Remove storage markers if they won't be used during code generation

The storage markers constitute a substantial portion of all MIR
statements. At the same time, for builds without any optimizations,
the storage markers have no further use during and after MIR
optimization phase.

If storage markers are not necessary for code generation, remove them.

compiler/rustc_mir/src/transform/mod.rs

@@ -42,6 +42,7 @@
 pub mod nrvo;
 pub mod promote_consts;
 pub mod remove_noop_landing_pads;
+pub mod remove_storage_markers;
 pub mod remove_unneeded_drops;
 pub mod required_consts;
 pub mod rustc_peek;
@@ -493,6 +494,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 
     // The main optimizations that we do on MIR.
     let optimizations: &[&dyn MirPass<'tcx>] = &[
+        &remove_storage_markers::RemoveStorageMarkers,
         &const_goto::ConstGoto,
         &remove_unneeded_drops::RemoveUnneededDrops,
         &match_branches::MatchBranchSimplification,

compiler/rustc_mir/src/transform/remove_storage_markers.rs

+//! This pass removes storage markers if they won't be emitted during codegen.
+
+use crate::transform::MirPass;
+use rustc_middle::mir::*;
+use rustc_middle::ty::TyCtxt;
+
+pub struct RemoveStorageMarkers;
+
+impl<'tcx> MirPass<'tcx> for RemoveStorageMarkers {
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        if tcx.sess.emit_lifetime_markers() {
+            return;
+        }
+
+        trace!("Running RemoveStorageMarkers on {:?}", body.source);
+        for data in body.basic_blocks_mut() {
+            data.statements.retain(|statement| match statement.kind {
+                StatementKind::StorageLive(..)
+                | StatementKind::StorageDead(..)
+                | StatementKind::Nop => false,
+                _ => true,
+            })
+        }
+    }
+}

src/test/mir-opt/remove_storage_markers.main.RemoveStorageMarkers.diff

+- // MIR for `main` before RemoveStorageMarkers
++ // MIR for `main` after RemoveStorageMarkers
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/remove_storage_markers.rs:6:11: 6:11
+      let mut _1: i32;                     // in scope 0 at $DIR/remove_storage_markers.rs:7:9: 7:16
+      let mut _2: std::ops::Range<i32>;    // in scope 0 at $DIR/remove_storage_markers.rs:8:14: 8:19
+      let mut _3: std::ops::Range<i32>;    // in scope 0 at $DIR/remove_storage_markers.rs:8:14: 8:19
+      let mut _5: ();                      // in scope 0 at $DIR/remove_storage_markers.rs:6:1: 11:2
+      let _7: ();                          // in scope 0 at $DIR/remove_storage_markers.rs:8:14: 8:19
+      let mut _8: std::option::Option<i32>; // in scope 0 at $DIR/remove_storage_markers.rs:8:14: 8:19
+      let mut _9: &mut std::ops::Range<i32>; // in scope 0 at $DIR/remove_storage_markers.rs:8:14: 8:19
+      let mut _10: &mut std::ops::Range<i32>; // in scope 0 at $DIR/remove_storage_markers.rs:8:14: 8:19
+      let mut _11: isize;                  // in scope 0 at $DIR/remove_storage_markers.rs:8:9: 8:10
+      let mut _13: i32;                    // in scope 0 at $DIR/remove_storage_markers.rs:8:9: 8:10
+      let mut _14: !;                      // in scope 0 at $DIR/remove_storage_markers.rs:8:5: 10:6
+      let _16: ();                         // in scope 0 at $DIR/remove_storage_markers.rs:8:20: 10:6
+      let mut _17: i32;                    // in scope 0 at $DIR/remove_storage_markers.rs:9:16: 9:17
+      scope 1 {
+          debug sum => _1;                 // in scope 1 at $DIR/remove_storage_markers.rs:7:9: 7:16
+          let mut _4: std::ops::Range<i32>; // in scope 1 at $DIR/remove_storage_markers.rs:8:14: 8:19
+          scope 2 {
+              debug iter => _4;            // in scope 2 at $DIR/remove_storage_markers.rs:8:14: 8:19
+              let mut _6: i32;             // in scope 2 at $DIR/remove_storage_markers.rs:8:14: 8:19
+              scope 3 {
+                  debug __next => _6;      // in scope 3 at $DIR/remove_storage_markers.rs:8:14: 8:19
+                  let _12: i32;            // in scope 3 at $DIR/remove_storage_markers.rs:8:9: 8:10
+                  let _15: i32;            // in scope 3 at $DIR/remove_storage_markers.rs:8:9: 8:10
+                  scope 4 {
+                      debug val => _12;    // in scope 4 at $DIR/remove_storage_markers.rs:8:9: 8:10
+                  }
+                  scope 5 {
+                      debug i => _15;      // in scope 5 at $DIR/remove_storage_markers.rs:8:9: 8:10
+                  }
+              }
+          }
+          scope 6 (inlined <std::ops::Range<i32> as IntoIterator>::into_iter) { // at $DIR/remove_storage_markers.rs:8:14: 8:19
+              debug self => _3;            // in scope 6 at $DIR/remove_storage_markers.rs:8:14: 8:19
+          }
+      }
+  
+      bb0: {
+-         StorageLive(_1);                 // scope 0 at $DIR/remove_storage_markers.rs:7:9: 7:16
+          _1 = const 0_i32;                // scope 0 at $DIR/remove_storage_markers.rs:7:19: 7:20
+-         StorageLive(_2);                 // scope 1 at $DIR/remove_storage_markers.rs:8:14: 8:19
+-         StorageLive(_3);                 // scope 1 at $DIR/remove_storage_markers.rs:8:14: 8:19
+          (_3.0: i32) = const 0_i32;       // scope 1 at $DIR/remove_storage_markers.rs:8:14: 8:19
+          (_3.1: i32) = const 10_i32;      // scope 1 at $DIR/remove_storage_markers.rs:8:14: 8:19
+          _2 = move _3;                    // scope 6 at $DIR/remove_storage_markers.rs:8:14: 8:19
+-         StorageDead(_3);                 // scope 1 at $DIR/remove_storage_markers.rs:8:18: 8:19
+-         StorageLive(_4);                 // scope 1 at $DIR/remove_storage_markers.rs:8:14: 8:19
+          _4 = move _2;                    // scope 1 at $DIR/remove_storage_markers.rs:8:14: 8:19
+          goto -> bb1;                     // scope 2 at $DIR/remove_storage_markers.rs:8:5: 10:6
+      }
+  
+      bb1: {
+-         StorageLive(_6);                 // scope 2 at $DIR/remove_storage_markers.rs:8:14: 8:19
+-         StorageLive(_7);                 // scope 3 at $DIR/remove_storage_markers.rs:8:14: 8:19
+-         StorageLive(_8);                 // scope 3 at $DIR/remove_storage_markers.rs:8:14: 8:19
+-         StorageLive(_9);                 // scope 3 at $DIR/remove_storage_markers.rs:8:14: 8:19
+-         StorageLive(_10);                // scope 3 at $DIR/remove_storage_markers.rs:8:14: 8:19
+          _10 = &mut _4;                   // scope 3 at $DIR/remove_storage_markers.rs:8:14: 8:19
+          _9 = &mut (*_10);                // scope 3 at $DIR/remove_storage_markers.rs:8:14: 8:19
+          _8 = <std::ops::Range<i32> as Iterator>::next(move _9) -> bb2; // scope 3 at $DIR/remove_storage_markers.rs:8:14: 8:19
+                                           // mir::Constant
+                                           // + span: $DIR/remove_storage_markers.rs:8:14: 8:19
+                                           // + literal: Const { ty: for<'r> fn(&'r mut std::ops::Range<i32>) -> std::option::Option<<std::ops::Range<i32> as std::iter::Iterator>::Item> {<std::ops::Range<i32> as std::iter::Iterator>::next}, val: Value(Scalar(<ZST>)) }
+      }
+  
+      bb2: {
+-         StorageDead(_9);                 // scope 3 at $DIR/remove_storage_markers.rs:8:18: 8:19
+          _11 = discriminant(_8);          // scope 3 at $DIR/remove_storage_markers.rs:8:9: 8:10
+          switchInt(move _11) -> [0_isize: bb3, otherwise: bb4]; // scope 3 at $DIR/remove_storage_markers.rs:8:9: 8:10
+      }
+  
+      bb3: {
+          _0 = const ();                   // scope 3 at $DIR/remove_storage_markers.rs:8:5: 10:6
+-         StorageDead(_10);                // scope 3 at $DIR/remove_storage_markers.rs:8:18: 8:19
+-         StorageDead(_8);                 // scope 3 at $DIR/remove_storage_markers.rs:8:18: 8:19
+-         StorageDead(_7);                 // scope 3 at $DIR/remove_storage_markers.rs:8:18: 8:19
+-         StorageDead(_6);                 // scope 2 at $DIR/remove_storage_markers.rs:10:5: 10:6
+-         StorageDead(_4);                 // scope 1 at $DIR/remove_storage_markers.rs:10:5: 10:6
+-         StorageDead(_2);                 // scope 1 at $DIR/remove_storage_markers.rs:8:18: 8:19
+-         StorageDead(_1);                 // scope 0 at $DIR/remove_storage_markers.rs:11:1: 11:2
+          return;                          // scope 0 at $DIR/remove_storage_markers.rs:11:2: 11:2
+      }
+  
+      bb4: {
+-         StorageLive(_12);                // scope 3 at $DIR/remove_storage_markers.rs:8:9: 8:10
+          _12 = ((_8 as Some).0: i32);     // scope 3 at $DIR/remove_storage_markers.rs:8:9: 8:10
+-         StorageLive(_13);                // scope 4 at $DIR/remove_storage_markers.rs:8:9: 8:10
+          _13 = _12;                       // scope 4 at $DIR/remove_storage_markers.rs:8:9: 8:10
+          _6 = move _13;                   // scope 4 at $DIR/remove_storage_markers.rs:8:9: 8:10
+          _7 = const ();                   // scope 4 at $DIR/remove_storage_markers.rs:8:9: 8:10
+-         StorageDead(_13);                // scope 4 at $DIR/remove_storage_markers.rs:8:9: 8:10
+-         StorageDead(_12);                // scope 3 at $DIR/remove_storage_markers.rs:8:9: 8:10
+-         StorageDead(_10);                // scope 3 at $DIR/remove_storage_markers.rs:8:18: 8:19
+-         StorageDead(_8);                 // scope 3 at $DIR/remove_storage_markers.rs:8:18: 8:19
+-         StorageDead(_7);                 // scope 3 at $DIR/remove_storage_markers.rs:8:18: 8:19
+-         StorageLive(_15);                // scope 3 at $DIR/remove_storage_markers.rs:8:9: 8:10
+          _15 = _6;                        // scope 3 at $DIR/remove_storage_markers.rs:8:14: 8:19
+-         StorageLive(_16);                // scope 5 at $DIR/remove_storage_markers.rs:8:20: 10:6
+-         StorageLive(_17);                // scope 5 at $DIR/remove_storage_markers.rs:9:16: 9:17
+          _17 = _15;                       // scope 5 at $DIR/remove_storage_markers.rs:9:16: 9:17
+          _1 = Add(_1, move _17);          // scope 5 at $DIR/remove_storage_markers.rs:9:9: 9:17
+-         StorageDead(_17);                // scope 5 at $DIR/remove_storage_markers.rs:9:16: 9:17
+          _16 = const ();                  // scope 5 at $DIR/remove_storage_markers.rs:8:20: 10:6
+-         StorageDead(_16);                // scope 5 at $DIR/remove_storage_markers.rs:10:5: 10:6
+          _5 = const ();                   // scope 2 at $DIR/remove_storage_markers.rs:8:5: 10:6
+-         StorageDead(_15);                // scope 3 at $DIR/remove_storage_markers.rs:10:5: 10:6
+-         StorageDead(_6);                 // scope 2 at $DIR/remove_storage_markers.rs:10:5: 10:6
+          goto -> bb1;                     // scope 2 at $DIR/remove_storage_markers.rs:8:5: 10:6
+      }
+  }
+  

src/test/mir-opt/remove_storage_markers.rs

+// Checks that storage markers are removed at opt-level=0.
+//
+// compile-flags: -C opt-level=0 -Coverflow-checks=off
+
+// EMIT_MIR remove_storage_markers.main.RemoveStorageMarkers.diff
+fn main() {
+    let mut sum = 0;
+    for i in 0..10 {
+        sum += i;
+    }
+}

src/test/run-make/const_fn_mir/dump.mir

@@ -5,7 +5,6 @@ fn main() -> () {
     let _1: i32;                         // in scope 0 at main.rs:9:5: 9:10
 
     bb0: {
-        StorageLive(_1);                 // scope 0 at main.rs:9:5: 9:10
         _1 = foo() -> bb1;               // scope 0 at main.rs:9:5: 9:10
                                          // mir::Constant
                                          // + span: main.rs:9:5: 9:8
@@ -13,7 +12,6 @@ fn main() -> () {
     }
 
     bb1: {
-        StorageDead(_1);                 // scope 0 at main.rs:9:10: 9:11
         _0 = const ();                   // scope 0 at main.rs:8:11: 10:2
         return;                          // scope 0 at main.rs:10:2: 10:2
     }