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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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8
compiler/rustc_const_eval/src/const_eval/machine.rs
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@ -21,9 +21,10 @@ use super::error::*;
use crate::errors::{LongRunning, LongRunningWarn};
use crate::fluent_generated as fluent;
use crate::interpret::{
self, AllocId, AllocRange, ConstAllocation, CtfeProvenance, FnArg, Frame, GlobalAlloc, ImmTy,
InterpCx, InterpResult, MPlaceTy, OpTy, RangeSet, Scalar, compile_time_machine, interp_ok,
throw_exhaust, throw_inval, throw_ub, throw_ub_custom, throw_unsup, throw_unsup_format,
self, AllocId, AllocInit, AllocRange, ConstAllocation, CtfeProvenance, FnArg, Frame,
GlobalAlloc, ImmTy, InterpCx, InterpResult, MPlaceTy, OpTy, RangeSet, Scalar,
compile_time_machine, interp_ok, throw_exhaust, throw_inval, throw_ub, throw_ub_custom,
throw_unsup, throw_unsup_format,
};
/// When hitting this many interpreted terminators we emit a deny by default lint
@ -420,6 +421,7 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
Size::from_bytes(size),
align,
interpret::MemoryKind::Machine(MemoryKind::Heap),
AllocInit::Uninit,
)?;
ecx.write_pointer(ptr, dest)?;
}