intel/compiler/vec4: Add live interval validation pass

This could be improved somewhat with additional validation of the
calculated live in/out sets and by checking that the calculated live
intervals are minimal (which isn't strictly necessary to guarantee the
correctness of the program).  This should be good enough though to
catch accidental use of stale liveness results due to missing or
incorrect analysis invalidation.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4012>

src/intel/compiler/brw_vec4_live_variables.h

@@ -68,6 +68,9 @@ public:
    vec4_live_variables(const backend_shader *s);
    ~vec4_live_variables();
 
+   bool
+   validate(const backend_shader *s) const;
+
    int num_vars;
    int bitset_words;