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Auto merge of #110477 - miguelraz:canoodling2-electric-boogaloo, r=co…
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…mpiler-errors

Don't allocate on SimplifyCfg/Locals/Const on every MIR pass

Hey! 👋🏾 This is a first PR attempt to see if I could speed up some rustc internals.

Thought process:

```rust
pub struct SimplifyCfg {
    label: String,
}
```
in [compiler/src/rustc_mir_transform/simplify.rs](https://github.com/rust-lang/rust/blob/7908a1d65496b88626e4b7c193c81d777005d6f3/compiler/rustc_mir_transform/src/simplify.rs#L39) fires multiple times per MIR analysis. This means that a likely string allocation is happening in each of these runs, which may add up, as they are not being  lazily allocated or cached in between the different passes.

...yes, I know that adding a global static array is probably not the future-proof solution, but I wanted to lob this now as a proof of concept to see if it's worth shaving off a few cycles and then making more robust.
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bors committed Apr 19, 2023
2 parents da48140 + fc27ae1 commit 9e7f72c
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Showing 4 changed files with 56 additions and 48 deletions.
29 changes: 11 additions & 18 deletions compiler/rustc_mir_transform/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -296,7 +296,7 @@ fn mir_const(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> &Steal<
&Lint(check_const_item_mutation::CheckConstItemMutation),
&Lint(function_item_references::FunctionItemReferences),
// What we need to do constant evaluation.
&simplify::SimplifyCfg::new("initial"),
&simplify::SimplifyCfg::Initial,
&rustc_peek::SanityCheck, // Just a lint
],
None,
Expand Down Expand Up @@ -334,11 +334,7 @@ fn mir_promoted(
pm::run_passes(
tcx,
&mut body,
&[
&promote_pass,
&simplify::SimplifyCfg::new("promote-consts"),
&coverage::InstrumentCoverage,
],
&[&promote_pass, &simplify::SimplifyCfg::PromoteConsts, &coverage::InstrumentCoverage],
Some(MirPhase::Analysis(AnalysisPhase::Initial)),
);

Expand Down Expand Up @@ -467,10 +463,7 @@ fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>
pm::run_passes(
tcx,
body,
&[
&remove_uninit_drops::RemoveUninitDrops,
&simplify::SimplifyCfg::new("remove-false-edges"),
],
&[&remove_uninit_drops::RemoveUninitDrops, &simplify::SimplifyCfg::RemoveFalseEdges],
None,
);
check_consts::post_drop_elaboration::check_live_drops(tcx, &body); // FIXME: make this a MIR lint
Expand All @@ -492,7 +485,7 @@ fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let passes: &[&dyn MirPass<'tcx>] = &[
&cleanup_post_borrowck::CleanupPostBorrowck,
&remove_noop_landing_pads::RemoveNoopLandingPads,
&simplify::SimplifyCfg::new("early-opt"),
&simplify::SimplifyCfg::EarlyOpt,
&deref_separator::Derefer,
];

Expand Down Expand Up @@ -525,7 +518,7 @@ fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
/// Returns the sequence of passes that do the initial cleanup of runtime MIR.
fn run_runtime_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let passes: &[&dyn MirPass<'tcx>] =
&[&lower_intrinsics::LowerIntrinsics, &simplify::SimplifyCfg::new("elaborate-drops")];
&[&lower_intrinsics::LowerIntrinsics, &simplify::SimplifyCfg::ElaborateDrops];

pm::run_passes(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::PostCleanup)));

Expand All @@ -551,7 +544,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
&lower_slice_len::LowerSliceLenCalls, // has to be done before inlining, otherwise actual call will be almost always inlined. Also simple, so can just do first
&unreachable_prop::UnreachablePropagation,
&uninhabited_enum_branching::UninhabitedEnumBranching,
&o1(simplify::SimplifyCfg::new("after-uninhabited-enum-branching")),
&o1(simplify::SimplifyCfg::AfterUninhabitedEnumBranching),
&inline::Inline,
&remove_storage_markers::RemoveStorageMarkers,
&remove_zsts::RemoveZsts,
Expand All @@ -564,23 +557,23 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
&multiple_return_terminators::MultipleReturnTerminators,
&instcombine::InstCombine,
&separate_const_switch::SeparateConstSwitch,
&simplify::SimplifyLocals::new("before-const-prop"),
&simplify::SimplifyLocals::BeforeConstProp,
&copy_prop::CopyProp,
&const_prop::ConstProp,
&dataflow_const_prop::DataflowConstProp,
//
// Const-prop runs unconditionally, but doesn't mutate the MIR at mir-opt-level=0.
&const_debuginfo::ConstDebugInfo,
&o1(simplify_branches::SimplifyConstCondition::new("after-const-prop")),
&o1(simplify_branches::SimplifyConstConditionPassName::AfterConstProp),
&early_otherwise_branch::EarlyOtherwiseBranch,
&simplify_comparison_integral::SimplifyComparisonIntegral,
&dead_store_elimination::DeadStoreElimination,
&dest_prop::DestinationPropagation,
&o1(simplify_branches::SimplifyConstCondition::new("final")),
&o1(simplify_branches::SimplifyConstConditionPassName::Final),
&o1(remove_noop_landing_pads::RemoveNoopLandingPads),
&o1(simplify::SimplifyCfg::new("final")),
&o1(simplify::SimplifyCfg::Final),
&nrvo::RenameReturnPlace,
&simplify::SimplifyLocals::new("final"),
&simplify::SimplifyLocals::Final,
&multiple_return_terminators::MultipleReturnTerminators,
&deduplicate_blocks::DeduplicateBlocks,
&large_enums::EnumSizeOpt { discrepancy: 128 },
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_mir_transform/src/shim.rs
Original file line number Diff line number Diff line change
Expand Up @@ -95,7 +95,7 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
&add_moves_for_packed_drops::AddMovesForPackedDrops,
&deref_separator::Derefer,
&remove_noop_landing_pads::RemoveNoopLandingPads,
&simplify::SimplifyCfg::new("make_shim"),
&simplify::SimplifyCfg::MakeShim,
&add_call_guards::CriticalCallEdges,
&abort_unwinding_calls::AbortUnwindingCalls,
],
Expand Down
48 changes: 32 additions & 16 deletions compiler/rustc_mir_transform/src/simplify.rs
Original file line number Diff line number Diff line change
Expand Up @@ -36,13 +36,31 @@ use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;
use smallvec::SmallVec;

pub struct SimplifyCfg {
label: String,
pub enum SimplifyCfg {
Initial,
PromoteConsts,
RemoveFalseEdges,
EarlyOpt,
ElaborateDrops,
Final,
MakeShim,
AfterUninhabitedEnumBranching,
}

impl SimplifyCfg {
pub fn new(label: &str) -> Self {
SimplifyCfg { label: format!("SimplifyCfg-{}", label) }
pub fn name(&self) -> &'static str {
match self {
SimplifyCfg::Initial => "SimplifyCfg-initial",
SimplifyCfg::PromoteConsts => "SimplifyCfg-promote-consts",
SimplifyCfg::RemoveFalseEdges => "SimplifyCfg-remove-false-edges",
SimplifyCfg::EarlyOpt => "SimplifyCfg-early-opt",
SimplifyCfg::ElaborateDrops => "SimplifyCfg-elaborate-drops",
SimplifyCfg::Final => "SimplifyCfg-final",
SimplifyCfg::MakeShim => "SimplifyCfg-make_shim",
SimplifyCfg::AfterUninhabitedEnumBranching => {
"SimplifyCfg-after-uninhabited-enum-branching"
}
}
}
}

Expand All @@ -57,11 +75,11 @@ pub fn simplify_cfg<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {

impl<'tcx> MirPass<'tcx> for SimplifyCfg {
fn name(&self) -> &str {
&self.label
&self.name()
}

fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
debug!("SimplifyCfg({:?}) - simplifying {:?}", self.label, body.source);
debug!("SimplifyCfg({:?}) - simplifying {:?}", self.name(), body.source);
simplify_cfg(tcx, body);
}
}
Expand Down Expand Up @@ -423,19 +441,17 @@ fn save_unreachable_coverage(
));
}

pub struct SimplifyLocals {
label: String,
}

impl SimplifyLocals {
pub fn new(label: &str) -> SimplifyLocals {
SimplifyLocals { label: format!("SimplifyLocals-{}", label) }
}
pub enum SimplifyLocals {
BeforeConstProp,
Final,
}

impl<'tcx> MirPass<'tcx> for SimplifyLocals {
fn name(&self) -> &str {
&self.label
fn name(&self) -> &'static str {
match &self {
SimplifyLocals::BeforeConstProp => "SimplifyLocals-before-const-prop",
SimplifyLocals::Final => "SimplifyLocals-final",
}
}

fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
Expand Down
25 changes: 12 additions & 13 deletions compiler/rustc_mir_transform/src/simplify_branches.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2,20 +2,19 @@ use crate::MirPass;
use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;

/// A pass that replaces a branch with a goto when its condition is known.
pub struct SimplifyConstCondition {
label: String,
}

impl SimplifyConstCondition {
pub fn new(label: &str) -> Self {
SimplifyConstCondition { label: format!("SimplifyConstCondition-{}", label) }
}
pub enum SimplifyConstConditionPassName {
AfterConstProp,
Final,
}

impl<'tcx> MirPass<'tcx> for SimplifyConstCondition {
fn name(&self) -> &str {
&self.label
/// A pass that replaces a branch with a goto when its condition is known.
impl<'tcx> MirPass<'tcx> for SimplifyConstConditionPassName {
fn name(&self) -> &'static str {
match self {
SimplifyConstConditionPassName::AfterConstProp => {
"SimplifyConstCondition-after-const-prop"
}
SimplifyConstConditionPassName::Final => "SimplifyConstCondition-final",
}
}

fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
Expand Down

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