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.

3 files changed, 126 insertions, 2 deletions

diff --git a/src/test/mir-opt/remove_storage_markers.main.RemoveStorageMarkers.diff b/src/test/mir-opt/remove_storage_markers.main.RemoveStorageMarkers.diff
new file mode 100644
index 00000000000..dd8a9251042
--- /dev/null
+++ b/src/test/mir-opt/remove_storage_markers.main.RemoveStorageMarkers.diff
@@ -0,0 +1,115 @@
+- // 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
+      }
+  }
+  
diff --git a/src/test/mir-opt/remove_storage_markers.rs b/src/test/mir-opt/remove_storage_markers.rs
new file mode 100644
index 00000000000..c144d3ff795
--- /dev/null
+++ b/src/test/mir-opt/remove_storage_markers.rs
@@ -0,0 +1,11 @@
+// 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;
+    }
+}
diff --git a/src/test/run-make/const_fn_mir/dump.mir b/src/test/run-make/const_fn_mir/dump.mir
index 3dac42c6782..45d018cf305 100644
--- a/src/test/run-make/const_fn_mir/dump.mir
+++ b/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
     }