Auto merge of #77876 - tmiasko:simplify-locals, r=wesleywiser

Remove unused set-discriminant statements and assignments regardless of rvalue

* Represent use counts with u32
* Unify use count visitors
* Change RemoveStatements visitor into a function
* Remove unused set-discriminant statements
* Use exhaustive match to clarify what is being optimized
* Remove unused assignments regardless of rvalue kind

22 files changed, 404 insertions, 163 deletions

diff --git a/compiler/rustc_mir/src/transform/simplify.rs b/compiler/rustc_mir/src/transform/simplify.rs
index f0c87bcf513..b7c9a3a8688 100644
--- a/compiler/rustc_mir/src/transform/simplify.rs
+++ b/compiler/rustc_mir/src/transform/simplify.rs
@@ -35,6 +35,7 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
 use smallvec::SmallVec;
 use std::borrow::Cow;
+use std::convert::TryInto;
 
 pub struct SimplifyCfg {
     label: String,
@@ -322,32 +323,17 @@ impl<'tcx> MirPass<'tcx> for SimplifyLocals {
         trace!("running SimplifyLocals on {:?}", body.source);
 
         // First, we're going to get a count of *actual* uses for every `Local`.
-        // Take a look at `DeclMarker::visit_local()` to see exactly what is ignored.
-        let mut used_locals = {
-            let mut marker = DeclMarker::new(body);
-            marker.visit_body(&body);
-
-            marker.local_counts
-        };
-
-        let arg_count = body.arg_count;
+        let mut used_locals = UsedLocals::new(body);
 
         // Next, we're going to remove any `Local` with zero actual uses. When we remove those
         // `Locals`, we're also going to subtract any uses of other `Locals` from the `used_locals`
         // count. For example, if we removed `_2 = discriminant(_1)`, then we'll subtract one from
         // `use_counts[_1]`. That in turn might make `_1` unused, so we loop until we hit a
         // fixedpoint where there are no more unused locals.
-        loop {
-            let mut remove_statements = RemoveStatements::new(&mut used_locals, arg_count, tcx);
-            remove_statements.visit_body(body);
-
-            if !remove_statements.modified {
-                break;
-            }
-        }
+        remove_unused_definitions(&mut used_locals, body);
 
         // Finally, we'll actually do the work of shrinking `body.local_decls` and remapping the `Local`s.
-        let map = make_local_map(&mut body.local_decls, used_locals, arg_count);
+        let map = make_local_map(&mut body.local_decls, &used_locals);
 
         // Only bother running the `LocalUpdater` if we actually found locals to remove.
         if map.iter().any(Option::is_none) {
@@ -363,14 +349,14 @@ impl<'tcx> MirPass<'tcx> for SimplifyLocals {
 /// Construct the mapping while swapping out unused stuff out from the `vec`.
 fn make_local_map<V>(
     local_decls: &mut IndexVec<Local, V>,
-    used_locals: IndexVec<Local, usize>,
-    arg_count: usize,
+    used_locals: &UsedLocals,
 ) -> IndexVec<Local, Option<Local>> {
     let mut map: IndexVec<Local, Option<Local>> = IndexVec::from_elem(None, &*local_decls);
     let mut used = Local::new(0);
-    for (alive_index, count) in used_locals.iter_enumerated() {
-        // The `RETURN_PLACE` and arguments are always live.
-        if alive_index.as_usize() > arg_count && *count == 0 {
+
+    for alive_index in local_decls.indices() {
+        // `is_used` treats the `RETURN_PLACE` and arguments as used.
+        if !used_locals.is_used(alive_index) {
             continue;
         }
 
@@ -384,149 +370,130 @@ fn make_local_map<V>(
     map
 }
 
-struct DeclMarker<'a, 'tcx> {
-    pub local_counts: IndexVec<Local, usize>,
-    pub body: &'a Body<'tcx>,
+/// Keeps track of used & unused locals.
+struct UsedLocals {
+    increment: bool,
+    arg_count: u32,
+    use_count: IndexVec<Local, u32>,
 }
 
-impl<'a, 'tcx> DeclMarker<'a, 'tcx> {
-    pub fn new(body: &'a Body<'tcx>) -> Self {
-        Self { local_counts: IndexVec::from_elem(0, &body.local_decls), body }
+impl UsedLocals {
+    /// Determines which locals are used & unused in the given body.
+    fn new(body: &Body<'_>) -> Self {
+        let mut this = Self {
+            increment: true,
+            arg_count: body.arg_count.try_into().unwrap(),
+            use_count: IndexVec::from_elem(0, &body.local_decls),
+        };
+        this.visit_body(body);
+        this
     }
-}
 
-impl<'a, 'tcx> Visitor<'tcx> for DeclMarker<'a, 'tcx> {
-    fn visit_local(&mut self, local: &Local, ctx: PlaceContext, location: Location) {
-        // Ignore storage markers altogether, they get removed along with their otherwise unused
-        // decls.
-        // FIXME: Extend this to all non-uses.
-        if ctx.is_storage_marker() {
-            return;
-        }
+    /// Checks if local is used.
+    ///
+    /// Return place and arguments are always considered used.
+    fn is_used(&self, local: Local) -> bool {
+        trace!("is_used({:?}): use_count: {:?}", local, self.use_count[local]);
+        local.as_u32() <= self.arg_count || self.use_count[local] != 0
+    }
 
-        // Ignore stores of constants because `ConstProp` and `CopyProp` can remove uses of many
-        // of these locals. However, if the local is still needed, then it will be referenced in
-        // another place and we'll mark it as being used there.
-        if ctx == PlaceContext::MutatingUse(MutatingUseContext::Store)
-            || ctx == PlaceContext::MutatingUse(MutatingUseContext::Projection)
-        {
-            let block = &self.body.basic_blocks()[location.block];
-            if location.statement_index != block.statements.len() {
-                let stmt = &block.statements[location.statement_index];
-
-                if let StatementKind::Assign(box (dest, rvalue)) = &stmt.kind {
-                    if !dest.is_indirect() && dest.local == *local {
-                        let can_skip = match rvalue {
-                            Rvalue::Use(_)
-                            | Rvalue::Discriminant(_)
-                            | Rvalue::BinaryOp(_, _, _)
-                            | Rvalue::CheckedBinaryOp(_, _, _)
-                            | Rvalue::Repeat(_, _)
-                            | Rvalue::AddressOf(_, _)
-                            | Rvalue::Len(_)
-                            | Rvalue::UnaryOp(_, _)
-                            | Rvalue::Aggregate(_, _) => true,
-
-                            _ => false,
-                        };
-
-                        if can_skip {
-                            trace!("skipping store of {:?} to {:?}", rvalue, dest);
-                            return;
-                        }
-                    }
-                }
-            }
-        }
+    /// Updates the use counts to reflect the removal of given statement.
+    fn statement_removed(&mut self, statement: &Statement<'tcx>) {
+        self.increment = false;
 
-        self.local_counts[*local] += 1;
+        // The location of the statement is irrelevant.
+        let location = Location { block: START_BLOCK, statement_index: 0 };
+        self.visit_statement(statement, location);
     }
-}
-
-struct StatementDeclMarker<'a, 'tcx> {
-    used_locals: &'a mut IndexVec<Local, usize>,
-    statement: &'a Statement<'tcx>,
-}
 
-impl<'a, 'tcx> StatementDeclMarker<'a, 'tcx> {
-    pub fn new(
-        used_locals: &'a mut IndexVec<Local, usize>,
-        statement: &'a Statement<'tcx>,
-    ) -> Self {
-        Self { used_locals, statement }
+    /// Visits a left-hand side of an assignment.
+    fn visit_lhs(&mut self, place: &Place<'tcx>, location: Location) {
+        if place.is_indirect() {
+            // A use, not a definition.
+            self.visit_place(place, PlaceContext::MutatingUse(MutatingUseContext::Store), location);
+        } else {
+            // A definition. Although, it still might use other locals for indexing.
+            self.super_projection(
+                place.local,
+                &place.projection,
+                PlaceContext::MutatingUse(MutatingUseContext::Projection),
+                location,
+            );
+        }
     }
 }
 
-impl<'a, 'tcx> Visitor<'tcx> for StatementDeclMarker<'a, 'tcx> {
-    fn visit_local(&mut self, local: &Local, context: PlaceContext, _location: Location) {
-        // Skip the lvalue for assignments
-        if let StatementKind::Assign(box (p, _)) = self.statement.kind {
-            if p.local == *local && context.is_place_assignment() {
-                return;
+impl Visitor<'_> for UsedLocals {
+    fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
+        match statement.kind {
+            StatementKind::LlvmInlineAsm(..)
+            | StatementKind::Retag(..)
+            | StatementKind::Coverage(..)
+            | StatementKind::FakeRead(..)
+            | StatementKind::AscribeUserType(..) => {
+                self.super_statement(statement, location);
             }
-        }
 
-        let use_count = &mut self.used_locals[*local];
-        // If this is the local we're removing...
-        if *use_count != 0 {
-            *use_count -= 1;
-        }
-    }
-}
+            StatementKind::Nop => {}
 
-struct RemoveStatements<'a, 'tcx> {
-    used_locals: &'a mut IndexVec<Local, usize>,
-    arg_count: usize,
-    tcx: TyCtxt<'tcx>,
-    modified: bool,
-}
+            StatementKind::StorageLive(_local) | StatementKind::StorageDead(_local) => {}
 
-impl<'a, 'tcx> RemoveStatements<'a, 'tcx> {
-    fn new(
-        used_locals: &'a mut IndexVec<Local, usize>,
-        arg_count: usize,
-        tcx: TyCtxt<'tcx>,
-    ) -> Self {
-        Self { used_locals, arg_count, tcx, modified: false }
-    }
+            StatementKind::Assign(box (ref place, ref rvalue)) => {
+                self.visit_lhs(place, location);
+                self.visit_rvalue(rvalue, location);
+            }
 
-    fn keep_local(&self, l: Local) -> bool {
-        trace!("keep_local({:?}): count: {:?}", l, self.used_locals[l]);
-        l.as_usize() <= self.arg_count || self.used_locals[l] != 0
+            StatementKind::SetDiscriminant { ref place, variant_index: _ } => {
+                self.visit_lhs(place, location);
+            }
+        }
     }
-}
 
-impl<'a, 'tcx> MutVisitor<'tcx> for RemoveStatements<'a, 'tcx> {
-    fn tcx(&self) -> TyCtxt<'tcx> {
-        self.tcx
+    fn visit_local(&mut self, local: &Local, _ctx: PlaceContext, _location: Location) {
+        if self.increment {
+            self.use_count[*local] += 1;
+        } else {
+            assert_ne!(self.use_count[*local], 0);
+            self.use_count[*local] -= 1;
+        }
     }
+}
 
-    fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
-        // Remove unnecessary StorageLive and StorageDead annotations.
-        let mut i = 0usize;
-        data.statements.retain(|stmt| {
-            let keep = match &stmt.kind {
-                StatementKind::StorageLive(l) | StatementKind::StorageDead(l) => {
-                    self.keep_local(*l)
-                }
-                StatementKind::Assign(box (place, _)) => self.keep_local(place.local),
-                _ => true,
-            };
-
-            if !keep {
-                trace!("removing statement {:?}", stmt);
-                self.modified = true;
-
-                let mut visitor = StatementDeclMarker::new(self.used_locals, stmt);
-                visitor.visit_statement(stmt, Location { block, statement_index: i });
-            }
+/// Removes unused definitions. Updates the used locals to reflect the changes made.
+fn remove_unused_definitions<'a, 'tcx>(used_locals: &'a mut UsedLocals, body: &mut Body<'tcx>) {
+    // The use counts are updated as we remove the statements. A local might become unused
+    // during the retain operation, leading to a temporary inconsistency (storage statements or
+    // definitions referencing the local might remain). For correctness it is crucial that this
+    // computation reaches a fixed point.
+
+    let mut modified = true;
+    while modified {
+        modified = false;
+
+        for data in body.basic_blocks_mut() {
+            // Remove unnecessary StorageLive and StorageDead annotations.
+            data.statements.retain(|statement| {
+                let keep = match &statement.kind {
+                    StatementKind::StorageLive(local) | StatementKind::StorageDead(local) => {
+                        used_locals.is_used(*local)
+                    }
+                    StatementKind::Assign(box (place, _)) => used_locals.is_used(place.local),
 
-            i += 1;
+                    StatementKind::SetDiscriminant { ref place, .. } => {
+                        used_locals.is_used(place.local)
+                    }
+                    _ => true,
+                };
 
-            keep
-        });
+                if !keep {
+                    trace!("removing statement {:?}", statement);
+                    modified = true;
+                    used_locals.statement_removed(statement);
+                }
 
-        self.super_basic_block_data(block, data);
+                keep
+            });
+        }
     }
 }
 
diff --git a/src/test/codegen-units/item-collection/instantiation-through-vtable.rs b/src/test/codegen-units/item-collection/instantiation-through-vtable.rs
index 63966a7ec97..ce6757a047c 100644
--- a/src/test/codegen-units/item-collection/instantiation-through-vtable.rs
+++ b/src/test/codegen-units/item-collection/instantiation-through-vtable.rs
@@ -1,6 +1,5 @@
 // ignore-tidy-linelength
-// compile-flags:-Zprint-mono-items=eager
-// compile-flags:-Zinline-in-all-cgus
+// compile-flags:-Zprint-mono-items=eager -Zinline-in-all-cgus -Zmir-opt-level=0
 
 #![deny(dead_code)]
 #![feature(start)]
diff --git a/src/test/codegen/lifetime_start_end.rs b/src/test/codegen/lifetime_start_end.rs
index 9df46bb3dd1..da35789ce8d 100644
--- a/src/test/codegen/lifetime_start_end.rs
+++ b/src/test/codegen/lifetime_start_end.rs
@@ -1,4 +1,4 @@
-// compile-flags: -O -C no-prepopulate-passes
+// compile-flags: -O -C no-prepopulate-passes -Zmir-opt-level=0
 
 #![crate_type = "lib"]
 
@@ -18,10 +18,10 @@ pub fn test() {
 // CHECK: [[S_b:%[0-9]+]] = bitcast { i32, i32 }** %b to i8*
 // CHECK: call void @llvm.lifetime.start{{.*}}(i{{[0-9 ]+}}, i8* [[S_b]])
 
-// CHECK: [[S__4:%[0-9]+]] = bitcast { i32, i32 }* %_4 to i8*
+// CHECK: [[S__4:%[0-9]+]] = bitcast { i32, i32 }* %_5 to i8*
 // CHECK: call void @llvm.lifetime.start{{.*}}(i{{[0-9 ]+}}, i8* [[S__4]])
 
-// CHECK: [[E__4:%[0-9]+]] = bitcast { i32, i32 }* %_4 to i8*
+// CHECK: [[E__4:%[0-9]+]] = bitcast { i32, i32 }* %_5 to i8*
 // CHECK: call void @llvm.lifetime.end{{.*}}(i{{[0-9 ]+}}, i8* [[E__4]])
 
 // CHECK: [[E_b:%[0-9]+]] = bitcast { i32, i32 }** %b to i8*
diff --git a/src/test/codegen/loads.rs b/src/test/codegen/loads.rs
index e164f5115ff..3c9ecec2cbf 100644
--- a/src/test/codegen/loads.rs
+++ b/src/test/codegen/loads.rs
@@ -1,4 +1,4 @@
-// compile-flags: -C no-prepopulate-passes
+// compile-flags: -C no-prepopulate-passes -Zmir-opt-level=0
 
 #![crate_type = "lib"]
 
diff --git a/src/test/codegen/naked-functions.rs b/src/test/codegen/naked-functions.rs
index 493c1b9f0ba..5e76f1d67e6 100644
--- a/src/test/codegen/naked-functions.rs
+++ b/src/test/codegen/naked-functions.rs
@@ -1,4 +1,4 @@
-// compile-flags: -C no-prepopulate-passes
+// compile-flags: -C no-prepopulate-passes -Zmir-opt-level=0
 
 #![crate_type = "lib"]
 #![feature(naked_functions)]
diff --git a/src/test/codegen/refs.rs b/src/test/codegen/refs.rs
index 15f99fd0c22..b4cc26f3f9d 100644
--- a/src/test/codegen/refs.rs
+++ b/src/test/codegen/refs.rs
@@ -1,4 +1,4 @@
-// compile-flags: -C no-prepopulate-passes
+// compile-flags: -C no-prepopulate-passes -Zmir-opt-level=0
 
 #![crate_type = "lib"]
 
diff --git a/src/test/incremental/hashes/closure_expressions.rs b/src/test/incremental/hashes/closure_expressions.rs
index 7372cbc9156..4a00a6c72f7 100644
--- a/src/test/incremental/hashes/closure_expressions.rs
+++ b/src/test/incremental/hashes/closure_expressions.rs
@@ -7,7 +7,7 @@
 
 // build-pass (FIXME(62277): could be check-pass?)
 // revisions: cfail1 cfail2 cfail3
-// compile-flags: -Z query-dep-graph -Zincremental-ignore-spans
+// compile-flags: -Z query-dep-graph -Zincremental-ignore-spans -Zmir-opt-level=0
 
 #![allow(warnings)]
 #![feature(rustc_attrs)]
@@ -53,7 +53,7 @@ pub fn change_parameter_pattern() {
 }
 
 #[cfg(not(cfail1))]
-#[rustc_clean(cfg="cfail2", except="hir_owner_nodes, typeck")]
+#[rustc_clean(cfg="cfail2", except="hir_owner_nodes, typeck, optimized_mir")]
 #[rustc_clean(cfg="cfail3")]
 pub fn change_parameter_pattern() {
     let _ = |(x,): (u32,)| x;
diff --git a/src/test/incremental/hashes/enum_constructors.rs b/src/test/incremental/hashes/enum_constructors.rs
index 4161c6a6bfc..26ff6b109dc 100644
--- a/src/test/incremental/hashes/enum_constructors.rs
+++ b/src/test/incremental/hashes/enum_constructors.rs
@@ -7,7 +7,7 @@
 
 // build-pass (FIXME(62277): could be check-pass?)
 // revisions: cfail1 cfail2 cfail3
-// compile-flags: -Z query-dep-graph -Zincremental-ignore-spans
+// compile-flags: -Z query-dep-graph -Zincremental-ignore-spans -Zmir-opt-level=0
 
 #![allow(warnings)]
 #![feature(rustc_attrs)]
diff --git a/src/test/mir-opt/simplify-locals.rs b/src/test/mir-opt/simplify-locals.rs
new file mode 100644
index 00000000000..dca8f30c894
--- /dev/null
+++ b/src/test/mir-opt/simplify-locals.rs
@@ -0,0 +1,74 @@
+// compile-flags: -C overflow-checks=off
+
+#![feature(box_syntax)]
+#![feature(thread_local)]
+
+#[derive(Copy, Clone)]
+enum E {
+     A,
+     B,
+}
+
+// EMIT_MIR simplify_locals.c.SimplifyLocals.diff
+fn c() {
+    let bytes = [0u8; 10];
+    // Unused cast
+    let _: &[u8] = &bytes;
+}
+
+// EMIT_MIR simplify_locals.d1.SimplifyLocals.diff
+fn d1() {
+    // Unused set discriminant
+    let _ = E::A;
+}
+
+// EMIT_MIR simplify_locals.d2.SimplifyLocals.diff
+fn d2() {
+    // Unused set discriminant
+    {(10, E::A)}.1 = E::B;
+}
+
+// EMIT_MIR simplify_locals.r.SimplifyLocals.diff
+fn r() {
+    let mut a = 1;
+    // Unused references
+    let _ = &a;
+    let _ = &mut a;
+}
+
+#[thread_local] static mut X: u32 = 0;
+
+// EMIT_MIR simplify_locals.t1.SimplifyLocals.diff
+fn t1() {
+    // Unused thread local
+    unsafe { X };
+}
+
+// EMIT_MIR simplify_locals.t2.SimplifyLocals.diff
+fn t2() {
+    // Unused thread local
+    unsafe { &mut X };
+}
+
+// EMIT_MIR simplify_locals.t3.SimplifyLocals.diff
+fn t3() {
+    // Unused thread local
+    unsafe { *&mut X };
+}
+
+// EMIT_MIR simplify_locals.t4.SimplifyLocals.diff
+fn t4() -> u32 {
+    // Used thread local
+    unsafe { X + 1 }
+}
+
+fn main() {
+    c();
+    d1();
+    d2();
+    r();
+    t1();
+    t2();
+    t3();
+    t4();
+}
diff --git a/src/test/mir-opt/simplify_locals.c.SimplifyLocals.diff b/src/test/mir-opt/simplify_locals.c.SimplifyLocals.diff
new file mode 100644
index 00000000000..dbac7dff9e2
--- /dev/null
+++ b/src/test/mir-opt/simplify_locals.c.SimplifyLocals.diff
@@ -0,0 +1,28 @@
+- // MIR for `c` before SimplifyLocals
++ // MIR for `c` after SimplifyLocals
+  
+  fn c() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/simplify-locals.rs:13:8: 13:8
+      let _1: [u8; 10];                    // in scope 0 at $DIR/simplify-locals.rs:14:9: 14:14
+-     let mut _2: &[u8];                   // in scope 0 at $DIR/simplify-locals.rs:16:20: 16:26
+-     let mut _3: &[u8; 10];               // in scope 0 at $DIR/simplify-locals.rs:16:20: 16:26
+-     let _4: &[u8; 10];                   // in scope 0 at $DIR/simplify-locals.rs:16:20: 16:26
+      scope 1 {
+          debug bytes => _1;               // in scope 1 at $DIR/simplify-locals.rs:14:9: 14:14
+          scope 2 {
+          }
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/simplify-locals.rs:14:9: 14:14
+          _1 = [const 0_u8; 10];           // scope 0 at $DIR/simplify-locals.rs:14:17: 14:26
+-         StorageLive(_2);                 // scope 1 at $DIR/simplify-locals.rs:16:20: 16:26
+-         _3 = &_1;                        // scope 1 at $DIR/simplify-locals.rs:16:20: 16:26
+-         _2 = move _3 as &[u8] (Pointer(Unsize)); // scope 1 at $DIR/simplify-locals.rs:16:20: 16:26
+-         StorageDead(_2);                 // scope 1 at $DIR/simplify-locals.rs:16:26: 16:27
+          _0 = const ();                   // scope 0 at $DIR/simplify-locals.rs:13:8: 17:2
+          StorageDead(_1);                 // scope 0 at $DIR/simplify-locals.rs:17:1: 17:2
+          return;                          // scope 0 at $DIR/simplify-locals.rs:17:2: 17:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/simplify_locals.d1.SimplifyLocals.diff b/src/test/mir-opt/simplify_locals.d1.SimplifyLocals.diff
new file mode 100644
index 00000000000..76bf175d073
--- /dev/null
+++ b/src/test/mir-opt/simplify_locals.d1.SimplifyLocals.diff
@@ -0,0 +1,18 @@
+- // MIR for `d1` before SimplifyLocals
++ // MIR for `d1` after SimplifyLocals
+  
+  fn d1() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/simplify-locals.rs:20:9: 20:9
+-     let mut _1: E;                       // in scope 0 at $DIR/simplify-locals.rs:22:13: 22:17
+      scope 1 {
+      }
+  
+      bb0: {
+-         StorageLive(_1);                 // scope 0 at $DIR/simplify-locals.rs:22:13: 22:17
+-         discriminant(_1) = 0;            // scope 0 at $DIR/simplify-locals.rs:22:13: 22:17
+-         StorageDead(_1);                 // scope 0 at $DIR/simplify-locals.rs:22:17: 22:18
+          _0 = const ();                   // scope 0 at $DIR/simplify-locals.rs:20:9: 23:2
+          return;                          // scope 0 at $DIR/simplify-locals.rs:23:2: 23:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/simplify_locals.d2.SimplifyLocals.diff b/src/test/mir-opt/simplify_locals.d2.SimplifyLocals.diff
new file mode 100644
index 00000000000..c06fa09053c
--- /dev/null
+++ b/src/test/mir-opt/simplify_locals.d2.SimplifyLocals.diff
@@ -0,0 +1,38 @@
+- // MIR for `d2` before SimplifyLocals
++ // MIR for `d2` after SimplifyLocals
+  
+  fn d2() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/simplify-locals.rs:26:9: 26:9
+-     let mut _1: E;                       // in scope 0 at $DIR/simplify-locals.rs:28:22: 28:26
+-     let mut _2: (i32, E);                // in scope 0 at $DIR/simplify-locals.rs:28:5: 28:17
+-     let mut _3: E;                       // in scope 0 at $DIR/simplify-locals.rs:28:11: 28:15
+  
+      bb0: {
+-         StorageLive(_1);                 // scope 0 at $DIR/simplify-locals.rs:28:22: 28:26
+-         discriminant(_1) = 1;            // scope 0 at $DIR/simplify-locals.rs:28:22: 28:26
+-         StorageLive(_2);                 // scope 0 at $DIR/simplify-locals.rs:28:5: 28:17
+-         StorageLive(_3);                 // scope 0 at $DIR/simplify-locals.rs:28:11: 28:15
+-         discriminant(_3) = 0;            // scope 0 at $DIR/simplify-locals.rs:28:11: 28:15
+-         (_2.0: i32) = const 10_i32;      // scope 0 at $DIR/simplify-locals.rs:28:6: 28:16
+-         (_2.1: E) = const E::A;          // scope 0 at $DIR/simplify-locals.rs:28:6: 28:16
+-                                          // ty::Const
+-                                          // + ty: E
+-                                          // + val: Value(Scalar(0x00))
+-                                          // mir::Constant
+-                                          // + span: $DIR/simplify-locals.rs:28:6: 28:16
+-                                          // + literal: Const { ty: E, val: Value(Scalar(0x00)) }
+-         StorageDead(_3);                 // scope 0 at $DIR/simplify-locals.rs:28:15: 28:16
+-         (_2.1: E) = const E::B;          // scope 0 at $DIR/simplify-locals.rs:28:5: 28:26
+-                                          // ty::Const
+-                                          // + ty: E
+-                                          // + val: Value(Scalar(0x01))
+-                                          // mir::Constant
+-                                          // + span: $DIR/simplify-locals.rs:28:5: 28:26
+-                                          // + literal: Const { ty: E, val: Value(Scalar(0x01)) }
+-         StorageDead(_1);                 // scope 0 at $DIR/simplify-locals.rs:28:25: 28:26
+-         StorageDead(_2);                 // scope 0 at $DIR/simplify-locals.rs:28:26: 28:27
+          _0 = const ();                   // scope 0 at $DIR/simplify-locals.rs:26:9: 29:2
+          return;                          // scope 0 at $DIR/simplify-locals.rs:29:2: 29:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/simplify_locals.r.SimplifyLocals.diff b/src/test/mir-opt/simplify_locals.r.SimplifyLocals.diff
new file mode 100644
index 00000000000..85cf398d316
--- /dev/null
+++ b/src/test/mir-opt/simplify_locals.r.SimplifyLocals.diff
@@ -0,0 +1,31 @@
+- // MIR for `r` before SimplifyLocals
++ // MIR for `r` after SimplifyLocals
+  
+  fn r() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/simplify-locals.rs:32:8: 32:8
+      let mut _1: i32;                     // in scope 0 at $DIR/simplify-locals.rs:33:9: 33:14
+-     let mut _2: &i32;                    // in scope 0 at $DIR/simplify-locals.rs:35:13: 35:15
+-     let mut _3: &mut i32;                // in scope 0 at $DIR/simplify-locals.rs:36:13: 36:19
+      scope 1 {
+          debug a => _1;                   // in scope 1 at $DIR/simplify-locals.rs:33:9: 33:14
+          scope 2 {
+              scope 3 {
+              }
+          }
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/simplify-locals.rs:33:9: 33:14
+          _1 = const 1_i32;                // scope 0 at $DIR/simplify-locals.rs:33:17: 33:18
+-         StorageLive(_2);                 // scope 1 at $DIR/simplify-locals.rs:35:13: 35:15
+-         _2 = &_1;                        // scope 1 at $DIR/simplify-locals.rs:35:13: 35:15
+-         StorageDead(_2);                 // scope 1 at $DIR/simplify-locals.rs:35:15: 35:16
+-         StorageLive(_3);                 // scope 2 at $DIR/simplify-locals.rs:36:13: 36:19
+-         _3 = &mut _1;                    // scope 2 at $DIR/simplify-locals.rs:36:13: 36:19
+-         StorageDead(_3);                 // scope 2 at $DIR/simplify-locals.rs:36:19: 36:20
+          _0 = const ();                   // scope 0 at $DIR/simplify-locals.rs:32:8: 37:2
+          StorageDead(_1);                 // scope 0 at $DIR/simplify-locals.rs:37:1: 37:2
+          return;                          // scope 0 at $DIR/simplify-locals.rs:37:2: 37:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/simplify_locals.t1.SimplifyLocals.diff b/src/test/mir-opt/simplify_locals.t1.SimplifyLocals.diff
new file mode 100644
index 00000000000..991a0721cca
--- /dev/null
+++ b/src/test/mir-opt/simplify_locals.t1.SimplifyLocals.diff
@@ -0,0 +1,22 @@
+- // MIR for `t1` before SimplifyLocals
++ // MIR for `t1` after SimplifyLocals
+  
+  fn t1() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/simplify-locals.rs:42:9: 42:9
+-     let _1: u32;                         // in scope 0 at $DIR/simplify-locals.rs:44:14: 44:15
+-     let mut _2: *mut u32;                // in scope 0 at $DIR/simplify-locals.rs:44:14: 44:15
+      scope 1 {
+      }
+  
+      bb0: {
+-         StorageLive(_1);                 // scope 0 at $DIR/simplify-locals.rs:44:5: 44:17
+-         StorageLive(_2);                 // scope 1 at $DIR/simplify-locals.rs:44:14: 44:15
+-         _2 = &/*tls*/ mut X;             // scope 1 at $DIR/simplify-locals.rs:44:14: 44:15
+-         _1 = (*_2);                      // scope 1 at $DIR/simplify-locals.rs:44:14: 44:15
+-         StorageDead(_2);                 // scope 0 at $DIR/simplify-locals.rs:44:17: 44:18
+-         StorageDead(_1);                 // scope 0 at $DIR/simplify-locals.rs:44:17: 44:18
+          _0 = const ();                   // scope 0 at $DIR/simplify-locals.rs:42:9: 45:2
+          return;                          // scope 0 at $DIR/simplify-locals.rs:45:2: 45:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/simplify_locals.t2.SimplifyLocals.diff b/src/test/mir-opt/simplify_locals.t2.SimplifyLocals.diff
new file mode 100644
index 00000000000..6c9ed96e78f
--- /dev/null
+++ b/src/test/mir-opt/simplify_locals.t2.SimplifyLocals.diff
@@ -0,0 +1,22 @@
+- // MIR for `t2` before SimplifyLocals
++ // MIR for `t2` after SimplifyLocals
+  
+  fn t2() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/simplify-locals.rs:48:9: 48:9
+-     let _1: &mut u32;                    // in scope 0 at $DIR/simplify-locals.rs:50:14: 50:20
+-     let mut _2: *mut u32;                // in scope 0 at $DIR/simplify-locals.rs:50:19: 50:20
+      scope 1 {
+      }
+  
+      bb0: {
+-         StorageLive(_1);                 // scope 0 at $DIR/simplify-locals.rs:50:5: 50:22
+-         StorageLive(_2);                 // scope 1 at $DIR/simplify-locals.rs:50:19: 50:20
+-         _2 = &/*tls*/ mut X;             // scope 1 at $DIR/simplify-locals.rs:50:19: 50:20
+-         _1 = &mut (*_2);                 // scope 1 at $DIR/simplify-locals.rs:50:14: 50:20
+-         StorageDead(_2);                 // scope 0 at $DIR/simplify-locals.rs:50:22: 50:23
+-         StorageDead(_1);                 // scope 0 at $DIR/simplify-locals.rs:50:22: 50:23
+          _0 = const ();                   // scope 0 at $DIR/simplify-locals.rs:48:9: 51:2
+          return;                          // scope 0 at $DIR/simplify-locals.rs:51:2: 51:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/simplify_locals.t3.SimplifyLocals.diff b/src/test/mir-opt/simplify_locals.t3.SimplifyLocals.diff
new file mode 100644
index 00000000000..2d5fb352f8b
--- /dev/null
+++ b/src/test/mir-opt/simplify_locals.t3.SimplifyLocals.diff
@@ -0,0 +1,26 @@
+- // MIR for `t3` before SimplifyLocals
++ // MIR for `t3` after SimplifyLocals
+  
+  fn t3() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/simplify-locals.rs:54:9: 54:9
+-     let _1: u32;                         // in scope 0 at $DIR/simplify-locals.rs:56:14: 56:21
+-     let mut _2: &mut u32;                // in scope 0 at $DIR/simplify-locals.rs:56:15: 56:21
+-     let mut _3: *mut u32;                // in scope 0 at $DIR/simplify-locals.rs:56:20: 56:21
+      scope 1 {
+      }
+  
+      bb0: {
+-         StorageLive(_1);                 // scope 0 at $DIR/simplify-locals.rs:56:5: 56:23
+-         StorageLive(_2);                 // scope 1 at $DIR/simplify-locals.rs:56:15: 56:21
+-         StorageLive(_3);                 // scope 1 at $DIR/simplify-locals.rs:56:20: 56:21
+-         _3 = &/*tls*/ mut X;             // scope 1 at $DIR/simplify-locals.rs:56:20: 56:21
+-         _2 = &mut (*_3);                 // scope 1 at $DIR/simplify-locals.rs:56:15: 56:21
+-         _1 = (*_2);                      // scope 1 at $DIR/simplify-locals.rs:56:14: 56:21
+-         StorageDead(_3);                 // scope 0 at $DIR/simplify-locals.rs:56:23: 56:24
+-         StorageDead(_2);                 // scope 0 at $DIR/simplify-locals.rs:56:23: 56:24
+-         StorageDead(_1);                 // scope 0 at $DIR/simplify-locals.rs:56:23: 56:24
+          _0 = const ();                   // scope 0 at $DIR/simplify-locals.rs:54:9: 57:2
+          return;                          // scope 0 at $DIR/simplify-locals.rs:57:2: 57:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/simplify_locals.t4.SimplifyLocals.diff b/src/test/mir-opt/simplify_locals.t4.SimplifyLocals.diff
new file mode 100644
index 00000000000..e0e9b3ef406
--- /dev/null
+++ b/src/test/mir-opt/simplify_locals.t4.SimplifyLocals.diff
@@ -0,0 +1,22 @@
+- // MIR for `t4` before SimplifyLocals
++ // MIR for `t4` after SimplifyLocals
+  
+  fn t4() -> u32 {
+      let mut _0: u32;                     // return place in scope 0 at $DIR/simplify-locals.rs:60:12: 60:15
+      let mut _1: u32;                     // in scope 0 at $DIR/simplify-locals.rs:62:14: 62:15
+      let mut _2: *mut u32;                // in scope 0 at $DIR/simplify-locals.rs:62:14: 62:15
+      scope 1 {
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 1 at $DIR/simplify-locals.rs:62:14: 62:15
+          StorageLive(_2);                 // scope 1 at $DIR/simplify-locals.rs:62:14: 62:15
+          _2 = &/*tls*/ mut X;             // scope 1 at $DIR/simplify-locals.rs:62:14: 62:15
+          _1 = (*_2);                      // scope 1 at $DIR/simplify-locals.rs:62:14: 62:15
+          _0 = Add(move _1, const 1_u32);  // scope 1 at $DIR/simplify-locals.rs:62:14: 62:19
+          StorageDead(_1);                 // scope 1 at $DIR/simplify-locals.rs:62:18: 62:19
+          StorageDead(_2);                 // scope 0 at $DIR/simplify-locals.rs:63:1: 63:2
+          return;                          // scope 0 at $DIR/simplify-locals.rs:63:2: 63:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/while_let_loops.change_loop_body.PreCodegen.after.32bit.mir b/src/test/mir-opt/while_let_loops.change_loop_body.PreCodegen.after.32bit.mir
index 523ecb5ec1a..dae0cbb65a4 100644
--- a/src/test/mir-opt/while_let_loops.change_loop_body.PreCodegen.after.32bit.mir
+++ b/src/test/mir-opt/while_let_loops.change_loop_body.PreCodegen.after.32bit.mir
@@ -3,7 +3,6 @@
 fn change_loop_body() -> () {
     let mut _0: ();                      // return place in scope 0 at $DIR/while_let_loops.rs:5:27: 5:27
     let mut _1: i32;                     // in scope 0 at $DIR/while_let_loops.rs:6:9: 6:15
-    let mut _2: std::option::Option<u32>; // in scope 0 at $DIR/while_let_loops.rs:7:28: 7:32
     scope 1 {
         debug _x => _1;                  // in scope 1 at $DIR/while_let_loops.rs:6:9: 6:15
     }
@@ -11,10 +10,7 @@ fn change_loop_body() -> () {
     bb0: {
         StorageLive(_1);                 // scope 0 at $DIR/while_let_loops.rs:6:9: 6:15
         _1 = const 0_i32;                // scope 0 at $DIR/while_let_loops.rs:6:18: 6:19
-        StorageLive(_2);                 // scope 1 at $DIR/while_let_loops.rs:7:28: 7:32
-        discriminant(_2) = 0;            // scope 1 at $DIR/while_let_loops.rs:7:28: 7:32
         _0 = const ();                   // scope 1 at $DIR/while_let_loops.rs:7:5: 10:6
-        StorageDead(_2);                 // scope 1 at $DIR/while_let_loops.rs:10:5: 10:6
         StorageDead(_1);                 // scope 0 at $DIR/while_let_loops.rs:11:1: 11:2
         return;                          // scope 0 at $DIR/while_let_loops.rs:11:2: 11:2
     }
diff --git a/src/test/mir-opt/while_let_loops.change_loop_body.PreCodegen.after.64bit.mir b/src/test/mir-opt/while_let_loops.change_loop_body.PreCodegen.after.64bit.mir
index 523ecb5ec1a..dae0cbb65a4 100644
--- a/src/test/mir-opt/while_let_loops.change_loop_body.PreCodegen.after.64bit.mir
+++ b/src/test/mir-opt/while_let_loops.change_loop_body.PreCodegen.after.64bit.mir
@@ -3,7 +3,6 @@
 fn change_loop_body() -> () {
     let mut _0: ();                      // return place in scope 0 at $DIR/while_let_loops.rs:5:27: 5:27
     let mut _1: i32;                     // in scope 0 at $DIR/while_let_loops.rs:6:9: 6:15
-    let mut _2: std::option::Option<u32>; // in scope 0 at $DIR/while_let_loops.rs:7:28: 7:32
     scope 1 {
         debug _x => _1;                  // in scope 1 at $DIR/while_let_loops.rs:6:9: 6:15
     }
@@ -11,10 +10,7 @@ fn change_loop_body() -> () {
     bb0: {
         StorageLive(_1);                 // scope 0 at $DIR/while_let_loops.rs:6:9: 6:15
         _1 = const 0_i32;                // scope 0 at $DIR/while_let_loops.rs:6:18: 6:19
-        StorageLive(_2);                 // scope 1 at $DIR/while_let_loops.rs:7:28: 7:32
-        discriminant(_2) = 0;            // scope 1 at $DIR/while_let_loops.rs:7:28: 7:32
         _0 = const ();                   // scope 1 at $DIR/while_let_loops.rs:7:5: 10:6
-        StorageDead(_2);                 // scope 1 at $DIR/while_let_loops.rs:10:5: 10:6
         StorageDead(_1);                 // scope 0 at $DIR/while_let_loops.rs:11:1: 11:2
         return;                          // scope 0 at $DIR/while_let_loops.rs:11:2: 11:2
     }
diff --git a/src/test/ui/lint/issue-69485-var-size-diffs-too-large.rs b/src/test/ui/lint/issue-69485-var-size-diffs-too-large.rs
index 49d489d9168..0895f4c18e3 100644
--- a/src/test/ui/lint/issue-69485-var-size-diffs-too-large.rs
+++ b/src/test/ui/lint/issue-69485-var-size-diffs-too-large.rs
@@ -1,5 +1,6 @@
 // build-fail
 // only-x86_64
+// compile-flags: -Zmir-opt-level=0
 
 fn main() {
     Bug::V([0; !0]); //~ ERROR is too big for the current
diff --git a/src/test/ui/lint/issue-69485-var-size-diffs-too-large.stderr b/src/test/ui/lint/issue-69485-var-size-diffs-too-large.stderr
index d31ce9cfe0c..51eac95afb9 100644
--- a/src/test/ui/lint/issue-69485-var-size-diffs-too-large.stderr
+++ b/src/test/ui/lint/issue-69485-var-size-diffs-too-large.stderr
@@ -1,5 +1,5 @@
 error: the type `[u8; 18446744073709551615]` is too big for the current architecture
-  --> $DIR/issue-69485-var-size-diffs-too-large.rs:5:12
+  --> $DIR/issue-69485-var-size-diffs-too-large.rs:6:12
    |
 LL |     Bug::V([0; !0]);
    |            ^^^^^^^
diff --git a/src/test/ui/recursion/issue-38591-non-regular-dropck-recursion.rs b/src/test/ui/recursion/issue-38591-non-regular-dropck-recursion.rs
index 658def0ad5a..c857eb459b8 100644
--- a/src/test/ui/recursion/issue-38591-non-regular-dropck-recursion.rs
+++ b/src/test/ui/recursion/issue-38591-non-regular-dropck-recursion.rs
@@ -5,6 +5,7 @@
 
 // build-fail
 // normalize-stderr-test: ".nll/" -> "/"
+// compile-flags: -Zmir-opt-level=0
 
 struct S<T> {
     t: T,