compiler: fix loopdepth tracking in array slicing expression in escape analysis

    
    In the gc compiler, for slicing an array, its AST has an implicit
    address operation node. There isn't such node in the gofrontend
    AST. During the escape analysis, we create a fake node to mimic
    the gc compiler's behavior. For the fake node, the loopdepth was
    not tracked correctly, causing miscompilation. Since this is an
    address operation, do the same thing as we do for the address
    operator.
    
    Fixes golang/go#36404.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/213643

From-SVN: r279984

gcc/go/gofrontend/MERGE

-6fa9657df508ff4d7760cf1abfad3611ba808561
+e0790a756e9ba77e2d3d6ef5d0abbb11dd71211b
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/escape.cc

@@ -1906,7 +1906,8 @@ Escape_analysis_assign::expression(Expression** pexpr)
             this->context_->track(addr_node);
 
             Node::Escape_state* addr_state = addr_node->state(this->context_, NULL);
-            addr_state->loop_depth = array_state->loop_depth;
+            if (array_state->loop_depth != 0)
+              addr_state->loop_depth = array_state->loop_depth;
           }
       }
       break;