nir/large_constants: Handle incomplete derefs

This pass works entirely with variables, all we have to do is ignore any
derefs we see which we can't chase back to the variable.  The one
interesting case we have to handle is if we have a complex use of a
deref_var.  In that case, we have to flag it non-constant.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6210>

diff --git a/src/compiler/nir/nir_opt_large_constants.c b/src/compiler/nir/nir_opt_large_constants.c
index 25c402920332d0c20875be3ec33ae8601b58d889..53bcea9322a5f7db00e88b121659257cfcaaabdf 100644 (file)
--- a/src/compiler/nir/nir_opt_large_constants.c
+++ b/src/compiler/nir/nir_opt_large_constants.c
@@ -199,6 +199,19 @@ nir_opt_large_constants(nir_shader *shader,
     */
    nir_foreach_block(block, impl) {
       nir_foreach_instr(instr, block) {
+         if (instr->type == nir_instr_type_deref) {
+            /* If we ever see a complex use of a deref_var, we have to assume
+             * that variable is non-constant because we can't guarantee we
+             * will find all of the writers of that variable.
+             */
+            nir_deref_instr *deref = nir_instr_as_deref(instr);
+            if (deref->type == nir_deref_type_var &&
+                deref->mode == nir_var_function_temp &&
+                nir_deref_instr_has_complex_use(deref))
+               var_infos[deref->var->index].is_constant = false;
+            continue;
+         }
+
          if (instr->type != nir_instr_type_intrinsic)
             continue;
 
@@ -228,6 +241,9 @@ nir_opt_large_constants(nir_shader *shader,
 
          if (dst_deref && dst_deref->mode == nir_var_function_temp) {
             nir_variable *var = nir_deref_instr_get_variable(dst_deref);
+            if (var == NULL)
+               continue;
+
             assert(var->data.mode == nir_var_function_temp);
 
             struct var_info *info = &var_infos[var->index];
@@ -253,6 +269,9 @@ nir_opt_large_constants(nir_shader *shader,
 
          if (src_deref && src_deref->mode == nir_var_function_temp) {
             nir_variable *var = nir_deref_instr_get_variable(src_deref);
+            if (var == NULL)
+               continue;
+
             assert(var->data.mode == nir_var_function_temp);
 
             /* We only consider variables constant if all the reads are
@@ -334,6 +353,9 @@ nir_opt_large_constants(nir_shader *shader,
                continue;
 
             nir_variable *var = nir_deref_instr_get_variable(deref);
+            if (var == NULL)
+               continue;
+
             struct var_info *info = &var_infos[var->index];
             if (info->is_constant) {
                b.cursor = nir_after_instr(&intrin->instr);
@@ -352,6 +374,9 @@ nir_opt_large_constants(nir_shader *shader,
                continue;
 
             nir_variable *var = nir_deref_instr_get_variable(deref);
+            if (var == NULL)
+               continue;
+
             struct var_info *info = &var_infos[var->index];
             if (info->is_constant) {
                nir_instr_remove(&intrin->instr);