glsl: Convert ir_call to be a statement rather than a value.

Aside from ir_call, our IR is cleanly split into two classes:
- Statements (typeless; used for side effects, control flow)
- Values (deeply nestable, pure, typed expression trees)

Unfortunately, ir_call confused all this:
- For void functions, we placed ir_call directly in the instruction
  stream, treating it as an untyped statement.  Yet, it was a subclass
  of ir_rvalue, and no other ir_rvalue could be used in this way.
- For functions with a return value, ir_call could be placed in
  arbitrary expression trees.  While this fit naturally with the source
  language, it meant that expressions might not be pure, making it
  difficult to transform and optimize them.  To combat this, we always
  emitted ir_call directly in the RHS of an ir_assignment, only using
  a temporary variable in expression trees.  Many passes relied on this
  assumption; the acos and atan built-ins violated it.

This patch makes ir_call a statement (ir_instruction) rather than a
value (ir_rvalue).  Non-void calls now take a ir_dereference of a
variable, and store the return value there---effectively a call and
assignment rolled into one.  They cannot be embedded in expressions.

All expression trees are now pure, without exception.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/glsl/opt_constant_variable.cpp b/src/glsl/opt_constant_variable.cpp
index 3fa7c3b..18c2801 100644
--- a/src/glsl/opt_constant_variable.cpp
+++ b/src/glsl/opt_constant_variable.cpp
@@ -127,6 +127,7 @@ ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
 ir_visitor_status
 ir_constant_variable_visitor::visit_enter(ir_call *ir)
 {
+   /* Mark any out parameters as assigned to */
    exec_list_iterator sig_iter = ir->get_callee()->parameters.iterator();
    foreach_iter(exec_list_iterator, iter, *ir) {
       ir_rvalue *param_rval = (ir_rvalue *)iter.get();
@@ -143,6 +144,17 @@ ir_constant_variable_visitor::visit_enter(ir_call *ir)
       }
       sig_iter.next();
    }
+
+   /* Mark the return storage as having been assigned to */
+   if (ir->return_deref != NULL) {
+      ir_variable *var = ir->return_deref->variable_referenced();
+      struct assignment_entry *entry;
+
+      assert(var);
+      entry = get_assignment_entry(var, &this->list);
+      entry->assignment_count++;
+   }
+
    return visit_continue;
 }