[Mesa-dev] [PATCH] spirv: Work around the Doom shader bug

[Jason Ekstrand]

Doom shipped with a broken version of GLSLang which handles samplers as
function arguments in a way that isn't spec-compliant.  In particular,
it creates a temporary local sampler variable and copies the sampler
into it.  While Dave has had a hack patch out for a while that gets it
working, we've never landed it because we've been hoping that a game
update would come out with fixed shaders.  Unfortunately, no game update
appears on to be on the horizon and I've found this issue in yet another
application so I think we're stuck working around it.  Hopefully, we can
delete this code one day.

Cc: Dave Airlie <airlied at redhat.com>
---
 src/compiler/spirv/vtn_private.h   | 14 ++++++++++++++
 src/compiler/spirv/vtn_variables.c | 14 ++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/src/compiler/spirv/vtn_private.h b/src/compiler/spirv/vtn_private.h
index 59fcc94..a377c90 100644
--- a/src/compiler/spirv/vtn_private.h
+++ b/src/compiler/spirv/vtn_private.h
@@ -288,6 +288,20 @@ struct vtn_variable {
    nir_variable *var;
    nir_variable **members;
 
+   /**
+    * In some early released versions of GLSLang, it implemented all function
+    * calls by making copies of all parameters into temporary variables and
+    * passing those variables into the function.  It even did so for samplers
+    * and images which violates the SPIR-V spec.  Unfortunately, two games
+    * (Talos Principle and Doom) shipped with this old version of GLSLang and
+    * also happen to pass samplers into functions.  Talos Principle received
+    * an update fairly shortly after release with an updated GLSLang.  Doom,
+    * on the other hand, has never received an update so we need to work
+    * around this GLSLang issue in SPIR-V -> NIR.  Hopefully, we can drop this
+    * hack at some point in the future.
+    */
+   struct vtn_access_chain *copy_prop_sampler;
+
    struct vtn_access_chain chain;
 };
 
diff --git a/src/compiler/spirv/vtn_variables.c b/src/compiler/spirv/vtn_variables.c
index 0f0cc1c..974adb5 100644
--- a/src/compiler/spirv/vtn_variables.c
+++ b/src/compiler/spirv/vtn_variables.c
@@ -96,6 +96,10 @@ rewrite_deref_types(nir_deref *deref, const struct glsl_type *type)
 nir_deref_var *
 vtn_access_chain_to_deref(struct vtn_builder *b, struct vtn_access_chain *chain)
 {
+   /* Do on-the-fly copy propagation for samplers. */
+   if (chain->var->copy_prop_sampler)
+      return vtn_access_chain_to_deref(b, chain->var->copy_prop_sampler);
+
    nir_deref_var *deref_var;
    if (chain->var->var) {
       deref_var = nir_deref_var_create(b, chain->var->var);
@@ -1613,6 +1617,16 @@ vtn_handle_variables(struct vtn_builder *b, SpvOp opcode,
    case SpvOpStore: {
       struct vtn_access_chain *dest =
          vtn_value(b, w[1], vtn_value_type_access_chain)->access_chain;
+
+      if (glsl_type_is_sampler(dest->var->type->type)) {
+         vtn_warn("OpStore of a sampler detected.  Doing on-the-fly copy "
+                  "propagation to workaround the problem.");
+         assert(dest->var->copy_prop_sampler == NULL);
+         dest->var->copy_prop_sampler =
+            vtn_value(b, w[2], vtn_value_type_access_chain)->access_chain;
+         break;
+      }
+
       struct vtn_ssa_value *src = vtn_ssa_value(b, w[2]);
       vtn_variable_store(b, src, dest);
       break;
-- 
2.5.0.400.gff86faf