glsl: Track variable usage, use that to enforce semantics

In particular, variables cannot be redeclared invariant after being
used.

Fixes piglit test invariant-05.vert and bugzilla #29164.

NOTE: This is a candidate for the 7.9 and 7.10 branches.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/glsl/ir.h b/src/glsl/ir.h
index 9668c9439ad..57e89f0f6bf 100644
--- a/src/glsl/ir.h
+++ b/src/glsl/ir.h
@@ -295,6 +295,15 @@ public:
    unsigned invariant:1;
 
    /**
+    * Has this variable been used for reading or writing?
+    *
+    * Several GLSL semantic checks require knowledge of whether or not a
+    * variable has been used.  For example, it is an error to redeclare a
+    * variable as invariant after it has been used.
+    */
+   unsigned used:1;
+
+   /**
     * Storage class of the variable.
     *
     * \sa ir_variable_mode