nir/opt_deref: Add a deref mode specialization optimization
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6332>
diff --git a/src/compiler/nir/nir_deref.c b/src/compiler/nir/nir_deref.c
index 6af7580..ab5e66b 100644
--- a/src/compiler/nir/nir_deref.c
+++ b/src/compiler/nir/nir_deref.c
@@ -935,6 +935,30 @@
return true;
}
+/* Restrict variable modes in casts.
+ *
+ * If we know from something higher up the deref chain that the deref has a
+ * specific mode, we can cast to more general and back but we can never cast
+ * across modes. For non-cast derefs, we should only ever do anything here if
+ * the parent eventually comes from a cast that we restricted earlier.
+ */
+static bool
+opt_restrict_deref_modes(nir_deref_instr *deref)
+{
+ if (deref->type == nir_deref_type_var) {
+ assert(deref->modes == deref->var->data.mode);
+ return false;
+ }
+
+ nir_deref_instr *parent = nir_src_as_deref(deref->parent);
+ if (parent == NULL || parent->modes == deref->modes)
+ return false;
+
+ assert(parent->modes & deref->modes);
+ deref->modes &= parent->modes;
+ return true;
+}
+
static bool
opt_remove_sampler_cast(nir_deref_instr *cast)
{
@@ -1259,6 +1283,10 @@
switch (instr->type) {
case nir_instr_type_deref: {
nir_deref_instr *deref = nir_instr_as_deref(instr);
+
+ if (opt_restrict_deref_modes(deref))
+ progress = true;
+
switch (deref->deref_type) {
case nir_deref_type_ptr_as_array:
if (opt_deref_ptr_as_array(&b, deref))
