[Mesa-dev] [PATCH 2/5] glsl: Move constant expression handling from calls to signatures.

[Kenneth Graunke]

When translating a call from AST to HIR, we need to decide whether it
can be evaluated to a constant before emitting any code (namely, the
temporary declaration, assignment, and call.)

Soon, ir_call will become a statement taking a dereference of where to
store the return value, rather than an rvalue to be used on the RHS of
an assignment.  It will be more convenient to try evaluation before
creating a call.  ir_function_signature seems like a reasonable place.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/glsl/ir.h                       |    6 ++++++
 src/glsl/ir_constant_expression.cpp |   27 +++++++++++++++++++--------
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/src/glsl/ir.h b/src/glsl/ir.h
index f809867..9bf3b70 100644
--- a/src/glsl/ir.h
+++ b/src/glsl/ir.h
@@ -440,6 +440,12 @@ public:
    virtual ir_visitor_status accept(ir_hierarchical_visitor *);
 
    /**
+    * Attempt to evaluate this function as a constant expression, given
+    * a list of the actual parameters.  Returns NULL for non-built-ins.
+    */
+   ir_constant *constant_expression_value(exec_list *actual_parameters);
+
+   /**
     * Get the name of the function for which this is a signature
     */
    const char *function_name() const;
diff --git a/src/glsl/ir_constant_expression.cpp b/src/glsl/ir_constant_expression.cpp
index f0299a2..4264847 100644
--- a/src/glsl/ir_constant_expression.cpp
+++ b/src/glsl/ir_constant_expression.cpp
@@ -986,18 +986,29 @@ ir_call::constant_expression_value()
    if (this->type == glsl_type::error_type)
       return NULL;
 
+   return this->callee->constant_expression_value(&this->actual_parameters);
+}
+
+
+ir_constant *
+ir_function_signature::constant_expression_value(exec_list *actual_parameters)
+{
+   const glsl_type *type = this->return_type;
+   if (type == glsl_type::void_type)
+      return NULL;
+
    /* From the GLSL 1.20 spec, page 23:
     * "Function calls to user-defined functions (non-built-in functions)
     *  cannot be used to form constant expressions."
     */
-   if (!this->callee->is_builtin)
+   if (!this->is_builtin)
       return NULL;
 
    unsigned num_parameters = 0;
 
    /* Check if all parameters are constant */
    ir_constant *op[3];
-   foreach_list(n, &this->actual_parameters) {
+   foreach_list(n, actual_parameters) {
       ir_constant *constant = ((ir_rvalue *) n)->constant_expression_value();
       if (constant == NULL)
 	 return NULL;
@@ -1019,7 +1030,7 @@ ir_call::constant_expression_value()
    ir_constant_data data;
    memset(&data, 0, sizeof(data));
 
-   const char *callee = this->callee_name();
+   const char *callee = this->function_name();
    if (strcmp(callee, "abs") == 0) {
       expr = new(mem_ctx) ir_expression(ir_unop_abs, type, op[0], NULL);
    } else if (strcmp(callee, "all") == 0) {
@@ -1067,7 +1078,7 @@ ir_call::constant_expression_value()
       for (unsigned c = 0; c < op[0]->type->components(); c++)
 	 data.f[c] = atanhf(op[0]->value.f[c]);
    } else if (strcmp(callee, "dFdx") == 0 || strcmp(callee, "dFdy") == 0) {
-      return ir_constant::zero(mem_ctx, this->type);
+      return ir_constant::zero(mem_ctx, type);
    } else if (strcmp(callee, "ceil") == 0) {
       expr = new(mem_ctx) ir_expression(ir_unop_ceil, type, op[0], NULL);
    } else if (strcmp(callee, "clamp") == 0) {
@@ -1158,7 +1169,7 @@ ir_call::constant_expression_value()
    } else if (strcmp(callee, "fract") == 0) {
       expr = new(mem_ctx) ir_expression(ir_unop_fract, type, op[0], NULL);
    } else if (strcmp(callee, "fwidth") == 0) {
-      return ir_constant::zero(mem_ctx, this->type);
+      return ir_constant::zero(mem_ctx, type);
    } else if (strcmp(callee, "greaterThan") == 0) {
       assert(op[0]->type->is_vector() && op[1] && op[1]->type->is_vector());
       for (unsigned c = 0; c < op[0]->type->components(); c++) {
@@ -1264,7 +1275,7 @@ ir_call::constant_expression_value()
       float length = sqrtf(dot(op[0], op[0]));
 
       if (length == 0)
-	 return ir_constant::zero(mem_ctx, this->type);
+	 return ir_constant::zero(mem_ctx, type);
 
       for (unsigned c = 0; c < op[0]->type->components(); c++)
 	 data.f[c] = op[0]->value.f[c] / length;
@@ -1315,7 +1326,7 @@ ir_call::constant_expression_value()
       const float dot_NI = dot(op[1], op[0]);
       const float k = 1.0F - eta * eta * (1.0F - dot_NI * dot_NI);
       if (k < 0.0) {
-	 return ir_constant::zero(mem_ctx, this->type);
+	 return ir_constant::zero(mem_ctx, type);
       } else {
 	 for (unsigned c = 0; c < type->components(); c++) {
 	    data.f[c] = eta * op[0]->value.f[c] - (eta * dot_NI + sqrtf(k))
@@ -1379,5 +1390,5 @@ ir_call::constant_expression_value()
    if (expr != NULL)
       return expr->constant_expression_value();
 
-   return new(mem_ctx) ir_constant(this->type, &data);
+   return new(mem_ctx) ir_constant(type, &data);
 }
-- 
1.7.6.1