[Mesa-dev] [PATCH 04/23] i965/fs: Don't emit dumb SEL

[Ian Romanick]

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

With previous changes to emit more ir_triop_csel, the i965 channel
expressions pass can generate sequences like:

    mov(8)          g45<1>F      1F
    (+f0) sel(8)    g40<1>F      g45<8,8,1>F 1F

There are no shader-db changes now, but this prevents a large number of
regressions from a later commit (glsl: Optimize certain if-statements to
ir_triop_csel).

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Cc: Tapani Pälli <tapani.palli at intel.com>
---
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index e39dab3..1fbef5f 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -708,6 +708,15 @@ fs_visitor::visit(ir_expression *ir)
       break;
 
    case ir_triop_csel:
+      /* After splitting an expression like 'v = csel(cond, vec4(a, b, c, 1),
+       * vec4(d, e, f, 1))', there will be a 'v.w = csel(cond, 1, 1)'.  Detect
+       * this, and avoid emitting the spurious SEL.
+       */
+      if (ir->operands[1]->equals(ir->operands[2])) {
+         ir->operands[1]->accept(this);
+         return;
+      }
+
       if (try_opt_frontfacing_ternary(ir))
          return;
 
-- 
2.1.0