[Mesa-dev] [PATCH 12/24] glsl: Add predicate to determine if an IR node has side effects.

[Francisco Jerez]

And fix the dead code elimination pass so atomic writes aren't
optimized out in cases where the return value isn't used by the
program.
---
 src/glsl/ir.h              | 16 ++++++++++++++++
 src/glsl/opt_dead_code.cpp |  3 ++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/glsl/ir.h b/src/glsl/ir.h
index c4b4677..4f506a3 100644
--- a/src/glsl/ir.h
+++ b/src/glsl/ir.h
@@ -139,6 +139,17 @@ public:
    virtual class ir_jump *              as_jump()             { return NULL; }
    /*@}*/
 
+   /**
+    * Determine if an IR instruction has side effects other than its
+    * returned value(s).  Optimization passes are expected to be
+    * especially careful with reordering or removing these, unless
+    * they know what they are doing.
+    */
+   virtual bool has_side_effects() const
+   {
+      return false;
+   }
+
 protected:
    ir_instruction()
    {
@@ -2120,6 +2131,11 @@ public:
 
    virtual ir_visitor_status accept(ir_hierarchical_visitor *);
 
+   virtual bool has_side_effects() const
+   {
+      return true;
+   }
+
    /** Kind of atomic instruction. */
    enum ir_atomic_opcode op;
 
diff --git a/src/glsl/opt_dead_code.cpp b/src/glsl/opt_dead_code.cpp
index b65e5c2..fd05034 100644
--- a/src/glsl/opt_dead_code.cpp
+++ b/src/glsl/opt_dead_code.cpp
@@ -81,7 +81,8 @@ do_dead_code(exec_list *instructions, bool uniform_locations_assigned)
 	  */
 	 if (entry->var->mode != ir_var_function_out &&
 	     entry->var->mode != ir_var_function_inout &&
-             entry->var->mode != ir_var_shader_out) {
+             entry->var->mode != ir_var_shader_out &&
+             !entry->assign->rhs->has_side_effects()) {
 	    entry->assign->remove();
 	    progress = true;
 
-- 
1.8.3.4