glsl: Add lowering pass for GLSL ES 3.00 pack/unpack operations (v4)

Lower them to arithmetic and bit manipulation expressions.

v2: Rewrite using ir_builder [for idr].
v3: Comment typos. [for mattst88]
v4: Fix arithmetic error in comments.
    Factor out a shift instruction.
    Don't heap allocate factory.instructions.
    [for paul]

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com> (v2)
Reviewed-by: Matt Tuner <mattst88@gmail.com> (v3)
Reviewed-by: Paul Berry <stereotype441@gmail.com> (v4)
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>

src/glsl/Makefile.sources

@@ -60,6 +60,7 @@ LIBGLSL_FILES = \
 	$(GLSL_SRCDIR)/lower_mat_op_to_vec.cpp \
 	$(GLSL_SRCDIR)/lower_noise.cpp \
 	$(GLSL_SRCDIR)/lower_packed_varyings.cpp \
+	$(GLSL_SRCDIR)/lower_packing_builtins.cpp \
 	$(GLSL_SRCDIR)/lower_texture_projection.cpp \
 	$(GLSL_SRCDIR)/lower_variable_index_to_cond_assign.cpp \
 	$(GLSL_SRCDIR)/lower_vec_index_to_cond_assign.cpp \

src/glsl/ir_optimization.h

@@ -37,6 +37,25 @@
 #define MOD_TO_FRACT       0x20
 #define INT_DIV_TO_MUL_RCP 0x40
 
+/**
+ * \see class lower_packing_builtins_visitor
+ */
+enum lower_packing_builtins_op {
+   LOWER_PACK_UNPACK_NONE               = 0x0000,
+
+   LOWER_PACK_SNORM_2x16                = 0x0001,
+   LOWER_UNPACK_SNORM_2x16              = 0x0002,
+
+   LOWER_PACK_UNORM_2x16                = 0x0004,
+   LOWER_UNPACK_UNORM_2x16              = 0x0008,
+
+   LOWER_PACK_HALF_2x16                 = 0x0010,
+   LOWER_UNPACK_HALF_2x16               = 0x0020,
+
+   LOWER_PACK_HALF_2x16_TO_SPLIT        = 0x0040,
+   LOWER_UNPACK_HALF_2x16_TO_SPLIT      = 0x0080,
+};
+
 bool do_common_optimization(exec_list *ir, bool linked,
 			    bool uniform_locations_assigned,
 			    unsigned max_unroll_iterations);
@@ -74,6 +93,7 @@ bool lower_variable_index_to_cond_assign(exec_list *instructions,
 bool lower_quadop_vector(exec_list *instructions, bool dont_lower_swz);
 bool lower_clip_distance(gl_shader *shader);
 void lower_output_reads(exec_list *instructions);
+bool lower_packing_builtins(exec_list *instructions, int op_mask);
 void lower_ubo_reference(struct gl_shader *shader, exec_list *instructions);
 void lower_packed_varyings(void *mem_ctx, unsigned location_base,
                            unsigned locations_used, ir_variable_mode mode,