Update const prop

Author: jonas-schievink

src/librustc_mir/transform/const_prop.rs

@@ -331,7 +331,6 @@ struct ConstPropagator<'mir, 'tcx> {
     // by accessing them through `ecx` instead.
     source_scopes: IndexVec<SourceScope, SourceScopeData>,
     local_decls: IndexVec<Local, LocalDecl<'tcx>>,
-    ret: Option<OpTy<'tcx, ()>>,
     // Because we have `MutVisitor` we can't obtain the `SourceInfo` from a `Location`. So we store
     // the last known `SourceInfo` here and just keep revisiting it.
     source_info: Option<SourceInfo>,
@@ -403,22 +402,23 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             source_scopes: body.source_scopes.clone(),
             //FIXME(wesleywiser) we can't steal this because `Visitor::super_visit_body()` needs it
             local_decls: body.local_decls.clone(),
-            ret: ret.map(Into::into),
             source_info: None,
         }
     }
 
     fn get_const(&self, local: Local) -> Option<OpTy<'tcx>> {
+        let op = self.ecx.access_local(self.ecx.frame(), local, None).ok();
+
         if local == RETURN_PLACE {
             // Try to read the return place as an immediate so that if it is representable as a
             // scalar, we can handle it as such, but otherwise, just return the value as is.
-            return match self.ret.map(|ret| self.ecx.try_read_immediate(ret)) {
+            return match op.map(|ret| self.ecx.try_read_immediate(ret)) {
                 Some(Ok(Ok(imm))) => Some(imm.into()),
-                _ => self.ret,
+                _ => op,
             };
         }
 
-        self.ecx.access_local(self.ecx.frame(), local, None).ok()
+        op
     }
 
     fn remove_const(&mut self, local: Local) {