[MIR] Deaggregate structs to enable further optimizations #35168
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| Original file line number | Diff line number | Diff line change |
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@@ -31,55 +31,55 @@ impl<'tcx> MirPass<'tcx> for Deaggregator { | |
| None => { return; }, | ||
| _ => {} | ||
| }; | ||
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| // Do not trigger on constants. Could be revised in future | ||
| if let MirSource::Fn(_) = source {} else { return; } | ||
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| let mut curr: usize = 0; | ||
| for bb in mir.basic_blocks_mut() { | ||
| let idx = match get_aggregate_statement(curr, &bb.statements) { | ||
| Some(idx) => idx, | ||
| None => continue, | ||
| }; | ||
| // do the replacement | ||
| debug!("removing statement {:?}", idx); | ||
| let src_info = bb.statements[idx].source_info; | ||
| let suffix_stmts = bb.statements.split_off(idx+1); | ||
| let orig_stmt = bb.statements.pop().unwrap(); | ||
| let StatementKind::Assign(ref lhs, ref rhs) = orig_stmt.kind; | ||
| let (agg_kind, operands) = match rhs { | ||
| &Rvalue::Aggregate(ref agg_kind, ref operands) => (agg_kind, operands), | ||
| _ => span_bug!(src_info.span, "expected aggregate, not {:?}", rhs), | ||
| }; | ||
| let (adt_def, variant, substs) = match agg_kind { | ||
| &AggregateKind::Adt(adt_def, variant, substs) => (adt_def, variant, substs), | ||
| _ => span_bug!(src_info.span, "expected struct, not {:?}", rhs), | ||
| }; | ||
| let n = bb.statements.len(); | ||
| bb.statements.reserve(n + operands.len() + suffix_stmts.len()); | ||
| for (i, op) in operands.iter().enumerate() { | ||
| let ref variant_def = adt_def.variants[variant]; | ||
| let ty = variant_def.fields[variant].ty(tcx, substs); | ||
| let rhs = Rvalue::Use(op.clone()); | ||
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| // since we don't handle enums, we don't need a cast | ||
| let lhs_cast = lhs.clone(); | ||
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| // FIXME we cannot deaggregate enums issue: 35186 | ||
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| let lhs_proj = Lvalue::Projection(Box::new(LvalueProjection { | ||
| base: lhs_cast, | ||
| elem: ProjectionElem::Field(Field::new(i), ty), | ||
| })); | ||
| let new_statement = Statement { | ||
| source_info: src_info, | ||
| kind: StatementKind::Assign(lhs_proj, rhs), | ||
| }; | ||
| debug!("inserting: {:?} @ {:?}", new_statement, idx + i); | ||
| bb.statements.push(new_statement); | ||
| } | ||
| curr = bb.statements.len(); | ||
| bb.statements.extend(suffix_stmts); | ||
| } | ||
| } | ||
| } | ||
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can you leave a comment as to why we do this
if-- iirc, otherwise this triggers in constants. Seems like this may be just a temporary limitation, if we improve our constant handling a la miri.