[Mesa-dev] [PATCH 3/4] glsl: Constant-fold built-in functions before outputting IR

[Paul Berry]

Rearranged the logic for converting the ast for a function call to
hir, so that we constant fold before emitting any IR.  Previously we
would emit some IR, and then only later detect whether we could
constant fold.  The unnecessary IR would usually get cleaned up by a
later optimization step, however in the case of a builtin function
being used to compute an array size, it was causing an assertion.

Fixes Piglit test array-size-constant-relational.vert.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38625
---
 src/glsl/ast_function.cpp |   16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/glsl/ast_function.cpp b/src/glsl/ast_function.cpp
index 34a82f8..5b6ed3b 100644
--- a/src/glsl/ast_function.cpp
+++ b/src/glsl/ast_function.cpp
@@ -199,6 +199,20 @@ match_function_by_name(exec_list *instructions, const char *name,
        */
       ir_call *call = new(ctx) ir_call(sig, actual_parameters);
       if (!sig->return_type->is_void()) {
+         /* If the function call is a constant expression, don't
+          * generate the instructions to call it; just generate an
+          * ir_constant representing the constant value.
+          *
+          * Function calls can only be constant expressions starting
+          * in GLSL 1.20.
+          */
+         if (state->language_version >= 120) {
+            ir_constant *const_val = call->constant_expression_value();
+            if (const_val) {
+               return const_val;
+            }
+         }
+
 	 ir_variable *var;
 	 ir_dereference_variable *deref;
 
@@ -211,8 +225,6 @@ match_function_by_name(exec_list *instructions, const char *name,
 	 deref = new(ctx) ir_dereference_variable(var);
 	 ir_assignment *assign = new(ctx) ir_assignment(deref, call, NULL);
 	 instructions->push_tail(assign);
-	 if (state->language_version >= 120)
-	    var->constant_value = call->constant_expression_value();
 
 	 deref = new(ctx) ir_dereference_variable(var);
 	 return deref;
-- 
1.7.6