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Re-enable removal of ZST writes to unions

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This commit is contained in:
Ben Kimock 2022-12-03 17:00:05 -05:00
parent e960b5e774
commit 74a270ac93
6 changed files with 44 additions and 60 deletions
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27
compiler/rustc_mir_transform/src/remove_zsts.rs
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@ -1,8 +1,7 @@
//! Removes assignments to ZST places.
use crate::MirPass;
use rustc_middle::mir::tcx::PlaceTy;
use rustc_middle::mir::{Body, LocalDecls, Place, StatementKind};
use rustc_middle::mir::{Body, StatementKind};
use rustc_middle::ty::{self, Ty, TyCtxt};
pub struct RemoveZsts;
@ -35,9 +34,6 @@ impl<'tcx> MirPass<'tcx> for RemoveZsts {
if !layout.is_zst() {
continue;
}
if involves_a_union(place, local_decls, tcx) {
continue;
}
if tcx.consider_optimizing(|| {
format!(
"RemoveZsts - Place: {:?} SourceInfo: {:?}",
@ -63,24 +59,3 @@ fn maybe_zst(ty: Ty<'_>) -> bool {
_ => false,
}
}
/// Miri lazily allocates memory for locals on assignment,
/// so we must preserve writes to unions and union fields,
/// or it will ICE on reads of those fields.
fn involves_a_union<'tcx>(
place: Place<'tcx>,
local_decls: &LocalDecls<'tcx>,
tcx: TyCtxt<'tcx>,
) -> bool {
let mut place_ty = PlaceTy::from_ty(local_decls[place.local].ty);
if place_ty.ty.is_union() {
return true;
}
for elem in place.projection {
place_ty = place_ty.projection_ty(tcx, elem);
if place_ty.ty.is_union() {
return true;
}
}
return false;
}