Fix project_deref() implementation

I'm not really sure what is wrong here, but I was getting load
type mismatches in the debuginfo code (which is the only place
using this function).

Replacing the project_deref() implementation with a generic
load_operand + deref did the trick.

Author: nikic

compiler/rustc_codegen_ssa/src/mir/debuginfo.rs

@@ -274,7 +274,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 match *elem {
                     mir::ProjectionElem::Deref => {
                         indirect_offsets.push(Size::ZERO);
-                        place = place.project_deref(bx);
+                        place = bx.load_operand(place).deref(bx.cx());
                     }
                     mir::ProjectionElem::Field(field, _) => {
                         let i = field.index();

compiler/rustc_codegen_ssa/src/mir/place.rs

@@ -402,18 +402,6 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
         downcast
     }
 
-    pub fn project_deref<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) -> Self {
-        let target_ty = self.layout.ty.builtin_deref(true).expect("failed to deref");
-        let layout = bx.layout_of(target_ty.ty);
-
-        PlaceRef {
-            llval: bx.load(bx.backend_type(layout), self.llval, self.align),
-            llextra: None,
-            layout,
-            align: layout.align.abi,
-        }
-    }
-
     pub fn storage_live<Bx: BuilderMethods<'a, 'tcx, Value = V>>(&self, bx: &mut Bx) {
         bx.lifetime_start(self.llval, self.layout.size);
     }