[Mesa-dev] [PATCH] i965/fs: Allow copy propagation on ATTR file registers.

[Kenneth Graunke]

This especially helps with NIR because we currently emit MOVs at the top
of the shader to copy from various ATTR registers to a giant VGRF array
of all inputs.  (This could potentially be done better, but since
there's only ever one write to each register, it should be trivial to
copy propagate away...)

With NIR - only vertex shaders:
total instructions in shared programs: 3083505 -> 2868128 (-6.98%)
instructions in affected programs:     2977237 -> 2761860 (-7.23%)
helped:                                18653

Without NIR - only vertex shaders:
total instructions in shared programs: 2724564 -> 2708831 (-0.58%)
instructions in affected programs:     593696 -> 577963 (-2.65%)
helped:                                3134

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_fs.cpp                  | 1 +
 src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp | 5 ++++-
 2 files changed, 5 insertions(+), 1 deletion(-)

No apparent Piglit regressions.  Please scrutinize though, I spent very
little actual thought on this, so I may have missed something stupid.

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 9a415ff..6fa90d2 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -3235,6 +3235,7 @@ fs_visitor::lower_load_payload()
                    * destination may be used.
                    */
                   assert(inst->src[i].file == IMM ||
+                         inst->src[i].file == ATTR ||
                          inst->src[i].file == UNIFORM);
                   mov->force_writemask_all = true;
                }
diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
index 764741d..56f4fa1 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
@@ -283,7 +283,8 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
 
    if (entry->src.file == IMM)
       return false;
-   assert(entry->src.file == GRF || entry->src.file == UNIFORM);
+   assert(entry->src.file == GRF || entry->src.file == UNIFORM ||
+          entry->src.file == ATTR);
 
    if (entry->opcode == SHADER_OPCODE_LOAD_PAYLOAD &&
        inst->opcode == SHADER_OPCODE_LOAD_PAYLOAD)
@@ -382,6 +383,7 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
       inst->src[arg].reg_offset = entry->src.reg_offset;
       inst->src[arg].subreg_offset = entry->src.subreg_offset;
       break;
+   case ATTR:
    case GRF:
       {
          assert(entry->src.width % inst->src[arg].width == 0);
@@ -598,6 +600,7 @@ can_propagate_from(fs_inst *inst)
            ((inst->src[0].file == GRF &&
              (inst->src[0].reg != inst->dst.reg ||
               inst->src[0].reg_offset != inst->dst.reg_offset)) ||
+            inst->src[0].file == ATTR ||
             inst->src[0].file == UNIFORM ||
             inst->src[0].file == IMM) &&
            inst->src[0].type == inst->dst.type &&
-- 
2.2.1