intel/compiler/fs: 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_fs_live_variables.cpp

@@ -323,6 +323,47 @@ fs_live_variables::~fs_live_variables()
    ralloc_free(mem_ctx);
 }
 
+static bool
+check_register_live_range(const fs_live_variables *live, int ip,
+                          const fs_reg &reg, unsigned n)
+{
+   const unsigned var = live->var_from_reg(reg);
+
+   if (var + n > unsigned(live->num_vars) ||
+       live->vgrf_start[reg.nr] > ip || live->vgrf_end[reg.nr] < ip)
+      return false;
+
+   for (unsigned j = 0; j < n; j++) {
+      if (live->start[var + j] > ip || live->end[var + j] < ip)
+         return false;
+   }
+
+   return true;
+}
+
+bool
+fs_live_variables::validate(const backend_shader *s) const
+{
+   int ip = 0;
+
+   foreach_block_and_inst(block, fs_inst, inst, s->cfg) {
+      for (unsigned i = 0; i < inst->sources; i++) {
+         if (inst->src[i].file == VGRF &&
+             !check_register_live_range(this, ip,
+                                        inst->src[i], regs_read(inst, i)))
+            return false;
+      }
+
+      if (inst->dst.file == VGRF &&
+          !check_register_live_range(this, ip, inst->dst, regs_written(inst)))
+         return false;
+
+      ip++;
+   }
+
+   return true;
+}
+
 void
 fs_visitor::invalidate_live_intervals()
 {

src/intel/compiler/brw_fs_live_variables.h

@@ -81,6 +81,8 @@ public:
    fs_live_variables(const backend_shader *s);
    ~fs_live_variables();
 
+   bool validate(const backend_shader *s) const;
+
    bool vars_interfere(int a, int b) const;
    bool vgrfs_interfere(int a, int b) const;
    int var_from_reg(const fs_reg &reg) const