[Mesa-dev] Clamp/saturate optimizations V2

[Abdiel Janulgue]

V2 of clamp/saturate optimizations

This patch series add the plumbing to support the GLSL IR instruction saturate().
Previously, saturate is implemented as min/max instructions. Most GPUs, however,
can probably perform saturate for free. With these changes, we can allow saturate
to be optimized as a single instruction.

In addition, the optimization try_emit_saturate was previously used to optimize
min/max operations to a saturate operation. It didn't work for code such as 
min(max(a, b), c) where (b == 0.0 and c < 1.0) and related cases.
With this infrastructure in place, we can optimize those operations easily in the
do_algebraic pass.

Changes since v1: 
 - Only remove the old try_emit_saturate operations after the new optimizations are
   in place. (Matt, Ian)
 - Output [min/max](saturate(x),b) instead of saturate([min/max](x,b)) as suggested
   by Ilia Mirkin.
 - The change above required some refactoring in the fs/vec4 backend to allow
   propagation of certain instructions with saturate flag to SEL. For other instructions,
   we don't propagate saturate instructions, similar to the previous behaviour.

Results:

helped: shaders/0ad/9.shader_test fs16:                   38 -> 37 (-2.63%)
helped: shaders/0ad/9.shader_test fs8:                    38 -> 37 (-2.63%)
helped: shaders/gst-gl-tunnel.frag fs16:                  65 -> 64 (-1.54%)
helped: shaders/gst-gl-tunnel.frag fs8:                   65 -> 64 (-1.54%)

total instructions in shared programs: 41595 -> 41591 (-0.01%)
instructions in affected programs:     206 -> 202 (-1.94%)

No piglit regressions observed.

Abdiel Janulgue (16):
      glsl: Add ir_unop_saturate
      glsl: Add constant evaluation of ir_unop_saturate
      glsl: Add a pass to lower ir_unop_saturate to clamp(x, 0, 1)
      ir_to_mesa, glsl_to_tgsi: lower ir_unop_saturate
      ir_to_mesa, glsl_to_tgsi: Add support for ir_unop_saturate
      i965/fs: Add support for ir_unop_saturate
      i965/vec4: Add support for ir_unop_saturate
      glsl: Implement saturate as ir_unop_saturate
      glsl: Optimize clamp(x, 0, 1) as saturate(x)
      glsl: Optimize clamp(x, 0.0, b), where b < 1.0 as min(saturate(x),b)
      glsl: Optimize clamp(x, b, 1.0), where b > 0.0 as max(saturate(x),b)
      i965/fs: Allow propagation of instructions with saturate flag to sel
      i965/vec4: Allow propagation of instructions with saturate flag to sel
      ir_to_mesa, glsl_to_tgsi: Remove try_emit_saturate
      i965/fs: Remove try_emit_saturate
      i965/vec4: Remove try_emit_saturate

 src/glsl/ir.cpp                                         |  2 +                        
 src/glsl/ir.h                                           |  1 +                        
 src/glsl/ir_builder.cpp                                 |  6 +-                       
 src/glsl/ir_constant_expression.cpp                     |  6 ++                       
 src/glsl/ir_optimization.h                              |  1 +                        
 src/glsl/ir_validate.cpp                                |  1 +                        
 src/glsl/lower_instructions.cpp                         | 29 +++++++++                
 src/glsl/opt_algebraic.cpp                              | 56 ++++++++++++++++++
 src/mesa/drivers/dri/i965/brw_fs.h                      |  1 -
 .../drivers/dri/i965/brw_fs_channel_expressions.cpp     |  1 +
 src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp   | 18 +++++-
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp            | 41 ++-----------
 src/mesa/drivers/dri/i965/brw_vec4.h                    |  1 -
 src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp | 75 +++++++++++++++---------
 src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp          | 25 ++------
 src/mesa/program/ir_to_mesa.cpp                         | 59 ++++---------------
 src/mesa/state_tracker/st_glsl_to_tgsi.cpp              | 63 ++++----------------
 17 files changed, 192 insertions(+), 194 deletions(-)