Mesa (master): glsl: Stop tree grafting if a variable is overwritten as an 'out' param.

[Kenneth Graunke]

Module: Mesa
Branch: master
Commit: 3c22e3516527ccb83f2667abfa0e6518c5938df8
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=3c22e3516527ccb83f2667abfa0e6518c5938df8

Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Thu Sep 22 15:04:56 2011 -0700

glsl: Stop tree grafting if a variable is overwritten as an 'out' param.

While reviewing some compiler cleanups I'd sent out, Paul noticed that
tree grafting wasn't taking "out" parameters into account.

Further investigation revealed that it isn't strictly necessary: ir_call
ends basic blocks, and tree grafting currently only operates on basic
blocks.  So calls already kill grafts.

However, just to be safe, this patch makes "out" parameters explicitly
kill grafts.  Paul and I both prefer this.  It's a bit clearer.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
Reviewed-by: Paul Berry <stereotype441 at gmail.com>

---

 src/glsl/opt_tree_grafting.cpp |   39 ++++++++++++++++++++++++++++-----------
 1 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/src/glsl/opt_tree_grafting.cpp b/src/glsl/opt_tree_grafting.cpp
index 22a1749..d32d14e 100644
--- a/src/glsl/opt_tree_grafting.cpp
+++ b/src/glsl/opt_tree_grafting.cpp
@@ -76,6 +76,8 @@ public:
    virtual ir_visitor_status visit_enter(class ir_swizzle *);
    virtual ir_visitor_status visit_enter(class ir_texture *);
 
+   ir_visitor_status check_graft(ir_instruction *ir, ir_variable *var);
+
    bool do_graft(ir_rvalue **rvalue);
 
    bool progress;
@@ -148,18 +150,17 @@ ir_tree_grafting_visitor::visit_enter(ir_loop *ir)
    return visit_stop;
 }
 
+/**
+ * Check if we can continue grafting after writing to a variable.  If the
+ * expression we're trying to graft references the variable, we must stop.
+ *
+ * \param ir   An instruction that writes to a variable.
+ * \param var  The variable being updated.
+ */
 ir_visitor_status
-ir_tree_grafting_visitor::visit_leave(ir_assignment *ir)
+ir_tree_grafting_visitor::check_graft(ir_instruction *ir, ir_variable *var)
 {
-   if (do_graft(&ir->rhs) ||
-       do_graft(&ir->condition))
-      return visit_stop;
-
-   /* If this assignment updates a variable used in the assignment
-    * we're trying to graft, then we're done.
-    */
-   if (dereferences_variable(this->graft_assign->rhs,
-			     ir->lhs->variable_referenced())) {
+   if (dereferences_variable(this->graft_assign->rhs, var)) {
       if (debug) {
 	 printf("graft killed by: ");
 	 ir->print();
@@ -172,6 +173,19 @@ ir_tree_grafting_visitor::visit_leave(ir_assignment *ir)
 }
 
 ir_visitor_status
+ir_tree_grafting_visitor::visit_leave(ir_assignment *ir)
+{
+   if (do_graft(&ir->rhs) ||
+       do_graft(&ir->condition))
+      return visit_stop;
+
+   /* If this assignment updates a variable used in the assignment
+    * we're trying to graft, then we're done.
+    */
+   return check_graft(ir, ir->lhs->variable_referenced());
+}
+
+ir_visitor_status
 ir_tree_grafting_visitor::visit_enter(ir_function *ir)
 {
    (void) ir;
@@ -195,8 +209,11 @@ ir_tree_grafting_visitor::visit_enter(ir_call *ir)
       ir_rvalue *ir = (ir_rvalue *)iter.get();
       ir_rvalue *new_ir = ir;
 
-      if (sig_param->mode != ir_var_in && sig_param->mode != ir_var_const_in)
+      if (sig_param->mode != ir_var_in && sig_param->mode != ir_var_const_in) {
+	 if (check_graft(ir, sig_param) == visit_stop)
+	    return visit_stop;
 	 continue;
+      }
 
       if (do_graft(&new_ir)) {
 	 ir->replace_with(new_ir);