X-Git-Url: https://git.libre-soc.org/?a=blobdiff_plain;f=src%2Fcompiler%2Fglsl%2Flower_if_to_cond_assign.cpp;h=37f1ec8600c82e0794389b36a4ae0112ef67638f;hb=f9ab60202d48c72afa6a6f2a8c27db1e0777ed16;hp=01a73357d456103e3473958347420468b4198d6e;hpb=654e9466b5304b040374e72c9e9a524bd1268362;p=mesa.git

diff --git a/src/compiler/glsl/lower_if_to_cond_assign.cpp b/src/compiler/glsl/lower_if_to_cond_assign.cpp
index 01a73357d45..37f1ec8600c 100644
--- a/src/compiler/glsl/lower_if_to_cond_assign.cpp
+++ b/src/compiler/glsl/lower_if_to_cond_assign.cpp
@@ -24,8 +24,14 @@
 /**
  * \file lower_if_to_cond_assign.cpp
  *
- * This attempts to flatten if-statements to conditional assignments for
- * GPUs with limited or no flow control support.
+ * This flattens if-statements to conditional assignments if:
+ *
+ * - the GPU has limited or no flow control support
+ *   (controlled by max_depth)
+ *
+ * - small conditional branches are more expensive than conditional assignments
+ *   (controlled by min_branch_cost, that's the cost for a branch to be
+ *    preserved)
  *
  * It can't handle other control flow being inside of its block, such
  * as calls or loops.  Hopefully loop unrolling and inlining will take
@@ -49,15 +55,20 @@
 #include "ir.h"
 #include "util/set.h"
 #include "util/hash_table.h" /* Needed for the hashing functions */
+#include "main/macros.h" /* for MAX2 */
 
 namespace {
 
 class ir_if_to_cond_assign_visitor : public ir_hierarchical_visitor {
 public:
-   ir_if_to_cond_assign_visitor(unsigned max_depth)
+   ir_if_to_cond_assign_visitor(gl_shader_stage stage,
+                                unsigned max_depth,
+                                unsigned min_branch_cost)
    {
       this->progress = false;
+      this->stage = stage;
       this->max_depth = max_depth;
+      this->min_branch_cost = min_branch_cost;
       this->depth = 0;
 
       this->condition_variables =
@@ -74,7 +85,14 @@ public:
    ir_visitor_status visit_leave(ir_if *);
 
    bool found_unsupported_op;
+   bool found_expensive_op;
+   bool found_dynamic_arrayref;
+   bool is_then;
    bool progress;
+   gl_shader_stage stage;
+   unsigned then_cost;
+   unsigned else_cost;
+   unsigned min_branch_cost;
    unsigned max_depth;
    unsigned depth;
 
@@ -84,12 +102,13 @@ public:
 } /* anonymous namespace */
 
 bool
-lower_if_to_cond_assign(exec_list *instructions, unsigned max_depth)
+lower_if_to_cond_assign(gl_shader_stage stage, exec_list *instructions,
+                        unsigned max_depth, unsigned min_branch_cost)
 {
    if (max_depth == UINT_MAX)
       return false;
 
-   ir_if_to_cond_assign_visitor v(max_depth);
+   ir_if_to_cond_assign_visitor v(stage, max_depth, min_branch_cost);
 
    visit_list_elements(&v, instructions);
 
@@ -112,6 +131,38 @@ check_ir_node(ir_instruction *ir, void *data)
    case ir_type_barrier:
       v->found_unsupported_op = true;
       break;
+
+   case ir_type_dereference_variable: {
+      ir_variable *var = ir->as_dereference_variable()->variable_referenced();
+
+      /* Lowering branches with TCS output accesses breaks many piglit tests,
+       * so don't touch them for now.
+       */
+      if (v->stage == MESA_SHADER_TESS_CTRL &&
+          var->data.mode == ir_var_shader_out)
+         v->found_unsupported_op = true;
+      break;
+   }
+
+   /* SSBO, images, atomic counters are handled by ir_type_call */
+   case ir_type_texture:
+      v->found_expensive_op = true;
+      break;
+
+   case ir_type_dereference_array: {
+      ir_dereference_array *deref = ir->as_dereference_array();
+
+      if (deref->array_index->ir_type != ir_type_constant)
+         v->found_dynamic_arrayref = true;
+   } /* fall-through */
+   case ir_type_expression:
+   case ir_type_dereference_record:
+      if (v->is_then)
+         v->then_cost++;
+      else
+         v->else_cost++;
+      break;
+
    default:
       break;
    }
@@ -176,24 +227,48 @@ ir_if_to_cond_assign_visitor::visit_enter(ir_if *ir)
 ir_visitor_status
 ir_if_to_cond_assign_visitor::visit_leave(ir_if *ir)
 {
+   bool must_lower = this->depth-- > this->max_depth;
+
    /* Only flatten when beyond the GPU's maximum supported nesting depth. */
-   if (this->depth-- <= this->max_depth)
+   if (!must_lower && this->min_branch_cost == 0)
       return visit_continue;
 
    this->found_unsupported_op = false;
+   this->found_expensive_op = false;
+   this->found_dynamic_arrayref = false;
+   this->then_cost = 0;
+   this->else_cost = 0;
 
    ir_assignment *assign;
 
    /* Check that both blocks don't contain anything we can't support. */
+   this->is_then = true;
    foreach_in_list(ir_instruction, then_ir, &ir->then_instructions) {
       visit_tree(then_ir, check_ir_node, this);
    }
+
+   this->is_then = false;
    foreach_in_list(ir_instruction, else_ir, &ir->else_instructions) {
       visit_tree(else_ir, check_ir_node, this);
    }
+
    if (this->found_unsupported_op)
       return visit_continue; /* can't handle inner unsupported opcodes */
 
+   /* Skip if the branch cost is high enough or if there's an expensive op.
+    *
+    * Also skip if non-constant array indices were encountered, since those
+    * can be out-of-bounds for a not-taken branch, and so generating an
+    * assignment would be incorrect. In the case of must_lower, it's up to the
+    * backend to deal with any potential fall-out (perhaps by translating the
+    * assignments to hardware-predicated moves).
+    */
+   if (!must_lower &&
+       (this->found_expensive_op ||
+        this->found_dynamic_arrayref ||
+        MAX2(this->then_cost, this->else_cost) >= this->min_branch_cost))
+      return visit_continue;
+
    void *mem_ctx = ralloc_parent(ir);
 
    /* Store the condition to a variable.  Move all of the instructions from