Rollup merge of #122290 - RalfJung:mir-printing, r=compiler-errors

MIR printing: print the path of uneval'd const

Currently it just prints `const _` which makes it impossible to say which constant is being referred to.

Also refer to promoteds in a consistent way; previously MIR printing would do
```
promoted[0] in C1: &Option<Cell<i32>> = {
    // ...
}
```
Now that should be
```
const C1::promoted[0]: &Option<Cell<i32>> = {
    // ...
}
```

We don't seem to have a test for that so I tried it by hand, it seems to work:
```
const main::promoted[12]: &[&str; 3] = {
    let mut _0: &[&str; 3];
    let mut _1: [&str; 3];
    let mut _2: &str;
    let mut _3: &str;
    let mut _4: &str;
    let mut _5: &str;

    bb0: {
        _3 = const "b";
        _2 = &(*_3);
        _5 = const "c";
        _4 = &(*_5);
        _1 = [const "a", move _2, move _4];
        _0 = &_1;
        return;
    }
}
```

Author: matthiaskrgr

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -67,7 +67,7 @@ fn eval_body_using_ecx<'mir, 'tcx>(
     trace!(
         "eval_body_using_ecx: pushing stack frame for global: {}{}",
         with_no_trimmed_paths!(ecx.tcx.def_path_str(cid.instance.def_id())),
-        cid.promoted.map_or_else(String::new, |p| format!("::promoted[{p:?}]"))
+        cid.promoted.map_or_else(String::new, |p| format!("::{p:?}"))
     );
 
     ecx.push_stack_frame(

compiler/rustc_middle/src/mir/consts.rs

@@ -7,6 +7,7 @@ use rustc_target::abi::{HasDataLayout, Size};
 
 use crate::mir::interpret::{alloc_range, AllocId, ConstAllocation, ErrorHandled, Scalar};
 use crate::mir::{pretty_print_const_value, Promoted};
+use crate::ty::print::with_no_trimmed_paths;
 use crate::ty::GenericArgsRef;
 use crate::ty::ScalarInt;
 use crate::ty::{self, print::pretty_print_const, Ty, TyCtxt};
@@ -489,9 +490,18 @@ impl<'tcx> Display for Const<'tcx> {
             Const::Ty(c) => pretty_print_const(c, fmt, true),
             Const::Val(val, ty) => pretty_print_const_value(val, ty, fmt),
             // FIXME(valtrees): Correctly print mir constants.
-            Const::Unevaluated(..) => {
-                fmt.write_str("_")?;
-                Ok(())
+            Const::Unevaluated(c, _ty) => {
+                ty::tls::with(move |tcx| {
+                    let c = tcx.lift(c).unwrap();
+                    // Matches `GlobalId` printing.
+                    let instance =
+                        with_no_trimmed_paths!(tcx.def_path_str_with_args(c.def, c.args));
+                    write!(fmt, "{instance}")?;
+                    if let Some(promoted) = c.promoted {
+                        write!(fmt, "::{promoted:?}")?;
+                    }
+                    Ok(())
+                })
             }
         }
     }

compiler/rustc_middle/src/mir/pretty.rs

@@ -496,7 +496,7 @@ fn write_mir_sig(tcx: TyCtxt<'_>, body: &Body<'_>, w: &mut dyn io::Write) -> io:
         _ => tcx.is_closure_like(def_id),
     };
     match (kind, body.source.promoted) {
-        (_, Some(i)) => write!(w, "{i:?} in ")?,
+        (_, Some(_)) => write!(w, "const ")?, // promoteds are the closest to consts
         (DefKind::Const | DefKind::AssocConst, _) => write!(w, "const ")?,
         (DefKind::Static(hir::Mutability::Not), _) => write!(w, "static ")?,
         (DefKind::Static(hir::Mutability::Mut), _) => write!(w, "static mut ")?,
@@ -509,6 +509,9 @@ fn write_mir_sig(tcx: TyCtxt<'_>, body: &Body<'_>, w: &mut dyn io::Write) -> io:
         // see notes on #41697 elsewhere
         write!(w, "{}", tcx.def_path_str(def_id))?
     }
+    if let Some(p) = body.source.promoted {
+        write!(w, "::{p:?}")?;
+    }
 
     if body.source.promoted.is_none() && is_function {
         write!(w, "(")?;

tests/mir-opt/building/custom/consts.consts.built.after.mir

@@ -10,9 +10,9 @@ fn consts() -> () {
 
     bb0: {
         _1 = const 5_u8;
-        _2 = const _;
+        _2 = const consts::<C>::{constant#0};
         _3 = const C;
-        _4 = const _;
+        _4 = const D;
         _5 = consts::<10>;
         return;
     }

tests/mir-opt/const_promotion_extern_static.BAR-promoted[0].SimplifyCfg-elaborate-drops.after.mir

@@ -1,6 +1,6 @@
 // MIR for `BAR::promoted[0]` after SimplifyCfg-elaborate-drops
 
-promoted[0] in BAR: &[&i32; 1] = {
+const BAR::promoted[0]: &[&i32; 1] = {
     let mut _0: &[&i32; 1];
     let mut _1: [&i32; 1];
     let mut _2: &i32;

tests/mir-opt/const_promotion_extern_static.BAR.PromoteTemps.diff

@@ -20,7 +20,7 @@
 -         _4 = &(*_5);
 -         _3 = [move _4];
 -         _2 = &_3;
-+         _6 = const _;
++         _6 = const BAR::promoted[0];
 +         _2 = &(*_6);
           _1 = move _2 as &[&i32] (PointerCoercion(Unsize));
 -         StorageDead(_4);

tests/mir-opt/const_promotion_extern_static.FOO-promoted[0].SimplifyCfg-elaborate-drops.after.mir

@@ -1,6 +1,6 @@
 // MIR for `FOO::promoted[0]` after SimplifyCfg-elaborate-drops
 
-promoted[0] in FOO: &[&i32; 1] = {
+const FOO::promoted[0]: &[&i32; 1] = {
     let mut _0: &[&i32; 1];
     let mut _1: [&i32; 1];
     let mut _2: &i32;

tests/mir-opt/const_promotion_extern_static.FOO.PromoteTemps.diff

@@ -22,7 +22,7 @@
 -         _4 = &(*_5);
 -         _3 = [move _4];
 -         _2 = &_3;
-+         _6 = const _;
++         _6 = const FOO::promoted[0];
 +         _2 = &(*_6);
           _1 = move _2 as &[&i32] (PointerCoercion(Unsize));
 -         StorageDead(_4);

tests/mir-opt/const_prop/bad_op_unsafe_oob_for_slices.main.GVN.32bit.panic-abort.diff

@@ -25,7 +25,7 @@
           StorageLive(_1);
           StorageLive(_2);
           StorageLive(_3);
-          _9 = const _;
+          _9 = const main::promoted[0];
           _3 = &(*_9);
           _2 = &raw const (*_3);
           _1 = move _2 as *const [i32] (PointerCoercion(Unsize));

tests/mir-opt/const_prop/bad_op_unsafe_oob_for_slices.main.GVN.32bit.panic-unwind.diff

@@ -25,7 +25,7 @@
           StorageLive(_1);
           StorageLive(_2);
           StorageLive(_3);
-          _9 = const _;
+          _9 = const main::promoted[0];
           _3 = &(*_9);
           _2 = &raw const (*_3);
           _1 = move _2 as *const [i32] (PointerCoercion(Unsize));