[Mesa-dev] [PATCH] glsl: interleave constant propagation and folding

[Timothy Arceri]

The constant folding pass can take a long time to complete
so rather than running throught the entire pass each time
a new constant is propagated (and vice versa) interleave them.

This change helps ES31-CTS.arrays_of_arrays.InteractionFunctionCalls1
go from around 2 min -> 23 sec.
---
 src/glsl/opt_constant_propagation.cpp | 46 +++++++++++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 2 deletions(-)

diff --git a/src/glsl/opt_constant_propagation.cpp b/src/glsl/opt_constant_propagation.cpp
index 10be8e8..ebe30d9 100644
--- a/src/glsl/opt_constant_propagation.cpp
+++ b/src/glsl/opt_constant_propagation.cpp
@@ -110,6 +110,8 @@ public:
    virtual ir_visitor_status visit_enter(class ir_if *);
 
    void add_constant(ir_assignment *ir);
+   void constant_folding(ir_rvalue **rvalue);
+   void constant_propagation(ir_rvalue **rvalue);
    void kill(ir_variable *ir, unsigned write_mask);
    void handle_if_block(exec_list *instructions);
    void handle_rvalue(ir_rvalue **rvalue);
@@ -132,8 +134,39 @@ public:
 
 
 void
-ir_constant_propagation_visitor::handle_rvalue(ir_rvalue **rvalue)
-{
+ir_constant_propagation_visitor::constant_folding(ir_rvalue **rvalue) {
+
+   if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
+      return;
+
+   /* Note that we do rvalue visitoring on leaving.  So if an
+    * expression has a non-constant operand, no need to go looking
+    * down it to find if it's constant.  This cuts the time of this
+    * pass down drastically.
+    */
+   ir_expression *expr = (*rvalue)->as_expression();
+   if (expr) {
+      for (unsigned int i = 0; i < expr->get_num_operands(); i++) {
+	 if (!expr->operands[i]->as_constant())
+	    return;
+      }
+   }
+
+   /* Ditto for swizzles. */
+   ir_swizzle *swiz = (*rvalue)->as_swizzle();
+   if (swiz && !swiz->val->as_constant())
+      return;
+
+   ir_constant *constant = (*rvalue)->constant_expression_value();
+   if (constant) {
+      *rvalue = constant;
+      this->progress = true;
+   }
+}
+
+void
+ir_constant_propagation_visitor::constant_propagation(ir_rvalue **rvalue) {
+
    if (this->in_assignee || !*rvalue)
       return;
 
@@ -216,6 +249,13 @@ ir_constant_propagation_visitor::handle_rvalue(ir_rvalue **rvalue)
    this->progress = true;
 }
 
+void
+ir_constant_propagation_visitor::handle_rvalue(ir_rvalue **rvalue)
+{
+   constant_propagation(rvalue);
+   constant_folding(rvalue);
+}
+
 ir_visitor_status
 ir_constant_propagation_visitor::visit_enter(ir_function_signature *ir)
 {
@@ -243,6 +283,8 @@ ir_constant_propagation_visitor::visit_enter(ir_function_signature *ir)
 ir_visitor_status
 ir_constant_propagation_visitor::visit_leave(ir_assignment *ir)
 {
+  constant_folding(&ir->rhs);
+
    if (this->in_assignee)
       return visit_continue;
 
-- 
2.4.3