glsl2: Fix copy propagation in the presence of derefs in array indexes.

We would clear the in_lhs flag early, avoiding copy propagation on the
array index variable (oops) and then copy propagating on the array
variable (ouch).  Just avoid all copy propagation on the LHS instead.

src/glsl/ir_copy_propagation.cpp

@@ -96,9 +96,29 @@ ir_copy_propagation_visitor::visit_enter(ir_function_signature *ir)
 ir_visitor_status
 ir_copy_propagation_visitor::visit_enter(ir_assignment *ir)
 {
-   (void) ir;
+   ir_visitor_status s;
+
+   /* Inline the rest of ir_assignment::accept(ir_hv *v), wrapping the
+    * LHS part with setting in_lhs so that we can avoid copy
+    * propagating into the LHS.
+    *
+    * Note that this means we won't copy propagate into the derefs of
+    * an array index.  Oh well.
+    */
    this->in_lhs = true;
-   return visit_continue;
+   s = ir->lhs->accept(this);
+   this->in_lhs = false;
+   if (s != visit_continue)
+      return (s == visit_continue_with_parent) ? visit_continue : s;
+
+   s = ir->rhs->accept(this);
+   if (s != visit_continue)
+      return (s == visit_continue_with_parent) ? visit_continue : s;
+
+   if (ir->condition)
+      s = ir->condition->accept(this);
+
+   return (s == visit_stop) ? s : visit_continue_with_parent;
 }
 
 ir_visitor_status
@@ -122,7 +142,6 @@ ir_copy_propagation_visitor::visit(ir_dereference_variable *ir)
     * other storage!
     */
    if (this->in_lhs) {
-      this->in_lhs = false;
       return visit_continue;
    }