Auto merge of #143271 - cjgillot:gvn-types, r=<try>

Store the type of each GVN value

MIR is fully typed, so type information is an integral part of what defines a value. GVN currently tries to circumvent storing types, which creates all sorts of complexities.

This PR stores the type along with the enum `Value` when defining a value index. This allows to simplify a lot of code.

r? `@ghost` for perf

Author: bors

compiler/rustc_mir_transform/src/gvn.rs

@@ -56,7 +56,7 @@ pub unsafe fn undef_union_as_integer() -> u32 {
 pub unsafe fn unreachable_direct() -> ! {
     // CHECK-LABEL: fn unreachable_direct(
     // CHECK: = const ();
-    // CHECK: = const () as Never (Transmute);
+    // CHECK: = const ZeroSized: Never;
     let x: Never = unsafe { transmute(()) };
     match x {}
 }

tests/mir-opt/const_prop/transmute.rs

@@ -15,7 +15,7 @@
 -         _2 = ();
 -         _1 = move _2 as Never (Transmute);
 +         _2 = const ();
-+         _1 = const () as Never (Transmute);
++         _1 = const ZeroSized: Never;
           unreachable;
       }
   }

tests/mir-opt/const_prop/transmute.unreachable_direct.GVN.32bit.diff

@@ -15,7 +15,7 @@
 -         _2 = ();
 -         _1 = move _2 as Never (Transmute);
 +         _2 = const ();
-+         _1 = const () as Never (Transmute);
++         _1 = const ZeroSized: Never;
           unreachable;
       }
   }

tests/mir-opt/const_prop/transmute.unreachable_direct.GVN.64bit.diff

@@ -18,7 +18,8 @@
 
       bb0: {
           _4 = copy _1 as *const T (PtrToPtr);
-          _5 = PtrMetadata(copy _4);
+-         _5 = PtrMetadata(copy _4);
++         _5 = const ();
           _6 = copy _1 as *const (&A, [T]) (PtrToPtr);
 -         _7 = PtrMetadata(copy _6);
 +         _7 = PtrMetadata(copy _1);

tests/mir-opt/gvn.generic_cast_metadata.GVN.panic-abort.diff

@@ -18,7 +18,8 @@
 
       bb0: {
           _4 = copy _1 as *const T (PtrToPtr);
-          _5 = PtrMetadata(copy _4);
+-         _5 = PtrMetadata(copy _4);
++         _5 = const ();
           _6 = copy _1 as *const (&A, [T]) (PtrToPtr);
 -         _7 = PtrMetadata(copy _6);
 +         _7 = PtrMetadata(copy _1);

tests/mir-opt/gvn.generic_cast_metadata.GVN.panic-unwind.diff

@@ -869,7 +869,7 @@ fn generic_cast_metadata<T, A: ?Sized, B: ?Sized>(ps: *const [T], pa: *const A,
 
             // Metadata usize -> (), do not optimize.
             // CHECK: [[T:_.+]] = copy _1 as
-            // CHECK-NEXT: PtrMetadata(copy [[T]])
+            // CHECK-NEXT: const ();
             let t1 = CastPtrToPtr::<_, *const T>(ps);
             let m1 = PtrMetadata(t1);
 

tests/mir-opt/gvn.rs

@@ -109,7 +109,6 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
     }
 
     bb4: {
-        StorageLive(_15);
         _14 = &mut _13;
         _15 = <Enumerate<std::slice::Iter<'_, T>> as Iterator>::next(move _14) -> [return: bb5, unwind: bb11];
     }
@@ -120,7 +119,6 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
     }
 
     bb6: {
-        StorageDead(_15);
         StorageDead(_13);
         drop(_2) -> [return: bb7, unwind continue];
     }
@@ -135,14 +133,13 @@ fn enumerated_loop(_1: &[T], _2: impl Fn(usize, &T)) -> () {
         StorageLive(_19);
         _19 = &_2;
         StorageLive(_20);
-        _20 = (copy _17, copy _18);
+        _20 = copy ((_15 as Some).0: (usize, &T));
         _21 = <impl Fn(usize, &T) as Fn<(usize, &T)>>::call(move _19, move _20) -> [return: bb9, unwind: bb11];
     }
 
     bb9: {
         StorageDead(_20);
         StorageDead(_19);
-        StorageDead(_15);
         goto -> bb4;
     }