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Add an InstSimplify for repetitive array expressions

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This commit is contained in:
Ben Kimock 2025-01-08 20:49:48 -05:00
parent fb546ee09b
commit a285d202cf
7 changed files with 176 additions and 0 deletions
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30
compiler/rustc_mir_transform/src/instsimplify.rs
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@ -48,6 +48,7 @@ impl<'tcx> crate::MirPass<'tcx> for InstSimplify {
ctx.simplify_ref_deref(rvalue);
ctx.simplify_ptr_aggregate(rvalue);
ctx.simplify_cast(rvalue);
ctx.simplify_repeated_aggregate(rvalue);
}
_ => {}
}
@ -68,6 +69,35 @@ struct InstSimplifyContext<'a, 'tcx> {
}
impl<'tcx> InstSimplifyContext<'_, 'tcx> {
/// Transform aggregates like [0, 0, 0, 0, 0] into [0; 5].
/// 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 {
return;
};
if fields.len() < 5 {
return;
}
let first = &fields[rustc_abi::FieldIdx::ZERO];
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| {
let Operand::Constant(field) = field else {
return false;
};
let field = field.const_.eval(self.tcx, self.typing_env, field.span);
field == Ok(first_val)
}) {
let len = ty::Const::from_target_usize(self.tcx, fields.len().try_into().unwrap());
*rvalue = Rvalue::Repeat(Operand::Constant(first.clone()), len);
}
}
/// Transform boolean comparisons into logical operations.
fn simplify_bool_cmp(&self, rvalue: &mut Rvalue<'tcx>) {
match rvalue {