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Auto merge of #112002 - saethlin:enable-sroa, r=oli-obk,scottmcm

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Enable ScalarReplacementOfAggregates in optimized builds

Like MatchBranchSimplification, this pass is known to produce significant runtime improvements in Cranelift artifacts, and I believe based on the perf runs here that the primary effect of this pass is to empower MatchBranchSimplification. ScalarReplacementOfAggregates on its own has little effect on anything, but when this was rebased up to include https://github.com/rust-lang/rust/pull/112001 we started seeing significant and majority-positive results.

Based on the fact that we see most of the regressions in debug builds (https://github.com/rust-lang/rust/pull/112002#issuecomment-1566270144) and some rather significant ones in cycles and wall time, I'm only enabling this in optimized builds at the moment.
This commit is contained in:
bors 2023-06-01 10:47:14 +00:00
commit 642c92e630
13 changed files with 313 additions and 342 deletions
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50
compiler/rustc_mir_transform/src/sroa.rs
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@ -6,23 +6,29 @@ use rustc_middle::mir::visit::*;
use rustc_middle::mir::*;
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_mir_dataflow::value_analysis::{excluded_locals, iter_fields};
use rustc_target::abi::FieldIdx;
use rustc_target::abi::{FieldIdx, ReprFlags, FIRST_VARIANT};
pub struct ScalarReplacementOfAggregates;
impl<'tcx> MirPass<'tcx> for ScalarReplacementOfAggregates {
fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
sess.mir_opt_level() >= 3
sess.mir_opt_level() >= 2
}
#[instrument(level = "debug", skip(self, tcx, body))]
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
debug!(def_id = ?body.source.def_id());
// Avoid query cycles (generators require optimized MIR for layout).
if tcx.type_of(body.source.def_id()).subst_identity().is_generator() {
return;
}
let mut excluded = excluded_locals(body);
let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
loop {
debug!(?excluded);
let escaping = escaping_locals(&excluded, body);
let escaping = escaping_locals(tcx, param_env, &excluded, body);
debug!(?escaping);
let replacements = compute_flattening(tcx, param_env, body, escaping);
debug!(?replacements);
@ -48,11 +54,45 @@ impl<'tcx> MirPass<'tcx> for ScalarReplacementOfAggregates {
/// - the locals is a union or an enum;
/// - the local's address is taken, and thus the relative addresses of the fields are observable to
/// client code.
fn escaping_locals(excluded: &BitSet<Local>, body: &Body<'_>) -> BitSet<Local> {
fn escaping_locals<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
excluded: &BitSet<Local>,
body: &Body<'tcx>,
) -> BitSet<Local> {
let is_excluded_ty = |ty: Ty<'tcx>| {
if ty.is_union() || ty.is_enum() {
return true;
}
if let ty::Adt(def, _substs) = ty.kind() {
if def.repr().flags.contains(ReprFlags::IS_SIMD) {
// Exclude #[repr(simd)] types so that they are not de-optimized into an array
return true;
}
// We already excluded unions and enums, so this ADT must have one variant
let variant = def.variant(FIRST_VARIANT);
if variant.fields.len() > 1 {
// If this has more than one field, it cannot be a wrapper that only provides a
// niche, so we do not want to automatically exclude it.
return false;
}
let Ok(layout) = tcx.layout_of(param_env.and(ty)) else {
// We can't get the layout
return true;
};
if layout.layout.largest_niche().is_some() {
// This type has a niche
return true;
}
}
// Default for non-ADTs
false
};
let mut set = BitSet::new_empty(body.local_decls.len());
set.insert_range(RETURN_PLACE..=Local::from_usize(body.arg_count));
for (local, decl) in body.local_decls().iter_enumerated() {
if decl.ty.is_union() || decl.ty.is_enum() || excluded.contains(local) {
if excluded.contains(local) || is_excluded_ty(decl.ty) {
set.insert(local);
}
}