nir: Add a function to determine if a source is dynamically uniform

Adds nir_src_is_dynamically_uniform which returns true if the source
is known to be dynamically uniform. This will be used in a later patch
to add a workaround for cases that only work with dynamically uniform
sources. Note that the function is not definitive, it can return false
negatives (but not false positives). Currently it only detects
constants and uniform accesses. It could easily be extended to include
more cases.

Reviewed-by: Matt Turner <mattst88@gmail.com>

src/glsl/nir/nir.c

@@ -1080,6 +1080,35 @@ nir_src_as_const_value(nir_src src)
    return &load->value;
 }
 
+/**
+ * Returns true if the source is known to be dynamically uniform. Otherwise it
+ * returns false which means it may or may not be dynamically uniform but it
+ * can't be determined.
+ */
+bool
+nir_src_is_dynamically_uniform(nir_src src)
+{
+   if (!src.is_ssa)
+      return false;
+
+   /* Constants are trivially dynamically uniform */
+   if (src.ssa->parent_instr->type == nir_instr_type_load_const)
+      return true;
+
+   /* As are uniform variables */
+   if (src.ssa->parent_instr->type == nir_instr_type_intrinsic) {
+      nir_intrinsic_instr *intr = nir_instr_as_intrinsic(src.ssa->parent_instr);
+
+      if (intr->intrinsic == nir_intrinsic_load_uniform)
+         return true;
+   }
+
+   /* XXX: this could have many more tests, such as when a sampler function is
+    * called with dynamically uniform arguments.
+    */
+   return false;
+}
+
 bool
 nir_srcs_equal(nir_src src1, nir_src src2)
 {

src/glsl/nir/nir.h

@@ -1784,6 +1784,7 @@ bool nir_foreach_dest(nir_instr *instr, nir_foreach_dest_cb cb, void *state);
 bool nir_foreach_src(nir_instr *instr, nir_foreach_src_cb cb, void *state);
 
 nir_const_value *nir_src_as_const_value(nir_src src);
+bool nir_src_is_dynamically_uniform(nir_src src);
 bool nir_srcs_equal(nir_src src1, nir_src src2);
 void nir_instr_rewrite_src(nir_instr *instr, nir_src *src, nir_src new_src);
 void nir_instr_move_src(nir_instr *dest_instr, nir_src *dest, nir_src *src);