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In simplify_repeated_aggregate, don't test first element against itself #139411

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Apr 6, 2025
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In simplify_repeated_aggregate, don't test first element against itself #139411

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6 changes: 3 additions & 3 deletions compiler/rustc_mir_transform/src/instsimplify.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -78,20 +78,20 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
/// GVN can also do this optimization, but GVN is only run at mir-opt-level 2 so having this in
/// InstSimplify helps unoptimized builds.
fn simplify_repeated_aggregate(&self, rvalue: &mut Rvalue<'tcx>) {
let Rvalue::Aggregate(box AggregateKind::Array(_), fields) = rvalue else {
let Rvalue::Aggregate(box AggregateKind::Array(_), fields) = &*rvalue else {
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This is just so fields is immutable, which makes it a bit easier to reason about, IMHO.

return;
};
if fields.len() < 5 {
return;
}
let first = &fields[rustc_abi::FieldIdx::ZERO];
let (first, rest) = fields[..].split_first().unwrap();
let Operand::Constant(first) = first else {
return;
};
let Ok(first_val) = first.const_.eval(self.tcx, self.typing_env, first.span) else {
return;
};
if fields.iter().all(|field| {
if rest.iter().all(|field| {
let Operand::Constant(field) = field else {
return false;
};
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