[Mesa-dev] [PATCH 18/22] glsl: Move 'foo = foo; ' optimization to opt_dead_code_local

[Ian Romanick]

From: "\"Ian Romanick\"" <idr at freedesktop.org>

From: Ian Romanick <ian.d.romanick at intel.com>

The optimization as done in opt_copy_propagation would have to be
removed in the next patch, and doing so would lead to some substantial
regressions.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Cc: Jason Ekstrand <jason at jlekstrand.net>
---
 src/compiler/glsl/opt_copy_propagation.cpp | 19 +++++++------------
 src/compiler/glsl/opt_dead_code_local.cpp  | 11 +++++++++++
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/src/compiler/glsl/opt_copy_propagation.cpp b/src/compiler/glsl/opt_copy_propagation.cpp
index b72ae5a..b8ef0de0 100644
--- a/src/compiler/glsl/opt_copy_propagation.cpp
+++ b/src/compiler/glsl/opt_copy_propagation.cpp
@@ -348,18 +348,13 @@ ir_copy_propagation_visitor::add_copy(ir_assignment *ir)
    ir_variable *lhs_var = ir->whole_variable_written();
    ir_variable *rhs_var = ir->rhs->whole_variable_referenced();
 
-   if ((lhs_var != NULL) && (rhs_var != NULL)) {
-      if (lhs_var == rhs_var) {
-	 /* This is a dumb assignment, but we've conveniently noticed
-	  * it here.  Removing it now would mess up the loop iteration
-	  * calling us.  Just flag it to not execute, and someone else
-	  * will clean up the mess.
-	  */
-	 ir->condition = new(ralloc_parent(ir)) ir_constant(false);
-	 this->progress = true;
-      } else if (lhs_var->data.mode != ir_var_shader_storage &&
-                 lhs_var->data.mode != ir_var_shader_shared &&
-                 lhs_var->data.precise == rhs_var->data.precise) {
+   /* Don't try to remove a dumb assignment of a variable to itself.  Removing
+    * it now would mess up the loop iteration calling us.
+    */
+   if (lhs_var != NULL && rhs_var != NULL && lhs_var != rhs_var) {
+      if (lhs_var->data.mode != ir_var_shader_storage &&
+          lhs_var->data.mode != ir_var_shader_shared &&
+          lhs_var->data.precise == rhs_var->data.precise) {
          assert(lhs_var);
          assert(rhs_var);
          _mesa_hash_table_insert(acp, lhs_var, rhs_var);
diff --git a/src/compiler/glsl/opt_dead_code_local.cpp b/src/compiler/glsl/opt_dead_code_local.cpp
index a403879..3cbc441 100644
--- a/src/compiler/glsl/opt_dead_code_local.cpp
+++ b/src/compiler/glsl/opt_dead_code_local.cpp
@@ -173,6 +173,17 @@ process_assignment(void *lin_ctx, ir_assignment *ir, exec_list *assignments)
    bool progress = false;
    kill_for_derefs_visitor v(assignments);
 
+   if (ir->condition == NULL) {
+      /* If this is an assignment of the form "foo = foo;", remove the whole
+       * instruction and be done with it.
+       */
+      const ir_variable *const lhs_var = ir->whole_variable_written();
+      if (lhs_var != NULL && lhs_var == ir->rhs->whole_variable_referenced()) {
+         ir->remove();
+         return true;
+      }
+   }
+
    /* Kill assignment entries for things used to produce this assignment. */
    ir->rhs->accept(&v);
    if (ir->condition) {
-- 
2.9.5