Mesa (master): glsl: Store glsl_type::vector_elements and :: matrix_columns as uint8_t

[Ian Romanick]

Module: Mesa
Branch: master
Commit: 3711abd780141b84a33f393446b05a6a385200d4
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=3711abd780141b84a33f393446b05a6a385200d4

Author: Ian Romanick <ian.d.romanick at intel.com>
Date:   Fri Oct 24 13:04:24 2014 -0700

glsl: Store glsl_type::vector_elements and ::matrix_columns as uint8_t

Due to the total number of bits used in the bitfield, this does not
increase the size of the structure.

It does, however, reduce the number of instructions required each time
one of these fields is accessed.  To access ::matrix_columns with the
bitfield, three instructions were required:

    movzbl 0x9(%rdx),%eax
    shr    %al
    and    $0x7,%eax

As a uint8_t, only one instruction is required.

    movzbl 0xa(%rdx),%eax

These fields are accessed *a lot*.

Valgrind callgrind results for a trace of Tesseract:

                 _mesa_Uniform4fv  _mesa_Uniform4f  _mesa_Uniform1i
Before (64-bit):       48,103,497       16,556,096          676,447
After  (64-bit):       45,722,616       15,737,964          670,607

                 _mesa_Uniform4fv  _mesa_Uniform4f  _mesa_Uniform1i
Before (32-bit):       61,472,611       21,051,222          821,361
After  (32-bit):       57,987,421       19,872,226          811,609

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Reviewed-by: Brian Paul <brianp at vmware.com>
Reviewed-by: Tapani Pälli <tapani.palli at intel.com>

---

 src/glsl/glsl_types.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/glsl/glsl_types.h b/src/glsl/glsl_types.h
index 6543041..096f546 100644
--- a/src/glsl/glsl_types.h
+++ b/src/glsl/glsl_types.h
@@ -153,8 +153,8 @@ struct glsl_type {
     * these will be 0.
     */
    /*@{*/
-   unsigned vector_elements:3; /**< 1, 2, 3, or 4 vector elements. */
-   unsigned matrix_columns:3;  /**< 1, 2, 3, or 4 matrix columns. */
+   uint8_t vector_elements;    /**< 1, 2, 3, or 4 vector elements. */
+   uint8_t matrix_columns;     /**< 1, 2, 3, or 4 matrix columns. */
    /*@}*/
 
    /**