Mesa (master): nir/large_constants: Handle incomplete derefs

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Module: Mesa
Branch: master
Commit: df9596353a60bd38bc0185501750a7f4da5a06c5
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=df9596353a60bd38bc0185501750a7f4da5a06c5

Author: Jason Ekstrand <jason at jlekstrand.net>
Date:   Wed Jul 15 20:12:33 2020 -0500

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 at microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6210>

---

 src/compiler/nir/nir_opt_large_constants.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/compiler/nir/nir_opt_large_constants.c b/src/compiler/nir/nir_opt_large_constants.c
index 25c40292033..53bcea9322a 100644
--- 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);