Auto merge of #145513 - beepster4096:erasedereftemps, r=saethlin,cjgillot

Validate CopyForDeref and DerefTemps better and remove them from runtime MIR

(split from my WIP rust-lang/rust#145344)

This PR:
- Removes `Rvalue::CopyForDeref` and `LocalInfo::DerefTemp` from runtime MIR
    - Using a new mir pass `EraseDerefTemps`
    - `CopyForDeref(x)` is turned into `Use(Copy(x))`
    - `DerefTemp` is turned into `Boring`
        - Not sure if this part is actually necessary, it made more sense in rust-lang/rust#145344 with `DerefTemp` storing actual data that I wanted to keep from having to be kept in sync with the rest of the body in runtime MIR
- Checks in validation that `CopyForDeref` and `DerefTemp` are only used together
- Removes special handling for `CopyForDeref` from many places
- Removes `CopyForDeref` from `custom_mir` reverting rust-lang/rust#111587
    - In runtime MIR simple copies can be used instead
    - In post cleanup analysis MIR it was already wrong to use due to the lack of support for creating `DerefTemp` locals
    - Possibly this should be its own PR?
 - Adds an argument to `deref_finder` to avoid creating new `DerefTemp`s and `CopyForDeref` in runtime MIR.
     - Ideally we would just avoid making intermediate derefs instead of fixing it at the end of a pass / during shim building
 - Removes some usages of `deref_finder` that I found out don't actually do anything

r? oli-obk

Author: bors

src/base.rs

@@ -600,11 +600,6 @@ fn codegen_stmt<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, cur_block: Block, stmt:
                     let val = codegen_operand(fx, operand);
                     lval.write_cvalue(fx, val);
                 }
-                Rvalue::CopyForDeref(place) => {
-                    let cplace = codegen_place(fx, place);
-                    let val = cplace.to_cvalue(fx);
-                    lval.write_cvalue(fx, val)
-                }
                 Rvalue::Ref(_, _, place) | Rvalue::RawPtr(_, place) => {
                     let place = codegen_place(fx, place);
                     let ref_ = place.place_ref(fx, lval.layout());
@@ -928,6 +923,7 @@ fn codegen_stmt<'tcx>(fx: &mut FunctionCx<'_, '_, 'tcx>, cur_block: Block, stmt:
                     let operand = codegen_operand(fx, operand);
                     lval.write_cvalue_transmute(fx, operand);
                 }
+                Rvalue::CopyForDeref(_) => bug!("`CopyForDeref` in codegen"),
             }
         }
         StatementKind::StorageLive(_)