glsl: Add uniform_locations_assigned parameter to do_dead_code opt pass

Setting this flag prevents declarations of uniforms from being removed
from the IR.  Since the IR is directly used by several API functions
that query uniforms in shaders, uniform declarations cannot be removed
after the locations have been set.  However, it should still be safe
to reorder the declarations (this is not tested).

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=41980
Tested-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Bryan Cain <bryancain3@gmail.com>
Cc: Vinson Lee <vlee@vmware.com>
Cc: José Fonseca <jfonseca@vmware.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>

src/glsl/opt_dead_code.cpp

@@ -42,7 +42,7 @@ static bool debug = false;
  * for usage on an unlinked instruction stream.
  */
 bool
-do_dead_code(exec_list *instructions)
+do_dead_code(exec_list *instructions, bool uniform_locations_assigned)
 {
    ir_variable_refcount_visitor v;
    bool progress = false;
@@ -94,10 +94,11 @@ do_dead_code(exec_list *instructions)
 	  */
 
 	 /* uniform initializers are precious, and could get used by another
-	  * stage.
+	  * stage.  Also, once uniform locations have been assigned, the
+	  * declaration cannot be deleted.
 	  */
 	 if (entry->var->mode == ir_var_uniform &&
-	     entry->var->constant_value)
+	     (uniform_locations_assigned || entry->var->constant_value))
 	    continue;
 
 	 entry->var->remove();
@@ -132,7 +133,12 @@ do_dead_code_unlinked(exec_list *instructions)
 	 foreach_iter(exec_list_iterator, sigiter, *f) {
 	    ir_function_signature *sig =
 	       (ir_function_signature *) sigiter.get();
-	    if (do_dead_code(&sig->body))
+	    /* The setting of the uniform_locations_assigned flag here is
+	     * irrelevent.  If there is a uniform declaration encountered
+	     * inside the body of the function, something has already gone
+	     * terribly, terribly wrong.
+	     */
+	    if (do_dead_code(&sig->body, false))
 	       progress = true;
 	 }
       }