[Mesa-dev] [PATCH 1/9] glsl: Allow built-in functions as constant expressions in OpenGL ES 1.00

[Ian Romanick]

From: Ian Romanick <ian.d.romanick at intel.com>

In d4a24745 (August 2012), Paul made functions calls not be constant
expressions in GLSL ES 1.00.  Since this feature was added in desktop
GLSL 1.20, we believed that it was added in GLSL ES 3.00.  That turns
out to be completely wrong.  Built-in functions have always been allowed
as constant expressions in GLSL ES, and the patch adds the (many) spec
quotations to prove it.

While we never previously encountered this, a later patch enfoces a GLSL
ES 1.00 rule that global variable initializers must be constant
expressions.  Without this fix, severl dEQP tests fail.

Fixes:

    tests/spec/glsl-es-1.00/compiler/const-initializer/from-function.frag
    tests/spec/glsl-es-1.00/compiler/const-initializer/from-function.vert
    tests/spec/glsl-es-1.00/compiler/const-initializer/from-sequence-in-function.frag
    tests/spec/glsl-es-1.00/compiler/const-initializer/from-sequence-in-function.vert

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Cc: "10.0 10.1 10.2 10.3 10.4 10.5 10.6 11.0" <mesa-stable at lists.freedesktop.org>

Yes, I know we don't maintain stable branches that far back, but that
*is* how far back this bug goes!
---
 src/glsl/ast_function.cpp | 51 ++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 46 insertions(+), 5 deletions(-)

diff --git a/src/glsl/ast_function.cpp b/src/glsl/ast_function.cpp
index 26d4c62..6538992 100644
--- a/src/glsl/ast_function.cpp
+++ b/src/glsl/ast_function.cpp
@@ -437,13 +437,54 @@ generate_call(exec_list *instructions, ir_function_signature *sig,
       }
    }
 
-   /* If the function call is a constant expression, don't generate any
-    * instructions; just generate an ir_constant.
+   /* Section 4.3.2 (Const) of the GLSL 1.10.59 spec says:
+    *
+    *     "Initializers for const declarations must be formed from literal
+    *     values, other const variables (not including function call
+    *     paramaters), or expressions of these.
+    *
+    *     Constructors may be used in such expressions, but function calls may
+    *     not."
+    *
+    * Section 4.3.3 (Constant Expressions) of the GLSL 1.20.8 spec says:
+    *
+    *     "A constant expression is one of
+    *
+    *         ...
+    *
+    *         - a built-in function call whose arguments are all constant
+    *           expressions, with the exception of the texture lookup
+    *           functions, the noise functions, and ftransform. The built-in
+    *           functions dFdx, dFdy, and fwidth must return 0 when evaluated
+    *           inside an initializer with an argument that is a constant
+    *           expression."
+    *
+    * Section 5.10 (Constant Expressions) of the GLSL ES 1.00.17 spec says:
     *
-    * Function calls were first allowed to be constant expressions in GLSL
-    * 1.20 and GLSL ES 3.00.
+    *     "A constant expression is one of
+    *
+    *         ...
+    *
+    *         - a built-in function call whose arguments are all constant
+    *           expressions, with the exception of the texture lookup
+    *           functions."
+    *
+    * Section 4.3.3 (Constant Expressions) of the GLSL ES 3.00.4 spec says:
+    *
+    *     "A constant expression is one of
+    *
+    *         ...
+    *
+    *         - a built-in function call whose arguments are all constant
+    *           expressions, with the exception of the texture lookup
+    *           functions.  The built-in functions dFdx, dFdy, and fwidth must
+    *           return 0 when evaluated inside an initializer with an argument
+    *           that is a constant expression."
+    *
+    * If the function call is a constant expression, don't generate any
+    * instructions; just generate an ir_constant.
     */
-   if (state->is_version(120, 300)) {
+   if (state->is_version(120, 100)) {
       ir_constant *value = sig->constant_expression_value(actual_parameters, NULL);
       if (value != NULL) {
 	 return value;
-- 
2.1.0