)
.map_err(|e| e.stable(tables))?;
@ -68,8 +69,11 @@ pub(crate) fn try_new_allocation<'tcx>(
.tcx
.layout_of(rustc_middle::ty::TypingEnv::fully_monomorphized().as_query_input(ty))
.map_err(|e| e.stable(tables))?;
let mut allocation =
rustc_middle::mir::interpret::Allocation::uninit(layout.size, layout.align.abi);
let mut allocation = rustc_middle::mir::interpret::Allocation::new(
layout.size,
layout.align.abi,
AllocInit::Uninit,
);
allocation
.write_scalar(
&tables.tcx,