GVN: Preserve derefs at unreachable

compiler/rustc_mir_transform/src/gvn.rs

@@ -1930,7 +1930,9 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, '_, 'tcx> {
  // Currently, only preserving derefs for trivial terminators like SwitchInt and Goto.
  let safe_to_preserve_derefs = matches!(
  terminator.kind,
- TerminatorKind::SwitchInt { .. } | TerminatorKind::Goto { .. }
+ TerminatorKind::SwitchInt { .. }
+ | TerminatorKind::Goto { .. }
+ | TerminatorKind::Unreachable
  );
  if !safe_to_preserve_derefs {
  self.invalidate_derefs();

tests/mir-opt/pre-codegen/two_unwrap_unchecked.rs

@@ -1,11 +1,14 @@
-// skip-filecheck
 //@ compile-flags: -O
 
 #![crate_type = "lib"]
 
 // EMIT_MIR two_unwrap_unchecked.two_unwrap_unchecked.GVN.diff
 // EMIT_MIR two_unwrap_unchecked.two_unwrap_unchecked.PreCodegen.after.mir
 pub fn two_unwrap_unchecked(v: &Option<i32>) -> i32 {
+ // CHECK-LABEL: fn two_unwrap_unchecked(
+ // CHECK: [[DEREF_V:_.*]] = copy (*_1);
+ // CHECK: [[V1V2:_.*]] = copy (([[DEREF_V]] as Some).0: i32);
+ // CHECK: _0 = Add(copy [[V1V2]], copy [[V1V2]]);
  let v1 = unsafe { v.unwrap_unchecked() };
  let v2 = unsafe { v.unwrap_unchecked() };
  v1 + v2

tests/mir-opt/pre-codegen/two_unwrap_unchecked.two_unwrap_unchecked.GVN.diff

@@ -41,12 +41,15 @@
 
  bb0: {
 - StorageLive(_2);
+- StorageLive(_3);
++ nop;
 + nop;
- StorageLive(_3);
  _3 = copy (*_1);
- StorageLive(_8);
+- StorageLive(_8);
++ nop;
  _8 = discriminant(_3);
- switchInt(move _8) -> [0: bb2, 1: bb3, otherwise: bb1];
+- switchInt(move _8) -> [0: bb2, 1: bb3, otherwise: bb1];
++ switchInt(copy _8) -> [0: bb2, 1: bb3, otherwise: bb1];
  }
 
  bb1: {
@@ -58,37 +61,43 @@
  }
 
  bb3: {
-  _2 = move ((_3 as Some).0: i32);
-  StorageDead(_8);
-  StorageDead(_3);
-- StorageLive(_4);
+- _2 = move ((_3 as Some).0: i32);
+- StorageDead(_8);
+- StorageDead(_3);
++ _2 = copy ((_3 as Some).0: i32);
 + nop;
++ nop;
+ StorageLive(_4);
  StorageLive(_5);
- _5 = copy (*_1);
+- _5 = copy (*_1);
++ _5 = copy _3;
  StorageLive(_9);
- _9 = discriminant(_5);
- switchInt(move _9) -> [0: bb4, 1: bb5, otherwise: bb1];
+- _9 = discriminant(_5);
+- switchInt(move _9) -> [0: bb4, 1: bb5, otherwise: bb1];
++ _9 = copy _8;
++ switchInt(copy _8) -> [0: bb4, 1: bb5, otherwise: bb1];
  }
 
  bb4: {
  unreachable;
  }
 
  bb5: {
- _4 = move ((_5 as Some).0: i32);
+- _4 = move ((_5 as Some).0: i32);
++ _4 = copy _2;
  StorageDead(_9);
  StorageDead(_5);
  StorageLive(_6);
  _6 = copy _2;
  StorageLive(_7);
-  _7 = copy _4;
+- _7 = copy _4;
 - _0 = Add(move _6, move _7);
-+ _0 = Add(copy _2, copy _4);
++ _7 = copy _2;
++ _0 = Add(copy _2, copy _2);
  StorageDead(_7);
  StorageDead(_6);
-- StorageDead(_4);
+  StorageDead(_4);
 - StorageDead(_2);
-+ nop;
 + nop;
  return;
  }

tests/mir-opt/pre-codegen/two_unwrap_unchecked.two_unwrap_unchecked.PreCodegen.after.mir

@@ -5,15 +5,12 @@ fn two_unwrap_unchecked(_1: &Option<i32>) -> i32 {
  let mut _0: i32;
  let mut _2: std::option::Option<i32>;
  let _4: i32;
- let mut _5: std::option::Option<i32>;
  scope 1 {
  debug v1 => _4;
- let _7: i32;
  scope 2 {
- debug v2 => _7;
+ debug v2 => _4;
  }
  scope 8 (inlined #[track_caller] Option::<i32>::unwrap_unchecked) {
- let mut _6: isize;
  scope 9 {
  }
  scope 10 (inlined #[track_caller] unreachable_unchecked) {
@@ -37,33 +34,18 @@ fn two_unwrap_unchecked(_1: &Option<i32>) -> i32 {
  }
 
  bb0: {
- StorageLive(_2);
  _2 = copy (*_1);
- StorageLive(_3);
  _3 = discriminant(_2);
- switchInt(move _3) -> [0: bb3, 1: bb1, otherwise: bb3];
+ switchInt(copy _3) -> [0: bb2, 1: bb1, otherwise: bb2];
  }
 
  bb1: {
- _4 = move ((_2 as Some).0: i32);
- StorageDead(_3);
- StorageDead(_2);
- StorageLive(_5);
- _5 = copy (*_1);
- StorageLive(_6);
- _6 = discriminant(_5);
- switchInt(move _6) -> [0: bb3, 1: bb2, otherwise: bb3];
- }
-
- bb2: {
- _7 = move ((_5 as Some).0: i32);
- StorageDead(_6);
- StorageDead(_5);
- _0 = Add(copy _4, copy _7);
+ _4 = copy ((_2 as Some).0: i32);
+ _0 = Add(copy _4, copy _4);
  return;
  }
 
- bb3: {
+ bb2: {
  unreachable;
  }
 }