Auto merge of rust-lang#110477 - miguelraz:canoodling2-electric-booga…

…loo, r=compiler-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.

compiler/rustc_mir_transform/src/lib.rs

@@ -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,
@@ -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)),
     );
 
@@ -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
@@ -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,
     ];
 
@@ -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)));
 
@@ -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,
@@ -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 },

compiler/rustc_mir_transform/src/shim.rs

@@ -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,
         ],

compiler/rustc_mir_transform/src/simplify.rs

@@ -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"
+            }
+        }
     }
 }
 
@@ -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);
     }
 }
@@ -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 {

compiler/rustc_mir_transform/src/simplify_branches.rs

@@ -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>) {