Mesa (staging/20.1): glsl: fix incorrect optimisation in opt_constant_variable()

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Module: Mesa
Branch: staging/20.1
Commit: cd6c24f649ed104a1f59212313ceff0ecc4ab087
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=cd6c24f649ed104a1f59212313ceff0ecc4ab087

Author: Timothy Arceri <tarceri at itsqueeze.com>
Date:   Wed Jun 10 15:19:22 2020 +1000

glsl: fix incorrect optimisation in opt_constant_variable()

When handling function inputs the optimisation pass incorrectly
assumes the inputs are undefined. Here we simply change things to
assume inputs have always been assigned a value. Any further
optimisations will be taken care of once function inlining takes
place.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2984
Fixes: 65122e9e8038 ("ir_constant_variable: New pass to mark constant-assigned variables constant.")

Reviewed-by: Danylo Piliaiev <danylo.piliaiev at globallogic.com>
Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer at amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5413>
(cherry picked from commit b33f811068596c2764f6396a885f7aab7d7d411c)

---

 .pick_status.json                           | 2 +-
 src/compiler/glsl/opt_constant_variable.cpp | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/.pick_status.json b/.pick_status.json
index b93dfce6ff9..6aa6c93c8f5 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -796,7 +796,7 @@
         "description": "glsl: fix incorrect optimisation in opt_constant_variable()",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": "65122e9e8038488e8c586eb609e434a90188de27"
     },
diff --git a/src/compiler/glsl/opt_constant_variable.cpp b/src/compiler/glsl/opt_constant_variable.cpp
index cc2760f5609..3f2b6a04b9f 100644
--- a/src/compiler/glsl/opt_constant_variable.cpp
+++ b/src/compiler/glsl/opt_constant_variable.cpp
@@ -165,6 +165,15 @@ ir_constant_variable_visitor::visit_enter(ir_call *ir)
 	 entry = get_assignment_entry(var, this->ht);
 	 entry->assignment_count++;
       }
+
+      /* We don't know if the variable passed to this function has been
+       * assigned a value or if it is undefined, so for now we always assume
+       * it has been assigned a value. Once functions have been inlined any
+       * further potential optimisations will be taken care of.
+       */
+      struct assignment_entry *entry;
+      entry = get_assignment_entry(param, this->ht);
+      entry->assignment_count++;
    }
 
    /* Mark the return storage as having been assigned to */