Rollup merge of #61532 - wesleywiser:const_prop_more, r=oli-obk

[const-prop] Support Rvalue::{Ref,Len} and Deref

Also fixes an ICE I found in testing.

r? @oli-obk

~~The final commit is just for a perf run. I'll remove it after that is completed.~~

src/test/mir-opt/const_prop/ref_deref.rs

@@ -0,0 +1,21 @@
+fn main() {
+    *(&4);
+}
+
+// END RUST SOURCE
+// START rustc.main.ConstProp.before.mir
+// bb0: {
+//     ...
+//     _2 = &(promoted[0]: i32);
+//     _1 = (*_2);
+//     ...
+//}
+// END rustc.main.ConstProp.before.mir
+// START rustc.main.ConstProp.after.mir
+// bb0: {
+//     ...
+//     _2 = const Scalar(AllocId(0).0x0) : &i32;
+//     _1 = const 4i32;
+//     ...
+// }
+// END rustc.main.ConstProp.after.mir

src/test/mir-opt/const_prop/reify_fn_ptr.rs

@@ -0,0 +1,25 @@
+fn main() {
+    let _ = main as usize as *const fn();
+}
+
+// END RUST SOURCE
+// START rustc.main.ConstProp.before.mir
+//  bb0: {
+//      ...
+//      _3 = const main as fn() (Pointer(ReifyFnPointer));
+//      _2 = move _3 as usize (Misc);
+//      ...
+//      _1 = move _2 as *const fn() (Misc);
+//      ...
+//  }
+// END rustc.main.ConstProp.before.mir
+// START rustc.main.ConstProp.after.mir
+//  bb0: {
+//      ...
+//      _3 = const Scalar(AllocId(1).0x0) : fn();
+//      _2 = move _3 as usize (Misc);
+//      ...
+//      _1 = const Scalar(AllocId(1).0x0) : *const fn();
+//      ...
+//  }
+// END rustc.main.ConstProp.after.mir

src/test/mir-opt/const_prop/slice_len.rs

@@ -1,22 +1,22 @@
-fn test() -> &'static [u32] {
-    &[1, 2]
-}
-
 fn main() {
-    let x = test()[0];
+    (&[1u32, 2, 3] as &[u32])[1];
 }
 
 // END RUST SOURCE
 // START rustc.main.ConstProp.before.mir
-//  bb1: {
+//  bb0: {
 //      ...
-//      _3 = const 0usize;
-//      _4 = Len((*_2));
-//      _5 = Lt(_3, _4);
-//      assert(move _5, "index out of bounds: the len is move _4 but the index is _3") -> bb2;
+//      _4 = &(promoted[0]: [u32; 3]);
+//      _3 = _4;
+//      _2 = move _3 as &[u32] (Pointer(Unsize));
+//      ...
+//      _6 = const 1usize;
+//      _7 = Len((*_2));
+//      _8 = Lt(_6, _7);
+//      assert(move _8, "index out of bounds: the len is move _7 but the index is _6") -> bb1;
 //  }
-//  bb2: {
-//      _1 = (*_2)[_3];
+//  bb1: {
+//      _1 = (*_2)[_6];
 //      ...
 //      return;
 //  }
@@ -24,13 +24,17 @@ fn main() {
 // START rustc.main.ConstProp.after.mir
 //  bb0: {
 //      ...
-//      _3 = const 0usize;
-//      _4 = Len((*_2));
-//      _5 = Lt(_3, _4);
-//      assert(move _5, "index out of bounds: the len is move _4 but the index is _3") -> bb2;
+//      _4 = const Scalar(AllocId(0).0x0) : &[u32; 3];
+//      _3 = const Scalar(AllocId(0).0x0) : &[u32; 3];
+//      _2 = move _3 as &[u32] (Pointer(Unsize));
+//      ...
+//      _6 = const 1usize;
+//      _7 = const 3usize;
+//      _8 = const true;
+//      assert(const true, "index out of bounds: the len is move _7 but the index is _6") -> bb1;
 //  }
-//  bb2: {
-//      _1 = (*_2)[_3];
+//  bb1: {
+//      _1 = (*_2)[_6];
 //      ...
 //      return;
 //  }

src/test/ui/consts/const-eval/promoted_errors.stderr

@@ -16,6 +16,12 @@ warning: attempt to divide by zero
 LL |     println!("{}", 1/(1-1));
    |                    ^^^^^^^
 
+warning: this expression will panic at runtime
+  --> $DIR/promoted_errors.rs:9:20
+   |
+LL |     println!("{}", 1/(1-1));
+   |                    ^^^^^^^ attempt to divide by zero
+
 warning: attempt to divide by zero
   --> $DIR/promoted_errors.rs:11:14
    |
@@ -34,6 +40,12 @@ warning: attempt to divide by zero
 LL |     println!("{}", 1/(false as u32));
    |                    ^^^^^^^^^^^^^^^^
 
+warning: this expression will panic at runtime
+  --> $DIR/promoted_errors.rs:14:20
+   |
+LL |     println!("{}", 1/(false as u32));
+   |                    ^^^^^^^^^^^^^^^^ attempt to divide by zero
+
 warning: attempt to divide by zero
   --> $DIR/promoted_errors.rs:16:14
    |