Auto merge of #71953 - oli-obk:const_prop_deaggregates, r=wesleywiser

Const prop aggregates even if partially or fully modified

r? @wesleywiser

cc @rust-lang/wg-mir-opt I'm moderately scared of this change, but I'm confident in having reviewed all the cases.

8 files changed, 284 insertions, 0 deletions

diff --git a/src/test/mir-opt/const_prop/mutable_variable.rs b/src/test/mir-opt/const_prop/mutable_variable.rs
new file mode 100644
index 00000000000..b3a2d80fa95
--- /dev/null
+++ b/src/test/mir-opt/const_prop/mutable_variable.rs
@@ -0,0 +1,8 @@
+// compile-flags: -O
+
+// EMIT_MIR rustc.main.ConstProp.diff
+fn main() {
+    let mut x = 42;
+    x = 99;
+    let y = x;
+}
diff --git a/src/test/mir-opt/const_prop/mutable_variable/rustc.main.ConstProp.diff b/src/test/mir-opt/const_prop/mutable_variable/rustc.main.ConstProp.diff
new file mode 100644
index 00000000000..c6c5b0cf726
--- /dev/null
+++ b/src/test/mir-opt/const_prop/mutable_variable/rustc.main.ConstProp.diff
@@ -0,0 +1,53 @@
+- // MIR for `main` before ConstProp
++ // MIR for `main` after ConstProp
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/mutable_variable.rs:4:11: 4:11
+      let mut _1: i32;                     // in scope 0 at $DIR/mutable_variable.rs:5:9: 5:14
+      scope 1 {
+          debug x => _1;                   // in scope 1 at $DIR/mutable_variable.rs:5:9: 5:14
+          let _2: i32;                     // in scope 1 at $DIR/mutable_variable.rs:7:9: 7:10
+          scope 2 {
+              debug y => _2;               // in scope 2 at $DIR/mutable_variable.rs:7:9: 7:10
+          }
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/mutable_variable.rs:5:9: 5:14
+          _1 = const 42i32;                // scope 0 at $DIR/mutable_variable.rs:5:17: 5:19
+                                           // ty::Const
+                                           // + ty: i32
+                                           // + val: Value(Scalar(0x0000002a))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable.rs:5:17: 5:19
+                                           // + literal: Const { ty: i32, val: Value(Scalar(0x0000002a)) }
+          _1 = const 99i32;                // scope 1 at $DIR/mutable_variable.rs:6:5: 6:11
+                                           // ty::Const
+                                           // + ty: i32
+                                           // + val: Value(Scalar(0x00000063))
+                                           // mir::Constant
+-                                          // + span: $DIR/mutable_variable.rs:6:9: 6:11
++                                          // + span: $DIR/mutable_variable.rs:6:5: 6:11
+                                           // + literal: Const { ty: i32, val: Value(Scalar(0x00000063)) }
+          StorageLive(_2);                 // scope 1 at $DIR/mutable_variable.rs:7:9: 7:10
+-         _2 = _1;                         // scope 1 at $DIR/mutable_variable.rs:7:13: 7:14
++         _2 = const 99i32;                // scope 1 at $DIR/mutable_variable.rs:7:13: 7:14
++                                          // ty::Const
++                                          // + ty: i32
++                                          // + val: Value(Scalar(0x00000063))
++                                          // mir::Constant
++                                          // + span: $DIR/mutable_variable.rs:7:13: 7:14
++                                          // + literal: Const { ty: i32, val: Value(Scalar(0x00000063)) }
+          _0 = const ();                   // scope 0 at $DIR/mutable_variable.rs:4:11: 8:2
+                                           // ty::Const
+                                           // + ty: ()
+                                           // + val: Value(Scalar(<ZST>))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable.rs:4:11: 8:2
+                                           // + literal: Const { ty: (), val: Value(Scalar(<ZST>)) }
+          StorageDead(_2);                 // scope 1 at $DIR/mutable_variable.rs:8:1: 8:2
+          StorageDead(_1);                 // scope 0 at $DIR/mutable_variable.rs:8:1: 8:2
+          return;                          // scope 0 at $DIR/mutable_variable.rs:8:2: 8:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/const_prop/mutable_variable_aggregate.rs b/src/test/mir-opt/const_prop/mutable_variable_aggregate.rs
new file mode 100644
index 00000000000..3c5fb4574b6
--- /dev/null
+++ b/src/test/mir-opt/const_prop/mutable_variable_aggregate.rs
@@ -0,0 +1,8 @@
+// compile-flags: -O
+
+// EMIT_MIR rustc.main.ConstProp.diff
+fn main() {
+    let mut x = (42, 43);
+    x.1 = 99;
+    let y = x;
+}
diff --git a/src/test/mir-opt/const_prop/mutable_variable_aggregate/rustc.main.ConstProp.diff b/src/test/mir-opt/const_prop/mutable_variable_aggregate/rustc.main.ConstProp.diff
new file mode 100644
index 00000000000..26f0250d94c
--- /dev/null
+++ b/src/test/mir-opt/const_prop/mutable_variable_aggregate/rustc.main.ConstProp.diff
@@ -0,0 +1,67 @@
+- // MIR for `main` before ConstProp
++ // MIR for `main` after ConstProp
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/mutable_variable_aggregate.rs:4:11: 4:11
+      let mut _1: (i32, i32);              // in scope 0 at $DIR/mutable_variable_aggregate.rs:5:9: 5:14
+      scope 1 {
+          debug x => _1;                   // in scope 1 at $DIR/mutable_variable_aggregate.rs:5:9: 5:14
+          let _2: (i32, i32);              // in scope 1 at $DIR/mutable_variable_aggregate.rs:7:9: 7:10
+          scope 2 {
+              debug y => _2;               // in scope 2 at $DIR/mutable_variable_aggregate.rs:7:9: 7:10
+          }
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/mutable_variable_aggregate.rs:5:9: 5:14
+          _1 = (const 42i32, const 43i32); // scope 0 at $DIR/mutable_variable_aggregate.rs:5:17: 5:25
+                                           // ty::Const
+                                           // + ty: i32
+                                           // + val: Value(Scalar(0x0000002a))
+                                           // mir::Constant
+-                                          // + span: $DIR/mutable_variable_aggregate.rs:5:18: 5:20
++                                          // + span: $DIR/mutable_variable_aggregate.rs:5:17: 5:25
+                                           // + literal: Const { ty: i32, val: Value(Scalar(0x0000002a)) }
+                                           // ty::Const
+                                           // + ty: i32
+                                           // + val: Value(Scalar(0x0000002b))
+                                           // mir::Constant
+-                                          // + span: $DIR/mutable_variable_aggregate.rs:5:22: 5:24
++                                          // + span: $DIR/mutable_variable_aggregate.rs:5:17: 5:25
+                                           // + literal: Const { ty: i32, val: Value(Scalar(0x0000002b)) }
+          (_1.1: i32) = const 99i32;       // scope 1 at $DIR/mutable_variable_aggregate.rs:6:5: 6:13
+                                           // ty::Const
+                                           // + ty: i32
+                                           // + val: Value(Scalar(0x00000063))
+                                           // mir::Constant
+-                                          // + span: $DIR/mutable_variable_aggregate.rs:6:11: 6:13
++                                          // + span: $DIR/mutable_variable_aggregate.rs:6:5: 6:13
+                                           // + literal: Const { ty: i32, val: Value(Scalar(0x00000063)) }
+          StorageLive(_2);                 // scope 1 at $DIR/mutable_variable_aggregate.rs:7:9: 7:10
+-         _2 = _1;                         // scope 1 at $DIR/mutable_variable_aggregate.rs:7:13: 7:14
++         _2 = (const 42i32, const 99i32); // scope 1 at $DIR/mutable_variable_aggregate.rs:7:13: 7:14
++                                          // ty::Const
++                                          // + ty: i32
++                                          // + val: Value(Scalar(0x0000002a))
++                                          // mir::Constant
++                                          // + span: $DIR/mutable_variable_aggregate.rs:7:13: 7:14
++                                          // + literal: Const { ty: i32, val: Value(Scalar(0x0000002a)) }
++                                          // ty::Const
++                                          // + ty: i32
++                                          // + val: Value(Scalar(0x00000063))
++                                          // mir::Constant
++                                          // + span: $DIR/mutable_variable_aggregate.rs:7:13: 7:14
++                                          // + literal: Const { ty: i32, val: Value(Scalar(0x00000063)) }
+          _0 = const ();                   // scope 0 at $DIR/mutable_variable_aggregate.rs:4:11: 8:2
+                                           // ty::Const
+                                           // + ty: ()
+                                           // + val: Value(Scalar(<ZST>))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable_aggregate.rs:4:11: 8:2
+                                           // + literal: Const { ty: (), val: Value(Scalar(<ZST>)) }
+          StorageDead(_2);                 // scope 1 at $DIR/mutable_variable_aggregate.rs:8:1: 8:2
+          StorageDead(_1);                 // scope 0 at $DIR/mutable_variable_aggregate.rs:8:1: 8:2
+          return;                          // scope 0 at $DIR/mutable_variable_aggregate.rs:8:2: 8:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/const_prop/mutable_variable_aggregate_mut_ref.rs b/src/test/mir-opt/const_prop/mutable_variable_aggregate_mut_ref.rs
new file mode 100644
index 00000000000..fc13cbf2abd
--- /dev/null
+++ b/src/test/mir-opt/const_prop/mutable_variable_aggregate_mut_ref.rs
@@ -0,0 +1,9 @@
+// compile-flags: -O
+
+// EMIT_MIR rustc.main.ConstProp.diff
+fn main() {
+    let mut x = (42, 43);
+    let z = &mut x;
+    z.1 = 99;
+    let y = x;
+}
diff --git a/src/test/mir-opt/const_prop/mutable_variable_aggregate_mut_ref/rustc.main.ConstProp.diff b/src/test/mir-opt/const_prop/mutable_variable_aggregate_mut_ref/rustc.main.ConstProp.diff
new file mode 100644
index 00000000000..44203ac327a
--- /dev/null
+++ b/src/test/mir-opt/const_prop/mutable_variable_aggregate_mut_ref/rustc.main.ConstProp.diff
@@ -0,0 +1,58 @@
+- // MIR for `main` before ConstProp
++ // MIR for `main` after ConstProp
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/mutable_variable_aggregate_mut_ref.rs:4:11: 4:11
+      let mut _1: (i32, i32);              // in scope 0 at $DIR/mutable_variable_aggregate_mut_ref.rs:5:9: 5:14
+      scope 1 {
+          debug x => _1;                   // in scope 1 at $DIR/mutable_variable_aggregate_mut_ref.rs:5:9: 5:14
+          let _2: &mut (i32, i32);         // in scope 1 at $DIR/mutable_variable_aggregate_mut_ref.rs:6:9: 6:10
+          scope 2 {
+              debug z => _2;               // in scope 2 at $DIR/mutable_variable_aggregate_mut_ref.rs:6:9: 6:10
+              let _3: (i32, i32);          // in scope 2 at $DIR/mutable_variable_aggregate_mut_ref.rs:8:9: 8:10
+              scope 3 {
+                  debug y => _3;           // in scope 3 at $DIR/mutable_variable_aggregate_mut_ref.rs:8:9: 8:10
+              }
+          }
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/mutable_variable_aggregate_mut_ref.rs:5:9: 5:14
+          _1 = (const 42i32, const 43i32); // scope 0 at $DIR/mutable_variable_aggregate_mut_ref.rs:5:17: 5:25
+                                           // ty::Const
+                                           // + ty: i32
+                                           // + val: Value(Scalar(0x0000002a))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable_aggregate_mut_ref.rs:5:18: 5:20
+                                           // + literal: Const { ty: i32, val: Value(Scalar(0x0000002a)) }
+                                           // ty::Const
+                                           // + ty: i32
+                                           // + val: Value(Scalar(0x0000002b))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable_aggregate_mut_ref.rs:5:22: 5:24
+                                           // + literal: Const { ty: i32, val: Value(Scalar(0x0000002b)) }
+          StorageLive(_2);                 // scope 1 at $DIR/mutable_variable_aggregate_mut_ref.rs:6:9: 6:10
+          _2 = &mut _1;                    // scope 1 at $DIR/mutable_variable_aggregate_mut_ref.rs:6:13: 6:19
+          ((*_2).1: i32) = const 99i32;    // scope 2 at $DIR/mutable_variable_aggregate_mut_ref.rs:7:5: 7:13
+                                           // ty::Const
+                                           // + ty: i32
+                                           // + val: Value(Scalar(0x00000063))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable_aggregate_mut_ref.rs:7:11: 7:13
+                                           // + literal: Const { ty: i32, val: Value(Scalar(0x00000063)) }
+          StorageLive(_3);                 // scope 2 at $DIR/mutable_variable_aggregate_mut_ref.rs:8:9: 8:10
+          _3 = _1;                         // scope 2 at $DIR/mutable_variable_aggregate_mut_ref.rs:8:13: 8:14
+          _0 = const ();                   // scope 0 at $DIR/mutable_variable_aggregate_mut_ref.rs:4:11: 9:2
+                                           // ty::Const
+                                           // + ty: ()
+                                           // + val: Value(Scalar(<ZST>))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable_aggregate_mut_ref.rs:4:11: 9:2
+                                           // + literal: Const { ty: (), val: Value(Scalar(<ZST>)) }
+          StorageDead(_3);                 // scope 2 at $DIR/mutable_variable_aggregate_mut_ref.rs:9:1: 9:2
+          StorageDead(_2);                 // scope 1 at $DIR/mutable_variable_aggregate_mut_ref.rs:9:1: 9:2
+          StorageDead(_1);                 // scope 0 at $DIR/mutable_variable_aggregate_mut_ref.rs:9:1: 9:2
+          return;                          // scope 0 at $DIR/mutable_variable_aggregate_mut_ref.rs:9:2: 9:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/const_prop/mutable_variable_no_prop.rs b/src/test/mir-opt/const_prop/mutable_variable_no_prop.rs
new file mode 100644
index 00000000000..8c9cd005096
--- /dev/null
+++ b/src/test/mir-opt/const_prop/mutable_variable_no_prop.rs
@@ -0,0 +1,12 @@
+// compile-flags: -O
+
+static mut STATIC: u32 = 42;
+
+// EMIT_MIR rustc.main.ConstProp.diff
+fn main() {
+    let mut x = 42;
+    unsafe {
+        x = STATIC;
+    }
+    let y = x;
+}
diff --git a/src/test/mir-opt/const_prop/mutable_variable_no_prop/rustc.main.ConstProp.diff b/src/test/mir-opt/const_prop/mutable_variable_no_prop/rustc.main.ConstProp.diff
new file mode 100644
index 00000000000..1e9cbe6024c
--- /dev/null
+++ b/src/test/mir-opt/const_prop/mutable_variable_no_prop/rustc.main.ConstProp.diff
@@ -0,0 +1,69 @@
+- // MIR for `main` before ConstProp
++ // MIR for `main` after ConstProp
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/mutable_variable_no_prop.rs:6:11: 6:11
+      let mut _1: u32;                     // in scope 0 at $DIR/mutable_variable_no_prop.rs:7:9: 7:14
+      let _2: ();                          // in scope 0 at $DIR/mutable_variable_no_prop.rs:8:5: 10:6
+      let mut _3: u32;                     // in scope 0 at $DIR/mutable_variable_no_prop.rs:9:13: 9:19
+      let mut _4: *mut u32;                // in scope 0 at $DIR/mutable_variable_no_prop.rs:9:13: 9:19
+      scope 1 {
+          debug x => _1;                   // in scope 1 at $DIR/mutable_variable_no_prop.rs:7:9: 7:14
+          let _5: u32;                     // in scope 1 at $DIR/mutable_variable_no_prop.rs:11:9: 11:10
+          scope 2 {
+          }
+          scope 3 {
+              debug y => _5;               // in scope 3 at $DIR/mutable_variable_no_prop.rs:11:9: 11:10
+          }
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/mutable_variable_no_prop.rs:7:9: 7:14
+          _1 = const 42u32;                // scope 0 at $DIR/mutable_variable_no_prop.rs:7:17: 7:19
+                                           // ty::Const
+                                           // + ty: u32
+                                           // + val: Value(Scalar(0x0000002a))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable_no_prop.rs:7:17: 7:19
+                                           // + literal: Const { ty: u32, val: Value(Scalar(0x0000002a)) }
+          StorageLive(_2);                 // scope 1 at $DIR/mutable_variable_no_prop.rs:8:5: 10:6
+          StorageLive(_3);                 // scope 2 at $DIR/mutable_variable_no_prop.rs:9:13: 9:19
+          StorageLive(_4);                 // scope 2 at $DIR/mutable_variable_no_prop.rs:9:13: 9:19
+          _4 = const {alloc0+0x0: *mut u32}; // scope 2 at $DIR/mutable_variable_no_prop.rs:9:13: 9:19
+                                           // ty::Const
+                                           // + ty: *mut u32
+                                           // + val: Value(Scalar(alloc0+0x0))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable_no_prop.rs:9:13: 9:19
+                                           // + literal: Const { ty: *mut u32, val: Value(Scalar(alloc0+0x0)) }
+          _3 = (*_4);                      // scope 2 at $DIR/mutable_variable_no_prop.rs:9:13: 9:19
+          _1 = move _3;                    // scope 2 at $DIR/mutable_variable_no_prop.rs:9:9: 9:19
+          StorageDead(_3);                 // scope 2 at $DIR/mutable_variable_no_prop.rs:9:18: 9:19
+          StorageDead(_4);                 // scope 2 at $DIR/mutable_variable_no_prop.rs:9:19: 9:20
+          _2 = const ();                   // scope 2 at $DIR/mutable_variable_no_prop.rs:8:5: 10:6
+                                           // ty::Const
+                                           // + ty: ()
+                                           // + val: Value(Scalar(<ZST>))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable_no_prop.rs:8:5: 10:6
+                                           // + literal: Const { ty: (), val: Value(Scalar(<ZST>)) }
+          StorageDead(_2);                 // scope 1 at $DIR/mutable_variable_no_prop.rs:10:5: 10:6
+          StorageLive(_5);                 // scope 1 at $DIR/mutable_variable_no_prop.rs:11:9: 11:10
+          _5 = _1;                         // scope 1 at $DIR/mutable_variable_no_prop.rs:11:13: 11:14
+          _0 = const ();                   // scope 0 at $DIR/mutable_variable_no_prop.rs:6:11: 12:2
+                                           // ty::Const
+                                           // + ty: ()
+                                           // + val: Value(Scalar(<ZST>))
+                                           // mir::Constant
+                                           // + span: $DIR/mutable_variable_no_prop.rs:6:11: 12:2
+                                           // + literal: Const { ty: (), val: Value(Scalar(<ZST>)) }
+          StorageDead(_5);                 // scope 1 at $DIR/mutable_variable_no_prop.rs:12:1: 12:2
+          StorageDead(_1);                 // scope 0 at $DIR/mutable_variable_no_prop.rs:12:1: 12:2
+          return;                          // scope 0 at $DIR/mutable_variable_no_prop.rs:12:2: 12:2
+      }
+  }
+  
+  alloc0 (static: STATIC, size: 4, align: 4) {
+      2a 00 00 00                                     │ *...
+  }
+