nir: Add a nir_ssa_def_all_uses_are_fsat() helper

Extracted from nir_lower_to_source_mods, this is useful for back-ends
which don't want to rely on NIR source and destination modifiers.

Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25000>

src/compiler/nir/nir.c

@@ -1636,6 +1636,25 @@ nir_def_components_read(const nir_def *def)
    return read_mask;
 }
 
+bool
+nir_def_all_uses_are_fsat(const nir_def *def)
+{
+   nir_foreach_use(src, def) {
+      if (nir_src_is_if(src))
+         return false;
+
+      nir_instr *use = nir_src_parent_instr(src);
+      if (use->type != nir_instr_type_alu)
+         return false;
+
+      nir_alu_instr *alu = nir_instr_as_alu(use);
+      if (alu->op != nir_op_fsat)
+         return false;
+   }
+
+   return true;
+}
+
 nir_block *
 nir_block_unstructured_next(nir_block *block)
 {

src/compiler/nir/nir.h

@@ -4595,6 +4595,7 @@ void nir_def_rewrite_uses_after(nir_def *def, nir_def *new_ssa,
 
 nir_component_mask_t nir_src_components_read(const nir_src *src);
 nir_component_mask_t nir_def_components_read(const nir_def *def);
+bool nir_def_all_uses_are_fsat(const nir_def *def);
 
 static inline bool
 nir_def_is_unused(nir_def *ssa)